cvm pres- ii

8/14/2019 CVM Pres- II

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The Estrus Cycle:The Estrus Cycle: the breeding pattern and behavior among the vertebrate are remarkably variable.the breeding pattern and behavior among the vertebrate are remarkably variable.

this is dependent on whether or not the breeding cycle is seasonal or intra-this is dependent on whether or not the breeding cycle is seasonal or intra-

seasonal.seasonal. Some mammals mate periodically throughout the year; others mate only duringSome mammals mate periodically throughout the year; others mate only during

a restricted breeding season.a restricted breeding season.

except the higher primates, all female mammals permit mating only at definiteexcept the higher primates, all female mammals permit mating only at definite

times calledtimes called heat or estrusheat or estrus..


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EstrusEstrus = a period in the estrus cycle during which the female mammal is= a period in the estrus cycle during which the female mammal isin a physiological and psychological readiness for mating, and hencein a physiological and psychological readiness for mating, and hence

sexually accepts the male.sexually accepts the male.

Repetition of the estrus period at a set interval constitutesRepetition of the estrus period at a set interval constitutes the estrus cycle.the estrus cycle.

Estrus cycle lengthEstrus cycle length; - varies remarkably in different vertebrate groups:; - varies remarkably in different vertebrate groups: Rat and Mouse - 4 to 5 day intervalRat and Mouse - 4 to 5 day interval Dogs - every 6 months (twice yearly)Dogs - every 6 months (twice yearly) Domestic cow and pig - 3 weeks (18 - 25 days)Domestic cow and pig - 3 weeks (18 - 25 days) Deer family and wild sheep - mating only once a year.Deer family and wild sheep - mating only once a year.


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Phases of the Estruss cyclePhases of the Estruss cycle a)a) EstrusEstrus = a period of sexual desire and acceptance of mating= a period of sexual desire and acceptance of mating

b)b) MetestrusMetestrus = a period of preparation for pregnancy - increasing P4 from= a period of preparation for pregnancy - increasing P4 from

developing CLdeveloping CL

c)c) DiestrusDiestrus = period of uterine quiescence - peak P4 level= period of uterine quiescence - peak P4 level

*d)*d) AnestrusAnestrus = extended diestrus during which the ovary quiescent= extended diestrus during which the ovary quiescent

( no functional structures); in seasonal breeders mostly( no functional structures); in seasonal breeders mostly

d)d) ProestrusProestrus = period immediately preceding next estrus= period immediately preceding next estrus


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The Estrus cycle contdThe Estrus cycle contdUterine & Ovarian Changes during Estrus cycle:Uterine & Ovarian Changes during Estrus cycle:

OvulationOvulation Pituitary hormonesPituitary hormones

releases ovum -releases ovum - FSH, LH, LTHFSH, LH, LTH

Corpus hemorrhagicumCorpus hemorrhagicum Ovarian hormonesOvarian hormones

Corpus luteum CLCorpus luteum CL progesterone P4progesterone P4

Corpus albicantes FollCorpus albicantes Foll estrogen E2estrogen E2

non-functionalnon-functional


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the production and the effects of estradiol (E2) are allocated precisely tothe production and the effects of estradiol (E2) are allocated precisely to

the periods of proestrus and estrus the periods of proestrus and estrus follicular phasefollicular phase

the production and effects of progesterone are allocatedthe production and effects of progesterone are allocated

to the periods of metestrus and diestrus to the periods of metestrus and diestrus luteal phaseluteal phase

considerable overlap in the presence and operation of these two hormonesconsiderable overlap in the presence and operation of these two hormones


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The gonadotropic hormones from anterior pituitaryThe gonadotropic hormones from anterior pituitary::

FSH; LH; LTH under the influence of GnHRH from theFSH; LH; LTH under the influence of GnHRH from the

hypothalamushypothalamus

FSHFSH, responsible for directing the maturation of the follicle and production, responsible for directing the maturation of the follicle and productionof estrogenof estrogen

LHLH, joins with FSH in promoting follicular maturation and estradiol, joins with FSH in promoting follicular maturation and estradiol

production;production;also controls the development of the corpus luteum + P4 roductionalso controls the development of the corpus luteum + P4 roduction

FSH and LH together are responsible for ovulationFSH and LH together are responsible for ovulation

(major role by LH cf. LH surge)(major role by LH cf. LH surge)

LTHLTH, possibly identical to prolactin (PL), possibly identical to prolactin (PL)

- regulates milk letdown;- regulates milk letdown;

believes to stimulate progesterone secretion by the CL.believes to stimulate progesterone secretion by the CL.


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Regulation of the secretion and release of theseRegulation of the secretion and release of these

hormones is via a negative feedbackhormones is via a negative feedback

mechanismmechanism


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CLEAVAGE - In Eutharian MammalsCLEAVAGE - In Eutharian Mammals

including human, monkey, mouse, etcincluding human, monkey, mouse, etc

is holoblasticis holoblastic

Microlecithal but the blastomeres tend to show size differences from the start ofMicrolecithal but the blastomeres tend to show size differences from the start of

segmentationsegmentation

initial division occurs within 24 hr of ovulation and during uterine passage andinitial division occurs within 24 hr of ovulation and during uterine passage and

within intact zona pellucidawithin intact zona pellucida

24 hr post ovulation = first segmentation division within the zona pellucida, into a24 hr post ovulation = first segmentation division within the zona pellucida, into a

smaller and a larger blastomeresmaller and a larger blastomere 48 hr post ovulation = two successive divisions, first by the larger cell and then the48 hr post ovulation = two successive divisions, first by the larger cell and then the

lower cell, giving further smaller and larger cells/blastomeres.lower cell, giving further smaller and larger cells/blastomeres.


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Cleavage in eutharian mammals contdCleavage in eutharian mammals contd

Further cell divisions leads to attainment of 16-cell stage by 96 hr post ovulation; byFurther cell divisions leads to attainment of 16-cell stage by 96 hr post ovulation; bywhich time the developing ovum has almost reached the uterus.which time the developing ovum has almost reached the uterus.

This could be termed aThis could be termed a blastocyst;blastocyst; and the cavity within calledand the cavity within called blastocystblastocyst

cavity or primary yolk sac.cavity or primary yolk sac.

Day 5 post ovulation, the number of blastomeres has reached 100; uterine fluid is beingDay 5 post ovulation, the number of blastomeres has reached 100; uterine fluid is beingabsorbed thru the zona into the blastocyst, creating a single cavity; and also forcingabsorbed thru the zona into the blastocyst, creating a single cavity; and also forcingrearrangement of the blastomeres into outer flattened cells and inner cells that arerearrangement of the blastomeres into outer flattened cells and inner cells that are

eccentrically located with the flattened outer cells.eccentrically located with the flattened outer cells.

At this stage, the embryo is referred to as aAt this stage, the embryo is referred to as ablastocyst;blastocyst;

and the outer flattened cells calledand the outer flattened cells called trophoblasttrophoblast, and the inner cells,, and the inner cells, calledcalled inner cellinner cellmass.mass.


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Gastrulation in mammalsGastrulation in mammals Birds and mammals are both descendants of reptilian species. Therefore, it is notBirds and mammals are both descendants of reptilian species. Therefore, it is not

surprising that mammalian development parallels that of reptiles and birds.surprising that mammalian development parallels that of reptiles and birds.

What is surprising is that the gastrulation movements of reptilian and avian embryos,What is surprising is that the gastrulation movements of reptilian and avian embryos,

which evolved as an adaptation to yolky eggs, are retained even in the absence of largewhich evolved as an adaptation to yolky eggs, are retained even in the absence of large

amounts of yolk in the mammalian embryo.amounts of yolk in the mammalian embryo.

The mammalian inner cell mass can be envisioned as sitting atop an imaginary ball ofThe mammalian inner cell mass can be envisioned as sitting atop an imaginary ball of

yolk following instructions that seem more appropriate to its ancestors.yolk following instructions that seem more appropriate to its ancestors.


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Modifications for Development Within Another OrganismModifications for Development Within Another Organism

Instead of developing in isolation within an egg, most mammals have evolved theInstead of developing in isolation within an egg, most mammals have evolved theremarkable strategy of developing within the mother herself. The mammalianremarkable strategy of developing within the mother herself. The mammalianembryo obtains nutrients directly from its mother and does not rely on stored yolk.embryo obtains nutrients directly from its mother and does not rely on stored yolk.

This evolution has entailed a dramatic restructuring of the maternal anatomy (such asThis evolution has entailed a dramatic restructuring of the maternal anatomy (such asexpansion of the oviduct to form the uterus) as well as the development of a fetalexpansion of the oviduct to form the uterus) as well as the development of a fetalorgan capable of absorbing maternal nutrients.organ capable of absorbing maternal nutrients.

This fetal organthe placenta is derived primarily from embryonic trophoblast cells,This fetal organthe placenta is derived primarily from embryonic trophoblast cells,supplemented with mesodermal cells derived from the inner cell mass.supplemented with mesodermal cells derived from the inner cell mass.


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Placentation contdPlacentation contd

first, the extraembryonic somatopleure elevates over all sides of the embryo to providefirst, the extraembryonic somatopleure elevates over all sides of the embryo to providean amnion and chorion.an amnion and chorion.

at same time the allantois grows out of the hindgut, expands into the coelom and fusesat same time the allantois grows out of the hindgut, expands into the coelom and fuses

with chorion.with chorion.

a large yolk is initially established but later declines rapidly as the allantois enlarges.a large yolk is initially established but later declines rapidly as the allantois enlarges.

Placenta -Placenta - a structure produced by appositioning of the extraembryonic membranes witha structure produced by appositioning of the extraembryonic membranes with

the endometrium for the purpose of physiological exchange between the fetus and mother.the endometrium for the purpose of physiological exchange between the fetus and mother.


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Origin : Formation - consists of two parts:Origin : Formation - consists of two parts:

- Fetal and Maternal sources- Fetal and Maternal sources i) fetal placenta/componenti) fetal placenta/component - furnished by the extraembryonic membranes- furnished by the extraembryonic membranes

amnion, chorion, allantois, yolk sacamnion, chorion, allantois, yolk sac

chorion:chorion: most external and makes immediate contact with the uterinemost external and makes immediate contact with the uterineendometrium; vascular supply which is acquired from aIIantois.endometrium; vascular supply which is acquired from aIIantois.

Two sources of chorionic vascularization in mammals viz:Two sources of chorionic vascularization in mammals viz:

i) the vitelline circulation provided by the yolk sac andi) the vitelline circulation provided by the yolk sac and

ii) allantoic circulation provided by the allantois.ii) allantoic circulation provided by the allantois.

yolk sacyolk sac; remains rudimentary in most mammals;; remains rudimentary in most mammals; allantoisallantois vascularizes the chorion.vascularizes the chorion.

The fetal circulation is therefore said to be chorioallantoic.The fetal circulation is therefore said to be chorioallantoic.


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ii) maternal placenta/componentii) maternal placenta/component - furnished by a single uterine endometrium.- furnished by a single uterine endometrium.

the established chorioallantoic membrane lies in apposition to the uterine endometrium.the established chorioallantoic membrane lies in apposition to the uterine endometrium.

as this membrane enlarges it establishes a close intimacy with the endometrium.as this membrane enlarges it establishes a close intimacy with the endometrium.

as the fetal placenta (chorioallantoic) has allantoic blood vessels running into and fromas the fetal placenta (chorioallantoic) has allantoic blood vessels running into and from

the fetus, and maternal vessels run to and from the maternal placenta (endometrium), thethe fetus, and maternal vessels run to and from the maternal placenta (endometrium), the

two circulations are brought very close together.two circulations are brought very close together.

But there is no fusion between these two blood systems; fetal blood does not circulate inBut there is no fusion between these two blood systems; fetal blood does not circulate in

the mother & maternal blood does not circulate in the fetusthe mother & maternal blood does not circulate in the fetus. Materials are passed from. Materials are passed fromone to the other through tissue barriers.one to the other through tissue barriers.


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PlacentaPlacenta ((a structure produced by appositioning of the extraembryonic membranes with the endometrium for the purposea structure produced by appositioning of the extraembryonic membranes with the endometrium for the purpose

of physiological exchange between the fetus and mother).of physiological exchange between the fetus and mother).

CLASSIFICATIONCLASSIFICATION

via: i) histological (on basis of number of tissue barriers between the twovia: i) histological (on basis of number of tissue barriers between the twocirculations: ii) gross shape: fate of tissues)circulations: ii) gross shape: fate of tissues)

i) histologicali) histological

i) Epitheliochoriali) Epitheliochorial

6 tissue layers 6 tissue layers

presenting apposition of fetal (chorionic epithelium) and maternalpresenting apposition of fetal (chorionic epithelium) and maternal(endometrial epithelium) components and six tissue barriers between the(endometrial epithelium) components and six tissue barriers between thetwo circulations.two circulations.

- in porcine, equine)- in porcine, equine)

ii) Syndeschorialii) Syndeschorial 5 layers 5 layers intimate fusion of the maternal and fetal components results in destructionintimate fusion of the maternal and fetal components results in destruction

of the uterine epithelium; only 5 layers left.of the uterine epithelium; only 5 layers left. - in ruminants (sheep, cows, deer etc)- in ruminants (sheep, cows, deer etc)


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iiiiii) Endotheliochorial) Endotheliochorial 4 layers 4 layers uterine mucosa is reduced and chorionic epithelium comes in contact with the wallsuterine mucosa is reduced and chorionic epithelium comes in contact with the walls

of the maternal blood vessels: 4 layersof the maternal blood vessels: 4 layers - in carnivores dogs, cats, etc- in carnivores dogs, cats, etc

iv) Hemochorial- 3 layersiv) Hemochorial- 3 layers one in which the maternal endothelium also disappears and the chorionicone in which the maternal endothelium also disappears and the chorionic

epithelium is bathed directly in maternal blood; 3 layers.epithelium is bathed directly in maternal blood; 3 layers. - in primates and rodents- in primates and rodents

ii) gross shapeii) gross shape

Placentas could also be classified on the basis of shapePlacentas could also be classified on the basis of shape i)i) diffusediffuse (Epitheliochorial)(Epitheliochorial)

ii)ii) cotyledonarycotyledonary (syndesmochorial)(syndesmochorial) iii)iii) zonaryzonary (endotheliochorial)(endotheliochorial) iviv) discoidal) discoidal (Hemochorial) Note;(Hemochorial) Note;


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Apposition of fetal and maternal components and six tissue barriers between theApposition of fetal and maternal components and six tissue barriers between thetwo circulations, is the primitive type from which others have been derived.two circulations, is the primitive type from which others have been derived.

These derivations reflect a changeover from apposition to some degree of fusionThese derivations reflect a changeover from apposition to some degree of fusion

of the two placental components which in turn involves some measure ofof the two placental components which in turn involves some measure of

destruction of maternal tissues.destruction of maternal tissues.


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In the ruminants (cattle, sheep) the fetal and maternal components are fused soIn the ruminants (cattle, sheep) the fetal and maternal components are fused sointimately as to result in the destruction of the uterine epithelium, thus bringing theintimately as to result in the destruction of the uterine epithelium, thus bringing thechorion into contact with the connective tissue of the uterine mucosa. Only fivechorion into contact with the connective tissue of the uterine mucosa. Only fivebarriers therefore lie between the twobarriers therefore lie between the two

bloodstreams. This situation is termedbloodstreams. This situation is termed syndesmochorialsyndesmochorial

(Figure 9.21b).(Figure 9.21b).

EEndotheliochorialndotheliochorial placenta (Figure 9.21C)placenta (Figure 9.21C)

is one in which the uterine mucosa is reduced and the chorionic epithelium comes inis one in which the uterine mucosa is reduced and the chorionic epithelium comes incontact with the walls of the maternal bloodcontact with the walls of the maternal blood


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* placentas exhibit thicker layer at earlier stages of development than later. For* placentas exhibit thicker layer at earlier stages of development than later. For

example, the primate placenta is initially Epitheliochorial and acquires itsexample, the primate placenta is initially Epitheliochorial and acquires its

Hemochorial status later.Hemochorial status later.

* Degree of union of the fetal and maternal components of the placenta varies:* Degree of union of the fetal and maternal components of the placenta varies:

i)i) Deciduous placentaDeciduous placenta = one in which the union of the components is so intimate= one in which the union of the components is so intimate

that at birth a variable amount of maternal tissue is lost.that at birth a variable amount of maternal tissue is lost.

ii)ii)Non-deciduous placentaNon-deciduous placenta = mere apposition of the two components of the= mere apposition of the two components of the

placenta; and separation of the components is easily effected at birth and there isplacenta; and separation of the components is easily effected at birth and there is

no loss of maternal tissuesno loss of maternal tissues..


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PLACENTA - FUNCTIONSPLACENTA - FUNCTIONS::

i) Filtration - transmission of nutrients + oxygen into and nitrogenous wastesi) Filtration - transmission of nutrients + oxygen into and nitrogenous wastesbetween fetus and motherbetween fetus and mother

ii) Storage - stores materials such as fat, glycogen and ironii) Storage - stores materials such as fat, glycogen and iron

iii) Participates in the metabolism of proteiniii) Participates in the metabolism of protein

iv) Functions as endocrine gland (hCG, progesterone,iv) Functions as endocrine gland (hCG, progesterone,

v) Protection of the fetus (physical and immunological)v) Protection of the fetus (physical and immunological)


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The Human Placenta is characterized as:The Human Placenta is characterized as:

i) Discoidal (reference to gross shape)i) Discoidal (reference to gross shape)

ii) Hemochorial (chorionic villi bathed in maternal blood)ii) Hemochorial (chorionic villi bathed in maternal blood)

iii) Deciduous (loss of endometrial tissues at birth)iii) Deciduous (loss of endometrial tissues at birth)

iv) Chorioallantoic (by reason of allantoic blood supply to chorion eveniv) Chorioallantoic (by reason of allantoic blood supply to chorion eventhough the allantois proper is rudimentarythough the allantois proper is rudimentary


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Human Development and PlacentationHuman Development and Placentation

Between 5 and 6 days postovulation, the blastocyst will be lying in the uterineBetween 5 and 6 days postovulation, the blastocyst will be lying in the uterine

cavitycavity

the trophoblast differentiates into two portions viz:the trophoblast differentiates into two portions viz:

i) polar trophoblast = portion that overlies the inner cell mass;i) polar trophoblast = portion that overlies the inner cell mass;

this makes contact with the endometrium; multiplies rapidly and invades thethis makes contact with the endometrium; multiplies rapidly and invades the

endometrium deeply and establishesendometrium deeply and establishes implantationimplantation


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These invading trophoblasts differentiate into layers;These invading trophoblasts differentiate into layers;

- the original inner cellullar cytotrophoblast,- the original inner cellullar cytotrophoblast,

- and outer syncytial syntrophoblast .- and outer syncytial syntrophoblast .

the syntrophoblast invades further and deeper into the endometrium;the syntrophoblast invades further and deeper into the endometrium;releases substances that block any rejection of the embryo by thereleases substances that block any rejection of the embryo by the

mother:mother:

; serves as nutritive and protective organ.; serves as nutritive and protective organ.


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concurrently, theconcurrently, the inner cell massinner cell mass sort themselves and differentiatesort themselves and differentiate

into primary endoderm and formative cells; and by furtherinto primary endoderm and formative cells; and by further

organization, form theorganization, form the forerunners of the anmion or amniogenicforerunners of the anmion or amniogenic

layer and amniotic cavitylayer and amniotic cavity

by day 9 postovulation, blastocyst is totally beneath the uterineby day 9 postovulation, blastocyst is totally beneath the uterine

epithelium and fully embedded in the mucosa.epithelium and fully embedded in the mucosa.


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Events Between 13th and 20th clay post ovulationEvents Between 13th and 20th clay post ovulation::

i)i) extraembryonic coelomextraembryonic coelom formed, and villi formed fromformed, and villi formed from

syncytrophoblastic strands;syncytrophoblastic strands;

the trophoblast then becomesthe trophoblast then becomes chorion and chorionic villichorion and chorionic villi

through mesodermalization of the trophoblast and its villi.through mesodermalization of the trophoblast and its villi.


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ii) small secondaryii) small secondary yolk sacyolk sac is establishedis established

iii) formation of a definitiveiii) formation of a definitive somatopleuricsomatopleuricamnionamnion;;

body stalkbody stalk: rudimentary (a fingerlike projection of: rudimentary (a fingerlike projection ofendoderm - aendoderm - a rudimentaryrudimentary

allantoisallantois, ultimately grows into the matrix of the body stalk., ultimately grows into the matrix of the body stalk.

Note that, unlike the pig and many other mammals,Note that, unlike the pig and many other mammals, the human allantois does notthe human allantois does not

expand into the extraembryonic coelom, but remains as a rudiment within theexpand into the extraembryonic coelom, but remains as a rudiment within the

body stalk)body stalk)


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iv) Conversion of the bilaminar embryonic disc to trilaminar disc.iv) Conversion of the bilaminar embryonic disc to trilaminar disc.

By 16-17 post ovulation, blastocyst is fully implanted in the endometriumBy 16-17 post ovulation, blastocyst is fully implanted in the endometrium

and chorionic villi elaborated over entire surface. Once implantation isand chorionic villi elaborated over entire surface. Once implantation iscompleted one could distinguish 3 topographical areas in the endometrium,completed one could distinguish 3 topographical areas in the endometrium,

viz:viz:

Placenta Desidua basalis maternal placentaPlacenta Desidua basalis maternal placenta

D. capsularisD. capsularis

D. parietalisD. parietalis

EEM TrophoblastEEM Trophoblast placentaplacenta

a) hindgut extension to choriona) hindgut extension to chorion or chorionic membraneor chorionic membrane

b) Yolk sacb) Yolk sac

SomatopleureSomatopleure c) chorionc) chorion ++ d) amniond) amnion


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i) desidua basalis - area immediately beneath the blastocysti) desidua basalis - area immediately beneath the blastocyst

ii) desidua capsularis - that encapsulating the lumen-ward surface of theii) desidua capsularis - that encapsulating the lumen-ward surface of the

chorionchorion

iii) desidua parietalis- area lining the remainder of the uterusiii) desidua parietalis- area lining the remainder of the uterus..


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with advance gestation, the chorionic villi facing the decidua basaliswith advance gestation, the chorionic villi facing the decidua basalisenlarge and branch while the villi facing the decidau capsularis regress.enlarge and branch while the villi facing the decidau capsularis regress.

by 4th month gestation, decidau capsularis portion of the chorion is villus-by 4th month gestation, decidau capsularis portion of the chorion is villus-free: and is calledfree: and is called chorion leavechorion leave

The decidua basalis chorion bearing villi is calledThe decidua basalis chorion bearing villi is called chorion frondosumchorion frondosum

Q ti iQ ti i


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Questions -reviewQuestions -review1. Choose the correct answer from the following: The human placenta is1. Choose the correct answer from the following: The human placenta is

described as:described as:DiffuseDiffuse c)c) zonaryzonary

bb)) CotyledonaryCotyledonary dd) discoid) discoid

2. Which of the following is not a normal function of the human placenta:2. Which of the following is not a normal function of the human placenta:

vii)vii)Filtration iv) endocrine gland (hCG, progesterone,Filtration iv) endocrine gland (hCG, progesterone,

viii)viii)StorageStorage v) immuno-protectivev) immuno-protective

iii) metabolism of protein vi) fertilizationiii) metabolism of protein vi) fertilization

3. The trophoblast becomes chorion and chorionic villi through3. The trophoblast becomes chorion and chorionic villi throughmesodermalization of the trophoblast and its villi.mesodermalization of the trophoblast and its villi. T/FT/F

4.4. Select the correct word/answer from the following: The component(s) ofSelect the correct word/answer from the following: The component(s) ofthe maternal placenta include:the maternal placenta include:

a) endometrium; b) chorion; c) amnion; d) allantois; e) chorioallantoisa) endometrium; b) chorion; c) amnion; d) allantois; e) chorioallantois

5. The human placenta is endocrine as it produces gonadotropins (LH/FSH)5. The human placenta is endocrine as it produces gonadotropins (LH/FSH)

at pregnancyat pregnancy T/FT/F


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MORPHOGENESISMORPHOGENESIS

GROWTHGROWTH

DIFFERENTIATIONDIFFERENTIATION

INDUCTTONINDUCTTON TERAGOLOGYTERAGOLOGY


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Growth and DifferentiationGrowth and Differentiation

two basic processes involved in the transformation of a single celltwo basic processes involved in the transformation of a single cell

into a complex organism:into a complex organism:

i) Growthi) Growth = incr in size and/or no. of cells.= incr in size and/or no. of cells.

Ii) DifferentiationIi) Differentiation = is the variation among cells descended= is the variation among cells descended

from the original cell.from the original cell.


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GROWTH:GROWTH: 3 basic mechanisms:3 basic mechanisms:

i) increase in no. of cellsi) increase in no. of cells

ii) increase in size of cellsii) increase in size of cells

iii) incr. in extracellular materialiii) incr. in extracellular material

in early embryonic stagesin early embryonic stages major growth mechanism is incr in size ofmajor growth mechanism is incr in size ofcells by prolifera; embryo as a whole; also in the individual embr.cells by prolifera; embryo as a whole; also in the individual embr.

structures.structures.


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DIFFERENTIATIONDIFFERENTIATION

in a population of daughter cells different from the parent cellsin a population of daughter cells different from the parent cells

result in different cells; the different cells tend to form different structures.result in different cells; the different cells tend to form different structures.

The forming of these differentiated cells into their respective structures, isThe forming of these differentiated cells into their respective structures, is

referred to as MORPHOGENESIS.referred to as MORPHOGENESIS.

Morphogenic processMorphogenic process = a process in which a mass of cells becomes a structure= a process in which a mass of cells becomes a structure

with a defined shape.with a defined shape.

e.g. Single layer of epithelial cells transforms into a branched structure suche.g. Single layer of epithelial cells transforms into a branched structure suchas a gland.as a gland.

INDUCTIONINDUCTION


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INDUCTIONINDUCTION

developing organism made up of group of many organogenic fields which aredeveloping organism made up of group of many organogenic fields which are

interrelated.interrelated.

Thus for normal devel of an organism as a whole, some mechanism must beThus for normal devel of an organism as a whole, some mechanism must be

present to ensure that an orderly sequence of events occurspresent to ensure that an orderly sequence of events occurs

The phenomenon of ensuring that order prevails in the embryo as a whole, isThe phenomenon of ensuring that order prevails in the embryo as a whole, is

that ofthat ofinduction.induction.


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INDUCTION initiates a preprogrammed series of events in the jnduced cellINDUCTION initiates a preprogrammed series of events in the jnduced cellpopulation.population.

In each system, inductors emerge in strict sequential manner usually a primary,In each system, inductors emerge in strict sequential manner usually a primary,secondary, tertiary etc inductors.secondary, tertiary etc inductors.

The induced cell population must be in a stage of differentiation, whereby theyThe induced cell population must be in a stage of differentiation, whereby they

areare COMPETENTCOMPETENT to be affected by the inductorsto be affected by the inductors

The cells permanently induced are said to beThe cells permanently induced are said to be DETERMINEDDETERMINED..


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Mechanism of InductionMechanism of Induction::

not exactly known.not exactly known.

assumed that some messengers are transferred from inductor to inducedassumed that some messengers are transferred from inductor to induced

cell population;cell population;

Messengers such as macromolecules, collage; cell fractions; whole cellMessengers such as macromolecules, collage; cell fractions; whole cell

ions.ions.


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PRINCIPLES OF TERATOLOGYPRINCIPLES OF TERATOLOGY

The Study of Abnormal DevelopmentThe Study of Abnormal Development Timing of TeratogenTiming of Teratogen::

development of the embryo consists of a group of cells that are growing-->development of the embryo consists of a group of cells that are growing-->

differentiating --> and undergoing morphogenesis:differentiating --> and undergoing morphogenesis:


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at different rates and at different times; But in strictly controlled sequenceat different rates and at different times; But in strictly controlled sequence

of eventsof events

Timing of these events --> necessary for normal developmentTiming of these events --> necessary for normal development

Susceptibility to a teratogen varies with the developmental stage of theSusceptibility to a teratogen varies with the developmental stage of the

embryo at the time of exposure.embryo at the time of exposure.

Teratogen -> embryo -->a) no effect b) severe effectTeratogen -> embryo -->a) no effect b) severe effect


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Critical Stages (CS)Critical Stages (CS) stage during development when the embryo will be most severely affectedstage during development when the embryo will be most severely affected

CS for each organ system and structureCS for each organ system and structure

CS of morphogenic field is time at which it is undergoingCS of morphogenic field is time at which it is undergoing differentiationdifferentiation

The earlier in differentiation the attack, the more severe.The earlier in differentiation the attack, the more severe.e.g. Insult of time of NOTOCHORD inductione.g. Insult of time of NOTOCHORD induction

malformation of entire HEAD ; at a later stage,--> only affects the eye.malformation of entire HEAD ; at a later stage,--> only affects the eye.


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Developmental Stages (DS)Developmental Stages (DS) The critical role of time is explained in terms of the effect produced atThe critical role of time is explained in terms of the effect produced at

specific developmental stages.specific developmental stages.

Devel of embryo and its morphogenic field may be divided into 3 develDevel of embryo and its morphogenic field may be divided into 3 devel

stages :stages :

a) Stage of predifferentiationa) Stage of predifferentiation

b) Stage of early differentiation & organogenesisb) Stage of early differentiation & organogenesis c) stage of advance organogenesis = growth, histogenesis,c) stage of advance organogenesis = growth, histogenesis,

functional maturation.functional maturation.

P diff ti ti t + t tPre differentiation stage + teratogen


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Pre-differentiation stage + teratogenPre-differentiation stage + teratogen a) lethal to embryo b)no effect at alla) lethal to embryo b)no effect at all ReasonReason

Cells at this stage have not undergone differentiation and so haveCells at this stage have not undergone differentiation and so havesame potential as the zygote. Therefore, insult ---> destroys all thesame potential as the zygote. Therefore, insult ---> destroys all thecells and kill embryo or leaves cells which have full potential tocells and kill embryo or leaves cells which have full potential toform an entire embryo -> potential develop of normal embryo.form an entire embryo -> potential develop of normal embryo.


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Early differentiation and organogenesis phase is the phase when the system isEarly differentiation and organogenesis phase is the phase when the system is

most susceptible to insults structural malformation.most susceptible to insults structural malformation.

Resistance to insults increases after the third stage; because this stage is afterResistance to insults increases after the third stage; because this stage is after

organs and structures form.organs and structures form.

Only functional and growth retardation rather than structural related may beOnly functional and growth retardation rather than structural related may be

affectedaffected..


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It follows that the placenta is a product of the decidua basalis and chorionIt follows that the placenta is a product of the decidua basalis and chorion

frondosum; the decidua basalis representing the maternal component; and thefrondosum; the decidua basalis representing the maternal component; and the

chorion frondosum representing the fetal component of the placentachorion frondosum representing the fetal component of the placenta


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Umbilical cordUmbilical cord -- further expansion of the amnion presses thefurther expansion of the amnion presses themesoderm of the body stalk into a cordlike structure within which themesoderm of the body stalk into a cordlike structure within which the

allantois and neck of the yolk sac are embedded.allantois and neck of the yolk sac are embedded.

This structure is the umbilical cord. The umbilical (allantoic) arteries andThis structure is the umbilical cord. The umbilical (allantoic) arteries andveins course through this cord. The right umbilical vein eventuallyveins course through this cord. The right umbilical vein eventually

disappears, and only rudiments of the yolk sac and allantois persist.disappears, and only rudiments of the yolk sac and allantois persist.

Umbilical cordUmbilical cord = allantois + yolk sac + body stalk= allantois + yolk sac + body stalk


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ORGANOGENESISORGANOGENESIS

Formation of the organ system in the body:Formation of the organ system in the body: SkinSkin Cardiovascular systemCardiovascular system

Genitourinary systemGenitourinary system Digestive systemDigestive system CNSCNS OthersOthers


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THE SKINTHE SKIN

EmbryogenesisEmbryogenesis

Morpho-anatomyMorpho-anatomy

functionsfunctions


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A tAnatom

y


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AnatomyAnatomy keratin is the material from which hair, feathers, claws and etc., are made.keratin is the material from which hair, feathers, claws and etc., are made.

Stratum corneum = the outermost layer of the epidermis constitutes anStratum corneum = the outermost layer of the epidermis constitutes animpermeable membrane called stratum corneum.impermeable membrane called stratum corneum.

TheThe epidermisepidermis

- stratum corneum (outer area) + stratum germinativum (inner portion)- stratum corneum (outer area) + stratum germinativum (inner portion)

- has no blood vessels and no blood supply of its own- has no blood vessels and no blood supply of its own;;

- depends on the vascularization of the dermis to which the structural- depends on the vascularization of the dermis to which the structural

germinativum is adjacentgerminativum is adjacent..


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Functions - skin:Functions - skin: protective against:protective against:

i) mechanical injuriesi) mechanical injuries

ii) invasion by microorganismsii) invasion by microorganisms

iii) loss of moistureiii) loss of moisture

iv) predators - poison-producing glands; pigmentation; odor;iv) predators - poison-producing glands; pigmentation; odor;

external armour- scales etcexternal armour- scales etc

ThermoregulationsThermoregulations


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physiologicallyphysiologically - dissipation of heat via bloodstream (contraction- dissipation of heat via bloodstream (contraction

and relaxation of blood vessels)and relaxation of blood vessels)

physicallyphysically by: evaporation of sweat by mammalian skin forby: evaporation of sweat by mammalian skin for

cooling: conservation of heat via insulating materials as oil and fat,cooling: conservation of heat via insulating materials as oil and fat,

mammalian hair, and feathers of birdsmammalian hair, and feathers of birds..


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EExcretory organxcretory organ supplements the kidney as a mechanism for excretion - most concentratedsupplements the kidney as a mechanism for excretion - most concentrated

solute in sweat is NaCl; minerals such as K, Mg, and nitrogenous wastessolute in sweat is NaCl; minerals such as K, Mg, and nitrogenous wastes

also appear in sweat to some degree.also appear in sweat to some degree.

Organ of secretionOrgan of secretion::(the integument is also an organ of secretion)(the integument is also an organ of secretion)

a variety of cutaneous glands provides useful products: mucus-secretinga variety of cutaneous glands provides useful products: mucus-secreting

glands in fishes and amphibians; oil-secreting glands in mammalian skin;glands in fishes and amphibians; oil-secreting glands in mammalian skin;milk-secreting glands of mammalsmilk-secreting glands of mammals

Skin contdSkin contd


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Organ of respiration:Organ of respiration:

in fishes and amphibians; in all other vertebrates including human, somein fishes and amphibians; in all other vertebrates including human, somedegree of gaseous exchange takes (oxygen and carbon dioxide) takes placedegree of gaseous exchange takes (oxygen and carbon dioxide) takes place

to some extent.to some extent.

As a sense organAs a sense organ skin serves as a vehicle for an array of cutaneous sense organs by whichskin serves as a vehicle for an array of cutaneous sense organs by which

animals maintain contact with their external environment.animals maintain contact with their external environment.

these include: receptors for senses of: touch,these include: receptors for senses of: touch, temperature, pressure, and pain.temperature, pressure, and pain.

Th D iTh D i


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The DermisThe Dermis in contrast to the epidermis, dermis consists more of cell products than ofin contrast to the epidermis, dermis consists more of cell products than of

cells.cells.

composed of network of connective tissue fibers derived from the originalcomposed of network of connective tissue fibers derived from the original

segmented dermatomesegmented dermatome

in the dermis are: lots of blood vessels, nerves, lymph vessels, smoothe muscle,in the dermis are: lots of blood vessels, nerves, lymph vessels, smoothe muscle,

sense organs, deposits of fats, and array of epidermal and dermal derivativessense organs, deposits of fats, and array of epidermal and dermal derivatives..


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Origin of SkinOrigin of Skin:: all vertebrate skin originated from two embryonic sources: theall vertebrate skin originated from two embryonic sources: the ectodermectoderm

and mesoderm somatopleureand mesoderm somatopleure..

the entire ectoderm exclusive of the part dedicated to the neural tube, maythe entire ectoderm exclusive of the part dedicated to the neural tube, maybe regarded as prospective epidermis of the skin.be regarded as prospective epidermis of the skin.


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The dermis originates from the dermatome subdivision of the epimere.The dermis originates from the dermatome subdivision of the epimere.

The dermatomal components of the somites resolve themselves intoThe dermatomal components of the somites resolve themselves into

mesenchymal cells, which multiply and deploy to all regions of themesenchymal cells, which multiply and deploy to all regions of the

embryo.embryo.


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Function:Function:


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keratin is the material from which hair, feathers, claws andkeratin is the material from which hair, feathers, claws andetc., are made.etc., are made.

Stratum corneum = the outermost layer of the epidermisStratum corneum = the outermost layer of the epidermisconstitutes an impermeable membrane called stratum corneum.constitutes an impermeable membrane called stratum corneum. The epidermis has no blood vessels and no blood supply ofThe epidermis has no blood vessels and no blood supply of

its own; depends on the vascularization of the dermis to whichits own; depends on the vascularization of the dermis to whichthe stratura germinativum is adjacent.the stratura germinativum is adjacent.

Functions - skin:Functions - skin: protective against:protective against: i) mechanical injuriesi) mechanical injuries ii) invasion by microorganismsii) invasion by microorganisms iii) loss of moistureiii) loss of moisture iv) predators - poison-producing glands; pigmentation; odor;iv) predators - poison-producing glands; pigmentation; odor;

external armour- scales etcexternal armour- scales etc



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Thermoregulationsg physiologically - dissipation of heat via bloodstreamphysiologically - dissipation of heat via bloodstream

(contraction and relaxation of bvs)(contraction and relaxation of bvs)

physically by: evaporation of sweat by mammalian skin forphysically by: evaporation of sweat by mammalian skin forcooling: conservation of heat such insulating materials as oil andcooling: conservation of heat such insulating materials as oil andfat, mammalian hair, and feathers of birds.fat, mammalian hair, and feathers of birds.

- E- Excretory organxcretory organ

supplements the kidney as a mechanism for excretion - mostsupplements the kidney as a mechanism for excretion - mostconcentrated solute in sweat is NaCl; minerals such as K, Mg,concentrated solute in sweat is NaCl; minerals such as K, Mg,and nitrogenous wastes also appear in sweat to some degree.and nitrogenous wastes also appear in sweat to some degree.

- O- Organ of secretionrgan of secretion:: (the integument is also an organ of secretion)(the integument is also an organ of secretion) a variety of cutaneous glands provides useful products: mucus-secretinga variety of cutaneous glands provides useful products: mucus-secreting

glands in fishes and amphibians; oil-secreting glands in mammalian skin;glands in fishes and amphibians; oil-secreting glands in mammalian skin;milk-secreting glands of mammalsmilk-secreting glands of mammals



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Skin cont dSkin cont d

- organ of respiration:- organ of respiration:

in fishes and amphibians; in all other vertebrates includingin fishes and amphibians; in all other vertebrates includinghuman, some degree of gaseous exchange takes (oxygen andhuman, some degree of gaseous exchange takes (oxygen and

carbon dioxide) takes place to some extentcarbon dioxide) takes place to some extent..

-- as a sense organas a sense organ skin serves as a vehicle for an array of cutaneous sense organs by whichskin serves as a vehicle for an array of cutaneous sense organs by which

animals maintain contact with their external environment.animals maintain contact with their external environment.

these include: receptors for senses of: touch,these include: receptors for senses of: touch,

temperature, pressure, and pain.temperature, pressure, and pain.

Th D iTh D i


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The DermisThe Dermis in contrast to the epidermis, dermis consists more of cell productsin contrast to the epidermis, dermis consists more of cell products

than of cells.than of cells. composed of network of connective tissue fibers derived from thecomposed of network of connective tissue fibers derived from the

original segmented dermatomeoriginal segmented dermatome in the dermis are: lots of blood vessels, nerves, lymph vessels,in the dermis are: lots of blood vessels, nerves, lymph vessels,

smoothe muscle, sense organs, deposits of fats, and array ofsmoothe muscle, sense organs, deposits of fats, and array ofepidermal and dermal derivatives.epidermal and dermal derivatives.

Origin of SkinOrigin of Skin:: all vertebrate skin originated from two embryonic sources: the ectoderm andall vertebrate skin originated from two embryonic sources: the ectoderm and

mesoderm somatopleure.mesoderm somatopleure. the entire ectoderm exclusive of the part dedicated to the neural tube, may bethe entire ectoderm exclusive of the part dedicated to the neural tube, may be

regarded as prospective epidermis of the skin.regarded as prospective epidermis of the skin.


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Origin of the DermisOrigin of the Dermis

the dermis originates from the dermatome subdivision of thethe dermis originates from the dermatome subdivision of the

epimere. The dermatomal components of the somites resolveepimere. The dermatomal components of the somites resolvethemselves into mesenchymal cells, which multiply and deploy tothemselves into mesenchymal cells, which multiply and deploy to

all regions of the embryo.all regions of the embryo.

in mammals and birds, it appears that while the dermatomein mammals and birds, it appears that while the dermatomefurnishes the dermis of the dorsal and dorsolateral portions of thefurnishes the dermis of the dorsal and dorsolateral portions of the

body, the dermis of the flank and ventral surface of the body is abody, the dermis of the flank and ventral surface of the body is a

derivative of the mesoderm of the somatopleurederivative of the mesoderm of the somatopleure..

Cutaneous GlandsCutaneous Glands


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Cutaneous GlandsCutaneous Glands glands in the skin are either unicellular or multicellularglands in the skin are either unicellular or multicellular

all glands originate in the epidermisall glands originate in the epidermis

unicellular glands: - are modified single cells scatteres among other cells in the epidermisunicellular glands: - are modified single cells scatteres among other cells in the epidermis

multicellular glands: - formed as ingrowth from the stratum germinativum into the dermis;multicellular glands: - formed as ingrowth from the stratum germinativum into the dermis;

arc either tubular (straight, coiled, or branched) or alveolar (sacklike) (simple sacs, orarc either tubular (straight, coiled, or branched) or alveolar (sacklike) (simple sacs, or

moderately or elaboratelymoderately or elaborately

branched - Fig 10-2)branched - Fig 10-2)

1. Cyclostomes:1. Cyclostomes:

unicellular type of gland: mostly mucus secretingunicellular type of gland: mostly mucus secretinggiving thick, slimy protective skin coat as found in hagfishesgiving thick, slimy protective skin coat as found in hagfishes


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2. Fishes:2. Fishes:

both unicellular and alveolar glandsboth unicellular and alveolar glands

3. Amphibians3. Amphibians:: skin plays important role in respirationskin plays important role in respiration alveolar mucous and glands predominate in amphibiansalveolar mucous and glands predominate in amphibians

there are also instances of specialized tubular glands as wellthere are also instances of specialized tubular glands as well

unicellular glands also occur in amphibians - on snouts of larval frogs andunicellular glands also occur in amphibians - on snouts of larval frogs andsalamandersalamander

Functions of these glands include: READING assignmentFunctions of these glands include: READING assignment


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4. Reptiles and Birds:4. Reptiles and Birds: skin of birds and reptiles is virtually devoid of glands.skin of birds and reptiles is virtually devoid of glands. existing glands secrete products related to breeding behaviorexisting glands secrete products related to breeding behavior

and/or defense.and/or defense. in crocodiles and turtles, a gland beneath the jaw (crocodiles)in crocodiles and turtles, a gland beneath the jaw (crocodiles)

secrete a substance called musk in the breeding season; no skinsecrete a substance called musk in the breeding season; no skin

glands in lizard; some snakes have glands in the cloacaI regionglands in lizard; some snakes have glands in the cloacaI region

In birdsIn birds, the only gland is the uropygial gland (branched alveiolar), the only gland is the uropygial gland (branched alveiolar)

on dorsal side of bosy at base o the tail = supplies oil which theon dorsal side of bosy at base o the tail = supplies oil which the

bird collects on its beak and uses in the preening of its plumage.bird collects on its beak and uses in the preening of its plumage.


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M l tdMammals contd


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Mammals contdMammals contd

Sweat glandsSweat glands: -: - simple tubular glands; its watery secretionssimple tubular glands; its watery secretionsenables the skins function thermoregulation and excretion.enables the skins function thermoregulation and excretion.

Human, the horse and the bear, sweat glands are widespread over the body.Human, the horse and the bear, sweat glands are widespread over the body.

Other mammals have no sweat glands at all.Other mammals have no sweat glands at all.

In others - rats, cats, mice, glands are confined to specific localities - undersideIn others - rats, cats, mice, glands are confined to specific localities - underside

of the paws; in deer - base of the tail;of the paws; in deer - base of the tail;

rabbits on the lips; sheep, cattle, pigs on the muzzle and snoutsrabbits on the lips; sheep, cattle, pigs on the muzzle and snouts


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Mammary or milk glandsMammary or milk glands are modified sweat glands found in all mammalsare modified sweat glands found in all mammals Embryogeny:Embryogeny:

first appearance of a pair of thickening of epidermal ectoderm alongfirst appearance of a pair of thickening of epidermal ectoderm alongthe ventrolateral body wallthe ventrolateral body wall these thickening are calledthese thickening are called mammarymammary

ridge or milk lineridge or milk line;;

further thickening of the ridge produces a roughly spherical massfurther thickening of the ridge produces a roughly spherical mass

projecting into the subjacent dermisprojecting into the subjacent dermis cords of cells then ramify withincords of cells then ramify within

the surrounding dermis which finally produce a branch-work.the surrounding dermis which finally produce a branch-work.


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Mammary or milk glands contdMammary or milk glands contd


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Mammary or milk glands cont dMammary or milk glands cont d

In due course the cords hollow out to create a duct system converging at theIn due course the cords hollow out to create a duct system converging at the

surface, where an epidermal nipple is elevated,surface, where an epidermal nipple is elevated, At birth,At birth, no further development occurs in males, but elaboration of theno further development occurs in males, but elaboration of the

mammae resumes in females with the advent of sexual maturity.mammae resumes in females with the advent of sexual maturity.

NipplesNipples a) true nipples: rodents = single mammary duct; or carnivores and humans =a) true nipples: rodents = single mammary duct; or carnivores and humans =

several. ducts pass directly to the outside.several. ducts pass directly to the outside.

True nipples: single duct in rodentTrue nipples: single duct in rodent

multiple ducts in human & carnivoresmultiple ducts in human & carnivores

Mammary glands contdMammary glands contd


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y g

b) false nipple: or teat :b) false nipple: or teat : found in horses and cattle:found in horses and cattle:

in which the ducts open into a chamber at the base of the projection, from where ain which the ducts open into a chamber at the base of the projection, from where asecondary tube leads to the exterior and it is from the epithelium along the course of thesecondary tube leads to the exterior and it is from the epithelium along the course of themilk line that the mammary glands arise.milk line that the mammary glands arise.

______________________________________________

In humans, sea cows, elephants and batsIn humans, sea cows, elephants and bats == a single pair ofa single pair of

pectoral mammaepectoral mammae In cattle, horsesIn cattle, horses= one or two pairs of inguinal mammae appear= one or two pairs of inguinal mammae appear In rats, and miceIn rats, and mice= 3 pairs of thoracic and 3 pairs of abdominal mammaie= 3 pairs of thoracic and 3 pairs of abdominal mammaie

In pigs and dogsIn pigs and dogs= five or six pairs are arranged in a continuous= five or six pairs are arranged in a continuousseries from the chest to groin.series from the chest to groin.

S lS l


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ScalesScales

Epidermal scales:Epidermal scales:

are derivatives of the stratum corneum, the keratinized surface component ofare derivatives of the stratum corneum, the keratinized surface component of

the dermis; well developed in reptiles; occurs in lizards, turtles, crocodilesthe dermis; well developed in reptiles; occurs in lizards, turtles, crocodiles

snakes (devel from the stratum germinativum)snakes (devel from the stratum germinativum)

confined to the legs and feet in birds;confined to the legs and feet in birds; when occurs in mammals, epidermal scales are found on the tail as in beavers,when occurs in mammals, epidermal scales are found on the tail as in beavers,

rats, mice, and opossum.rats, mice, and opossum.

are lacking in fishes: found rarely in amphibiansare lacking in fishes: found rarely in amphibians

* Dermal scale: Read in text* Dermal scale: Read in text


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FEATHERSFEATHERS

Functions include:Functions include: For heat insulation; flight; protective coloration; sexual displayFor heat insulation; flight; protective coloration; sexual display

Types:Types:

i) hair feathers; ii) down feathers: iii) contour feathersi) hair feathers; ii) down feathers: iii) contour feathers

Hair feathersHair feathers: smallest and simplest variety: scattered widely over the body under: smallest and simplest variety: scattered widely over the body underthe contour feathers.the contour feathers.

Down feathers:Down feathers: complex and composed of a short hollow basalcomplex and composed of a short hollow basal

quill, buried in the skin, from which they spray a number of filamentous barbsquill, buried in the skin, from which they spray a number of filamentous barbsbearing tiny barbules along their margins. Underlying the contour feathers overbearing tiny barbules along their margins. Underlying the contour feathers overmuch of the body, the down feathers provide effective insulation for the adult bird.much of the body, the down feathers provide effective insulation for the adult bird.


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Scales contdScales contd

Contour feathers:Contour feathers: the large feathers that ensheathe the body and provide its characteristicthe large feathers that ensheathe the body and provide its characteristic

configuration. A typical contour feather consists of a lengthwise axis and a flatconfiguration. A typical contour feather consists of a lengthwise axis and a flat

vane.vane.


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FORMATIONFORMATION


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FORMATION:FORMATION: first there is aggregation of dermal cells immediately beneath the epidermis.first there is aggregation of dermal cells immediately beneath the epidermis.

continued proliferation of the dermal aggregation results in a conical elevation, thecontinued proliferation of the dermal aggregation results in a conical elevation, thedermal papilla, ensheathed by epidermisdermal papilla, ensheathed by epidermis

thus formed the feather germ grows rapidly outward as a tapering epidermal cylinderthus formed the feather germ grows rapidly outward as a tapering epidermal cylinderfilled with a vascular mesodermal core.filled with a vascular mesodermal core.

the epidermis at base of the papilla sinks in and the feather germ projects from a pitthe epidermis at base of the papilla sinks in and the feather germ projects from a pitcalled follicle. From this point onward, down and contour feathers showcalled follicle. From this point onward, down and contour feathers show

developmental differencesdevelopmental differences..


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HAIRHAIR

characteristic of mammals,characteristic of mammals, hair is entirely epidermal in origin and compositionhair is entirely epidermal in origin and composition

structure of typical hair:structure of typical hair:

Compare the origins: Feather is d Dermal; Hair - epidermalCompare the origins: Feather is d Dermal; Hair - epidermal


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Two portions:Two portions:projecting shaft and a root which lies in a pit called hairprojecting shaft and a root which lies in a pit called hair

follicle.follicle. At the base, the root expands into a hollow bulb into which a small dermalAt the base, the root expands into a hollow bulb into which a small dermal

papilla projects, carrying blood vessels and nerves.papilla projects, carrying blood vessels and nerves.

the living cells at the end of the root constantly multiply to lengthen the shaft;the living cells at the end of the root constantly multiply to lengthen the shaft;

and in the process. the cells gradually die so that the hair proper becomesand in the process. the cells gradually die so that the hair proper becomescomposed of dead, cornified cells.composed of dead, cornified cells.


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Formation of hair:Formation of hair: formation of hair begins with epidermis alone unlike feathers whoseformation of hair begins with epidermis alone unlike feathers whose

development is initiated by a preliminary aggregation of dermal cells.development is initiated by a preliminary aggregation of dermal cells.


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Hair contdHair contd


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Hair cont dHair cont d

at the site of the presumptive hair, an epidermal nodule is formedat the site of the presumptive hair, an epidermal nodule is formedby a local proliferation of the stratum germinativum (Fig. 10-17\)by a local proliferation of the stratum germinativum (Fig. 10-17\)

the nodule extends down into the dermis as a tongue of tissue whose deeper endthe nodule extends down into the dermis as a tongue of tissue whose deeper end

becomes enlarged to form a bulb (10-1 7B)becomes enlarged to form a bulb (10-1 7B)

the bulb soon is inverted into a cup into which the vascular dermis pushesthe bulb soon is inverted into a cup into which the vascular dermis pushes

and aggregates to form a dermal papilla (10- I 7C).and aggregates to form a dermal papilla (10- I 7C).


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Concurrently, the deep-lying portion of the epidermal tongue splits to formConcurrently, the deep-lying portion of the epidermal tongue splits to forma central strand and a surrounding epithelium.a central strand and a surrounding epithelium.

the central strand becomes the root and shaft of the hair; the surroundingthe central strand becomes the root and shaft of the hair; the surroundingtissue provides the wall of the follicle. The follicular wall proliferates totissue provides the wall of the follicle. The follicular wall proliferates to

form the sebaceous gland.form the sebaceous gland.

as the embryonic hair grows its shaft pushes towards the surface byas the embryonic hair grows its shaft pushes towards the surface bymaking an opening through the center of the still solid epithelial cylinder.making an opening through the center of the still solid epithelial cylinder.


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MiscellaneousMiscellaneous

Beaks or bills, of birds: --Beaks or bills, of birds: -- horny epidermal sheaths enclosing thehorny epidermal sheaths enclosing thebones of the upper and lower jaws constitute bills or beaks of birds.bones of the upper and lower jaws constitute bills or beaks of birds.

Similar cornification of epidermis on the edges of the digits serve asSimilar cornification of epidermis on the edges of the digits serve as clawsclaws

(reptile, birds, some mammals, some amphibians);(reptile, birds, some mammals, some amphibians); hoofshoofs (horses, cattle, deer,(horses, cattle, deer,pigs, etc), and nails (humans and other primates).pigs, etc), and nails (humans and other primates).

The SkeletonThe Skeleton


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The SkeletonThe Skeleton

some form of skeleton in all living animals for protection and supportsome form of skeleton in all living animals for protection and support all skeletons may be grouped into one category called CONNECTIVE TISSUEall skeletons may be grouped into one category called CONNECTIVE TISSUE composed of varying quantities and combinations of mucopolysaccharide andcomposed of varying quantities and combinations of mucopolysaccharide and

proteins (collagen)proteins (collagen)

Connective tissue:Connective tissue:

- 2 functional groups- 2 functional groups binding c.t & supportive c.tbinding c.t & supportive c.t i) binding c.t.i) binding c.t.= tendons, ligaments, and fasciae= tendons, ligaments, and fasciae TendonsTendons connectconnect musclemuscle totobones or cartilagebones or cartilage

LigamentsLigaments unitunit skeletal partsskeletal parts.. FasciaeFasciae are sheets of c. t. serving to bind constituent cells together into a definitiveare sheets of c. t. serving to bind constituent cells together into a definitive

organ; such as muscle cells into the mass of an individual muscle or nerve fibers into aorgan; such as muscle cells into the mass of an individual muscle or nerve fibers into anerve.nerve.


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ii) supportive c. tii) supportive c. t..= provide the skeleton around (= provide the skeleton around (endoskeletonendoskeleton) or within) or within((exoskeletonexoskeleton) which an animal is built.) which an animal is built.


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Skeletal DevelopmentSkeletal Development


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Skeletal DevelopmentSkeletal Development Notochord:Notochord:

present in all vertebrate embryospresent in all vertebrate embryos

replaced by the vertebral column and base of the skull, in the adult vertebratesreplaced by the vertebral column and base of the skull, in the adult vertebrates

is still present in the lower Chordate adults (cyclostome and elasmobranchs) - as softis still present in the lower Chordate adults (cyclostome and elasmobranchs) - as soft

flexible rod beneath the neural tubeflexible rod beneath the neural tube

composed of vesicular tissue, external sheath and a surrounding membrane run from thecomposed of vesicular tissue, external sheath and a surrounding membrane run from the

infundibulum of the brain back to the terminus of the fleshy part of the tail.infundibulum of the brain back to the terminus of the fleshy part of the tail.

Skeletal Development contdSkeletal Development contd


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b) the Cartilage:b) the Cartilage: is a prominent skeletal material of the embryos of ALL vertebrate.is a prominent skeletal material of the embryos of ALL vertebrate.

is a major skeletal material of adults of cyclostome, (chondrichthyes and ais a major skeletal material of adults of cyclostome, (chondrichthyes and afew degenerate groups of Osteichthymes. Bone is the major skeletal material infew degenerate groups of Osteichthymes. Bone is the major skeletal material in

the higher vertebrates.the higher vertebrates.

Is a c.t whose intracellular matrix is composed of complex protein within whichIs a c.t whose intracellular matrix is composed of complex protein within whichthere is spread a network of colagenous fibers.there is spread a network of colagenous fibers.

the matrix is a product of cartilage cells (chondrocytes) which lie in smallthe matrix is a product of cartilage cells (chondrocytes) which lie in smallspaces (lacunae) within the matrix.spaces (lacunae) within the matrix.


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cartilage is surrounded by a dense c. tissue calledcartilage is surrounded by a dense c. tissue calledperichondriurn, to which tendons and ligaments becomeperichondriurn, to which tendons and ligaments become

attachedattached..

Cartilage exists in several forms viz:Cartilage exists in several forms viz: a) hyaline cartilage: - homogeneous and translucent matrix witha) hyaline cartilage: - homogeneous and translucent matrix with

few fibersfew fibers

b) elastic cartilage - the matrix is fibrous and elasticb) elastic cartilage - the matrix is fibrous and elastic

c)c) calcified cartilagecalcified cartilage: - contains deposits of calcium salts hard: - contains deposits of calcium salts hardbut brittle texturedbut brittle textured



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FormationFormation cartilage is a derivative of embryonic mesenchymal cells.cartilage is a derivative of embryonic mesenchymal cells. first, embryonic c.t. cells (mesenchyme) begin to aggregate.first, embryonic c.t. cells (mesenchyme) begin to aggregate.

the branching mesenchymal cells gradually round up and definitivethe branching mesenchymal cells gradually round up and definitive

mesenchymal cells (chondrocytes) start secreting matrix.mesenchymal cells (chondrocytes) start secreting matrix.

laying down of more and more matrix by chondrocytes forces the chondrocyteslaying down of more and more matrix by chondrocytes forces the chondrocytes

further apartfurther apart;.;.



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Skeletal Development contdSkeletal Development cont d chondrocytes eventually become isolated in small spaces (lacunae) within thechondrocytes eventually become isolated in small spaces (lacunae) within the

matrix. (fig. 11-2).matrix. (fig. 11-2).

division and formation of more matrix by the internal chondrocytes adds to thedivision and formation of more matrix by the internal chondrocytes adds to the

growth of the matrix and cartilagegrowth of the matrix and cartilage

Deposition of more matrix from outer surface by the perichondriumDeposition of more matrix from outer surface by the perichondrium

supplements the growth of the cartilage.supplements the growth of the cartilage.

This ability of cartilage to grow both by internal expansion and externalThis ability of cartilage to grow both by internal expansion and external

deposition stands in strong contrast to the growth of bone.deposition stands in strong contrast to the growth of bone.

c) Bone:c) Bone:


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like cartilage, bone is a derivative of embryonic mesenchyme, consists oflike cartilage, bone is a derivative of embryonic mesenchyme, consists ofa matrix within which cells (osteocytes) are buried.a matrix within which cells (osteocytes) are buried.

matrix is fibrillar; contains hard, complex mineral subst. composed mainlymatrix is fibrillar; contains hard, complex mineral subst. composed mainly

of crystals of calcium phosphate - Calcium hydroxide combination knownof crystals of calcium phosphate - Calcium hydroxide combination known

as apatite.as apatite.

Like cartilage, the bone cells (osteocytes) that secrete the matrix lie inLike cartilage, the bone cells (osteocytes) that secrete the matrix lie in

lacunae.lacunae.

Lacunae are linked with one another via canaliculi (a branching network ofLacunae are linked with one another via canaliculi (a branching network of

minute canals into which project the radiating processes of the osteocytes.minute canals into which project the radiating processes of the osteocytes.In cartilage, the lacunae and hence, the chondrocytes. are isolated fromIn cartilage, the lacunae and hence, the chondrocytes. are isolated from

each other.each other.


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Types:Types: * intramembraneous or dermal/membrane bone where the mesenchymal* intramembraneous or dermal/membrane bone where the mesenchymal

precursor is succeeded directly by bone.precursor is succeeded directly by bone.

intracartilaginous or cartilage/replacement bone = the originalintracartilaginous or cartilage/replacement bone = the originalmesenchyme first provides a cartilaginous model, which is then destroyedmesenchyme first provides a cartilaginous model, which is then destroyed

and replaced by bone.and replaced by bone.

Note:Note: These terms refer only to the sequence of events in bone development,These terms refer only to the sequence of events in bone development,

for when fully formed, bones of both types arefor when fully formed, bones of both types arestructurally alike.structurally alike.

Formation:Formation:


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a) membrane bone:a) membrane bone: first, mesenchymal cells congregate at the site of a future bone; cluster andfirst, mesenchymal cells congregate at the site of a future bone; cluster and

arrange themselves in an interlacing network of strands.arrange themselves in an interlacing network of strands.

each strand starts to secrete collagen resulting in a framework ofeach strand starts to secrete collagen resulting in a framework of

collagenous fibers.collagenous fibers.

each fiber is invested by the c.t. cells that produced it; and deposition ofeach fiber is invested by the c.t. cells that produced it; and deposition of

calcium salts begincalcium salts begin


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the mesenchymal cells, now called OSTEOBLASTS extract the necessarythe mesenchymal cells, now called OSTEOBLASTS extract the necessaryraw materials from the blood supply in the area, and lay down bone saltsraw materials from the blood supply in the area, and lay down bone saltsaround the fibers.around the fibers.

This then creates a scattering of bars and plates (This then creates a scattering of bars and plates (trabeculaetrabeculae) of bone.) of bone.

As more layers are added to the bone, some of the osteoblasts are caught inAs more layers are added to the bone, some of the osteoblasts are caught intheir own deposits and there, in their individual Iacunae.their own deposits and there, in their individual Iacunae.

In the Iacunae, the osteocytes cease to function as active bone formers;In the Iacunae, the osteocytes cease to function as active bone formers;they assume maintenance of the already formed bone.they assume maintenance of the already formed bone.


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Osteocytes in lacunae are interconnected byOsteocytes in lacunae are interconnected by

li li d h i l i k d bli li d th t i l i k d b


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canaliculi; and thus materials picked up bycanaliculi; and thus materials picked up by

osteocytes adjacent to blood vessels, areosteocytes adjacent to blood vessels, are

distributed throughout the bone matrix.distributed throughout the bone matrix.

Osteoblasts formation ofOsteoblasts formation of

Osteocytes maintenance ofOsteocytes maintenance of

Osteoclast breaking down ofOsteoclast breaking down of


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the remaining osteoblasts continue to add to the trabeculae; and as they enlarge,the remaining osteoblasts continue to add to the trabeculae; and as they enlarge,

come together and fuse into a continuous latticework.come together and fuse into a continuous latticework.

bone in this condition is called cancellous or spongy bone. The area betweenbone in this condition is called cancellous or spongy bone. The area between

the trabeculae are occupied by c.t., which is rapidly becomes vascularized; andthe trabeculae are occupied by c.t., which is rapidly becomes vascularized; and

so constitutes the bone marrow.so constitutes the bone marrow.

mesenchymal cell concentration appears around the primary cancellous bone tomesenchymal cell concentration appears around the primary cancellous bone to

form the periosteum.form the periosteum.


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within the periosteum, certain cells assume the role of osteoblasts and resumewithin the periosteum, certain cells assume the role of osteoblasts and resume


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deposition of bone.deposition of bone.

Bone is laid down in dense, parallel sheets; resulting in an external layer of compactBone is laid down in dense, parallel sheets; resulting in an external layer of compactbone investing the cancellous bone within.bone investing the cancellous bone within.


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physiological maintenance of compact bone is facilitated by an arrayphysiological maintenance of compact bone is facilitated by an array

of canals constituting the Harvesian System.of canals constituting the Harvesian System.

The compact bone becomes perforated by long branching and anastomosingThe compact bone becomes perforated by long branching and anastomosing

Harvesian canals.. which communicate externally with the periosteurn andHarvesian canals.. which communicate externally with the periosteurn and

internally with the marrow cavities.internally with the marrow cavities.


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Note that:Note that: i) no fundamental difference between compact and cancellous bone, other than thei) no fundamental difference between compact and cancellous bone, other than the

degree of density.degree of density.

ii) Both are a product of osteoblastsii) Both are a product of osteoblasts

iii) both are vital tissues maintained by entrapped but intercommunicatingiii) both are vital tissues maintained by entrapped but intercommunicating

osteocytes.osteocytes.

iv) the Harvesian Systems are not of universal occurrence among vertebrates. Mostiv) the Harvesian Systems are not of universal occurrence among vertebrates. Most

amphibia, some reptiles, and many smaller mammals do not have them.amphibia, some reptiles, and many smaller mammals do not have them.


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b) Cartilage boneb) Cartilage bone The intramembranous bone (described above) is largely confined withThe intramembranous bone (described above) is largely confined with

parts of the skull, and the shoulder girdle. Elsewhere, bone is preceded byparts of the skull, and the shoulder girdle. Elsewhere, bone is preceded by

cartilagecartilage

Events of formation are essentially the same as those in intramembranousEvents of formation are essentially the same as those in intramembranous

bone development. Only difference is the added rise and decline of thebone development. Only difference is the added rise and decline of the

cartilaginous precursor.cartilaginous precursor.


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some bone is the product of the osteoblasts brought in by the invading mesensenchyme:some bone is the product of the osteoblasts brought in by the invading mesensenchyme:

some is a product of surviving cartilage cells that transform to osteoblast.some is a product of surviving cartilage cells that transform to osteoblast.

ASSIGNED READING - for details.ASSIGNED READING - for details.


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BONE - AS A TISSUEBONE - AS A TISSUE::


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Bone as a tissue is revealed in the formation of both types of bones from embryonicBone as a tissue is revealed in the formation of both types of bones from embryonicmesenchymal cells; and in the fact of themesenchymal cells; and in the fact of the dynamism of bonedynamism of bone - that is, bone is- that is, bone is

constantly being remodeled (formed by osteobIasts, and broken down byconstantly being remodeled (formed by osteobIasts, and broken down byosteoclasts)osteoclasts)

serves as theserves as the source of supplysource of supply of calcium and phosphate required for theof calcium and phosphate required for themaintenance of physiological mechanims in the body,maintenance of physiological mechanims in the body,

isis a reservoira reservoirof Ca and P that is drawn upon to satisfy structural requirements:of Ca and P that is drawn upon to satisfy structural requirements:

Bone is the reservoir for Ca and P, which are added to and substracted fromBone is the reservoir for Ca and P, which are added to and substracted frombloodstream as required through the turnover mechanism in bone. e.g. In birds -bloodstream as required through the turnover mechanism in bone. e.g. In birds -calcium for the egg shell is drawn from the bone.calcium for the egg shell is drawn from the bone.

BONE - AS AN ORGANBONE - AS AN ORGAN:: i)i) flat bonesflat bones (of the skull) composed of reduced cancellous area(of the skull) composed of reduced cancellous area


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i)i) flat bonesflat bones (of the skull) composed of reduced cancellous area,(of the skull) composed of reduced cancellous area,

containing masses of marrow, sandwiched between upper and lower layerscontaining masses of marrow, sandwiched between upper and lower layers

of compact bone.of compact bone.

ii)ii) long boneslong bones (of the appendages) derived from the cartilaginous model of(of the appendages) derived from the cartilaginous model of

bone formation.bone formation.


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Bone structure and growth:Bone structure and growth:


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Bone structure and growth:Bone structure and growth:

Consists of a longConsists of a long shaft,shaft, diaphysisdiaphysis, with, with epiphysisepiphysisat each endat each end.. Ossification begins in the center of diaphysis and progresses toward each end.Ossification begins in the center of diaphysis and progresses toward each end.

Elongation is provided by steady creation of new cartilage at end of epiphysealElongation is provided by steady creation of new cartilage at end of epiphysealends; and ossification follows until adult length is attained.ends; and ossification follows until adult length is attained.

In lower vertebrates, the epiphyses remain cartilaginous throughout adult life.In lower vertebrates, the epiphyses remain cartilaginous throughout adult life.


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In mammals and some reptiles, accessory ossifications later appear in theIn mammals and some reptiles, accessory ossifications later appear in theepiphyses, ossification that fuses with the diaphysis only after full adultepiphyses, ossification that fuses with the diaphysis only after full adult

size is reached (Fig 11-8E).size is reached (Fig 11-8E).

Irregular boneIrregular bone (of the vertebrae; limb girdles) formation commences with(of the vertebrae; limb girdles) formation commences with

appearance of several primary endochondral centers;appearance of several primary endochondral centers;

which are supplemented by secondary centers.which are supplemented by secondary centers.

The original cancellous bone is replaced in part and supplemented byThe original cancellous bone is replaced in part and supplemented byperiosteal deposition of compact bone.periosteal deposition of

cvm pres- ii

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