growing fetus ppt
TRANSCRIPT
8/6/2019 Growing Fetus Ppt
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(8th edition)
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Development - the gradual modification of anatomical structures during theperiod from fertilization to maturity
y Major Phases of Development
fertilization - fusion of the male and femalegametes
embryological development - first two monthsafter fertilization
fetal development - from the beginning of the9th week until birth
postnatal development - commences at birth
(8th edition)
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Terms to denote Fetal Growth
OVUM
- From ovulation to fertilization
ZYGOTE
- From fertilization to implantation
EMBR Y O
- From implantation to 5-8 weeks
FETUS
- From 5-8 weeks until term(8th edition)
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Gestation - the time spent in prenatal
development
y Can be divided into 3 three month trimesters:
first trimester - embryological development
and early fetal development; this trimesterbegins with fertilization; the basic structure of all the major organ systems appear
second trimester - development of organs andorgan systems; by the end of this trimester thefetus looks human
(8th edition)
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third trimester - characterized by rapid fetalgrowth; by early in this trimester most of the
organ systems become fully functional; thistrimester ends in birth.
(8th edition)
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Fertilization
y A lso referred as conception, impregnation, orfecundation
y Is the union of an ovum and a spermatozoon.
y
Involves the fusion of two haploid gametes with 23 chromosomes each to produce a zygotethat contains 46 chromosomes.
y fertilization generally occurs in the outer thirdof fallopian tube, ampullar portion.
y oocyte - it is surrounded by corona radiata which is a protective layer of cells, and a ring of polysaccharide fluid the zona pellucida thenthe oocyte will travel through the uterine tubetoward the uterus.
(8th edition)
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y sperm (fig. 28.2) - are introduced into the femalereproductive tract; of the 200 million spermatozoaejaculated into the vagina, about 10,000 enter theuterine tube, and fewer than 100 sperm reach theegg.
y
Reaches the cervix within eighty seconds.y Reaches the fallopian tube within 5 minutes after
deposition.
(8th edition)
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y the acrosomal cap of sperm contains the enzyme
hyaluronidase which breaks down the bondsbetween the cells of the corona radiata
y dozens of sperm are needed to penetrate thecorona radiata
y a single sperm makes contact with the oocytemembrane through CA P ACIT A TION- a finalprocess that sperm must undergo to be redy for
fertilization.y Consist of changes in the plasma-membrane of the
sperm head, which reveal the sperm- bindingreceptor sites.
(8th edition)
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(8th edition)
Cleavage (fig. 28.4) - is a series of cell divisions that subdivide the
cytoplasm of the zygote
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y
Then the zygote migrates over the next 3- 4days towards the uterus.
yThe first division is completed roughly 24hours after fertilization
yThe following divisions occur at 10-12 hourintervals:
morula - solid ball of cells that results after3 days of cleavage; all of the cells areidentical; the morula reaches the uterus onday 4
(8th edition)
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blastocyst - hollow ball of cells after 3
more days of cleavage (6th day)the cells are no longer identical
the inner cavity is called the blastocele
(=b
lastocyst cavity); the outer layer of cells is called the trophoblast
the inner cell mass is a group of cells that will become the embryo; the trophoblastprotects the inner cell mass from theoutside environment
(8th edition)
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Implantation (fig. 28.5)- seven days after fertilization, implantation begins as
the blastocyst connects to the endometrium of the uterus
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(8th edition)
y The trophoblast erodes a path through theendometrium by secreting hyaluronidase
y The trophoblast continues to enlarge and spreadinto the surrounding endometrium
y The erosion of uterine glands releases nutrients
that are absorbed by the trophoblast anddistributed by diffusion to the inner cell mass.
y Trophoblastic extensions encircle endometrialcapillaries
y Capillary walls are destroyed and maternal blood
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y percolates through trophoblastic channels called
lacunaey V illi - extend from the trophoblast into the
endometrium and larger endometrial blood vessels are surrounded and broken down resulting
in greater blood flow through the lacunaey Implantation most often occurs in the fundus or
body of the uterus;
y Ectopic pregnancy - when implantation occursanywhere but the uterus; if implantation takesplace in the uterine tubes it can be life-threatening
(8th edition)
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Embryonic Development: Gastrula to Fetus
y A mniotic cavity - formed by the time of implantation inthe blastocyst; this cavity is formed when the inner massseparates from the trophoblast
y There are two layers of cells that comprise the inner mass.
(AMNIOTIC cavity and the yolk sac)
y The 3 Germ Layers - these three layers of cells willdifferentiate into all of the structures of the body:
ectoderm - will form the skin, hair, nails, brain, spinalcord, epithelium of nasal passages, and mouth
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mesoderm - will form the bones, muscles, heart, blood vessels, kidneys
endoderm - will form the pancreas, thyroid gland, liver,
urinary bladder, respiratory epithelium, digestiveepithelium
(8th edition)
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y Four extraembryonic membranes:
yolk sac - important site of blood cell formation
amnion - surrounds the fluid-filled amniotic cavity which protects the embryo
allantois - will give rise to the urinary bladder
chorion - combination of mesoderm and trophoblastthat will form the placenta
y Chorionic villi - branch and enlarge within theendometrium; embryonic blood vessels develop within each
villus and blood blood f low begins in them by thebeginning of the 3rd week; they provide the surface area foractive and passive exchange of gases, nutrients, and wasteproducts between fetal and maternal blood streams
(8th edition)
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y Placentation - the enlarging chorion becomes
the placenta
by the end of the 4th week a body stalk hasformed that connects the embryo and chorion;
the body stalk contains blood vessels that carry blood to and from the placenta
the placenta becomes concentrated in a disc-shaped area in the endometrium
near the end of the first trimester the fetusmoves farther from the placenta
(8th edition)
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the fetus and placenta remain connected by the
umbilical cord which now contains the placentalblood vessels
the placenta provides nutrients to the embryo-fetus, a site for gas exchange between the
mother and the embryo-fetus, and a place wherethe embryo-fetus can get rid of its wastes
Latin word for pancake
(8th edition)
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y Umbilical arteries - these paired arteries carry bloodfrom the embryo-fetus to the placenta (fig. 28.14)
y Umbilical vein - this vein carries nutrient and oxygen richblood from the placenta to the embryo-fetus (fig. 28.14)
*Mother and baby's blood do not mix!
(8th edition)
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The Endocrine Placenta - the placenta produces and
releases hormones
(8th edition)
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y hCG - human chorionic gonadotropin appears in the
bloodstream soon after implantation the presence of hCG in the urine is a reliable indication
of pregnancy; pregnancy kits test for the presence of thishormone
hCG maintains the integrity of the corpus luteum andpromotes the secretion of progesterone
in the absence of hCG the pregnancy would end as theendometrium is sloughed off; in the presence of hCG,
the corpus luteum persists for 3-4 monthsby the end of the 1st trimester the placenta is secreting
estrogens and progesterone and the corpus luteum is nolonger needed
(8th edition)
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y hPL - human placental lactogen; helps prepare the
mammary glands for milk productiony Relaxin - peptide hormone that has several functions:
relaxin increases the flexibility of the pubic symphysis which permits the pelvis to expand during delivery
it triggers the dilation of the cervix which allows thefetus to move out of the uterus and into the vaginalcanal
it suppresses the release of oxytocin by the
hypothalamus and delays the onset of labor contractionsy Progesterone and Estrogens - maintain the endometrial
lining which allows the pregnancy to continue; at the endof the third trimester, estrogen production accelerates,
which stimulates labor(8th edition)
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(8th edition)