sperm oogenesis

8/4/2019 Sperm Oogenesis

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Ploidy: Number of sets of

chromosomes in a cell

Haploid (n)-- one set chromosomes

Diploid (2n)-- two sets chromosomes

Eggs and sperm are haploid (n)


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Developmental stages of

spermatogenesis

In the course of spermatogenesis the germ cellsmovetowards the lumen as they mature.

A-spermatogonium

-spermatogonium

!rimary spermatocyte (" spermatocyte order I)

#econdary spermatocyte (" spermatocyte order II)

#permatid #perm cell (" spermato$oon)


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%he spermatogenesis can &e su&di'ided into

two successive sections

%he first comprises the cells from thespermatogonium up to and including the

secondary spermatocyte and is termed

spermatocytogenesis. %he second one comprises the

differentiationmaturation of the sperm cell*

starting with the spermatid phase and istermed spermiogenesis (or

spermiohistogenesis).


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%he appro+imate 64 daycycle of the

spermatogenesis can &e su&di'ided into four

phases that last differing lengths of time

,itosis of the spermatogonia-- days--- /p to the

primary spermatocytes

0irst meiosis-- 21 days-- 0or the di'ision of the primary

spermatocytes to form secondary spermatocytes

#econd meiosis-- A few hours-- 0or the spermatids#permiogenesis-- 21 days--- /p to the completed

sperm cells

Total 64 days


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perma ocy ogenes s

Among the spermatogonia(all in all*

o'er &illion in &oth testicles) that formthe &asal layer of the germinal epithelium*

se'eral types can &e distinguished

certain type "cells are seen asspermatogonia that di'ide mitotically and

reproduce themsel'es where &y the

spermatogonia population is maintained.


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%he &eginning of spermatogenesis in which the

daughter cells (second group of type " cells)

remain &ound together &y thin bridges ofcytoplasm. %hrough the preser'ation of these

cytoplasmic connections* spermatogonia are

inducted into the spermatogenesis process.

After a further mitotic di'ision type #

spermatogoniaare engendered that also

di'ide themsel'es mitotically into primaryspermatocytes (I).


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%he freshly created primary spermatocytes($)now enter into the first meiosis.

%hey then go immediately into the # phase(that is* into the preleptotenemeiosis)*dou&le their internal DA* lea'e the &asalcompartment and reach the special milieu ofthe luminal compartment.

0ollowing the # phase* these cells attain thecomple+ stage of the prophase of the

meiosisand &ecome there&y noticeablyvisiblewith a light microscope.


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%his prophase* which lasts %4 days* can &e

di'ided into fi'e sections

&eptotene 'ygotene

Pachytene

Diplotene

Diainesis


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In the prophase in e'ery germ cell a

new com&ination of maternal and

paternal genetic material occurs.

After the long prophase follow the

metaphase* anaphase and telophasethat ta3e much less time.

4ne primary spermatocyte yields two

secondary spermatocytes.


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%he secondary spermatocytesgo directly intothe second meiosis* out of which the spermatidsemerge.

#ince in the secondary spermatocytes neitherDA reduplication nor a recom&ination of thegenetic material occurs* the second meiosis canta3e place 5uic3ly.

It lasts only around fi'e hours and for that reasonsecondary spermatocytes are rather seldom seenin a histological section.

%hrough the di'ision of the chromatids of a

secondary spermatocyte* two haploid spermatidsarise that contain only half the original DAcontent.


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esides the sperm cells the

spermatidsare the smallest cells of

the germinal epithelium. In a processlasting se'eral wee3s (so-called

spermiogenesis or

spermiohistogenesis) they are

transformed into spermatocytes with

the acti'e assistance of the #ertoli6scells.


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spermatogenesis wa'e


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As in the diagram* spermatogenesiswa'es mo'e in spirals - li3e a

cor3screw - towards the inner part ofthe lumen.

4utside* on the edge of the tu&uleand at the &eginning of the spiral* liethe spermatogonia7 and* at the end of

the spiral* the fully de'eloped spermcells are in the lumen.


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perm ogenes s(spermatohistogenesis) and

structure of the sperm cell

%he differentiation of the spermatids intosperm cells is called spermiogenesis. It

corresponds to the final part of

spermatogenesis and comprises the

following indi'idual processes that partially

proceed at the same time


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Nuclear condensation thic3ening andreduction of the nuclear si$e*

condensation of the nuclear contents intothe smallest space.

"crosome formation 0orming a cap(acrosome) containing en$ymes that playan important role in the penetrationthrough the pellucid $one of the oocyte.

lagellum formation generation of the

sperm cell tail. *ytoplasma reduction elimination of all

unnecessary cytoplasm.


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.A+onemal structure*

first flagellar

primordium

2.8olgi comple+

9.Acrosomal 'esicle

1.!air of centrioles

(distal and pro+imal):7,itochondrion

.ucleus

;.0lagellar primordium

.Acrosomal cap


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Nuclear condensation%he nucleus &ecomes smaller* denser and

ta3es on a characteristic* flattened form.#een from a&o'e* the nucleus is o'al and*from the narrow side* is pear-shaped.

%he acrosome lies o'er the tip. ucleus andacrosome form the sperm cell6s head that is&ound to the mid-piece &y a short nec3.


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"crosome formation%he 8olgi comple+ engender the

'esicles* which then merge into alarger formation that settles close tothe cell nucleus and finally in'erts itself

li3e a cap o'er the largest part of thenucleus. %he acrosome correspondsfunctionally to a lysosome and thuscontains lysosomal en$ymes(hyaluronidase among others).


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Development of theflagellum%he future a+onemal structuregrows out of one centriole

(distal). %his consists of a&undle of nine peripheraldou&le microtu&ules and two

single ones in the center.


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0our parts of the finished flagellum can &edistinguished

%he neccontains the two centrioles (pro+imal

and distal) among other things. %he mid piececonsists of a sheath of ring-

shaped mitochondria grouped around thea+oneme to pro'ide the energy for the flagellarmo'ement.

%he principle piecehas a sheath of ring fi&ersaround the a+oneme.

%he tailconsists of only the =?2 structure of thea+oneme

%he mature sperm cell is appro+imately > mmlong and completely en'eloped &y the plasmamem&rane.


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. . !lasma mem&rane2.4uter acrosomal mem&rane9.Acrosome1.Inner acrosomal mem&rane

:.ucleus.!ro+imal centriole;.@est of the distal centriole.A+oneme.Anulus2.@ing fi&ers

A.Head.ec3.,id pieceD.!rincipal pieceE.Endpiece%he mature sperm cell is slender7 in the middle part* the mitochondria are thic3 andring-shaped. %he DA in the nucleus is ma+imally condensed.

&e dig+s interstitial cells and


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&eydig+s interstitial cells and

hormonal regulation

etween the seminal canals lie Beydig6sinterstitial cells. %hese are endocrine cells thatmainly produce testosterone* the male se+ualhormone* and release it into the &lood and intothe neigh&oring tissues.

An initial acti'e stage of these cells occurs duringthe em&ryonic de'elopment of the testis. Bater in

Cu'enile life* due to the influence of the &,(luteini$ing hormone) secreted &y the anteriorhypophysis (pituitary gland)* Beydig6s interstitialcells enter a second* long lasting stage of acti'ity.

%ogether with the hormones secreted &y theadrenal corte+* testosterone initiates pu&erty andthus the maturation of the sperm cells.

es os erone pro uc on s rec e y


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es os erone pro uc on s rec e y(luteini$ing hormone)* secreted &y the anterior

lo&e of the hypophysis.

%here &y testosterone can &e transported &y

#ertoli6s cells into the luminal compartment

and there &e concentrated. %estosterone isdecisi'e for spermatogenesis.

%estosterone is also carried away 'ia &loodand lymph fluid. %estosterone has effects on all

tissues* especially also on the &rain during

de'elopment as well as on the se+ual organs.


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4ogenesis

0ollowing the immigration of the primordial germcellsinto the gonadal ridge* they proliferate* are

en'eloped &y coelomic epithelial cells* and form

germinal cords that * though* 3eep their connection

with the coelom epithelium. ow a cortical $one (corte+ o'arii) and a medulla can

&e distinguished* where&y it should &e mentioned that

in females the germinal cords ne'er penetrate into the

medullary $one.

In the genital primordium the following processes then

ta3e place


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A wave of proliferation&egins that lasts

from the :th wee3 to the ;th month

primary germ cells arise in the cortical$one 'ia mitosis of oogonia clones*

&ound together in cellular &ridges* that

happens in rapid succession.

%he cell bridgesare necessary for a

synchronous onset of the su&se5uentmeiosis.


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ith the onset of the meiosis (earliest

onset in the prophase in the 2th wee3)

the designation of the germ cells changes. %hey are now called primary oocytes.

%he primary oocytes &ecome arrested in

the diplotene stage of prophase I (theprophase of the firstmeiotic di'ision).


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#hortly &efore &irth* all the fetal oocytes in thefemale o'ary ha'e attained this stage. %hemeiotic resting phase that then &egins is called

the dictyoteneand it lasts till puberty* duringwhich each month (and in each month thereafteruntil menopause) a pair of primary oocytescomplete the first meiosis.

4nly a few oocytes (secondary oocytes plus onepolar &ody)* though* reach the second meiosisand the su&se5uent o'ulation. %he remainingoocytes that mature each month &ecome atretic.

%he primary oocytes that remain in the o'ariescan stay in the dictyotene stage up tomenopause* in the e+treme case* without e'ermaturing during a menstrual cycle.


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hile the oogonia transform into primary

oocytes* they &ecome restructured so that at

the end of prophase I (the time of thedictyotene) each one gets en'eloped &y a

single layer of flat* follicular epithelial cells

(descendents of the coelomic epithelium).

(oocyte ? follicular epithelium " primordial

follicle).


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4n the one hand* the female germ cell

that at &irth is called the primary oocyte*

and which can de'elop further only during(and after) pu&erty (hormonal cycle is

necessary).

4n the other hand* the follicular epitheliumthat can de'elop further from the

primordial follicle 'ia se'eral follicle

stageswhile oocytes remain in their

primary state.


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%he developmental se-uenceof

the female germ cells is as

follows

Primordial germ cell .

oogonium . primary oocyte .primary oocyte in the

dictyotene


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%he developmental se-uenceof a

follicle goes through 'arious follicle

stages Primordial follicle . primary follicle .

secondary follicle . tertiary follicle

(graafian follicle)

#ince a follicle can die at any moment in

its de'elopment (" atresia)* not all reachthe tertiary follicle stage.


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!tructure of the ovary

An o'ary is su&di'ided into cortical(o'arian corte+) and medullarycompartments(o'arian medulla).

oth &lood and lymph 'essels are found inthe loose connecti'e tissue of the o'arianmedulla.In the cortical compartmentthe oocytes

are present within the various folliclestages.


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%he se+ hormones influence the primordial follicles togrow and a restructuring to ta3e place.

0rom the primordial follicles the primary follicles*

secondary follicles* and tertiary follicles de'elop in turn. 4nly a small percentageof the primordial follicles reach

the tertiary follicle stage - the great maCority meet theirend &eforehand in the 'arious maturation stages.

Barge follicles lea'e scars &ehind in the cortical

compartment and the small ones disappear without atrace.

%he tertiary follicles get to &e the largest and* shortly

&efore o'ulation* can attain a diameter up to 2.: mmthrough a special spurt of growth. %hey are then termedgraafian follicles.


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.!rimordial follicle

2.!rimary follicle

9.#econdary follicle

1.%ertiary follicle:.Antrum folliculi

.umulus oophorus


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%he follicle stages from primordial

follicle to tertiary follicle

Primordial follicle

At the time of birthall the sur'i'ing primary

oocytes are surrounded &y thin/ single layers

of so-called follicular epithelial cells. %hese aredelimited from the rest of the o'arian stroma &y

a thin &asal lamina.

0ollicular epithelial cells are former coelomic

epithelial cells. %he primordial follicles alwaysform the ma0ority of the follicles in the ovary.


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/nder the influence of the se+ hormones

some of themare a&le to develop

furtherto one or more. Although this further de'elopment can

already ta3e place sporadically in the time

&efore &irth and up to pu&erty* the mainpart occurs as soon as a regular hormonal

cycle is esta&lished.

!articularly the last phase of thematuration of a tertiary follicle to &ecome a

large follicle* ready to rupture* remains

reser'ed for the time of regular cycles.


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Primary follicle

In the transition of theprimordial follicles into

primary follicles.


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A.!rimordial follicle

.!rimary follicle

.4ocyte2.0ollicular epithelium


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!econdary folliclehen primary follicles sur'i'e* secondary follicleswith follicular epitheliums encompassing multiple

rowsare engendered. %heir identifying characteristic is a fluid-filled ca'ity*the antral follicle.

%his is now called the stratum granulosum. In thesecondary follicles a glycoprotein layer* the pellucid

$one* &etween the oocyte and follicular epithelium&ecomes 'isi&le.

ytoplasmic processes of the granulosa cells that lieupon it reach the oocyte through the pellucid 1oneand there&y assure their maintenance function.4utside the &asal lamina the stroma o'arii organi$esitself to &ecome theca folliculi cells.

#econdary follicle


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.4ocyte2.!ellucid $one9.#tratum granulosum

1.%heca folliculi cells


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Tertiary follicleIf the secondary follicles sur'i'e* tertiary folliclesare engendered.

%he oocyte lies at the edge in a mound made ofgranulosa epithelial cells* the cumulusoophorus.

In the meantime it has grown so large that itscellular nucleus has attained the si$e of a wholeprimordial follicle.

%he connecti'e tissue around the follicle hasalready clearly differentiated itself into a theca

interna* well supplied with capillaries* out oflarge* lipid-rich cells (hormone production) and atheca e+terna* which forms a transition to thestroma o'arii and contains larger 'essels.


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.4ocyte2.!ellucid $one9.#tratum granulosum

1.%heca interna:.%heca e+terna.Antral follicle;.umulus oophorus (8ranulosa cells*

together with the oocyte)


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Decisi'e for a successful folliclegrowth is a well-de'eloped net of

capillaries in the theca interna. %he precise steering mechanism that

leads to the selection of a follicle and

its su&se5uent maturation to &ecomea graafian follicle is still un3nown.

efore o'ulation a growth spurt of the

tertiary follicles ta3es place.


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2raafian follicle

%his corresponds to anespecially large tertiary folliclethat can &e e+pected to suffice

for o'ulation.

Phase ":


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Phase ":!rimordial germ cells grow* proliferate and &ecome sheathed with coelomicepithelial cells. 8onadal cords arise7 th to


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4ne terms the decline or theregression of follicles of each stage at

e'ery time in the life of a womanfollicular atresia.

%hese follicles do not o'ulate and the

name is deri'ed from that fact. 0ollicle atresia occurs more

intensely* though* at certain moments

(fetal period* early postnatal* &egin ofthe menarche).


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3planations for the onset of heightened atresiaare:

a) in the 54th wee:

Already during the meiotic prophase* mainly in thepachytene stage(lasts the longest* around 9wee3s)* the cells are especially suscepti&le andsuccum&.

ith the formation of the primordial follicle in the

th wee3 the follicular atresiaalso &egins as anadditional reason for the decline in the num&er ofgerm cells.

oth processes together cause the germ cell countto shrin3 to a third (somewhat o'er 2 million o'ary)of the ma+imum num&er.


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postnatal:During the fetal period se+ hormones are producedin the placenta. %his results in a high estrogen le'el

in the &lood of the mother and of the fetus. %his gi'es rise to a considera&le maturation of the

primordial follicles up to the tertiary follicle phase inthe female fetus.

hen the se hormone level in the fetus sinsafter &irth all of the pre'iously matured follicles&ecome atretic (a slight withdrawal &leeding cane'en occur in the newly &orn from the :th to the>th day).

!er o'ary there are then less than 2 million germcells present afterwards.

during puberty:ith th t f & t ( t d 2 f )


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ith the onset of pu&erty (at around 2 years of age) anelevated production of estrogenoccurs again* whichleads to a maturation of the inner and outer genderattri&utes.

After pu&erty is past* around 2:>6>>> germ cells proo'ary remain. ith the onset of a regular cycle a nearlylinear decline commences that with 1> years of ageincreases.

ith the continuous decrease of the follicle cell count theproduction of estrogen is also reduced constantly. ithroughly :> years of age when follicles are no longerpresent* the estrogen production ceases andmenopause ensues

It is assumed the dictyotene stage of meiosis representsa special condition for oocytes that e+hi&its great sta&ilitywith regard to outer physical and chemical influences. Incontrast* the earlier stages* especially the pachytene*are more sensiti'e.

Th i l


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The ovarian cycle

4f the roughly :>>6>>> follicles that are

present in the two o'aries at the &eginning

of se+ual maturity* only around 1 reach

the graafian follicle stage and are thusa&le to release oocytes (o'ulation). %his

num&er is simply deri'ed &y multiplying

the num&er of cycles per year (2) and thenum&er of years in which a woman is

fertile (1>).


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I th t f thi h l t l i th


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In the centerof this hormonal control is thehypothalamamics.hypophysial (pituitarygland) systemwith the two hypophysial

gonadotropins 0#H and BH. %he pulsating li&eration of 8n@H &y the

hypothalamus is the fundamental preconditionfor a normal control of the cyclic o'arian

function. %his cyclic acti'ity releases 0#H and BH* &oth of

which stimulate the maturation of the follicles inthe o'ary and trigger ovulation.

During the o'arian cycle* estrogen is produced&y the theca interna and follicular cells (in theso-called follicle phase) and progesterone &y thecorpus luteum (so-called luteal phase).

%h t l i it f th h l l


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%he control circuit of the hormonal cycle

has two essential control elements

%he pulsatileli&eration of 8n@H* as wellas 0#H and BH

As a rule the ovarian cycle lasts %


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As a rule* the ovarian cycle lasts %

days. It is su&di'ided into two phases

ollicle phase recruitmentof a so-calledfollicle cohort and* within this* the selection

of the mature follicle. %his phase ends

with ovulation.

3stradiolis the steering hormone.

ormally* it lasts 1 days* &ut this can

vary considerably7

&uteal phase progesteron production

&y the yellow &ody (" corpus luteum)

and lasts 1 days (relati'ely constant).


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A.0ollicle phase.Buteal phase

.!rimary follicle

D.#econdary follicleE.%ertiary follicle0.8raafian follicle

E2 Estradiol

!r !rogesteroneBH Buteini$ing hormone0#H 0ollicle stimulating hormone

ll % ll Di i i ! d t


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ell %ype ell Di'ision !roduct

#permatagonium (2)/ndergoes ,itosis

!rimary #permatocyte (2) !rimary #permatocyte (2)/ndergoes

,eiosis I F results in

2 #econdary #permatocytes () #econdary #permatocyte ()/ndergoes

,eiosis II* results in #permatid ().

#permatid ()--,aturation - no cell di'ision--#perm cell ()


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4ogonium (2)de'elopment - no cell di'ision--!rimary 4ocyte (2).

!rimary 4ocyte (2)/ndergoes ,eiosis I ---#econdary 4ocyte () and 0irst !olar ody().

#econdary 4ocyte ()/ndergoes ,eiosis II(stimulated &y fertili$ation from sperm)-----4'um () and #econd !olar ody ()

sperm oogenesis

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