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BLOK IVBIOLOGI MANUSIA

A Kuliah 1. Asal usul mahluk hidup Dosen - K M A

- S H

II. !e"ilaku mahluk hidup Dosen - # M $ - S N A

III. Mahluk hidup dan lin%kun%an Dosen - # M $ - K M A#AM KULIAH & ' ( )* M+NI

B !"ak,ikum Game,o%enesis +m"io%enesis& es,is O/a"ium 0a, +m"2o a2am

3 kelompok Mahasis4a a5 '* mahasis4a $ak,u p"ak,ikum 6 7 8 9am

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- "i4ani =0$? - Lusia Ha2a,i =LH? - Si,i Hildani hai =SH?

D Ins,"uk,u" !"ak,ikum - N ; > - # M $ - L H - S H - 0 $ - S N A

+. MA+0I !0AKIKUM GAM+OG+N+SIS @ es,is 0a, O/a"ium 0a, +m"ioa2am =) ahap sa9a?



:AAAN KULIAH BLOK IV

O!IK BIOLOGI MANUSIA

KOM!++NSI ANG AKAN DI:A!AI @

Memahami kai,an masalah keseha,an dan kedok,e"an da"i pen%e,ahuan ,en,an%asal usul manusia s,"uk,u" sel homeos,asis pe"ilaku makhluk hidup dan pe"anlin%kun%an dan in,e"aksin2a den%an manusia

SASA0AN !+MB+LA#A0AN @

1. Memahami asal usul makhluk hidupCi"i Ci"i makhluk dan homeos,asisdalam kai,ann2a den%an masalah keseha,an dan kedok,e"an =:6!1?

6. Memahami pe"ilaku makhluk hidup dalam kai,ann2a den%an masalahkeseha,an dan kedok,e"an =:6?8. Memahami e"a%ai ak,o" lin%kun%an dan kai,ann2a den%an manusia

masalah Keseha,an dan kedok,e"an =:6?'. Memahami mekanisme Homeos,asis dalam upa2a mempe",ahankan

keseiman%an un%si sis,em ,uuh a%a" ,e,ap no"mal ,e"hadap pe"uahanlin%kun%an in,e"nal dan eks,e"nal ,uuh manusia =:6?.

MA+0I KULIAH

1. ASAL USUL MAKHLUK HIDU!Men9elaskan ,en,an% ,eo"i e/olusi makhluk hidup dan kehidupan di mukaumi ini. Unsu" unsu" 2an% ,e"lia, dalam pemen,ukan makhluk hidupsiklus ai" Ea4an Ehu9an ,"uk,u" sel :a"a Ca"a klasiikasi makhluk hidupCi"i Ci"i makhluk hidup dan homeos,asis.

6. !+0ILAKU MAKHLUK HIDU!Men9elaskan kai,an %en dan pe"ilaku seleksi alam men9elaskan e/olusidan pe"ilaku sosial. Memahami mekanisme pe"ilaku melalui pemahaman,e"hadap pe"sepsi pada he4an. Mampu memahami kompleksi,as pe"ilakuden%an men9elaskan ,en,an% @ ins,iC, pen%amilan kepu,usan danmen,ali,as pada he4an.

8. MAKHLUK HIDU! DAN LINGKUNGANNAMen9elaskan ,en,an% populasi "an,ai makanan dan keseiman%anekolo%is dan pe"an manusia dalam keseiman%an ekolo%is. Men9elaskan,en,an% konsep lin%kun%an pe"manen se9a"ah pemukiman danpe"u"uan Men9elaskan p"oses "e/olusi a%"ikul,u" pe",anian danu"anisasi Men9elaskan pen%a"uh di/e"si,as manusia . Men9elaskan



pe"is,i4a 2an% e"kai,an den%an polusi 2an% mempen%a"uhi manusia danln%kun%ann2a. Men9elaskan pen,in%n2a pen%elolaan sume" da2a alam2an% melipu,i konse"/asi kuali,as lin%kun%an dan sume" da2a alam.Men9elaskan pe"keman%an io,eknolo%i penCe%ahan dan penCema"anpolusi di lin%kun%an hidup.

'. HOM+OSASISMen9elaskan pe"an homeos,asis dalam men%a,u" kons,ansi lin%kun%anin,e"nal ,uuh a%a" ,e,ap dalam keseiman%an 2an% op,imal a%a" ,e,apdapa, e"un%si den%an no"mal melalui mekanisme umpan alk ne%a,idan posi,i. Men9elaskan p"oses homeos,asis pada sis,em Ca"io/asCula"sis,em "espi"asisis,em u"ina"ius o"%an %e"ak dan pendukun% sis,em o,o,sis,em s2a"a. Sis,em endok"in dansis,em "ep"oduksi.

Buku 0u9ukan @

1. S2/ia S. Made" Human Biolo%2 F,h edi,ionMC G"a4hill Hi%he" +duCa,ionBos,on 6**'.

6. Gleen and Susan oole Unde"s,andin% Biolo%2 o" Ad/anCe Le/elS,anle2 ho"ne2 !u.L,d. :ha,elam UK 1.

8. :ampell N.A e, all Biolo%2 ),h edi,ion Addison $esle2 Lon%man InC.Ne4 o"k 1.



1. Human body as whole

a. Biologi Manusia

i. The Origin of Life :

o Early thories of the origin of life

o Oparin’s Theoryo The age of the earth

o The dawn of life

The question of how life began on earth has perplexed humans throughout

history and is still unanswered. The bestsupported hypothesis at present is

that life arose spontaneously through the asso!iation of atoms and mole!ules present on the early earth. This hypothesis has been supported by the

dis!o"ery that "irtually all of the small organi! mole!ules out of whi!h the

ma!romole!ules of life are !onstru!ted !an be synthesi#ed under !onditionsthought to be present on the early earth. $ome of these mole!ules ha"e been

found in meteorites% indi!ating that su!h mole!ules !an indeed be synthsi#ed

abioti!ally% that is% without the inter"ention of li"ing things.There is a huge gap between the !onstru!tion of small organi! mole!ules% li&e

nu!leotides and amino a!ids% and the assembly of a li"ing !ell. 'lthough

efforts to show how this gap might ha"e been !rossed are being made% we still

ha"e little more than ideas of what steps must ha"e been ne!essary.There is some fossil e"iden!e for the existen!e of li"ing organisms (.) billion

years ago% only a billion years after the formation of the earth. The

spontaneous assembly of li"ing things probably has not o!!urred sin!e then be!ause any newly synthesi#ed organi! mole!ules would ha"e been

!onsumed% oxidi#ed by the atmosphere.

Evolution : The Mechanisms: The Classification of Life.



iii. Ecology : The Biology of Populations and Environment

o Energy flow through the biosphere

o The !y!les of matter in the biosphere

o The 6rowth of populations

o *ntera!tions between spe!ies

o Human e!ology 3 pestilen!e and !ompeting for food

The si#e of populaton in!reases when the birth rate ex!eeds the death rate. 7eath

rates in the human population ha"e de!lined in the last !entury% than&s largely toin!reased food produ!tion and a dramati! de!line in the toll ta&en by infe!tious

diseases.

On!e a parasite enters its host% it may ,1- &ill the host% ,4- be &illed by the host%,(- !oexist with the host for an indefinite period of time. 2hi!h of these out!ome

o!!urs depends on ,1- the number of in"ading parasites% ,4- their pathognei!ity%

that is% the se"erity of the damage they !an !ause% ,(- the natural defenses of thehost% and ,5- the effe!ti"eness of any teratment that may be gi"en.

8ertebrates !ombat in"ading parasites by a "ariety of men!hanisms% in!ludings!a"enging them with phago!yti! !ells and manufa!turing antibodies% whi!h aid

in the destru!tion of the parasites..Two broad !ategories of infe!tious diseases are found in human. ,1- $ome

parasites !ause a brief illness% whi!h is followed by either the death of the host or

the elimination of the parasite and a longli"ed immunity. *n either !ase% the patient is !ontagious to others for only a brief period. Measles% mumps% and

smallpox are examples. These diseases are higly densitydepedent. They !an be

maintained only in a population where a large number of sus!eptible indi"idualsli"e !lose enough for the parsites to pass easily from person to person. ,4- 9ertain

parasites establish protra!ted% sometimes lifelong% infe!tions in the host. 'n

Effe!ti"e immunity fails to de"elop. The host usually remains !ontagious forothers for the entire period. $u!h infe!tions are relati"ely densityindependentthey !an exist indefinitely in small populations. Malaria% tuber!ulosis% and

s!histosomiasis are !ommon examples.

$in!e world war **% a steadily in!reasing number of drugs% e.g. antibioti!s% ha"e been dis!o"ered that &ill parasites without seriously damaging the host. *n ea!h

!ase% the drug affe!ts a metaboli! pro!ess of the parasite that does not o!!ur in the

host.

o 9arrying !apa!ity% pest !ontrol% 77T% pesti!ides.



4. $ystem of Human Body

i. :eprodu!tion system

'natomi

$i&lus menstruasi

6ametogenesis

/ertili#ation is still pre!eded by meiosis% but the produ!ts of meiosis are the

gametes themsel"es. To !arry out their fun!tion most effe!ti"ely% gametes should bemotile ,so they !an meet and unite- and supplied with food reser"es to furnish energy

and material for the de"eloping embryo. These two requirements are rather

in!ompatible. The solution is 3 one gemete% the sperm% that is motle and small and one

gemete% the egg% that is filled with food reser"es.$perm !ells are little more than flgellated nu!lei. They are produ!ed in testes by

spe!iali#ed !ells !alled spermatogonia. $permatogonia% whi!h are diploid% may di"ide

by mitosis to produ!e additional spermatogonia or they may be transormed in

spermato!ytes. Meiosis of ea!h spermato!yte results in the produ!tion of four haploid!ells% the spermatids. These then be!ome transformed into sperm !ells% losing most of

their !ytoplasm in the pro!ess.Eggs are produ!ed in o"aries. 7iploid oogonial !ells di"ide by mitosis to produ!e

additional oognial !ells. *n fa!t% by the time the female human fetus ,a de"eloping

baby- is 1) wee&s old% multipli!ation of oogonia is almost !ompleted. This !ertainly ;ustifies 2eismann’s emphasis on the early isolation of the germplasm from the

somaplasm< The beginning of egg formation o!!urs when oogonia start growing and

be!ome transformed into primary oo!ytes. These diploid !ells enter prophase of the

first meioti! di"ision and at that point their de"elopment stops. Then thousands of primary oo!ytes begin a period of mar&ed !ell growth. Ea!h is en!losed in a !luster of

!ells !alled a folli!le. /ood materials are transferred from the folli!le !ells to the

growing oo!yte. 2hen the phase of de"elopment is !ompleted% the egg !ell is a largesphere !ontaining in its !ytoplasm large quantities of 7='% :='% yol&% mito!ondria%

and oil droplets. 's growth of the primary oo!yte nears !ompletion% the first meioti!

di"ision * !ompleted% too. The !ytoplasm is not distributed equally to the twodaughter !ells% but almost all of it passes to ;us one of them. The other !ell is !alled o

polar body. 't this time% the egg is ready for release from the folli!le% a pro!ess

&nown as o"ulation. The folli!le and o"ary walls rupture% allowing the egg to pass

into the body !a"ity.



6ametogenesis

>:E8*E26ametes are the reprodu!ti"e !ells where unite to initiate the de"elopment of a

new indi"idual. There are 3

the o"a of the female the spermato#oa of the male

The gametes themsel"es ? the !ells that gi"e rise to them !onstitute the indi"idual’s germ

plasm. The other !ells of the body% whi!h ta&e no dire!t part in the produ!tion of gametesare !alled somati! !ells or the somatoplasm.

6amatogenesis is the pro!esses by whi!h germ plasm is !on"erted into higly

spe!iali#ed sex !ells that are !apable of unitiy at fertili#ation and produ!ing a new being.9ommonly% gametogenesis is di"ided into four ma;or phases 3

1. the origin of the germ !ells ? their migration to the gonads

4. the multipli!ation of the germ !ells in the gonads through the pro!ess of mitosis

(. redu!tion of the number of !hromosomes by onehalf by meiosis

5. the final stages of maturation ? differentiation of the gametes into spermato#oonor o"a that are !apable of fertili#ing or being fertili#ed

+E':=*=6 OB@E9T*8E$

'fter studying this se!tion% you should be able to3 understand the origin of the germ !ells ? their migration to the gonads

understand the basi! prin!iples of mitosis ? meiosis

understand ? explain the pro!ess of spermatogenesis ? oogenesis

understand the differentiation of the gametes into spermato#oon or o"a

understand the maturation of the sperm

!ompared the pro!ess of spermatogenesis ? oogenesis

The origin of primordial germ cells & their migration to the gonads

/uture gametes !an be identified among the endodermal !ells of the yol& or yol&

sa!. These !ells% !alled primordial germ !ells% !an be re!ogni#ed by their large si#e ?!lear !ytoplasm ? by !ertain histo!hemi!al !hara!teristi!s% su!h as high al&aline

phosphatase a!ti"ity in mammals. >rimordial germ !ells in human embryos !an be

re!ogni#ed first time at 1A somite in the splan!hnopleure of the yol& sa!.How do they get to the gonads The primordial germ !ells be!ome !apable of

amoeboid mo"ements ? migrate up through the dorsal mesentery and into the gonads.

There is some e"iden!e of !hemi!al attra!tants that stimulate the migration of primordial

germ !ells to the gonads. The orientation ? physi!al !hara!teristi! of the substrate helpguide the germ !ells to the gonads.

Proliferation of germ cells y mitosis

The germ !ells enter a proliferati"e phase in whi!h their numbers in!rease greatly

by means of mitosis. Mitoti!ally a!ti"e germ !ells in the female are !alled oogonia in themale they are &nown as spermatogonia.



*n the human female% inten!e mitoti! a!ti"ity between the se!ond ? fifth months

of pregnan!y bring the population of oogonia from a few thousand to about C million.

The number of oo!ytes then falls sharply% mainly be!ause of atresia ,naturaldegeneration- and by se"enth month most of the oo!ytes ha"e entered the prophase of

their meioti! di"ision. This brings to an end the proliferati"e phase of gametogenesis in

the female.Mitosis begins in the gonad of the early embryo% but it !ommonly persist

throughout the life span at the male. The testes always retain a germinati"e population of

spermatogonia. Beginning at puberty% periodi! wa"es of mitosis produ!e subpopulationsof spermato!ytes that enter meiosis as syn!hronous groups. This a!ti"ity !ontinues as

long as the male is !apable of reprodu!tion.

Meiosis

One of fundamental requirements in the sexual reprodu!tion is that the normal

number of !hromosomes must be maintained from one generation to another% by the

redu!tion of the !hromosomal !omplement of the gametes from the diploid ,4n- to thehaploid ,1n- !ondition during gametogenesis.

' ma;or requirement of meiosis is that ea!h haploid gamete must a!quire a!omplete set of !hromosomes. Det meiosis is the phase during whi!h new !ombinations

of geneti! material% some arising from maternal genes and others from paternal genes% are

assembled. 6eneti! re!ombination o!!urs by31. the random distribution of maternal or paternal !hromosomes to the daughter !ells

4. the ex!hanging of portions of homologous !hromosomes by !rossing o"er at

spe!ifi! phases of meiosis.

Thus at the beginning of meiosis the !ell !an be des!ribed as 4n% 5! in other words% the !ell !ontains the normal number ,4n- of !hromosomes% but be!ause of

repli!ation% its 7=' !ontent ,5!- is double the normal amount ,4!-. The ob;e!t of meiosis

is to produ!e haploid gametes with a 1n% 1! !omplement of geneti! material. The firstmeioti! di"ision% !alled the redu!tional di"ision% results in the formation of two

geneti!ally dissimilar daughter !ells ,1n% 4!-. *n the se!ond% or equational% meioti!

di"ision ea!h of the pre"ious two !ells produ!es two geneti!ally identi!al daughter !ells,1n% 1!- that !an now be properly !alled gametes.

!permatogenesis and oogenesis compared

*n !ontrast to spermatogonia% ea!h of whi!h gi"es rise to four fun!tional

spermato#oa as the result of two meioti! di"isions% an oogonium produ!es only one

"iable o"um*n the human female% the first meioti! di"ision begins in the embryos and meiosis

is not !ompleted until the onset of puberty at the earliest or ;ust before menopause at the

latest. $permatogenesis does not begin until puberty but is then !ontinuous throughoutlife. There are no prolonged meioti! arrests during spermatogenesis. 'rrest in the

pro!ess of meiosis are prominent during oogenesis. The first o!!urs during prophase *%

espe!ially in the diplotene phase. The diplotene arrest in meiosis !an be "ery prolonged

o"er 5 years in some human o"a. The first meioti! arrest is often bro&en by hormonal



!hanges% and meiosis resumes% only to be arrested again at metaphase **. The se!ond

arrest is released with fertili#ation or artifi!ial a!ti"ation of the egg.

The mature spermato#oon is mar&edly smaller than the spermatogonium and ishighly motile. The mature o"a be!ome larger than oogonia. 7uring de"elopment the egg

stores both energy sour!es and pre!ursors of proteins and nu!lei! a!ids. $perm !ells% by

!ontrast% shed most of their !ytoplasm and must rely on the seminal fluid as an energysour!es. *n anti!ipation of future requirements% the egg produ!es and store up mu!h

:='% whereas there is little or no :=' synthesis during the later stages of

spermatogenesis.

!permatogenesis

The transition from mitoti!ally a!ti"e primordial germ !ells to maturespermato#oa is !alled spermatogenesis and it in"ol"es as sweeping series of stru!tural

transformations. This pro!ess !an be bro&en down into three prin!ipal phases3

1. mitoti! multipli!ation

4. meiosis(. spermiogenesis

Mitoti! multipli!ation

$permatogonia ha"e been subdi"ided into two main populations3

1. Type' spermatogonia represent the stem!ell population. 2ithin this populationis a group of dar&% non!y!ling !ell that may be longterm reser"e !ells

4. $ome of these !ells be!ome mitoti!ally a!ti"e pale !ells% whi!h ultimately gi"e

rise to typeB spermatogonia. These are !ells whi!h be!ome !ommitted to lea"ing

the mitoti! !y!le and whi!h go on finish the pro!ess of spermatogenesis.

Meiosis

'fter the final round of 7=' dupli!ation% the typeB !ells are !alled preleptotenespermato!ytes and are ready to pass through the meioti! phase of spermatogenesis.

7uring the first meioti! di"ision ea!h primary spermato!yte di"ides into two equal

daughter !ells. 2ith the onset of the se!ond meioti! di"ision% these !ells are &nown asse!ondary spermato!ytes. /our haploid spermatids result from the se!ond meioti!

di"ision.

The spermatids undergo a profound transformation from relati"ely ordinary

loo&ing !ells to the extremely spe!iali#ed spermato#oa. The third phase inspermatogenesis is !alled spermiogenesis or spermatid metamorphosis.

$permiogenesis*n the metamorphosis of a spermatid many radi!al !hanges o!!ur.

't the end of the se!ond maturation di"ision the nu!leus is in typi!al interphase

!ondition% with dispersed% finely granular !hromatin and a re!onstituted nu!lear menbrane. The nu!leus begins to lose fluid% with a resultant de!rease in its si#e

and a !on!entration of its !hromatin. This !ontinues until the !ompa!ted

!hromatin !omes to !onstitute the bul& of the head of the spermato#oon



The !ytoplasm streams away from the nu!leus% whi!h will be!ome the sperm

head% lea"ing only a thin layer !o"ering the nu!leus.

>art of the !ytoplasm !ontaining the 6olgi apparatus be!omes !on!entrated at theapi!al end of the de"eloping sperm head% and the a!rosome ta&e shape

2ithin the !ytoplasm the !entrioles appear to be a point of an!horage for the

de"eloping flagellum. The posterior !entriole mo"es away from the anterior oneand ta&es on the shape of ring en!ir!ling the flagellum

Mito!hondria begin to form a spiral in"estment about the proximal part of the

flagellum ' spermiogenesis !ontinues% the remaining !ytoplasm disintegrates% lea"ing the

mature spermato#oon stripped of all nonessential parts.

*t !onsist of31. a head !ontaining the nu!leus and a!rosome

4. a midle pie!e !ontaining the proximal part of the flagellum% the !entrioles

from whi!h it arose% and the mito!hondrial helix% whi!h a!ts as an energy sour!e

(. the tail% a highly spe!iali#ed flagellum

The fun!tion of $ertoli !ells31. being the target !ells for /$H

4. synthesi#ing of an androgenbinding protein that maintains a high !on!entration

of testosterone inside the seminiferous tubule(. maintaining the bloodtestis barrier

5. !reating an en"ironment that is important in the differentiation of sperm !ells

). fa!ilitating the release of mature spermato#oa

A. degrading the residual !ytoplasm that is shed during spermiogenesis.

The bloodtestis barrier is ne!essary to pre"ent the body’s immune system from

destroying the maturing sperm !ells% whi!h are antigeni!ally different from the rest of the body. The bloodtestis barrier !onsist of a !ontinuously interlo!&ing sheet of $ertoli !ell

pro!esses% whi!h are atta!hed to one another by tight ;un!tions. Outside the barrier are

spermatogonia and spermato!ytes that are ;ust entering into meiosis. $permato!ytes in the#ygotene stage of meiosis pass through the bloodtestis barrier.

$permatogenesis is not a random pro!ess. The earliest stages of spermatogenesis

o!!ur at periphery of the tubule% and progressi"ely later stages are en!ountered !loser tothe lumen. Howe"er% all stages of spermatogenesis are not seen in the same se!tion of the

seminiferous tubule. Typi!ally% se"eral generations of de"eloping sperm !ells are present

along any radial line drawn in a !ross se!tion of a tubule% and all !ells within a gi"engeneration are in the same stage. *n the human% the time required for a spermatogonium

to de"elop into a spermato#oon is about A5 days.

$perm maturation

7uring their leisurely transit from the seminifeorus tubules to the tail of the

epididymis% where they are retained until their e;a!ulation% the spermato#oa are exposed

to a series of different humoral en"ironments within the male genital du!t system. The



metaboli! apparatus of the spermato#oa be!omes more !apable of translating !hemi!al

energy into a !ertain degree of motility. The head of sperm be!omes !o"ered with a

gly!oprotein !oating whi!h must be remo"ed in the female reprodu!ti"e tra!t beforefertili#ation o!!ur. ' final phase of sperm maturation in the male reprodu!ti"e tra!t might

better be !alled a!ti"ation% after e;a!ulated spermato#oa ha"e !ome into !onta!t with the

seminal fluid se!reted by the seminal "esi!le and prostate gland. The seminal fluid pro"ides the fun!tionally mature sperms with an external energy sour!e whi!h allows

them to gain full motility. /urther !hanges of sperm !ells in the female reprodu!ti"e tra!t

will be des!ribed in the se!tion on fertili#ation.

Oogenesis

't birth the human o"aries !ontain about 4 million oo!ytes ,many of whi!h are

already degenerating- that ha"e been arrested in the diplotene stage of the first meioti!

di"ision. These oo!ytes are already surrounded by a layer of folli!ular !ells% or granulosa

!ells% and the !omplex of the o"um and its surrounding !ellular in"estment is &nown as afolli!le. Of all the germ !ells present in the o"ary% only about 5 ,one per menstrual

!y!le- will rea!h maturity and be!ome o"ulated. The remainder de"elop to "aryingdegrees and then undergo atresia ,degeneration-.

*n human the primary oo!yte plus its in!omplete !o"ering of flattened folli!ular

!ells is !alled a primordial folli!le. +ater in the fetal period% when the folli!ular !ells ha"eformed a !omplete layer around the primary oo!yte% the !omplex is !alled a primary

folli!le. Essentially% all the oo!ytes% remain arrested in the diplotene stage at least until

puberty. $ome of these !ells may not progress past the diplotene stage until the woman’s

last reprodu!ti"e !y!le ,age 5) to ) years-. The #ona pellu!ida% a translu!ent non!ellular membrane% also begins to form around the oo!yte after the first layer of folli!ular !ells is

!omplete. ' thin basement membrane !alled the membrana granulosa forms around the

granulosa !ells of the folli!le. =o blood "essels are found inside the membrana granulosa%and both the oo!yte and the granulosa !ells must rely on diffusion for nourishment and

oxygen.

The earliest stages of de"elopment of primary folli!les ,up to se"eral layers of folli!ular !ells- appear to o!!ur without the mediation of sex hormones. The next step in

folli!ular de"elopment is the formation of a fluidfilled !a"ity !alled the antrum within

the layers of granulosa !ells. This step depend on the presen!e of pituitary gonadotropi!

hormones ,/$H- and the probable mediation of estrogens produ!ed within the folli!le.2hen the antrum has formed% the folli!le is &nown as a se!ondary folli!le% but the oo!yte

within the folli!le is still a primary oo!yte and remains arrested in the diplotene stage.

The se!ondary folli!le be!omes further en"eloped in a layer of modified o"arian!onne!ti"e tissue ,stromal- !ells. 2hen first formed% this layer is &nown as the the!a

folli!uli% but it !ontinues to diffrentiate into two layers. The inner layer% the the!a interna%

is glandular in nature and is higly "as!ulari#ed% whereas the outer the!a externa retainsthe !hara!teristi!s of a !onne!ti"etissue !o"ering.

The hormonally stimulated folli!le now rapidly in!reases in si#e and is &nown as

tertiary ,6raafian- folli!le. The enlarging folli!le mo"es toward the surfa!e of the o"ary%

and the in!reasing liquor folli!uli ultimately !auses it to protrude abo"e the general



surfa!e !ontour. 2hen an o"ary is exposed surgi!ally% a nearly ripe folli!le loo&s li&e a

water blister. $u!h a folli!le is nearly ready to rupture and release its !ontained o"um.

2ithin the folli!le the egg% surrounded by se"eral layers of granulosa !ells% protrudes intothe antrum as the !umulus oophorus. @ust before o"ulation the folli!le is produ!ing large

amounts of estradiol. +H re!eptors are plentiful on both the the!al and granulosa !ells%

and the granulosa !ells also !ontain a high !on!entration of /$H re!eptors. The o"um has been release from its meioti! blo!& in the diplotene stage and goes to finish its first

meioti! di"ision% releasing the first polar body. The folli!le is now ready to respond to the

preo"ulatory +H and /$H surge and !omplete the first stage of its !y!le by releasing theo"um.

'tresia of folli!le

Only a minute per!entage of the o"a and folli!les in the o"ary rea!h maturity. Theothers undergo "arious degrees of maturational !hanges and then begin to degenerate.

This pro!ess is &nown as folli!ular atresia% and a folli!le that is in"ol"ed in degeneration

is said to be atreti!. The regulatory fa!tors underlying atresia of folli!les ha"e not been

!ompletely defined% but there is in!reasing e"iden!e that atreti! folli!les are defi!ient inre!eptors for gonadotropins or estradiol.

9orpus luteum

The history of an o"arian folli!le by no means ends when the folli!le has liberated

its !ontained o"um. 9ells of both the stratum granulosum and the the!a interna be!omein"ol"ed in the formation of the !orpus luteum. The !orpus luteum% so !alled be!ause of

its yellow !olor in fresh material% grows rapidly and be!omes an endo!rine organ%

se!reting both estrogen and progesterone.

One of the ma;or fun!tions of progesterone is to prepare the lining of the uterus tore!ei"e and implant the fertili#ed o"um. *f pregnan!y does not o!!ur% the !orpus luteum

gradually loses its sensiti"ity to pituitary gonadotropins% probably by losing +H ? /$H

re!eptors on its !ells% and it then regresses. *f pregnan!y o!!urs% the !orpus luteumundergoes a greatly prolonged period of growth and may attain a diameter of 4 to ( !m

in humans. The !orpus luteum of pregnan!y is maintained by !horioni! gonadotropin

se!reted by the !ells of the embryo and its surrounding membranes.2hen either type of !orpus luteum begins to degenerate% the !ellular part of the

organ disintegrates and fibrous !onne!ti"e tissue ta&es its pla!e. 's this !onne!ti"e tissue

grows older and more !ompa!t% it gradually ta&es on the !hara!teristi! whitish

appearan!e of s!ar tissue and is !alled a !orpus albi!ans.

materi biolman

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