The Reproductive System
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THE REPRODUCTIVE SYSTEM Ma ria Sus an dani
Th e a bility to re produce is one of th e ch aract erist ics o f a ll li vi ng t hings. Tw o basi c typ es of repro ducti on: – Sexu al reproduct ion p ro duce s of fsp ring t hat a re genetica lly diff erent from th eir parents. – Ase xu al reproduct ion p ro duce s of fsp ring genetica lly identi ca l t o th eir p arent. Anima ls’ re product ive syst ems ca n b e divid ed into the i nternal re product ive o rg ans a nd th e e xt ernal genita lia. Th e gonads are the a ct ual organs t hat produce the game tes. In t he m ale, te stes (si ngular = t est is) p ro duce sp erm , and in t he f ema le, ova ries ma ke eggs.
Asexual Reproduction
Fi ssio n, buddin g, fra gme ntati on, a nd th e f orma tion of rh iz om es a nd st olo ns a re so me o f t he me ch anism s t hat allow organisms to re produce ase xu ally. Ase xu al re product io n allows an o rg anism to rapidly produce man y offsp rin g wit hout f indin g a ma te, and ma ting. Th e l ack of genetic va riability in a se xu ally rep ro duci ng p opulatio ns ca n be d etrime nt al w hen envi ronmenta l co ndit ions c ha nge quickl y.
Growth and asexual reproduction involve mitosis
Th e w ay in whic h ce lls d ivi de d uring g ro wt h i s ca lled m ito si s Ma ny livin g o rganism s u se mi tosis to m ake co mp lete n ew organism, b y growi ng a new o ne out of t hemse lve s (ca lled a se xu al reproduct ion)
Mitosis makes new cells with the same genes as the old one
Th e n ucl eus of a ce ll co nta in s th reads o f DN A, ca lled ch ro mo so mes . Huma n ce ll s, fo r exa mp le , ha ve 46 ch romo so mes. In e ach ch romoso me s, t here are ma ny loci where gene is loca te d Mi tosi s i s a m eth od of ce ll d ivi si on w hich m ake s two new ce lls w ith exa ctl y the sa me numb er of ch rom oso me s, carryi ng exa ctl y th e sa me genes a s the o ld one.
Asexual reproduction produces genetically identical offspring
In a se xu al reprodu ct ion, the n ew o rganisms produce d are genetica lly id entica l t o t heir parent, and to each o th er A g ro up o f geneti ca lly i dentica l organism is call ed a clo ne
Bacteria reproduce by binary fission
Bacte ri a a re m ade o f a si ngle ce lls, wit h a si ngle ci rcu la r m olecu le of DNA When th e bact erium is a bout t o divi de, an e xa ct co py o f t he DN A i s ma de; th e ce ll then d ivi des in to t wo wit h one D NA mo lecu le in each half. Th ose ce lls are geneti ca lly i dentica l to t he o ri gin al ce ll. Th is m eth od of ase xu al rep ro ducti on is ca lled b inary
Fungi produce spores asexually
Plants can be propagated asexually
Ma ny plants are a ble t o reproduce ase xu ally Fo r exa mp le: – By fo rma tion o f t uber, in potato es – By ta ki ng cu tt ing, in ca ssa va etc
Tissue culture
Me thods of produci ng la rg e n umbers of genetica lly identi ca l pla nt s Very large numb ers of p lants ca n be gro wn from a si ngle p lant.
Sexual Reproduction
In se xu al reproduc ti on n ew in divi duals a re produce d by th e fu si on of haploid gamete s to form a dipl oid zyg ote . Sperm a re m ale g amete s, ova (ovu m si ngular) a re fema le g amete s. Me iosi s produce s ce ll s tha t are geneti ca lly d ist in ct from each oth er; Fe rtili za tion i s th e fus io n of two su ch d ist incti ve ce lls t hat prod uce s a uniq ue new co mbin ati on o f allele s , th us incr easi ng v ari ati on.
Human Reproduction and Development
Huma n reproduct ion e mploys i nternal f ertiliza tion, and depends o n th e inte gra te d act io n o f hormo nes , the nerv ous syst em , a nd th e re pro ducti ve syst em . Go na ds are se x organs t hat p ro duce g amete s. Ma le gonads are t he te st es , which produce sp erm and ma le se x hormones. Fe ma le gonads a re t he ova rie s , wh ich produce eggs (ova ) and fe male se x hormo nes.
The Male Reproductive System
Te ste s are su sp ended outsi de th e abdomi nal c av it y by th e scr otum . Semi nife rous t ubules a re in si de each t esti s, and are where sp erm are p roduce d b y me iosi s. About 250 me ters (850 fe et) of tubule s are packe d in to each te st is. Spermato cyt es i nsi de th e tu bul es divid e b y me iosi s to p ro duce sp erma tid s that in t urn deve lop i nto ma ture sp erm.
The male reproductive system
The male reproductive system
Spermatogenesis
Sperm p ro ducti on begins a t puberty a t co ntinue s throughout l ife, wi th se ve ral hundred mi llion sp erm being produce d e ach day. Once sp erm fo rm they m ove i nto t he epididymi s , where they m atu re a nd are st ored.
Human Sperm
Male Sex Hormones
Th e anterior p itui tary produce s foll icl e-st imu lati ng hormone (F SH) and luteinizi ng hormo ne (LH) . Acti on of LH i s co ntro ll ed by t he gonadotro pin -r eleasin g hormo ne ( Gn RH ) . LH st imu lates ce lls i n th e se mi nifero us t ubules t o se cr ete te st ost ero ne , w hic h has a ro le i n sp erm product ion a nd deve loping m ale se co ndary se x ch aract erist ics. FS H acts on ce ll s to help i n sp erm m atu ra ti on. Negati ve fe edback by t est oste ro ne co ntrols th e act io ns of G nRH .
Details of the testes.
The Female Reproductive System
The female gonads, ovaries, are located within the lower abdominal cavity.
Th e o va ry co ntains m any follicl es co mp ose d of a deve loping e gg su rro unded b y an o ute r laye r of foll icl e ce lls. Each e gg begins oogenesi s as a primary oocyte . A t birth e ach fema le c arr ies a l ife time su pply o f deve loping o ocyt es, each of wh ich is i n Pro phase I. A d eve loping egg (se co ndary oocyte ) i s release d each mo nth f rom p uberty unti l me nopause , a to ta l of 4 00-5 00 e ggs.
Ovary
Oogenesis.
Ovarian Cycles
After pu ber ty the ovar y c ycle s be twee n a follic ular ph as e (ma tur in g follicles ) and a lut eal phase (pr esen ce of the cor pus lu teu m ). Th es e cyclic ph as es ar e int errupt ed only by pr egna nc y and con tinu e un til meno pa us e, w he n repr od uc tive cap ab ilit y en ds . Th e ovar ia n cycle last s us ually 28 day s. Dur in g the fir st phase, the oo cyte mat ures wit hin a follicle. At mid po int of the cy cle, the ooc yte is rele as ed from the ov ary in a pr oces s kno wn as ovulation . Following ov ulat io n the follicle for ms a cor pu s lu teum whic h synthe siz es and pr ep ar es ho rmo ne s to prepa re the ut erus for pr egna nc y. Th e secon da ry oo cyte pas ses in to the ov id uc t
Ovulation is he release of an egg from the ovary, when the egg cell mature.
The secondary oocyte passes into the oviduct (fallopian tube or uterine tube). The oviduct is connected to the uterus.
Th e u terus h as an i nner l aye r, t he endome trium , in which a fe rti lize d e gg imp lants. At th e lowe r e nd of the u terus th e ce rvix co nnect s the u terus to the va gina , tha t se rve s as t he birth ca nal.
Hormones and Female Cycles
Th e o va ri an cycl e is hormonally r egulated in two phase s. Th e f ollic le se cr etes est rogen befo re ov ul ation; th e co rpu s lute um se cre tes b oth e st rogen and progest erone aft er o vu latio n. Ho rmones from th e hyp othala mus a nd anterior pitu itary co ntro l the ova rian cycl e. Th e o va ria n cycl e co ve rs e ve nts in the o va ry; th e men st rual cycl e o ccu rs i n th e ute ru s.
Hormonal controls and the functioning of the female reproductive system.
Men str ua l c ycles var y f ro m b etwe en 15 a nd 31 da ys. Th e first d ay o f the c ycle is th e firs t da y of blood flow (d ay 0) kno wn a s m ens tru at ion. Dur ing mens tru at ion t he u ter ine lin ing is b ro ken d ow n an d she d a s m ens tru al flow. FSH an d LH a re s ecre te d on da y 0 , b eg inning b ot h t he me ns tru al cycle a nd th e ova ria n cyc le. Bot h F SH a nd LH stim ulat e t he mat ura tion of a sing le foll ic le in o ne of t he ov arie s and t he sec ret ion o f es tro ge n. Risin g levels o f e str og en in t he blood trig ge r sec ret ion o f LH, whic h stim ula te s f oll ic le mat ura tion an d ovu lation ( da y 1 4, or m idc ycle). L H stim ula te s t he r em aining fo llicle c ells t o for m th e c orp us luteu m, wh ich pro du ces bo th es tro ge n and p ro ges ter on e. Cli ck her e to view a "m ov ie" of t he ho rm one seq ue nce s. Es tro ge n and p ro ges ter on e stim ulat e t he de velo pm en t o f the e ndo met rium an d p re pa ra tion of th e u te rine inner li ning for im plan ta tion o f a z ygo te. I f p re gn anc y d oes no t occ ur, the d ro p in FS H and L H cau se th e cor pu s lu te um to disint eg ra te. T he dr op in h or mon es als o cau ses th e slough ing o ff of t he inner li ning o f t he ut er us by a ser ies o f mus cle con tr ac tions of th e u te ru s.
Hormonal changes and the female reproductive cycles.
The mammalian reproductive system
The reproductive system of rats are similar to those of humans, except that : 1. The male rats have proportionally larger seminal vesicles, which are found on each side of the bladder. 2. The female rats have a V- shaped uterus with two branches, one on the left and one the right ; and very short oviducts which go from each branch of the uterus to the ovaries.
Human gametes Sperm . Very small, about 0, 05mm Looks lik e a tadpol e Cons ists of a head, a middl e piece and a t ail. The head cont ains a nuc leus whic h cont ains the haploi d num ber of chromos om es . The middle piece cont ains many m it oc hondria which supply energy for sw im ming. The tail allow s t he sperm to sw im . Ovum. much larger t han sperm , about 0,1 mm spheric al- shaped surrounded by a prot ec tiv e mem brane out side t he cell mem brane. cannot mov e by t hems el ves . contains f ood reserv e which provides food f or t he early dev elopm ent of the embryo. .
Form at ion of iden tical twins and frat ern al twins If a single fertilized ovum separates into embryos by mitotic cell division, identical twins will be formed. The twins are of the same sex and look alike. They share the same genetic make – up. On the other hand, if two separate ova are ovulated at the same time and both are fertilized, fraternal twins will result. The twins may be of the same sex or different sexes are not alike in appearance. Their genetic make – up is different. How do es a fert ilized ov um de velop into an embry o ? After fert ilization, the zygote wi ll pa ss dow n the ov iduc t to the times uteru s. Duri ng its jou rn ey, it di vides many times by mitot ic cel l di vision to pr od uc e a ba ll of cel ls and bec om es an embry o. Af ter re ac hin g the uteru s, it attaches firmly on to the thi ckened uter ine wall. Thi s proc ess is cal led im pl antat ion . It mark s the be ginn ing of preg nan cy
Placenta. When the embryo implants, it produces finger- like villi which grow into the wall of the uterus. Inside the villi are the embryo’s blood capillaries which are in close contact with the mother’s blood capillaries in the uterine wall. But they do not join. The mother and the embryo have their own blood supplies. The embryonic villi together with some maternal uterine tissue make up a disc- shaped temporary organ inside the uterus called the placenta The placenta is attached to the embryo by the umbilical cord. The cord contains two umbilical arteries carrying blood from the embryo to the placenta, and an umbilical vein returning blood from the placenta to the embryo.
The placenta allows the exchange of materials between the embryo and the mother without any mixing of their blood. Nutrients , oxygen and antibodies diffuse from the mother’s blood into the embryo’s blood. Carbon dioxide and other metabolic waste diffuse in the opposite direction. The placenta is adapted to the exchange of materials as follows : – The surface area for the exchange of materials is greatly increased the presence of villi The walls of the blood vessels separating the blood of the embryo and the blood of the mother are very thin. This allows easy diffusion of materials between the embryo and the mother.
Am niotic f luid As em bry o d eve lops, it b ecom es en clos ed in a me mbr an e sac call ed t he am nio n . The me mbra ne s ecr et es amn iot ic fluid su rr ou nding th e emb ry o. Th e f luid has fu nc tions : 1. It ser ve s a s a cu shion fo r pr ot ect ing t he em bry o aga inst sho ck . 2. It pr ov id es a const ant e nviro nm ent ar ou nd th e emb ry o e.g c onst ant t em per at ure 3. It pr ev ent s t he em bry o fro m d esic ca tion . 4. It allows th e emb ry o t o move ar ou nd ea sily Th e e mbr yo con tinu es t o gr ow . Aft er ab ou t e ight we ek s wh en the m ain or ga ns ha ve bee n for me d, th e e mbr yo is ca ll ed a fet us .. In hum an s, it nor ma lly t ake s 3 9 we ek s fr om fe rt iliza tion t o birt h.
Th e a bility to re produce is one of th e ch aract erist ics o f a ll li vi ng t hings. Tw o basi c typ es of repro ducti on: – Sexu al reproduct ion p ro duce s of fsp ring t hat a re genetica lly diff erent from th eir parents. – Ase xu al reproduct ion p ro duce s of fsp ring genetica lly identi ca l t o th eir p arent. Anima ls’ re product ive syst ems ca n b e divid ed into the i nternal re product ive o rg ans a nd th e e xt ernal genita lia. Th e gonads are the a ct ual organs t hat produce the game tes. In t he m ale, te stes (si ngular = t est is) p ro duce sp erm , and in t he f ema le, ova ries ma ke eggs.
Asexual Reproduction
Fi ssio n, buddin g, fra gme ntati on, a nd th e f orma tion of rh iz om es a nd st olo ns a re so me o f t he me ch anism s t hat allow organisms to re produce ase xu ally. Ase xu al re product io n allows an o rg anism to rapidly produce man y offsp rin g wit hout f indin g a ma te, and ma ting. Th e l ack of genetic va riability in a se xu ally rep ro duci ng p opulatio ns ca n be d etrime nt al w hen envi ronmenta l co ndit ions c ha nge quickl y.
Growth and asexual reproduction involve mitosis
Th e w ay in whic h ce lls d ivi de d uring g ro wt h i s ca lled m ito si s Ma ny livin g o rganism s u se mi tosis to m ake co mp lete n ew organism, b y growi ng a new o ne out of t hemse lve s (ca lled a se xu al reproduct ion)
Mitosis makes new cells with the same genes as the old one
Th e n ucl eus of a ce ll co nta in s th reads o f DN A, ca lled ch ro mo so mes . Huma n ce ll s, fo r exa mp le , ha ve 46 ch romo so mes. In e ach ch romoso me s, t here are ma ny loci where gene is loca te d Mi tosi s i s a m eth od of ce ll d ivi si on w hich m ake s two new ce lls w ith exa ctl y the sa me numb er of ch rom oso me s, carryi ng exa ctl y th e sa me genes a s the o ld one.
Asexual reproduction produces genetically identical offspring
In a se xu al reprodu ct ion, the n ew o rganisms produce d are genetica lly id entica l t o t heir parent, and to each o th er A g ro up o f geneti ca lly i dentica l organism is call ed a clo ne
Bacteria reproduce by binary fission
Bacte ri a a re m ade o f a si ngle ce lls, wit h a si ngle ci rcu la r m olecu le of DNA When th e bact erium is a bout t o divi de, an e xa ct co py o f t he DN A i s ma de; th e ce ll then d ivi des in to t wo wit h one D NA mo lecu le in each half. Th ose ce lls are geneti ca lly i dentica l to t he o ri gin al ce ll. Th is m eth od of ase xu al rep ro ducti on is ca lled b inary
Fungi produce spores asexually
Plants can be propagated asexually
Ma ny plants are a ble t o reproduce ase xu ally Fo r exa mp le: – By fo rma tion o f t uber, in potato es – By ta ki ng cu tt ing, in ca ssa va etc
Tissue culture
Me thods of produci ng la rg e n umbers of genetica lly identi ca l pla nt s Very large numb ers of p lants ca n be gro wn from a si ngle p lant.
Sexual Reproduction
In se xu al reproduc ti on n ew in divi duals a re produce d by th e fu si on of haploid gamete s to form a dipl oid zyg ote . Sperm a re m ale g amete s, ova (ovu m si ngular) a re fema le g amete s. Me iosi s produce s ce ll s tha t are geneti ca lly d ist in ct from each oth er; Fe rtili za tion i s th e fus io n of two su ch d ist incti ve ce lls t hat prod uce s a uniq ue new co mbin ati on o f allele s , th us incr easi ng v ari ati on.
Human Reproduction and Development
Huma n reproduct ion e mploys i nternal f ertiliza tion, and depends o n th e inte gra te d act io n o f hormo nes , the nerv ous syst em , a nd th e re pro ducti ve syst em . Go na ds are se x organs t hat p ro duce g amete s. Ma le gonads are t he te st es , which produce sp erm and ma le se x hormones. Fe ma le gonads a re t he ova rie s , wh ich produce eggs (ova ) and fe male se x hormo nes.
The Male Reproductive System
Te ste s are su sp ended outsi de th e abdomi nal c av it y by th e scr otum . Semi nife rous t ubules a re in si de each t esti s, and are where sp erm are p roduce d b y me iosi s. About 250 me ters (850 fe et) of tubule s are packe d in to each te st is. Spermato cyt es i nsi de th e tu bul es divid e b y me iosi s to p ro duce sp erma tid s that in t urn deve lop i nto ma ture sp erm.
The male reproductive system
The male reproductive system
Spermatogenesis
Sperm p ro ducti on begins a t puberty a t co ntinue s throughout l ife, wi th se ve ral hundred mi llion sp erm being produce d e ach day. Once sp erm fo rm they m ove i nto t he epididymi s , where they m atu re a nd are st ored.
Human Sperm
Male Sex Hormones
Th e anterior p itui tary produce s foll icl e-st imu lati ng hormone (F SH) and luteinizi ng hormo ne (LH) . Acti on of LH i s co ntro ll ed by t he gonadotro pin -r eleasin g hormo ne ( Gn RH ) . LH st imu lates ce lls i n th e se mi nifero us t ubules t o se cr ete te st ost ero ne , w hic h has a ro le i n sp erm product ion a nd deve loping m ale se co ndary se x ch aract erist ics. FS H acts on ce ll s to help i n sp erm m atu ra ti on. Negati ve fe edback by t est oste ro ne co ntrols th e act io ns of G nRH .
Details of the testes.
The Female Reproductive System
The female gonads, ovaries, are located within the lower abdominal cavity.
Th e o va ry co ntains m any follicl es co mp ose d of a deve loping e gg su rro unded b y an o ute r laye r of foll icl e ce lls. Each e gg begins oogenesi s as a primary oocyte . A t birth e ach fema le c arr ies a l ife time su pply o f deve loping o ocyt es, each of wh ich is i n Pro phase I. A d eve loping egg (se co ndary oocyte ) i s release d each mo nth f rom p uberty unti l me nopause , a to ta l of 4 00-5 00 e ggs.
Ovary
Oogenesis.
Ovarian Cycles
After pu ber ty the ovar y c ycle s be twee n a follic ular ph as e (ma tur in g follicles ) and a lut eal phase (pr esen ce of the cor pus lu teu m ). Th es e cyclic ph as es ar e int errupt ed only by pr egna nc y and con tinu e un til meno pa us e, w he n repr od uc tive cap ab ilit y en ds . Th e ovar ia n cycle last s us ually 28 day s. Dur in g the fir st phase, the oo cyte mat ures wit hin a follicle. At mid po int of the cy cle, the ooc yte is rele as ed from the ov ary in a pr oces s kno wn as ovulation . Following ov ulat io n the follicle for ms a cor pu s lu teum whic h synthe siz es and pr ep ar es ho rmo ne s to prepa re the ut erus for pr egna nc y. Th e secon da ry oo cyte pas ses in to the ov id uc t
Ovulation is he release of an egg from the ovary, when the egg cell mature.
The secondary oocyte passes into the oviduct (fallopian tube or uterine tube). The oviduct is connected to the uterus.
Th e u terus h as an i nner l aye r, t he endome trium , in which a fe rti lize d e gg imp lants. At th e lowe r e nd of the u terus th e ce rvix co nnect s the u terus to the va gina , tha t se rve s as t he birth ca nal.
Hormones and Female Cycles
Th e o va ri an cycl e is hormonally r egulated in two phase s. Th e f ollic le se cr etes est rogen befo re ov ul ation; th e co rpu s lute um se cre tes b oth e st rogen and progest erone aft er o vu latio n. Ho rmones from th e hyp othala mus a nd anterior pitu itary co ntro l the ova rian cycl e. Th e o va ria n cycl e co ve rs e ve nts in the o va ry; th e men st rual cycl e o ccu rs i n th e ute ru s.
Hormonal controls and the functioning of the female reproductive system.
Men str ua l c ycles var y f ro m b etwe en 15 a nd 31 da ys. Th e first d ay o f the c ycle is th e firs t da y of blood flow (d ay 0) kno wn a s m ens tru at ion. Dur ing mens tru at ion t he u ter ine lin ing is b ro ken d ow n an d she d a s m ens tru al flow. FSH an d LH a re s ecre te d on da y 0 , b eg inning b ot h t he me ns tru al cycle a nd th e ova ria n cyc le. Bot h F SH a nd LH stim ulat e t he mat ura tion of a sing le foll ic le in o ne of t he ov arie s and t he sec ret ion o f es tro ge n. Risin g levels o f e str og en in t he blood trig ge r sec ret ion o f LH, whic h stim ula te s f oll ic le mat ura tion an d ovu lation ( da y 1 4, or m idc ycle). L H stim ula te s t he r em aining fo llicle c ells t o for m th e c orp us luteu m, wh ich pro du ces bo th es tro ge n and p ro ges ter on e. Cli ck her e to view a "m ov ie" of t he ho rm one seq ue nce s. Es tro ge n and p ro ges ter on e stim ulat e t he de velo pm en t o f the e ndo met rium an d p re pa ra tion of th e u te rine inner li ning for im plan ta tion o f a z ygo te. I f p re gn anc y d oes no t occ ur, the d ro p in FS H and L H cau se th e cor pu s lu te um to disint eg ra te. T he dr op in h or mon es als o cau ses th e slough ing o ff of t he inner li ning o f t he ut er us by a ser ies o f mus cle con tr ac tions of th e u te ru s.
Hormonal changes and the female reproductive cycles.
The mammalian reproductive system
The reproductive system of rats are similar to those of humans, except that : 1. The male rats have proportionally larger seminal vesicles, which are found on each side of the bladder. 2. The female rats have a V- shaped uterus with two branches, one on the left and one the right ; and very short oviducts which go from each branch of the uterus to the ovaries.
Human gametes Sperm . Very small, about 0, 05mm Looks lik e a tadpol e Cons ists of a head, a middl e piece and a t ail. The head cont ains a nuc leus whic h cont ains the haploi d num ber of chromos om es . The middle piece cont ains many m it oc hondria which supply energy for sw im ming. The tail allow s t he sperm to sw im . Ovum. much larger t han sperm , about 0,1 mm spheric al- shaped surrounded by a prot ec tiv e mem brane out side t he cell mem brane. cannot mov e by t hems el ves . contains f ood reserv e which provides food f or t he early dev elopm ent of the embryo. .
Form at ion of iden tical twins and frat ern al twins If a single fertilized ovum separates into embryos by mitotic cell division, identical twins will be formed. The twins are of the same sex and look alike. They share the same genetic make – up. On the other hand, if two separate ova are ovulated at the same time and both are fertilized, fraternal twins will result. The twins may be of the same sex or different sexes are not alike in appearance. Their genetic make – up is different. How do es a fert ilized ov um de velop into an embry o ? After fert ilization, the zygote wi ll pa ss dow n the ov iduc t to the times uteru s. Duri ng its jou rn ey, it di vides many times by mitot ic cel l di vision to pr od uc e a ba ll of cel ls and bec om es an embry o. Af ter re ac hin g the uteru s, it attaches firmly on to the thi ckened uter ine wall. Thi s proc ess is cal led im pl antat ion . It mark s the be ginn ing of preg nan cy
Placenta. When the embryo implants, it produces finger- like villi which grow into the wall of the uterus. Inside the villi are the embryo’s blood capillaries which are in close contact with the mother’s blood capillaries in the uterine wall. But they do not join. The mother and the embryo have their own blood supplies. The embryonic villi together with some maternal uterine tissue make up a disc- shaped temporary organ inside the uterus called the placenta The placenta is attached to the embryo by the umbilical cord. The cord contains two umbilical arteries carrying blood from the embryo to the placenta, and an umbilical vein returning blood from the placenta to the embryo.
The placenta allows the exchange of materials between the embryo and the mother without any mixing of their blood. Nutrients , oxygen and antibodies diffuse from the mother’s blood into the embryo’s blood. Carbon dioxide and other metabolic waste diffuse in the opposite direction. The placenta is adapted to the exchange of materials as follows : – The surface area for the exchange of materials is greatly increased the presence of villi The walls of the blood vessels separating the blood of the embryo and the blood of the mother are very thin. This allows easy diffusion of materials between the embryo and the mother.
Am niotic f luid As em bry o d eve lops, it b ecom es en clos ed in a me mbr an e sac call ed t he am nio n . The me mbra ne s ecr et es amn iot ic fluid su rr ou nding th e emb ry o. Th e f luid has fu nc tions : 1. It ser ve s a s a cu shion fo r pr ot ect ing t he em bry o aga inst sho ck . 2. It pr ov id es a const ant e nviro nm ent ar ou nd th e emb ry o e.g c onst ant t em per at ure 3. It pr ev ent s t he em bry o fro m d esic ca tion . 4. It allows th e emb ry o t o move ar ou nd ea sily Th e e mbr yo con tinu es t o gr ow . Aft er ab ou t e ight we ek s wh en the m ain or ga ns ha ve bee n for me d, th e e mbr yo is ca ll ed a fet us .. In hum an s, it nor ma lly t ake s 3 9 we ek s fr om fe rt iliza tion t o birt h.
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