The information in this document is meant to cover the IB syllabus for topics 6.6 and 11.4 (HL OL!". The Male and Female Reproductive Systems
Images from http://www.dannynicholson.co.uk/learningzone/ody/organs/organs!.htm
Reproductive Hormones
Reproducti"e hormones are in"ol"ed in the changes of puerty# puerty# and in regulation of the menstrual cycle. In females#
$ollicle %timulating Hormone &$%H' and (uteinizing Hormone &(H' are produced y the anterior pituitary gland. )strogen and progesterone are produced y the o"ary. o"ary. $%H# (H# estrogen * progesterone work together to control the menstrual cycle. $%H stimulates maturation of an o"um within its follicle. +s the follicle grows# it egins producing estrogen# which inhiits $%H# ut stimulates stimulates (H product production. ion. )strogen )strogen also increases increases the thicknes thickness s of the endometrium. stimul ulat ates es o"ula o"ulati tion on and and form format atio ion n of the the corp corpus us lute luteum um## whic which h (H stim produces progesterone. ,rogesterone &-the pregnancy hormone' maintains the endometrium and inhi inhii its ts prod produc ucti tion on of $%H $%H * (H# (H# ther there ey y inhi inhii iti ting ng o"ul o"ulat atio ion. n. If fert fertil iliz izat atio ion n does does not not occu occurr# the the corp corpus us luteu luteum m reak reaks s down down## and the the pituitary gland will start producing $%H again to stimulate another follicle. +t this point# the endometrium is epelled from the uterus &menstruation'. )strogen also plays a role in puerty: it promotes the de"elopment of the female secondary seual characteristics.
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
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In males#
$%H promotes spermatogenesis &production of male gametes'. (H &in males# called interstitial cell stimulating hormone or I6%H' stimulates secretion of testosterone. 7estosterone and other hormones collecti"ely known as androgens are produced y the (eydig cells &near lood "essels of the interstitial tissue of the testes'. It stimulates pre8natal de"elopment of the male genitalia# de"elopment of secondary se characteristics &during puerty' and maintenance of the se dri"e. 7estosterone also stimulates maturation of sperm from secondary spermatocytes.
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
Gonads & Gametogenesis
7he se organs# or gonads# are responsile for production of gametes# or gametogenesis.
Image from http://www.io.miami.edu/dana/!13/gametogenesis.5pg
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
In females# the o"aries produce o"a # or eggs# y the process of oogenesis# a specialized form of meiosis which only results in formation of one haploid cell: • • • •
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oogenesis egins in utero# efore a female ay is e"en orn a large numer of oogonia are formed y mitosis oogonia undergo cell growth# enlarging an d forming primary oocytes primary oocytes egin meiosis ut stop in prophase I# remaining dormant until puerty egins at onset of puerty# some follicles will egin to de"elop# in response to $%H# and the primary oocyte inside will complete the 9rst meiotic di"ision two cells of uneual sizes are formed – cytoplasm and organelles are gi"en to one cell &now called a secondary oocyte'; the second is essentially a nucleus in a cell memrane < this structure is called a polar ody the polar ody e"entually disintegrates and is reasored y the ody the secondary oocyte proceeds to meiosis II# stopping in prophase II meiosis II completes if the cell is fertilized: this forms an o"um and a second polar ody
In males# the testes produce sperm# y the process of spermatogenesis# also a form of meiosis; howe"er each round of spermatogenesis produces four spermatids# or immature sperm. Ovary Structure
Image from http://www.tarleton.edu/=anatomy/o"ary.5pg
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
Image from http://www.proteinatlas.org/histology.php>content4id?01
Testis Structure
Image from http://www.we8ooks.com/e(irary/@edicine/,hysiology/Reproducti"e/testis.5pg
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
Image from http://www.proteinatlas.org/tissue4dictionary/testish!.5pg
%perm are released from the ody within semen# or seminal Auid. It is produced y se"eral glands: %eminal esicles – –
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two pouches located in the pel"ic region ehind the ladder supply a "iscous# nutrient8rich &citric acid# amino acids# fructose' alkaline secretion that forms a part of the seminal Auid supply aout C1D of the "olume of seminal Auid
,rostate Eland –
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largest of all male reproducti"e glands &aout the size of a chestnut'; located 5ust eneath the ladder contriutes aout 21D of the seminal Auid it secretes a thin# milky8white alkaline Auid similar to that of the seminal "esicles; neutralizes acidic Auids oth in the male urethra and the female "agina so that the sperm are not damaged
Bulourethral Eland &6owperFs Eland' – –
pea8sized gland located eneath the prostate gland contriutes aout !1D of the seminal Auid
)pididymis –
tightly8coiled tue located on top of the testis &2 m long if stretched out'
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sperm are stored in the epididymis for aout 0 weeks while they mature# de"elop motility and ecome capale of fertilization
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
Image from http://faculty.southwest.tn.edu/rurkett/repro4!G.5pg Image from http://distance.stcc.edu/+and,/+,/+,0pages/reprod/spermato.htm
Comparing Spermatogenesis and Oogenesis
%imilarities: ●
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Both spermatogenesis * oogenesis in"ol"e mitosis and cell growth efore undergoing meiosis. 7he hormones (H and $%H are in"ol"ed in regulation of oth processes.
ierences: ● ●
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%permatogenesis occurs in the testes# while oogenesis occurs in the o"aries. %permatogenesis starts at puerty# while oogenesis starts during gestation &fetal de"elopment'. %permatogenesis occurs until death# while oogenesis ceases at menopause. %permatogenesis occurs continuously# whole oogenesis is cyclic &menstrual cycle'. @illions of sperm are created daily# while only one o"um &or two' is produced e"ery 0J days. )5aculation of sperm can occur at any time# while o"ulation only occurs once per menstrual cycle. %perm are produced y eual di"isions# producing four spermatids# while uneual di"isions in oogenesis result in the production of only one o"um. %permatogenesis doesnFt produce polar odies# while oogenesis produces 0 or C polar odies. %permatogenesis reuires testosterone# while oogenesis does not.
Pregnancy
6opulation is the physical contact etween the male and female reproducti"e structures that is needed for sperm to mo"e from the male to the female ut does not necessarily result in fertilization due to the use of a contracepti"e# infertility# or timing. A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
$ertilization is the fusion of male and female gametes# forming a zygote. ●
7he acrosome reaction is when the sperm comes into contact with the coats surrounding the egg# and as the contact takes place the acrosome &an enzyme8 9lled "acuole at the tip of the sperm' ursts open and releases enzymes that digest the 5elly coat of the egg.
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7he sperm memrane then comes in contact with the egg cell memrane and the two memranes fuse# followed y the entry of the sperm nucleus into the cytoplasm of the egg.
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7he cortical reaction results as the sperm comes in contact with the egg cell memrane# triggering changes to the egg cell memrane making it impossile for other sperm cells to enter.
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+fter fertilization# the chromosomes of the male and female gametes line up at the cellFs euator in preparation for mitosis. %ince this di"ision is not followed y cell growth# and simply clea"es the cell into two smaller ones# it is called a clea"age di"ision. %e"eral clea"age di"isions occur# resulting in the formation of a solid all of cells# the morula# which in humans reaches the uterus aout 3 days after fertilization. Kneual di"isions in the morula occur# resulting in the formation of a Auid89lled space in the middle – it is now a hollow all of cells called a lastocyst. 7he lastocyst implants in the endometrium aout L days after conception. uring 9rst 0 to 3 weeks of de"elopment the emryo otains nutrients directly from the endometrium. Howe"er# tissues grow out from the de"eloping emryo and mingle with the endometrium and form the placenta.
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@aterials are echanged etween the maternal and fetal lood in the placenta.
7he placenta is a fetal tissue which in"ades the maternal tissue &the uterus'. It is disk8shaped and grows to aout the size of a dinner plate weighing less than ! kg. iusion of material etween the maternal and emryonic circulatory systems pro"ides nutrients# echanges respiratory gases# and disposes of metaolic wastes for the emryo. Blood from the emryo tra"els to the placenta through arteries of the umilical cord and returns "ia the umilical "ein# passing through the li"er of the emryo.
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In addition# the placenta plays an endocrine role in maintaining pregnancy. In early pregnancy# it secretes human chorionic gonadotopin. +fter the reakdown of the corpus luteum# the placenta secretes oth estrogen and progesterone. If the le"els of these hormones are not maintained# the pregnancy will aort spontaneously ecause the uterus has not maintained fa"ourale conditions for fetal growth.
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H6E acts like pituitary (H to maintain secretion of progesterone and estrogens y the corpus luteum through the 9rst trimester. In the asence of this hormonal o"erride# the decline in maternal (H due to inhiition of the pituitary y progesterone would result in menstruation and spontaneous aortion of the
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
emryo. (e"els of H6E in the maternal lood are so high that some is ecreted in the urine# where it can e detected in pregnancy tests. ●
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$or the net two months# the growing ay is called an emryo# and is arely discernile as human. In the third month of pregnancy# the growing ay starts to look more human# and is known as a fetus until its irth. 7he fetus is supported and protected y the amniotic sac and amniotic Auid.
7he fetus Aoats in the amniotic Auid. 7he Auid is constantly circulated y the fetus swallowing and MinhalingM it# and MehalingM and urinating into it. +mniotic Auid pro"ides cushioning protection to the fetus. It allows for freedom of fetal mo"ement# which permits symmetrical musculoskeletal de"elopment. It maintains a relati"ely constant temperature surrounding the fetus# which protects it from heat loss. It permits proper lung de"elopment# ecause it is inhaled into * ehaled from the lungs.
Birth
+pproimately CJ weeks after conception# the fetus is ready to lea"e the uterus.
Before irth# progesterone le"els will drop. It will send a signal to the etra8emryonic memranes – which leads to the secretion of prostaglandins. ,rostaglandins initiate uterine contractions. 6ontraction of the uterus pushes the ayFs head against the cer"i# causing it to dilate. Ner"e endings in the cer"i and uterus tell the rain that contractions are occurring# and the posterior pituitary gland will secrete oytocin. ytocin# prostaglandins and a positi"e feedack system cause the uterine contractions to ecome stronger and longer in duration. Ohen the cer"i is fully dilated &!1 cm'# stage one of irth# &laour' is complete. (aour can take many hours. %tage two &epulsion' occurs as powerful contractions force the ay out of the uterus. %tage two usually lasts no more than one hour. nce the ay has een orn# the uterus has nothing to push against – this ends the positi"e feedack loop# and contractions diminish. 7he 9nal stage of irth is epulsion of the placenta# caused y a few more uterine contractions.
A. De Jon g/TFS S 2009
IB Biology Notes – Human Reproduction
Fertiliation !"#F$ %ome couples are unale to concei"e due to infertility issues such as locked $allopian tues or a low sperm count. I$ is one common way that couples with fertility issues are ale to ecome pregnant. ● + drug is in5ected once a day for three weeks# to stop the womanPs normal menstrual cycle. ● (arge doses of $%H are in5ected once a day for !18!0 days to stimulate the o"aries to de"elop many follicles. H6E is in5ected C2 hours efore egg collection# to loosen the eggs in their follicles ● and to make them mature. 7he man pro"ides semen y e5aculating into a container. 7he sperm are ● processed to concentrate the healthiest ones. ● 7he eggs are etracted from the follicles using a de"ice inserted through the wall of the "agina. )ach egg is mied with sperm in a ,etri dish# which is kept in an incuator ● o"ernight. 7he ,etri dishes are checked the net day to see if fertilization has occurred. ● 7wo or three emryos are selected and placed# "ia a long plastic tue into the ● uterus. ● +out two weeks after placing the emryos# a pregnancy test is done to see if any emryos ha"e implanted. ● + scan is done aout a month after placing the emryos# to see if the pregnancy is continuing normally. 7he hearteat should e "isile. in vitro
%thical Concerns Regarding "#F Pros ●
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Cons
promotes fertility in childless couples suering due to genetic disease could e reduced if emryos were screened efore transferring to the uterus.
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A. De Jon g/TFS S 2009
against religious principles multiple irths are more likely# and carry a greater risk to the mother doctors decide which emryos are transferred to the uterus – so humans are deciding who li"es * dies more emryos are produced than are normally implanted in one procedure – spares may e destroyed if they are not stored for later procedures