Reproductive System Male & Female. Reproductive System consists of gonads –reproductive organs –make gametes & hormones ducts –receive & transport gametes.

Reproductive System

Male & Female

Reproductive System• consists of

• gonads– reproductive organs– make gametes & hormones

• ducts– receive & transport gametes

• accessory glands & organs

• external genitalia

Male Reproductive System• Testes

– paired, plum sized structures – produce sperm & hormones

• Epididymus• Ductus Deferens• Urethra• Ejaculatory ducts

– nourish, store, transport & mature sperm.

• Accessory structures• Seminal vesicles• Prostate• Bulbourthral or Cowper’s glands• External genitalia• Scrotum

– contains testes• Penis

Testes Development• form inside body cavity next to kidneys• connective tissue fibers extend from

testes to posterior wall of peritoneum• gubernaculum testes• fibers do not grow in length as fetus

grows• lock testes into place• as body enlarges, testes position

changes• move inferiorly & anteriorly toward

anterior abdominal wall• 7th month of fetal growth is rapid• hormones cause gubernaculum testes to

contract• during this time testes move through

abdominal musculature bringing small pockets of peritoneal cavity with them forming spermatic cord

• extend between abdomino-pelvic cavity & testes

– enclose ductus deferens, blood vessels, nerves & lymph vessels

Testes Location• come to be suspended

outside abdominal cavity by scrotum,– pouch of skin

• keeps testes away from body at optimal temperature for sperm development

• normal body temperature too hot for sperm growth & development

• temperature in scrotum is about 2° C (3.6° F) lower

The Scrotum• divided internally into 2

chambers• partition between marked

by raised thickening-raphe

• surrounded by 2 tunics• tunica vaginalis

– lines scrotal cavity & testes

• tunica albuginea– dense fibrous capsule

containing great deal of collagen fibers

• fibers form septa– divide testis into lobules

The Scrotum• each lobule has 1-4 convoluted

seminiferous tubules• produce sperm in process

called spermatogenesis• each seminiferous tubule forms

loop that is connected to maze of passageways-rete testis

• 15-20 efferent ductules connect rete testes to epididymus

• areolar tissue fills spaces between tubules

• within spaces are Leydig or interstitial cells– produce androgens

Spermatogenesis• spermatozoa production

begins at outermost layer of cells in seminiferous tubules

• proceeds toward lumen• 3 phases• spermatocytogenesis

– proliferative phase– stem cells-spermatogonia

divide by mitosisdaughter cellsstem cells& primary spermatocytes

• meiosis– production of haploid gametes

• spermiogenesis– metamorphosis of spermatids

into spermatozoa

Spermatocytogenesis• begins at puberty• continues through life• spermatozoa originate from

spermatogonia cells– line basement membrane of

seminiferous tubules– divide continually by mitosis

• until puberty all daughter cells are spermatogonia

• during puberty, each division yields 2 cell types: A & B

• Type A– remains at basement membrane– maintains germ cell line

• Type B– pushes toward lumen– become primary spermatocytes

Meiosis• primary spermatocytes divide by

meiosis– special cell division-reduction

divisiongametes or sperm– half number of chromosomes

(haploid-1N) as somatic cells– number of chromosomes in

gametes = 23– egg + sperm = 46 chromosomes-

2N-diploid number• allows for recombination of

haploid gametes at fertilization without increasing number of chromosomes each generation

• meiosis involves duplication & exchange of genetic material

• 2 cell divisions-reduces chromosome number– yields 4 spermatids

• immature gametes

Meiosis• Meiosis I

– primary spermatocytes2 secondary spermatocytes

• Meiosis II– 2 secondary spermatocytes4

spermatids

• During meiosis I duplicated sister chromatids come in close contact with their homologous pairs

• Portions of homologous chromosomes are exchanged-crossing over-at chiasma– mixes maternal & paternal genes

forming new combinations

• 4 daughter cells are formed each containing 23 chromosomes with different genetic composition

Spermiogenesis• last stage of sperm production• Spermatids are spherical cells

with centrally located nuclei– correct number of

chromosomes but not motile

• must be transformed into functional spermatozoa

• Nuclear & cytoplasmic changes take place resulting in spermatozoa

• restructuring includes• condensation• acrosome formation• tail formation• mitochondrial spiral formation• removal of extraneous

cytoplasm

Sperm Structure• Head

– contains genetic information– flattened & almost entirely filled with

nucleus containing DNA• at tip of nucleus is acrosome

– contains hydrolytic enzymes– used to enter egg during fertilization

• acrosome reaction• Midpiece

– houses metabolic processes– contains mitochondria

• provide energy for movement• arranged in spiral around microtubules• Tail or Flagellum

– locomotion– allows sperm to move in corkscrew

motion• cells contain no ER, Golgi, or lysosomes

– reduces cell size & mass• there is no glycogen

– cell must absorb nutrients

Spermiogenesis• ends with release of

spermatozoa from Sertoli cell into lumen of tubules

• sperm then move into epididymis for storage & further maturation

• Sertoli cells– sustentacular cells or nurse

cells • attached to seminiferous tubular

capsule & extend toward lumen• spermatocytes & spermatids are

surrounded by cytoplasm of these cells

• at spermiation, spermatids lose attachment to sustentacular cells

• at appropriate timecytoplasm of spermatid is pinched off by Sertoli cell

Sustentacular or Sertoli Cells• form & maintain blood-testis barrier

– isolates seminiferous tubules from general circulation

– essential to preserve differences– prevents cells of immune system

from coming into contact with spermatozoa which have antigens on their cell membranes

• cells are large• form tight junctions producing outer

basal compartment containing spermatogonia & inner lumenal compartment

• basal compartment -below tight junctions– has contact with circulatory

system• spermatogonia develop to primary

spermatocytes here• meiosis is completed• spermatids develop in luminal

compartment

Sustentacular or Sertoli Cells• Spermiogenesis requires

sustentacular cells to provide nutrients & chemical stimuli which promote spermatid development

• cells secrete inhibin which depresses production of FSH by pituitary GnRh from hypothalamus– important in feedback control of

spermatogenesis• cells secretes ABP

– androgen binding protein– binds androgens in fluid of

tubules elevates concentrations of androgen stimulates spermiogenesis

• cells secrete Mullerian-inhibiting factor

• during fetal development• causes regression of Mullerian ducts

which become oviducts in females

Fetal Development

Epididymis• spermatozoa move into

epididymis from lumen of seminiferous tubules – mature and are store

• coiled tube bound to posterior border of testes

• start of male reproductive tract• Head

– receives spermatozoa• Body

– extends along posterior margin of testes

• Tail – connects with ductus deferens &

stores sperm• sperm-functionally immature

– incapable of locomotion or fertilization

Epididymis• monitors & adjusts composition of

fluid made by seminiferous tubules• recycles damaged spermatozoa• stores & protects sperm• facilitates maturation• sperm pass through in 2 weeks• can be stored here for several months• when leave-mature but immobile &

incapable of fertilizing eggs• to become mobile must undergo

capacitation– epididymus secretes unidentified

substance preventing premature capacitation

• occurs in 2 steps• first

– mix with secretions of seminal vesicles• second

– exposure to female reproductive tract

Ductus Deferens• from tail of epididymus sperm

enter ductus deferens• pseudostratified, ciliated columnar

epithelium & peristaltic contractions move sperm along duct

• just before sperm reach prostate & seminal vesicles

• lumen enlarges into ampulla• where ampulla joins with seminal

vesicle-ejaculatory duct begins• short duct which penetrates

prostate & empties into urethra– common passage for both

urinary & reproductive systemstip of penis

Accessory Glands

• Activate

• Nourish

• Propel sperm along reproductive tract

• Buffer acidity

Seminal Vesicles• behind bladder• drained by ductus deferens• contribute about 60% of total volume of

semen– sperm + associated fluid

• contains• Fructose

– main energy source– easily metabolized by sperm

• Prostaglandins– stimulates female uterine

contractions to move semen into uterus

• Fibrinogen– forms temporary clot in vagina

• secretions are slightly alkaline– help neutralize acid from prostate &

vagina• when mixed with seminal secretions

sperm undergo first step in capacitation• begin to move flagellum

Prostate Gland• seminal vesicles empty into

ejaculatory ducts which empty into urethra

• initial segment of urethra surrounded by prostate gland– largest accessory gland in male

reproductive system• prostatic fluid

– slightly acidic– contributes 20-30% of semen

volume• contains seminal plasmin

– antibiotic which may help prevent urinary track infections in males

• needs great deal of zinc• insufficient dietary zinc can lead to

prostate enlargement– can constrict urethra to point of

interfering with urination

Bulbourethral or Cowper’s Glands

• small pair of glands located along urethra below prostate

• provide less than 5% of secretion in seminal fluid

• thick, alkaline mucus• may serve as a lubricant &

help neutralize urinary acids• urethra goes through penis

– contains 3 cylinders of spongy, erectile tissue

Control of Spermatogenesis • done by endocrine interactions of

hypothalamus, pituitary gland & somatic cells of testis

• Hypothalamusgonadotropin-releasing hormone-GnRH anterior pituitaryLH-luteinizing hormone & FSH-follicle stimulating hormone– without GnRHtestes atrophy &

sperm production ceases• GnRH-released in pulses

– at 60-90 minute intervals• pulse frequency remains relatively steady• insures plasma levels of FSH, LH &

testosterone remain within specific range throughout adult life

• FSHsustentacular cells of seminiferous tubulespromotes spermatogenesis & spermiogenesissecrete androgen binding protein

• ABP binds to androgensprompts spermatogenic cells to bind & concentrate testosteronestimulates spermatogenesis

Control of Spermatogenesis• rate of spermatogenesis

regulated by negative feedback mechanism involving GnRH, FSH & inhibin

• GnRHFSHspermatogenesis spermatogenesis accelerates inhibin secreted by sustentacular cells inhibits GnRH & FSH

• sperm count highinhibin high hypothalamusinhibits GnRH & at anterior pituitaryinhibits FSH

• LH or ICSH-interstitial cell stimulating hormone interstitial cellstestosterone

Androgens• steroid hormones made from

cholesterol• diffuse across cell membranes• bind to intracellular

receptorssteroid-hormone-receptor complex binds to DNA in nucleusactivates genes enhances synthesis of proteins in target cells

• stimulates spermatogenesis & formation of functional sperm

• affects CNSlibido• stimulates metabolism

– especially protein synthesis & muscle growth

• establishes & maintains secondary sex characteristics

• maintains accessory glands & organs

Female Reproductive System

Female Reproductive System• much more complicated than

male• produces sex hormones• produces gametes• protects & supports developing

fetus• Principle organs• Ovaries

– located in lower abdominal cavity

• Uterine tubes• Uterus• Vagina• External genitalia• Ovaries, uterine tubes & uterus

are enclosed in an extensive mesentery- broad ligament– limits side to side movement

& rotation

Ovaries• paired, small, lumpy, almond

shaped structures near lateral walls of pelvic cavity– position stabilized by

mesovarium & ovarian & suspensory ligaments

• contain major blood vessels• produce immature gametes-

oocytes• secrete hormones-estrogens,

progestins & inhibin-important in feedback control of FSH production

• visceral peritoneum-germinal epithelium covers each ovary

• beneath germinal epithelium lies tunica albuginea-dense connective tissue layer

• internal tissues or stroma can be divided into cortex & medulla

• gametes made in cortex

Oogenesis• ovum production

• begins before birth

• accelerates at puberty

• ends at menopause

• between puberty & menopause ova are produced on monthly basis– part of ovarian cycle

Oogenesis• gamete production• nuclear events in meiosis-same as in

males• cytokinesis is different

– cytoplasm of primary oocyte is unevenly distributed during meiotic divisions

– results in 1 ovum containing most of original cytoplasm + 3 smaller, non-functional polar bodies which will later degenerate

• not good for females to make millions of ova as males make millions of sperm

– cannot carry million fetuses– ova need great deal of nutrients to

get embryo through first set of embryonic divisions

Oogenesis• Oogonia (germ cells) complete mitotic

divisions before birth– between 3rd & 7th month

• meiosis begins before birth• development freezes at start of first meiotic

division in prophase I of meiosis I– primary oocytes

• primary oocytes remain in suspended development until puberty

• at puberty, as FSH levels riseovarian cycle begins

• each month after puberty primary oocytes are stimulated to undergo further development

– only when signaled by hormones will primary oocyte continue process of meiosis & complete first meiotic division

• not all primary oocytes survive until puberty• at birth there are 2 X 106 primordial follicles

each containing primary oocyte• primary oocyte + follicular cells = primary or

primordial follicle• by puberty only 400,000 are left

– others have degenerated or undergone atresia

Oogenesis• ovaries release secondary

oocyte as product of first meiotic division & not mature ovum

• oocyte & ovum-not interchangeable

• secondary oocyte is suspended at metaphase of meiosis II– will not complete meiosis until

fertilization

• If secondary oocyte comes in contact with spermatozoan fertilization beginssecondary oocyte undergoes second meiotic divisionovum + another polar body

• ovum is ready to fuse with spermatozoan

Ovarian Cycle• Primordial or ovarian follicles

– specialized structures located in cortex

– found in clusters-egg nests• consists of developing egg-primary

oocyte surrounded by one outer layer of follicle cells

• Primary oocyte + follicle cells surrounding = primordial follicle

• at birth each female carries lifetime supply of oocytes-each in Prophase I

• every 28 days, after puberty until menopause, one primordial follicle is activated & stimulated to begin to enlarge & complete first meiotic division

• ovarian cycle.• 2 phases• follicular or preovulatory stage• luteal or post ovulatory stage

Hormones & Female Reproductive Cycle

• interactions of pituitary gland, hypothalamus & gonads are responsible for female reproductive cycle– more complicated in females

because two cycles• ovarian & uterine• must be coordinated• if not properly coordinated infertility • GnRH from hypothalamus begins cycle• GnRH pulse frequency & amplitude

change throughout ovarian cycle• changes in pulse frequency are

controlled by circulating estrogens & progestins

• estrogens increase pulse frequency• progestins decrease pulse frequency• changes in pulse frequency are

essential to normal FSH & LH production & therefore to control of ovulation

• absent or constant (no pulses)FSH & LH production stops within hours

Estrogen• FSHfollicle development• as follicle enlarge-thecal cells

androstenedione– intermediate in synthesis of sex

hormones• androstenedione is absorbed by

granulose cells3 types of estrogens• estradiol, estrone & estriol• Estradiol

– most abundant– has most pronounced effects

• Estrogen– dominant hormone before ovulation– stimulates bone & muscle growth– maintains secondary sex

characteristics– affects CNS activity-especially

hypothalamus-libido– maintains functional accessory

reproductive glands & organs– initiates repair & growth of

endometrium

Ovarian Cycle-Follicular Phase• FSHstimulates primordial

follicle primary follicle• in primary follicle, follicular cells

enlarge & divide repeatedly creating several layers of follicular cells around oocyte– cells are now granulosa cells

• microvilli from granulosa cells-surrounded by glycoprotein layer-zona pellucida

• as granulosa cells enlarge & multiply; adjacent cells in stroma form thecal cell layer around follicle– thecal cells + granulose cells

make sex hormones

Ovarian Cycle• early in follicular stage

estrogen levels are low• GnRH pulse frequency is 16-

24 per dayFSH dominant hormone

• only few primordial follicles continue to step

• wall of follicle thickens & granulosa cells secrete follicular fluid or liquor folliculi– fluid accumulates in small

pocketsgradually expands separates inner & outer follicle layers secondary follicle

• follicle continues to enlarge as fluid continues to accumulate

• FSH levels decline due to secretion of inhibin

Ovarian Cycle• as fluid accumulatesforms tertiary

follicle-Graafian follicle• by 10th -14th day of cycle, follicle

spans entire width of cortex• Distorts capsule creating bulge• oocyte projects into antrum

– expanded chamber of follicle• oocyte is surrounded by many

granulosa cells• primary oocyte has been suspended in

prophase of meiosis I• as tertiary follicle developsLH

risesprompts primary oocyte to complete meiosis Isecondary oocyte + polar bodyenters meiosis II & stops at metaphasse

• estrogen levels continue to increase• GnRH pulse frequency increases to 36

per day– stimulates LH secretion

• at about day 10, estrogen stops inhibiting LH secretion & stimulates it

Ovarian Cycle• day 14• secondary oocyte & surrounding

granulosa cells lose connection to follicle wall

• granulosa cells drift free forming corona radiata

• 14 estrogen levels peak• GnRH pulse frequency increases to

every 30 minutesmassive LH release• causes rupture of follicle wall and

ovulation• secondary oocyte & corona radiata are

ejected into pelvic cavity• occurs about 34-35 hours after LH

surge • egg is released near opening of

toviduct or Fallopian tube• Cilia in toviduct set up currentsdraw

egg in• sperm are presentegg is fertilized

near far end of oviductquickly finishes meiosis embryo starts to divide & grow as it travels to uterus

Luteal Phase of Ovarian Cycle• tertiary follicle is empty & collapses• ruptured vessels bleed into antrum• remaining granulosa cells invade

area & proliferatecorpus luteum– stimulated by LH surge

• lipids in corpus luteum used to make progestins-primarily progesterone– principle hormone after

ovulation• progesterone production increases

& GnRH decreases to 1-4 pulses per day– stimulates more LH production

than FSH production• LH maintains corpus luteum

– continues to secrete progesterone

Progesterone• stimulates maturation of

uterine lining-endometrium• enhances blood supply to

functional zone• enhances secretion of uterine

glands in preparation for fertilized egg

• trip down Fallopian tube takes about week as cilia propel unfertilized egg or embryo to uterus

• once growing embryo reaches uterus, it will implant & begin to secrete its own hormones to maintain endometrium

• corpus luteum remains for first 6 weeks of gestation

Post Ovulation• 12 days post ovulation corpus

luteum becomes non-functional– leads to menses

• first phase of uterine cycle• if egg not fertilizeddies &

disintegrates as corpus luteum disintegrates progesterone production fallsbuilt-up endometrium is shed

• progesterone & estrogen levels fall fibroblasts invade nonfunctional corpus

• knot of scar tissue-corpus albicans• involution of corpus luteum is end of

ovarian cycle• new cycle begins with activation of

another group of primordial follicles as GnRH pulse frequency increases and FSH production steps up

Uterine Tubes-Fallopian tubes or Oviducts

• once secondary oocyte exits ovary• travels down uterine or fallopian

tubes– hollow & muscular

• 3 segments• Infundibulum

– closest to ovary– expanded funnel with many finger

like projections-fimbriae• Ampula

– middle part of tube– smooth muscle layers that

increase in thickness as tube nears uterus

• Isthmus– short segment connected to

uterine wall– ciliated, columnar epithelium with

scattered mucin secreting cells

Path of Oocyte• oocyte is transported with ciliary

movements & peristaltic contractions down uterine tube toward uterus

• few hours before ovulation, sympathetic & parasympathetic fibers turn beating & peristalsis actions on

• takes 3-4 days to go from infundibulum to uterine cavity

• for fertilization-secondary oocyte must meet spermatozoan during 1st 12-24 hours of passage

• fertilization occurs near boundary of ampulla & isthmus

• uterine tube nourishes oocyte & sperm as well as pre-embryo divisions after fertilization

Uterus • pear shaped, small structure with

thick, muscular walls-myometrium– makes up 90% of uterine mass

• uterus provides mechanical protection, nutritional support & waste removal for developing embryo & fetus

• contraction of wallsdelivers fetus• broad ligament & 3 pairs of

suspensory ligaments stabilize its position & limit range of movement

• divided into 2 anatomical regions• body or corpus

– largest region– rounded part-fundus lies superior to

uterine tube attachment & ends at constriction or isthmus

• Cervix– area inferior from isthmus &

continuing to vagina

Uterus• lining-endometrium

– inner, glandular lining– comprises 10% of uterine

mass

• contains rich capillary supply to bring food to developing embryo

• vast number of uterine glands open onto endometrial surface

• estrogenuterine glands & blood vessels to change

Endometrium• histologically can be

divided into 2 zones• Functional zone

– closest to uterine cavity– undergoes cyclic changes– contains most uterine

glands

• Basilar zone– lies adjacent to

myometrium– attaches endometrium to

myometrium– contains terminal branches

of endometrial glands– structure remains constant

Uterine Cycle-Menstrual Cycle• consists of repeating changes in endometrial structure• cycle averages 28 days with range between 21-35• first cycle occurs at menarche• last begins menopause• 3 phases• Menses• Proliferative stage• Secretory stage • occurs in response to hormones associated with ovarian cycle• two cycles must coordinate to have proper reproductive function• menses & proliferation occur during follicular phase of ovarian

cycle• secretory phase corresponds to luteal phase of ovarian cycle

Menses• begins uterine cycle• functional zone degenerates• spiral arteries constrictblood flow

endometrium slows no oxygen or nutrientssecretory glands & other tissues deteriorate

• arterial walls weakened ruptureblood pours into connective tissue of functional zone blood cells & degenerating tissues break awayenter uterine lumen

• straight arteries that feed basilar zone are unaffected

• tissue sloughing is gradual• repairs begin immediately• before end of menses all

functional zone is lost• stages lasts 1-7 days

Proliferative Phase• begins after menses• epithelial cells of uterine

glands in basilar zone multiply & spread across endometrial surface restoring integrity of lining

• takes place as primary & secondary follicles enlarge

• stimulated & sustained by estrogen secreted by follicles

Secretory Phase• endometrial glands

enlargesecretions accelerate• arteries supplying wall

elongate & spread through functional zone

• occurs under stimulation by progestins & estrogens from corpus luteum

• persists as long as corpus luteum remains intact

• peaks about 12 days post ovulation

• over next 2 daysglandular activity decreasesuterine cycle endscorpus luteum stops making hormonesnew cycle begins with menses

Vagina• relatively-thin-walled, elastic

muscular tube• extends between cervix &

vestibule• space bounded by external

genitalia• repository for sperm• birth canal• Lumen-lined by

nonkeratinized, stratified squamous epithelium

• contains bacteria which are usually harmless

• metabolic activity of these bacteria make vagina acidic which restricts pathogen growth