Transcript Reproductive System

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
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Epididymus
Ductus Deferens
Urethra
Ejaculatory ducts
– nourish, store, transport &
mature sperm.
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Accessory structures
Seminal vesicles
Prostate
Bulbourthral or Cowper’s glands
External genitalia
Scrotum
– contains testes
• Penis
Testes Development
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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
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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 thickeningraphe
• 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 mitosisdaughter
cellsstem 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
divisiongametes or sperm
– half number of chromosomes
(haploid-1N) as somatic cells
– number of chromosomes in
gametes = 23
– egg + sperm = 46 chromosomes2N-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 spermatocytes2
secondary spermatocytes
• Meiosis II
– 2 secondary spermatocytes4
spermatids
• During meiosis I duplicated sister
chromatids come in close contact
with their homologous pairs
• Portions of homologous
chromosomes are exchangedcrossing 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
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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 timecytoplasm
of spermatid is pinched off by
Sertoli cell
Sustentacular or Sertoli Cells
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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
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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
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occurs in 2 steps
first
– mix with secretions of seminal vesicles
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– 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
systemstip of penis
Accessory Glands
• Activate
• Nourish
• Propel sperm along reproductive
tract
• Buffer acidity
Seminal Vesicles
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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
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done by endocrine interactions of
hypothalamus, pituitary gland & somatic
cells of testis
Hypothalamusgonadotropin-releasing
hormone-GnRH anterior pituitaryLHluteinizing hormone & FSH-follicle
stimulating hormone
– without GnRHtestes 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
FSHsustentacular cells of seminiferous
tubulespromotes spermatogenesis &
spermiogenesissecrete androgen
binding protein
ABP binds to androgensprompts
spermatogenic cells to bind &
concentrate testosteronestimulates
spermatogenesis
Control of Spermatogenesis
• rate of spermatogenesis
regulated by negative
feedback mechanism
involving GnRH, FSH &
inhibin
• GnRHFSHspermatogene
sis spermatogenesis
accelerates inhibin secreted
by sustentacular cells
inhibits GnRH & FSH
• sperm count highinhibin
high hypothalamusinhibits
GnRH & at anterior
pituitaryinhibits FSH
• LH or ICSH-interstitial cell
stimulating hormone
interstitial cellstestosterone
Androgens
• steroid hormones made from
cholesterol
• diffuse across cell membranes
• bind to intracellular
receptorssteroid-hormonereceptor complex binds to DNA in
nucleusactivates genes
enhances synthesis of proteins in
target cells
• stimulates spermatogenesis &
formation of functional sperm
• affects CNSlibido
• 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 gametesoocytes
• 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
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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
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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
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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 riseovarian 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 beginssecondary
oocyte undergoes second meiotic
divisionovum + another polar
body
• ovum is ready to fuse with
spermatozoan
Ovarian Cycle
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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
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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
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FSHfollicle development
as follicle enlarge-thecal cells
androstenedione
– intermediate in synthesis of sex
hormones
androstenedione is absorbed by
granulose cells3 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
• FSHstimulates 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 cellssurrounded 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 1624 per dayFSH 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
pocketsgradually 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
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as fluid accumulatesforms tertiary
follicle-Graafian follicle
by 10th -14th day of cycle, follicle
spans entire width of cortex
Distorts capsule creating bulge
oocyte projects into antrum
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oocyte is surrounded by many
granulosa cells
primary oocyte has been suspended in
prophase of meiosis I
as tertiary follicle developsLH
risesprompts primary oocyte to
complete meiosis Isecondary
oocyte + polar bodyenters meiosis
II & stops at metaphasse
estrogen levels continue to increase
GnRH pulse frequency increases to 36
per day
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expanded chamber of follicle
stimulates LH secretion
at about day 10, estrogen stops
inhibiting LH secretion & stimulates it
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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 minutesmassive 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 currentsdraw
egg in
sperm are presentegg is fertilized
near far end of oviductquickly
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 & proliferatecorpus 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 fertilizeddies &
disintegrates as corpus luteum
disintegrates progesterone
production fallsbuilt-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
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pear shaped, small structure with
thick, muscular walls-myometrium
– makes up 90% of uterine mass
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uterus provides mechanical
protection, nutritional support &
waste removal for developing
embryo & fetus
contraction of wallsdelivers 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
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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
• estrogenuterine 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
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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
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begins uterine cycle
functional zone degenerates
spiral arteries constrictblood flow
endometrium slows no oxygen or
nutrientssecretory glands & other
tissues deteriorate
arterial walls weakened
ruptureblood pours into
connective tissue of functional
zone blood cells & degenerating
tissues break awayenter 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
enlargesecretions 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 daysglandular
activity decreasesuterine
cycle endscorpus luteum
stops making hormonesnew
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