Reproductive Physiology Flashcards
Function of the reproductive system
- provides gametes for procreation of species
- mating
- fertilization
Organs of the reproductive system
- called gonads
- pathway for gamete transport
- accessory organs and glands
Functions of gonads
- organs which produce gametes
- source of sex steroid hormones
Gonads of the male reproductive system
testis
Scrotal sac
- outside the body
- testes, blood vessels, nerves
Function of blood vessels in scrotal sac
- countercurrent blood flow to regulate temperature
- 2C below core body temperature for spermatogenesis
Function of spermatic cord in scrotal sac
- passes through slit in abdomen (inguinal canal)
- combination of vas deferens, blood vessels and nerves
Descent of testes
8 weeks - testes high in abdomen near kidneys
8-12 weeks - testes move down towards inguinal canal
7-9 months - testes pass through inguinal canal and rest in scrotum
birth - testes have have descended into scrotal space
Testes
- found inside scrotal sac
- male gonads
- divided into many compartments - highly twisted tubules called seminiferous tubules
- lead into rete testis network
- lead into efferent ductules
- lead into epididymis
Seminiferous tubules
- site of sperm production
- sit on basement membrane and contain a lumen
- cells are called spermatogenic cells
Mumps virus
- causes seminiferous tubules to become smaller
- lumen becomes bigger and spermatogenic cells look small
- effects spermatogenesis process
Leydig cells
- found in connective tissues surrounding seminiferous tubules
- also called interstitial cells
- produce hormone testosterone
Sertoli cells
- epithelial cells lining seminiferous tubule
- help the process of sperm development
- laid out side by side and sit on basement membrane
Smooth muscle cells
- just outside basement membrane
- muscle-like
- have contractile properties - help with peristalsis of sperm
Tight junctions
- join epithelial cells
- do not allow infections that harm sperm through
- create invisible ring-like structure
- form blood-testis barrier: form basal compartment and luminal compartment
7 Functions of Sertoli Cells
- support sperm development - trophic
- secrete luminal fluid for sperm housing
- secrete androgen-binding protein under influence of FSH: androgen buffer, maintains high luminal conc. of testosterone
- act as target cells for testosterone and FSH
- secrete inhibin
- phagocytosis of old/damaged sperm
- site of immunosuppression (blood testis barrier)
Testosterone - corticosteroid synthesis
- steroid hormone
- synthesized from cholesterol
- produced by adrenal cortex, gonads, and testes
In adrenal gland - corticosteroid synthesis
- intermediary hormone called progesterone is synthesized
- depends on enzymes present, progesterone is converted to mineralocorticoids, glucocorticoids, or androgens
In male gonads - corticosteroid synthesis
- formation of mineralocorticoids and glucocorticoids is bypassed in male gonads and more testosterone is produced
- testosterone receptors is located in intracellular locations - lipophilic nature to diffuse across membranes and influence gene transcription
In Leydig cells
cholesterol –> pregnenolone –> progesterone
- both progesterone and pregnenolone product androgens (testosterone)
4 ways testosterone is used/converted into
- as testosterone
- converted to dihydrotestosterone (DHT) by 5-alpha reductase in prostate gland
- concerted to estrogen by aromatase in liver, adipose tissue, brain and testes
- broken down into inactive molecules
Puberty (10-14 years)
- sexual maturation
- reproductive organs mature
- secondary sexual characteristics develop
Plasma testosterone levels during lifespan
- before birth: high peak of testosterone then decreases until birth
- neonatal: high peak of testosterone then decreases until childhood
- puberty until adulthood: high at puberty then slowly declines around age 40 - andropause
Sperm production during lifespan
- begins at onset of puberty with sharp rise until adulthood
- sperm production is maintained until age 40-45 then starts to decline
Hypothalamic-pituitary-leydig cell axis
higher centers –> cues/signals –> hypothalamus –> GnRH –> anterior pituitary –>
- LH –> Leydig cells –> testosterone
- FSH –> Sertoli cells
GnRH (gonadotropin releasing hormone)
- pulsatile secretion every 90 minutes
- called pulse generator
- pulsatile to activate receptors (would no activate if constant release of GnRH)
High frequency pulses of GnRH
- predominant secretion is luteinizing hormone (LH)
Low frequency pulses of GnRH
- predominant secretion is follicle stimulation hormone (FSH)
Testosterone in negative feedback regulator
- hypothalamus - dampens amplitude of pulsatile secretion
- anterior pituitary - causes decreased responsiveness due to down regulation of GnRH receptors
6 Effects of androgens
- stimulate spermatogenesis
- promote development of secondary sex characteristics during puberty and maintenance in adult life
- increase sex drive
- promote protein synthesis in skeletal muscle
- stimulate growth hormone secretion for bone growth
- promote development of male reproductive structures during embryonic life
Spermatogenesis
formation of the male gamete or sperm
Mitosis
- enlarge and split a cell into 2 identical daughter cells that are genetically identical to original cell
- one remains a spermatogonium to ensure numbers are not depleted
- the other is a committed cell called a primary spermatocyte with a 2n
Meiosis
- each daughter cell receives half the chromosomes
- reduced from 46 chromosomes, diploid to a 23 chromosome haploid
What comes after the secondary spermatocyte
each one gives two spermatids - 4 spermatids produced
Duration of primary spermatocyte to spermatozoa
64 days
Where does spermatogenesis occur
- seminiferous tubule in the space between two adjacent Sertoli cells
- tight junction divides basal and luminal compartment and allows primary spermatocyte to move through
What is spermiogenesis
- last stage of spermatogenesis
- spermatids mature into motile spermatozoa
- nucleus, acrosomal vesicle, flagella, remodeled cytoplasm
- 24 days
Head of a sperm
nucleus - contains haploid number of chromosomes
acrosome - vesicle at the tip containing enzymes necessary for fertilization
Midpiece of a sperm
many mitochondria which generate ATP needed for movement of tail
Tail of a sperm
whip-like movements propel sperm
Sperm maturation
- spermatozoa released into lumen in immature form
- fluid pressure generated by Sertoli cells pushes the sperm forward towards the epididymis
- reside in epididymis for 6-12 days
- fluid is reabsorbed and sperm is concentrated
- move to vas deferens by peristalsis
Inhibin
- peptide hormone
- regulate axis at level of anterior pituitary to decrease secretion of FSH
- does not act at hypothalamic level
Seminal fluid comes from 3 glands
- seminal vesicle
- prostate gland
- bulbourethral gland
Functions of seminal fluid
- dilution of sperm
- provides energy as fructose
- formation of semen clot (fibrin-like protein that forms plug)
Seminal vesicles
- secrete alkaline (balance acidic environment of female tract) fluid with fructose, enzymes (produce semen clot), and prostaglandins (cause contraction of female tract for sperm to move forward)
Prostate gland
- secrete citrate (energy for sperm) and enzymes (PSA breaks down seminal clot making semen for fluid and is biomarker for cancer)
Bulbourethral gland
- secrete viscous fluid with mucus
3 phases of neural control for male reproduction
- erection phase
- emission phase
- ejaculation phase
Erection phase
- parasympathetic nervous system
- relaxation of blood vessels and increased blood flow into tissue
Emission phase
- sympathetic nervous system - thoracolumbar division
- acts of muscle tissue of prostate gland, vas deferens and seminal vesicle
- causes smooth muscle contraction leading to movement of sperm from vas deferens with mixing of seminal fluid into urogenital tract
Ejaculation phase
- rapid contraction of skeletal muscle for semen expulsion outside of body
Parasympathetic control of erection
- causes release of nitric oxide
- NO stimulates cGMP
- cGMP acts on smooth muscle of blood vessel to vasodilation
- cGMP is broken down by enzyme phosphodiesterase
Erectile dysfunction
- treated with Viagra (Sildenafil)
- acts as a inhibitor of enzyme phosphodiesterase
- actions of cGMP are prolonged maintaining vasodilation and erection
2 final sperm maturation processes
- capacitation
- acrosome reaction
Capacitation
- occurs as sperm moves through female reproductive tract
- receptors are made available through the removal of the glycoprotein layer
- area of acrosomal cap is altered
- tail movements change from wave-like to whiplash
Acrosomal reaction
- binding of sperm with zona pellucida (egg outer layer)
- creating pores which acrosomal enzymes can be released by exocytosis
- enzymes allow sperm to digest a path through zona pellucida to oocyte
3 characteristics of female repro system
- cyclic changes in activity - menstrual cycle
- restricted periods of fertility - ovulation
- limited production of gametes
Menarche
- onset of puberty
- first menstrual cycle
Menopause
- lost ability to reproduce around 45-50
Female gonads
ovaries
Female reproductive tract
uterus, Fallopian tubules, vaginal canal
Ovaries
site of ova maturation
- specifically opening of fallopian tubes
Uterine tubes
- fallopian tubes or oviducts
- transport ova from ovaries to uterus
- fimbria stick out and sit close to ovary
- fimbria have ciliated cells which capture and move egg
Site of fertilization
uterine tube
Movement of ovum through uterine tube
- initially - peristaltic contractions
- mostly - ciliary actions
- duration - 4 days to uterus
Ectopic pregnancy
- cilia does not move egg properly and will plant in fallopian tubes
3 layers of uterus
outer
- perimetrium - protective covering
- myometrium - smooth muscle
- endometrium - epithelial cells and connective tissue and glands to produce glycogen
inner
Ovary
- covered by capsular structure
- contains follicles suspended in connective tissue
- contains blood vessels
- contains follicles in different stages of growth
Names of follicle development
- primordial follicles
- primary follicles
- mature follicles
- corpus luteum
- corpus albicans
Corpus luteum
- mature follicle that released its egg
- remains and acts as endocrine gland
3 cycles in female body
- hormonal cycle
- ovarian cycle
- uterine cycle
- average 28 days
Ovarian cycle
2 phases
- follicular phase (first 14 days): development of follicles when eggs are growing
- ovulation: 14th day
- luteal phase (last 14 days): egg is released and related to secretory gland
Uterine cycle
3 phases
- menstrual phase (day 1-5): first day of bleeding and shedding of endometrial layer
- proliferative phase: development of growth, layers become wider and blood vessels grow
- secretory phase: further vascularization and development of uterine gland
- menstrual phase and proliferative coincide with follicular phase
- secretory phase coincide with luteal phase
Oogenesis
development of female gamete/oocyte
Folliculogenesis
maturation of ovarian follicle
- contributes and takes part in hormonal cycle
Primary oocyte stage
- each follicle contains 1 oocyte
- begins with primordial follicle stage: single oocyte surrounded by single layer of granulosa
- granulosa will begin mitosis
- granulosa secrete proteins and glycoproteins which form thick layer called zona pellucida
Preantral follicle stage
- many layers of granulosa cells
- connective tissues differentiate and become theca layer (internal and external)
- no antrum
Early antral follicle stage
- development of fluid-filled space known as antrum begins to form
Mature follicle stage
- major growth of antral space
- granulosa layers outside oocyte suspended in bridge-like fashion called cumulus oophorus
Corpus albicans stage
- empty follicle/endocrine structure will die off
- forms scar tissue and will dissipate
Random selection of pre-antral follicles
- 10-25 follicles are selected
- the follicle that secretes the highest amount of estrogen will be the dominant follicle
- remainder of follicles die off known as atresia or programmed cell death
Hormonal cycle
- estrogenic phase - first 14 days
- progestational phase - after ovulation
Early-mid-follicular phase
- day 1-7
- 10-25 have selected and grow rapidly
- estrogen is predominant hormone
- 2 cell compartment: granulosa and theca cells
- FSH causes granulosa cells to increase by mitosis
Theca cells
- has receptors for LH
- convert cholesterol –> progesterone –> androgens
- permeate granulosa cells which convert androgens to estrogen
- some estrogen moves into blood stream and some stay in antrum
FSH upregulates
- enzyme aromatase that converts androgens to estrogen in granulosa cells
Late follicular/corpus luteum phase
- day 7-14
- rise of estrogen causes granulosa cells to start developing LH receptors
- granulosa cells convert cholesterol to progesterone
- small rise in progesterone occurs towards late follicular phase
- increasing estrogen concentration
7 functions of granulosa cells
- secrete antral fluid
- provide nutrients for developing oocyte
- secrete paracrine factors that support follicular development
- secrete inhibin
- secrete estrogens
- have aromatase enzyme which converts androgens to estrogen
- secrete substance that forms zona pellucida
Hypothalamic-pituitary-ovarian axis in women
- GnRH released in pulsatile manner
- pulses change every 24 hours (males do every 90 minutes)
- anterior pituitary secretes 2 hormones: LH and FSH
acts on ovary and estrogen and progesterone
Estrogen has a negative feedback
- effects level of anterior pituitary and hypothalamus
- estrogen can either dampen the amplitude or reduce the responsiveness of the pituitary
Estrogen has a positive feedback
- increase amplitude or responsiveness of pituitary to GnRH
Progesterone has a ____ feedback
negative depending on phase of cycle
Oogenesis
beginning with oogonium to ovum
DNA replication
- early fetal development
- primary oocyte
- do not complete division in fetus
- meiotic arrest
- at birth all contain 46 chromosomes each with two sister chromatids (2n x 2)
Meiosis I
- monthly from puberty to menopause oocyte released from arrest to complete meiosis I
- 2 daughter cells called secondary oocyte and first polar body
- secondary oocyte has n x 2
- happens at time of ovulation from dominant follicle
Meiosis II
- occurs after fertilization only if secondary oocyte is fertilized by male gamete
- 2 daughter cells called ovum and second polar body produced
- ovum has n
Net result of oogenesis
- 1 egg with n number of chromosomes
Net result of spermatogenesis
- 4 spermatozoa with n numbers of chromosomes
estrogen and progesterone are not required for sexual ____ but for sexual ____
- differentiation
- maturation
Menstrual phase - menstrual cycle
- day 1-5
- shedding of uterine lining
- tissues die and slough into vagina causing menstrual flow
- triggered by decreased estrogen and progesterone
Proliferative phase - menstrual cycle
- day 5-14
- endometrial lining develops, layer grows, and glands enlarge
- smooth muscle layer thickens
- cervical glands secrete thin mucus
- estrogen stimulate uterine lining development
Secretory phase - menstrual cycle
- endometrium prepared for implantation
- blood supply increased
- glands enlarge and secrete glycogen-rich fluids
- cervical secretions more sticky forming plug
- progesterone mainly and estrogen
Estrogen has an inhibitory effect on
- gonadotropin secretion when estrogen levels are low during early-mid-follicular phase
Increase in FSH secretion at the end of the cycle:
- stimulates preantral and early antral follicles to grow
- increase in FSH due to decrease in progesterone, estrogen and inhibin
Rapidly increasing estrogen causes a sharp rise in
- LH surge
- positive feedback on gonadotropins
- upregulation on LH receptors
LH surge causes
- ovulation
- 18 hours before time
- remains for about 12 hours after following be LH and FSH decline
As LH and FSH level decrease, estrogen levels will
- decrease
- dominant follicle has ruptured and released oocyte
During luteal phase, estrogen levels
- peak again
- comes from corpus luteum as a temporary endocrine gland
Progesterone during follicular phase
- low
- near the end will rise a bit due to granulosa cells beginning to release progesterone
- after corpus luteum formed, there is large increase
Why do the gonadotropins, LH and FSH remain low throughout luteal phase
- estrogen and progesterone has negative feedback and suppresses LH and FSH
- gonadotropins levels must be kept low so another LH surge/ovulation does not occur in luteal phase
Low levels of estrogen have a ___ effect on ____ and levels will _____
- negative feedback
- FSH
- decrease
High levels of estrogen had a ____ effect on ____ and levels will ____
- positive feedback
- LH
- increase
Inhibin role
- decline in FSH levels during follicular phase
- causes atresia of the non dominant selected follicles
In the dominant follicle
- stimulation of meiosis I in the oocyte
- estrogen secretion starts decreasing after ovulation
- progesterone secretion increases
- ovulation
- transformation of follicle into corpus luteum
Fertilization
process by which male and female gametes fuse together to form zygote
Gestation
- length of time on intrauterine fetal development
- 9 months or 40 weeks
Embryo
first 2 months of life
Fetus
developing human from 2 months to birth
Parturtition
childbirth
Site of fertilization
Fallopian tube
Sperm is viable for
5 days
Oocyte is viable for
12-24 hours
Why do only several hundred sperm make it to uterine tubes?
- damage due to acidic environment in female tract
- loss of sperm from female reproductive tract due to leakage from cervix
- loss of energy
Capacitation
- previously regular wavelike action of sperm’s tail is replaced by whiplike action that propels sperm forward
- sperm’s plasma membrane becomes altered so it is capable of fusing with surface membrane
- occurs in female repro tract
Polyspermy
- egg that has been fertilized by more than one sperm
- not favored and prevented to maintain 2n chromosome
Steps of fertilization
many sperm bind to glycoprotein receptors on zona pellucida –> binding triggers acrosomal reaction –> plasma membrane of sperm head is altered so enzymes exposed to outside –> enzymes digest zona pellucida –> first sperm to penetrate zona pellucida fuses with membrane –> egg secretory vesicles are released into space between zona pellucida and egg plasma membrane –> hardens layer
Blocks to polyspermy
- change in membrane potential
- release of contents from cortical granules
- enzymes enter and harden zona pellucida
- enzymes inactive sperm binding receptor
What happens to the oocyte during fertilization
- sperm fusion stimulated 2nd meiotic division of oocyte
- oocyte converted to fertilized ovum
- sperm plasma membrane disintegrates
- chromosome from sperm and ovum migrate to center
- DNA replicated to a zygote (2n)
Morula
- less than 16 cells
- zona pellucida intact
- cell cleavage: number of cells increase but no overall growth of size
- cells are totipotent
Identical twins
- division of totipotent morula cells
Fraternal twins
- fertilization of two oocytes
Blastocyst
- 4-5 days after fertilization
- lose totipotentiality and differentiate
- no zona pellucida
Outer cell of blastocyst
- trophoblast
- will become fetal placenta
Inner cell of blastocyst
- will become embryo
- when inner cell mass if pushed to one side of blastocyst, fluid filled cavity called blastocoel is formed
Implantation
- 6-7 days after fertilization
- sticky trophoblast cells anchor to endometrial lining
- proliferation into syncytiotrophoblast (fused) and cytotrophoblast (hormones)
Decidual response
- when fused syncytiotrophoblast layer penetrates endometrial layer, all blood vessels start branching closer to blastocyst
- gland-like structures provide glycogen from embryo
Placenta has 2 compartments
- fetal placenta - blastocyst
- maternal placenta - uterine tissue
Amnion
- innermost membrane that encloses the embryo fused with the chorion which is the outer layer
Chorion
- embryonic derived portion of placenta
- made of trophoblasts
- invades the maternal endometrium and develops finger-like projections called chorionic villi
Umbilical cord
- contains two umbilical arteries and an umbilical vein
- arteries carry deoxygenated nutrient depleted blood from fetus to placenta
- vein carries oxygenated nutrient rich blood from placenta to fetus
Functions of placenta
- temporary endocrine gland
- exchange tissue
- filter/immunological barrier
hCG
- very sharp peak at 2 months which then decreases and stays at low constant level
- released from chorionic layer of placenta
- helps maintain corpus luteum in early parts until placenta is formed and takes over
Progesterone and estrogen levels during pregnancy
- high increasing levels
- estrogen higher than progesterone
After delivery, progesterone and estrogen levels
drop
hPL
- growth hormone-like and anti-insulin like actions in mother
- keeps glucose and nutrient levels high in mother’s plasma providing more nutrition for fetus through placenta
- helps fetus take up more glucose into its own body
Progesterone functions during pregnancy
- decreases uterine contractions
- inhibits secretion of LH and FSH from anterior pituitary
- stimulates growth of alveolar ducts or glands
- causes cervical glands to secrete a sperm-unfriendly mucus
Estrogen functions during pregnancy
- causes growth of myometrium
- causes growth of mammary ducts
- inhibits LH and FSH from anterior pituitary
Hormone pathway during pregnancy
- cholesterol –> progesterone –> androgens –> estrogen
- SEE TABLE
Control of parturition
- weak uterine contractions develop and push fetus forwards to cervix
- pressure of fetus against cervix sends positive message to posterior pituitary to release oxytocin
- oxytocin acts on uterine myometrial layer binding to tissue and causing more contractions
Hormones involved in parturition
myometrial contractions increased by estrogen, prostaglandins, oxytocin and stretch from fetus’s head
Cervical ripening
- prepares the tissues to make cervix softer and easier for expansion
- due to prostaglandins and relaxin (progesterone inhibits this)
Mammary gland
- contain mammary glands that are the site of milk production and storage
- alveoli clustered into lobules and clustered into lobe
Birth to puberty - mammary glands
- breast tissue has rudimentary ducts
Puberty - mammary glands
- estrogen causes ducts to start growing and branch out
- progesterone causes growth of alveolar tissues
- fat is deposited around alveolar space
Pregnancy and lactation - mammary glands
- estrogen, progesterone, prolactin, hPL
- prolactin is released from anterior pituitary and promotes lactation and milk production
- oxytocin required for milk ejection/let-down
Galactopoiesis
- maintenance of lactation while mother is breast feeding
- requires prolactin
2 cells required for milk ejection
- alveolar epithelial cells - synthesize milk
- myoepithelial cells - contractile properties to expel milk, has receptors for oxytocin to cause contraction
Suckling
- activates tactile mechanoreceptors in mother’s breast tissue
- activates hypothalamus and stimulates oxytocin secretion
- causes contraction of myoepithelial cells and milk is ejected
Dopamine in mammary glands
- inhibits prolactin secretion for anterior pituitary cells
- suckling decreases dopamine secretion
Male chromosomes
XY
- presence of Y leads to development of male gonads - testes
Female chromosomes
XX
- absence of Y leads to development of female gonads- ovaries
Chromosomal sex is determined at
exact moment of fertilization
Gonadal sex is determed by
chromosomal sex
Site at where male or female gonads develop
urogenital ridge or gonadal ridge
Presence of Y chromosome of what gene
SRY gene
Female differentiation occurs by
default
Klinefelter’s syndrome
- Male XXY
- infertile - spermatogenesis does not occur
Turner’s syndrome
- Female XO
- streaked ovaries - do not look round but are flattened structures
Phenotypic sex
- dictated by factors produced by gonads
- determined by internal and external genitalia
Undifferentiated reproductive tract includes a
double genital duct system
Ducts in male differentiation
Wolffian ducts persist and Mullerian ducts regress
Ducts in female differentiation
Mullerian ducts persist and Wolffian ducts regress
Male differentiation
- testes produced by presence of Y
- testes secrete MIH from Sertoli cells
- Leydig cells secrete testosterone to develop male internal genitalia
- testosterone is converted to DHT by 5-alpha reductase which causes masculinization of male external genitalia
Male internal genitalia
- epididymis, vas deferens, seminal vesicles, ejaculatory ducts, testes
Male external genitalia
- penile structure and prostate gland
Female differentiation
- do not have MIH so Mullerian ducts persist and Wolffian duct regress due to lack of testosterone
- Mullerian duct will grow into female internal genitalia
- since no DHT, male external tissue does not develop
- some modulation due to estrogen
Female internal genitalia
- uterine structures, Fallopian tubes, cervix, vaginal space
Congenital adrenal hyperplasia - sexual disorders
- female genotype, male phenotype
- too much androgen production in fetal stage causes male external appearance
- decreased cortisol –> increase ACTH –> adrenal androgens –> mascularization
- infertile
Androgen insensitivity syndrome - sexual disorders
- male genotype, female phenotype
- tissues in body were unresponsive to testosterone during development
- testes developed corrected
- mutation in receptors of Wolffian ducts cannot bind testosterone
- male genitalia do not develop
- androgens converted to estrogen in target tissues to product female genitalia
- infertile
What triggers the onset of puberty
- increased secretion of GnRH, increased secretion of LH and FSH, increased secretion of sex steroids
- genetic influences and environmental influences alter GnRH levels
Prepubertal child
- hypothalamic-pituitary-gonadal axis is dormant because hypothalamus is suppressed
- low levels of GnRH, LH, FSH
- low levels of sex steroids provide strong negative feedback to higher centers
Time of puberty in the axis
- Kisspeptin - neuropeptide releases GnRH in hypothalamus
- Adipose tissue - source of hormone leptin which acts on hypothalamus to release kisspeptin to regulate pulse generator
Andropause
- in males
- start anywhere from age 40 onwards
- lowering of male hormones
Menopause
- in females
- reproductive status comes to a halt
- follicular depletion throughout life by apoptosis - atresia
- decreased responsiveness to gonadotrophs, decreased estrogen and inhibin
- ovulation and menstrual cycles become irregular and stop
- decreased E, I, P remove negative feedback
- FSH (especially) and LH increase
- cardiovascular effects and osteoporosis because of decreased estrogen
