reproductive system Flashcards
what are the 4 major functions of the reproductive system?
-production of gametes
-organs for mating
-fertilization
-propogation of species
what organs are involved in the reproductive system?
-gonads
-pathway of gamete transport
-accessory reproductive organs
why is the scrotal sack located outside of the body?
to keep the T ~2 degrees lower than normal body T
-needed for gamete production
what regulates the descent of the testes?
male hormones
-testosterone
what is cryptorchidism? what are risks of it?
a condition in which descent occurs but the testes don’t go all the way down into the scrotal sac
-if not corrected, infertility can occur do to lack of spermatogenesis
when does teste descent occur?
during fetal development
what kind of tubules are contained within the testes? what is their function?
seminiferous tubules
-sperm production
what cells are found on the basememt membrane of the seminiferous tubules?
spermatogenic cells
when does spermatogenesis begin?
at puberty
what is mumps? what does this cause? how is it prevented?
-a viral disease where lymph nodes get swollen whcih affects germ cells in the seminiferous tubules
-results in damage to germ cells and infertility
-prevemted by childhood vaccination
what cells in the testes are responsible for sperm and hormone production?
leydig cells (interstitial cells)
-secrete testosterone
sertoi cells (epithelial cells)
-support sperm development
smooth muscle (myoid cells)
-propel sperm through peristalsis
what is makes up the blood-testis barrier?
tight junctions, luminal compartment and basal compartment
what connects the cells on the testis?
tight junctions
what are the functions of the Sertoli cells?
main role: support sperm development
-trophic role; helps other hormones be secreted
-secretion of luminal fluid, inhibin, paracrine factors and adrogen-binding protein
-target cell for FSH
-phagocytosis for old/damaged sperm
-site of immunosuppression (blood testis barrier)
what is the affect of the secretion of androgen-binding protein?
it is an adrogen buffer which helps to maintain [adrogens] in the lumen
what are androgens?
hormones responsible for developing and maintaining masculine characteristics in reproductive tissues (notably the genital tract, secondary sexual characteristics, and fertility)
what does the secretion of paracrine factors from the sertoli cells do?
stimulates spermatogenesis
what does secretion of inhibin from the sertoli cells do?
it is the negative feedback hormone for FSH
-decreases the release of paracrine factors —> spermatogenesis
what does androgen binding protein bind to? why?
testosterone
-keeps the [testosterone] inside the lumen at a steady level
-high levels of hormones in the lumen will help spermatogenesis occur
What is the target cell for testosterone and FSH?
Sertoli cells
what is the function of gonads?
productoin of sperm and hormones
what is the epididymis?
an accessory duct repsonsible for maturation and storage of sperm
-it trasnports sperm to vas deferens
what is the vas deferens?
a coiled tube that carries semen out of the testes to the urethra in preperation for ejaculation
what is the function of accessory sex glands?
production of seminal fluid
how is corticosteroid synthesized?
cholesterol —> progesterone –> differentiation into adrenal androgens / corticoids depending on the enzymes present in the tissue
when does puberty start?
10-14; later in boys
what occurs during puberty?
-sexual matutration
-maturation of reproductive organs
-secondary sexual characteristics develop
what is DHT and whats does it do?
Dihydrotestosterone
-controls the health of prostate gland
-Causes receding hairline
Helps with skeletal muscle growth e.g. Wide shoulders etc
-Distribution of body/facial hair
what is the process of testosterone production?
cholesterol –> pregnenolone –> progesterone –> testosterone
what is occuring during the fetal peak of testosterone?
internal changes such as descending
what is occuring during the neonatal peak of testosterone?
a little bit of development occurs
what is occuring during the pubertal peak of testosterone?
sperm production begins
what does the hypothalamus release to produce LH and FSH?
releases GnRH to the anterior pituitary which releases LH and FSH
what cells do LH and FSH work on?
Leydig and sertoli, respectively
how is the hypothalamic pituitary-leydig cell axis regulated?
testosterone regulates this axis through negative feedback
what effects do androgens have?
-stimulation of spermatigenesis
-promotion of seondary sex charcateristics
-increased sex drive
-promote protein synthesis of skeletal muscle
-stimulate growth hormone secretion
-promote development of male reproductive structures
where does spermatogenesis occur?
in the seminiferous tubules
-from basement to lumen
-in the psace between adjacent Sertoli cells
what is the first step in spermatogenesis? what kind of cells does this create?
mitosis and differentiation
- 2n spermatognia which differentiate into 2n x2 primary spermatocytes
what is the second step in spermatogenesis? what kind of cells does this create?
meisosis 1
-n x2 secondary spermatocytes
what is the third step in spermatogenesis? what kind of cells does this create?
meiosis 2
- (n) spermatids
what is the final step of spermatogenesis? what does it create?
differentiation
-spermatozoa
how long does spermatogenesis last?
64 days
what is the purpose of mitosis in spermatogenesis?
ensures continuos supply of spermatogonia
what is the purpose of meiosis in spermatogenesis?
to split the number of chromosomes in half
what is spermiogenesis?
the rearrangement of cytoplasmic structures to form the final sperm structure
-no cell division occurs
how long does it take for spermiogensis to occur? from spermatid to spermatozoa
24 days
how often does sermiogenesis occur?
it occurs constantly, but there are staggered days of growth
what structure of the sperm is the most important?
the head
-it contains chromosomes and the acrosome
what is contained within the acrosome?
enzymes necessary for fertilization
what is the midpiece responsibile for in the sperm?
it contains the mitochondria and is a source of energy
what kind of movement can be seen by the sperm?
whiplike movement
what are the steps in sperm maturation?
1) spermatozoa are released into the lumen of seminiferous tubule and remain immotile for 20 days
2) pressure is generated from fluid secreted by sertoli cells which push sperm into the epididymis
-here they reside for 6-12 days and acquire motility
3) sperm moves to vas deferens until ejaculated
how does the movement of sperm differ throughout maturation?
the tail begins with a wavelike movement and progresses to a whiplash movement when activated
what are some causes of sperm defects?
incorrect shape / size of sperm
what is the purpose of androgen-binding protein?
keeps [testosterone] high
what is the importance of the pulse generatorin the hypothalamic-pituitarty-testicular axis?
the pulse generator releases GnRH in pulses in order to promote the effects of LH and FSH
-if released constantly at high rates, it has an inhibiting effect
what does FSH stimulate?
-gamerogenesis/ spermatogenesis
-androgen binding protein
what does LH stimulate?
androgen secretion
what do sertoli cells secrete to promote negative feedback?
they secrete inhibin which works on the anterior pituitary to inhinbit FSH secretion
what does the secretion of testosterone inhibit?
secretion of testosterone works on the anterior pituitary and the hypothalamus to inhibit secretion of GnRH (hypothalamus) and FSH/LH (anterior pituitary)
what is the purpose of the seminal vesicle?
it produces seminal fluid which
-dilutes sperm
-contains fructose for energy
-helps form semen clot
where do the contents from the vas deferens and seminal vesicle mix?
the common duct
what is the purpose of the semen clot?
it helps with propulsion and protectuion of the sperm
where do thr ezymes to form and breakdown semen clots come from?
enzymes to form come from seminal gland
enzymes to break down the clot comes from the prostate
what percentage of seminal fluid comes from the vesicles?
60%
what do the seminal vesicles secrete?
alkaline fluid with fructose, enzymes and prostaglandins
what does the prostate gland secrete?
citrate as an energy source, enzymes and prostate specific antigen (PSA) - helps break down semen clot
when does the prostate gland increase?
during hypertrophy and cancer
-used as a biomarker for cancer
what do bulbourethral glands secrete?
viscous fluid with mucous
exaplain the neural control repsonse in men
At rest, the smooth muscles remain contracted. There Is not enough blood flowing through the vascular vesicles–> penal structure is limited and you cant have sex
1) When stimulated, parasym stimulation goes to smooth muscles causes them to relax which increases blood flow -para sym nerves release nitric oxide as a NT, this causes vasodilation 2) Sympathetic dominates and emission must occur so contraction must happen. Smooth muscles contract which causes emission of content from vas deferens, seminal vesicle and prostate glands to move to the common area 3) Ejaculation occurs and the somatic system dominates- there is control of the skeletal muscle contraction
what is released by the parasympathetic nervous system in male sex response?
nitric oxide as a NT
-causes vasodilation
what nervous system dominates when blood flow in penis increases?
the parasympathetic NS
-causes relaxation of smooth muscle increasing blood flow
what nervous system dominates when emmision from penis occurs?
sympathetic NS
-contraction of smooth muscle causes contents to move to commmon duct
what system dominates when ejaculation occurs?
somatic system
what is the positive feedback in the male sex stimulation?
increased blood flow acts as a positive feedback system to continue to increase blood flow in erect tissue
explain how viagra helps with erectile dysfunction
Sildenafil, the active ingredient in Viagra, acts by inhibiting phosphodiesterase type 5 (PDE5), which increases levels of cyclic guanosine monophosphate (cGMP). This leads to the relaxation of smooth muscles in the penis, allowing for improved blood flow and facilitating erectile function during sexual stimulation.
why is there a low sperm count to reach the site of fertilization?
there is a large decline in sperm numbers due to the acidic environment in the uterus
what is capacitation?
the destabilization of the sperm head in order to make the membrane weaker
what is menarche?
the first period
what is the period of reproducion for women?
from menarche to menopause
when is menopause?
~45-50 years old
what are the female gonads?
ovaries
what is contained in the woman’s reproductive tracts?
uterus, uterine tubes and vagina
what is the function of the ovaries? what do they contain?
they are a site for ova maturation
-contain connective tissues with follicles
-separate from reproductive tract
what are uterine tubes?
also called: fallopian tubes or oviduct
they transport ova from ovaries to uterus
what is the purpose of the infundibulum and fimbriae?
they pick up and release the ovum
what kind of movement do the ovum experince through the uterine tubes?
initially - peritstaltic contractions
mostly -ciliary actions
how long does it take for ovum to move from ovary to uterus?
4 days
what is an ectopic pregnancy
An ectopic pregnancy occurs when a fertilized egg implants outside the uterus, often in the fallopian tubes
what is the function of the uterus? what structures lead to it ?
it is the site of fetal development
-body ; upper portion
-cervix; canal leading to vagina
-cervix + vagina; birth canal
what is the outer layer of the uterus called? what is it made of?
perimetric
-epithelial cells and connective tissue
what is the middle layer of the uterus? what is it made of?
myometrium
-thickest layer made of smooth muscle
what is the inner layer of the uterus called? what is it made of?
endometrium
-epithelial cells, connective tissue and numerous goands which produce secretions needed for pregnancy
what is the female gamete called?
egg or oocyte
what occurs during the ovarian cycle?
Follicular phase (Days 1-14):
Menstruation occurs at the beginning.
Follicle-stimulating hormone (FSH) stimulates follicle development.
One dominant follicle matures, while others degenerate.
The dominant follicle releases an egg (ovulation) around day 14.
Luteal phase (Days 15-28):
The remaining follicle cells form the corpus luteum.
Corpus luteum secretes estrogen and progesterone.
Hormones prepare the uterine lining for potential implantation.
If fertilization doesn’t occur, corpus luteum degenerates.
Hormone levels drop, triggering menstruation.
what is the uterine cycle?
preparation for potential pregnancy
Menstruation (Days 1-5): Shedding of the uterine lining if fertilization did not occur in the previous cycle.
Proliferative phase (Days 6-14): The endometrium thickens and becomes vascularized in response to rising estrogen levels, preparing for implantation.
Secretory phase (Days 15-28): After ovulation, progesterone from the corpus luteum further thickens the endometrium and promotes glandular secretion to support embryo implantation. If fertilization doesn’t occur, hormone levels drop, leading to menstruation and the start of a new cycle.
what is the hormonal cycle?
Day 1-14; estrogenic cycle- estrogen released into blood and helps with proliferation of endometrium
Day 14-28; pregestational cycle- progesterone released by corpus luteal which helps keep uterine wall lining to make secretions
https://youtu.be/Is1LOacgWkc?si=GR0aKsfKavIEYQPv
what do eggs start as?
primordial follicle
-oocyte
-single layer of specialized epithelial cells that divides to become more than one layer
what is the importance of theca and granulose cells in the follicles?
they play a large role in steroid hormone synthesis
what does the zona pellucida contain?
glycoproteins important for recognition of proteins coming from the sperm head - it is crucial for succesful fertilization and development
what kind of structure do follicles begin as?
primary oocyte surrounded by a single layer of epithelial cells
what occurs to the antrum as it grows? what is the importance of this structure?
it fills with fluid
-The antrum is crucial for follicular development, providing a microenvironment for oocyte growth, hormone production, and ovulation.
what is a Graafian follicle?
contains a mature, fully developed egg
-final stage of follicular development before ovulation
what triggers the loss of the corpus luteum function?
a decrease in LH levels in the absence of pregnancy
-leads to the degeneration of the corpus luteum and the onset of menstruation.
how many oocytes are present for olulation during a womens lifetime?
400
what kind of receptors do theca cells have? what kind of receptors do granulosa cells have?
theca cells- LH receptors
granulosa cells - FSH receptors
where do androgens go after the theca cells produce them?
They permeate the granulosa cells where they are converted to estrogen
what does the increased estrogen production from granulosa cells do?
stimulates further growth of granulosa cells
-up regulates LH receptors on the granulosa cells
what feeback has both positive and negative in the female body?
the estrogen feedback loop
-this is critical for the menstrual cycle
what kind of feedback do estrogen and progesterone have on the ovarian axis?
negative feedback at the level of the hypothalamus and the anterior pituitary
what kind of structure is the follicle prior to birth?
all follicles become primary oocytes prior to birth
-they then sit in meiotic arrest
when does meiosis 1 occur in oogenesis? what structure is the oocyte in?
during fetal development
-stops at 7 months of fetal life up until puberty
-the secondary oocyte and 1 polar body are present at this time
in what phase does meiosis 1 stop? when does this happen?
primary oocytes are arrested in phophase 1 of mieosis from 7 months fetal up until puberty
- 1st meotic division is completed just prior to ovulation
https://youtu.be/sff8dBkvg9s?si=qj9nRWOwQfKeEcG4
when does meiosis 2 occur?
completed after fertilization
at what point does the oocyte become (n)?
after meiosis 1
explain the hormone activity during menstration (day 1-5)
what does this do to the body?
E and P levels are low and shedding of uterine lining occurs
explain the hormone activity during the mid-follicular phase (~day 7)
what does this do to the body?
E levels rise as dominant follicle matures
-uterus lining begins to thicken and FSH is inhbited to prevent multiple follicle growth
explain the hormone activity during ovulation
what does this do to the body?
LH surge caused by increased E levels triggers ovulation
explain the hormone activity during the early luteal phase,
what does this do to the body?
the ruptured follicle produces E and P which prepare the uterine lining for potential implantation
why does FSH peak during ovulation?
FSH peaks before ovulation due to positive feedback from rising estrogen levels, stimulating final follicle maturation and coordinating with LH for ovulation
explain the hormone activity during the late luteal phase,
what does this do to the body?
E and P levels remain high unless fertilization doesn’t occur; which would result in degeneration on corpus luteum and decreased E and P levels
when in the cycle is the dominant follicle selected? what is released at this point?
just after day 7
-inhibin is released to decrease FSH and causes atresia of other follicles
explain the follicular phase (day 6-14)
- Days 6-7:
○ FSH levels rise, stimulating follicular development.
○ Estrogen levels begin to increase gradually (rise in estrogen levels is due to the dominant follicle)- Days 8-12:
○ Estrogen levels continue to rise, reaching a peak around Day 12.
○ LH levels begin to surge, triggering ovulation. - Day 14 (Ovulation):
○ LH surge peaks, inducing ovulation.
○ Estrogen levels are at their highest.
- Days 8-12:
explain the luteal phase (day 15-28)
- Days 15-20 (Early Luteal Phase):
○ Progesterone levels start to rise due to corpus luteum formation.
○ Estrogen levels remain elevated but begin to decline slightly.- Days 21-28 (Late Luteal Phase):
○ Progesterone levels peak around Day 20.
○ Estrogen levels decline sharply.
○ If fertilization does not occur, progesterone and estrogen levels decrease, leading to menstruation.
- Days 21-28 (Late Luteal Phase):
what occurs to the uterus during the menstrual phase?
shedding of the outermost uterus lining
what effects does estrogen have on the ovaries?
increases growth follicles and receptors for E, P, FSH and LH
what effects does estrogen have on the fallopian tubes?
increased growth, contractility, cilia activity and secretions
what effects does estrogen have on the uterus?
increased growth in endometrium / myometrium, increased contractility, blood flow and sensitivity to oxytocin
what effects does estrogen have on the cervix?
secretion of alakine and watery mucous (sperm-friendly)
what effects does estrogen have on the vagina?
proliferation and cornification of the epithelium
what effects does estrogen have on the breasts?
increased duct growth, fat deposition, size and pigmentation of areola
what effects does progesterone have on the ovaries?
decreased FSH induced E production, decreased E receptors
what effects does progesterone have on the Fallopian tubes?
decreased contractility, cilia numbers and secretions
what effects does progesterone have on the cervix?
production of sperm-unfriendly mucous
what effects does progesterone have on the vagina?
WBC infiltration, decreased cornification
what effects does progesterone have on the breasts?
increased alveolar growth
where does capacitation happen? how does it happen?
in the upper body of the uterus
-uterine secretions cause changes to surface of sperm membrane
how is polyspermy prevented?
through formation of the zona into a polyspermy block
how does fertilization occur?
Sperm-Zona Binding: Capacitated sperm bind to specific receptors on the zona pellucida
Acrosome Reaction: Binding triggers the acrosome reaction, during which the sperm releases enzymes to penetrate the zona pellucida.
Sperm-Egg Fusion: Upon reaching the egg’s plasma membrane, the sperm binds to receptors on the egg’s surface. This interaction triggers membrane fusion between the sperm and egg, allowing the sperm nucleus to enter the egg cytoplasm.
Cortical Reaction: Upon sperm entry, the egg undergoes a cortical reaction, where cortical granules release enzymes into the perivitelline space, modifying the zona pellucida to prevent polyspermy.
Formation of Male and Female Pronuclei: Inside the egg, the sperm nucleus and egg nucleus (female pronucleus) undergo decondensation and eventually merge to form the zygote, containing the diploid complement of chromosomes.
Zygote Formation: The fusion of genetic material from the sperm and egg forms a zygote, marking the beginning of embryonic development.
what is the function of the cortical granules?
they help in formation of the polyspermy block
-release contents onto zona which harden it
when fertilization occurs, what happens to the oocyte?
-2nd meiotic division
-sperm plasma membrane disintegrates
-chromosomes from sperm and ovum migrate to the centre
-DNA is replicated and forms a zygote
during meiotic division, what occurs during cleavage?
the cell divides but doesn’t increase in size
at what point is a cell called a morula? what can occur at this point?
3-4 days post-fertilization
-can reach the uterus at this point
at what point is a cell totipotent?
16-32 cells large
-potential to devlop into any bodily cell
at what point does an oocyte become a blastocyst? what are the structures that make it?
4-5 days post fertilization
-loss of zona pellucida
outer layer: trophoblast
-becomes placenta
inner cell mass
-becomes embryo
fluid filled cavity
-blastocoele
when is the totipotency of a cell lost?
4-5 days after fertilization when it becomes a blastocyst
when does implantation occur?
6-7 days after fertilization
-adheres to uterine wall
at what point of fetal development does the placenta begin to funtion and the heart begin to beat?
5 weeks
what is the function of amniotic fluid?
cushions the baby
what is the function of the chorionic villi?
they are essential for ensuring proper exchange of substances between maternal and fetal blood
-blood never makes direct contact
how does the placental unit act as an endocrine gland?
by producing and secreting various hormones essential for supporting pregnancy and fetal development. It functions similarly to other endocrine glands by releasing hormones directly into the bloodstream.
what is the function of HCG?
HCG allows the corpus luteum to live through the first trimester- it also allows it to secret estrogen and progesterone
-HCG levels rise rapidly after implantation
-shows up in urine and is the basis of pregnancy testing
-similar structure to LH
what is the function of HPL?
ssential for adjusting the mother’s metabolism and preparing her body for the nutritional demands of
pregnancy and breastfeeding
-increases insulin resistance to meet glucose needs for baby (higher blood pressure)
-helps with tissue growth
what is the affect of progesterone on the placenta?
-decreased uterine contractions
-inhibition of LH and FSH
-growth of mammary alveolar glands
-secretion of sperm unfriendly mucus
what is the affect of estrogen on the placenta?
-growth of uterus (myometrium)
-growth of mammary ducts
-inhibition of LH and FSH
what aids in the build-up of prostaglandins?
decreased progesterone and increased estrogen
what is the function of relaxin?
initially made by the corpus luteum then the placenta takes over. It has large affects on the mothers CVS and kidneys (regulation of fluid volume)
-promotion of CVS circulation
-relaxes smooth muscle in uterus
what hormones increase myometrial contractions?
E,Prostoglandins, oxytocin and stretching
what hormones inhibit myometrial contractions?
P and relaxin
what hormones increase cervical ripening?
Prostoglandins and relaxin
what hormones inhibit cervical ripening?
Progesterone
what fetal signals stimulate parturition?
fetal positioning
-pressure on the cervix increases contractions
what are the steps in parturition?
how do mammary glands grow?
1) birth-puberty: rudimentary ducts (few alveoli)
2) at puberty:
-ducts grow and branch (E)
-alveolar growth (P)
-deposition of fat and alveolar tissue
3)during pregnancy/lactation: full development (E,P,PRL,HPL,GF)
how is milk released?
- Oxytocin Release:
Stimulation: Suckling by the infant or other stimuli such as the sight or sound of the infant can trigger the release of oxytocin from the posterior pituitary gland.
Action: Oxytocin travels through the bloodstream to the mammary glands. - Myoepithelial Cell Contraction:
Oxytocin Action: Oxytocin binds to receptors on myoepithelial cells, which are specialized smooth muscle cells that surround the alveoli (milk-producing structures) and ducts in the mammary glands.
Contraction: Oxytocin stimulates the contraction of the myoepithelial cells, causing them to squeeze the alveoli and ducts. - Milk Ejection:
The contraction of the myoepithelial cells propels the milk from the alveoli and ducts toward the nipple, where it is available for the infant to consume. - Role of Epithelial Cells:
Milk Production: The epithelial cells lining the alveoli are responsible for producing and secreting milk.
Storage: Once milk is produced, it is stored within the alveoli until it is ejected.
what is the role of dopamine of the release of milk?
- Inhibitory Effect: Normally, dopamine inhibits prolactin release by acting on dopamine receptors in the anterior pituitary gland.
- Dopamine Decrease: During breastfeeding, the reduction of dopamine release leads to an increase in prolactin secretion.
what occurs when the chromosomal sex is XXY?
klinefelter’s syndrome (male)
-taller than average
-breast development
-small testes (infertile)
what does bipotential of gonads mean?
in the early stages of development gonads have bipotentioal; meaning they can differentiate into ovaries or testes
what occurs with the lack of an X chromosome?
turner’s syndrome (XO)
-streak ovaries
-short stature
-bronw spots
-no menstruation
-poor breast development
what does the secretion of mullerian inhibiting hormone do? where is it secreted from?
MIH is secreted from sertoli cells in testes
-causes regression of the Müllerian duct which causes regression of internal female genitalia
what does the secretion of DHT do to men?
causes masculinization of external male genitalia
what causes sexual differentiation for women?
the abscence of MIH allows the mullerian duct to grow into female genitalia
-abscence of T prevents the development of wolffian duct (no external male genitalia)
-abscence of DHT prevents masculinization
what is congenital adrenal hyperplasia? how does it affect the body?
a condition that may occur in females where they have ovaries but are outwardly male
-decreased cortisol–> increased ACTH–>increased androgen production–>masculinization of external genitalia
-infertile
what is androgen insensitivity syndrome? how does it affect the body?
a condition occuring in males where they have testes but are outwardly female
-androgens converted to E in target tissues
-abscence of ovaries, no menstrual cycles
-infertile
explain the hypothalamic-pituitary-gonadal axis in young child
Hypothalamus: Begins to release gonadotropin-releasing hormone (GnRH) in a pulsatile manner.
Pituitary Gland: In response to GnRH, the anterior pituitary secretes luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
Gonads: LH and FSH stimulate the gonads (testes in males and ovaries in females).
In Males: LH stimulates testosterone production; FSH supports spermatogenesis.
In Females: LH and FSH stimulate the production of estrogen and progesterone, as well as ovarian follicle maturation.
Sex Hormones: Testosterone, estrogen, and progesterone promote the development of secondary sexual characteristics, such as facial hair, voice changes, and breast development.
Feedback Loop: Rising sex hormone levels provide negative feedback to the hypothalamus and pituitary, regulating GnRH, LH, and FSH release.
explain the hypothalamic pituitary gonadal axis at the time of puberty
Leptin:
Produced by adipose (fat) tissue, leptin serves as a signal of energy stores in the body.
Leptin levels rise as a child approaches puberty and acts on the hypothalamus to stimulate GnRH release, signaling the body has sufficient energy reserves for reproductive function.
Kisspeptin:
A critical regulator of the HPG axis, kisspeptin is produced in the hypothalamus.
Kisspeptin stimulates GnRH neurons, increasing GnRH secretion, which in turn triggers the pituitary to release LH and FSH.
HPG Axis Reactivation:
GnRH Secretion: The pulsatile release of GnRH from the hypothalamus increases.
Pituitary Response: This leads the anterior pituitary gland to secrete LH and FSH.
Gonadal Activation: LH and FSH stimulate the gonads (testes in males and ovaries in females), leading to the production of sex hormones (testosterone in males and estrogen and progesterone in females).
Sex Hormones:
Males: Testosterone promotes the development of secondary sexual characteristics, such as muscle mass, body hair, and voice deepening.
Females: Estrogen and progesterone support the development of female secondary sexual characteristics, such as breast development and the onset of menstruation.
Feedback Mechanisms:
Rising sex hormone levels provide negative feedback to the hypothalamus and pituitary, modulating GnRH, LH, and FSH release.
what causes the delcline in reproductive capabilities?
Women: Ovarian function declines, leading to decreased levels of estrogen and progesterone. This causes fewer viable eggs and irregular ovulation, culminating in menopause, when reproductive capability ceases.
Men: Testosterone levels gradually decrease with age, affecting sperm production and quality. Reduced testosterone may also impact libido and sexual function.
