Male Reproductive Physiology Flashcards
Describe the Gonadotropin secretion over the lifetime
Fetus: small increase Childhood: Low and constant Puberty: Starts to increase Adult life: PULSATILE Old age: slow increase
How is puberty initiated by GnRH?
GnRH is secreted in a pulsatile manner
Pulsatile secretion of GnRH drives the pulsatile secretion of?
FSH and LH
What do FSH and LH stimulate secretions of?
Steroid sex hormones - Testosterone and Estradiol
Increased levels of steroid sex hormones (Testosterone and Estradiol) result in the appearance of what at puberty?
Secondary sex characteristics at puberty
_______ secretion rate of GnRH is necessary for reproductive function and puberty
Pulsatile
If a constant GnRH analogue is administered, what occurs?
NO puberty or reproductive function will be initiated!
– must be pulsatile
Main function of the Testes?
Spermatogenesis
Testosterone secretion
Why is the scrotum a lower temperature?
It is necessary for spermatogenesis within the testes
Where are sperm matured and stored?
Epididymis
The vas deferens ____ can also serve as a sperm storage site
Ampulla
Adult testis are ______ seminiferous tubules and _____ CT with leydig cells
80%
20%
Main function of the sertoli cells
Provide nutrients to differentiating sperm and create the blood-testis barrier
Main function of leydig cells
Synthesis and secretion of testosterone
3 main androgens secreted from testes?
Testosterone (main one)
DHT
Androstenedione
Where is the majority of Testosterone converted to DHT?
Peripheral tissues
What enzyme in the testes can convert Androstenedione to Testosterone?
17beta - hydroxysteroid dehydrogenase
What enzyme in testes and in peripheral tissues can convert Testosterone to DHT (dihydrotestosterone)?
5alpha - reductase
DHT binds to the androgen receptor in target tissues with a _____ affinity than testosterone?
Higher
What can the circulating testosterone be bound to in the blood?
Free
Albumin
SHBG (sex hormone binding globulin)
What binds to circulating testosterone in the blood the majority of the time?
SHBG
The most biologically important form of testosterone is bound to?
Nothing - free
DHT is important for what changes associated with puberty?
External male genitalia
If there is a 5alpha - reductase deficiency, what can become ambiguous?
External male genitalia due to low levels of DHT
What are the 2 sources for male estrogen?
Sertoli cells in seminiferous tubules
Adipose tissue
Estrogen can potentially have a role in what for males?
Spermatogenesis because sperm cells express an estrogen receptor
______ forms 80% of all male estrogen
Adipose tissue
Testosterone is converted to Estradiol with what enzyme?
Aromatase (CYP19)
Rate limiting step in testosterone synthesis?
Cholesterol –> Pregnenolone using the Desmolase enzyme
What is the main steriodogenic cell in the testes and why?
Leydig cells because they can synthesize and store cholesterol (precursor for testosterone)
What hormone acts on leydig cells to control their rate of testosterone synthesis?
LH
3 main actions of DHT
- External male genitalia formation
- Male hair distribution and its loss
- Prostate growth
Potential treatment for male pattern hair loss?
5alpha-reductase inhibitors to stop the formation of excess DHT
Benign Prostatic Hyperplasia (BPH)
Excessive urination, difficulty urinating, urinary urgency and dribbling
- majority of males over 80 have this
Describe DHT levels in males with BPH
NOT HIGHER than a regular male - normal levels
What may men with BPH have more of?
DHT receptors which will cause a larger enlargement of the prostate that compresses the prostatic urethra
LH binds to what cell?
Leydig cell
From the leydig cell, where can testosterone go?
Circulation or Sertoli cell (seminiferous tubule)
FSH binds to what cell?
Sertoli cell
What 3 products (besides mature sperm) can sertoli cells produce in response to FSH?
- Aromatase (testosterone –> estradiol)
- ABP (androgen binding protein, binds testosterone in the lumen of the sertoli cells)
- Inhibin (inhibits more FSH release)
What intracellular pathway is activated with LH or FSH bind to either leydig cells or sertoli cells?
cAMP - protein kinase A pathway
ABP action
Androgen binding protein
- Binds testosterone in the lumen of the seminiferous tubule to provide local testosterone source for developing spermatogonia
Aromatase action
Testosterone converted to estradiol
Inhibin action
Inhibits more FSH release from the anterior pituitary
3 phases of spermatogenesis?
- Mitotic phase
- Meiotic phase
- Spermiogenesis
Mitosis takes spermatogonia to?
Type A and Type B spermatogonia each with 2N DNA
Meiosis 1 takes Type B spermatogonia (2N) to?
Primary spermatocytes (4N) and then to Secondary spermatocytes (2N)
Meiosis 2 takes secondary spermatocytes (2N) to?
4 spermatids (1N)
Spermiogenesis takes spermatids to?
Spermatozoa
Where in the mature sperm is there mitochondria?
Middle piece
Residual body of the sperm is phagocytized by?
Sertoli cells
What is necessary for early division of sperm and without it, spermatogenesis will not occur?
Growth hormone
Sertoli cells need ____ to form sperm
FSH
Leydig cells need _____ to form testosterone
LH
What steroid hormones are essential for spermatogenesis?
Testosterone (leydig) and Estrogen (sertoli)
What does exogenous administration of androgens cause?
(-) feedback on pituitary to release less LH/FSH which DECREASES spermatogenesis
Job of seminal vesicals
Secrete nutrients, fructose and prostaglandins for sperm
What do prostaglandins do from the seminal vesical?
- make female mucous less thick so sperm can travel
- reverse peristaltic contractions in the female to move sperm from the uterus to the uterine tubes
Job of prostate gland
Secrete alkaline fluid to help neutralize acidic environment of vagina
Semen is composed of sperm and fluid from?
Vas deferens
Seminal vesicals
Prostate gland
Bulbourethral glands
What is the final pH of semen?
7.5
Less than _____ sperm = infertile
20 million
During flaccid state, blood flow to erectile tissue is?
Minimal
What is the main innervation during erection?
Parasympathetics
During erection, parasympathetic nerves cause the helicine arteries to release?
NO - nitric oxide
Helicine arteries supply?
Cavernous spaces
Once the helicine arteries release NO, what happens?
Guanylyl cyclase
Increased cGMP
Decreased calcium
= Relaxation of smooth muscle in the helicine arteries and blood can flow into cavernous spaces
Emission
Movement of semen from epididymis, vas deferens, seminal vesicals and prostate gland to ejaculatory duct
During emission, what is the main innervation?
Sympathetic
During emission, sympathetic control causes what 2 things?
- Peristaltic contractions of vas deferens
2. Closure of internal sphincter of bladder
Why is it important to close the internal sphincter of bladder during emission and with what surgery can the internal sphincter of the bladder be damaged?
To prevent retrograde ejaculation into the bladder
- Prostatectomy can damage this sphincter and cause retrograde ejaculation into the bladder
Ejaculation
Propulsion of semen out of male urethra
Contractions of what muscles cause ejaculation?
Bulbospongiosus
Ischiocavernosus
Ambiguity of external genitalia - testosterone age deficiency?
Early gestation
Inadequate testicular descent - testosterone age deficiency?
Late gestation
Poor secondary sexual development - testosterone age deficiency?
Puberty
Decreased libido, Decreased hair growth, and erectile dysfunction - testosterone age deficiency
Post-puberty
Kallman’s syndrome
GnRH neurons fail to migrate to hypothalamus during development
Symptoms of Kallman’s syndrome
Delayed or absent puberty and altered sense of smell
Klinefelter syndrome
47, XXY
- Phenotypically male but at puberty failure to induce normal testicular growth and spermatogenesis
Primary hypogonadism
Decreased testosterone
- klinefelter
Secondary hypogonadism
Decreased testosterone
Decreased LH/FSH
Tertiary hypogonadism
Decreased testosterone
Decreased LH/FSH
Decreased GnRH
- Kallman
Hyperprolactinemia inhibits?
FSH and LH secretion
Andropause
Gonadal sensitivity to LH and FSH decreases as you age which causes increased levels of LH and FSH and less androgen production
