Exam #4: Male Reproductive Physiology Flashcards
What is the function of the epididymis?
Remember that the epididymis connects the rete testis to the vas deferens. The functions of the epididymis include:
- Storage, maturation and transporation of sperm
- Development of sperm motility
- Reabsorption of aging sperm
*Note that H+ ions are secreted to maintain the sperm in an inactive state
What is the function of the vas deferes?
Remember that the Vas deferens connects the epididymis to the seminal vesicles. The functions of the Vas Deferens include:
- Storage of sperm in the ampulla
- Transportation of sperm
*Note that the ampulla contracts during ejaculation to propel sperm into the proximal urethra/ allows sperm to mix with prostatic and seminal vesicle fluids
What is the function of the seminal vesicle?
- The seminal vesicle produces roughly 60% of the fluid portion of the ejaculate i.e. semen
- Seminal fluid or semen consists of:
1) Fructose= energy for sperm
2) Prostaglandin= make the cervical environment more favorable for sperm survival & promote peristalsis of the uterus/ fallopian tubes
3) Fibrinogen= coagulation of semen that holds semen in deeper regions of the vagina and cervix
4) Seminogelin= suppresses motility of sperm in the coagulated semen
What is the function of the prostate gland?
The prostate gland secretes a milky fluid that constitutes roughly 39% of the fluid of semen and contains:
1) Ca++
2) Citrate
3) Prostatic acid phosphatase
4) Profibrinolysin= activated to plasmin that dissolves coagulated semen & frees sperm
5) HCO3 (bicarbonate)= neutralizes the acidic environment of the cervix, allowing sperm to become more motile
6) Prostate Specific Antigen (PSA)= hydrolyzes seminogelin, which causes sperm to become more motile
*****Note that PSA is a biomarker for prostate cancer
What is the function of the bulbouretheral gland?
Secretion of mucous into the urethra upon arousal
- Functions as a lubricant in the urethra
- Cleans the lumen of the urethra
*Note that the bulbouretheral gland is also known as “Cowper’s Gland”
What are Leydig cells? What is the function of the Leydig cells?
- Endocrine cells that secrete testosterone
- These cells are contained within the “peritubular compartment” of the testes, or the spaces between the tubules of the testes
What are Sertoli cells? What is the function of the Sertoli cells?
- Sertoli cells are cells contained with in the seminiferous tubules, or in the “intratubular space”
- Functions
1) This is where spermatogenesis occurs
2) Production and secretion of Androgen Binding Protein (ABP), which binds and concentrates testosterone in the area of spermatogenesis
Where is GnRH synthesized and released?
Hypothalamus
*Note that it is released in a pulsatile fashion that is controlled by the pulse generator in the hypothalamus
What is the function of GnRH?
Influences the release of the pituitary gonadotropes
Where is LH produced?
Anterior pituitary
What is the function of LH?
- Binds receptors on Leydig cells and stimulates testosterone production/ secretion
- Testosterone then diffuses to Sertoli cells to facilitate spermatogenesis
Where is FSH produced?
Anterior Pituitary
What is the function of FSH?
Stimulation of Sertoli cells to produce ABP
- ABP concentrates testosterone at the site of spermatogenesis
Why is it important to pulsatile secretion of GnRH?
- Constant high levels of GnRH causes a desensitization of GnRH receptors
- This can lead to a reduction in LH and FSH release
Outline the specific mechanism of action of LH on Leydig cells.
LH induces cholesterol to be converted into Testosterone
- LH binds to a GPCR on the Leydig cell
- cAMP increases (Gas)
- PKA increases
- Increased synthesis of steroidogenic enzymes that control testosterone synthesis
*Note that the testosterone produced by the Leydig cells with diffuse into the Stertoli cells and stimulate spermatogenesis
What is Estradiol? Where is Estradiol produced and what is its function?
Estradiol is a product of testosterone
- Estradiol is produced in the Sertoli cells
- Sertoli cells contain the enzyme Aromatase
- Aromatase converts Testosterone into Estradiol
- Estradiol diffuses back into the Leydig cells
Outline the specific mechanism of action of FSH on Sertoli cells.
Like LH, FSH binds to a GPRC on the Steroli cells
- Gas subunit activation increases cAMP
- PKA is increased
- Aromatase, ABP, and Inhibin are all produced in response to FSH binding to the Steroli cell
How is Testosterone synthesized? Draw & label the synthesis pathway of Testosterone & DHT synthesis. What is the rate-limiting enzyme?
- The rate limiting step of the production of Testosterone is the conversion of cholesterol to pregnolone via Cholesterol desmolase
- Pregnolone is converted by 17alpha-hydroxylase into intermediate products
- 3B-hydroxysteroid dehydrogenase (3B-HSD) makes Androstenedione
- 17B-Hydroxysteroid dehydrogenase cleaves Androstenedione into Testosterone
*****Note that Testosterone is converted into the DHT by 5a-reductase
How does testosterone production change throughout life?
- Spike in the fetal development to form male genitalia
- Spike in the neonate
- Spike in puberty and reaches a peak in adulthood
*Note that Testosterone production is not constant throughout the day either
How is testosterone transported in the blood?
Testosterone binds albumin in the blood & SHBG (sex-hormone-binding globulin)
- Note that the MAJORITY of testosterone is BOUND to albumin or SHBG, only a small amount is actually available
Why is there a decrease in testosterone production with age?
- Synthesis of Testosterone decreases with age
- Increased SHBG with age leads to a decrease in the bioavaliablity of Testosterone
Thus, there is a combinatorial effect of these two mechansisms
What is the risk of testosterone replacement therapy?
Increased risk of prostate cancer
What is the mechanism of Testosterone when it reaches a target cells?
1) Diffuses across membrane of target cell (lipophilic)
2) Binds to the androgen receptor in the nucleus
3) Altered gene transcription
How does the affinity of DHT for the androgen binding receptor compare to Testosterone?
The affinity of DHT is far greater than that of Testosterone
