Physiology of male reproduction Flashcards
Where is sperm produced?
Seminiferous tubules of the testes
What is the volume and pH of semen?
Volume 2-6ml
pH 7.2-7.6
What is the composition of semen?
1) Spermatozoa (10%)
2) Seminal vesicle fluid (60-70%)
* Fructose and other nutrients
* Fibrinogen to clot the semen
* Prostaglandins; uterine stimulation
* Last volume to be ejaculated
3) Prostate gland secretions (20%)
* Thin, milky secretions, alkaline
* Prostate specific antigen (PSA); protease to break down clotted semen
* Acid phosphatase: activates sperm
4) Bulbourethral gland secretions (10%)
* Mucoproteins; neutralise any urine and lubricate the urethra
* Released prior to ejaculation
How long can the sperm survive in the female reproductive tract?
24-72 hours
Where is sperm produced?
Seminiferous tubules
Where is sperm matured?
Efferent ductules and rete testis
Where is sperm stored?
Ductus deferens
What are key functions of sertoli cells?
1) Essential for providing nourishment for developing spermatogonia
2) Forms adhesions and gap junctions with all stages of developing sperm; directly provides structural support
3) Produce testicular fluid; secreted into the lumen of the seminiferous tubules, including androgen binding protein
4) ABP concentrates testosterone in the lumen; essential for development of spermatogenesis
What do leydig cells do?
Testosterone synthesis
How do leydig cells help with sperm motility?
There is a layer of contractile smooth muscle around the leydig cells to force out the sperm.
What is the blood-testis barrier?
The tight junction (direct contact between corresponding proteins on adjacent cells) that separates the lumen of the seminiferous tubules from the rest of the body. Prevents sperm from being attacked by the immune system.
How does meiosis occur safe from an immune response?
Primary spermatocytes are able to move past the blood-testes barrier.
How long do sperm spend in the epididymis and why?
30 days maturing and developing motility.
What are the key structural components of sperm?
Acrosome, nucleus, midpiece, principal piece and tail
What is the acrosome of the sperm?
A membrane bound compartment containing enzymes and proteins used to penetrate with the egg
What is the nucleus of the sperm?
Contains the chromosomes and is very highly condensed.
What is the midpiece of the sperm?
Contains many mitochondria which generate the ATP required to drive the whip-like movements of the tail.
What is the principle piece of the sperm?
Contains an intricate array of contractile microtubules that make use of ATP to drive the movement of the tail.
What is the role of the tail of the sperm?
Allows it to move faster. Side by side motions to develop speed.
What is semen?
An essential supporting factor of the survival and activation of sperm.
What is semen comprised of?
Spermatozoa (<10%)
* 15-150 million per millimetre
Seminal vesicle fluid (60%)
* Fructose and other nutrients for the sperm
* Fibrinogen to clot semen (keep it lodged in the female reproductive tract)
* Prostaglandins to stimulate the uterus
Prostate gland secretions (20%)
* Thin, milky, alkaline secretions
* Prostate specific antigen (PSA) to break down clotted sperm
* Acid phosphatase to activate sperm
Bulbourethral gland secretions (10%)
* mucoproteins to neutralise any urine in the urethra and lubricate the urethra
How long can sperm survive in the female reproductive tract?
24-72 hours
Why does ejaculated semen clot?
Due to fibrinogen and lodges at the base of the cervix so it doesn’t flow out. PSA slowly breaks down the clot so that the sperm can swim into the uterus.
What is capacitation?
The process of morphological, physiological and biochemical changes the sperm must go through before the sperm is capable of penetrating and fertilizing an ovum.
Why is capacitation necessary?
Because semen contains factors that stop the sperm from penetrating the ovum and these need to be removed in the female reproductive tract.
How does Hormonal Regulation I begin?
1) Pulsatile release of GnRH from the hypothalamus
2) GnRH acts on the anterior pituitary
3) Stimulates production of LH and FSH
What happens during Hormonal Regulation II?
LH stimulates leydig cells to produce testosterone –> FSH promotes LH receptor synthesis on leydig cells –> FSH stimulates spermatogenesis via the sertoli cells (synthesis and secretion of ABP into lumen of seminiferous tubules –> testosterone has paracrine action on sertoli cells –> testosterone converted to 17B-estradiol and 5alpha-dihydrotestosterone (DHT) to stimulate spermatogenesis –> sertoli cells synthesise ABP –> ABP concentrates testosterone in the lumen of the seminiferous tubules 100-fold higher than in the circulation –> testosterone transported to epididymis for sperm maturation
What enzyme converts testosterone into 5a-DHT?
5a-reductase
Which enzyme converts testosterone into 5b-DHT?
5b-reductase
Which enzyme converts testosterone into 17b-estradiol?
Aromatase
How does Hormonal Regulation III occur?
Inhibin is a glycopeptide hormone produced by Sertoli cells in conjunction with spermatogenesis (stimulated by FSH) –> inhibin suppresses the release of FSH (but not LH) by negative feedback to the anterior pituitary –> sertoli cells have androgen receptors and respond to testosterone to support spermatogenesis
ALSO:
Testosterone limits its own secretion by negative feedback loops, to the hypothalamus (suppress secretion of kisspeptin, and thus suppress GnRH secretion) and anterior pituitary (suppress LH and FSH)
What are some actions of testosterone?
- Development of secondary sex characteristics during puberty
- Stimulates bone marrow growth for red cell production; haematocrit 45% in males, 40% in females
- Muscle mass
- Larynx (male voice)
- Beard growth
- Penis size and sperm production
