Male reproductive physiology Flashcards
1
Q
What are the two functions of the testes?
A
- Androgen production
- Spermatogenesis
2
Q
Hormonal control of testicular function
A
- The hypothalamus releases GnRH
- This stimulates the anterior pituitary to release FSH and LH
- FSH:
- Acts on Sertoli cells
- Induces spermatogenesis and inhibin B secretion
- Inhibin will negatively feedback on FSH
- LH:
- Acts on Leydig cells
- Stimulates the production of testosterone
- Testosterone will negatively feedback on LH
3
Q
Distinguish between primary and secondary testicular failure
A
- Primary:
- Occurs at level of the testes
- Increased FSH/LH; decreased testosterone/inhibin
- Secondary:
- Occurs at level of anterior pituitary/hypothalamus
- All hormones are decreased
4
Q
What are the three pathways through which testosterone acts?
A
- Direct pathway:
- Acts as testosterone
- Acts on muscles and virilisation
- Amplification pathway:
- Converted to DHT via 5-alpha reductase
- Acts on prostate and skin (pubic hair, sebum secretions)
- Diversification pathway:
- Converted to estradiol via aromatase
- Acts on the brain and bones (bone maturation, epiphyseal sealing)
5
Q
How is testosterone deactivated?
A
Testosterone is deactivated via hepatic oxidation or conjugation, and is secreted renally
6
Q
What causes the onset of puberty in males?
A
- Pulsatile release of GnRH causes an increase in LH levels
- Lh will stimulate Leydig cells to produce testosterone, which induces virilisation
- Testosterone’s metabolites perform other functions:
- Estradiol - bone
- Dihydrotestosterone - hair and acne
7
Q
What is the normal volume of the testes at different ages?
A
- Childhood: <3mL
- Puberty: 4-14mL
- Adulthood: 15-35mL
- NOTE: reduced teste volume is associated with reduced spermatogenesis
8
Q
What is required for spermatogenesis?
A
- Relies on high levels of testosterone and LH/FSH that act on Sertoli cells
- LH - androgen receptors
- FSH - surface receptors
9
Q
What is the counter-current heat exchange?
A
- The mechanism by which blood supply to the scrotum regulates the temperature of the testes
- Cool blood in the pampiniform plexus will cool blood that is travelling to the testes via the spermatic cord
10
Q
What is a syncytium?
A
- Male germ cells do not complete cytokinesis during meiosis and mitosis - hence, they form a multi-nucleate bundle of cells called a syncytium
- This is to ensure that all germ cells are exposed to the same chemical signals from the X and Y chromosomes
11
Q
What is spermiogenesis?
A
- Last step in spermatogenesis - forms spermatozoa
- Process:
- Nuclear compaction
- Cytoplasm largely discarded
- Tail develops from a pair of centrioles near nucleus
- Acrosome develops from the Golgi body
12
Q
Detail the histology of the seminiferous tubules
A
- Spermatagonium: found between basal lamina and Sertoli cells
- Primary spermatocytes: between Sertoli cells and lumen
- Spermatids: these are round
- Leydig cells: outside the seminiferous tubules
- Sertoli cells: triangular nucleus
13
Q
Outline the ejaculatory pathway
A
- Seminiferous tubules
- Retes testes
- Efferent tubules
- Epididymis
- Vas deferens
- Ejaculatory duct
- Prostatic urethra
14
Q
What drives an erection?
A
- Visual input - occipital lobe
- Olfactory input - thalamus
- Tactile input - rhiencephalon
- Imaginative - limbic system
15
Q
What is the pathway for an erection?
A
- Relaxation of cavernosal smooth muscle:
- Release of NO from autonomic cavernous nerves
- Guanylyl cyclase activity
- cGMP - decrease intracellular Ca2+, efflux of K+
- Blood flow into lacunar spaces increases:
- Increased inflow: dilated cavernosal artery
- Decreased outflow: elongation of the subtunical vein
- Lacunar space expands and subtunical space compresses and blood pressure increases inside the lacunar space
