68 Production of seminal fluid Flashcards
Spermiogenesis pathway
- Spermatocyte –> spermatid –> spermatozoon
* Occurs in seminiferous tubules
Function of acrosome?
- Contains enzymes that break down the outer membrane of the ovum (zona pellucida)
- Allowing the haploid nucleus in the sperm cell to join with the haploid nucleus in the ovum
Spermatogenesis production per fay?
200 million/ day
• ~ 2300/sec
What is the process of sperm transfer to epidydmis?
• Sperm in seminiferous tubules in a large volume of fluid
- washes sperm into rete testis, vasa efferentia and epididymis
• If vasa efferentia blocked, seminiferous tubules and testis swells
• 6-12 days to travel through vasa efferentia and epididymis
• Various products secreted into the seminal fluid in the epididymis
List the changes to spermatozoa in epididymis?
- Concentration
- Sperm modelling
- Metabolism
- Motility
- Membrane
Changes to spermatozoa in epididymis in concentration?
100-fold (5 x 10^7/ml entering 5 x 10^9/ml leaving)
Changes to spermatozoa in epididymis in sperm modelling?
- Nuclear condensation and acrosome shaping completed
* Cytoplasmic droplet shed
Changes to spermatozoa in epididymis in metabolism?
- ↑ dependence on external fructose for glycolytic energy
- Little oxidative metabolism
- ↑ intracellular pH (due to Na+/H+ exchange)
Changes to spermatozoa in epididymis in motility?
- ↑ disulphide bridges between proteins in outer dense fibres of tail
- [cAMP] ↑ in tail
- Acquires the capacity for forward movement
Changes to spermatozoa in epididymis in membrane?
Composition of various components change
Where is seminal fluid formed?
Accessory glands
Role of seminal fluid?
Provides nutrients to protect spermatozoa
Which infectious agents exploit seminal fluid?
- Hep. B
* HIV
Seminal fluid in testes?
- Vol (ml): 0.1-0.2
* Contains spermatozoa
Seminal fluid in seminal vesicle?
- Vol (ml): 1-3
* Alkaline, gelatinous
Seminal fluid in prostate?
- Vol (ml): 0.5-1
* Acidic, watery
Seminal fluid in bulbourethral glands?
- Vol (ml): 0.1-0.2
* Viscous, clear
List the major constituents of ejaculate?
- Spermatozoa
- Fructose
- Inositol
- Citric acid
- Glycerylphosphorylcholine
- Acid phosphatase
Spermatozoa in ejaculate?
- Conc (mM): 50-150/nl
* Main source: testes
Fructose in ejaculate?
- Conc (mM): 8-37
- Main source: seminal vesicle + ampulla
- Function: anaerobic energy metabolism
Inositol in ejaculate?
- Conc (mM): 1-3
- Main source: testes + epididymis
- Function: osmotic ballast
Citric acid in ejaculate?
- Conc (mM): 5-73
- Main source: prostate
- Function: Ca2+ chelator - depresses semen coagulation
Glycerlyphosphorylcholine in ejaculate?
- Conc (mM): 2-3
- Main source: epididymis
- Function: used as a source of choline in phospholipid metabolism
Acid phosphatase in ejaculate?
- Main source: prostate
* Function: cleaves choline from glycerophosphorylcholine
What major constituents of ejaculate are from testes?
- Spermatozoa
* Inositol (also from epididymis)
What major constituent of ejaculate is from seminal vesicle?
Fructose (also from ampulla)
What major constituent of ejaculate is from ampulla?
Fructose (also from seminal vesicle)
What major constituents of ejaculate is from epididymis?
- Inositol (also from testes)
* Glycerylphosphorylcholine
What major constituents of ejaculate are from prostate?
- Citric acid
* Acid phosphatase
Penis must be turgid to introduce semen into the female genital tract. How does this happen?
Haemodynamic changes:
• Involves corpora cavernosa
– singular = corpus cavernosum
– sinuses along most of the length of the penis
3 sources of arousal?
- Erotic psychological stimuli (e.g. visual, olfactory)
- Tactile stimuli at the level of the brain
- Tactile stimuli can also mediate local spinal reflexes
Sympathetic nerves in penis?
- Lower thoracic and lumbar spinal segments
- Maintains flaccidity
- Supplies accessory glands
Parasympathetic nerves in penis?
- Control centre in sacral spinal segments
- ↑ activity produces turgidity
- Supplies corpus cavernosum
What is the tumescence of the penis?
Erection centre in the sacral spinal cord mediates the erection reflex
Actions of tumescence of the penis?
- Dilation of arterioles to corpus cavernous and c. spongiosum
- Closing of arteriovenous shunts that normally bypass the c. cavernosa
- Probably also occlusion of veins draining the penis
Parasympathetic relaxation of vascular smooth muscle during erection?
- Ach acts on vascular endothelial cells
- Indirectly triggers release nitric oxide
- NO causes relaxation of vascular smooth muscle
Failure to obtain an erection can result from?
- Mechanical damage to c. cavernosa
- Obstruction of the arteries to the penis
- Drugs that block parasympathetic actions
- Psychological factors
- Stress associated with high sympathetic activity:
• NA causes vasoconstriction of penile arterioles and so inhibits erection
Sympathetic role in ejaculation?
- Ejaculatory centre in lower thoracic and lumbar spinal cord
- Signals to ducts of genital tract and to bulbocavernosus muscle at the base of penis
What are the 2 phases of ejaculation?
- Emission phase:
• Smooth muscle contraction in walls of genital tract
• Expels semen into urethral bulb - Expulsion phase:
• Rhythmic contractions of penis and bulbocavernosus muscle
• Ejects semen in spurts
What is ejaculation normally followed by?
Refractory phase of 10 mins to an hour
What is the composition of ejaculate (not uniform)?
- First component: Prostate
• Rich in acid phosphatase and citric acid - Second component: Vas deferens
• Rich in spermatozoa - Third component: Seminal vesicle
• Rich in fructose
What is coagulation followed by?
Liquefaction
