Production of Seminal Fluid

Question 1

Describe the axonemal structure of the sperm

Answer 1

• central pair of tubules with 9 pairs arranged in a ring around it
• dynein regulatory complex responsible for sperm motility

Question 2

Describe the structure of the testes

Answer 2

• coiled seminiferous tubules converging onto the rete testes
• branches into efferent ductules which enter head of epididymis
• tail of epididymis becomes vas deferens

Question 3

Describe the changes to the spermatozoa in the epididymis

Answer 3

• concentration increases 100-fold
• sperm modelling: nuclear condensation and acrosome shaping
• metabolic changes: increased dependency on external fructose and increase in intracellular pH
• motility changes: increased disulphide bridges between proteins in outer dense fibres of tail, cAMP increase in tail
• membrane component changes

Question 4

Describe the locations and compositions of seminal fluid

Answer 4

• testes (0.1-0.2mls): spermatozoa
• seminal vesicle (1-3mls): alkaline and gelatinous
• prostate (0.5-1mls): acidic, watery
• bulbourethral glands (0.1-0.2mls): viscous, clear

Question 5

What are the main constituents of ejaculate and their main sources?

Answer 5

• spermatozoa: testes
• fructose: seminal vesicle and ampulla
• inositol: testes and epididymis
• cirtric acid: prostate
• glycerylphosphryl-choline: epididymis
• acid phosphatase: prostate

Question 6

What are the functions of the constituents of ejaculate?

Answer 6

• fructose: anaerobic energy metabolism
• inositol: osmotic ballast
• citric acid: Ca2+ chelator, depresses semen coagulation
• glycerylphosphoryl-choline: source of choline in phospholipid metabolism
• acid phosphatase: cleaves choline from glycerophosphorylcholine

Question 7

Describe the anatomy of the penis

Answer 7

• corpora cavernosum: 2 sinuses side by side and corpus spongiosum which surrounds the urethra
• dorsal vessels
• profunda artery

Question 8

What are ways that arousal can be elicited?

Answer 8

• erotic psychological stimuli

- tactile stimuli at level of the brain (can also mediate local spinal reflexes)

Question 9

What is the role of the autonomic NS for the penis?

Answer 9

SNS:

• maintains flaccidity
• originating from thoracic and lumbar spinal segments

PSNS:

• produces turgidity
• control centre in sacral spinal segments

Question 10

Describe the process resulting in tumescence of the penis

Answer 10

• stimulation of erection centre in sacral spinal cord
• causes dilation of arterioles to c. cavernosa and c. spongiosum
• causes closing of aterovenous shunts that normally bypass c.cavernosa

Question 11

How does the PSNS relax vascular smooth muscle?

Answer 11

• ACh acts on vascular endothelial cells causing an indirect release of NO

Question 12

What is viagra?

Answer 12

PDE inhibitors (promotes penile erection)

Question 13

What can cause erectile dysfunction?

Answer 13

• mechanical damage to c. cavernosa
• obstruction of arteries to penis
• drugs that block PSNS action
• psychological factors

Question 14

Describe the process of ejaculation

Answer 14

• sympathetic mediated
• signals to ducts of genital tract and bulbocavernosus muscle at base of penis
• emission: smooth muscle contraction in walls of genital tracts, expels semen into urethral bulb
• expulsion: rhythmic contractions of penis and bulbocavernosus muscle ejects semen in spurts

Question 15

Describe the 3 different compositions of ejaculate

Answer 15

1: in prostate - rich in acid phosphate and citric acid
2: vas deferens - rich in spermatozoa
2: seminal vesicle - rich in fructose