Spermatogenesis

Question 1

What is Spermatogenesis?

Answer 1

formation of haploid sperm from primordial germ cells in the seminiferous tubules of testes

Question 2

What is the Site of sperm production?

Answer 2

seminiferous tubules

Question 3

What is the Site of sperm storage?

Answer 3

epididymis

Question 4

Why do testes lie outside the body?

Answer 4

1.5-2ºC below body temperature for sperm development because overheating reduces sperm count

Question 5

Describe the Sperm pathway structures.

Answer 5

Seminiferous tubules
>rete testis
>efferent ductules
>epididymis
>vas deferens

Question 6

What lines the seminiferous tubules?

Answer 6

Sertoli cells

Question 7

What are Spermatogonia?

Answer 7

diploid primary germ cells in basement membrane of seminiferous tubules which give rise to spermatocytes by mitosis

Question 8

What is the Fate of spermatogonia?

Answer 8

a) Commit to becoming sperm and undergo two meiotic divisions (after becoming primary spermatocytes) to become mature sperm
b) Divide by mitosis and replenish themselves

Question 9

What initiates sperm production?

Answer 9

testosterone

Question 10

How do sertoli cells control spermatogenesis?

Answer 10

There are tight junctions between Sertoli cells in seminiferous tubule walls which form the Adluminal compartment.

> Sertoli cells secrete growth factors, hormones, signalling molecules into Adluminal compartment to control environment in which sperm are developing

Question 11

Outline the Development of sperm in seminiferous tubule.

Answer 11

Spermatogonia in basement membrane
-mature between Sertoli cells, moving slowly towards the central lumen where they finish development, and then to the epididymis for storage

Question 12

What do the regions between seminiferous tubules contain?

Answer 12

Leydig cells, blood vessels, lymphatics, interstitial fluid

Question 13

What are Leydig cells?

Answer 13

A cell that produces testosterone and other androgens and is located between the seminiferous tubules of the testes.

Question 14

Describe the Sperm Stages during Spermatogenesis.

Answer 14

1) Spermatogonia (diploid)
- type Ad spermatogonia divide mitotically to produce more type Ad spermatogonia, maintaining population of spermatogonia
- or divide mitotically to produce type Ap spermatogonia, which then differentiate to type B spermatogonia and subsequently primary spermatocytes (which then undergo meiosis)
2) Primary Spermatocytes (46XY diploid)
- move into adluminal compartment & duplicate their DNA producing identical sister chromatids
- crossing over between non-sister chromatids
- undergo meiosis I to produce secondary spermatocytes
3) Secondary Spermatocytes (23X+23Y)
- haploid number of chromosomes arranged as chromatids
- undergo meiosis II to produce 4 haploid spermatids
4) Spermatids
- round spermatids differentiate to elongated spermatids
5) Spermatozoa
- mature sperm extrude into lumen of seminiferous tubule

Question 15

Define Spermiogenesis.

Answer 15

differentiation of spermatids into spermatozoa (elongation, loss of cytoplasm and movement of cellular contents)

Question 16

Describe the process of Steroid Production in Testes.

Answer 16

LH stimulates Leydig cells to produce testosterone and androgens
-testosterone can cross over into seminiferous tubules to stimulate Sertoli cell function and control spermatogenesis

FSH stimulates Sertoli cells to produce oestrogens from androgens
-Sertoli cells die without FSH

Question 17

How do anabolic steroids affect the male HPG axis?

Answer 17

more steroids (testosterone) causes more negative feedback
>less FSH/LH released from pituitary
>Sertoli cells need FSH to survive, therefore there is Sertoli cell death and testicular atrophy

Question 18

What are the Effect of parasympathetic nervous system on male gonads?

Answer 18

• constricts venous drainage from penis
• vasodilation of arterial blood flow to penis
• penis becomes full of blood
• hydrostatic pressure causes penis to be ERECT

Question 19

What are the Effect of sympathetic nervous system on male gonads?

Answer 19

-causes smooth muscle contractions for sperm movement into epididymis, vas deferens, glands and urethra for EJACULATION

Question 20

What are the Effect of somatic nervous system on male gonads?

Answer 20

some somatic nervous control in synergy with sympathetic nervous control during ejaculation, causing for expulsion of glandular secretions/sperm and evacuation from urethra

*perineal branch of pudendal nerve from S2-S4

Question 21

What is Seminal fluid (Semen)?

Answer 21

sperm cells and secretions of seminal vesicles, prostate gland, and bulbourethral glands

Question 22

Describe the Secretions of seminal vesicles.

Answer 22

• comprise 50-70% of ejaculate
• proteins, enzymes, fructose, prostaglandins, vitamin C
• high fructose provides energy source
• high pH (alkaline) protects against acidic environment in vagina

Question 23

Describe the Secretions of prostate gland.

Answer 23

• comprise 30% of ejaculate
• milky/white fluid with <1% protein content including proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen involved in liquefaction after initial viscous sperm deposits near cervix
• high zinc concentration is antibacterial

Question 24

Describe the Secretions of bulbourethral gland.

Answer 24

-clear viscous secretion high in salt [Na+] known as pre-ejaculate which lubricates the urethra for spermatozoa to pass through, neutralising any traces of acidic urine

Question 25

Describe the Structure of sperm.

Answer 25

• no cytoplasm
• smallest cell in the body
• only provides DNA
• acrosome (invaginated membrane) containing digestive enzymes
• mitochondrial sheath- contains a lot of mitochondria for energy
• axoneme- microtubule based cytoskeleton in flagella