Spermatogenesis

Question 1

Spermatogonia

Answer 1

primary male germ cells

Question 2

Spermatocytes

Answer 2

immature haploid spermatozoa

Question 3

Spermatids

Answer 3

immature haploid spermatozoa

Question 4

Mitosis

Answer 4

Cell division giving rise to diploid daughter cells

Question 5

Meiosis

Answer 5

Cell division giving rise to haploid daughter cells

Question 6

Seminiferous tubules

Answer 6

testicular structures that are the site of spermatogenesis

Question 7

Spermiogenesis

Answer 7

final phase of sperm maturation

Question 8

Adluminal compartment

Answer 8

space between tight junctions of sertoli cells where sperm develop

Question 9

Epididymis

Answer 9

duct which conveys sperm from the testicle to the urethra

Question 10

Vas deferens

Answer 10

duct which conveys sperm from the testicle to the urethra

Question 11

Testes

Answer 11

Produce sperm and store it.
Produce hormones which regulate spermatogenesis.
Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5°C below body.
Overheating of testes reduces sperm count.
Well-vascularised, well-innervated.
Normal volume of testes approximately 15-25ml measured by orchidometer..

Testis is 90% seminiferous tubules, site of spermatogenesis.
600m long in each testis! Tubules are tightly coiled.
Tubules all lead to epididymis and ultimately vas deferens.

Question 12

Sertoli cells, tight junctions & adluminal compartment

Answer 12

Primary germ cells or spermatogonia on the basement membrane

Walls of tubule made up of tall columnar endothelial cells Sertoli cells. Tight junctions between these form Adluminal compartment.

Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells.

Spaces between the tubules are filled with blood and lymphatic vessels, Leydig cells and interstitial fluid.

Question 13

Sperm stages during spermatogenesis

Answer 13

Spermatogonia: Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.

Primary spermatocytes: They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis I. They are 46XY diploid.

Secondary spermatocytes: Secondary spermatocyctes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.

Spermatids: Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.

Spermatozoa: Mature sperm extruded into the lumen

Question 14

Spermatogenesis

Answer 14

New cycle every 16 days, entire process takes approximately 74 days.
1. Mitotic proliferation of spermatogonia.
2. Meiosis and development of spermatocytes.
3. Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
Each cell division from a spermatogonium to a spermatid is incomplete - the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development.
Syncytia at various stages of development throughout seminiferous tubule giving continuous supply.

Question 15

Hypothalamic / Pituitary / Gonadal Axis

Answer 15

diagram

Question 16

Steroid production in the testis

Answer 16

Leydig cells contain LH receptors and primarily convert cholesterol into androgens.
Intra-testicular testosterone levels are 100x those in plasma.
Androgens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis.
Sertoli cells contain FSH receptors and converts androgens to oestrogen.
FSH establishes a quantitatively normal Sertoli cell population.
Androgen initiates and maintains sperm production.

Question 17

Oogonia v Spermatogonia

Answer 17

Oogonia all laid down in foetus.
Begin meiosis to make oocyte before birth.
Cannot make more oogonia by mitosis.
Limited supply.

Spermatogonia laid down in foetus.
Begin meiosis to make spermatocyte after puberty OR…Divide mitotically to make more spermatogonia.
Lifetime supply.

Question 18

Erection and ejaculation

Answer 18

Vasodilation of the corpus cavernosum. Partial constriction of the venous return.
Autonomic nervous system causes co-ordinated smooth muscle contractions of vas
deferens, glands and urethra.

Parasympathetic control = erection POINT
Sympathetic nervous system control movement of sperm into epididymis, vas deferens, penile urethra = emission SHOOT
Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4) = Expulsion of the glandular secretions& evacuation of urethra. SCORE

Question 19

Ejaculate

Answer 19

300 million sperm produced per day on average.
3,500 per second so 9 million during this lecture
approximately 120 million in average ejaculate
Normal ejaculate volume is 1.5ml - 6ml.
around one third to just over a teaspoon full
Initial portion of the ejaculate is most sperm rich.
99.9% lost before reaching ampulla of the uterine tube.
around 120,000 sperm get near to egg, only one enters
Seminal fluid consists of secretions from: seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid

Question 20

Seminal fluid

Answer 20

Bulbo-Urethral Gland
Produces a clear viscous secretion
high in salt, known as pre-ejaculate.
This fluid helps to lubricate the urethra for spermatozoa to pass through, neutralizing traces of acidic urine.

Seminal Vesicles
Secretions comprise 50-70% of the ejaculate. Contains proteins, enzymes,fructose, mucus, vitamin C and prostaglandins. High fructose concentrations provide energy source.
High pH protects against acidic environment in vagina.

Prostate
Secretes milky or white fluid roughly 30% of the seminal fluid. Protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen which are involved in liquefaction. High zinc concentration 500–1,000 times that in the blood is antibacterial.

diagram

Question 21

Semen analysis

Answer 21

Volume 1.5 – 6.0 ml
Sperm concentration >15million/ml
Liquefaction <30 minutes
Motility >40%
Progressive motility >32%
Vitality (live) >58%
Morphology (normal forms) >4%
pH >7.2
Leucocytes <1 million/ml

diagram

Question 22

Spermatozoon

Answer 22

diagram