Gametes and HPG axis

Question 1

What type of cells are gametes and how many chromosomes do they carry?

Answer 1

Haploid cells - 23 individual chromosomes

Question 2

When do germ cells migrate to the developing gonads?

Answer 2

6 weeks of development

Question 3

Give a quick summary of what happens after the germ cells colonise the gonads…

Answer 3

1) proliferate by mitosis
2) reshuffle genetic material
3) reduce to haploid by meiosis
4) mature to sperm/ova

Question 4

What are phases of mitosis? (IPPMAT)

Answer 4

Interphase, prophase, prometaphase, metaphase, anaphase, telophase

Question 5

What are spermatogonia?

Answer 5

In the male, XY germ cells colonise the medulla of the testes, proliferate by mitosis, forming spermatogonia.

Question 6

When do seminiferous tubules form?

Answer 6

At puberty - cords hollow out to form seminiferous tubules (250-750/testis)

Question 7

Describe the process of spermatogenesis.

Answer 7

Spermatogonia divide by mitosis - form 64 linked diploid cells - called primary spermatocytes
Meiosis I - produce 2 haploid 2ndry spermatocytes
Meiosis II - produce 4 spermatids
(per primary spermatocyte)

Question 8

In reference to the tubule, where are spermatogonia and spermatids present?

Answer 8

Spermatogonia - at the edges of seminiferous tubules - constantly replaced by mitosis - late in life
Spermatids - close to lumen of tubule
Very little quality assurance of sperm prod.

Question 9

What is spermiogenesis?

Answer 9

Maturation of spermatids into fully differentiated spermatozoa

Question 10

What are major morphological changes that the spermatids undergo while passing down the rete testes, efferent duct and epididymis?

Answer 10

• form: head containing nucleus and mid-piece containing mitochondria
• form: acrosome from golgi apparatus
• elongation of one centriole to form a tail
• loss of excess cytoplasm

Question 11

What is the function of the acrosome?

Answer 11

Contains digestive enzymes that break down the zona pellucida - glycoprotein layer surrounding the ovum

Question 12

Describe the spermatogenic waves.

Answer 12

Sperm produced continuously to exploit limitations of female fertility BUT
Spermatogenesis occurs in sequential waves along length of seminiferous tubules

Question 13

How often do spermatogenic waves occur?

Answer 13

Whole process takes 70 days, new groups of spermatogonia recruited every 16 days

Question 14

What are oogonia?

Answer 14

In the female, XX germ cells colonise the cortex of the ovaries, they proliferate by mitosis, forming oogonia

Question 15

How many oogonia does the female have at birth?

Answer 15

7 million - peak at mid gestation - start to die/not replaced
2 million - remain end of gestation - all enter meiosis before birth

Question 16

Describe the process of oogenesis and how it meets with a sperm.

Answer 16

Meiosis I stall at prophase - result is a diploid primary oocyte surrounded by single layer of granulosa cells in a primordial follicle
Puberty - 1 or 2 primary oocytes develop per month
Prior to ovulation - meiosis I resumes - produce haploid 2ndry oocyte and the first polar body - stalled in metaphase of meiosis II until contact with sperm
Completes division to give one mature haploid ovum and second polar body

Question 17

What does successful fertilisation require?

Answer 17

Fertilisation
A system of support for the conceptus, embryo and finally foetus in the female
Birth at the right time

Question 18

Describe the HPG axis:

Answer 18

Hypothalamus - GnRH -> Ant. Pituitary - FSH/LH -> gonad

Question 19

How is GnRH produced?, where is it produced?

Answer 19

Decapeptide produced by cleavage of pre-pro-GnRH

Produced by hypothalamus. Pulsatile release every 1-2 hours, transferred along pituitary stalk

Question 20

Which hormones below are produced by the posterior pituitary gland?
ACTH, TSH, ADH, FSH, LH, Prolactin, Oxytocin

Answer 20

ADH (vasproessin) and Oxytocin (labour and lactation)

Question 21

Describe the male hormonal system/axis.

Answer 21

Hypothalamis -GnRH-> Pituitary:
- FSH -> sertoli cells -> nurse immature sperm
- LH -> leydig cells -> testosterone
Inhibin and testosterone - neg feedback

Question 22

How much testosterone is produced in humans and what happens to it after migrating to the seminiferous tubules?

Answer 22

Produced by leydig cells = 4-10 mg/day
Migrate to seminiferous tubules:
Converted to dihydrotestosterone (more active) by sertoli cells
Binds to androgen receptors in sertoli cells
Stimulates sperm production

Question 23

Describe the interaction between oestrogen and LH surge

Answer 23

Follicle is growing - oestrogen is rising -> -ve feedback on hypothalamus and pituitary
Dominant follicle (mid-cycle) - very high oestrogen -> +ve feedback
Leads to LH surge

Question 24

Describe interaction of corupus luteum, LH and progesterone and oestrogen

Answer 24

Disrupted follicle forms corpus luteum
LH stimulates corpus luteum to secrete progesterone and oestrogen
Corpus luteum expands
-ve feedback

Question 25

What physiological changes does oestrgeon bring?

Answer 25

• Inc muscular contractions in uterine tubes and uterus, facilitate sperm passage
• Proliferation of uterine lining to prep for implantation
• Makes cervical mucus thin and alkaline - sperm entry
• Support breast development
• Female body fat distribution, hair, genitals, bone growth