Gametes and HPG axis Flashcards
What type of cells are gametes and how many chromosomes do they carry?
Haploid cells - 23 individual chromosomes
When do germ cells migrate to the developing gonads?
6 weeks of development
Give a quick summary of what happens after the germ cells colonise the gonads…
1) proliferate by mitosis
2) reshuffle genetic material
3) reduce to haploid by meiosis
4) mature to sperm/ova
What are phases of mitosis? (IPPMAT)
Interphase, prophase, prometaphase, metaphase, anaphase, telophase
What are spermatogonia?
In the male, XY germ cells colonise the medulla of the testes, proliferate by mitosis, forming spermatogonia.
When do seminiferous tubules form?
At puberty - cords hollow out to form seminiferous tubules (250-750/testis)
Describe the process of spermatogenesis.
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)
In reference to the tubule, where are spermatogonia and spermatids present?
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.
What is spermiogenesis?
Maturation of spermatids into fully differentiated spermatozoa
What are major morphological changes that the spermatids undergo while passing down the rete testes, efferent duct and epididymis?
- 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
What is the function of the acrosome?
Contains digestive enzymes that break down the zona pellucida - glycoprotein layer surrounding the ovum
Describe the spermatogenic waves.
Sperm produced continuously to exploit limitations of female fertility BUT
Spermatogenesis occurs in sequential waves along length of seminiferous tubules
How often do spermatogenic waves occur?
Whole process takes 70 days, new groups of spermatogonia recruited every 16 days
What are oogonia?
In the female, XX germ cells colonise the cortex of the ovaries, they proliferate by mitosis, forming oogonia
How many oogonia does the female have at birth?
7 million - peak at mid gestation - start to die/not replaced
2 million - remain end of gestation - all enter meiosis before birth
Describe the process of oogenesis and how it meets with a sperm.
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
What does successful fertilisation require?
Fertilisation
A system of support for the conceptus, embryo and finally foetus in the female
Birth at the right time
Describe the HPG axis:
Hypothalamus - GnRH -> Ant. Pituitary - FSH/LH -> gonad
How is GnRH produced?, where is it produced?
Decapeptide produced by cleavage of pre-pro-GnRH
Produced by hypothalamus. Pulsatile release every 1-2 hours, transferred along pituitary stalk
Which hormones below are produced by the posterior pituitary gland?
ACTH, TSH, ADH, FSH, LH, Prolactin, Oxytocin
ADH (vasproessin) and Oxytocin (labour and lactation)
Describe the male hormonal system/axis.
Hypothalamis -GnRH-> Pituitary:
- FSH -> sertoli cells -> nurse immature sperm
- LH -> leydig cells -> testosterone
Inhibin and testosterone - neg feedback
How much testosterone is produced in humans and what happens to it after migrating to the seminiferous tubules?
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
Describe the interaction between oestrogen and LH surge
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
Describe interaction of corupus luteum, LH and progesterone and oestrogen
Disrupted follicle forms corpus luteum
LH stimulates corpus luteum to secrete progesterone and oestrogen
Corpus luteum expands
-ve feedback
What physiological changes does oestrgeon bring?
- 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
