Gametogenesis and assisted reproductive technologies

Question 1

Describe spermatogenesis

Answer 1

it occurs within the testis and mature testis composed of tightly packed tube.
PGC give rise to spermatogonia which can undergo mitotic proliferation and differentiate to form primary spermatogocytes and further undergo meiosis to form spermatids

Question 2

Function of sertoli cells

Answer 2

• Support differentiation from spermatogonium to mature sperm
  
  • Provide nutritional support and optimum hormonal environment for spermatogenesis

Question 3

Describe the regulation of spermatogenesis

Answer 3

it is regulated by hypothalamic pituitary axis GnRH is released from hypothalamus which stimulates production of Luteinizing hormone and follicle stimulating hormone from anterior pituitary
LH stimulates leydig cells to release testosterone and synergise with FSh to stimulate function of sertoli cells

Question 4

Describe the process of oogenesis

Answer 4

1. Precursor of ovum, Oogonium develops into a primary oocyte -> start process of meiosis
   
   2. Once antral follicle formed, first stage of meiosis completed releasing egg from ovary contains 44+ XX chromosomes (secondary oocyte)and first polar body(44+XX)
   3. the secondary oocyte does not complete the second meiotic division, but stops at metaphase II (the meiotic arrest).
   4. After fertilisation, folllicle converted into corpus luteum (persists for about one week )

Question 5

Describe the regulation of oogenesis

Answer 5

• Control of gamete production is regulated by hormones from hypothalamic- pituitary axis
• high levels of LH needed for ovulation
• Increase levels of oestrogens from follicle stimulate the release of LH from anterior pituitary gland which further stimulates the follicle until it ruptures, releasing oocyte

Question 6

Describe change in hormones in ovulation

Answer 6

• levels of oestrogen rise during the latter part of the follicular phase, and stimulate very rapid increases in LH and FSH levels just before ovulation
• during lute phase, peptide hormone levels fall to baseline levels, and oestrogen and progesterone levels increase rapidly
• levels of 2 steroid hormones decline during the last week of the cycle and precipitate the loss of the endometrial lining of the uterus, and hence menstruation (mensus)

Question 7

Describe process of ovulation

Answer 7

• Once oocyte has been ovulated, it enters the Fallopian tube associated with the ovary
  
  • Moved by cilia in the fallopian tube towards the uterus
• Fertilization normally take place within the fallopian tube (12-24 hrs of ovulation
  
  • Then oocyte degenerates

Question 8

Describe the activation of sperm

Answer 8

• Sperms released from epididymis and are deposited in the cervical of female reproductive tract
• The fluid surrounding sperm is produced by seminal vesicles, prostate and bulbourethral glands
  
  • Containing fructose, calcium and zinc
    ○ Necessary to activate the swimming movements of sperm
    ○ Provides alkaline environment optimal for sperm survival
• Second activation -> Capacitation
  
  • Take place as sperm through female reproductive tract during journey from cervix through uterus and meet an egg
  • Involves a change to the head of the sperm so acrosome lie activates and enzyme can digest the outer layer of oocyte and allow sperm entry
    ○ Acrosome contains enzyme needed for sperm to access egg

Question 9

Describe fertilisation

Answer 9

1) Oocyte is surrounded by cumulus (corona radiata) attach to it and relase with it at ovulation
2) Activated sperm release acrosomal enzymes which digest these cells and zone pellucida
3) One sperm fuses with the oocyte cell membrane
4) Sperm enters the egg
5) Fertilisation causes the release of cortical granules which fuses the membrnae and harden zona pellucida
- Stops any other sperm entering the egg
6) The tightly packed chromosome in the nucleus in sperm unwind -> decondensation
- Allow formation of male pronucleus ot fertilised eggs
7) The process of meisos is completed -> haploid set of maternal chromosomes
- Grouped to form female pronucleus (not tightly packed)
8) Second polar body released from oocyte
9) Once both pronuclei formed, haploid sets are duplicated to form identical paried chromatids
- Pronuclei fuse to form a nucleus is tetraploid
10) This is followed by initiation of mitosis in the fertilisation egg and generation of mitotic spindle

Question 10

What are possible assisted reproduction

Answer 10

Hormonal treatments 
In vitro fertilisation 
IVF followed by surrogacy
Intra-cytoplasmic sperm injection 
three parent embryos