Gametogenesis

Question 1

What are the main differences between oogenesis and spermatogenesis?

Answer 1

Question 2

What are the 2 main functions of meiosis?

Answer 2

• reduce chromosome number in gamete to 23
• ensure every gamete is genetically unique

Question 3

Explain how a fertilised oocyte goes through meiosis I and meiosis II to give 4 daughter cells

Answer 3

Question 4

How many daughter cells are made in men vs women?

Answer 4

Men- 4 daughter cells

Women - only 1 as 3 become polar bodies

Question 5

How does genetic variation arise in meiosis?

Answer 5

• Cross over- DNA exchanged between 2 homologous regions
• Independent assortment- random organisation of bivalent on metaphase plate
• Random segregation - random allele distribution amoung 4 gametes

Question 6

Where does spermatogenesis occur and in what compartment?

Answer 6

Within semineferous tubules of the testes

• spermatogonia reside in basal compartment

Question 7

What is the function of tight junctions between the basal and adluminal compartment of the semineferous tubules?

Answer 7

• maintains different cellular environments between 2 compartments
• stops immunological response to sperm

Question 8

How long are spermatagonia available for?

Answer 8

70 years

Question 9

Spermatagonia divide by mitosis to give which 2 cell types?

Answer 9

• Ad spermatogonium - resting reserve stock
• Ap spermatagonium - active stock- maintain stock from puberty onwards
  
  • produce type B spermatogonia to give primary spermatocytes

Question 10

Which steps make spermatagonia become spermatozoa?

Answer 10

Question 11

What is the spermatogenic cycle?

Answer 11

Legnth of time it takes for spermatids at the same stage of the cycle to show up again

Question 12

What is the spermatogenic wave?

Answer 12

The distance between spermatids at the same level of maturation

Question 13

What is the legnth of the spermatogenic cycle in a human?

Answer 13

~16 days

Question 14

Explain the process of spermiogenesis

Answer 14

• Spermatids released into the lumen of semineferous tubules= spermiation
• Spermatids remodel as they pass through ST, through rete testes and ductuli efferentes into epididymis
• In epididymis spermatids become spermatozoa
• Until they reach the epididymis they spermatids are non-motile, process helps them become motile

Question 15

Explain how the structure of sperm relates to its funciton

Answer 15

• Head contains nucleus - genetic info
• Acrosome layer- allows penetration of zona pelliculida
• Tail- provides motility
• Mitochondria- produce ATP to drive flagella tail

Question 16

What secretions make up semen?

Answer 16

• seminal vesicle secretions (~70%)
• prostate secretions (~25%)
• Sperm (2-5%)
• Bulbourehtral gland secretions (Cowper gland)

Question 17

What is sperm capacitation?

Answer 17

Final step of maturation occurs in the female genital tract

Glycoproteins and cholesterol are removed to activate sperm signalling pathway ⇒ allows sperm to bind to zona pellucida of oocyte

Question 18

With regards to capacitation, what is important to remember in in vitro fertilisation?

Answer 18

Sperm must be incubated with capacitation media to mimick environment of female reproductive tract to activate the signicalling pathways of sperm

Question 19

When does maturation of oocytes begin?

Answer 19

At birth

Question 20

How does oogenesis start before birth?

Answer 20

• Germ cells arise in gonadal cortex from the yolk sac and differentiate to oogonia
• oogonia proliferate by mitosis
• 3rd month - oogenia arranged in clusters surrounded by flat epithelial cells
• Majority continue to divide by mitosis but some divide by mitosis and then arrest in prophase of meisosis I as primary oocytes

Question 21

What happens to the number of primary oocytes between before birth?

Answer 21

They drop due to atresia

A mechanism of quality control

Question 22

What is primordial follicle?

Answer 22

A primary oocyte surrounded by flat follicular cells

Question 23

How many oocytes remain by puberty?

Answer 23

~40,000

Question 24

What are the 3 stages that oocytes go through to mature each month?

Answer 24

1. Pre-antral
2. Antral
3. Pre-ovulatory

Question 25

Describe what happens to the oocyte during the **pre-antra**l stage

Answer 25

Follicular cells of primordial follicle proliferate and change from flat→ **cuboidal** to produce statified epithelium of **granulosa cells** Cell now called the primary **follicle**

Question 26

Describe what happens to the oocyte during the **antral stage**

Answer 26

* Primary follicle develps and fluid spaces appear between granulosa cells * Collective space called the **antrum** * Outer fibrous layer becomes **theca externa** * Inner secretory layer becomes **theca interna** * Follicle is now a **secondary follicle**

Question 27

What hormone do the granulosa cells of the primary and secondary follicle secrete?

Answer 27

Oestrogen

Question 28

Describe what happens to the oocyte during the **pre-ovulatary stage**

Answer 28

* Surge in **LH** induces growth phase * Follicle completes meiosis 1 → **2 haploid cells** of **unequal size** * each daughter cells have 23 chromosomes and 46 chromatids * One cell recieves **most cytoplasm**, polar bodies recieve very little * Follicle with cytoplasm enters **meiosis II** but arrests in **metaphase** before ovulation

Question 29

When is Meiosis II completed?

Answer 29

Upon **fertilisation** If not fertilised oocyte degrades 24hrs later

Question 30

What is the name given to the only oocyte chosen to fully mature?

Answer 30

**Graafian Follicle**

Question 31

Explain what happens when ovulation occurs?

Answer 31

* FSH and LH stimulate **rapid growth** of follicle a few days before ovulation * LH surge increases **collegenase** activity * Prostaglandins increase and cause **muscular contractions** in ovarian wall * Oocyte breaks out of ovary

Question 32

What is the **corpus luteum?** What is it's function?

Answer 32

Remaining granulosa and theca cells after ovulation ⇒ change to lutein cells Secrete **oestrogen and progesterone** to stimulate uterine mucosa to prepare for embryo implant

Question 33

How long does the corpus luteum remain for after ovulation?

Answer 33

Set time of **14 days** if no ferfilisation occurs

Question 34

How are oocytes transported into fallopian tubes after ovulation?

Answer 34

Sweeping movements of **fimbrae** and of cilia on epithelial lining of uterine tube Propels oocyte down fallopian tube

Question 35

Explain what happens to the corpus luteum if **no fertilisation** occurs?

Answer 35

Corous luteum degenerates Forms fibrotic scar tissue called **corpus albicans** Progesteron production decreases causing menstrual bleeding

Question 36

Explain what happens to the corpus luteum if **fertilisation occurs**?

Answer 36

* Embryo secretes **human chorionic gonadotropin** which prevents degeneration of corpus luteum * CL continues to grow and forms corpus luteum of pregnancy → **corpus luteum graviditatis** * Secretes progesterone until **4th month** of gestation

Question 37

After 4th month of gestation, what is the main source of progesterone?

Answer 37

The placenta