Lecture 1.2: Origins of the Gametes Flashcards
What is spermatogenesis?
Gamete maturation in males
What is oogenesis?
Gamete maturation in females
How many gametes do males produce?
200million/day
How many gametes do females produce?
12-13/year
What are Gametes?
They are haploid cells that can undergo fusion of their
nuclei at fertilisation to form a zygote
What are the General Principles of Gamete Formation (Gametogenesis)?
Primordial germ cells colonise the primordial gonad (Cortex vs. Medulla of primordial gonad)
After colonising the gonad, PGCs:
* Proliferate by mitosis
* Reshuffle genetically and eventually reduce to
haploid by meiosis
* Cyto-differentiate into mature gametes
Overview of the Formation of the Female Gamete
- Germ cells colonise the gonadal cortex
- Proliferate, by mitosis and become oogonia
- These then turn into primary oocytes which
undergo meiosis - They then arrest at diplotene stage (a resting phase
between prophase and metaphase of the first
meiotic division) until puberty
What are Oogonia? What happens to them?
- Diploid cells
- Proliferate rapidly by several mitotic divisions
- Max numbers reached mid-gestation (7 million)
- Most die during gestation, ie when still a fetus.
What is it called when a primary oocyte gets surrounded by single layer of flat epithelial granulosa
cells?
Primordial Follicle
How many Primordial Follicles is a female born with?
Female is born with ovaries that contain ~2 million primordial follicles
How many Primordial Follicles does a female have at puberty?
40,000
Why is there a decrease in Primordial Follicles between birth and puberty?
Most become atretic in childhood
How long is the average menstrual cycle?
~28 days
What happens in the Menstrual Cycle?: Days 1-7
Uterus lining breaks down and menstruation occurs
What happens in the Menstrual Cycle?: Days 8-11
The lining of the womb thickens in preparation for the egg
What happens in the Menstrual Cycle?: Days 12-17
Ovulation occurs (usually on day 14)
What happens in the Menstrual Cycle?: Days 18-25
If fertilisation has not occurred the luteum corpus fades away
What happens in the Menstrual Cycle?: Days 26-28
The uterine lining detaches leading to menstruation
What are the 3 Phases of Menstruation?
1) Preparatory Phase: Days 0-12 (follicular or
proliferative phase)
2) Ovulation: Around days 12-14
3) Waiting Phase: Days 14-28 (luteal or
secretory phase)
Stages of Follicular Development
Primordial follicles develop into pre-antral follicles
What is the structure of Primordial Follicles?
Oocyte
Follicular Cell
Stromal Cell
What is the structure of an Early Pre-Antral Follicle?
Oocyte
Follicular Cell
Zona pellucida begins to form
What is the structure of a Late Pre-Antral Follicle?
Oocyte
Follicular Cell
Zona pellucida forms
Stratum granulosa forms
Theca
What is the structure of an Antral Follicles?
Oocyte
Follicular Cell
Zona pellucida
Granulosa Cells
Antrum in granulosa cells
Theca interna
Theca externa
What is the structure of Pre-Ovulatory/Graafian Follicles?
Growth of Follicles (in Menstrual Cycle) (6)
- Under influence of FSH & LH a few follicles
grow bigger (to ~20mm) - The Theca Interna secretes increasing
amounts of oestrogen - One follicle becomes dominant and destined
for ovulation - Capable of rupture to release ovum
- LH surge triggers rupture and the oocyte and
surrounding cumulus oophorus floats away
out of the ovary - Other activated follicles degenerate
