Lecture 37- Female reproductive system 2 Flashcards
What is the female germ cell?
Oogonia
What is oogenesis?
Formation and development of the oocyte (female gamete) from oogonia.
What cell division processes does oogenesis require?
Mitosis and meiosis
In females when are gametes made via oogenesis and how does this differ to males?
-Lifetime supply of gametes produced before birth
-Development then continues between puberty and menopause in a Cyclic nature (1 ovulation every 28ish
days)
-Differs from males where oogenesis continues across life
What do oocytes develop within?
- Ovarian follicles (surround the oocyte)
- These also undergo changes
- 1 oocyte exists per follicle
Once the developed oocyte exits the ovary what happens to the follicle?
Undergoes change to form the corpus luteum (major endocrine organ= Produce inhibin + estrogen+ progesterone )
What happens to the corpus luteum if fertilisation doesn’t occur?
Breaks down to become the corpus albicans
Does the oocyte move around the ovary when it develops?
No, stays in same place diagrams just set out like that to make stages clear
Does the oocyte move around the ovary when it develops?
No, stays in same place diagrams just set out like that to make stages clear
In female oogenesis what happens before birth?
- Oogonium (diploid, 2n=46) in gonad. Undergo mitosis so population increases (stops before birth)
- Oogonia differentiate to form primary oocytes (diploid, 2n=46). These are encased in primordial follicle. Many primary oocytes undergo atresia (cell death)
- Primary oocytes start meiosis. Meiosis halts at prophase I. Halts until puberty begins
In female oogenesis what happens before birth?
- Oogonium (diploid, 2n=46) in gonad. Undergo mitosis so population increases (stops before birth)
- Oogonia differentiate to form primary oocytes (diploid, 2n=46). These are encased in primordial follicle. Many primary oocytes undergo atresia (cell death)
- Primary oocytes start meiosis. Meiosis halts at prophase I. Halts until puberty begins
What happens in oogenesis from puberty to menopause?
- Under GnRH influence, small number of follicles recruited each ovarian/menstrual cycle.
- Only one oocyte will complete development and ovulate (within dominant follicle).
- Primary oocyte completes meiosis I forming a secondary oocyte and 1st polar body (both haploid, n=23).
- Secondary oocyte starts meiosis II. Halts at metaphase II and is suspended until fertilisation.
Is the number of oocytes in a female fixed before birth?
Yes, at puberty females have ~300,000 oocytes
What happens in oogenesis at fertilisation? What happens if not fertilized?
- Meiosis II resumes when the sperm penetrates plasma membrane of the ovum at fertilisation.
- If not fertilize, will degenerate (called atresia) and therefore never complete meiosis.
How do polar bodies form? When do they form?
- Happens when unequal division occurs. Although both cells produced in division are haploid all the cytoplasm and organelles have gone into oocyte.
- 2 are produced as occurs in both meiosis 1 and meiosis 2 of oogenesis
- The polar body in meiosis 1 usually dies but can undergo further division in meiosis 2 to create 2 more
- The polar bodies at end (either 1 or 3 depending on if meiosis 2 went ahead) all die
Describe the general sequence of changes in oogenesis (included chromosome numbers)…
Oogonium: 2n=46
Primary oocyte: 2n=46 :arrested at prophase 1
(present before birth)
Secondary oocyte: n=23 :halted at metaphase 2
Polar body: n=23
(change that occurs each month from puberty to menopause)
Fertilised ova (zygote): 2n=46 (metaphase 2 completes)
