11.4 Sexual Reproduction Flashcards
Where does gametogenesis occur?
ovaries or seminiferous tubules of testes
Describe spermatogenesis.
In the seminiferous tubule, spermatogonia grow, which become spermatocytes.
The primary spermatocyte carries out the first meiotic division, and the secondary spermatocyte carries out the second meiotic division.
The two divisions of meiosis produce 4 spermatids, which differentiate into sperm cells.
Describe Oogenesis.
Oogonium grows until they become primary oocytes. They start the first meiotic division, but then the process is stopped, until puberty, where monthly once oocyte will continue with the first meiotic division, forming 2 cells of unequal size. One cell gets the entire cytoplasm, forming the secondary oocyte, and the other one becomes the polar body. The secondary oocyte begins meiosis 2, but stops during metaphase, and leaves the ovary and goes into the oviduct. There, it will only finish meiosis if it is fertilised.
When does spermatogenesis occur, and oogenesis?
Spermatogenesis: puberty, continuously
Oogenesis: embryo development
How many sperm cells are produced in spermatogenesis and how many secondary oocytes are produced in oogenesis? How much cytoplasm do they have?
4 sperm cells all have equally much cytoplasm, 1 secondary oocyte that has all the cytoplasm (the rest are polar bodies)
What are the 3 important mechanisms during fertilisation?
- Capacitation - chemicals released by uterus dissolve sperm cholesterol coat, makes sperm more mobile
- Acrosome Reaction - when the sperm reaches the zona pellucida, its acrosome fuses with it and releases digestive enzymes which makes it soft and enables the sperm to travel to the egg and release the nucleus.
- Cortical Reaction - Once the sperm has penetrated the egg, the cortical granules release enzymes into the zona pellucida and they destroy sperm binding cites and thicken harden the jelly coat.
What produces hCG?
the blastocyst that has implanted itself in the endometrium lining
What does hCG do?
It prevents the degeneration of the corpus luteum, so that progesterone and oestrogen keep being produced, which inhibit FSH and LH, and keep the endometrium lining.
When is there no more hCG?
After 8-10 weeks, the placenta has grown enough to produce enough progesterone itself, thus no longer needing the corpus luteum, let alone hCG.
How does the placenta facilitate the exchange of materials between fetus and mother?
Oxygen, nutrients, water, antibodies all come from mother to kiddo
Which roles do the hormones secreted by the placenta play?
It secretes progesterone and estrogen, replacing the effect of the follicles.
Estrogen makes strong uterine muscles and mammary glands. Progesterone keeps endometrium lining.
How does positive feedback play a role during birth?
Fetal growth -> streching of cervix -> detected -> hormone oxytocin is released -> uterine muscles contract -> even less space -> more streching of cervix -> etc.
