Aspects of Human Reproduction Flashcards
What is the production of gametes called?
Gametogenesis
What is SPERMATOGENESIS?
The production of sperm.
Where does spermatogenesis take place?
SEMINIFEROUS TUBULES in the testes. Process begins at outer edge of GERMINAL EPITHELIUM and new cells form towards inner edge.
Outline spermatogenesis (4)
1) SPERMATOGONIA (diploid cells) divide by mitosis to form more diploid cells which grow into spermatogonia and the larger PRIMARY SPERMATOCYTES.
2) Primary spermatocyte divides by the first division of meiosis into haploid SECONDARY SPERMATOCYTES.
3) Secondary spermatocytes go through the second division of meiosis to form haploid SPERMATIDS.
4) The spermatids differentiate into SPERMATOZOA. Their tails hang free in the luman of the tubule and their heads are attached to the wall.
What protects the cells involved in spermatogenesis, and how?
SERTOLI CELLS. Nourish and protect developing sperm cells, ineract with hormones produced in pituitary gland to help regulate sperm production.
What happens during the MENUSTRUAL CYCLE? (7)
1) The ANTERIOR PITUITARY GLAND secretes LH and FSH.
2) In the ovary, one follicle becomes the ‘dominant’ follicle (GRAFIAN FOLLICLE), The follicle cells around the SECONDARY OOCYTE proliferate to form a wall many cells thick called the THECA. The presence of FSH and LH stimulates cells surrounding the follicle (granulosa cells) to secrete OESTROGEN.
3) Presence of oestrogen in blood has negative feedback effect on production of FSH and LH, levels of the two hormones fall.
4) Oestrogen stimulates the ENDOMETRIUM (uterus lining) to proliferate (thicken and develop blood capillaries).
5) When oestrogen concentration reaches 2-4times its level at the beginning of the cycle, it stimulates a surge in the secretion of LH and (lesser extent) FSH.
6) Surge of LH causes dominant follicle (GRAFIAN FOLLICLE) to burst and shed its SECONDARY OOCYTE into the OVIDUCT.
7) The Grafian follicle collapses to form the CORPUS LUTEUM formed from GRANULOSA CELLS, which secrete PROGESTERONE (maintains lining of the uterus, making it ready to receive and embryo).
What is OVULATION?
When the SECONDARY OOCYTE is released.
What is MENSTRUATION?
When the endometrium lining is shed. This is caused by the degeneration of the corpus luteum, which secretes progesterone.
What is CONTRACEPTION?
Prevention of the fertilisation of the secondary oocyte.
What methods prevent the embryo from implanting into the lining of the uterus?
ANTI-IMPLANTATION METHODS.
How are BIRTH CONTROL PILLS taken?
For most types of oral contraceptive, one pill is taken daily for 21 days, and stop (or take an inactive pill) for 7 days during menstruation.
How do BIRTH CONTROL PILLS work?
They contain STEROID HORMONES that suppress ovulation. Usually synthetic rather than natural, as they are broken down less rapidly.
What do birth control pills contain, and what do they do?
Some contain PROGESTERONE only but most contains both PROGESTERONE and OESTROGEN (combined oral contraceptives). These inhibit the secretion of LH and FSH from the anterior pituitary gland.
Describe follicular activity throughout the days when a pill is taken.
Follicular activity remains low and consistent during days when the pill is taken. During days 21-28, when no pill is taken, follicular activity rise. Disappearance of oestrogen and progesterone allows LH and FSH to be secreted, and they stimulate the development of a follicle in the ovary.
Describe OOGENESIS (5)
1) When a girl is still an embryo, GERMINAL EPITHELIAL CELLS in her developing ovaries divide to form diploid OOGONIA.
2) Within a few weeks, these begin to divide by meiosis, but only reaching prophase I. These are PRIMARY OOCYTES.
3) At puberty, some of these primary oocytes move from prophase I to end of first meiotic division, forming two haploid cells (the much bigger SECONDARY OOCYTE and the other POLAR BODY).
4) the secondary oocyte continues into second meiotic division, but doesn’t get further than metaphase II.
5) If the girl’s released secondary oocyte in her oviduct is fertilised, it becomes an ovum and continues division by meiosis.
What surrounds developing oocytes?
Developing oocytes are inside follicles in the ovary, also produced by the germinal epithelium. The wall of the follicle contains several types of cell, including GRANULOSA CELLS, which surround and protect the oocyte, and secrete hormones.
What is the function of GnRH in both sexes?
It stimulates the anterior lobe of the pituitary gland.
What is the function of FSH in women, and where is it secreted from?
Secreted from the pituitary gland, FSH stimulates the development of follicles within the ovary.
What is the function of oestrogen and where is it secreted from?
Secreted by ganulosa cells, it stimulates the repair of the uterus wall, and inhibits release of FSH (no new follicles develop incase pregnancy results) and also inhibits release of LH until shortly after ovulation. Then the level of oestrogen rises in a surge, which then stimulates the release of LH and FSH.
What is the function of LH in women, and where is it secreted from?
Secreted from the pituitary gland, a surge of LH causes ovulation and developement of the corpus luteum. LH feeds back to inhibit oestrogen release, as a result, LH and FSH levels fall.
What is the function of progesterone and where is it secreted from?
Secreted by the corpus luteum, it stimulates the thickening and vascularisation of the uterus wall (preparation for pregnancy).
What is the function of LH (also known as ICSH) in men, and where is it secreted from?
Released by the anterior lobe of the pituitary gland, it stimulates the leydig cells that produce testosterone.
What are LEYDIG CELLS?
Found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH).
What is the function of FSH in men, and where is it secreted from?
Released from the anterior pituitary gland, it stimulates the seminiferous tubules, including Sertoli cells, which produce sperm in response.
