Reproduction Flashcards
What are the components of the male reproductive system?
Testis - source of sperm and testosterone.
Epididymis - carries sperm to vas deferens from testes and sperm finishes maturation here
Vas deferens - transports sperm from epididymis to urethra
Prostate gland
Urethrae
What are the regulatory hormones for controlling the male reproductive system and where are they produced?
Gonadotrophin releasing hormone (GnRH) - pulsitile release (correlates to LH pulsitility)
- Hypothalamus
Luteinising hormone (LH) - pulsitile release, affects the leydig cells which produces testosterone. - Anterior pituitary
Follicle stimulating hormone (FSH) - prolonged and less pulsitile release, affects the sertoli cells (essential for spermatogenesis - they respond to FSH and Testosterone) in seminiferous tubules
- Anterior pituitary
Testosterone (T) - has a negative feed back effect which suppress the release of GnRH and LH.
- Testis
What are the cells in the testes? What are their roles?
The testis is made up of two major compartments
- interstitial compartment - leydig cells - secrete testosterone to stimulate Sertoli cells to produce sperm
- seminiferous tubules - Sertoli cells - it helps spermatogenesis and secretes inhibin (inhibin is negative feedback on FSH)
What are the stages of spermatogenesis?
Primordial germ cells (divide by mitosis) (2n)
Spermatogonium (2n)
Primary spermatocyte (meiosis starts) (2n)
Secondary spermatocyte (n)
Spermatids (n)
Mature sperm in lumen (n)
Summarise male reproductive function
- Starts at puberty
- Functions continually
- Normally continues throughout the rest of life
- Sperm quantity and quality generally decreases with increasing age
- LH stimulates testosterone production
- FSH and testosterone sustain Sertoli cell function
- Sertoli cells support spermatogenesis
Summarise female reproductive function
- Starts at puberty
- Functions cyclically
- Normally operates until ~45 years of age
- Egg quality generally decreases with increasing age
- FSH stimulates (some) development of ovarian follicles & 17b-estradiol synthesis
- LH stimulates progesterone production
- The steroids regulate uterine endometrium
Where does LH and FSH act on in females?
Ovaries - the steroid hormones produced (Progesterone and oestrogen) have a negative feedback on GnRH and LH/FSH release.
Describe the female HPO axis during each phase.
Follicular phase - when the main follicle is maturing in the ovary. GnRH (Hypothalamus) –> FSH, LH (anterior pituitary) –> Estradiol + (some progesterone) (ovaries). The Estradiol has a negative feedback effect on the hypothalamus and anterior pituitary.
Midcycle - GnRH (Hypothalamus) –> FSH, LH (anterior pituitary) –> Estradiol (ovaries). The Estradiol has a positive feedback effect on the hypothalamus and anterior pituitary. Positive feedback = you get a rapid increase of LH, FSH and Oestrogen until ovulation. Build up to ovulation.
Luteal phase - once ovulation has taken place the luteal phase happens and everything goes back to normal. GnRH (Hypothalamus) –> FSH, LH (anterior pituitary) –> progesterone + (some oestrogen) (ovaries). The progesterone has a negative feedback effect on the hypothalamus and anterior pituitary.
The average human menstrual cycle is 28 days. Ovulation is day 14.
Describe the changes in thickness of the endometrium and what controls it?
2-4 mm - High levels of eostrogen produced in the first part of the ovarian cycle.
7-16 mm - The effect of both progesterone and oestrogen
2-4 mm - endometrium breaks as all the hormones decrease
This is just like the pill - take 21 days or progestogens and oestrogens then 7 days off.
Describe folliculogenesis/oogenesis
1) Primordial follicle - developed during intrauterine life. Matures into a:
2) Primary follicle.
3) Antral follicle
4) Ruptured follicle - Ovulation
5) Corpus luteum
Both primordial follicles and primary follicles contain a primary oocyte.
The primary follicle develops with luteal cells being formed around it.
Primordial germ cell –> oogonium –> primary oocyte –> secondary oocyte –> ovum
How long does a follicle take to complete its development?
3 months
Summarise oogenesis
Ovulation = release of mature oocyte (egg) from the ovary
Oocyte is 2n at this stage, in meiotic arrest (metaphase II)
Enters the Fallopian tube
Needs to be fertilised within 24 hours, as it degenerates after this
What happens during fertilisation?
1) Sperm chemoattracted to the egg
2) Gets through the cells of corona radiata and zona pellucida
3) Male DNA unwinds to form a pronucleus (haploid)
4) Fertilisation occurs - Male and female pronucleus combine. Chromosomes mix, spindle form and separate to form two identical cells. At some point before the spindles form both the male and female DNA must have duplicated for mixing so two identical cells can be formed.
Describe how fertilisation ensures there are 2 copies of each chromosome (1 father and 1 mother) before division?
1) Meosis of maternal chromosomes resumes, forming female pronucleus (23 chromatids), and 2nd polar body.
2) Sperm chromosomes decondense to form male pronucleus (23 chromatids).
3) Chromatids in both pronuclei are duplicated
4) Nuclear membranes break down and male and female chromosomes mix
5) They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells (1st cleavage division of the embryo).
