Reproductive physiology

Question 1

Label the male reproductive tract

Answer 1

Kenhub

Testis - source of sperm and testosterone. Testosterone determines the development of male sexual features in utero - important role before birth. Then it starts having its effect again at puberty - testosterone production increases in puberty.

Question 2

What are the regulatory hormones for controlling the male reproductive system and where are they produced?

Answer 2

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 T) in seminiferous tubules
- Anterior pituitary

Testosterone (T) - has a negative feed back effect which suppress the release of GnRH and LH.
- Testis

Question 3

What do sertoli cells produce?

Answer 3

Inhibin - inhibits the production of FSH

Homeostatic feedback control system

Question 4

What happens during spermatogenesis?

Answer 4

The testis is made up of two major compartments
- interstitial compartment - leydig cells
- seminiferous tubules - sertoli cells
Basically during spermatogenesis you start with diploid division and then it eventually goes haploid. 1 diploid precursor gives rise to 4 halpoid spermatids.
All the sperm are stored in the epididymis.

Duplication then meiosis
See diagram

Question 5

Summarise male reproductive function

Answer 5

• 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

Question 6

Summarise female reproductive function

Answer 6

• 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

Question 7

Where does LH and FSH act on in females?

Answer 7

Ovaries - the steroid hormones produced (Progesterone and oestrogen) have a negative feedback on GnRH and LH/FSH release.

Question 8

Describe the changes in the female HPO axis?

Answer 8

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 reinforcement = 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. Compare this to slide 11

Question 9

Describe the changes in thickness of the endometrium and what controls it?

Answer 9

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.

Question 10

Describe folliculogenesis/oogenesis

Answer 10

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

Oogenesis takes place over a time frame of 3 months.

Question 11

Summarise oogenesis

Answer 11

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

Question 12

What happens during fertilisation?

Answer 12

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.

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) They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells (1st cleavage division of the embryo).

See diagram