Reproductive physiology

Question 1

What are the two main functions of the male reproductive system?

Answer 1

The provision of androgens (primarily testosterone) to initiate and sustain the necessary male phenotype.

The production of mature sperm.

Question 2

Describe the male Hypothalamic-gonadal axis

Answer 2

• Hypothalamus produces GnRH
• Gonadotrophs in anterior pituitary release LH and FSH
• LH acts on Leydig cells to promote testosterone production
• Testosterone acts to inhibit gonadotroph production in the hypothalamus and anterior pituitary
• FSH and testosterone bind to androgen binding protein (ABP)
• ABP activates Sertoli cells
• Sertoli cells produce inhibin which inhibits gonadotroph production in the anterior pituitary

Question 3

Where are leydig cells found?

Answer 3

Interstitial compartment of the testies

Question 4

How is GnRH, LH and FSH released?

Answer 4

GnRH and LH are released in a very pulsatile fashion

FSH is released in a less pulsatile way and is more constant

Question 5

What is the function of sertoli cells?

Answer 5

1. Produce inhibin
2. Support development of sperm precursors into mature sperm

Question 6

Where is sperm produced?

Answer 6

Seminiferous tubules

Question 7

What is the pathway of sperm in ejaculation?

Answer 7

1. Sperm produced in seminiferous tubules
2. Stored in epididymis
3. Pass into vas deferens (contractile) - mixed with fluid from seminal vesicles
4. Leaves via the ejaculatory duct
5. Enters the urethra - mixes with the secretions of the prostate gland

Question 8

Does sperm change with age?

Answer 8

Yes

Sperm quantity and quality generally decreases with increasing age

Question 9

When does female reproductive function generally stop?

Answer 9

Approx. 45 years old

Question 10

Do female eggs change with age?

Answer 10

Yes

Egg quality generally decreases with increasing age – gradual decline

Question 11

Describe the female Hypothalamic-gonadal axis

Answer 11

• Hypothalamus produces GnRH
• Gonadotrophs in anterior pituitary release LH and FSH
• FSH stimulates (some) development of ovarian follicles & 17b-estradiol synthesis
• LH stimulates progesterone production
• FSH and LH negatively feedback at the hypothalamus and anterior pituitary

Question 12

How does the female Hypothalamic-gonadal axis change during mensturation?

Answer 12

1. Follicular phase:

• The dominant hormone produced by ovary is ESTRADIOL
• Estradiol has NEGATIVE feedback on the anterior pituitary and the hypothalamus

1. Midcyle

• The dominant hormone produced by ovary is ESTRADIOL
• Estradiol has POSITIVE feedback on the anterior pituitary and the hypothalamus

1. Luteal phase

• The dominant hormone produced by ovary is PROGESTERONE
• Progesterone has NEGATIVE feedback on the anterior pituitary and the hypothalamus

Question 13

Which phase in menstruation can change length?

Answer 13

Luteal phase

Question 14

What is a common cause of change in menstruation length and how does it change it?

Answer 14

Stress - prolongs it

Question 15

What causes endometrial remodelling?

Answer 15

Oestrogen begins the process of endometrial hyperplasia in the proliferative phase

Combination of progesterone and oestrogen is more effective at promoting endometrial hyperplasia

Question 16

What are the phases of endometrial remodelling?

Give a time course

Answer 16

Day 1-5: Menstrual phase (5 days)

Day 5-14: Proliferative phase (9 days)

Day 14-27: Secretory phase (13 days)

Day 27-28: Ischemic phase (1 day)

Question 17

What is the pathway for maturation of an ovarian follicle?

Answer 17

1. Primordial follicle containing primary oocyte
2. Primary follicle
3. Antral follicle
4. Ruptured follicle
5. Corpus luteum
6. Degenerating corpus luteum

Question 18

How does body temperature change during the menstrual cycle?

Answer 18

Raises aprox 0.5^oc after ovulation (day 14)

Question 19

When does the maturation of ovarian follices take place?

Answer 19

1. Primordial follicle -produced during intrauterine life
2. Meiosis 1 is paused at prophase until puberty
3. Meiosis 2 is paused at metaphase until fertilisation

Question 20

How long does folliculogenesis take?

Answer 20

Aprox 3 months from Primary follicle to graffian follicle

Question 21

How long does the oocyte last once it is released from the ovary?

Answer 21

24 hours

Question 22

Which ovary releases an oocyte each month?

Answer 22

Usually alternates

Sometimes can release one from each (non-identical twins)

Question 23

How does fertilisation occur?

Answer 23

1. Passage of sperm through uterus
2. Passage of sperm into Fallopian tube
3. Swim from there to Fallopian tube ampulla
4. Survival of the fittest (a few days)
5. Capacitation – takes time within uterus
   * Capacitation is essential preparation before the sperm meet the oocyte
6. When reach fallopian tubes are chemo-attracted to egg
7. Sperm produce enzymes to degrade outer layers of egg

• Acrosome reaction: penetration of Zona Pellucida (& Coronal cells)

Question 24

What happens when a sperm enters an egg?

Answer 24

1. Calcium flux
2. Meosis of maternal chromosomes resumes, forming female pronucleus (23 chromatids), and 2nd polar body.
3. Change in Zona Pellucida to prevent additional sperm fusing with zygote.
4. Sperm chromosomes decondense to form male pronucleus (23 chromatids).
5. Chromatids in both pronuclei are duplicated
6. They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells (1st cleavage division of the embryo).

Question 25

How is the brain linked to sex?

Answer 25

1. Mesolimbic dopaminergic system - Pathway for reward and pleasure * Encourages intercourse and thus the continuation of our race 1. Nigrostriatal tract - control of movement 2. Hypothalamus and pituitary - neuroendocrine pathways regulating fertility and pregnancy

Question 26

What is the mechanism of an erection?

Answer 26

* Spinal cord initiates increased parasympathetic activity of efferent pudendal nerve fibres to pudendal artery * Increases the activity of Nitric Oxide Synthase (NOS), and hence nitric oxide (NO) * NO increases production of cyclic GMP which induces dilatation of arterial smooth muscle. * counteracts sympathetic-maintained myogenic tone * increases blood flow in corpus cavernosum * which compresses the dorsal vein, restricting the outflow of blood

Question 27

How is the urethra protected from increased pressure during an erection?

Answer 27

The urethra is protected from increased pressure by surrounding corpus spongiosum (less turgid)

Question 28

How does viagra prevent loss of an erection?

Answer 28

* Cyclic GMP is normally de-activated by a phosphodiesterase enzyme, and this will reverse the changes leading to penile erection. * Viagra inhibits the phosphodiesterase, thus potentiating the effects of cyclic GMP.

Question 29

What can cause an erection?

Answer 29

1. 'Sexy thoughts' activate the limbic system which in turn stimulates the spinal cord 2. Tactile stimulus on the penis stimulates afferent pudendal nerve fibres to the spinal cord

Question 30

What happens mid-cycle to allow sperm to enter the uterus?

Answer 30

* Cervical mucus is normally hostile to sperm * This forms a physical barrier to sperm * Cervical mucus changes at mid-cycle * This change permits sperm to enter uterus