1. Reproductive Physiology

Question 1

What two systems are connected in males? What impact does this have?

Answer 1

The testes is connected with the urinary system which also deals with the provision of sperm.
This means that if one of these systems malfunctions it is likely to impact the other one

Question 2

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

Answer 2

The provision of androgens (mainly testosterone) to initiate and sustain the male sexual features
The production of mature sperm.

Question 3

How do testosterone levels change in a male as he ages?

Answer 3

Testosterone has an important function before birth but this is reduced in the first 12 years of life where testosterone is greatly reduced. Kicks in again during puberty

Question 4

Outline the structure of the male reproductive tract and sperm secretion

Answer 4

The male reproductive tract can be seen as the epididymis, going through the vas deferens which loops around the bladder and joins the ureter in the penis where the sperm will come out
There is one epididymis within each scrotal sac. Sperm are released from the testis and stored here prior to ejaculation. At ejaculation sperm pass through the two Vas Deferens (which are contractile), and is mixed with fluid from the seminal vesicles. The fluid then leaves the ejaculatory duct, and passes into the urethra where it mixes with secretions from the prostate gland.

Question 5

What are the main hormones that control male reproduction and where are they released from?

Answer 5

Gonadotrophin releasing hormone (GnRH) – from the hypothalamus (acts on the pituitary)

Luteinising hormone (LH) and Follicle stimulating hormone (FSH) – from the anterior pituitary

Testosterone (T) – Testis

Question 6

What is the initial hormone that is released which causes the secretion of other male hormones?

Answer 6

GnRH produced in hypothalamus, and acts on the anterior pituitary to give rise to FSH and LH (enter the bloodstream, but only have effects on the testes).

Question 7

How are LH and FSH released from the anterior pituitary?

Answer 7

LH release is pulsatile and FSH also has some pulsality

Question 8

Where does LH act? What does it give rise to?

Answer 8

Leydig cells: lie outside of the seminiferous tubules in the interstitial compartment of the testes. They are the primary source of androgens in ALL male mammals. This gives rise to testosterone, which is released into the testes. LH acts here.

Question 9

How is testosterone production regulated?

Answer 9

The testosterone produced by the leydig cells negatively feedbacks to the hypothalamus to suppress the production of GnRH and LH causing a fall in testosterone production

Question 10

Where does the FSH produced by the anterior pituitary act? What is its function?

Answer 10

FSH acts on sertoli cells in the seminiferous tubules which support the process of spermatogenesis as they convert precursors of sperm into mature sperm. FSH is critical for all reproductive processes in males. Function of Sertoli cells is driven by FSH and testosterone together.

Question 11

How is FSH production controlled?

Answer 11

Sertoli cells produce inhibin, an inhibitory peptide that acts on the HPA and inhibits the production of FSH

Question 12

What are the two general parts of the testes?

Answer 12

The testes is made up of two compartments – the interstitial compartment where the Leydig cells are and the seminiferous tubules where sperm are produced

Question 13

Why are there more primary spermatocytes than mature sperm?

Answer 13

In the initial stages of sperm division, we start of with normal mitotic division so the cells remain diploid but in the latter stages there is a switch to miotic division so haploid sperm are produced
As mitosis produces four cells, there are many more cells that are developed through mitotic division that the later miotic division. This means there is a very large pool of primary spermatocytes which then converge into mature sperm

Question 14

What happens to sperm with increasing age?

Answer 14

Sperm quantity and quality generally decreases with increasing age

Question 15

What happens to egg cells with increasing age?

Answer 15

Egg quality generally decreases with increasing maternal age – at around 35 years is the point where this is most noticeable

Question 16

What are the functions of LH and FSH in women?

Answer 16

FSH stimulates (some) development of ovarian follicles and 17beta-oestradiol synthesis 
LH stimulates progesterone production and also has a role in sustaining oestradiol  
The steroids regulate uterine endometrium during the menstrual cycle

Question 17

What are the hormones involved in the female reproductive tract? Where are they released from and where do they act?

Answer 17

LHRH released from the hypothalamus, going to the pituitary to release LH
LHRH also drives FSH production from the pituitary gland.
LH and FSH act on the ovaries. The ovaries give rise to progesterone and oestrogen (which themselves feedback on the hypothalamus and pituitary gland). These then act on the uterus rather than the LH and FSH itself.

Question 18

What are the different phases of the ovarian cycle?

Answer 18

Follicular phase - first 10 days
Mid-cycle/Ovulation
Luteal phase - last 10-15 days

Question 19

How do the hormone levels and their actions change throughout the ovarian cycle?

Answer 19

In the follicular phase the main follicle is being matured in the ovaries. GnRH is produced causing LH and FHS production. The ovaries are stimulated with estradiol which negatively feedbacks to the hypothalamus.
In the mid-cycle, the system changes. Oestradiol begins to exert a positive feedback effect, to enhance the activity of the hypothalamus and pituitary to release GnRH instead of suppressing it leading to LH/FSH being produced. There is the LH SURGE at this point in the cycle which causes the switch in mechanism to a positive feedback one. The ovary is still making oestradiol at this point.
The hormones continue to increase - this is the buildup to ovulation
In the luteal phase (occurs once ovulation has taken place), the feedback mechanism goes back to negative. However, progesterone is mainly being produced instead of oestrogen from the ovary - previously both hormones were being produced from the ovaries but oestrogen was dominant. There is still negative feedback.

Question 20

What happens to hormones during pregnancy?

Answer 20

Progesterone levels RISE, and continues to do so for the whole length of pregnancy
This switches off the whole hypothalamic-pituitary axis
The menstrual cycle completely comes to a halt during pregnancy (due to progesterone –ve feedback)

Question 21

How does the thickness of the endometrium vary?

Answer 21

At minimum, the endometrium is between 2-4 mm thick and at maximum it can be 2-16mm thick

Question 22

What causes the thickness of the endometrium to change?

Answer 22

The proliferation of the endometrium is driven by the steroids produced in the developing follicle
The high levels of oestrogen produced by the follicle in the first part of the ovarian cycle feed into the early part of the development of the endometrium whereas the combination of progesterone and oestrogen feeds into the second part of the endometrial cycle and further increases the thickness of the lining

Question 23

Why is a thick endometrium lining needed?

Answer 23

This peak thickness of the endometrium is when implantation would be expected

Question 24

What are the two parts of the endometrial cycle and which hormones control them?

Answer 24

The first part of the endometrial cycle is the proliferative phase, led by oestrogen, and the second part is the secretory phase, led by progesterone

Question 25

How do the endometrial and ovarian cycles interlink?

Answer 25

The follicular and proliferative stage occur simultaneously as do the luteal and secretory phase

Question 26

What causes the endometrium to break down during menstruation?

Answer 26

Gonadotrophin levels fall during the luteal phase, towards the end the menstrual cycle, so there is also a low level of activity from the corpus luteum which all causes the endometrium to break down

Question 27

What are primordial follicles?

Answer 27

Developed during female interuterine life. A girl is born with many primordial follicles but not all of them will turn into mature eggs. There is a gradual development from a primordial follicle to a primary follicle

Question 28

Outline the process of oogenesis

Answer 28

We start with a primary oocyte, living inside a primordial follicle
The early stages are not dependent on LH and FSH
This is NOT MONTHLY – it takes place over a longer time period. The conversion of a primary follicle through to ovulation takes about 3 months
The follicle starts growing independent of the sex hormones
Eventually, one follicle becomes dominant – it grows more quickly than the others
The dominant follicle enters the secondary part of the development, to become the antral follicle
The antral follicle gives rise to the egg that is released
The other follicles enter the process of atresia and break down
Normally, one ovary produces one dominant follicle per cycle (not always the case)

Question 29

How long does the process of oogenesis/folliculogeness take?

Answer 29

3 months

Question 30

When is the first meiotic division of oogenesis completed and what happens after this?

Answer 30

The first meiotic division is completed during the formation of the secondary follicle, linked to the LH surge. Meiosis II follows immediately after this, but pauses in metaphase II

Question 31

How is a single follicle released from the ovaries?

Answer 31

The human ovaries contain multiple follicles at all stages of development at any time, with one dominant follicle entering the later stages to form a secondary (Graafian) follicle.
The ovaries usually alternate the release of the follicle

Question 32

Outline the process of meiosis in oogenesis

Answer 32

Both the first meiotic division and the second meiotic division are paused during follicle development. Meiosis I starts during embryonic development, but halts at the diplotene stage of prophase I (primary follicle); this persists until puberty when meiosis resumes as secondary follicles develop. Only fertilisation can cause the completion of meiosis in a human oocyte

Question 33

What happens to the gametes during fertilisation?

Answer 33

The sperm swims to where the egg is in the fallopian tube. It starts binding to the zona pellucida on the outside of the egg. The sperm produces digestive enzymes to digest their way through the zona pellucida. Eventually, one sperm will RELEASE its nucleus into the cytoplasm of the egg.
The nucleus then begins to expand rapidly in size, and converts itself to the male pro-nucleus (haploid). Simultaneously, the egg completes meiosis, and switches from being 2n chromosomes to n chromosomes (becomes haploid). We end up with a female pro-nucleus. The two pro-nuclei merge to form a group of 2n chromosomes.

Question 34

What happens after fertilisation?

Answer 34

Meiosis of maternal chromosomes resumes, forming female pro-nucleus (23 chromatids), and 2nd polar body
Sperm chromosomes de-condense to form male pro-nucleus (23 chromatids)
Chromatids in both pro-nuclei are duplicated
They align on the mitotic spindle, and are separated into 2 identical ‘daughter’ cells
This is done at the 1st cleavage division of the embryo