Male and Female Reproductive Physiology: Control of Testicular and Ovarian Function

Question 1

What cells are contained in the seminiferous tubules?

Answer 1

Germ cells

Sertoli cells

Question 2

What cells are contained in the interstitial space?

Answer 2

Leydig cells - secrete testosterone

Question 3

Do sertoli cells regenerate?

Answer 3

No, they have a constant number throughout adult life.

Question 4

What do sertoli cells do?

Answer 4

They regulate and support function of germ cells

Question 5

What regulates sertoli cell function?

Answer 5

Function dependent on Follicle Stimulating Hormone (FSH) and Testosterone.

Question 6

How are sertoli cells joined to each other?

Answer 6

Via tight junctions, this creates what is known as a blood testes barrier.

Question 7

What is the function of sertoli cells?

Answer 7

Protect spermatocyte/spermatids from autoimmune response; prevents toxins from entering tubules (blood-testes barrier and tight junctions between sertoli cells)

Support and nourish developing germ cells

Phagocytosis of residual cytoplasm during spermiogenesis

Release of spermatids into lumen of tubule (spermiation)

Secretory - >100 proteins including androgen binding protein (ABP), antimullerian hormone (AMH), and inhibin

Question 8

What is AMH important for?

Answer 8

Sexual differentiation

Question 9

What is ABP important for?

Answer 9

Transport and storage of androgens.

Question 10

How does spermatogenesis take place?

Answer 10

Rounds of mitosis form multiple stem cells from which to start producing sperm. (spermatogonium)

Rounds of meiosis to reduce chromosome number.

Cytoplasmic remodelling.

Question 11

What are the products of the mitotic phase of spermatogenesis?

Answer 11

Spermatogonium produce type A and type B spermatogonia. Type A stay as stem cells and keep forming more spermatogonia.

Type B spermatogonia become primary spermatocytes and undergo 1st meiotic division to form secondary spermatocytes then a 2nd.meiotic division to form spermatids

Question 12

Are primary spermatocytes diploid or haploid?

Answer 12

Diploid

Question 13

Are secondary spermatocytes diploid or haploid?

Answer 13

Haploid with homologous chromosomes next to each other.

Question 14

Are spermatids diploid or haploid?

Answer 14

Haploid with the chromosome number half of the secondary spermatocytes

Question 15

What does spermiogenesis produce?

Answer 15

It converts spermatids into spermatozoa

Question 16

How often is spermatogenesis undergone?

Answer 16

Stem cells enter into spermatogenesis approximately every 16 days and spermatogenesis takes approximately 64 days to complete..

Question 17

Why is it that males are often fertile all the time?

Answer 17

Because of the spermatogenic wave: Adjacent tubules are at different stages of the seminiferous cycle

Question 18

How is spermatogenesis controlled?

Answer 18

Via the hypothalamus - pituitary - gonadal axis.

GnRH -> FSH +LH:

FSH acts on sertoli cells to produce androgen receptors

LH acts on Leydig cells which produce androgens which act on sertoli cells by binding to androgen receptors.

Both of these together regulate spermatogenesis.

Question 19

What are the actions of testosterone?

Answer 19

Acts on sertoli cells to make sperm

Produces 5alphaDHT which is more potent than testosterone

Acts on pituitary and hypothalamus as negative feedback for LH secretion (reducing LH production)

Forms oestradiol which also acts as negative feedback

Question 20

What does inhibin B do?

Answer 20

It is produced by sertoli cells as negative feedback on the anterior pituitary which reduces FSH secretion.

Question 21

What are the stages of oogenesis?

Answer 21

Oogonium undergoes mitosis to produce more oogonia.

primary oocytes are produced during prophase of the first meiotic division but it stops there until just prior to ovulation.

Meiosis reduces number of chromosomes to form secondary oocyte. Meiosis forms 1 polar body and 1 viable secondary oocyte. Secondary oocyte is also arrested. This time at metaphase 2.

Second meiotic division results in ovum and 2 more polar bodies.

Ovum finishes meiosis after fertilization.

Question 22

When do oogonia normally first form?

Answer 22

Early in foetal life (first 20 weeks)

Question 23

When do follicles first develop?

Answer 23

Follicles and oocytes develop during embryonic life.

Question 24

When do oogonia undergo mitosis?

Answer 24

Maximum numbers at approximately 20 weeks of gestation.

Question 25

When does follicular atresia occur?

Answer 25

At any stage of follicular development.

Question 26

What is follicular atresia?

Answer 26

Hormonally controlled apoptosis.

Question 27

Why do follicles undergo apoptosis?

Answer 27

Due to absence of essential trophic factors during formation or maturation.

Question 28

Which stage of follicular growth and maturation is gonadotropin-independent?

Answer 28

The preantral stage. (first 270 days)

Question 29

What stage of follicle formation requires gonadotropins?

Answer 29

Conversion of a pre-antral follicle to an antral follicle.

Question 30

What are the stages of follicle maturation?

Answer 30

Primordial follicles are the first to develop during gestation. Pre-antral follicles form when oocyte starts growing and this occurs over 270 days. In response to gonadotropins antral follicles are formed More oestrogen stimulates antral expansion of one of the follicles and this is the dominant follicle. (dominant follicle increases in size from 7 - 25mm)

Question 31

Which cells produce androgens in follicles?

Answer 31

Granulosa cells cooperate with thecal cells to produce androgens.

Question 32

What surrounds a primordial follicle?

Answer 32

Single layer of squamous-like granulosa cells

Question 33

What surrounds pre-antral follicle.

Answer 33

It is also known as multi-laminar follicle due to presence of several layers of granulosa and thecal cells around the follicle.

Question 34

What forms the corpus luteum?

Answer 34

Formed from ruptured follicle - granulosa and thecal cells (after ovulation) Granulosa lutein and theca lutein cells.

Question 35

What happens when the corpus luteum is formed?

Answer 35

LH and angiogenic factors stimulate a rich vascular network that surrounds it. Cholesterol is sequestered within these cells to create progesterone.

Question 36

What does the corpus luteum secrete?

Answer 36

Progesterone Oestradiol Inhibin A

Question 37

What happens to corpus luteum in the absence of pregnancy?

Answer 37

It regresses after 12 - 14 days and forms scar tissue (Corpus albicans)

Question 38

What causes luteolysis?

Answer 38

Human Chorionic Gonadotropin stimulation. In primates it is not caused by decrease in LH or LH receptors

Question 39

What triggers endometrium buildup?

Answer 39

Oestrogen increase after ovulation. This is then maintained by progesterone which is produced from the corpus luteum

Question 40

How is the ovarian cycle controlled?

Answer 40

Via the hypothalamus - pituitary - gonadal axis. GnRH is produced -> FSH + LH produced FSH acts on granulosa cells to stimulate growth of the follicle. LH acts on thecal cells to produce androstenedione which go to granulosa cells to be converted to oestradiol which is then converted into oestrogen. Oestrogen acts autocrinally resulting in lots of oestrogen production which exerts a positive feedback loop of LH production increase

Question 41

What does oestradiol do?

Answer 41

It acts as negative feedback for the hypothalamus and the anterior pituitary gland. Decreases FSH and LH levels. Acts on granulosa cells to further stimulate growth of follicles. This results in an oestrogen surge.

Question 42

How do the thecal and granulosa cells produce oestradiol?

Answer 42

Thecal cell: LH stimulates cAMP cAMP increases cholesterol Cholesterol forms androstenedione Androstenedione goes to granulosa cell Granulosa cell: FSH activates cAMP which upregulates aromatase Androstenedione is converted by aromatase into 17beta oestradiol 17beta oestradiol is released into blood

Question 43

What 2 hormones stimulate granulosa cell proliferation?

Answer 43

Androgen + FSH

Question 44

What causes the oestradiol surge?

Answer 44

Aromatase activity increases E2 synthesis which results in granulosa cell proliferation which results in more E2 synthesis.