Gonads

Question 1

What are the gonads?

Answer 1

Testes in males

Ovaries in females

Question 2

What are the main functions of the gonads?

Answer 2

Gametogenesis

Steroidogenesis of Androgens (more in males) and Oestrogens/Progesterones (more in females)

Question 3

What are the names for immature sperm and egg cells?

Answer 3

Spermatogonia

Oogonia

Question 4

When does production of Oogonia ‘stop?’

Answer 4

After 24 weeks

Question 5

When does spermatogenesis begin?

Answer 5

Puberty - due to testosterone and gonadotrophin releasing hormone

Question 6

How long does spermatogenesis take?

Answer 6

~70 days in total

Question 7

Describe the steps of Spermatozoa production:

Answer 7

Germ Cells 44+XY

Differentiate to spermatogonia 44+XY

Mitotic division to primary spermatocytes 44+XY (50:50 to produce spermatogonia as well)

First meiotic division to produce secondary spermatocytes 22X/Y

Second meiotic division to produce spermatids 22X/Y

Spermatids become spermatozoa 22X/Y

Question 8

Describe the spermatogonia pool:

Answer 8

Undergo differentiation and self-renewal, so pool remains throughout life; males retain some capability for whole life - producing 300-600 sperm/gm testis/second (1000 sperm for every heartbeat)

Question 9

Describe Oogenesis:

Answer 9

Germ Cells 44XX

Differentiate to oogonia 44XX

Mitotic division to primary oocytes 44XX - early in embryogenesis, also develop a layer of cells around self to form a primordial follicle

Primordial follicles undergo arrest of meiosis until puberty

First meiotic division to produce secondary oocytes 22X and first polar body (just membrane and chromosomes - with no cytoplasm or resources)

Second meiotic division occurs to produce ovum 22X (retains all cell resources) with second polar body (that has no cell resources)

Question 10

What is the initial number of primordial follicles and how many remain by puberty?

Answer 10

6 million to 0.5 million

Due to atresia

Question 11

Describe the anatomy the testes:

Answer 11

Coiled seminiferous tubules connect to the rete testis.

Semen leaves the testis through the Vasa efferentia through the epididymis into the vas deferens

Question 12

What happens to the testis during puberty?

Answer 12

Testosterone causes maturation of coiled seminiferous tubules to allow spermatogenesis

Question 13

How does the Vas Deferens expel fluid?

Answer 13

Surrounded with smooth muscle

Question 14

What are the cells in the testes that produce Testosterone and androgens?

Answer 14

Leydig cells

Question 15

What are the cells present in the Seminiferous tubules, and how are they arranged?

Answer 15

Sertoli cells

Elongates, connected at periphery by tight junctions forming the blood-testes barrier.

Question 16

What does the blood-testis barrier do?

Answer 16

Stops blood molecules entering the tubules

Question 17

Where are spermatogonia present in seminiferous tubules?

Answer 17

Around the outside

Question 18

How do spermatogonia undergo maturation?

Answer 18

Cross membrane of sertoli cells, in which they mature and develop before release into the lumen of the tubule

Question 19

What receptors do Sertoli cells contain and why?

Answer 19

FSH/Androgen receptors which act as the primary control of spermatogenesis

Question 20

What happens when FSH binds to sertoli cells?

Answer 20

Inhibin and androgen binding protein produced which are associated with developing spermatocytes and forming their protective enviroment

Question 21

What is contained in the ovaries?

Answer 21

Graafian follicles
Follicles undergoing atresia
Corpus luteum

Question 22

What is a Graafian follicle?

Answer 22

Ovum in follicular fluid surrounded by Granulosa and Thecal cells

Question 23

What is the corpus luteum?

Answer 23

After an egg is released, the follicle converts to an empty corpus luteum

Question 24

When does the menstrual cycle start?

Answer 24

On the first day of bleeding.

Question 25

What are the two parts of the menstrual cycle?

Answer 25

Ovarian cycle - Follicular phase followed by luteal phase Endometrial cycle - Lining of uterus with superficial and deep stromal layer; proliferative phase followed by secretory phase

Question 26

What is the Proliferative phase of the Endometrial cycle?

Answer 26

Mitosis of cells lining uterus, causing wall thickening inducing oestrogen and progesterone receptors

Question 27

What is the secretory phase of the menstrual cycle?

Answer 27

Progesterone and oestradiol produced in the luteal phase causes the endometrium to stop proliferating by reducing oestrogen receptors whilst increasing secretory activity to make it suitable for implantation

Question 28

What are the four main hormones active in the menstrual cycle?

Answer 28

FSH LH Oestradiol Progesterone

Question 29

Describe the levels of FSH during the cycle:

Answer 29

Increased at beginning to stimulate follicles to start growing and developing oestradiol. Peaks around 13 days Looks like 'W'

Question 30

Describe levels of oestradiol during the cycle:

Answer 30

Negative feedback decreases of FSH levels Low at beginning Peaks at 12 days, peaks again (less) around 20 days (Looks like 'M')

Question 31

Describe the levels of LH during the cycle:

Answer 31

Surge of gonadotrophins on day 14 triggers ovulation of dominant follicle

Question 32

Describe the levels of Progesterone during the cycle:

Answer 32

Corpus luteum secretes progesterone (and a little oestrogen) to have a negative feedback effect, keeping LH/FSH low; decline if no fertilisation, so negative feedback lessons so LH/FSH rise to cause follicle maturation 

Question 33

Describe the four stages of the ovarian cycle:

Answer 33

Follicles spontaneously selected in groups for development to the pre-antral stage with no gonadotrophin stimulation FSH causes development to early antral follicles, growing and developing to late antral follicles, and producing oestrogen Dominant follicle selected, and others die in atresia, while dominant grows to Graafian follicles for ovulation After ovulation, forms corpus luteum; granulosum cells grow, enlarge and produce a lot of progesterone for release to the blood for 13-14 days

Question 34

Which days of the cycle are the proliferative phase and secretory phase?

Answer 34

Proliferative: 1-14 Secretory: 15-28

Question 35

Where does reduction of testosterone occur?

Answer 35

``` Reduction to Dihydrotestosterone: Prostate Testes Seminal vesicles Skin Brain Adenohypophysis ```

Question 36

Where does aromatisation of testosterone occur?

Answer 36

``` Aromatisation to oestrogens: Adrenals Testes Liver Skin Brain ```

Question 37

What are the principle uses of androgens?

Answer 37

Development of genitalia and promotion of foetal growth Spermatogenesis and growth of secondary sex characteristics in adults

Question 38

What are the main effects of Oestrogens?

Answer 38

Stimulate endometrial mitosis and LH surge in menstrual cycle Decreases renal salt reabsorption by competitively inhibiting aldosterone Negative feedback on gonadotrophin releasing hormone

Question 39

What are the main effects of progestogens?

Answer 39

Stimulates secretory activity in endometrium/cervix ready for implantation of eggs (Negatively regulates Gonadotrophin releasing hormone)

Question 40

Describe the Hypothalamo-Pituitary-Testicular Axis:

Answer 40

GnRH released in pulses every hour from hypothalamus Causes pulses of LH/FSH release from APG LH = endocrine, FSH = gametes LH stimulates Leydig cells to make testosterone FSH stimulates Sertoli cells to support spermatogenesis Testosterone negatively feedbacks hypothalamus/APG Inhibin produced by Sertoli cells also has negative feedback on hypothalamus/APG

Question 41

Describe the Hypothalamo-Pituitary-Ovarian Axis:

Answer 41

GnRH released in pulses every hour from hypothalamus Causes pulses of LH/FSH release from APG LH/FSH release oestradiol (feedback on LH/FSH) Inhibin release also has negative feedback on hypothalamus

Question 42

Name the 5 phases of the Menstrual cycle:

Answer 42

``` Early Follicular Early-mid follicular Mid follicular Late follicular Luteal Phase ```

Question 43

What happens in the early follicular phase?

Answer 43

Day 1 - Day 5; 5-10 eggs start to enlarge and grow, competing with each other to grow, so only one (Graafian) follicle will become dominant; FSH produced by APG causes follicles to grow and produce oestradiol 

Question 44

What happens in the early-mid follicular stage?

Answer 44

Follicles growing release oestradiol (begins to negatively feedback on LH/FSH to decrease levels; autocrine feedback loop arises, where more oestrogen production stimulates increased granulosa cell growth, in turn leading to more oestrogen 

Question 45

What happens in the Mid follicular stage?

Answer 45

Oestrogen and inhibin reduces FSH to LH to very low levels, so all follicles regress except the Graafian follicle 

Question 46

What happens in the Late follicular stage?

Answer 46

Oestrogen reaches high level and when bypasses threshold, causes a positive feedback loop on GnRH/LH secretion to cause an LH surge and ovulation

Question 47

What happens in the Luteal phase?

Answer 47

Corpus luteum produces progesterone (men should NOT produce) to prepare the endometrium for implantation 

Question 48

What happens if the egg is not fertilised by the end of the Luteal phase?

Answer 48

If no fertilisation then progesterone, oestrogen and inhibin have a direct negative feedback on the APG to reduce LH/FSH production, and indirectly on GnRH

Question 49

What is Amenorrhoea?

Answer 49

Absence of menstrual cycle

Question 50

What is the difference between primary and secondary amenorrhoea?

Answer 50

Primary: periods never start Secondary: periods stop after having some

Question 51

What is Oligomenorrhoea?

Answer 51

Infrequent periods; less than every six weeks

Question 52

What is Infertility defined as?

Answer 52

Couple unable to get pregnant following 12 months of regular unprotected sex; can be caused by pituitary failure, prolactinoma (prolactin inhibits LH/FSH), testicular failure (e.g. Klinefelter), ovarian failure (e.g. Turner's), polycystic ovarian syndrome (most common - 1in8)