Gonads

Question 1

What are the main functions of the gonads?

Answer 1

Production of gametes

Production of steroid sex hormones

Question 2

Outline the process of spermatogenesis.

Answer 2

1) Spermatogonia surrounding seminiferous tubules divide by mitosis, one daughter cell → 1°spermatocyte (2n), other daughter cell stays as spermatogonium to allow continual production of sperm
2) 1°spermatocyte moves through gaps between sertoli cells, crossing tight junction
3) 1° spermatocyte divided in meiosis 1 to produce 2 2° spermatocytes
4) 2 2° spermatocytes divide in meoisis 2 to produce 4 spematids which enter luminal compartments for nutrition
5) Spermatids differentiate to spermatozoa in spermiogenesis
6) Spermatozoa travel to epididymis for flagella development and mitochondrial gain

Question 3

What is spermatogenesis?

Answer 3

Male gametogenesis
Begins at puberty in response to testosterone and GnRH
Spermatogonia pool constantly replaced ∴ not depleted with age
1000 sperm per heartbeat

Question 4

What is oogenesis?

Answer 4

Female gametogenesis
Occurs in utero but delayed to be finished after puberty
2-4 million eggs created in utero, decreases to 0.5m by puberty due to atresia

Question 5

Outline the process of oogenesis.

Answer 5

1) Oogonia (2n) germ cells divide by mitosis to produce oogonia in utero
2) Oogonia differentiate to 1° oocytes and a layer of granulosa cells form primordial follicle
3)1°oocytes being meiosis 1 but undergo meiotic arrest UNTIL AFTER PUBERTY
4) Few primordial follicles per menstrual cycle are selected and proceed with meiosis forming 2° oocyte (N) and 1st polar body
5) Graafian follicle’s 2° oocyte released, and when fertilised, second meiotic division occurs to form an ovum and a 2nd polar body
(failure to fertilise = no ovum, no 2nd meiosis)

Question 6

What are key differences between female and male gametogenesis?

Answer 6

Pool of spermatogonia remain available throughout life
Gametogenesis occurs at puberty in males, but is started in utero in females
All cells produce oocytes in oogenesis, but 50:50 spermatogonia spermatocyte ration in males
Polar bodies formed in oogenesis instead of two cells
Meiosis 2 only occurs in oogenesis if egg is fertilised, produces 1 ovum, meiosis 2 produces 4 spermatids in spermatogenesis

Question 7

What are the testes and how do they develop?

Answer 7

Male sexual endocrine gland
Increased testosterone at puberty causes testes maturation and spermatogenesis
Development occurs in abdomen before descension to scrotum to ensure 2-3°C below core temp for spermatogenesis

Question 8

What are the main structures within the testes and their purposes?

Answer 8

Seminiferous tubules
-coiled tubules packed into testes, lumen surrounding it packed with sertoli cells, tight junctions prevent blood entering lumen but spermatocytes can cross for maturation
Sertoli cells
-have FSH/androgen receptors
-control spermatogenesis
-produce inhibin and androgen binding protein
Leydig cells
-outside tubules
-LH receptors
-Respond to stimulation by producing testosterone
Vasa efferentia
-drain sperm from the rete testis to the epididymis
Epididymis
-Secrete nutrients and allow sperm to gain flagella and mitochondria
Vas deferens
-Surrounded by smooth muscle to allow expulsion

Question 9

What are the main structures found in ovaries?

Answer 9

Follicles
-Formed before birth
-Contain oocytes and other layers of cells
-Some undergo atresia, others maturing
Graafian follicles
-1°oocyte in follicular fluid surrounded by granulosa and then thecal cells
Corpus luteum
- after egg is released, follicle becomes empty corpus luteum

Question 10

What are the phases of the menstrual cycle?

Answer 10

1) Early follicular phase
2) Early-mid follicular phase
3) Mid follicular phase
4) Late follicular phase
5) Luteal phase

Question 11

What is the menstrual cycle?

Answer 11

representation of the ovarian and endometrial cycles together
28 days
starts on the first day of bleeding

Question 12

What are the physiological changes associated with the early follicular phase of the menstrual cycle?

Answer 12

5-10 eggs start to enlarge and compete with each otehr to grow (only one can become the Graafian follicle of this cycle)
Pulsatile release of GnSH leads to secretion of FSH from APG
Stimulates follicle growth and production of oestradiol

Question 13

What are the physiological changes associated with the early-mid follicular phase of the menstrual cycle?

Answer 13

Follicles growing release oestradiol
-negatively feeds back on LH/FSH to decrease levels
More oestradiol production stimulates increased granulosa cell growth, leading to more oestradiol - autocrine feedback

Question 14

What are the physiological changes associated with the mid follicular phase of the menstrual cycle?

Answer 14

Oestradiol and inhibin reduce FSH
Causes all follicles to undergo atresia apart from Graafian follicle
Graafian follicle no longer requires FSH to devlop and keeps growing and producing oestradiol

Question 15

What are the physiological changes associated with the late follicular phase of the menstrual cycle?

Answer 15

High oestradiol eventially bypasses a threshold causing a +ve feedback loop on GnRH/LH secretion
Surge in LH causes ovulation

Question 16

What are the physiological changes associated with the luteal phase of the menstrual cycle?

Answer 16

Corpus luteum produces progesterone to prepare the endometrium for implantation
If no fertilisation:
-progesterone, oestrogen and inhibin have direct -ve feedback on APG to inhibit FSH, LH and GnSH
-without FSH corpus luteum atrophies
-CL stops producing progesterone and oestrogen ∴ no longer inhibiting APG and FSH begins to prepare the next eggs

Question 17

Explain the endocrine regulation of the menstrual cycle.

Answer 17

FSH increased @ start, stimulats follicle growth, growth and devlopment = oestradiol
Oestradiol hs -ve feedback effect, causes decrease in FSH
High oestradiol causes surge in LH at day 14 to trigger ovulation of dominant follicle
Corpus luteum secretes progesterone , -ve feedback keeps LH and FSH low
Decline in progesterone if no fertilisation, -ve feedback lessens ∴ FSH/LH rise to cause follicle maturation again

Question 18

What are the phases of the endometrial cycle and their triggers?

Answer 18

Proliferative phase influenced by oestrogen from the maturing follicles
Secretory phase influenced by progesterone from corpus luteum

Question 19

What are the features of the proliferative phase of the endometrial cycle?

Answer 19

mitosis of cells lining uterus causes wall to thicken
induces oestrogen and progesterone receptors
Glands enlarge and coil; increased blood supply

Question 20

What are the features of the secretory phase of the endometrial cycle?

Answer 20

Endometrium stops proliferating due to progesterone
Reduces oestrogen receptors and increases secretory activity to make suitable for implantation
Glands secrete; mucosa are engorged with blood
at end of secretory phase endometrium becomes necrotic and is shed

Question 21

Explain the process of testicular steroidogenesis

Answer 21

Occurs in Leydig cells when stimulated by LH
Testosterone produced from cholesterol
Cholesterol → pregnenolone → progesterone → testosterone

Question 22

Explain the process of ovarian steroidogenesis

Answer 22

Oocytes surrounded by granulosa cells then thecal cells with LH receptors
LH binding to receptors causes thecal cell stimulation to produce androgens
Androgens diffuse to granulosa cells, which have FSH receptors
FSH binding to receptors activates aromatase
Converts androgens to oestradiol
In corpus luteun phase androgens converted to progesterone

Question 23

What happens to testosterone after it is produced?

Answer 23

Reduced to DHT by 5α-reductase in prostate, testes, seminal vesicles,skin, brain and adenohypophysis
Aromatised to oestradiol using aromatase in adrenals, testes, liver, skin and brain

Question 24

How is testosterone/DHT transported?

Answer 24

60% bound to globulin, 38% to albumin, 2% in blood
Sex hormone binding globulin in blood
Androgen binding globulin in seminiferous fluid

Question 25

What are the principle actions of androgens in the foetus?

Answer 25

development of male internal/external genitalia and promotion of foetal growth

Question 26

What are the principle actions of androgens in adults?

Answer 26

Spermatogenesis
growth of 2° sexual characteristics
protein/bone anabolism
male sexual behaviour
pubertal growth spurt
Effects mediated by conversion to oestrogen

Question 27

What are the reproductive effects of oestrogens?

Answer 27

Stimulates:
endothelial proliferation and LH surge in menstrual cycle
vaginal secretions
breast growth
decreases sebaceous gland secretion

Question 28

What are other effects of oestrogens?

Answer 28

Feedback on GnRH
Stimulate osteoblasts
Metabolic actions and behavioural effects :
-increased salt reabsorption
-plasma protein synthesis
-rate of hormone release

Question 29

What are the main effects of progestogens in the human body?

Answer 29

Stimulates secretory activity in endometrium/cervix
-vely regulates GnRH
Increases basal body temp
Stimulates breast alveolar system growth
Decreases renal salt reabsorption - competitive inhibitor for aldosterone

Question 30

Outline the hypothalamo-pituitary-testicular axis.

Answer 30

1) GnRH released in pulses each hour from hypothalamus
2) GnRh causes pulsative LH/FSH release from APG
3) LH stimulates Leydig cells to produce testosterone
4) FSH stimulates sertoli cells to support spermatogenesis

Question 31

How is the hypothalamo-pituitary-testicular axis regulated?

Answer 31

Testosterone exerts a -ve feedback loon on hypothalamus and APG
Inhibin produced by sertoli cells also has -ve feedback loop

Question 32

Outline the hypothalamo-pituitary-ovarian axis.

Answer 32

1) GnRH released in pulses each hour from hypothalamus
2) Causes pulsatile release of LH/FSH from APG
3) FSH causes follicle maturation
4) Maturing follicles produce oestrogen - has -ve feedback on APG and hypothalamus
5) High oestrogen activates +ve feedback receptors in hypothalamus to cause LH surge
6) Corpus luteum secretes progesterone - -ve feedback FSH/LH, if egg not fertilised then will reduce to allow new cycle

Question 33

What is amenorrhoea, and what is the difference between primary and secondary amenorrhoea?

Answer 33

Absence of menstrual cycles
1° if never had a period
2° absence for 3 months or more in woman who has previously had cycles

Question 34

What are potential causes of 2° amenorrhoea?

Answer 34

Lactation/pregnancy

hyperprolactinaemia

Question 35

Define infertility

Answer 35

couple unable to get pregnant after 12 months of regular unprotected sex

Question 36

What are potential causes of infertility?

Answer 36

Pituitary failure
Prolactinoma
Testicular failure e.g. mumps, kleinfelters
Ovarian failure e.g. turners
Polycystic ovary syndrome - infrequent periods
Hyper-androgenaemia