4.10 - The Reproductive System

Question 1

What do the testes do?

Answer 1

• male gonad
• produce sperm - spermatogenesis (produce mature spermatozoa)
• suspended in scrotum to keep temperature 2-3 degrees lower than rest of the body - any higher and sperm production ceases

Question 2

Describe the anatomy of the testes.

Answer 2

• a capsule surrounded by three connective tissue layers (inside –> outside):
• tunica vasculosa - contains blood vessels
• tunica albuginea - thick layer forming the septa that divides testis into lobules
• tunica vaginalis - covers testis and epididymis
• approximately 300 lobules each with 1-4 seminiferous tubules which have closed loops and drain into rete testis then epididymis for storage, then vas deferens
• vas deferens is surrounded by smooth muscle and is what is cut in vasectomy with minimal incision - also palpable
• arterial blood supply - testicular arteries from the aorta via the spermatic cord
• lymphatic drainage - para-aortic lymph nodes

Question 3

What does the epididymis do?

Answer 3

• a single tightly-coiled tube that stores and matures sperm - if not ejaculated, then broken down
• is palpable
• nutrients (e.g. fructose) and glycoprotein secretion into epididymal fluid (induced by androgens)

Question 4

What happens in the efferent ducts?

Answer 4

• tubular reabsorption resulting in concentration
• induced by oestrogen, which is formed from testosterone

Question 5

What does the vas/ductus deferens do?

Answer 5

Transports sperm from testicles to penis

Question 6

What do the prostate and seminal vesicles do?

Answer 6

Secrete seminal fluid to support ejaculated sperm

Question 7

What is seminal fluid made of?

Answer 7

• fructose
• citric acid (nutrient)
• bicarbonate (to neutralise vaginal acidity)
• fibrinogen (thickener)
• fibrinolytic enzymes

Question 8

What does the penis do?

Answer 8

Deposits sperm in vagina

Question 9

What three muscles make up the penis?

Answer 9

• 2 x corpora cavernosa
• 1 x corpora spongiosum

Question 10

What type of nervous stimulation leads to erection and ejaculation?

Answer 10

• Parasympathetic for erection due to arterial relaxation leading to increasing pressure obstructing venous drainage
• Sympathetic for ejaculation
• Point and Shoot

Question 11

What do the bulbo-urethral glands do?

Answer 11

Secrete sugar-rich mucus into urethra for lubrication and contribute to pre-ejaculatory emission from penis

Question 12

What is the spermatic cord?

Answer 12

• suspends the testes, formed at deep inguinal ring and passes along inguinal canal down to scrotum

Contains:

• vas deferens
• testicular artery
• pampiniform plexus of veins
• autonomic and GF nerves
• lymph vessels

Question 13

Which part of the female reproductive tract is situated in and which is out of the peritoneal cavity?

Answer 13

Ovaries are inside peritoneal cavity, remainder is outside

Question 14

What do the fallopian tubes do?

Answer 14

• lined by cilia and have spiral muscle = through peristalsis and wafting of cilia, the oocyte gets moved down the tube
• if this motility is slow then susceptible to ectopic pregnancies
• fertilisation usually occurs in ampulla - widest section

Question 15

What supports the uterus to stop it prolapsing out of the vagina?

Answer 15

Supported by tone of pelvic floor (levator ani and coccygeus muscles) and ligaments (broad, round, uterosacral)

Question 16

What are the layers of the uterus?

Answer 16

• serosa (peritoneal covering) - perimetrium
• myometrium (thick smooth muscle layer sensitive to hormones)
• endometrium (specialised epithelium)

Question 17

What happens to endometrium at the end of the menstrual cycle?

Answer 17

• endometrium shed at menses
• progesterone levels fall –> intermittent vasoconstriction of arterioles in endometrium –> ischaemia/necrosis causing shedding and haemorrhage of menstruation

Question 18

Where is the ureter around the cervix and why is it important?

Answer 18

• ureter is 1cm lateral to cervix on either side
• important when considering cervical cancer

Question 19

How is sterility maintained?

Answer 19

• all areas superior to cervix are sterile
• shedding of endometrium
• thick cervical mucus
• narrow external os (hole in middle of cervix)
• acidity - oestrogen stimulates vaginal epithelium to secrete glycogen which the bacteria digest producing lactic acid which lowers pH to kill other pathogens
• antibiotics can disrupt this causing overgrowth and infections like candiasis

Question 20

What kind of mucus does oestrogen vs progesterone promote?

Answer 20

• oestrogen promotes thin watery mucus allowing sperm to pass
• progesterone promotes thick viscous mucus - one of the methods of the progesterone only pill

Question 21

What is the arterial blood supply of ovaries and uterus?

Answer 21

• ovaries - ovarian arteries from aorta
• uterus/vagina - uterine arteries

Question 22

What is the lymphatic drainage of ovaries and uterus?

Answer 22

• ovaries = para-aortic lymph nodes
• uterus/vagina = iliac, sacral, aortic and inguinal lymph nodes

Question 23

What are male germ cell levels like across lifespan?

Answer 23

• gametogenesis begins at puberty
• spermatogonia undergo differentiation and self-renewal to maintain pool for subsequent spermatogenic cycles through life (continuous fertility)
• produce 1500 mature sperm/second

Question 24

What are female germ cell levels like across lifespan?

Answer 24

• before birth, multiplication of oogonia to 6mil/ovary
• form primary oocytes within ovarian follicles (= primordial follicle) which begin meiosis (halted in prophase)
• some primordial follicles degenerate (atresia) leaving 2mil/ovary at birth
• due to further atresia, by puberty <0.5mil/ovary remain

Question 25

What are the steps to spermatogenesis?

Answer 25

- happens in intratubular compartment of seminiferous tubules - 2n germ cell - spermatogonium (44XY) - diploid - mitosis - primary spermatocytes (44XY) - 1st meiotic division - secondary spermatocytes (22X or 22Y) - haploid - 2nd meiotic division - spermatids (22X or 22Y) - differentiation - spermatozoa (22X or 22Y)

Question 26

What are seminiferous tubules made of?

Answer 26

- tunica propria - several layers of flattened cells forming a basement membrane next to which spermatogonia lie - Leydig cells (between tubules) - Sertoli cells (within tubules) - spermatogonium - primary spermatocyte - spermatid

Question 27

How does spermatogenesis happen across the tubule?

Answer 27

- spermatogonia next to tunica propria mature and move inwards forming primary and secondary spermatocytes (latter is rarely seen) and ultimately spermatids that are released into duct - continuous fertility is achieved as spermatogenesis at different stages in different parts of tubule

Question 28

What do Sertoli cells do?

Answer 28

- have FSH receptors and are within seminiferous tubules - support developing germ cells by assisting their movement into tubular lumen, transfer nutrient from capillaries to them, phagocytosis of damaged germ cells - make inhibin and activin (has negative/positive feedback on FSH secretion from pituitary) - make anti-Mullerian hormone (AMH) to aid regression of Mullerian ducts in male sex development which otherwise would form fallopian tubes/uterus/cervix --> FSH promotes AMH transcription in absence of androgen signalling, testosterone inhibits - make androgen-binding protein (ABP)

Question 29

What do Leydig cells do?

Answer 29

- have LH receptors between seminiferous tubules - pale cytoplasm as cholesterol-rich - on LH stimulation, secrete androgens like testosterone, dehydroepiandrosterone (DHEA) and androstenedione (all aromatised to oestrogens)

Question 30

What are the steps to oogenesis?

Answer 30

- polar bodies - small haploid cells as oocyte cytoplasm does not divide evenly, undergoes apoptosis - 2n germ cell --> oogonium (44XX) - diploid - mitosis - primary oocytes (44XX) - 1st meiotic division - secondary oocytes (22X) + 1st polar bodies - haploid - 2nd meiotic division - ootids (22X) + 2nd polar bodies - differentiation - ova (22X)

Question 31

What happens to oogonia in 2nd trimester of pregnancy?

Answer 31

All oogonia in foetus develop into primary oocytes (forming primordial follicles)

Question 32

What is menarche?

Answer 32

- the first menstrual cycle (between 10-16 years old) - menarche --> first meiotic division - sperm fusion --> second meiotic division

Question 33

What are the steps to folliculogenesis (follicle development)?

Answer 33

1. primordial follicle (primary oocyte at birth) 2. primary (aka preantral) follicle - primary oocyte and layers of granulosa cells and outer theca cells 3. secondary (aka antral) follicle - fluid-filled cavity (antrum) develops and has FSH+LH receptors 4. mature (aka Graafian/preovulatory) follicle - forms due to LH surge and secondary oocyte formed 5. ruptures surface of ovary --> liberated ovum 6. corpus luteum - produces progesterone and oestrogen (stimulated by LH/hCG) and in pregnancy, production of these is taken over by placenta

Question 34

What do theca cells do?

Answer 34

- associated with outer part of ovarian follicles - bind LH to produce androgens - support folliculogenesis - structural and nutritional support of growing follicle - overactivity of theca cells is one of commonest causes of infertility due to hyperandrogenism

Question 35

What do the granulosa cells do?

Answer 35

- associated with inner part of ovarian follicles - bind FSH to aromatise androgens from theca cells to oestrogens (by aromatase) - secrete inhibin and activin (negative/positive feedback of FSH secretion from pituitary) - after ovulation they turn into granulosa lutei cells that produce progesterone (negative feedback on hypothalamus and anterior pituitary, and promotes pregnancy by maintaining endometrium) and relaxin (prepares endometrium for pregnancy and softens pelvic ligaments/cervix)

Question 36

How does the dominant follicle form?

Answer 36

- lots of follicles initially develop but dominant follicle takes over - as it produces most oestrogen (this shuts down FSH stimulation of other follicles)

Question 37

What is human steroidogenesis?

Answer 37

- granulosa can make progesterone but stops there, then gets androgens from theca cells to convert to oestrogens - in men, steroidogenesis occurs in Leydig cells - cholesterol is the basis

Question 38

Describe the hypothalamic-pituitary-gonadal (HPG) axis?

Answer 38

Kisspeptin --> GnRH (gonadotropin releasing hormone, hypothalamus) --> LH/FSH (pituitary, gonadotroph --> release) --> gonads (targets - testes/ovaries) --> oestrogen/testosterone/progesterone/androgen (target hormones)

Question 39

What effect does hyperprolactinaemia have on the HPG axis?

Answer 39

- prolactin binds to prolactin receptors on kisspeptin neurones in hypothalamus - inhibits kisspeptin release - decreases in downstream GnRH, LH, FSH, testosterone, oestrogen - leads to oligomenorrhoea (> 35 days menses) or amenorrhoea (3-6 month no menses) / low libido / infertility / osteoporosis

Question 40

What kind of release does GnRH and FSH/LH have?

Answer 40

Pulsatile

Question 41

What kind of rhythm do sex steroids (especially testosterone) have?

Answer 41

Diurnal rhythm