The Reproductive System

Question 1

What 5 chemicals is the seminal fluid composed of?

Answer 1

Fructose, Citric acid, Bicarbonate to neutralise acidic vaginal environment, Fibrinogen to thicken and Fibrinolytic enzymes.

Question 2

Describe anatomy of the penis

Answer 2

Consists of 3 muscles: 2 corpora cavernosa and 1 corpora spongiosum. Also contains the urethra and surface lined with foreskin.

Question 3

What is the function of the corpora cavernosa and corpora spongiosum?

Answer 3

The penis is composed of three cylinders encased in a sheath called the bucks fascia. These three cylinders are the corpus spongiosum and two corpora cavernosa known as the corpus cavernosum of penis. The corpus cavernosum forms most of the penis and contains blood vessels that fill with blood to help make an erection. The corpora spongiosum is a column of spongy tissue that runs through the shaft (body) and glans (head) of the penis. The corpus spongiosum surrounds the urethra (the tube through which urine and sperm pass from the body). It contains blood vessels that fill with blood to help make an erection and keep the urethra open during the erection.

Question 4

What autonomic systems control erection and ejaculation?

Answer 4

Parasympathetic stimulation causes erection and Sympathetic stimulation causes ejaculation - point and shoot.

Question 5

What are the 9 structures found in the spermatic cord?

Answer 5

vas deferens, testicular artery, pampiniform plexus of veins, autonomic nerves, lymph vessels, artery of vas, cremasteric artery, genital branch of genitofemoral nerve, remnants of processus vaginalis

Question 6

Describe anatomy and function of: Testes, Epidydimis, Vas Deferens, Prostate+Seminal Vesicles, Penis, Bulbo-urethral glands, Spermatic Cord

Answer 6

Testes- produce sperm; suspended in scrotum to keep temperature 2-3 degrees lower than body. If temp increases then sperm production ceases.

Epidydimis – stores and matures the sperm – if not ejaculated -> broken down

Ductus (vas) deferens- transports sperm to penis

Prostate (Chestnut, PR) and seminal vesicles- secrete seminal fluid to support ejaculated sperm

Penis- deposits sperm in vagina – made up of 3 muscles (2x corpora cavernosa and 1 x corpus spongiosum). Erection is due to arterial relaxation due parasym stim, which results in increasing pressure which obstructs venous drainage

Bulbo-urethral glands just below prostate (= Cowpers glands), secrete sugar-rich mucus into urethra for lubrication and contribute to pre-ejaculatory emissions from penis.

Spermatic cord suspends the tests, is formed at deep inguinal ring and passes along inguinal canal and then down to scrotum.

Question 7

Describe arterial blood supply and lymphatic drainage of testes

Answer 7

Testicular arteries from the aorta via the spermatic cord form arterial supply. Para-aortic lymph nodes responsible for lymphatic drainage.

Question 8

Describe anatomy of capsule of testes

Answer 8

Each testis is surrounded by a capsule of 3 connective tissue layers (starting nearest the testis):
Tunica vasculosa – contains blood vessels.
Tunica albuginea is thick layer that forms the septa dividing the testis into lobules.
Tunica vaginalis covering testis AND epidydimis.

Question 9

Describe inner anatomy of testes

Answer 9

Containes approx 300 lobules in each testis separated by septa. Each lobule contains 1-4 coiled seminiferous tubules which have closed loops. Seminiferous tubules drain into rete testis and then the epidydimis for storage which is a comma-shaped structure that can be palpated. It is a single, tightly coiled tube. At the end is the vas deferens.

Question 10

Describe anatomy and function of vas deferens

Answer 10

Vas deferens surrounded by smooth muscle, and travels with the testicular artery/veins/nerves in the spermatic cord. Easily palpable in scrotum ‘ this allows male sterilisation by vasectomy with only minimal incision. Empties into the junction with the duct of the seminal vesicle.

Question 11

Describe arterial supply and lymphatic drainage of three major organs of female reproductive system

Answer 11

Ovaries supplied by ovarian arteries (from aorta). Lymphatic drainage by para-aortic LNs. Uterus and vagina supplied by uterine arteries (from internal iliac a). Lymphatic drainage by Iliac, sacral, aortic and inguinal LNs.

Question 12

Describe anatomy of ovaries and fallopian tube

Answer 12

The ovaries are found in the peritoneal cavity while remainder is outside. Fallopian tube with its fimbriae open into this cavity. Fallopian tubes lined by cilia and have spiral muscle surrounding this lining (sensitive to oestrogen levels). Fertilisation usually occurs in widest section- called ampulla.

Question 13

What increases susceptibility to ectopic pregnancy?

Answer 13

Through peristalsis and wafting of cilia in fallopian tube the oocyte gets moved down the tube. If motility is slow then susceptible to ectopic.

Question 14

Describe anatomy of uterus

Answer 14

Uterus supported (preventing prolapse into vagina) by tone of pelvic floor (levator ani and coccygeus muscles) + ligaments (such as broad ligament and round ligament and uterosacral ligaments). The fundus is found at superior end of uterus. Uterus lined by specialised epithelium called the endometrium. Layers of uterus: serosa (peritoneal covering), myometrium (thick smooth muscle layer sensitive to hormones (eg oxt) and endometrium.

Question 15

What causes menstrual bleeding?

Answer 15

Arterioles of superficial endometrial layer have spiral appearance and as prog levels fall at end of menstrual cycle-> intermittent vasoconstriction -> ischaemia/necrosis causing shedding and haemorrhage of menstration. Endometrium therefore shed.

Question 16

How is sterility maintained in female reproductive system?

Answer 16

Infection can travel from external into peritoneal cavity (causing peritonitis) hence CERVIX acts as a barrier. Sterility maintained by:

1. frequent shedding of endometrium
2. thick cervical mucus
3. narrow external os
4. acidity (oestrogen stimulates the vaginal epithelium to secrete glycogen which the lactobacilli digest releasing lactic acid; this lowers the pH of the vagina below 4.5 so preventing infection by other organisms.)

Antibiotics can disrupt this natural flora causing overgrowth and infections such as candidiasis (thrush)

Question 17

How do different hormones alter vaginal discharge?

Answer 17

Oestrogen promotes thin watery mucus (allowing sperm to pass) while prog promotes thick viscous mucus- this is one of the methods by which the progesterone only pill works.
Cells around external os collected and examined in smear test.

Question 18

How is the vagina lubricated during sexual arousal?

Answer 18

During sexual arousal, vagina lubricated by secretions from the greater vestibular (Bartholins) glands next to the introitus (external vaginal orifice).

Question 19

Describe gametogenesis in males

Answer 19

Gametogenesis begins at puberty. Spermatogonia undergo differentiation and self-renewal so pool available for subsequent spermatogenic cycles throughout life (continuous fertility). Produce ~1,500 mature sperm/second.

Question 20

Describe gametogenesis in females

Answer 20

Before birth, a multiplication of Oogonia to ~ 6 million/ovary occurs. Form first stage Oocytes within ovarian follicles (= primordial follicle). These begin meiosis (halted in prophase). Some primordial follicles degenerate (atresia). At birth ~2 million/ovary remain
PUBERTY. By puberty <0.5 million/ovary remain (due further atresia).

Question 21

Describe process of spermatogenesis

Answer 21

Spermatogonium is 44XY and undergoes mitosis producing 44XY first stage spermatocyte. This undergoes first meiotic division to form second stage spermatocyte with 22X or 22Y. Second meiotic division forms spermatids and finally differentiation occurs to form spermatozoa. Process occurs within intratubular compartment of seminiferous tubules and takes ~ 64 days till ready for release. 1500/second.
Germ cells are diploid (46ch) but final spermatozoa are haploid (23ch).

Question 22

Describe structure of seminiferous tubule

Answer 22

Each seminiferous tubule is surrounded by tunica propria, composed of flattened cells, several cells thick forming a basement membrane. Most of the cells that lie against the basement membrane and have round nuclei are spermatogonia. These then mature as they move inwards forming primary and secondary spermatocytes (rarely seen) and ultimately the spermatids that are released into duct.

Sertoli Cells are within the tubule and support spermatogenesis by secreting hormones. Leydig cells are found outside the tubules, which secrete hormones.

Question 23

What is the function of Sertoli cells?

Answer 23

1. Support developing germ cells by assisting movement of germ cells to tubular lumen, transfer nutrients from capillaries to developing germ cell and [phagocytosis of damaged germ cells.
2. Hormone synthesis - Inhibin & Activin (-ve or +ve on FSH), Anti-Mullerian Hormone (AMH), Androgen-Binding Protein (ABP)
   Has FSH receptors

Question 24

What is the purpose of inhibin and activin?

Answer 24

Inhibin and activin provide -ve and +ve feedback respectively on FSH secretion from thepituitary.

Question 25

What is the purpose of AMH?

Answer 25

AMH is glycoprotein produced by immature Sertoli cellsto aid regression of Müllerian ducts in male sex development which would otherwise go onto form the fallopian tubes/uterus/cervix.

Question 26

What is the purpose of ABP?

Answer 26

ABP directs T from leydig cells to germ cells. ABP release stimulated by FSH.

Question 27

How do inhibin B, FSH, AMH and testosterone interact?

Answer 27

Inhibin B expression and secretion are positively correlated with Sertoli cell function, sperm number, and are negatively correlated with FSH.
Follicle-stimulating hormone (FSH) promotes AMH transcription in the absence of androgen signaling, whiletestosteronehas been shown to inhibit the transcriptional activation of AMH.

Question 28

What are the notable features and function of Leydig cells?

Answer 28

Found between seminiferous tubules. Have a pale cytoplasm as cholesterol-rich and have LH receptors. Main function is hormone synthesis. On LH stimulation, secrete androgens: Testosterone (oestrogens), Androstenedione, Dehydroepiandrosterone (DHEA) (can be aromatised to oestrogens).

Question 29

Describe female gametogenesis

Answer 29

Oogonium containing 44XX undergoes mitosis in the 2nd trimester of pregnancy forming 1st-degree oocyte. These undergo meiotic division to form 2nd-degree oocytes containing 22X at menarche. Upon sperm fusion undergoes a second meiotic division to form ootids which differentiates into ova.

Question 30

Why do females have a limited number of oocytes?

Answer 30

Oognium are formed from the germ cells. Initially around 6 million oogonia per ovary. In 2nd trimester of pregnancy all oogonia develop into 1o oocytes and enter the 1st meiotic division (prophase). Meiotic division halted at this stage until menarche. Granulosa cells surround the oocyte to form primordial follicles.
As no more oogonia, then impossible to increase the number of oocytes – and so the entire oocyte reserve is formed at birth (~2 million per ovary due atresia). By puberty down to <0.5million/ovary.

Question 31

How is the ova produced?

Answer 31

At menarche, a few primordial follicles recommence growth partly dependent on FSH. Secondary oocytes are produced and released that are capable of fertilisation. First polar body (small haploid cell with virtually no cytoplasm) degenerates. Fusion of 2o oocyte and sperm causes calcium influx resulting in stimulation of the 2nd meiotic division forming the ova (ovum) – this is the functional gamete.

Question 32

Describe folliculogenesis in the ovary

Answer 32

A primordial follicle is present at birth containing the first degree oocyte and this develops into a primary follicle containing layers of granulosa cells and outer theca cells along with the oocyte. At menarche, the follicle develops into a secondary follicle where fluid-filled cavity (antrum) develops along with FSH and LH receptors. It develops into a mature/Graafian follicle once oocyte matures to form a 2nd-degree oocyte and is formed due to an LH surge. The follicle then ruptures during ovulation and the ovum is released. Remaining follicular structure forms the corpus luteum. This produces progesterone & oestrogen (stim by LH/HCG). If fertilised, maintains hormone levels for first few weeks of pregnancy. Later, progesterone & oestrogen production taken over by placenta.

Question 33

What is the purpose of Theca cells?

Answer 33

Associated with outer part of ovarian follicles.
1. Support folliculogenesis
Structural & nutritional support of growing follicle
2. Hormone synthesis
LH stimulates synthesis of androgens - play an essential role in fertility by producing the androgens (from cholesterol) required for ovarian estrogen biosynthesis.
Overactivity -> hyperandrogenism which is one of the commonest causes of infertility. PCOS also caused by overstim of Theca cells.
Vascular system allows for communication with pituitary axis and delivery of nutrients to these very active cells.

Question 34

What happens to Theca cells in follicles that ovulate?

Answer 34

During development, the majority of follicles undergo atresia, and the theca cells are often the final follicular cell type to die. For those follicles that do ovulate, the theca cells then undergo hormone-dependent differentiation into luteinized thecal cells of the corpus luteum

Question 35

What is the function of Granulosa cells?

Answer 35

Associated with inner part of ovarian follicles.
1. Hormone synthesis
FSH stimulates granulosa cells to convert androgens to oestrogens (by aromatase). Secrete Inhibin & Activin. (effects on FSH)
2. After ovulation
Turn into granulosa lutein cells that produce:
Progesterone (-ve feedback, promote pregnancy by maintaining endometrium)
Relaxin (helps endometrium prepare for pregnancy and softens pelvic ligaments/cervix)

Question 36

What is the function of inhibin and activin?

Answer 36

Inhibinsare polypeptides secreted by the (Sertolicellsin the testis)granulosa cellsin the ovary, which inhibit thereleaseof FSH but not LH from the pituitary.Inhibinis also synthesized by the placenta.
Activin stims FSH secretion.

Together they help regulate FSH secretion and local sex steroid levels balancing oestrogens and androgens.

Question 37

What is the function of progesterone and relaxin?

Answer 37

Progesterone. Secreted in 2nd half of cycle by CL. Negative feedback on hypothalamus and ant pit. Main actions are to promote pregnancy by maintaining and stimulating secretions of the endometrium

Relaxinis secreted into the circulation by the corpus luteum and placenta. (Role in men uncertain - ?enhance sperm motility)

Question 38

Describe hypothalamo-pituitary-gonad axis of oestrogen and androgen production

Answer 38

Kisspeptin produced in the hypothalamus, which binds to receptors on GnRH neurones, stimulating GnRH production. This stimulates the pituitary by travelling through hypophyseal portal circulation. When stimulated, gonadotrophs produce LH/FSH which binds to targets in the gonads, stimulating androgen/oestrogen/progesterone production.

Question 39

How does hormone production vary?

Answer 39

GnRH and LH pulsatile release – varying frequency and amplitude. Sex Steroids diurnal rhythm – testosterone + oestrogen (testosterone highest in the morning and decreases through the day).

Question 40

What inhibits kisspeptin neurones?

Answer 40

Hyperprolactinaemia. Prolactin binds to prolactin receptors on kisspeptin neurons in hypothalamus. Inhibits kisspeptin release. This decreases downstream GnRH/LH/FSH/T/Oest. Leads to oligomenorrhea, amenorrhea, low libido, Infertility, Osteoporosis.

Question 41

What feedback loops drive the menstrual cycle?

Answer 41

Hypothalamic Kisspeptin & GnRH

Pituitary LH & FSH

Ovarian Oestrogen, Progesterone, Activin, Inhibin

Question 42

What are the two types of cycles and what are their phases?

Answer 42

The ovarian cycle is comprised of follicular phase, ovulation (=pre-ovulatory phase) and luteal Phase

The uterine cycle is comprised of menstrual phase, proliferative phase and secretory phase.

Question 43

What happens in the follicular phase?

Answer 43

LH and FSH rises. FSH stimulates follicles to mature and they start making oestrogen which slowly rises.

Oestrogens stimulate the synthesis of LH receptors in the granulosa cells and growth accelerates. Most of the oestrogen is from the dominant follicle and FSH now dips due neg feedback.

As oestrogen levels rise there is a switch to positive feedback @ pituitary, resulting in an LH surge and lesser extent FSH.

LH surge results in final maturation and then release of dominant follicle. The other follicles regress (atresia).

Question 44

What happens in the menstrual cycle of the uterine cycle?

Answer 44

During the menstrual phase the ischaemic and necrotic functional layer of the endometrium is shed along with blood from the degenerating spinal arteries. Oestrogen then causes the proliferative phase where the endometrium proliferates to form a new functional layer and the cervical mucus thins to allow sperm passage.

Question 45

What happens during the luteal phase?

Answer 45

Average length is 14d as determined by the lifespan of the CL (~10d) which secretes progesterone and oestrogen. Prog dominant and inhibits LH and FSH and so slowly the CL involutes unless rescued by hCG (human chorionic gonadotrophin) produced by implanting conceptus. As CL involutes then prog and oestrogen subside again allowing FSH and LH to rise for next cycle.

Question 46

What happens during proliferative and secretory phase of uterine cycle?

Answer 46

Endometrium differentiates and secretes a glycogen-rich fluid in preparation for a potential embryo. As prog and E then fall, the spiral arteries supplying the functional endometrium begin to constrict causing ischaemia and necrosis. If pregnancy occurs then progesterone and oestrogen remain high due continued lifespan of the CL (via hCG) so endometrium therefore not shed.

Question 47

What effect does ovulation have on body temperature?

Answer 47

Day after ovulation, body temperature increases by at least 0.5 C due to progesterone.

Question 48

Describe semen formation

Answer 48

Testis forms the sperm. Tubular fluid reabsorption occurs in efferent ducts resulting in concentration (induced by oestrogen). Nutrients (eg fructose) & glycoprotein secretion into epididymal fluid in epidydimis (induced by androgens).

Question 49

Where is seminal fluid made?

Answer 49

Mainly in accessory sex glands (seminal vesicles, prostate, bulbourethral glands). Small contribution from epidydimis and testis).

Question 50

What seminal fluid components are produced where?

Answer 50

Epididymis/testis: inositol, carnitine, glycerylphosphorylcholine
Accessory sex glands: fructose, fibrinogen, citric acid (Ca2+ chelator), acid phosphatase, fibrinogenase

Question 51

When and how does capacitation of sperm occur?

Answer 51

1. Loss of glycoprotein ‘coat’
2. Change in surface membrane characteristics
3. Develop whiplash movements of tail
   Occurs only in the female reproductive tract. Capacitation of sperm is:
4. Takes place in ionic & proteolytic environment of the Fallopian tube
5. Oestrogen-dependent
6. Ca2+-dependent

Question 52

Describe acrosome action when it meets the egg

Answer 52

Zona Pellucida is a glycoprotein layer surrounding the plasma membrane of the oocyte. Sperm binds to ZP3
(= sperm receptor). Ca2+ influx into sperm (stimulated by progesterone). Release of hyaluronidase to break down polysaccharides & proteolytic enzymes (from acrosome).

Question 53

Where does fertilisation occur and what occurs during fertilisation?

Answer 53

Occurs within the Fallopian tube in ampulla. Triggers cortical reaction where cortical granules release molecules which degrade Zona Pellucida (e.g. ZP2 & 3). Therefore prevents further sperm binding as no receptors. Diploid cell formed and expulsion of second polar body (a small haploid cell formed during oogenesis) occurs.

Question 54

How does conceptus develop?

Answer 54

Continues to divide as it moves down Fallopian tube to uterus (3-4 days). Receives nutrients from uterine secretions. This free-living phase can last for ~ 9-10 days.

Question 55

What happens around 8th day of conceptus development?

Answer 55

8 cell conceptus compacts to form morula at day 4 and then forms a blastocyst. Around day 8-9, this blastocyst implants in uterine wall.

Question 56

What are the phases of implantation?

Answer 56

Attachment phase: outer trophoblast cells contact uterine surface epithelium
Decidualisation phase: changes in underlying uterine stromal tissue (within a few hours)
Requires progesterone domination in the presence of oestrogen. Progesterone prepares endometrium for implantation.

Question 57

How does the blastocyst promote implantation?

Answer 57

The blastocyst contains trophoblast cells around its periphery, enclosing the inner mass cells. Both the blastocyst and endometrial lining produce IL-11 and LIF, promoting attachment. IL-11 causes trophoblast migration and decidualisation. LIF stimulates adhesion of blastocyst to endometrial cells.

Question 58

What happens during decidualisation?

Answer 58

1. Glandular epithelial secretion
2. Glycogen accumulation in stromal cell cytoplasm
3. Growth of capillaries
4. Increased vascular permeability (→oedema)
   Factors such as Interleukin-11 (IL11), histamine, certain prostaglandins & TGFb (TGFb promotes angiogenesis) are also involved. This occurs within a few hours of attachment.

Question 59

How do hormones change over pregnancy?

Answer 59

hCG initially spikes from conception till 8-9 weeks after which it experiences a steep fall till 13 weeks, from where its concentrations gradually decrease until the end of the pregnancy. Progesterone is the dominant hormone and while there is a small initial spike at conception, it steadily increases until 37-38 weeks where it peaks and then steeply falls. Oestradiol also gradually rises from 4 weeks until 38-39 weeks where it suddenly falls at birth. Human placental lactogen follows the same trend.

Question 60

What is the role of human placental lactogen?

Answer 60

Made by placenta and modulates maternal metabolism to provide nutrients for fetus. For example causes insulin resistance therefore more glucose circulating for fetus. Its role in lactation is actually unclear.