Reproductive System

Question 1

Hypothalamic and Pituitary Hormones (Involved with Reproductive System)

Answer 1

GnRH- Releasing peptide secreted by neurosecreotory cells of the hypothalamus- targets the gonadotrophs of the anterior pituitary. Moves from primary plexus to secondary plexus in the ant.pituitary.
FSH- Produced in the A.P by gonadotrophs. Stimulates gamete synthesis and development in both genders.
LH- Produced in the A.P by gonadotrophs. Stimulates oestrogen synthesis by ovaries, stimulates ovulation and testosterone synthesis by the Leydig cells.
Oxytocin: Peptide produced by neurosecretory cells in the hypothalamus and stored in the posterior hypothalamus. Stimulates lactation and initiates positive feedback loop of smooth muscle contraction.

Question 2

Hormones produced by the Gonads

Answer 2

Androgens: Produced by the Leydig cells of the testes under FSH influence. Include testosterone, and the more potent 5a- DHT. Responsible for spermatogenesis, the development of male primary and secondary sexual characteristics and muscle development.
Oestrogens: Produced by the granulosa cells of the growing follicle. Includes the more potent oestradiol (fertility and menstrual cycle), oestrone (produced lifelong in females and to a lesser extent males), and oestriol (made by the placenta).
Responsible for development of primary and secondary female sexual characteristics, endometrial development, menstrual cycle regulation, and bone growth.

Question 3

Sex Determination- Male

Answer 3

Y-chromosome contains the SRY gene, which codes for a transcription factors which regulates expression of other genes.
SRY gene converts gonadal ridges into testis, which specialise into Sertoli cells and Leydig cells.
Sertoli cells produce anti-Mullerian hormone to degenerate Mullerian duct. Leydig cells produce testosterone, stimulating the development of the Wolffian duct into the epididymis, vas deferens, seminal vesicle and ejaculatory duct.
The urogenital sinus develops into the prostate and the bladder.

Question 4

Sex determination-female

Answer 4

Absence of SRY gene means development goes down the default path of female development. Mullerian duct develops into fallopian tubes without the interference of AMH, and the absence of testosterone results in the degeneration of the Wolffian duct. Gonadal ridges are converted into the ovaries.
The Mullerian ducts fuse at the distal ends to form the vagina (upon fusion with urogenital sinus), cervix and uterus.

Question 5

External genitalia specialisation- Male

Answer 5

Occurs due to the presence of DHT.
Genital tubercle swells to form the glans penis.
Urethral folds bend around to form a cylinder that would become the corpus spongiosum which surrounds the spongy urethra. The labioscrotal swellings bend around similarly to form what would become the corpora cavernosa.

Question 6

External genitalia specialisation- female

Answer 6

The genital tubercle shrinks to form the clitoris.
The urethral folds spreads and forms the labora minora with its edge, and the vestibule with the gap.
The labora majora is formed by the spreading labioscrotal swelling.

Question 7

Hormonal Onset of Puberty

How is puberty progress measured

Answer 7

Increase in plasma LH levels indicate higher GnRH release. This also means FSH levels will be high.
Initially this occurs only at night but can also occur during the day in late puberty.
Tanner stages roughly outline when certain changes should occur during puberty,

Question 8

Development of Male Secondary Sexual Characteristics

IN ORDER

Answer 8

Testicular enlargement (starts at around 10-13)- enlargement of Leydig cells to produce more testosterone.
Pubic hair development: 6 months after testicular enlargement and auxiliary hair development follows 18 months after. Facial hair follows later.
Penile enlargement: Within 1 year of testicular enlargement.
Spermarche: Sperm detected in urine. Around 13-14 years old. The beginning of the growth spurt coincides with the start of spermache, and reach max strength 3-4 years later.

Question 9

Development of Female Secondary Sexual Characteristics

Answer 9

Breast development start at around 10-11. Initially forms a breast bud, but full breast development occurs after progesterone secretions by the corpus luteum occurs.
Pubic hair growth initiates 6 months after breast bud growth due to androgen exposure. Auxiliary hair growth occurs a year after.
Growth spurt at 11-12 due to presence of oestrogen and androgens- pubic symphysis close.
Menarche- First menstrual bleed at 12-13. First ovulation 6-9 months later, and the first cycle up to 2 years later, as the body adapts to the oestrogen positive feedback.
Timing of Menarche depends on the body mass of the female- a critical mass is required for the female to support pregnancy and lactation. Trend is that menarche has been moving forward.

Question 10

Precocious and Delayed Puberty

Answer 10

Precocious: Puberty onset before 7 in females and 9 in males due to overproduction of GnRH.
Delayed: Puberty onset does not occur at 13 in females and 14 in males due to inadequate GnRH production and inadequate stimulation of gonads.

Question 11

Stages of Menopause

Answer 11

Pre-menopause: Regular cycles up to around 46.
Menopausal transition: From 46 to around 50-52. Irregular cycles.
Post-menopause: Menstrual cycles cease and any remaining ovaries stop responding to hormonal stimulation a year after during Ovarian senescence.
Perimenopause includes the period of menopausal transition and postmenopause before ovarian senescence.

Question 12

Symptoms of Menopause

Answer 12

Due to oestrogen deprivation during perimenopause, as only oestrone is produced.
Vasomotor symptoms: Hot flushes due to unstable vascular system.
Genitourinary changes: Atrophy of reproductive tract and vagina dryness.
Osteoporosis.
Behavioural and psychological changes.

Question 13

Organs of the Female Reproductive Tract- Vagina and Cervix

Answer 13

Vagina: Elastic 7.5-9cm long tube. Passageway for sperm, eliminated menstrual fluids and the penis during intercourse.
The foetus passes through this during childbirth, and it can distend to fit the foetus.
Cervix: Widened part of the reproductive tract, opening to the uterus at the internal os and the vagina at the external os. Contains cervical mucus to protect sperm and provide nutrients.

Question 14

Organs of the Female Reproductive Tract-Uterus

Answer 14

30-40g pear shaped organ. Positioned in anteflexion over the bladder. Provides protection, nutrition and waste removal for the developing embryo.
Stratum functionalis: Grows during the follicular phase under the influence of oestrodiol and is maintained by progesterone. Lost entirely during menstruation.
Stratum basalis: Attaches stratum functionalis to the mymetrium.
Myometrium: Smooth muscle which causes contractions during childbirth.

Question 15

Organs of the Female Reproductive Tract- Ovaries

Answer 15

5-10g oval structures with small bumps. Attached directly to the uterus via the hilus, which contains the innervation and vascularisation.
Made up of the ovarian cortex and the ovarian medulla.
Cortex: Contains the ovarian follicles as they mature. They will move along the edge of the ovary.
Medulla: Contains highly vascularised CT ovarian stroma and secretory cells.

Question 16

Process of follicular development. GIB NUMBERS TOO.

Answer 16

6million primordial follicles produced during embryonic development. These are follicles with ONE layer of flattened granulosa cells.
The majority of primordial follicles die off by the time of birth, leaving only 1-2 million. At puberty, this is reduced further to 40000.
Meanwhile, oogonia begin meiosis I after birth, and completes it upon reaching puberty,
In a primary follicle, there is a layer of glycoproteins around the oocyte and cuboidal granulosa cells called the zona pellucida. The granulosa cells are surrounded by a basement membrane. On the outer edge of the basement membrane, thecal cells from the stroma form the theca.
Only a dominant follicle (selected on day 3 of the follicular cycle) develops into a secondary follicle-usually one producing most oestrodiol.
In a secondary follicle, the antrum is formed from follicular fluid. The innermost 2-3 layers of granulosa cells make up the corona radiata, while the rest make up the cumulus oophorus. The theca divides into the fibrous, protective theca externa, and the androgen secreting theca interna (the androgen is converted by granulosa cells to oestradiol).
Just before ovulation, the antrum grows large enough to form a space surrounding the oocyte except for a stalk joining it to the Graafian follicle.

Question 17

Post ovulatory Events and Structures

Answer 17

As ovulation occurs, the Graafian follicle ruptures and forms the corpus hemorrhagicum, while the oocyte and its corona radiata and cumulus oosphorus are expelled.
Basement membrane and antrum degenerates and replaced with vasculature.
LH stimulates luteinisation of thecal and granulosa cells (forms corpus luteum), which causes them to secrete more progestagens.
Futile cycle: Progestagens provide a negative feedback to LH secretion, which leads to degeneration of corpus luteum into corpus albicans. Absence of progestagens leads to menstruation.
Fertile cycle: Fertilisation causes the chorion to produce hCG, which results in perpetuation of the corpus luteum and continued progestagen production. Placenta also contributes to progesterone production.

Question 18

Phases and Hormones of the Menstrual Cycle

Answer 18

Menstrual phase: Corpus luteum breakdown causes progesterone levels to drop. Endothelium degenerates.
Follicular Phase: LENGTH VARIES. As the follicle grows, the granulosa and theca cells produce more and more oestradiol. Initially, this has a negative feedback on GnRH secretion, but 36+hrs of high oestradiol concentration leads to positive feedback. This causes the LH spike which brings about menstruation.
Luteal phase: Always 14 days Progesterone from corpus luteum turns off the positive feedback. Initially, the high levels of FSH and LH maintains the corpus luteum, but negative feedback of progesterone on GnRH will stop maintenance of corpus luteum, leading to falling progesterone concentration. Hence, endometrium is not maintained and menstruation occurs.

Question 19

Structure of Seminiferous Tubules

Answer 19

Sertoli cells are found living the walls of the tubules as a single layer.
There is a basal compartment between the Sertoli cell and the basement membrane where spermatogonia are found. Sertoli cells form tight junctions just below the basal compartments to form the blood-testis barrier to regulate substance movement in/out of the tubule.
Leydig cells are found outside the basement membrane in the interstitial space of testes. They are responsible for the secretion of testosterone.

Question 20

Process of the Spermatogenesis

Answer 20

Diploid spermatogonia in the basal compartments undergo mitosis to form many diploid daughter cells (primary spermatocyte). Everytime a stem spermatogonium divides, one remains as a stem cell while others continue dividing.
Primary spermatocytes are found in the adluminal compartments-gaps between Sertoli cells.
After primary spermatocytes completes meiosis I, it becomes a secondary spermatocyte. A secondary spermatocyte completes meiosis II to form a spermatid.
After meiosis, the daughter cells remain attached as some proteins required for survival are found on the x chromosome.
During development, excess organelles and cytoplasm is phagocytosed as a residual body by the Sertoli cells. Spermatids are moulded by Sertoli cells into more aerodynamic shapes. This process is called spermiogenesis or cytodifferentiation.

Question 21

Effect of FSH, LH and Kisspeptin on testicular function AND how their secretion is regulated.

Answer 21

FSH:Glycoprotein hormone that targets Sertoli cells and stimulates the secretion of androgen-binding protein. Allows transport of the steroid androgen in the blood, and its storage in testes to allow constant spermatogenesis.
LH: Glycoprotein hormone targetting Leydig cells to stimulate secretion of testosterone and hence 5a-DHT. 5a-DHT is responsible for secondary sexual characteristics in males such as hair/genital growth, pattern baldness aggression and libido.
Testosterone regulates GnRH secretion by negative feedback. Sertoli cells produce inhibin, which only inhibits FSH by negative feedback. Allows more exquisite control.
Kisspeptin regulates the secretion of GnRH.

Question 22

Types of Male Infertility

Answer 22

Oligospermia: Insufficient sperm per mL of ejaculate (anything below 20 mil/mL).
Azoospermia: No sperm in ejaculate- DOESN’T MEAN SPERM IS NOT PRODUCED.
Immotile sperm: Sperm present in ejaculate but are not motile. Sometimes sperm count can also be reduced.

Question 23

Treatment for Male Infertility

Answer 23

IVF: Sample of ejaculate is collected, concentrated and then mixed with oocytes in a petri dish. Requires a minimum of 50,000 sperm per mL.
ICSI: Treatment for azoospermia and immotile sperm. Sperm is isolated by micropipette from ejaculate or biopsy of testis, then injected directly into an oocyte.

Question 24

Path taken by sperm through the male reproductive tract

Answer 24

Sperm is formed in seminiferous tubules and empties into the rete testes.
The rete testes empty into the epididymis, which it takes 14 days to traverse and allows maturation and concentration of sperm. The sperm then travels along the vas deferens to the ampulla of the vas deferens, where sperm can be stored for up to several months.
Seminal vesicle is found next to the ampulla, and the seminal duct joins the vas def. to form the ejaculatory duct in the prostate.
Urethra joins to form the Prostatic urethra, which becomes the spongy urethra

Question 25

Organs of the Female Reproductive Tract- Fallopian Tubes

Answer 25

Tube conducting the oocyte from the ovary to the uterus.
Glycogen and lipid rich environment to nourish sperm and oocytes.
Has fimbriae on the ovarian side, which draws the oocyte into the fallopian tubes. Horseshoe bend near the middle called the ampulla where fertilisation occurs. Lined with both ciliated and nonciliated columnar epithelia. Cilia beat to move the oocyte (along with the contractile motion of the smooth muscle walls) while the nonciliated secrete nutrients.
Ectopic pregnancy occurs due to cilia failure, meaning the oocyte is implanted too soon. Risk factors: Smoking, chlamydia and aging.
Isthmus is a straight connection to the uterus.

Question 26

Secretions of the Cowper’s Gland

Answer 26

Cowper’s Glands: Secretes an alkaline pre-ejaculatory fluid which neutralises the acidic urethral environment and lubricates the tract.

Question 27

Secretions of the Seminal Vesicle

Answer 27

Seminal vesicle: Mucoid substance. Contains fructose as a respiratory substrate for the sperm. Contains prostaglandins as a stimulant of smooth muscle contraction-causes female reproductive tract to push sperm along.
Contains clotting proteins to form a coagulum in the female reproductive system as to prevent ejaculate loss due to physical activity.
Makes up 60% of the ejaculate by volume

Question 28

Secretion of the Prostate Gland

Answer 28

Slightly acidic to balance out the alkalinity of the seminal fluid to create a buffered environment.
Contains citrate for the Krebs cycle for more ATP.
Contains phosphates and calcium- Ca2+ required for muscle contraction.
Contains prostatic specific antigen to break down the coagulum.

Question 29

Incidence, symptoms, and treatment of Benign Prostatic Hypoplasia

Answer 29

Caused by excess growth of prostatic tissue, occluding the urethra.
Rare in young men. Up to 35% in 70+ and 90% in 85+.
Treatment: 5a-reductase inhibitors to prevent conversion to 5aDHT, which stimulates prostate growth.
Surgery-prostatic urethral lift.
Symptoms: Difficulty voiding the bladder. Incomplete voiding. Involuntary voiding. Post voiding dribbling. Pain during urination.
Leads to a column of liquid which allows conduction of infection into the bladder and kidneys.

Question 30

Anatomy of the Penis

Answer 30

Two large corpora cavernosa make up the majority of the mass. These contain sinuses which may fill with blood during an erection. Contains deep arteries with smooth muscle walls.
Corpus spongiosum surrounds the flattened penile urethra, found ventrally to the corpora cavernosa.
Veins are found ventral to the corpora cavernosa.
Smooth muscle is also found throughout erectile tissue.

Question 31

Mechanism of Erection

Answer 31

Upon sexual stimulation, production of NO and prostaglandin E1 due to parasympathetic innervation stimulates the action of secondary cGMP. This leads to relaxation of smooth muscle, allowing vasodilation and more drainage of blood into the erectile tissue. Smooth muscle relaxation in the erectile tissue also allows blood to engorge the erectile tissue more easily.
Veins are compressed during erection to prevent drainage of blood from erectile tissue.
Expansion of the c.spongiosum prevents the occlusion of the urethra.

Question 32

Erectile dysfunction and how it is cured

Answer 32

Erectile dysfunction is due to hyperactivity of phosphodiesterase, which breaks down cGMP. Viagra.sildenafil acts as an inhibitor of phosphodiesterase and ensures that cGMP levels remain high enough to cause erection.