Sexual Differentiation

Question 1

Describe the glans penis.

Answer 1

Bulbous sensitive area at distal end of penis. Homologs of female clitoral glans.

Question 2

Describe foreskin.

Answer 2

Retractable double layer fold of skin and mucous membrane covering the glans penis. Possible functions include keeping the glans moist, protecting the development of the penis in utero, or enhancing sexual pleasure due to the presence of nerve receptors.

Question 3

Describe the scrotum.

Answer 3

Pouch of skin that hangs behind penis. Contains and protects the testes. Contains numerous blood vessels and nerves. Scrotum can contract and relax to protect testes from changes in temperature.

Question 4

Describe the epididymis.

Answer 4

Narrow, tightly coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. Maturation and storage of sperm.

Question 5

Describe the vas deferens.

Answer 5

Long muscular tube from the epididymis into pelvic cavity, to just behind the bladder. Transports mature sperm to the urethra in preparation for ejaculation.

Question 6

Describe the ejaculatory ducts.

Answer 6

Formed from fusion of the vas deferens and seminal vesicles. Empty into the urethra.

Question 7

Describe the urethra.

Answer 7

Tube carrying urine from the bladder to outside the the body. In humans additional function to expel sperm.

Question 8

Describe the seminal vesicles.

Answer 8

Sac like pouches attach to the vas deferens near the base of the bladder. Produce fructose rich fluid that provides sperm with a source of energy. Fluid of seminal vesicles makes up the majority of ejaculatory fluid,

Question 9

Describe the prostate gland.

Answer 9

Walnut sized structure below the bladder and in front of the rectum. Contributes additional fluid to ejaculatory fluid. Fluid produced by prostate gland helps nourish sperm. Urethra runs through the centre of the prostate gland.

Question 10

Describe the bulbourethral glands.

Answer 10

Also known as cowper’s glands. Pea sized structures located on side of urethra below the prostate gland. Produce clear slippery fluid that empties directly into the urethra serving to lubricate the urethra and neutralise any acidity that may be present due to residual presence of urine in the urethra.

Question 11

Describe the testis.

Answer 11

Male gonads. Organ that produces sperm. Egg shaped structures. Grow about 1 inch in length. Rest inside the scrotum. Also produce hormones, including testosterone which stimulate the production of sperm.

Question 12

Which chromosome has the dominant effect in genetic determination of sex?

Answer 12

The Y chromosome. Genes present on the Y chromosome are responsible for determination of male differentiation. SRY (Sex determining region of the Y) gene carried in the p arm of the Y chromosome.

Question 13

What is the default pathway for sexual differentiation?

Answer 13

Female. Decisive influences are the presence or absence of testosterone and antimullerian hormone produced by the testis.

Question 14

By what point is sexual differentiation achieved?

Answer 14

Sexual differentiation is achieved by mid gestation. Series of programmed events leads to the transformation of the primary gonads, the internal and external genitalia.

Question 15

What is the gonadal primordium?

Answer 15

The gonadal primordium is the ventral surface of the primitive kidney. Independently of genetic sex the the gonadal primordium is colonised by primordial germ cells forming the gonadal ridge.

Question 16

By what stage does differentiation of the gonads into testis or ovaries occur?

Answer 16

By the 7th week of gestation.

Question 17

Describe the formation of the ovarian cortex.

Answer 17

Primordial germ cells proliferate and cluster moving inside the gonad to form the ovarian cortex. Oocytes within the ovary are blocked at the diplotine stage of first meiosis. They remain in this stage until ovulation.

Question 18

How many primary oocytes are present in the ovary at 5 months of foetal life? How many are present after birth?

Answer 18

At 5th month of foetal life the ovary contains 7 million primary oocytes. After 7 months no more oocytes are produced by the foetal ovary. By birth the number of oocytes has fallen to 2 million.

Question 19

What determines the formation of the internal and external genitalia?

Answer 19

Hormones secreted by the foetal gonads determines the formation of the internal and external genitalia.

Question 20

What are the internal genitalia derived from?

Answer 20

Wollfian ducts and Müllerian ducts.

Question 21

What does the Wolffian duct become in males?

Answer 21

Wolffian ducts serve as excreting ducts to the metanephros. As definitive kidney becomes functional in the presence of androgens it becomes the vas deferens.

Question 22

What does the Müllerian duct differentiate into in females?

Answer 22

In female the Müllerian ducts differentiate into the oviduct, uterus and upper part of the vagina.

Question 23

What hormone causes the regression of the Müllerian duct on makes?

Answer 23

AMH.

Question 24

The external and urogenital genitalia are similar in both sexes up until what week of foetal development?

Answer 24

9th week.

Question 25

Describe female genital development.

Answer 25

External genitalia differentiate from genital tubercle and the two lateral urethral folds and labioscrotal swellings. Female genital development begins with formation of vaginal plaque from Müllerian tubercle. Vaginal plaque forms canal and upper part opens to uterine cervix. Clitoris forms from genital tubercle. Labioscrotal swellings do not fuse and perineal anogenital distance does not decrease.

Question 26

Describe genital development in the male.

Answer 26

In the make the pelvic portion of the cloaca undegoes much greater, pushing before it in the phalic portion. The labioscrotal folds extend around between the pelvic portion and the anus and form a scrotal area.

Question 27

Describe the mons pubis.

Answer 27

Also called mons veneris. Soft fatty tissue covering the pubic bone. Protects the pubic bone and the vulva from impact of sexual intercourse.

Question 28

Describe the labia majora.

Answer 28

The outer fleshy lips of the external genitalia. Made up of loose connective and adipose tissue and smooth muscle. Contains numerous sweat and oil glands, used to produce lubrication.

Question 29

Describe the labia minora.

Answer 29

The inner lips of the external genitalia. Thin stretches of tissue that protects the vagina, urethra and clitoris. Contains sebaceous glands.

Question 30

Describe the clitoris.

Answer 30

Small white oval between the top of the labia minora and the clitoral hood. Small structure made from spongy tissue. Only function is sexual pleasure. Similar to male penis but does not contain any part of the urethra

Question 31

Describe the urethra.

Answer 31

Opens just below the clitoris. Passage of urine from bladder to outside world.

Question 32

Describe the perineum.

Answer 32

Short stretch of skin between vagina and anus.

Question 33

Describe the penis.

Answer 33

Male reproductive organ. Also serves to pass urine. Description of erection - sexual arousal, sinuses within erectile tissue fill with blood, arteries in penis dilate increasing blood flow into three spongy chambers of penis. Causes one is to lengthen and stiffen. Engorgement of penile tissue causes compression of the penile veins and reduces blood flow out of penis.

Question 34

What is the main hormone required for normal external development of the male genitals?

Answer 34

DHT.

Question 35

What happens to the urethral folds during genital development.

Answer 35

In both sexes they elongate and fuse. This splits the cloacal membrane located in between the urethral folds into the urogenital membrane up at the top and the anal membrane below.

Question 36

At around week 10-11 what happens to the genital tubercle?

Answer 36

The genital tubercle in males has elongated moving away from the anal opening and beginning to form the shaft and the head of the penis.

In females the genital tubercle moves inwards, closer to the anal opening and begins to form the clitoris.

Question 37

What happens after genital tubercle development to the urethral folds?

Answer 37

The urethral folds in the male will fuse all the way forming the urethra inside the penile shaft.

In females the urethral folds do not fuse, they will begin to form the labia minora, the inner skin folds of the vaginal area.

Question 38

What happens in weeks 16-18 with regards to genital differentiation?

Answer 38

The enlargement of the labioscrotal tissue in males will fuse forming the scrotum. Folds of tissue extending from the labioscrotal swelling will also fuse around the urethral folds completing the formation of the shaft of the penis.

In females the labioscrotal swellings will form the labia majora. The urethral folds will fuse in some places forming the vaginal and urethral opening. Clitoral development in females will be completed as the genital tubercle continues to shrink.

Question 39

At wash at point is genital development complete?

Answer 39

Around week 20.

Question 40

Describe make and female sexual differentiation of the outer genitals.

Answer 40

Under the influence of androgens, mostly DHT, the male tissues will enlarge and fuse to create a penis and the scrotum. In comparison, the female tissue will develop into the female tissues in the absence of androgens.

1) . First, in both sexes the urethral folds elongate and fuse. This splits the cloacal membrane, located in between the urethral folds, into the urogenital membrane up at the top and the anal membrane below.
2) . At 10-11 weeks the male and female genitals are distinctly different. The genital tubercle in males has elongated, moving away from the anal opening and beginning to form the shaft and head of the penis, while in females it moves inwards, closer to the anal opening and begins to form the clitoris,
3) . The urethra, folds in the male will fuse all the way, forming the urethra inside the penile shaft. However, in females they do not fuse. Instead they will begin to form the labia minora.
4) . By week 16-18 genital differentiation is almost complete and the foetus is visually identified as male or female during the ultrasound.

The enlargement of the labioscrotal tissue in males. These swellings will fuse, forming the scrotum. Also, folds of tissue extending from the labioscrotal swelling will also fuse around the urethral folds, completing formation of the shaft of the penis.

In females, the labioscrotal swellings will form the labia majora. The urethral folds will fuse in some places, forming the vaginal and urethral openings. Clitoral development in females will be completed as the genital tubercle continues to shrink.