Origin of the sexes

Question 1

Describe the internal male genitalia

Answer 1

• testis
• duct system (epididymis, vas deferens, urethra)
• seminal vesicles
• prostate gland
• bulbo-urethral glands

Question 2

Describe the internal female genitalia

Answer 2

• ovaries
• fallopian tube
• uterus
• cervix
• vagina

Question 3

Describe the external male genitalia

Answer 3

• penis (genital tubercle and fold)
• scrotum (labioscrotal swelling)
• glans penis (allantois)
• scrotal Raphe (urethral groove)

Question 4

Describe the external female genitalia

Answer 4

• vagina (orifice of urogenital sinus)
• vestibule (urogenital sinus)
• labia majora (labioscrotal swelling)
• labia minora (genital tubercle and fold)
• clitoris (allantois)

Question 5

Describe male gonadal development (4th week)

Answer 5

• presence of Y (SRY)
• primordial germ cells from yolk sac endoderm migrate
• arrive at genital ridge and mitose repeatedly
• populate genital ridge with ‘precursor gametes’
• cause coelomic epithelium to become sex cords
• sex cords (SC) enlarge and split to form primitive testis
• SC housed within testicular medulla (mesenchyme)
• primordial germ cells form spermatogonia
• sex cord cells form precursor sertoli cells
• mesenchyme forms leydig cells

Question 6

Describe female gonadal development (4th week)

Answer 6

• absence of Y
• primordial germ cells from yolk sac endoderm migrate
• arrive at genital ridge and mitose repeatedly
• populate genital ridge with ‘precursor gametes’
• cause coelomic epithelium to become sex cords
• germ cells form primordial oocytes
• oocyte epithelia forms granulosa cells
• mesenchyme forms thecal cells

Question 7

List some common abnormalities of genital tract development

Answer 7

• cloacal partitioning defects
• hypospadias
• bicornuate uterus - when mullerian fusion is impaired
• cervical and vaginal atresia
• micropenis (2.5 SD below)
• ambiguous genitalia

Question 8

What are the secondary male sexual characteristics?

Answer 8

• increase body size
• change in body composition and fat distribution
• hair and skin
• facial hair and male pattern baldness
• odour

Question 9

What are the secondary female characteristics?

Answer 9

• decrease in body size relative to males (smaller height)
• subcutaneous fat distribution
• hair and skin
• thelarche

Question 10

Explain female internal genitalia differentiation

Answer 10

• primordial kidney produces a Wolffian duct
• –> extends to the urogenital sinus (primitive bladder)
• mesonephric ridge produces the Mullerian duct
• –> extends to the urogenital ridge
• absence of MIS allows mullerian duct to persist
• forms vaginal plate and initiates uterus development
• forms fallopian tubes, uterus and upper 1/3 of the vagina
• lateral folding of ridges brings the mullerian ducts together. They fuse to form one space, the uterus.
• in the absence of testosterone, wolffian system goes

Question 11

Explain male internal genital differentiation

Answer 11

• primordial kidney produces a Wolffian duct
• –> extends to the urogenital sinus (primitive bladder)
• mesonephric ridge produces the Mullerian duct
• –> extends to the urogenital ridge
• Sertoli precursors secrete MIS
• Mullerian ducts degenerate
• Leydig precursors secrete testosterone
• testosterone guides differentiation of wolffian ducts

Question 12

Explain the descent of the testes

Answer 12

• gubernaculum descends anterior to pubic symphysis
• testis follows
• gains layer of tunica vaginalis
• outside of peritoneum - through inguinal canal

Question 13

Explain the descent of the ovaries

Answer 13

• gubernaculum attaches ovary to labioscrotal folds
• ovary descends to pelvis
• stops at level of fallopian tube
• cord inferior to this is the round ligament of uterus
• this cord descends through the inguinal canal

Question 14

What are the main reproductive hormones?

Answer 14

• GnRH
• Prolactin releasing hormone
• oxytocin
• FSH
• LH
• prolactin
• oestrogen
• progesterone
• hCG
• inhibin (inhibits FSH secretion)
• testosterone

Question 15

Describe the process of spermatogenesis

Answer 15

• germ cells form spermatogonia - self renewing
• produce A and B type spermatogonia
• B type mitose to form 64 primary spermatocytes
• these undergo meiosis to form spermatids
• remodelled by spermiogenesis to form spermatozoa
• process occurs as cells migrate through ducts
• finish maturation in epididymis

Question 16

What is the spermatogenic cycle and spermatogenic wave?

Answer 16

spermatogenesis is continuous. Each wave of production sweeps across the length of the tubule, known as the spermatogenic wave. The spermatogenic cycle is the time it takes for the reappearance of the same stage of sperm maturation within a specific segment.

Question 17

What are the roles of:

1) rete testis
2) epididymis
3) vas deferens
4) seminal vesicles
5) prosate
6) bulbourethral glands

Answer 17

1. collect spermatozoa from seminiferous tubules
2. storage and maturation of sperm
3. connects epididymis to seminal vesicle & ejaculatory duct
4. forms ejaculatory duct with epididymis. produces seminal fluid (60% ejaculate) i.e. fructose & prostaglandins
5. prostatic secretions: zinc, citrate, proteases. Aid liquefaction of the initial ejaculate to enable sperm to escape viscous ejaculate.

Question 18

Describe the ovarian cycle

Answer 18

• primordial germ cells form 7 million oogonia
• only 2 million enter and arrest in prophase I
• these are primary oocytes
• no more are generated. Increase age - increase risk
• at puberty, some follicles develop further:
  
  1. pre-antral follicle (zona pellucida forms)
  2. antral/ Graafian follicle (forms fluid filled antrum)
  3. pre-ovulatory follicle (LH receptors appear)
• LH surge causes ovulation
• meiosis I completes and arrests pending sperm
• corpus luteum increases and secretes progesterone and oestrogen