Unit 2: Endocrine control of sexual maturity

Question 1

Biological changes in puberty

Answer 1

1. neurosecretory factors and/or hormones
2. modulation of somatic growth
3. initiation of the development of sexual organs

Question 2

The role of hypothalamic-pituitary-gonadal axis in puberty

Answer 2

• activated in puberty
• induce ovarian and testicular sex hormone secretion
• results in biological, morphological and physiological changes in puberty
• increase in GnRH release increases pituitary responsiveness to GnRH (up regulation) which results in FSH and LH release and ultimately sex steroid relase from gonads. Secondary sexual characteristics develop

Question 3

Effects of sex steroid production in puberty

Answer 3

1. appearance and maintenance of secondary sexual characteristics
2. attaining capacity of reproduction

Question 4

Periods of life when the hypothalamic-pituitary-gonadal axis is activated

Answer 4

1. mid trimester of foetal life - testosterone masculinises the brain and FSH causes folliculogenesis
2. early neonatal period - due to the decrease in steroid hormones after birth (disinhibition effect)
3. puberty to reproductive years - pulsatile release at first, later throughout the day

Question 5

Factors that initiate puberty

Answer 5

• exact cause unknown, but few postulations
  1. Leptin - caused by the change in adiposity in girls. Leptin stimulates hypothalamus to release GnRH
  2. Melatonin - anti-gonadotropic. In adolescents secretion decrease at night, correlates to when GnRh is released

Question 6

Explain the brain-testicular axis

Answer 6

FSH:
1. FSH stimulates the secretion of ABP (androgen binding protein) by the sertoli cells

2. ABP prompts spermatogenic cells to bind and concentrate testosterone
3. Locally, ABP and testosterone = final trigger to spermatogenesis
4. FSH indirectly makes sertoli cells more receptive to the stimulatory effects of testosterone
5. High sperm count causes the release of inhibit by sertoli cells. Inhibin negatively feeds back on the pituitary to decrease FSH release.

LH:

1. LH binds to Leydig (interstitial cells) and stimulates testosterone production
2. testosterone negatively feeds back on hypothalamus and pituitary to inhibit LH release.
   a) Act directly on hypothalamus
   b) Reduce LH producing cells’ responsiveness to GnRH & exert inhibitory effects on FSH and LH producing cells

Question 7

General effects of testosterone

Answer 7

1. initiates spermatogenesis
2. development of secondary sexual characteristics
3. synthesised from cholesterol
4. 98% are circulating in blood, bound to SHBG (44%) and serum albumin (54%)
5. activates genes
6. targets accessory reproductive organs, causes them to grow and assume adult size and function.
7. in adult males, plasma concentration of testosterone is responsible for the maintenance of accessory reproductive organs.

Question 8

Deficiency of testosterone

Answer 8

1. accessory organs atrophy
2. semen volume decline
3. erection and ejaculation impaired
4. sterility and impotence

Question 9

Secondary sexual characteristics in males

Answer 9

1. pubic, axillary and facial hair
2. hair growth in chest and other areas
3. larynx enlarge
4. skin thicken and become coarser

Question 10

Somatic effects of testosterone

Answer 10

1. thicken and lengthening of bones
2. skeletal muscle mass and size increase
3. epiphyseal plate closure occur late in puberty

Question 11

Metabolic effects of testosterone

Answer 11

1. anabolic
2. increased haematopoeisis
3. increased basal metabolic rate

Question 12

Neural effects of testosterone

Answer 12

1. increased libido
2. masculinises brain (brain areas responsible for sexual arousal)
3. agressiveness