13 - Male Endocrinology and Puberty Flashcards
Source, target and action of GnRH in males
Source: hypothalamus
Target: gonadotroph cells (anterior pituitary)
Action: release FSH and LH
FSH source, target and action in males
Source: gonadotroph cells (anterior pituitary)
Target: sertoli cells (testes)
Action:
- maintain spermatogenesis
- stimulate androgen binding protein (ABP) production
Source, target and action of LH in males
Source: gonadotroph cells (anterior pit)
Target: leydig cells (testes)
Action: testosterone production
Leydig cells equivalent to theca interna cells
Source, target of T4 in males
Source: leydig cells (testis)
Target:
- hypothalamus/ brain
- reproductive tract
- muscle
Action of T4 in males
Male sexuality:
- increase sexual beh and characteristics
- decrease GnRH production
- increase spermatogenesis
- increase muscle development
- accessory sex glands
Source, target and action of androgen binding protein
Source: sertoli cells (testes)
Target: N/A
Action: binds T4 in seminiferous tubules to stimulate spermatogenesis
Source, target and action of inhibin in males
Source: sertoli cells (testis)
Target: gonadotroph cells (anterior pit)
Action: inhibit FSH secretion
Slides 8,9
Positive and negative feedback
Hypothalamic-hypophyseal testicular axis
Large concentrations of T4 do what?
Reduce spermatogenesis and fertility
How does GnRH discharge work in males
No surge center
Discharged in frequent pulses or bursts
Pulses last for a few moment and occur several times a day
How does LH, FSH and testosterone surge work
LH and FSH surges induced by GnRH pulses
Testosterone surges induced by LH (continued stimulation for spermatogenesis)
Slides 11,12,13
GnRH, LH, FSH surge
T4 and LH
Steroid secretion patterns
What is puberty
Process of acquiring reproductive competence
Characteristics of pubescent process in the male
- behavioural traits are expressed
- ejaculation ability
- spermatozoa present in ejaculate
- adequate sperm production to accomplish fertilization
What is the limiting factor of the onset of puberty in males? How
Hypothalamus
Onset of puberty requires secretion of GnRH at frequency and quantities appropriate to stimulate gonadotropin (FSH and LH) release by anterior pituitary a levels adequate to support gametogenesis
In the male, onset of puberty occurs due to…
Decreased hypothalamic sensitivity to negative feedback of testosterone
Five endocrine steps leading to puberty in the male
- Increase in GnRH pulse amplitude/ freq = increase in LH and FSH
- Leydig and sertoli cells mature, T4 remains basal
- When T4 production increases, LH and FSH decrease due to negative feedback on hypo
- T4 continues to increase from leydig cells in response to LH
- T4 builds to adult levels (so does GnRH pulses)
Slide 17
Slides 18,19
Figures
Puberty age range in cattle, sheep, horses, dogs, cats, swine
Cattle: 7-18 months
Sheep: 6-9 months
Swine: 3-8 months
Horses: 13-18 months
Dogs: 5-12 months
Cats: 8-10 months
Factors affecting onset of puberty in males
- plane of nutrition
- rate of growth
- exposure to environmental cues
- genetic background
Slide 22
Metabolic signals on GnRH
What environmental conditions affect puberty in males?
- photoperiod (seasonal breeders: sheep, goats, horses): T4 levels and testes size varies with season
- social contact (male-female, male-male)
Slides 24, 25
Testicular size and T4 concentrations in male polar bears
Why is early onset of puberty in males important?
Reduce generation interval and advance genetic improvement
- genetically superior males produce semen earlier/longer
- limit “down-time” waiting for onset of puberty
