Midterm 2 - Lecture 15

Question 1

GnRH

Answer 1

Source: Hypothalamus
Target: Gonadotroph cells in anterior pituitary
Action: Release FSH & LH

Question 2

FSH

Answer 2

Source: Gonadotroph cells in anterior pituitary
Target: Sertoli cells in testes
Action: Maintenance of spermatogenesis and Stimulate androgen binding protein (ABP) production

Question 3

LH

Answer 3

Source: Gonadotroph cells in anterior pituitary
Target: Leydig cells in testes
Action: T4 production

Question 4

What are Leydig cells the equivalent of?

Answer 4

Follicular theca interna cells

Question 5

What are Sertoli cells the equivalent of?

Answer 5

Follicular granulosa cells

Question 6

T4

Answer 6

Source: leydig cells (testis)
Target: hypothalamus, reproductive tract, muscle
Action: male sexuality
- increase sexual behaviour and characteristics
- decrease GnRH production
- increase spermatogenesis
- increase muscle development
- cause accessory sex glands to develop

Question 7

Androgen Binding Protein (ABP)

Answer 7

Source: sertoli cells (testes)
Target: N/A
Action: binds T4 in seminiferous tubules to stimulate spermatogenesis

Question 8

Inhibin

Answer 8

Source: sertoli cells (testes)
Target: gonadotroph cells (anterior pituitary)
Action: inhibits FSH secretion

Question 9

What are all reproductive fxns ultimately controlled by?

Answer 9

positive and negative feedback

Question 10

Positive effects of male endocrinology

Answer 10

• GnRH stimulates FSH & LH production by Ant Pit
• LH stimulates T4 production by the Leydig cells
• FSH stimulate sertoli cells to produce ABP and Inhibin
• ABP binds T4 in the seminiferous tubules and T4 stimulates spermatogenesis

Question 11

Negative effects of male endocrinology

Answer 11

• T4 inhibits GnRH production by the hypothalamus
• inhibin inhibits FSH production by the Anterior Pituitary

Question 12

Male Hormonal Cycle

Answer 12

Hypothalamus has no surge center
- discharges GnRH in frequent pulses or bursts
- GnRH pulses last for a few moments and occur several times a day
- LH and FSH surges induced by GnRH pulses
- T4 surges induced by LH: continual T4 stimulation is needed for spermatogenesis

*cycle occurs over a few hours

Question 13

Puberty

Answer 13

the process of acquiring reproductive competence

Question 14

What are the pubescent processes in the male?

Answer 14

• behavioral traits expressed
• ejaculation
• spermatozoa present in ejaculate
• adequate sperm production to accomplish fertilization

Question 15

What is the limiting factor to the onset of puberty?

Answer 15

Hypothalamus!
- onset of puberty requires secretion of GnRH at frequency and quantities appropriate to stimulate gonadotropin (FSH & LH) release by the ant pit at levels adequate to support gametogenesis
- in the male, onset of puberty occurs due to decreased hypothalamic sensitivity to negative feedback of T4

Question 16

5 endocrine steps leading to puberty in the male

Answer 16

1. increase in GnRH pulse amplitude and frequency drives an increase in LH and FSH
2. Leydig and Sertoli cells mature in response to the increase in LH and FSH but T4 remains basal
3. when T4 production increases, LH and FSH decrease (implies GnRH pulse decrease)- due to negative feedback T4 by hypothalamus
4. T4 continues to increase from Leydig cells in response to LH
5. T4 “builds” to adult levels (also GnRH pulse amplitude and frequency)

Question 17

Cattle age of puberty

Answer 17

7-18 months

Question 18

Sheep age of puberty

Answer 18

6-9 months

Question 19

Swine age of puberty

Answer 19

3-8 months

Question 20

Horse age of puberty

Answer 20

13-18 months

Question 21

Dog age of puberty

Answer 21

5-12 months

Question 22

Cat age of puberty

Answer 22

8-10 months

Question 23

Factors affecting onset of puberty

Answer 23

• plane of nutrition
• rate of growth
• exposure to environmental cues
• genetic background

Question 24

Environmental conditions that affect male puberty

Answer 24

Photoperiod - seasonal breeders
- sheep, goats, horses
- T4 levels and testes size vary with season

Social Contact (male-female, male-male)
- not well understood

Question 25

Early onset of puberty in males

Answer 25

Reduce generation interval and advance genetic improvement
- reduction in age of puberty would result in genetically superior males producing semen earlier and longer
- limit “down-time” waiting for the onset of puberty
- applicable to sires used in AI studs