Lecture 7: Hormonal Regulation of Male Reproductive

Testosterone induces nonreproductive organs. * Appearance of which type of hair? * Enhanced growth of which hair? What happens to the voice? * What happens to the skin? * What happens to bones? * What happens to skeletal muscles? * What happens to basal metabolic rate? What is Basal Metabolic Rate? * What happens to libido?

* Appearance of pubic, axillary, and facial hair (puberty) * Enhanced growth of chest hair; deepening of the voice * Skin thickens and becomes oily * Bones grow, increase in density * Skeletal muscles increase in size and mass * Boosts basal metabolic rate (how fast you burn through calories to make ATP) * Libido (sex drive) in males is quite high

The HPG axis regulates production of gametes and sex hormones through 3 interacting sets (pairs) of hormones. Which hormones are these?

* GnRH (Gonadotropin-releasing hormone) * FSH (Follicle-stimulating hormone) and LH (Luteinizing hormone) * Testosterone and Inhibin

What do these hormones do? - GnRH - FSH and LH - Testosterone and Inhibin

- GnRH: stimulates secretion of FSH and LH - FSH and LH: directly stimulates testes to produce Testosterone and Inhibin for sperm production. - Testosterone and Inhibin: Testosterone stimulates an increase in spermatogenesis. Inhibin inhibits further secretion of FSH.

Testosterone is transformed to exert its effects on some target cells. Which two substances is it transformed into?

1) Dihydrotestosterone 2) Estradiol

1) Dihydrotestosterone 2) Estradiol What are these?

1) Dihydrotestosterone: in prostate for proper prostate function. 2) Estradiol: in some neurons in the brain (this is the main type of estrogen in females)

How long does it take to achieve balance (testosterone and sperm production)?

3 years to achieve; but then production is fairly stable throughout life

Rising testosterone levels → feedback inhibition on hypothalamus to inhibit what? and inhibition on pituitary to inhibit what?

GnRH release FSH and LH release

What is the HPG axis?

Hypothalamic-pituitary-gonadal (HPG) axis; a sequence of hormonal regulatory events involving hypothalamus, anterior pituitary gland, and testes

without this hormone, testosterone production decreases.

LH

An ↑ Testosterone will also increase production of which type of cells?

RBCs

Sequence of Regulatory Events: 1) Hypothalamus releases Gonadotropin-releasing hormone (GnRH) → Anterior pituitary secretes ____. 2) FSH causes sustentocytes to release androgen-binding protein (ABP) keeps a high concentration of ___ near spermatogenic cells → spermatogenesis. 3) LH prods interstitial endocrine cells → testosterone → ___.

Sequence of Regulatory Events: 1) Hypothalamus releases Gonadotropin-releasing hormone (GnRH) → Anterior pituitary secretes FSH and LH. 2) FSH causes sustentocytes to release androgen-binding protein (ABP) keeps a high concentration of TESTOSTERONE near spermatogenic cells → spermatogenesis. 3) LH prods interstitial endocrine cells → testosterone → increase in Spermatogenesis.

LH: Target: Reaction:

Target: Interstitial (endocrine) cells Reaction: secretion of testosterone

FSH: Target: Reaction:

Target: sustentocytes (Sertoli cells) in testes Reaction: secretion of Androgen-binding protein (ABP

Which hormone ↑ Spermatogenesis (Spermatids → Sperm) in testes?

Testosterone

Testosterone is synthesized from what?

cholesterol

Some testosterone stays locally in testes because ABP captures it and concentrates it in that area; other testosterone does what?

enters blood vessels and is carried throughout the body and has widespread effects on the body (i.e., male characteristics---deepening of voice, etc)

What is the main type of estrogen in females?

estradiol

What are tropins?

hormones that act on other endocrine glands

Testosterone is a steroid hormone. Are steroid hormones hydrophilic or hydrophobic?

hydrophobic

Why do males tend to have deepening of the voice?

lengthening of vocal cords in larynx and getting larger

FSH stimulates secretion of Androgen-binding protein (ABP). What does ABP do?

localizes within seminiferous tubules walls and it binds/concentrates testosterone in tubules = stimulate spermatogenesis.

What is libido?

sex drive

Testosterone →

sex organ maturation, development/maintenance secondary sex characteristics, libido (sex drive)

* prompts spermatogenesis * targets all accessory organs * has multiple anabolic (building) effects throughout the body * deficiency leads to atrophy; semen volume declines; erection and ejaculation impaired

testosterone

Which gland is often called the Master of the Master Gland?

the Hypothalamus

from which gland are hormone releasing hormones secreted?

the Hypothalamus

Without GnRH and gonadotropins (FSH, LH), what happens to the testes?

they atrophy; sperm and testosterone production cease

If testosterone amounts are deficient in the body; how Is this treated?

with testosterone replacement

People who take testosterone supplements (body builders) have what effects? What happens to the Semineferous tubules?

↓ in FSH and ↓in LH production = spermatogenesis will be affected. You won't have ABP either and this has a negative effect on sperm cell production...SF tubules shrivel up.