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(Hormone Function)

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anterior pituitary drives changes

during puberty

controlled by GnRH from

hypothalamus

begins to secrete FSH, LH

LH

targets interstitialendocrinocytes

testosterone

dihydrotestosterone (DHT)

FSH - Sustentacular cells

Androgen-binding protein

(ABP) concentrates androgens

for spermatids

Inhibin negative feedback to

the pituitary and hypothalamus

Hormones of brain-testicular axis

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Development testosterone stimulates

pattern developmentbefore birth (internal ducts)

DHT external genitals Testosterone converted to

estrogens in brain braindevelopment

Puberty testosterone & DHTstimulate enlargement ofmale sex organs andsecondary sexualcharacteristics

Hormones of brain-testicular axis

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Onset of Puberty

FSH and LH secretion is high innewborn, but falls to low levels in fewweeks.

At puberty:

Brain maturation increases GnRHsecretion.

Decreased sensitivity of gonadotropin to

negative feedback. During late puberty, pulsatile secretion

of LH and FSH increase during sleep.

Stimulate a rise in sex steroid secretion.

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Onset of Puberty (continued)

Stimulates rise in

testosterone and

estradiol-17b.

Produce secondarysexual characteristics.

Age of onset related to

the % of body fat and

physical activity in the

female

Leptin secretion from

adipocytes may be

required for puberty.

Insert fig. 20.10

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Male Reproductive System

Testes:

Seminiferoustubules: Contain receptor

proteins for FSHin Sertoli cells.

FSH stimulatesspermatogenesisto occur.

Leydig cells: LH stimulates

secretion oftestosterone.

Contain receptorproteins for LH.

Insert fig. 20.12

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Control of LH and FSH Secretion

Negative feedback: Testosterone inhibits LH and

GnRH production. Maintain relatively constant

secretion of LH and FSH.

Declines gradually in menover 50 years of age.

Testosterone converted toDHT, which inhibits LH.

Inhibin inhibits FSH secretion.

Aromatization reactionproducing estradiol in thebrain, is required for the

negative feedback effects.

Insert fig. 20.13

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Endocrine Function of the Testes

Testosterone and itsderivatives areresponsible forinitiation andmaintenance of body

changes in puberty. Stimulate growth ofmuscles, larynx, and bonegrowth until sealing of theepiphyseal discs.

Promote hemoglobin

synthesis. Act in paracrine

fashion, responsiblefor spermatogenesis.

Insert fig. 20.15

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Testosterone:

Sources: Interstitial Cells in Testes

Targets & Functions: Body in general

Stimulates the development of male

secondary sexual characteristics including:

development of male genitalia

male skeleton and muscle development

male patterns for hair growth

increased RBC production & higher

metabolic rate

Seminiferous tubules Necessary for the completion of

spermatogenesis

Anterior Pituitary

Moderate inhibition of pituitary andhypothalamus

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Sertoli Cells

Form blood-testes barrier: Prevents autoimmune destruction of sperm.

Produce FAS ligand which binds to the FAS receptoron surface to T lymphocytes, triggering apoptosis of

T lymphocytes.Prevents immune attack.

Secrete inhibin.

Phagocytize residual bodies: May transmit information molecules from germ cells

to Sertoli cells.

Secrete androgen-binding protein (ABP): Binds to testosterone and concentrates testosterone

in the tubules.

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Leydig Cells

produce/secrete testosterone

located outside seminiferous tubules

active in fetus till birth, puberty onward

some testosterone converted to estradiol

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Effects of Testosterone

At puberty testosterone promptsspermatogenesis

Causes reproductive organs to grow &assume adult functions

As adult normal levels of testosterone are

required to maintain normal structure &function of reproductive organ

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Testosterone

develop/maintain secondary sex

characteristics :

metabolism anabolic

inhibit pituitary LH secretion

- mental, hair growth, larynx, muscles

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Estrogen Secretion

Sertoli and Leydig cells secrete smallamounts of estradiol.

Receptors found in Sertoli and Leydig cellsand accessory organs.

May be responsible for:

Negative feedback in brain.

Sealing of epiphyseal plates.

Regulatory function in fertility.

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Hormonal Control of

Spermatogenesis Formation of primary spermatocytesand entry into early prophase I, beginduring embryonic development.

Spermatogenesis arrested until

puberty. Testosterone required for completion

of meiosis and spermatid maturation.

Secrete paracrine regulators:

IGF-1. Inhibin.

Transforming growth factor.

FSH necessary in the later stages of

spermatid maturation.

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Thank you!