RSK.6-Male Repro Physiology
Transcript of RSK.6-Male Repro Physiology
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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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