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GENERAL FUNCTIONOF ENDOCRINE SYSTEM
PHYSIOLOGY DEPARTEMENT
MEDICAL SCHOOL OF
UNIVERSITAS SUMATERA UTARA
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Location of Major Endrocrine Organs
Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 9.3
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HYPOTHALAMUS
The release of hormones from both the posterior
and anterior pituitary is directly controlled by
hypothalamus
Posterior pituitary connects to hypothalamus by
a neural pathway
Anterior pituitary connects to the hypothalamus
by unique vascular link
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Hypothalamic hormones
Thyrotropin RH (TRH) Thyrotropin, Prolactin
Gonadotropin RH (GnRH) LH, FSH
Corticotropin RH (CRH) Adrenocorticotropin
Hormone Target Pituitary Hormone
Growth hormone RH (GHRH) Growth hormone
Prolactin-inhibiting factor (PIF) Prolactin, Thyrotropin
(Dopamine)
Growth hormone IH (GHIH) Growth hormone(somatostatin)
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Complex endocrine pathways involving
pituitary and hypothalamus
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Hormones of the Pituitary Gland
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The Posterior Pituitary
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Neurohormones
Synthesized by neurons in the supraopticand paraventricular nuclei
Small peptides synthesized in the cell
bodies and transported to the posterior
pituitary by specific carrier proteins
Antidiuretic hormone (ADH) andoxytocin
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Antidiuretic Hormone (ADH)
Antidiuretic actions
Vasopressor actions
- increases permeability of the collecting
ducts to water
- V2
receptors
- constricts vascular smooth muscle cells
- V1 receptors, non-hormonal
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diabetes insipidus
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Oxytocin
Breast-feeding
Childbirth (parturition)
- contracts the myoepithelial cells of thealveoli
- classic neuroendocrine reflex
- in late pregnancy, uterine smooth
muscle (myometrium) becomessensitive to oxytocin
- positive feedback
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Growth Hormone
Does not have a target gland as other
pituitary hormones.
Promotes growth in all tissues.
Major targets: protein and lipid metabolism
Mechanisms: transcriptional and translational
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Physiologic effects of GH
Anabolic effects:
promotion of protein synthesis and amino acidtransport
decreased catabolism of proteins and aminoacids
Stimulation of bone growth and cartilageformation:
Cell division and protein synthesis Differentiation of condrocites to osteogenic
cells and deposition of bone
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PROLACTIN
Breast is main site of action. Episodic release
PRL secretion induced by high estrogen and hCG
PRH oxytocin
PRL inhibitor : PIH (dopamine)
most dominant
PRL inhibits LHRH secretion TRH can act as a PRL stimulator
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Secretion: mediated through hypothalamus-
pituitary secretions
Steroidal hormones:
Thyroxine (T4) and Triiodothyronine (T3):
both regulate production of ATP from glucose,
affects metabolic rate
Calcitonin: lowers blood calcium levels
Thyroid Gland
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PHYSIOLOGICAL EFFECTS OF THYROID
HORMONES
Increase O2 consumption of almost all
active tissues
(in part by mobilising fatty acids) Increase cardiac output
Needed for normal brain development
Needed for normal growth and skeletal
maturation
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Negative feedback homeostasis:
T3 and T4 effects on TSH and TRH
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Secretion: response to lowered bloodcalcium levels
Hormone: Parathyroid hormone (PTH),nonsteroidal
Removes calcium and phosphate from bone
Increases absorption of calcium by thedigestive tract
Increases renal retention of calcium andexcretion of phosphate
Parathyroid Glands
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Structures: islets of Langerhans
Hormones: nonsteroidal
Glucagon: made by alpha cells, raises blood
sugar
Insulin: made by beta cells, lowers blood sugar
Pancreas: Endocrine Functions
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Roles of Insulin and Glucagon inRegulating Blood Glucose
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Adrenal Gland
epinephrinenorepinephrine
cortisol
aldosterone
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Cortisol exerts
negative feedback on
ACTH and CRH
Cortisol effects
Synergizes glucagon
and epinephrine
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Secretion of Cortisol
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Cortisol Effects
Increases in blood[glucose] (gluconeogenesis and glycogenolysis)
[amino acids] (protein catabolism)
[fatty acids] (lipolysis)
Permissive for action of glucagon and
epinephrine(synergism)
Anti-inflammatory (prevents actions of cytokines)
Negative feedback
reduces CRH (hypothalamus)
reduces ACTH (anterior pituitary)
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Adrenal medulla: neuroendocrine organ
Secretion: sympathetic nervous system
Hormones: nonsteroidal
Epinephrine and Norepinephrine:
enhance function of sympathetic nervous
system
(Fight or flight)
Adrenal Glands: Medulla
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Roles of the Hypothalamus and Adrenal Glands in the
Stress Response
Copyright 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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LH and FSH
LH/ FSH functionOvary
ova
oestrogenprogesterone
Testes
sperm
testosterone
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TESTES
Testosterone synthesised from Leydig
cells
LH stimulates this release Sertoli cells play important role in
spermatogenesis
FSH stimulates Sertoli cells
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OVARIES
FSH stimulate follicle maturation
Granular cell secrete estrogen
LH stimulate follicle maturation in the last
periode and surge preceeds ovulation
Corpus luteum secrete progesteron
Mechanism negative feed back fromprogesteron and estrogen reduce FSH/LH
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Hormone: testosterone (steroidal)
Functions:
Regulates development and normal
functioning of sperm, male reproductive
organs, male sex drive
Development of male secondary sex
characteristics
Testes
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Hormones (steroidal) and functions:
Estrogen: initiates development of
secondary sex characteristics, regulatesmenstrual cycle
Progesterone: regulates menstrual cycle
Ovaries
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