Download Endocrine System

Endocrine System
Dr Khamis Al Hashmi
Department of physiology
Room # 006
Ext. 3435
Email: [email protected]
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Nervous Vs Endocrine system
 Nervous
and endocrine systems acts
together to coordinate functions of body
system.
 Nervous system releases;
Neurotransmitors
 Endocrine
system releases; Hormones
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Nervous Vs Endocrine system (cont.)
Characteristic
Nervous system
Endocrine system
Mediators molecules Neurotransmitters Hormones
Site of mediator
action
Close to site of
release
Far from site of
release
Types of target cells Muscle cells,
Cells throughout
the body
Time to onset of
action
Seconds to hours
Duration of action
gland cells, other
neurons
Within
milliseconds
Briefer
(milliseconds)
Longer (seconds
3
to days)
Endocrine Vs Exocrine glands
Exocrine gland: secrete their products into
ducts that carry the secretion into body
cavities, into lumen of organs, or to the outer
surface of the body.
 E.g. Sweat, sebaceous, mucus, digestive
glands.


Endocrine glands: secrete their products into
the interstitial fluid surrounding the secretory
cells
diffused into blood capillaries
carried to target cells.
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Definitions
Hormone:
is a mediator molecule that is released in
one part of the body but regulates activity of cells in
other parts of the body.
Target cell:
A cells whose activity is affected by a
particular hormone.
Receptor: A specific molecule or cluster of molecules
that recognizes and binds a particular ligand (hormone)
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Circulating hormones Vs Local hormones
A) Circulating hormones
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B) Local hormones:
1) Paracrines
E.g. Nitric oxide.
IL2
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2) Autocrines
E.g. IL2
Local hormones usually are inactivated quickly
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Chemical classes of hormones
a)
Water-soluble hormones:
-
Amine hormones
(Retain an amino group
(NH3+)
-
-
Peptide and protein hormones
Eicosanoid hormones (derived from
arachidonic acid. Eg. Prostaglandins, leukotrienes)
b)
Lipid-soluble hormones:
-
Steroid hormones
Thyroid hormones
Nitric oxide
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a) Water soluble hormone
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b) Lipid soluble hormone
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Hormone transport in the blood
 Water
soluble hormones circulate in a
free form (Unbound).
 Lipid soluble hormones bound to
transport proteins. (>90%).
Importance:
- Increase the solubility in blood.
- Slow the rate of excretion by kidney or
degradation by liver.
- Provide a ready reserve of hormone.
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Responsiveness of a target cell to a hormone
depend on:
1) Concentration of the hormone
2) Number of receptors
3) Influence by other hormone (hormones interaction)
1) Concentration of the hormone
–
The hormone’s rate of secretion (all hormones)
–
Rate of metabolic inactivation and excretion (all hormones)
–
Rate of metabolic activation (few hormones)
–
Extent of binding to plasma protein (lipophilic hormones)
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Control of hormone secretion

Important to prevent overproduction or
underproduction
Three types of signals:
1. Signals from the nervous system
Eg. Nerve impulse to adrenal medulla
2.
Chemical changes in the blood.
Eg. Blood Ca2+ level
3.
Epinephrine
parathyroid hormone
Other hormone
Eg. Ant. Pituitary hormones
glands
hormones of other
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Negative-feedback control
Short loop feedback
long loop feedback
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Positive-feedback
control
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Diurnal (circadian) rhythm

The secretion rate of many hormones rhythmically
fluctuate up and down as function of time.
– Diurnal (or circadian), i.e. “day-night”. characterised
by repetitive oscillations in hormone levels that are
very regular and have a frequency of one cycle every
24 hours. Eg. Cortisol secretion.
– Other rhythm. Monthly menstrual period.

Negative feedback control mechanisms operate to
maintain whatever set point is established for that
time.
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Clearance of hormones from the blood
– Metabolic destruction by the tissues
– Binding with the tissues.
– Excretion by the liver into the bile.
– Excretion by the kidneys into urine.
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2) Number of receptors
Down regulation:
A hormone present in excess
–
–
–
–
–
Receptors
Destruction of the receptor by lysosomes
Decrease production of receptors
Inactivation of some of the receptor molecules
Inactivation of some of the intracellular signaling molecules
Temporary sequestration of the receptor to the inside of
the cell.
Up regulation:
A hormone is deficient
Receptors
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3) Hormones interaction:
Permissiveness (permissive effect): powerful action of a
hormone on target cells require a simultaneous or recent
exposure to a second hormone.
Eg. Epinephrine and thyroid hormones in lipolysis.
Synergism (synergistic effect): the effect of two hormones
acting together is greater or more extensive than the effect of
each hormone acting alone.
Eg. FSH and estrogen for normal development of oocytes in
ovaries.
Antagonism (antagonistic effect): one hormone opposes the
action of another hormone.
Eg. Insulin and glucagon.
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Endocrine dysfunction
a)
Decrease in hormone activity



Decrease in hormone secretion by the
endocrine gland (hyposecretion).
Increase removal of the hormone from the
blood
Abnormal tissue responsiveness to the
hormone:

Lack of target cell receptors.
Lack of an enzyme essential to the target cell
response
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b)
Increase in hormone activity



Increase in hormone secretion by the
endocrine gland (hypersecretion)
Reduced plasma protein binding of the
hormone (too much free, biologically active
hormone
Decreased removal of the hormone from
the blood:

Decreased inactivation.
Decreased excretion
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Location of endocrine glands
Organ
Hormones secreted
Hypothalamus
Releasing and inhibitory hormones (e.g.
thyrotropin releasing hormones,
growth
hormone
inhibitory
hormone), ADH, oxytocin.
Anterior pituitary gland
Tropic
hormones:
ACTH,
LH,FSH), GH, prolactin.
Posterior pituitary gland
Oxytocin, ADH (vasopressin)
Thyroid gland
Thyroxine, Tri- iodothyronine.
Adrenal gland
Mineralocorticoids (e.g. aldosterone),
glucocorticoids
(e.g.
cortisol),
catecholamines (e.g. epinephrine,
nor-epinephrine).
Parathyroid glands
Parathyroid hormone.
Pancreatic Islets
Insulin, glucagon.
Gonads
Testosterone, estradiol.
TSH
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Hypothalamus and pituitary gland
Anterior pituitary
HypothalamicHypophyseal
portal system
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Posterior Pituitary
Hypothalamohypophyseal
tract
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Hypothalamus
Hormones
Target cells
Major function
Releasing hormones:
TRH, CTR, GnRH, GHRH,
PRH
Anterior pituitary
Stimulate release of
particular anterior
pituitary hormone.
Inhibiting hormones:
GHIH, PIH
Anterior pituitary
inhibit release of
particular anterior
pituitary hormone.
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Anterior pituitary gland
Hormones
Target cells
Major function
Thyroid stimulating hormone (TSH)
Thyroid follicular cells
Stimulates T3 and T4 secretion
Adrenocorticotropic hormone (ACTH)
Zona fasciculata and reticularis
of adrenal cortex
Stimulates cortisol secretion
Growth hormone (GH)
Bone; soft tissue
Essential for growth
Metabolic effects; protein
metabolism, fat mobilization and
glucose conservation
Liver
Stimulates IGF secresion
Female: ovarian follicles
Promote follicular growth and
development; stimulates estrogen
secretion
Follicle-stimulating hormone (FSH)
Males: Seminiferous tubules in
testes
Luteinizing hormone
Prolactin
Females: ovarian follicle and
corpus luteum
Stimulates sperm production
Stimulates ovulation, corpus luteum
development, estrogen and
progesterone secresion
Males: inerstitial cells of leydig
in testes
Stimulates testosterone secretion
Females: mammary glands
(breast)
Promotes breast development;
stimulates milk secresion
Males
Uncertain
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Posterior pituitary
Hormones
Target cells
Major function
Antidiuretic hormone
(ADH), Vasopressin
Kidney tubules
Increase water
reabsorption
Arterioles
Produces
vasoconstriction
Uterus
Increase contractility
Oxytocin
Mammary glands Causes milk ejection
(Breast)
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Thyroid Gland
Hormones
Target cells
Major function
Tetraiodothyronine (T4 or
thyroxin); Triiodothyronine (T3)
Most cells
Increase metabolic
rate; essential for
normal growth and
nerve development
Calcitonin
Bone
Decrease plasma
calcium concentration
Parathyroid Gland
Hormones
Target cells
Major function
Parathyroid hormone
(PTH)
Bone, kidneys, intestine.
Increases plasma
calcium concentration;
decrease plasma
phosphate
concentration; stimulates
vitamin D activation
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Adrenal gland
Hormones
Target cells
Major function
Cortex:
Zona
glomerulosa
Mineralocorticoid
(Aldosterone)
Kidney tubules
Increases Na+
reabsorptionand K+
excresion
Zona Fasiculata
and reticularis
Glucocorticoid
(cortisol)
Most cells
Increases blood
glucose at the
expense of protein
and fat store;
contributes to
stress adaptation
Androgens
Female: bone
and brain
Pubertal growth
spurt and sex drive
Sympathetic
receptor site
throughout the
body
Contributes to
stress adaptation
and blood pressure
regulation
Medulla
Epinephrine and
norepinephrine
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Pancreas (Islets of langerhans)
Hormones
Target cells
Major function
Beta (β) cells
Insuline
Most cells
Promotes cellular
uptake, use and
storage of
absorbed nutrients
Alpha (α) cells
Glucagon
Most cells
Important for
maintain nutrient
levels in blood
during
postabsorptive
state
D cells
Somatostatin
Digestive
system
Pancreatic islet
cells
Inhibits digestion
and absorption of
nutrients
Inhibits secretion
of all pancreatic
hormones
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Ovaries
Hormones
Target cells
Major function
Estrogen
Female sex organs;
body as whole.
Promotes follicular
development,
development of
secondary
characteristics,
stimulate uterine and
breast growth.
Bone
Promotes closer of
epiphyseal plate
Uterus
Prepare for pregnancy
Progesterone
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Testes
Hormones
Target cells
Major function
Testosterone
Male sex organs; body
as whole
Stimulate sperm
production;
development of
secondary
characteristics;
Promotes sex drive
Testes and ovaries secret inhibin that acts on the anterior
pituitary to inhibit secretion of follicle stimulating hormone.
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