Download Human Physiology

Endocrine system
Dicky Moch Rizal
Dept. Of Physiology, Fac.Medicine, GMU
Endocrine system maintains
homeostasis
The concept that hormones acting on distant
target cells to maintain the stability of the
internal milieu was a major advance in
physiological understanding.
The secretion of the hormone was evoked by a
change in the milieu and the resulting action on
the target cell restored the milieu to normal.
The desired return to the status quo results in
the maintenance of homeostasis
Endocrine vs. Nervous System
• Major communication systems in the body
• Integrate stimuli and responses to changes in
external and internal environment
• Both are crucial to coordinated functions of
highly differentiated cells, tissues and organs
• Unlike the nervous system, the endocrine system
is anatomically discontinuous.
Nervous system
•The nervous system exerts
point-to-point control through
nerves, similar to sending
messages by conventional
telephone. Nervous control is
electrical in nature and fast.
Hormones travel via the bloodstream to
target cells
•The endocrine system
broadcasts its hormonal messages
to essentially all cells by secretion
into blood and extracellular fluid.
Like a radio broadcast, it requires a
receiver to get the message - in the
case of endocrine messages, cells
must bear a receptor for the
hormone being broadcast in order
to respond.
A cell is a target because is has a specific
receptor for the hormone
Most hormones circulate in blood, coming into contact with essentially all cells.
However, a given hormone usually affects only a limited number of cells, which
are called target cells. A target cell responds to a hormone because it bears
receptors for the hormone.
Principal functions of the endocrine
system
• Maintenance of the internal environment in the
body (maintaining the optimum biochemical
environment).
• Integration and regulation of growth and
development.
• Control, maintenance and instigation of sexual
reproduction, including gametogenesis, coitus,
fertilization, fetal growth and development and
nourishment of the newborn.
Types of cell-to-cell signaling
Classic endocrine hormones travel
via bloodstream to target cells;
neurohormones are released via
synapses and travel via the
bloostream; paracrine hormones
act on adjacent cells and autocrine
hormones are released and act on
the cell that secreted them. Also,
intracrine hormones act within the
cell that produces them.
Response vs. distance traveled
Endocrine action: the hormone is distributed in blood and binds to distant target
cells.
Paracrine action: the hormone acts locally by diffusing from its source to target
cells in the neighborhood.
Autocrine action: the hormone acts on the same cell that produced it.
Hormone receptors
• Hormone receptor characteristic
▫ Distinguish their hormones from other molecules
▫ Bind to their hormones even the concentration
hormone exceeding low
▫ Undergo a conformational change when bound to the
hormone
▫ Catalyze biochemical events or transmit change in
molecular transformation to adjacent moleculesthat
produce a biochemical change
Human Physiology
Endocrine System
• Control pathways
• May be
▫ Local pathways
 Paracrine and autocrine responses
 In or in the vicinity of the cells or tissues
▫ Long-Distance pathways
 Response loops
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Stimulus
Sensor/receptor
Afferent pathway
Integrating center
Efferent pathway
Effector
Responses
Human Physiology
Endocrine System
• Negative feedback loops
▫ Stabilizing a function and maintain it withing a
normal range
▫ Response is in opposition to stimuli
▫ Homeostatic control
• Positive feedback loops
▫ Response reinforces the stimulus
▫ Response destabilizes the variable
▫ Requires an event outside the loop to stop them
Human Physiology
Endocrine System
Disturbance
Negative feedback
_
Controlled
system
Sensor
Error
signal
Output
Set-point
adjuster
Inverting
amplifier
Human Physiology
Endocrine System
• Control systems vary in their speed &
specificity
▫ Specificity
 Nervous control very specific
 Hormonal control more general
▫ Nature of signal
 Nervous system uses both electrical and chemical
 Endocrine system uses only chemicals
▫ Speed
 Nervous system much faster, up to 120 m/sec
 Endocrine system much slower
▫ Duration of action
 Nervous system shorter, very brief
 Endocrine system lasts longer
Human Physiology
Endocrine System
▫It brings about changes via chemical
messengers, hormones, released into the blood
stream and carried to target organs.
▫Endocrinology - the study of hormones and
the endocrine organs.
▫Endocrine system - all of the glands that
secrete hormones
 Endocrine and exocrine glands
▫Exocrine glands - have ducts through which
their nonhormonal products travel to the
membrane surface and to the exterior (epithelial
surface)
Human Physiology
Endocrine System
▫Endocrine glands - release their substances into the
surrounding fluid (ductless glands). They include the
pituitary, thyroid, parathyroid, adrenal, pineal, and
the thymus glands. Also included are the pancreas
and gonads. The hypothalamus is called a
neuroendocrine organ.
▫Know Fig 7.2
Inputs to endocrine cells
Neural control
• Neural input to hypothalamus stimulates
synthesis and secretion of releasing factors
which stimulate pituitary hormone production
and release
Chronotropic control
• Endogenous neuronal rhythmicity
• Diurnal rhythms, circadian rhythms (growth
hormone and cortisol), Sleep-wake cycle;
seasonal rhythm
Episodic secretion of hormones
• Response-stimulus coupling enables the
endocrine system to remain responsive to
physiological demands
• Secretory episodes occur with different
periodicity
• Pulses can be as frequent as every 5-10 minutes
Episodic secretion of hormones
• The most prominent episodes of release occur
with a frequency of about one hour—referred to
as circhoral
• An episode of release longer than an hour, but
less than 24 hours, the rhythm is referred to as
ultradian
• If the periodicity is approximately 24 hours, the
rhythm is referred to as circadian
▫ usually referred to as diurnal because the increase
in secretory activity happens at a defined period of
the day.
Circadian (chronotropic) control
Human Physiology
Endocrine System
Human Physiology
Endocrine System, Hormones
• Hormones - chemical messengers carried by
the blood from endocrine glands to the cell
upon which they act.
▫ Are chemical messengers
▫ Secreted into the blood by endocrine cells or
neurons
▫ Affect distal targets
• Affect target cells by controlling
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Rate of enzymatic reactions
Transport of molecules across cell membrane
Gene expression and protein synthesis
Stimulation of mitosis
Human Physiology
Endocrine System, Hormones
• Classification
▫ Peptide hormones - 3 or more amino acids
▫ Steroid hormones - derived from cholesterol
▫ Amine hormones - single amino acids
• Know Table 7-1
Human Physiology
Endocrine System, Hormones
• Classification, Peptide hormone - eg: Insulin
▫ Synthesis - RER, preprohormone
▫ Packaged in vescicles
▫ In Golgi apparatus, pre to pro hormone then to
hormone and fragments
▫ Released into ECF when cell is signaled to do so
▫ Transported in blood, half-life - minutes
▫ Mechanism of action - bind to cell surface
receptors. Many use cAMP and some use tyrosine
kinase
▫ Action - open or close membrane channels or
modulate metabolic enzymatic activity or
transport proteins
Human Physiology
Endocrine System, Classification
•Peptide hormone synthesis, packaging, and
release
Figure 7-3
Human Physiology
Endocrine System, Hormones
• Classification, Steroid hormones, eg: estradiol
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Synthesis - SER, lipophilic, sythesized as needed
Found bound (inactive) to protein carriers in blood
Half-life - hours
Mechanism - diffuses across cell membrane to
cytoplasmic and nuclear receptors. Interact with
DNA
▫ Slow response by cells - hours
▫ Fig 7.7
Human Physiology
Endocrine System, Hormones
• Action of Steroid Hormones
Human Physiology
Endocrine System, Hormones
• Classification, Amine hormones
▫ Nitrogen-containing
▫ Most derived from tryptophan or tyrosine
▫ They behave like peptide hormones (catecholamines) or
like steroid hormones (thyroid hormones)
▫ Thyroid hormones: produced by thyroid gland found in
the lower part of the neck. It secretes 3 hormones:
 Thyroxine - T4
 Triiodothyromine - T3
 Calcitonin
▫ The first two are collectively known as thyroid hormones
(TH) and contain iodine
▫ Virtually every tissue in the body is affected by TH
Human Physiology
Endocrine System, Hormones
• Amine hormone, Adrenal medullary hormones
▫ The adrenal gland consists of a medullary and
cortical section. The cortex secretes steroid
hormones.
▫ The adrenal medulla secretes two hormones
 Epinephrine (E) and
 Norepinephrine (NE)
▫ These are also called catecholamines
Human Physiology
Endocrine System, Hormones
• Second messenger mechanisms of amino acidbased hormones
Human Physiology
Endocrine System, Hormones
• Steroid hormones
▫ Produced by the adrenal cortex, the gonads, and
the placenta
▫ Precursor is cholesterol
▫ Synthesis of steroid hormones
Human Physiology
Cholesterol
Endocrine System
Pregnenolone
Progesterone
17-Hydroxyprogesterone
Dihydroepiandr♂sterone
(Androgens)
Androstenedione
Testes
Corticosterone
(Glucorticoids)
Aldosterone
(Mineralocorticoid)
Cortisol
Testosterone
Ovaries
Estradiol
Human Physiology
Endocrine System, Hormones
• Direct gene activation mechanism of steroid
hormones
Human Physiology
Endocrine System, Hormones
• Hormonal Specificity
▫ All major hormones circulate to virtually all
tissues (target cells), but for these cells to
respond to a hormone, they must have a specific
protein receptor on their plasma membrane or in
their interior.
• Hormone-target interaction depends on:
▫ Blood levels of the hormone
▫ The relative number of receptors for that hormone
▫ The affinity of the bond between the hormone and
the receptor
• Up-regulation and down-regulation
Human Physiology
Endocrine System, Hormones
• Onset, Duration, and Half-life
▫ Onset varies greatly, from almost immediately to
hours or days
▫ Duration can range from several minutes to
several hours
▫ Half-life is the length of time the hormone
concentration takes to drop by half
 From a fraction of a minute to several hours
▫ Concentration determined by its rate of release
and the speed of deactivation and removal
Human Physiology
Endocrine System, Control of Hormone Release
• Endocrine glands are stimulated by humoral,
neural and hormonal means.
▫ Humoral stimuli - changing levels of blood ions
and nutrients. Example:-↓calcium
→↑parathyroid hormone
▫ Neural stimuli - nerve fiber stimulates hormonal
release. Example:-↑nervous input to adrenal
medulla → release of catecholamines
• Hormonal stimuli (tropic hormones) - endocrine
glands release their hormones in response to
hormones produced by other endocrine organs.
Example:-hypothalamic hormones → anterior
pituitary to release hormones → other endocrine
glands to produce even more hormones
Human Physiology
Endocrine System, Neurohormones
• Hypothalamic-pituitary system
▫ Pituitary gland - lies just below hypothalamus, in
pocket of bone at base of brain. Consists of two
adjacent lobes - the anterior pituitary and the
posterior piruitary
▫ Posterior pituitary hormones
 Oxytocin and vasopressin are released
 Made in hypothalamus, move down the neural axons
and accumulate in the axon terminals in the posterior
pituitary
 Vasopressin - blood pressure and kidney function
 Oxytocin - breasts and uterine contractions
Human Physiology
Endocrine System, Neurohormones
• Hypothalamus and Anterior Pituitary
▫ The hypothalamus also secretes hormones that
control the secretion of ALL the anterior pituitary
hormones. The basic pattern is as follows:
 Secretion of a hypothalamic hormone, which controls
secretion of
 An anterior pitiutary hormone, which controls the
secretion of
 A hormone from some other endocrine organ/gland
▫ Anterior Pituitary Hormones
 At least eight secreted, six with well-established
functions
Human Physiology
Endocrine System, Neurohormones
Human Physiology
Stimulus
Endocrine System, Neurohormones
Hypothalamus
↑Hormone 1 Secretion
↑Plasma Hormone 1
Anterior Pituitary
↑Hormone 2 Secretion
↑Plasma Hormone 2
Third Endocrine Gland
↑Hormone 3 Secretion
↑Plasma Hormone 3
Target Cells
Human Physiology
Endocrine System
• Hypothalamic Releasing Hormones
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Corticotropin Releasing Hormone (CRH)
Thyrotropin Releasing Hormone (TRH)
Growth Hormone Releasing Hormone (GHRH)
Somatostatin (SS) also called Growth hormone
releasing Inhibitin Hormone (GIH)
▫ Gonadotropin Releasing Hormone (GnRH)
▫ Prolactin Releasing Hormone (PRH)
▫ Prolactin releasing Inhibiting Hormone (PIH)
Human Physiology
Endocrine System
• Anterior Pituitary Hormones
▫ Gonadotropic Hormones
 Follicle-Stimulating Hormone (FSH)
 Luteinizing Hormone (LH)
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Growth Hormone (GH)
Thyroid-stimulating Hormone (TSH)
Prolactin
AdrenoCorticoTropic Hormone (ACTH)
▫ β-Lipotropic Hormone
▫ β-Endorphin
Human Physiology
Hypothalamus
GnRH
FSH
and
LH
Gonads
Germ cell
development
Hormones-estrogen,
progesterone and
testosterone
GHRH
SS
TRH
Anterior
Pituitary
GROWTH
TSH
HORMONE
Liver
Other
organs
IGF-1
Growth
Metabolism
Thyroid
Thyroxine
T3
PIH
PRH
PROLACTIN
Breasts
Development
Milk
CRH
ACTH
Adrena
l
cortex
Cortiso
l
Summary of Hypothalamic-anterior-pituitary system
Human Physiology
Endocrine System
Human Physiology
Endocrine System
Human Physiology
Endocrine System