Download physiology hormone-1

Hormone physiology
All the things you forgot or never
learned from Science collage
Dr. Maha Daghestani
Today lecture
Introduction to endocrinology
„ Know and understand what a hormone is
„ Mechanism of hormone action
„ Regulation of hormone secretion
„ Types of endocrine disorder
„
Endocrine System
A regulatory system, like the nervous
system.
„ Uses chemical messengers instead of nerve
impulses.
„ Goes into blood stream, travels to effectors
and causes an effect.
„
Endocrine Glands
„
„
Compare exocrine with endocrine
glands.
The body contains two types of glands:
„
Exocrine glands secrete their products into
ducts or directly onto epithelial surfaces.
„
Endocrine glands secrete their products
called hormones, into the extracellular fluid
around the secretory cells. The secretion
then diffuses into the blood for distribution
throughout the body.
Which organs are endocrine only?
„ Hypothalamus
„ Pituitary
„ Pineal
gland
Thymus gland
Parathyroid
Thyroid
Name other organs that have some
endocrine function
„ Pancreas
„ Kidneys
„ small
intestine
gonads (2)
stomach
heart
„ placenta
The pituitary (hypophysis) attached to the
underside of the brain
Pineal gland
The thyroid, situated in the neck close to
the larynx
The Parathyroids, associated with the thyroid but
comprising separate structures
Thymus
Thymus gland
gland
The adrenals, situated on top of each kidney
The endocrine portion of the pancreas
The ovaries
The testes
Testes anatomy and histology
Non-hormonal cell-to-cell communication
Paracrine example: histamine released by injured cells causes
local capillary walls to become more permeable, allowing more
white blood cells and fluid to leak into injured area.
Autocrine example: various cytokines involved in development
and cell differentiation act both as autocrines and as paracrines.
Endocrine system — signaling molecule needs to be
carried around the body by the blood stream to be
considered a "true hormone."
Example: insulin, from
pancreatic beta cells
Example: acetylcholine — neuromuscular
junction, heart, various gastrointestinal functions
Example: epinephrine (adrenaline),
released by adrenal medulla
(essentially a large cluster of
sympathetic nerve cells) to affect
heart rate and contractility, blood
vessel diameters, and short-term
energy usage
Hormones
„
"A chemical substance, synthesized by a
specific organ or tissue and secreted into
the blood stream, in which it is carried to
other specific sites in the body, where it
exerts its action(s)".
Chemically, hormones may be conveniently
divided into the following classes of organic
compound:
„ proteins (eg. insulin) and peptides (eg.
oxytocin)
„ amino acid derivatives (eg. thyroxine)
„ steroids (eg. cortisol)
„
Hormones are usually transported in the
blood bound to plasma proteins or to
proteins specific to the particular
hormone
„ Blood Levels of Hormones will depend
on:
„
The rate of secretion, which may be
divided into:
„ the rate of synthesis
„ The rate of removal
„
Hormone Overview
„
Protein/peptide hormones
–
–
–
Preprohormone synthesis is directed by mRNA
on endoplasmic reticulum
Peptides cleaved from preprohormone to
produce a prohormone, after which more
peptides are cleaved by the Golgi apparatus to
form a hormone.
Hormone is then stored in secretory granules
for later release
Hormone overview
„
Steroid hormones
–
„
derivatives of cholesterol
Amine hormones
–
derivatives of tyrosine (thyroid hormone,
epinephrine, norepinephrine)
Regulation of hormone secretion
1- Negative feedback
–
–
Most common mechanism of hormone secretion
regulation
Hormone has effects that directly or indirectly
down regulate further secretion
2- Positive feedback
–
self perpetuating (uncommon).
3-Mineral ions concentration.
4-Concentration of organic nutrients
Mechanisms of Hormone Action
„
Though hormones are able to reach where
ever the blood circulates, they are only able
to act upon specific cells that possess
receptors specific to that particular
hormone.
„ Such cells are termed target cells (target
tissues, or target organ).
„
TARGET CELL
A TARGET CELL is a cell that responds
to a hormone. Target cells must have
receptors for a hormone.
„ - A RECEPTOR is a protein able to bind
with a hormone No receptor ————>
not a target cell
„ - The number of receptors on a target cell
is constantly changing. - 2000-100,000
receptors per cell
„
Proteins, peptides and amines
„
Proteins, peptides and amines are not lipid
soluble thus they cannot pass across the
plasma membranes of cells. The receptors
for such hormones are present on the
outside of the cell membrane. Binding of
the hormone with its membrane receptor
causes the production within the cell of a
second messenger compound which then
exerts the hormone's actions within the cell.
The second messenger
„
The second messenger modifies activities
within the cell. These activities could
include changing enzyme action, altering
protein synthesis (through messenger
RNA) or opening or closing membrane
channels.
Examples of second messengers include:
- cyclic adenosine monophosphate (cAMP),
-cyclic guanosine monophosphate
-(cGMP),inositol triphosphate (IP3) and
-calcium ions.
Proteins
„
„
„
„
„
„
freely circulating
dissolved in the blood
travel on their own
very available
effect lasts minutes to an hour
(immediate response, short term)
Cell membrane
Cell membrane
Membrane protein
Protein actions
Steroid/Thyroid Hormones
transported bound to special transport
proteins
„ when a hormone is bound to a transport
protein it is "unavailable"
„ small amount available (dissolved in
blood)
„ 99% is stored on transport proteins "in
reserve"
„
Steroid/Thyroid Hormones
„
„
„
when the 1 % binds to the receptor , the
hormone level in the blood drops and another
1% is released, from the transport proteins and
then replenished by the secretory glands and
cells
this increases the time of availability of the
hormone - hours to days————> weeks
offers a gradual, long term response
Endocrine disorder
Hyposecretion
A- primary hyposecretion
B- Secondary hyposecretion
Hypersecretion
A- primary hypersecretion
B- Secondary hypersecretion
Hyporesponsiveness
Relation between hormones
Antagonism (Insulin,Glucagon)
Antagonist
Synergism (estrogen, progesterone)
Permissive action( GH, Epinephrine,
cortisol).
Thank you