Lecture 3: Hormones General overview of hormones (peptide, steroid, and amide). Includes information on each type, examples and more general hormone information.

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16 Oct 2011

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Physiology Lecture 3
Hormones are classified into three subsets: Peptide, steroid and amine.
Peptide hormones are made of 3 amino acids or more, and make up most hormones.
They are made in advance and stored in vesicles to await a stimulus to signal that they
are needed. They are not bonded to carriers and therefore have a short half life, and are
water soluble. They are too large to pass into a cell, therefore their receptors are on the
cell’s plasma membrane.
o For example, insulin is first preproinsulin and modified to proinsulin in the ER.
After that it goes to the Golgi apparatus where it is made into insulin, along with
the nonactive peptide fragment C peptide. It’s stored in a vesicle and awaits a
signal to undergo exocytosis and enter the blood.
Steroid hormones are made only from cholesterol and are made on demand. They are
water insoluble and so are bonded to carriers and have a long half life. Their receptors
are in the cytoplasm or nucleus and as such they can have a direct effect on gene
o Examples of cholesterol derivatives include Cortisol, Aldosterone (Adrenal
cortex) and Estradiol (ovary).
Amine hormones are made from one amino acid.
o Typtophan derivate: Melatonin (Peptide/Steroid)
o Tyrosine derivative: Catecholamines (peptide) thyroid hormones (steroids)
Melatonin is a darkness hormone and secreted while we sleep. It receives directions
from the genes that regulate our biological clock.
Catecholamines include dopamine, norepinephrine and epinephrine.
Thyroid hormones include T4 and T3.
Active hormones are regulated by the rate their made and the rate they’re cleared from
the plasma. They can be cleared via endocytosis on target cells, or by being metabolized
in the liver and excreted from the kidneys.
The needed concentrations of hormones are very low, down in the nano or picomolar
range but have effects that can range to the millimolar range. The level of hormones can
be measured via immunoassay (levels in blood and urine) or immunocytochemistry
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