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Textbook notes-Chapter 7

Biological Sciences
Course Code
Ingrid L.Stefanovic

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Chapter 7
x Hormones are chemical messengers secreted into the blood by specialized cells and are
responsible for many long term functions of the body
x Hormones act on their target cells by
-controlling rates of enzymatic reactions
-controlling the transport of ions or molecules across cell membranes
-controlling gene expression and synthesis of proteins
What Makes a Chemical a Hormone
x Hormones exert their effect at very low concentrations and are transported to distant
targets in the blood
Hormones are Secreted by a Cell or Group of Cells
x Hormones are secreted by endocrine glands, which are derived from epithelial tissue
x Molecules that acts as hormones (neurohormones, cytokines) are secreted by classic
and isolated endocrine glands
Hormones are Secreted into the Blood
x Pheromones are specialized ectohormones that act on other organisms of the same
species to elicit a physiological or behavioural response
x Hormones are usually secreted into the blood
Hormones are Transported to Distant Targets
x Growth factors are substances that influence cell growth and division but are usually
autocrines and paracrine
x Hormones usually travel to distant targets
Hormones Exert their Effect at Very Low Concentrations
x One hallmark of a hormone is its ability to act at low concentrations
x Chemical signals such as histamine that are transported into blood at high
concentrations are not hormones
Hormones Act by Binding to Receptors
x All hormones bind to target receptors and causes a biochemical response
Hormone Action Must Be Terminated
x Hormones in the bloodstream are degraded by enzymes found primarily in the liver and
x The metabolites of hormones are excreted in urine

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x The rate of hormone is indicated by a hormones half-life; indicates how long a hormone
is active in the body
The Classification of Hormones
x Hormones are divided in three main chemical classes; peptide hormones (amino acids),
steroid hormones (derived from cholesterol), amine hormones (tryptophan and
Most Hormones are Peptides/Proteins (refer to Figure 7.3)
Peptide Hormone Synthesis
x Similar to protein synthesis; initial peptide is an inactive protein called a
x Preprohormone moves through the rough ER to be converted into a prohormone
x Prohormone moves to the Golgi complex where enzymes chop the prohormone into its
active form (called post-translational modification)
x Secretory vesicles contain the prohormones until they receive a secretory signal
Transport in the Blood and Half-Life of Peptide Hormones
x Peptide hormones are water soluble and generally dissolve easily in the extracellular
fluid for transport throughout the body; short half life
Cellular Mechanism of Action of Peptide Hormones
x Peptide hormones are lipophobic so they are unable to enter the target cell; bind to
surface membrane receptors to cause signal transduction
x cAMP are secondary messengers, which cause rapid responses by modifying existing
Steroid Hormones are Derived from Cholesterol
x Steroid hormones have a similar chemical structure because they are derived from
x Steroid hormones are made in only a few organs (adrenal cortex, placenta, and
gonads), unlike peptide hormones which are made in many tissues
Steroid Hormone Synthesis and Release
x Cells that secrete steroid hormones have large amounts of smooth ER, the organelle
where steroids are released
x Steroids are lipophillic
Transport in the Blood and Half-Life of Steroid Hormones
x Steroid hormones are not soluble in plasma and other body fluids; must bind to carrier
protein molecules
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