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Chapter 7

Chapter 7 notes


Department
Biological Sciences
Course Code
BIOD27H3
Professor
A.Elia
Chapter
7

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Chapter 7- Introduction to the Endocrine System
Hormones
-the specificity of a hormone depends on its receptors and their associated signal
transduction pathways
-a hormone is a chemical secreted by cell or group of cells into the blood for transport to a
distant target, where it is effective at very low concentrations
-pheromones are chemical signals secreted into the external environment
-hormones bind to receptors to initiate responses known as the cellular mechanism of
action
-hormone activity is limited by terminating secretion removing hormone from the blood,
or terminating activity at the target cell
-the rate of hormone breakdown is indicated by a hormone’s half life
The Classification of Hormones
-there are 3 types of hormones; peptide/protein hormones, composed of 3 or more amino
acids; steroid hormones, derived from cholesterol and amino acid derived hormones
derived from either tyrosine or tryptophan
-peptide hormones are made as inactive preprohormones and processed to prohormones.
Prohormones are chopped into active hormone and peptide fragments that are co-
secreted.
-Peptide hormones dissolve in the plasma and have a short half life. They bind to surface
receptors on their target cells and initiate rapid cellular responses through signal
transduction. In some instances, peptide hormones also initiate synthesis of new proteins.
-Steroid hormones are synthesized as they are needed. They are hydrophobic and most
steroid hormones in the blood are bound to protein carriers. Steroids have an extended
half life
-Traditional steroid hormones are inside the target cell, where they turn genes on or off
and direct the synthesis of new proteins. Cell response is slower than with peptide
hormones. Steroid hormones may bind to membrane receptors and have nongenomic
effects
-Amine hormones may behave like a typical peptide hormones or like a combination of a
steroid hormone and a peptide hormone
Control of Hormone Release
-classic endocrine cells act as both sensor and integrating center in the simple reflex
pathway
-many endocrine reflexes involve the nervous system either through neurohormones or
through neurons that influence hormone release
-the pituitary gland is composed of the anterior pituitary (true endocrine gland) and
posterior pituitary (extension of brain)
-the posterior pituitary releases 2 neurohormones, oxytocin, and vasopressin, that are
made in hypothalamus
-trophic hormones control the secretion of other hormones
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