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Chapter 7: Introduction to theEndocrine System
Created by Tanya Karakyriakou
Tags SCIBIO23 Semester 4
Created @April 11, 2021
** check slide 38 table (sort of summary for everything to test ur own understanding)
7.1 Hormones
hormones = chemical messengers secreted into the blood by specialized epithelial
cells
→ act on target cell in 3 ways:
1. by controlling rates of enzymatic reactions
2. by controlling transport of ions or molecules across cell membranes
3. by controlling gene expression and the synthesis of proteins
To identify an endocrine gland and hormone it produces:
1. remove gland
2. replace hormone
3. create excess hormone
What makes a chemical a hormone?
hormones are secreted by endocrine glands, isolated endocrine cells, neurons
(neurohormones) and cells of the immune system (cytokines)
ectohormones = signal molecules secreted into the external environment
pheromones = specialized ectohormones that act on other organisms of the same
species to elicit a physiological or behavioral response.
Chapter 7: Introduction to the Endocrine System 1
, **hormones have to be transported to a distant target; candidate hormones that are
not yet proven to travel long distances are called factors
growth factors act locally as autocrine or paracrine signals but don't travel far
in circulation
CCK in intestine as a hormone and neurons as a neurotransmitter/modulator
**hormones act at concentrations in the nanomolar (10-9) to picomolar (10-12)
range
Hormones act by binding to receptors
cellular mechanisms of action of hormone = the intracellular events through which
the hormone's message is carried out (the chemical response of a hormone after its
secretion)
Hormone actions must be terminated
→ hormone actions are terminated at some point to maintain balance
hormones in the blood stream are degraded into inactive metabolites by
enzymes of the liver and kidneys
rate of hormone breakdown = half life of the hormone in the circulation
7.2 The Classifications of Hormones
peptide/protein hormones → linked amino acids
steroid hormones → cholesterol derivatives
amino acid-derived hormones → modifications of single amino acids (tryptophan or
tyrosine)
Most hormones are peptide proteins
all hormones except steroid hormones and amino acid derivatives
Synthesis:
Chapter 7: Introduction to the Endocrine System 2
, 1. pre-pro-hormone (peptide hormone + signal sequence that direct protein into
rough ER lumen) in rough ER
2. pro-hormone (signal sequence removed; still inactive) in rough ER
3. Packaged into secretory vesicles in Golgi
4. post translational modification = secretory vesicles contain proteolytic
enzymes that chop pro-hormone into active hormone and other fragments.
5. co-secretion = fragments released in ECF
**water soluble and dissolve easily in ECF for transport
**receptor of target cell on membrane
** short half life (minutes long) (= time when half concentration of hormone is gone)
** pre-peptide hormones usually lipophobic so can't enter target cell; SO they bind to
surface membrane receptors
signal transduction pathways like cAMP second messenger systems or
tyrosine kinase
cAMP degraded by phosphodiesterase
**elicit rapid responses
Chapter 7: Introduction to the Endocrine System 3
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