BIOL373 Study Guide - Midterm Guide: Arnold Adolph Berthold, Endocrinology, Neurohormone
12 May 2018
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Unit 05 – Endocrine Regulatory Systems
1
Endocrinology
What is a hormone?
Hormone -> chemical messenger secreted into the blood by specialized cells; it
functionally travels via blood
• Neurohormones -> fast
• Endocrine hormones -> long-term and slower
They regulate long-term and/or on-going functions like:
• Growth and development
• Metabolism
• Regulation on internal env. (temp., water balance, ions)
• Reproduction
Hormones act on target cells by regulating:
• Enzyme activity (this is fast; activated via a phosphate)
• Ion transport across a membrane (Slow)
• Gene expressions -> protein synthesis
Arnold Adolph Berthold
• Long known that removing testes from farm animals reduced masculine
behaviour and phenotype
• Wondered whether effects were due to neural connections w/ testes
First formal experiment in endocrinology
• Used chickens
• Thought neurons ran everything
• Took out testes and then put them back -> has normal male development
• Thus, hormone from testes travelled via blood
Charles Brown-Sequard -> claimed he injected himself w/ extracts of testes ground
up in water causing sexual rejuvenation, extension of life, etc.
Unit 05 – Endocrine Regulatory Systems
2
Classis Approaches in Experimental Endocrinology
Ablate -> remove suspected gland that you think is producing the active substance
Replace -> gland or extract of gland
Create a situation of excess -> given too much of something
Classis hormones were identified through these approaches of isolating active
substances and characterizing them chemically
Major tool of endocrinologists:
• Biological assays -> put the testes extract in an organism and measure the
sex of the gonads
Endocrine vs Exocrine Glands
Endocrine -> ductless glands, needs to be near blood vessels to travel
• The hormone goes into blood -> heart -> everywhere in body
Exocrine -> duct glands
Features of Classis Hormones
• Secreted by a group of cells derived from epithelial tissue that form
discrete glands
• Secreted into the blood
• Travel to distant targets
• Act at very low conc. -> nanomolar (10-9), picomolar (10-12)
Non-classic Hormones
• Secreted by glands that are not obvious or identifiable (secreted by
neurons, immune cells, endocrine cells of gut; they are not clustered into
ducts)
• Act locally -> diffusion through ECF (testosterone travels a short distance)
• Clearly identified as hormones in one context, but also secreted within the
CNS as a neurotransmitter (dopamine)
Unit 05 – Endocrine Regulatory Systems
3
Hormones act via Receptors
• Target cells for a hormone are defined as those having receptors for that
hormone
o Target cells can increase/decrease sensitivity to a hormone by
increasing/decreasing receptor expression
• Location of receptor within the target cell is related to chemical features of
the hormone
• Binding to receptors sets off an intracellular signalling cascade
• There must be a way of terminating hormone signalling
o equilibrium between free and bound hormone:
- when you raise the level in blood, you push the equilibrium so that
there will be a higher chance of interaction b/w the receptor and
ligand
- to decrease the chances, you need to decrease the amount in the
blood by two ways -> decreased the amount secreted by the
primary gland OR use secretion mechanisms to break it down
• mechanisms to remove hormones from receptors:
o hormones in plasma are inactivated on their way through liver/kidney -
major determinant of hormone’s t1/2
o nonspecific proteases in ECF break them down (peptides)
o hormone-receptor complex can be internalized (endocytosis) by target
cell
Classifying Hormones
Ways to classify hormones
Source -> GI tract vs gonad vs anterior pituitary gland vs…
Mechanism of action -> GPCR or receptor tyrosine kinases (RTKs) or intracellular
receptors (ex steroids)
Chemistry -> peptide/protein or amine/AA or steroid
Document Summary
Hormone -> chemical messenger secreted into the blood by specialized cells; it functionally travels via blood: neurohormones -> fast, endocrine hormones -> long-term and slower. They regulate long-term and/or on-going functions like: growth and development, metabolism, regulation on internal env. (temp. , water balance, ions, reproduction. Hormones act on target cells by regulating: enzyme activity (this is fast; activated via a phosphate) Ion transport across a membrane (slow: gene expressions -> protein synthesis. Long known that removing testes from farm animals reduced masculine behaviour and phenotype: wondered whether effects were due to neural connections w/ testes. First formal experiment in endocrinology: used chickens, thought neurons ran everything, took out testes and then put them back -> has normal male development, thus, hormone from testes travelled via blood. Charles brown-sequard -> claimed he injected himself w/ extracts of testes ground up in water causing sexual rejuvenation, extension of life, etc.
