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Summary Biol 373 Midterm 1 Study Notes

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BIOL 373 University of Waterloo

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BIOL 373 University Of Waterloo

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biol 373 midterm 1
biol 373 midterm
which of the following is a buffer zone

Institution BIOL 373 University of Waterloo
Course BIOL 373 University of Waterloo

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BIOL 373 - Principles of Human Physiology 2 Midterm Exams, Study guide and Final Exam { A+ Guide} Fall 2024/2025

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Biol 373 Midterm 1 Study Notes

Unit 1: Introduction and Review

Function is the “why” – Why does the system exist? Why does the event occur?
Process is the “how” – How does a system work?  physiological mechanisms

Homeostasis is the maintenance of a relatively stable internal environment (especially
extracellular fluid) – oscillation around a set point

Walter Cannon – “flight or fight response” – expanded on Bernard’s concept of homeostasis

Study of homeostatic mechanisms = physiology
Failure to compensate for change = disease
Study of failure to compensate = pathophysiology

Local vs. Reflex Control

Control Systems and Homeostasis
Response loop: stimulus, sensor, input signal, integrating centre, output signal, target,
response
Negative feedback stabilizes variable
Feedforward control anticipates change
Positive feedback reinforces stimulus – not homeostatic

,Homeostasis is achieved by nervous and endocrine systems with their combination of electrical
and chemical signals
Electrical signal – changes in membrane potential – restricted to nerve and muscle cells
Chemical signal – excreted into ECF by all cells – responsible for most communication
Cells that respond to signals are ‘target cells’

Long range cell-cell communication
Endocrine: chemical (hormone) released into bloodstream and distributed throughout the
body

Neural: electrical signal travels down neuron; reaches end and is translated to chemical
signal (neurotransmitter) which transmits information to next cell

Neuro endocrine: electrical signal travels down neuron; reaches end and is secreted into
blood

Target cell
 Only cells that have receptors for that signal will respond to it – signal molecule that
binds to a particular receptor is its ligand
 Receptors are proteins that project outside of the membrane, or are within the cell in
the cytoplasm
 Chemical properties of signal molecules (ligands) determine what type of receptor
they will interact with
 Water soluble = hydrophilic = lipophobic  surface receptor
 Water insoluble = hydrophobic = lipophilic  intercellular receptor

,Location of Receptors and Types of Membrane Receptors

Modulation of Signal Pathways
 One ligand may have several different types of receptors – explains how same signal
can have different effects in different cell types

 Cells can change their response to signals by changing receptor number or sensitivity
– increase # can increase gene expression (up regulation); decrease # can internalize
surface receptors (down-regulation); change receptor sensitivity (for example
phosphorylation)

,  Receptors exhibit saturation, specificity, competition for their ligands (and molecules
similar to their ligands – e.g., relative affinities of adrenergic receptors with endogenous
ligands or agonists and antagonists competing with endogenous ligands

Many diseases and drugs disrupt signal pathways
Cholera
 intestinal infection, Vibrio cholerae, from contaminated food and water
 need to ingest ~100 million bacteria, but lower doses can cause infection in people
with reduced gastric acidity, young children and immune supressed individuals
 a few bacteria survive acidity of the stomach and can reach the small intestine and
attach to and invade intestinal epithelial cells and produce toxin

This G-protein signal last as long as the alpha and beta-gamma subunits are free which is as long
as the G-alpha-subunit is bound to GTP

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