Physiology 31 Lecture
Chapter 6 – Communication, Integration, and Homeostasis
I. Overview
A. Cell-to-Cell Communication
B. Signal Pathways
C. Cell Membrane Receptors
D. Novel Signal Molecules
E. Modulation of Signal Pathways
F. Control Pathways: Response & Feedback Loops
II. Cell-to-Cell Communication
A. The two basic methods of physiological communication (_________) are chemical and
electrical
1. __________ signals are changes in a cell’s membrane potential (voltage) via the flow of
ions, as occurs in nerve impulses
2. ____________ signals result from cells secreting chemicals (e.g., hormones and
neurotransmitters) into the extracellular space and blood stream
3. Cells that receive electrical or chemical signals are _______ cells
B. Four types of cell-to-cell communication are
1. ________ cytoplasmic transfer of signals through gap junctions
2. ____________-dependent signaling – surface molecules of one cell bind to surface
molecules of another cell
3. _________ chemical communication by chemicals that diffuse through the
extracellular fluid
4. Long ____________ communication via both electrical signals from nerve cells and
chemical signals in the blood stream
C. ______ Junctions transfer chemical and electrical signals
1. Gap junctions are protein ________ between adjacent cells
2. When open, gap junctions allow ______ and small molecules to diffuse from cell to cell
3. Gap junctions are found between many cells, including ________ and smooth muscle
cells, lung and liver cells, and some neurons
D. ____________-dependent signals require cell-to-cell contact
1. Direct cell-to-cell contact signaling occurs in the ___________ system, and during
growth and development
2. Cell Adhesion Molecules (_____s) bind some cells together and participate in cell-tocell signaling
E. Paracrines & Autocrines are _______ chemical signals distributed by diffusion
1. _______________ are chemicals (e.g., histamine) secreted into the interstitial fluid in
the extracellular space, and diffuse to ________ target cells
2. _______________ are chemicals that act on the same cell that secreted the chemical
F. Electrical signals, Horomones, & Neurohormones carry out long ______________
communication
1. Endocrine gland cells secrete chemical messengers called ____________ into the blood
stream
a. Hormones travel in the blood stream to their _________ cells
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b. Target cells have specific ____________ for the hormones
2. The __________ system uses both chemical and electrical signals
a. ____________ signals travel to the end of a neuron and trigger the release of a
chemical signal (neurocrine) to a target cell
b. Neuro________ may be
1) Neuro____________ – fast acting chemical secreted across a gap between the
neuron and its target cell
2) Neuro___________ – slow acting paracrine or autocrine chemicals
3) Neuro___________ – chemicals secreted into the blood stream
G. Cytokines act as both ________ and long-distance signals
1. ___________ are regulatory molecules produced by all nucleated cells; they control cell
development, differentiation, and immune response
2. In development and differentiation, cytokines are autocrine or ___________
3. In stress and inflammation, cytokines are transported through the ________ stream
III. Signal Pathways
A. All _________ pathways share these common features
1. A signal molecule (_________, or 1st messenger) binds to its receptor.
2. Ligand binding activates the __________
3. The receptor activates intracellular signal molecules (____ ___________)
4. The last ___________ molecule in the pathway either
a. ____________ a target protein to create a response, or
b. Initiates _____________ of a target protein
B. _____________ are located inside the cell or in the cell membrane
1. Target cell receptors are found in the __________, the cytosol, or in the cell
__________
2. Chemical ___________ molecules are either water soluble (lipophobic) or lipid soluble
(lipophilic)
a. ________ soluble signals (e.g., peptide hormones) bind to receptors on the target
cell ___________ and trigger an intracellular response
b. _________ soluble signals (e.g., steroid hormones) usually diffuse through the
target cell membrane and bind to cytoplasmic or _________ receptors
1) Receptor activation often turns on or off a _______ that directs protein synthesis
C. Membrane ____________ facilitate signal transduction
1. Signal ___________ is the transmission of information from one side of the membrane
to another via membrane proteins
2. Signal transduction ___________ use membrane proteins and intracellular 2nd
messengers to produce an intracellular response
a. A signal molecule binds to and activates a membrane ________
b. Some pathways activate protein ___________ that transfer a phosphate from _____
to a protein (i.e., phosphorylation)
c. Other pathways activate amplifier __________ (e.g., adenylyl and guanylyl cyclase)
that create 2nd messenger molecules (e.g., Ca2+, cAMP, cGMP)
d. 2nd ___________, in turn can
1) Open or close ____ channels, which creates electrical signals
2) Increase intracellular ___________ levels
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3) Change enzyme activity, especially in ___________ (phosphorylators) and
______________ (dephosphorylators)
e. __________ modified by calcium binding and phosphorylation control
1) Metabolic ___________
2) ________ proteins for muscle contraction and cytoskeletal movement
3) Proteins that regulate ______ activity and protein synthesis
4) Membrane ___________ and receptor proteins
f. A signal transduction pathway is a _________ that begins when a stimulus (signal
molecule) activates another molecule, which activates another, etc., until a product is
eventually formed
IV. Cell Membrane ___________ include receptor enzymes, G protein-linked, integrin, and
ligand gated receptors
A. Receptor-_______ have protein kinase or guanylyl cyclase activity
1. Receptor enzymes have receptors on the extracellular side of the membrane that activate
__________ in the intracellular side
2. Receptor __________ (e.g., the insulin tyrosine kinase receptor) transfer phosphates
from _____ to a protein
3. ____________ cyclase converts GTP to cyclic GMP (______), a second messenger
4. __________ for receptor enzymes include growth factors, cytokines, and the hormone
insulin
B. Most signal transduction uses ___ proteins
1. ___ ___________-coupled receptors span the cell membrane, and are linked to a G
protein on the cytoplasmic side
2. Ligands that bind to these receptors include ___________, growth factors, and
neurotransmitters
3. Ligand binding causes the G protein to exchange GDP for _____, thus activating the G
protein
4. An ________ G protein can either
a. Open an _____ channel in the membrane, or
b. Alter __________ activity on the cytoplasmic side
C. ___ ___________-coupled Adenylyl cyclase-cAMP is the signal transduction system for
many ________ soluble hormones
1. __________ cyclase is a membrane enzyme that converts ATP to the 2nd messenger
cyclic AMP (_____)
2. cAMP activates protein kinase A, which _________________ other proteins
D. G protein-linked receptors also use _____-derived 2nd messengers
1. Ligand binding activates phospholipase C (___-__)
2. PL-C converts a membrane ___________ into 2 2nd messengers – diacylglycerol
(DAG) and inositol triphosphate (IP3)
a. _____ interacts in the membrane with protein kinase C, which ______________
cytosolic proteins
b. ____ enters the cytoplasm and binds to a ________ channel on the ER, which opens
the channel and allows Ca2+ to diffuse out
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E. ____________ receptors transfer information from the ECM
1. Integrins are integral proteins that mediate blood clotting, wound repair, and other
__________ functions
2. Ligands include antibodies and blood __________ molecules
3. Integrins attach to the _____________, and ligand binding can activate intracellular
enzymes or alter cytoskeletal organization
4. Genetic defects in integrin proteins can result in defective WBCs and ____________
F. _________-________ ion channels initiate rapid intracellular responses via electrical
impulses
1. These channels are found in _______ and muscle cell membranes
2. When a _________ (e.g., acetylcholine) binds, it opens or closes the _____ channel,
altering the membrane’s electrical potential
V. Novel Signal Molecules
A. Calcium is an important intracellular ________
1. ____________ enters the cytosol from
a. _______cellular fluid via Ca2+ channels, or
b. Intracellular compartments (e.g., ____), released by 2nd messengers, such as _____
2. Once in the cytosol, Ca2+ affects cell activity by binding to
a. ____________ protein, which alters enzyme activity or the open state of ion channels
b. _________ proteins that alter movement of contractile proteins (e.g., troponin) or
cytoskeletal proteins (e.g., microtubules)
c. Other regulatory proteins that trigger ___________ of secretory vesicles (as in insulin
secretion)
d. _____ channels, to alter their open state (e.g., Ca2+ activated K+ channel of nerve
cells)
B. _________ are short-lived signal molecules
1. Nitric oxide (____) is an autocrine/paracrine gas formed from the amino acid _________
and oxygen
a. NO diffuses into target cells and activates guanylyl cyclase, which in turn forms the
2nd messenger ______
b. In the brain, NO acts as a neuron___________
c. Blood vessel endothelial cells produce NO, which relaxes adjacent smooth muscle
cells, causing vaso________
2. Carbon monoxide (____) is produced in minute amounts, and has an action similar to
NO.
C. _______________ are important lipid paracrine signal molecules
1. Eicosanoids are all derived from _______________ acid, a 20 carbon fatty acid in the
cell membrane
2. Two major __________ of eicosanoids are
a. _____________, produced by lipoxygenase, contribute to asthmatic attacks and
anaphylactic allergic reactions
b. _____________, produced by cycloxygenase (COX), include prostaglandins and
thromboxanes
1) _____________ are involved in inflammation, pain, and fever
2) _____________ stimulate vasoconstriction and blood clotting
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3) Nonsteroidal anti-inflammatory drugs (__________s) prevent inflammation by
inhibiting _______ enzymes
4) Steroidal anti-inflammatory drugs (______s) block arachidonic acid release
VI. Modulation of Signal Pathways
A. ____________ exhibit saturation, specificity, and competion
1. Like enzymes, each receptor binds to a __________ molecule (ligand) or related
molecule.
2. The _____________ may be agonistic or antagonistic
a. ___________ are ligands that activate receptors
b. ______________ are competitors that block receptor activity
3. Different forms of a receptor (___________) can bind the same ligand and have
different effects (e.g., epinephrine can bind to α & β adrenergic receptors)
B. Up- and Down-Regulation of receptors enables cells to _________ cellular response
1. ________-regulation is a ____________ in a cell’s number of receptors or their
binding affinity, often in response to _______ ligand concentrations (e.g., high insulin
concentrations cause a down-regulation of insulin receptors in type II diabetes)
2. ___-regulation is an _________ in a cell’s number of receptors, often in response to
_____ ligand concentrations, which increases the cell’s sensitivity to the ligand
C. Cells have mechanisms for ___________ signal pathways, such as
1. ______________ the signal molecule, or
2. Breaking down the receptor-ligand _________
D. Pharmacologists investigate signaling ________________ to design drugs to treat disease.
Examples of signal blockers are
1. ____________ channel blockers to treat high blood pressure
2. ____________s for treating estrogen-dependent cancers
3. _________ inhibitors that prevent the formation of inflammatory prostaglandins
VIII. ____________ Pathways: Response and Feedback Loops
A. _________________ responses have 3 components
1. A ______________ or change in a regulated variable
2. A cell or tissue that _____________ the stimulus and initiates a response
3. Cells or tissues that carry out the ___________
B. Homeostasis may be maintained by ________ or long-distance pathways
1. Local pathways include paracrine and ___________ responses
2. Long distance responses include __________ control pathways, which consist of
___________ loops that begin with a stimulus and end with a response
a. ____________ or change is perceived by a
b. _____________ (e.g., sensory neuron) that sends out an
c. Input (___________) Signal to an
d. _____________ center that evaluates the incoming signal, compares it to a
____________, then sends an
e. Output (____________) signal (e.g., nerve impulse or hormone) to an
f. ____________ (target cell or tissue) that carries out a
g. ____________ to restore homeostasis
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D. Negative and positive _________ loops modulate the response loop
1. ____________ feedback is when a change is sensed and a response is initiated to
______ the change and restore homeostasis
2. _____________ feedback is when a change is sensed and a response is sent to
_____________ the change (e.g., hormonal control of uterine contractions during
childbirth)
E. Feed____________ control allows the body to anticipate change and start the response
loop in anticipation of the change (e.g., salivation at the sight or smell of ______)
F. Biological rhythms result from changes in the __________
1. Reflexes that occur in a predictable manner, such as hormonal cycles, are called
biological __________
2. __________________ rhythms are those that coincide with light and dark cycles (e.g.,
blood pressure and body temperature)
G. Control systems vary in their _______ and specificity
1. Nervous control is __________ and more specific than endocrine control, but is usually
of ___________ duration
2. Endocrine control is ___________ and less specific, but is longer ____________ and is
usually amplified
3. Many reflex pathways are combinations of ___________ and ____________ control
mechanisms