Studied by 2 people
Cell-to-Cell Communication
need to convey a huge amount of information very quickly
Electrical Physiological Signal
change in cell’s membrane potential
Chemical Physiological Signal
molecules secreted into extracellular fluid
Local Communication
Gap Junctions
Cell-to-Cell Contact
Paracrine/Autocrine Signals
Gap Junctions
simplest way of transferring information is through cytoplasmic bridges
connexins provide channels
good for ions and small molecules, not large molecules
found in nearly all cell types
Cell-to-Cell Contact
some communication requires that surface molecules on one cell bind to those on another
contact dependent signalling
important during growth and development
an example is how nerve cells send out long extensions to reach distal ends of limbs with multiple cells involve
Paracrine/Autocrine Signals
paracrine act in the immediate vicinity of the cell that secreted the signal
autocrine acts on the cell that secreted it
in some cases molecules can act as both
diffuse through interstitial fluid
several important classes of molecules act as local signals
Histamine
example of a paracrine signal
stored in certain cells of immune system
released in response to allergic reactions injury or infection
causes blood vessels to dilate and capillaries to become more permeable
releases white blood cells and antibodies
also important in increasing stomach acidity in much the same way
Long Distance Communication
may be electrical or chemical
endocrine cell uses hormones
chemical signals secreted into blood and are distributed throughout body
nervous system uses a combination of electrical and chemical signals (neurochemicals and neurotransmitters)
Neurotransmitters
diffuse across narrow extracellular space and have a rapid effect
Neurohormones
released into blood and affects cells farther away
Why do some cells respond to a chemical signal and other cells ignore it?
target cell receptor proteins, which are proteins
if a cell has a receptor for the signal molecule a response is initiated
Signaling Path Features
a) signal molecule is ligand (binds to receptor molecule)
b) ligand-receptor complex activated
c) activated receptor activates intracellular molecule
d) response initiated
Antihistamines
compete with binding sites with the histamine molecules and as a result get less of a response
good when histamine response is more severe than necessary
Pathways
can be very complex
generally a lot of steps before a response is initiated
most physiological processes use some variation of these pathways
many drugs/illnesses work by influencing these pathways
Modulation of Signal Pathways
different cells may respond differently to one kind of signal molecule (ligands)
response depends on the receptor and its associated pathways
One Ligand with Multiple Receptors
epinephrine dilates blood vessels in skeletal muscle while also constricting blood vessels in intestine
How does one chemical have opposite effects?
the response depends on the receptor, not the ligand
epinephrine A-receptor in intestinal blood vessel (alpha)
epinephrine B-receptor in skeletal muscle blood vessel (beta) binding results in cell dilation
Specificity and Competition
different ligand molecules with similar structures may be able to bid with the same receptor
example is norepinephrine and epinephrine
Norepinephrine and Epinephrine
example of specificity and competition
both bind to class of receptors called adrenergic receptors which demonstrates specificity of receptors since they can’t bind with anything else
both can bind to alpha and beta receptors but they have slightly different affinities
dopamine can compete with epinephrine and norepinephrine
Agonist
ligand activates receptor
elicits a response
Antagonists
ligands occupies binding site
prevents a response
Agonists and Antagonists
pharmacologists use this principle to design drugs
depending on the similarity of the drug molecule to the ligand molecule, get different effects
can modify effects of certain cells
Hormone Disruptors
can mimic particular hormones resulting in increased cellular response
can block particular hormones resulting in decreased cellular response (none or less)
Homeostatic Reflex Pathways
cellular signalling systems responsible for maintaining homeostasis
long distance reflex pathways involve two control systems, nervous and endocrine system
involves seven steps
Stimulus
first step in the homeostatic reflex pathway
disturbance or change that sets pathway in motion
an example can be a change in temperature, blood pressure or oxygen concentration
Sensor
second step in the homeostatic reflex pathway
a multicellular receptor that responds to changes in the environment
skin is covered in less complex receptors to detect changes in temperature, touch, vibration, pain
many internal sensors for body position, blood pressure, oxygen levels
Input Signal
third step in the homeostatic reflex pathway
varies depending on type of reflex
not found in endocrine reflex since stimulus acts directly on endocrine cell
serves as both sensor and integrating center
Integrating Center
fourth step in the homeostatic reflex pathway
in neural reflexes, integrating center lies within central nervous system
interpret and initiate a response
Output Signal
fifth step in the homeostatic reflex pathway
nervous system electrical and chemical signals transmitted by a neuron
endocrine system hormones that travel in blood
Target
sixth step in the homeostatic reflex pathway
neural pathway includes muscles, glands and adipose tissue
endocrine pathway includes cells that have proper receptor
Response
seventh step in the homeostatic reflex pathway
cellular response that takes place in target cells
systemic response is the overall change in the organism
Neural Reflex
example of neuronal homeostatic control
in dim light a signal is received from sympathetic nervous system and the pupils dilate
in bright light a signal is received from the parasympathetic nervous system and the pupils constrict
Endocrine Reflex
example of endocrine homeostatic control mechanisms
the endocrine cell acts as the sensor and integrating center
low blood concentration of calcium leads to the release of parathyroid hormone
stimulates the release of calcium into blood
Cellular Response
specific cells respond
Systemic Response
whole body responds
