Communication and Integration

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

1. Gap Junctions
2. Cell-to-Cell Contact
3. 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