Communication and Integration

• need to convey a huge amount of information very quickly

• change in cell’s membrane potential

• molecules secreted into extracellular fluid

1. Gap Junctions

2. Cell-to-Cell Contact

3. Paracrine/Autocrine Signals

• 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

• 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 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

• 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

• 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)

• diffuse across narrow extracellular space and have a rapid effect

• released into blood and affects cells farther away

• target cell receptor proteins, which are proteins

• if a cell has a receptor for the signal molecule a response is initiated

a) signal molecule is ligand (binds to receptor molecule)

b) ligand-receptor complex activated

c) activated receptor activates intracellular molecule

d) response initiated

• 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

• 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

• different cells may respond differently to one kind of signal molecule (ligands)

• response depends on the receptor and its associated pathways

• epinephrine dilates blood vessels in skeletal muscle while also constricting blood vessels in intestine

• 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

• different ligand molecules with similar structures may be able to bid with the same receptor

• example is 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

• ligand activates receptor

• elicits a response

• ligands occupies binding site

• prevents a response

• 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

• can mimic particular hormones resulting in increased cellular response

• can block particular hormones resulting in decreased cellular response (none or less)

• cellular signalling systems responsible for maintaining homeostasis

• long distance reflex pathways involve two control systems, nervous and endocrine system

• involves seven steps

• 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

• 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

• 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

• fourth step in the homeostatic reflex pathway

• in neural reflexes, integrating center lies within central nervous system

• interpret and initiate a response

• fifth step in the homeostatic reflex pathway

• nervous system electrical and chemical signals transmitted by a neuron

• endocrine system hormones that travel in blood

• sixth step in the homeostatic reflex pathway

• neural pathway includes muscles, glands and adipose tissue

• endocrine pathway includes cells that have proper receptor

• seventh step in the homeostatic reflex pathway

• cellular response that takes place in target cells

• systemic response is the overall change in the organism

• 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

• 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

• specific cells respond

• whole body responds