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Dit document bevat de inhoud van hoofdstuk 6 van het boek: 'Human Physiology: an integrated approach'. Een van de hoofdstukken die je moet kennen voor het examen van immunologie.
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Physiology, first year Biology (English)
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AlexandraDeGraeve19
Voorbeeld van de inhoud
CH 61. cell to cell communication
2 basic types of signals:
➢ electrical: changes in a cell’s membrane potential
➢ chemical: molecules secreted by cells into the ECF
➢ cells that respond to electrical or chemical signals are called target cells/ targets
★ chemical signals: responsible for most of communication in the body; they act as
ligands that bind to proteins to initiate a response
★ protein binding of chemical signals obeys the general rule for protein interactions:
specificity, affinity, competition, saturation
4 basic methods cell to cell communication:
➢ local communication: using gap junctions
➢ contact dependent signals: surface molecules from one cell bind to surface
molecules on another cell membrane
➢ chemicals that diffuse through the ECF to act on cells close by
➢ long distance communication: electrical and chemical signals carried by nerve
cells; chemical signals transported in the blood
→ simplest form of communication is the direct transfer of electrical and chemical signals
through gap junctions , protein channels that create cytoplasmic bridges between adjacent
cells.
- a gap junction forms from the union of membrane spanning proteins → CONNEXINS
on two adjacent cells
- united connexins create a protein channel (connexon) that can open and close
- channel open: connected cells work like a single cell that contains multiple nuclei
(syncytium); ions and small molecules (ATP; cAMP) diffuse directly from cytoplasm
of one cell to cytoplasm of the next; only electrical signals can pass directly from cell
to cell movement through gap junctions can be shut off completely
- larger molecules cannot pass the gap junctions
- some cell to cell communication requires that surface molecules on one cell
membrane bind to a membrane protein of another cell
- contact dependent signaling: occurs in immune system and during growth and
developing: such as nerve cells sends out long extensions that must grow from the
central axis of the body through to the distal ends of developing limbs
- cell adhesion molecules (CAMs): cell adhesion; act as receptors on cell to cell
signaling; linked to the skeleton or intracellular enzymes; transfer signals in both
directions across cell membranes
- contact dependent signaling is also know as juxtacrine signaling
- local communication: take solace through paracrine and autocrine signaling
★ paracrine signal: chemical that act on cells in the immediate vicinity of the cell that
secreted the signal
★ chemical signal that act on the cell that secreted is called an autocrine signal
, - some cases a molecules act as both an autocrine and paracrine signal
➢ paracrine and autocrine signal molecules: reach their target cells by diffusing through
the interstitial fluid
➢ distance is a limiting factor for diffusion; the effective range of paracrine signals is
restricted to adjacent cells
➢ parcine molecule: histamine: chemical released from damaged cells
→ histamine acts as a paracrine signal diffusing to capillaries in the immediate area of the
injury and making them more permeable to white blood cells and antibodies
- fluid also leaves the blood vessels and collects in interstitial space; causing swelling
around the area of injury
- cytokines: regulatory peptides; and eicosanoids are lipid derived paracrine and
autocrine signal molecules
- all cells in the body can release paracrine signals; long distance communication
between cells takes place through the nervous and endocrine systems
- endocrine: communicates by hormones: chemical signals that are secreted into the
blood and distributed all over the body by circulation; hormones come in contact with
most cells of the body; but only those cells with receptors for the hormone are target
cells
- nervous system: combination of chemical signals and electrical signals to
communicate over long distances
- electrical signal: travels along a nerve cell (neuron) until it reaches the end of the
cell; where it is translated into a chemical signal secreted by the neuron
- chemical signals: secreted by neurons: neurocrine molecules
- NT: of a neurocrine molecule diffuses from the neuron across a narrow extracellular
space to a target cell and has a rapid onset effect
- neuromodulator: neurocrine acts slowly as an autocrine or paracrine signal
- neurohormone: neurocrine diffuses into the blood for body wide distribution
- cytokines: communication molecules; cytokine: refers to peptides that modulate
immune response → recent years: variety of regulatory peptides: 4 or more alpha
helix bundles
- families of cytokines include: interferons; IL; colony stimulating factors; growth
factors; TNF chemokines
- cytokines: associated with immune response; control development and cell
differentiation
- cytokines function as autocrine or paracrine signals
- cytokines: not produced by cells the way hormones are; nucleated cell can secrete
cytokines at some point in its life span
- cytokines are made on demand; hormones are made in advance and stored
- intracellular signal pathways for cytokines are usually different from those for
hormones
- erythropoietin: control synthesis of RBC; considered a hormone but it is a cytokine
- autocrine signals: act on the same cell that secreted them
- paracrine signals: secreted by one cell and diffuse to adjacent cells
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