Physiology Wk 4 Flashcards
what is direct intracellular communication
physical contact between cells
through gap junctions and possibly through tunnelling nanotubes- they are minute tunnels that bridge the cytoplasm of neighbouring cells in some tissues. through gap junctions, ions and small molecules are directly exchanged between closely associated interacting cells without ever entering the ECF
through transient direct link-up of surface markers. some cells such as those of the immune system, have specialised markers on the surface membrane that allow them to directly link with certain other cells that have compatible markers for transient interactions. this is how the immune system destroys undesirable cells
what are the methods of indirect communication
paracrines are local chemical messengers whose effect is exerted only on neighbouring cells in the immediate environment of their site of secretion. autocrine is even more localised after being secreted, it acts only on the cell that secreted it.
one example of paracrine is histamine which is released from a specific type of connective tissue cell during an inflammatory response within an invaded or injured tissue. histamine dilates the blood vessels in the vicinity to increase blood flow to the tissue
describe neurotransmitters
are short range messengers, in response to electrical signals. NTs diffuse from their site of release across narrow extracellular space to act locally on the adjoining target cell which maybe another neuron. neurones may carry electrical signals for long distances or short distances across the synaptic cleft
describe hormones
are long range chemical messengers specifically secreted into the blood by endocrine glands in response to an appropriate signal. the blood carries messengers to other sites of the body, where they can exert their effects on their target cells some distance after release. only the. target cells of a particular hormone have membrane receptors for binding this hormone. non target cells are not influenced by any blood borne hormones that reach them
describe neurohormones
are hormones released inot the blood by neurosecretory neurons. they can respond and conduct electrical signals. neurosecretory neurons release a chemical messenger a neurohormone into the blood when an action potential reaches axon terminals. the neurohormone is then distributed through the blood to distant target cells.
vasopressin produced by nerve cells in the brain promotes water conservation in the kidneys during urine formation
what is signal transduction
refers to the process by which incoming signals are conveyed into the target cell where they are transformed into a dictated cellular response
what are lipid soluble extracellular chemical messengers such as cholesterol derived steroid hormones
gain entry into the cell by dissolving and passing the lipid bilayer of the target cell’s plasma membrane. these extracellular chemical messengers bind to receptors inside the target cell to initiate the desired intracellular response themselves, usually by changing gene activity, either suppressing or turning on the transcription of genes
water soluble extracellular chemical messengers cannot gain entry to target cell because they are poorly soluble in lipid and they cannot dissolve in the plasma membrane.
these include peptide hormones delivered by the blood, NTs released from nerve endings and paracrines released locally
the messengers bind to a specific receptor and trigger a sequence of intracellular events that controls particular cellular activity.
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methods or pathways by which water soluble extracellular messengers bind
Despite the wide range of possible responses, binding of a water-soluble extracellular messenger (also known as the first messenger) to its matching surface membrane receptor brings about the desired intracellular response by one of three general means, depending on receptor type.
1. Messenger binding to a chemically gated receptor-channel opens or closes the channel, with the resultant ion movement leading to the cell’s response.
2. Messenger binding to a receptor–enzyme complex activates tyrosine kinase, which phosphorylates designated proteins that lead to the cell’s response.
3. Messenger binding to a G-protein-coupled receptor acti- vates a second-messenger pathway that carries out the cell’s re- sponse.
what is the tyrosine kinase pathway
two extracellular messengers bind to two tyrosine kinase receptor enzymes, which pair, activating receptor enzymes protein kinase (tyrosine kinase) site that faces the cytoplasm
tyrosine kinase site self-phosphorylates receptor-enzyme’s tyrosines
inactive designated protein binds to phosphorylated receptor enzyme, which phosphorylates protein, activating it
active designated protein brings about desired response
what is the JAK/STAT pathway
Binding of an extracellular messenger to the receptor on the ECF side causes a conformational change in the receptor that activates the JAKs bound to the cytosolic side of the receptor. Activated JAKs phosphorylate signal transducers and activators of transcription (STAT) within the cytosol. Phosphorylated STAT moves to the nucleus and turns on transcription of selected genes, resulting in synthesis of new proteins that carry out the cellular response.
Some hormones, for example prolactin, the hormone that stimulates milk secretion in lactating mothers as well as cytokines, chemical mediators for the immune system
Activation of a second-messenger pathway via binding of a first messenger to a G-protein-coupled receptor. describe this
extracellular messenger (frist) messenger binds to the receptor
receptor activates G protein
G protein activates effector protein
effector. protein produces second messenger
second messenger activates protein kinase
protein kinase activates designated protein
active designated protein brings about desired response
