Introduction to cell signalling Flashcards
autocrine regulation
signalling molecule binds to target receptor on the cell it was secreted from
allows cell regulation through positive or negative feedback
somatostatin secretion in the stomach
autocrine regulation
somatostatin is secreted by D cells in the gastric glands
somatostatin binds to SST2R receptors on parietal cells to inhibit adenylyl cyclase decreasing cAMP which decreases gastric acid secretion
somatostatin induces a negative feedback loop of its own production by reducing its own secretion by binding to SST2R receptors on D cells
paracrine regulation
signalling molecule is secreted to the extracellular space and binds to receptors located on adjacent cells without passing through the circulatory system
histamine in the stomach
paracrine regulation
histamine is secreted by the enterochromaffin-like cells in the gastric glands due to acetylcholine
histamine binds to H2 receptors to activate adenylyl cyclase increasing cAMP which increases the number of proton pumps and gastric acid secretion from parietal cells.
endocrine regulation
signalling molecule is secreted from secretory glands to the circulatory system
receptors are located on or in cells of a target organ or tissue
the hypophyseal portal system
endocrine regulation
hormones such as ACTH are secreted from the cells of the pituitary glands into the connected circulatory vasculature
the HPA axis
endocrine regulation
stress > cerebral cortex > hypothalamus (CRH) > anterior pituitary (ACTH) > adrenal cortex (cortisol) > target tissue
elevated cortisol levels = negative feedback on CRH and ACTH
actions of cortisol
stimulates gluconeogenesis in the liver due to low plasma glucose
protein breakdown + liberation of free fatty acids
immune system suppression
facilitated stress response
maintains blood pressure
receptor types
ligand-gated ion channels - milliseconds
G-protein coupled receptors - seconds
Kinase-linked receptors - hours
nuclear receptors - hours
ligand-gated ion channels
signalling molecule binds to the receptor to open the ion channel and increase intracellular ion concentration which causes depolarisation
nicotinic acetylcholine receptor
ligand-gated ion channel
non-specific cation channels present in skeletal muscle
G-protein coupled receptors
ligand binds to GPCR causing a conformational change, and GDP is replaced by GTP
⍺-subunit dissociates and activates adenylyl cyclase which catayses the formation of cAMP from ATP
cAMP activates protein kinase A which exists in an R2C2 complex
⍺1 adrenoceptor
GPCR
G⍺q
activation of phospholipase C
increase in IP3 and DAG
vasoconstriction of blood vessels
⍺2 adrenoceptor
G⍺i
inhibition of adenylyl cyclase
decrease in cAMP, increase in K+ channels, decrease in Ca2+ channels
presynaptic inhibition of noradrenaline, relaxation of the GI tract
β1 adrenoceptor
G⍺s
stimulation of adenylyl cyclase
increase in cAMP
increased heart rate and cardiac muscle contraction
