Endocrine signalling Flashcards
(28 cards)
peptide hormones
hydrophilic
released via exocytosis
synthesised in advance (stores in vesicles)
transported dissolved in plasma
acts on extracellular receptors
steroid hormones
hydrophobic
released via diffusion
synthesised on demand
transported bound to plasma proteins (e.g. albumin)
acts on intracellular receptors (enters via channels) to act on transcription
amine hormones
can act as steroid or peptide hormones
derived from tryptophan and tyrosine
catecholamines
thyroid hormones
endocrine signalling
long range signalling where signalling molecules are released into the bloodstream
e.g. insulin release
paracrine signalling
short range signalling where signalling molecules are released into the extracellular fluid
e.g. signalling of alpha and beta cells by somatostatins from gamma cells
autocrine signalling
self signalling where signalling molecules bind the releasing cells receptors
e.g. most neurotransmitter and growth factor release
membrane-protein contact
direct contact of proteins on signalling cell surface interacts with receptors on the target cell
e.g. T cell signalling
receptor types
ligand gated receptors
g protein receptors
kinase linked receptors
nuclear receptors
ligand gated receptors
conformational change induced by ligand binding activated intracellular response
g protein receptors
receptor coupled to g-protein (7 transmembrane spanning regions)
on ligand binding, receptor has a conformational change and alpha subunit splits from g-protein complex and converts GDP to GTP
alpha subunit binds and activates/inhibits target
kinase linked receptors
consists of:
- extracellular binding domain
- signal transmembrane helix
- intracellular domain (tyrosine kinase linked)
on ligand binding, dimerisation activates receptor to promote binding and phosphorylation of the SH2-domain protein, once activated induces a cascade
nuclear receptors
Class I: cytoplasmic
Class II: nuclear
alter gene expression by recruiting co-activators/repressors and binding target DNA
thyroid hormones
hydrophobic (acting as steroid hormones)
tyrosine derivatives
stored as colloid in thyroid follicles
released by transport proteins
catecholamines
hydrophillic (acts as peptide hormones)
tyrosine derivatives
response driven feedback
response in target organ alter hormone levels which feedsback to the releasing gland to alter hormone release
axis driven feedback
regulation of multiple hormones within an endocrine axis
- one hormone can feedback to many organs/glands
feed-forward control
anticipatory response in anticipation of stimulus
e.g. cortisol release though the day
positive feedback
used to increase action of a controlled system in the body
e.g. childbirth
endocrine control of salt/water balance
- hypothalamus osmoreceptors shrink on osmolality increase
- post. pituitary releases ADH
- adrenal glands release aldosterone due to RAAS activation
- kidneys respond to ADH/aldosterone for sodium/water reabsorption
control of thirst
increase in plasma osmolality detected by osmoreceptors
decrease in plasma volume stimulates RAAS (aldosterone release)
signals lead to stimulation of hypothalamic thirst centre
ADH
acts on ADH V2 receptors on basolateral membrane of collecting tubules
- binding catalyses cAMP synthesis to activate PKA for phosphorylation causing aquaporin 2 vesicles to insert into apical membrane
Aldosterone
steroid hormone
binds intracellular mineralocorticoid receptors (MR) to upregulate epithelial sodium channels (ENaC) and potassium channels
stimulates Na+ resorption and K+ excretion by distal convoluted tubule and collecting ducts
release stimulated by RAAS
Natriuretic peptides
released by cardiac muscle in response to stretch
induces sodium/water secretion to lower blood volume
aquaporin 2
increases permeability to water, increases water reabsorption
