W12 Inter-organ Communication Flashcards
what are the two systems involved in coordination of fuel metabolism
nervous system: electrical signals originate in neuron cell body > travel very rapidly over long distances to axon tip > neurotransmitters released and diffuse to target cell (micrometers range)
endocrine system: hormones secreted into bloodstream > carry throughout body to target tissues (may be a meter or more away from the secreting cell)
what are neurohormones
class of hormones that originate from neurone from brain and diffuse through the blood stream
common eg: oxytocin and vasopressin
mode of action of different classes of hormones
plasma membrane receptors; second messengers: peptide, catecholamine, eicosanoid
nuclear receptors; transcriptional regulation: steroids, vitamin D, retinoid, thyroid
cytosolic receptor and second messenger: nitric oxide
what are cytokines and what do they respond to
they are large group of protein, peptides or glycoproteins that are secreted by specific cells of immune system
respond to: fasting and feeding cycles, circadian rhythm, cold exposure and exercise
what are some attributes that allow cytokines to regulate cellular activity in a coordinated interactive way
pleiotropy: one cytokine has many different functions
redundancy: several different cytokines can mediate the same or similar functions
synergism: occurs when the combined effect of two cytokines on cellular activity is greater than the additive effects of individual cytokines
antagonism: the effects of one cytokine inhibits or offsets the effects of another cytokine
difference between cytokines and hormones
hormones: class of proteins that act as signalling molecules; secreted by a given tissue and are used to communicate between organs > trigger integrative responses to specific stimuli
cytokines: class of small proteins that can be produced by broad variety of cells and act as signalling molecules; have high affinity to receptors > found in much lower concentrations than hormones
how can hormones and cytokines be classified by the way they get from the point of release to their target tissue
endocrine: hormones released into blood and carried to target cells throughout body
paracrine: hormones released into the extracellular space and diffuse to neighbouring target cells
autocrine: hormones released by and affect the same cell, binding to receptors on the cell surface
mechanism of action of lipophilic hormones
lipid-soluble hormone diffuses through plasma membrane
hormone binds with receptor in cytoplasm forming receptor-hormone complex
receptor-hormone complex enters the nucleus > triggers gene transcription
transcribed mRNA translated into proteins that alter cell activity
structure of receptors of lipophilic hormones
variable lengths A/B: regulatory domain
domain C: dna binding domain
domain D: nuclear-targeting sequence
domain E: hormone-binding domain
mechanism of action of hydrophilic hormones
water soluble hormones are membrane insoluble > bind to membrane receptors
binding activates G protein > activates adenylyl cyclase
adenylyl cyclase catalyses the conversion of ATP to cAMP (the second messenger in this pathway)
cAMP activates protein kinases
protein kinases phosphorylate proteins in cytoplasm > activate proteins > alter cell activity
what are the 2 functionally distinct parts of the pituitary gland
posterior pituitary: contains the axonal endings of many neutrons that originate in the hypothalamus
anterior pituitary: responds to hypothalamus hormones carried in the blood > produce tropic hormones or tropics
