L21 - Cellular Communication Flashcards
(14 cards)
what are the principal functions of the endocrine system
- maintain homeostasis
- regulation of growth and development
- control energy storage and use
- mediate the body’s response to environmental cues
what are the different types of hormone signalling
Hormone:
- hormone secreting glad cell, secretes into blood
- hormone often bound to a carrier protein in the blood
- reaches target cells in one or more distant places in the body
Neurotransmitter:
- electrical signal travels down neuron an neurotransmitter related
- neuron or effector cell in close proximity to site of neurotransmiter release
Paracrine:
- local cell releases paracrine substance
- target cells in close proximity to the site of release of paracrine substance
Autocrine:
- autocrine substance released from local cell
- autocrine substance acts on the same cell that secreted the substance
describe the specificity and targeting of hormones
secretory cell releases the hormone and it travels through the circulation
- only cells that express the correct receptor can respond
- hormone binds to receptor and cell makes a response
how can target cell sensitivity (responsiveness) be changed, and define permissiveness
- regulation: increased receptor expression (more likely hormone will bind)
- down-regulation: decrease receptor expression
permissiveness: hormone I requires hormone B for its full effect (eg. hormone B up regulates receptors for hormone A)
describe target cell sensitivity (affinity and competition)
- for a lower affinity receptor you need to have a lot more hormone bound to get a reasonably big respoinse
- for a higher affinity receptor don’t need as much hormone bound
- competitor - most are pharmacologically generated. takes big response and dampens it down
what are the possible fates of secreted hormones
endocrine cell secretes hormone
hormone circulates in the blood usually bound to carrier proteins
then…
- excreted in urine or faeces
- inactivated by metabolism
- activated by metabolism
- bind to receptor on target cell and produce a cellular response
what is synergy
synergy: maximum combined response is larger than addition of maximum individual responses
eg. fat cells
- thyroid hormone: little to no fatty acids released
- epinephrine: small amount of fatty acids released
- epinephrine + thyroid hormone: large amount of fatty acids released
what are the different chemical classifications of hormones
peptides: from free amino acids to large proteins
- lipophobic (doesn’t dissolve in fat easily) so can’t leave/enter cells: secreted by exocytosis and act on cell surface receptors
catecholamines: monoamine derivatives of tyroside
- lipophobic
steroids: synthesised from cholesterol
- lipophilic (don’t dissolve in fat easily) so can leave/enter cells: diffuse across the cell membrane as soon as synthesised and act on intracellular receptors
thyroid hormones: iodinated dipeptides synthesised from tyrosine
- lipophilic
describe cell surface receptors and the response second messengers make
- have to have a mechanism on the surface of the cell bc it is the only part the ligand can get to
- receptor can generate many molecules of second messenger
- second messengers scale up the response by activating lots of enzymes (phosphorylising them)
- and then those enzymes make lots more phosphorylated final products
response increases
also allows multiple responses in the same cell
describe Gs-(and Gi) protein-coupled receptor signal transduction (diagrams on slides)
- hormone binds
- G-protein dissociates. Galpha activates adenylyl cyclase
- cAMP generation
Gs: stimulates cAMP production
Gi: inhibits cAMP production
describe Gq-protein-coupled signal transduction
- hormone binds
- G-protein dissociates
- G-alpha activates phospholipase C
- inositol triphosphate (IP3) and diacylglycerol (DAG) are the second messengers
- DAG activates protein kinase C
- IP3 activates intracellular calcium release
describe intracellular receptors
N-terminal domain: this domain participates in gene activation
DNA-binding domain (DBD): subtle differences in te structure of this domain determine which segments of DNA are bound by different receptors
Hinge domain: this domain is required for nuclear receptors to localise in a cell nucleus
ligand-binding domain (LBD): differences in the shapes of the ligand-binding domains determine which messenger binds to a given receptor
describe steroid receptor signal transduction
- hormone dissociates from carrier protein and diffuses across all cell membranes
- only target cells express the specific hormone receptor
- receptor-hormone complex binds to DNA to alter gene transduction
describe thyroid hormone signal transduction
- most thyroid hormone diffuses across the cell membrane
- most T4 is converted to T3
- receptor needs a cofactor (RXR) to bind DNA for gene transcription
- permissive effects
