Lecture7&8- Principles of Hormone signalling Flashcards
What are the 2 major control systems of the vertebrate body ?
endocrine system
nervous system
required for effectuve cell-to -cell communication in large multicellualr organisms
What does the endocrine system do ?
moniter and co-ordinate the internal environment and produce changes if required -(homeostasis)
-helps organisms to respond & adapt to changes i external environment
-hormones -regualting growth development,metabolism and reproduction
How is hoemeostasis maintained ?
1.)stimulas prod change in variable
2.)detected by sensor
3.)input info sent along afferent pathway
4.)output: info sent efferent pathway to effector
5.)response of effector feeds back to influence magnitude of stimulas and returns variable to homeostasis
What is Homeostasis negative feedback loop ?
controlled variable = room temp,sensed by thermostat
effector = heater
What are hormones ?
a chemical agent prod and secreted bya spoecialised endocrine gland/tissue tht is transported in the blood stream to a sometime distant target where it elicits a phsiological
May be stimualtory or inhibitory
may act on several or 1 specific target tissue
responsive tissues must have specific receptors for particular hormone
what are endocrin glands ?
majopr function is to produce hormones in response to a physiological state
secrete hormones into the blood stream or locally exorine glands secrete substances
some gland can secrete more than 1 hormone
What are the principles of cell signalling ?
Individual cells must communicate with each other to carry out their functions-send and recieve signals
diffusible chem signals
-paracrine & autocrine signalling :local signals
endocrine signalling:via blood stream
gap junctions: connexins -also enable electrical coupling (synctium)
How does intercellualr communication work ?
release of diffusible chemicl signals with local effects
-Paracrine signalling
- Autocrine signalling
what is paracrine signalling ?
release of signal molecules that diffuse
short distances to affect nearby (neighbouring) target cells.
dont enter the blood stream
what is autocrine signalling ?
releases self stimulating molecules secreted signal also acts on cells that secreted it
dont enetr blood stream
What is endocrine signalling ?
release of signal molecules that diffuse over long distances to affect target cells
What is neuroendocrine signalling /neurosecretion ?
Secretion of hormones from neurons
What are the gap juctions between intercellular communication ?
-formed by connexins
-permit passage of ions and small molecules between cells enables metabolic coupling ,electrical coupling (synctium) and signalling via 2nd messenger (cAMP).
2-4 nm gaos between cells
What are contact-dependent (juxtacrine signalling ) ?
Communications between adjacent cells involving membrane bound signals & receptor molecules
What are the 3 main chemical classes of hormones ?
-Steroid
-Peptide & Protein
-Amine
Steroid hormones and examples ?
Cholosterol derivatives ;lipid-soluble (hydrophobic)
eg.)cortisol (adrenal cortex)
testosterone (testes)
What are Petide & protein hormones ?
give examples and what they are
Majority of hormones:water-soluble (hydrophillic)
-Small peptide :thyroptrophin-releasing hormone
-Protein (polpeptide):insulin,growth hormone(GH)
-Glycoprotein :follicle stimulating hormone (FSH)
What are amine hormones ?
modified amino acids
eg.)tyrosine derivatives;water*,lipid-solubles
hydrophillic/phobic respectively
*catecholamines :adrenaline,noradrenaline;thyroid hormones:triidothyroni
What are the 3 main chemical classes of hormones ?
Peptide & Protein-polypeptide(not lipid soluble)
Amine-derivatives(tyrosine,epinephrine)most not lipid solu
Steroid -cholesterol,cortisol-lipid soluble often binding to receptors
Hormone transport in circulation ?
Catelcholamines & peptide proteins -are water soluble transported dissolved in plasma
Steroid hormone are lipid soluble transported bound to specific carrier proteins in plasma (many diff types)
What is free hormone concentration ?
is physiologically important as bound hormone is not available to target cells (not affect )
free hormone + binding protein ↔ hormone protei complex
How do the receptors control the activigy of target cells ?
1.)opens ligand gated channels (ionotropic)[fast]
2.)activating enzyme/enzyme linked membrane receptors (catalytic receptors)
3.Activates metabotropic (g protein coupled) receptor:indirectly opens ion channels or activates 2 nd messenger [slow]
4.Diffuses across cell membrane to activate gene expression
How are signals detected in target cells ?
- when signals arrives at target cells the signal reception to detect the signals → receptors
- ligans binding initiates confromational change of receptors:
1.ligand gated channels
2.enzyme/enzymelinked
3.G protein coupled receptors (GPCR)
4.intracellular receptors
GPCRs mediate cellular responses in response to many hormones and neurot
How do steroid hormones work ?
- cholesterol derivatives;lipid soluble
- transported in blood bound to CP
- Readily cross plasma membrane .Diffuse out of ce.s that prod them → synthesised ‘on demand’
- bind receptors found inside the cell :intracellular receptors → regulate gene expression
CP-carrier proteins
vertebrates-gonads,adrenal glands,skin & placenta se
SH found in cyptoplasm,nucleus
Where are steroid hormones derived from ?
Cholesterol
6 carbon side chain is cleaved to form pregnenalone in the mitochondrian
-Pregnenalone travels to smooth ER where diff enzymatic processes produce different specific steroid molecules
-
effects of steroid hormoes usually take several hours -days
slow respon
What are peptide & protein hormones and its properties ?
Majority of hormones -water soluble
-packaged into vesicles;r=released via exocytosis when needed
-easily transported in blood without the need for carrier protein
-Bind receptors found on the cell surface–>indirectly open ion channels &/or activate 2nd messenger
Difference between peptide/protein
size or structure
peptides-smaller t
What are amines and their properties ?
Tyrosine derivatives;water or lipid soluble inclusing catecholamines & thyroid hormones
packaged into vesicles released by exocytsis when needed or siffuse out of cells that prod then synthesied on demand
easily transported u blood without carrier proteins
bind receptors found on cell surface or intracellularly
target cells may express different types of receptors –>capable of resp
What does the endocrine system excrete ?
specific classes of hormones
-steroid
-peptides & proteins
-amines
What are ligand gated ion channels ?
channel pore allowing specific solutes to enter the cell
-mostly at nerve terminals (synaptic signalling/transmission)
-secreted by -chromaffin cells of adrenal medulla~(considered specialised postganglionic sympathetic neurons)
How do enzyme/enzyme linked receptors work ?
Insulin receptors is 1
-Hormone binds to cell surface receptors
-Activated receptor functions as a tyrosine kinase
-interacts directly with other membranes proteins–>cellular responses
binding to α subunits induces conformational change resulting in autopho
What are GPCR’s ?
G protein coupled receptor
ligand binding to a GPCR activates G protein
:G protein bound to guanosine diphosphate (GDP) is inactive. The G protein is activated when bound to guanosine triphosphate (GTP).
-G protein dissociates :Gα and Gβγ interact with AC/PLC
AL/PLC-membrane bound-enzymes) & ion channels respectively
GCPRs
Do different G proteins exist ?
All act as ‘biochemical switches ‘–>modulate ion channel activity or alter rate of 2nd messenger production
e.g)cAMP,IP3 DAG
-can regulate various intracellular events
signalling cascade:series of events linking the change in 2nd messenger levels to final response
