phys

What is physiology?

the study of function of the body - how the body parts work and carry out their life sustaining activities

How is a constant steady state of internal environment achieved?

Homeostasis

What is intracellular fluid?

fluid inside the cell

What is extracellular fluid?

fluid outside the cell (blood plasma and interstitial fluid)

What is the major cation and anion in ECF?

Sodium cation and Chloride is anion

What is the major cation in ICF?

Potassium

What is transcellular fluid?

Fluid consisting of cerebrospinal, pleural, peritoneal and synovial fluids., secreted by epithelial cels and found in joints.

What are the components of a feedback mechanism?

Stimulus, receptors, CNS, effectors

What is negative feedback?

A response to a change in the body that counteracts or opposes the initial change.

What is positive feedback?

Feedback that increases the output of a process.

What did Langley's experiment with pilocarpine and atropine do?

Gave rise to the idea of receptors.

What is the effect of pilocarpine on heart rate and saliva production?

Pilocarpine slows heart rate and increases saliva production.

What do atropine do to pilocarpine?

Atropine blocks the actions of pilocarpine, as it is an antagonist.

What did Langley do with chicken leg muscles, nicotine and curare?

- Electrical stimulation caused contraction of muscle
- Application of nicotine to muscle also caused contraction
- Found that nicotine mimics electrical stimulation
- When curare applied to muscle, antagonised effects of electrical and nicotine stimulation

What happened when Langley cut back the nerves of the chicken leg muscles?

- applying nicotine to nerves caused contraction
- stimulating nerves produces substances that mimics action of nicotine

What did Ehrlich's experiment with blood cells show?

- Treated blood cells with different dyes
- Different cell took up different dyes
- Showed specificity of interaction between molecule and receptor

What are receptors?

Recognition sites for cell mediators (neurotransmitters/hormones), bind to molecules to modulate activity of cells.

What are cell mediators?

Extracellular signal molecules

What is cell signalling?

Where a receptor detects extracellular signal to generate intracellular signal(s).

What is signal transduction?

Process of converting extracellular signals into intracellular signals.

What is endocrine signalling?

Mediator (i.e. hormone) is secreted into the blood and transported around the body(long distance) to act on multiple receptors

What is paracrine signalling?

signalling molecules act locally (short distance), effecting neighbouring cells

What is neuronal signalling?

release of neurotransmitters to act on a target cell
- Long distance
- Fast acting
- Specific
- Synapses form between neurones and target

What is contact dependent signalling?

signalling molecules are expressed on the cell surface of one cell and bind to the receptors of another cell when the two come into contact.

What are some examples of endocrine signalling?

- Adrenaline
- Insulin

What are some examples of paracrine signalling?

- Histamine
- Nitrous oxide
- Lipid mediators

What are some examples drugs effecting neuronal signalling?

- synapses restricts signal between neurone and target
- drugs influence neurotransmitter synthesis
- Drugs interfere with storage, leading to depletion
- Drugs prevent neurotransmitter release
- Drugs interfere with receptors

What are some examples of contact dependent signalling?

- used in immune system ( T cells receptors detect antigen presenting cells and activate to recognised infected/damaged cells)
- Car-T immunotherapy (T cells activated to recognise and kill cancer tumour cells)

What are bioassays and what are they used for?

experimental assays where concentration/potency of a substance is measured by its produced biological response.
can be used for
- Measure pharmacological activity of new drug
- Investigate function of endogenous mediators
- Measure drug toxicity/side effects

What did Otto Loewi discover and how?

Discovered chemical transmission between neurotransmitters by showing the effect of acetylcholine as an endogenous neurotransmitter, using a frog heart.

What did Henry Dale do?

Later showed acetylcholine was used as a neurotransmitter at NMJ and autonomic ganglia.

What was Henry Dale's experiment?

- Used bioassays with dorsal muscle of leeches to measure acetylcholine release following stimulation of different preparations

What did Henry Dale's experiment show?

- showed neurones were defined by the neurotransmitter they synthesised/used
- Defined neurotransmitters as 'cholinergic', 'adrenergic' or 'gabaergic'

What is the experimental criteria for a substance to be a mediator?

For a substance to be a mediator:
- Must be released in sufficient amounts to produce biological action on target cells within appropriate time
- Application of sample of mediator produces original biological effect
- Interference with synthesis, release or action ablates/modulates original response

What is the production of mediators dependent on?

Depends on enzymes and active genes
- cells can produce more than one kind of mediator
- Some secretory vesicles store more than one type of transmitter

What are the two types of chemical mediators?

1.) Preformed and stored in specialised vesicles and released by exocytosis (allows for rapid communication)
2.) Mediator produced on demand, released by diffusion or constitutive secretion (takes longer to act)

What happens when neurons are stimulated?

- Action potential generated
- Acetylcholine released

What do vesicles involved in regulated exocytosis have?

- calcium sensor protein (synaptotagmin)
- Required for efficient membrane fusion

What enzyme is involved with cholinergic synapses?

Acetylcholinesterase

What do vesicular transporters do?

Load transmitters into synaptic vesicles

What is pharmacology?

The study of mechanisms by which drugs affect function of living things.

Where are most receptors found?

majority embedded in membrane
- Transmembrane domains
- Extracellular domain

What are the different classifications of receptors?

- Ligand-gated ion channels
- G-protein coupled receptors
- Kinase linked receptors
- Nuclear receptors

What are ligand-gated ion channel receptors?

- Binding site facing outside of cell with series of transmembrane spanning that possess ligand binding domain
- Allows formation of pores

What are G-protein coupled receptors?

- All proteins have 7 transmembrane domains
- Binding domain depends on sub-family and binding molecules
- When chemical mediator binds, G protein is activated

What are kinase-linked receptors?

- Binding in membrane by single transmembrane domain
- Involved in hormone and insulin signalling
- Signal transduction associated with kinase (phosphorylates proteins)
- Kinase can be part of receptor or attached as separate molecule to receptor protein

What are nuclear receptors?

- No transmembrane domain
- Found inside cytoplasm or nucleus
- DNA binding motifs
- Control transcription of specific genes

What is an agonist?

drug/molecule that binds to receptor to bring about a cellular response, leading to signal transduction

What is an antagonist?

Drug that inhibit response of agonist, bind to receptor but don't elicit a response

What is a ligand?

Any molecule/drug that binds to a receptor
- Can be agonistic or antagonistic

Which receptors are the fastest at signal transduction?

Ligand-gated ion channels are the most rapid (ms or less) as they only require a small conformational change.

Why are G-protein, kinase-linked and nuclear receptors slower?

- G-protein receptor mechanism is more complicated, receptor activates G protein that controls function of other proteins (channels/enzymes)
- Kinase-linked receptors take longer due to phosphorylation, gene transcription and protein synthesis (takes hours)
- Nuclear receptors require gene transcription and protein synthesis

What are ionotropic receptors?

receptors where the signalling molecule itself controls the opening/closing of an ion channel when they bind to the receptors (i.e. ligand-gated ion channels)

Describe the structure of a ligand-gated ion channels.

- Composed of 3-5 subunits
- Each subunit has 2-4 transmembrane spanning domains (TMs)
- Complex arrangement to form central aqueous pore

What are the different classifications of ligand-gated ion channels?

- Cys-loop type (pentameric assembly)
- Ionotropic glutamate type (tetrameric assembly)
- P2X type (trimeric assembly)
- calcium release type (tetrameric assembly)

What is myasthenia gravis?

-An autoimmune neuromuscular disease where antibodies attack nicotinic receptors leading to fluctuating muscle weakness and fatigue.
-Treated using drugs that inhibit acetylcholinesterase, prevents breakdown of Ach
- Immunosuppressants used to lower immune response to nicotinic receptors

How does signal transduction occur in Metabotropic G-protein coupled receptors?

- 7 transmembrane domains (heptahelical)
- Regulate effector proteins via heterotrimeric GTP-binding protein
- When agonist bound, helices stabilised
- When antagonist bound, helices are destabilised and shape formed is non-conductive
- When agonist binds to GPcR, signal transduction occurs via activation of heterotrimeric G proteins

How many types of G proteins are there?

- 20 types
- same G protein can be used on different receptors
- Different G proteins control different functions of effectors

How does signal transduction occur in heterotrimeric G proteins?

- Composed of 3 subunits (alpha, beta, gamma)
- inactive alpha subunit associated with GDP has high affinity for beta-gamma subunit
- When agonist binds to receptor it undergoes structural rearrangement (involves intracellular loops that join TMs)
- Subunits joining changes structure of alpha subunit which lowers affinity for GDP, alpha subunit now has high affinity for GTP (alpha subunit activates)
- Receptor detaches from alpha subunit
- Beta-gamma subunit also detaches
- Receptor and beta-gamma subunit free to interact with other molecules
- cycle can repeat if agonist bound to another receptor

How is signal transduction switched off?

- Switched off as a result of enzymatic activity of alpha-subunit (alpha subunit \= GTPase)
- Hydrolysis of GTP into GDP causes conformational change of alpha subunit
- Affinity for beta-gamma subunit returns
- G protein is deactivated

What downstream effect does the alpha subunit have on effector proteins?

regulates enzymes involved in 2nd messenger production (Gs, Gi, Gg)

What do Gs, Gi and Gg do?

Gs - adenylyl cyclase regulates increased cAMP levels
Gi - adenylyl cyclase regulates decreased cAMP levels
Gg - phospholipase C (PLC) regulates increase of IP3 + DAG and increased calcium

What downstream effect does the beta-gamma subunit have on effector proteins?

- Beta-gamma regulates ion channels
- GIRK \= potassium channel opened by G protein beta-gamma subunit that inhibits action potential firing

What is adenylate cyclase?

- 2nd messenger
- enzyme that converts ATP to cAMP
- small

What determines the levels of cAMP?

The activity of adenylyl cyclase and cAMP phosphodiesterase

What regulates signal transduction downstream of cAMP?

Proteins (protein kinase (PKA), EPAC, and CREB (transcription factor))

What is protein kinase?

an enzyme that transfers phosphate groups from ATP to a protein
- Reguates phosphorylation of effector protein
- 2 subunits (regulatory and catalytic)
- cAMP binds to regulatory subunit, catalytic subunit activated and interacts with downstream targets
- Leads to phosphorylation

How is signalling amplified through GPcR regulated 2nd messenger cascades?

- Gg regulates phospholipase C which leads to generation of 2nd messengers IP3 and DAG which lead to increased intracellular calcium and activation of protein kinase C

Which GPcR and signalling is involved with smooth muscle contraction?

Gg and PLC signalling
- Muscarinic M3 receptors (ach)
Histamine (H1)

Why is it useful to know which receptor a cell expresses and what type of signalling is involved?

Helps to predict the effects of the receptor activation and drug action.

What is the autonomic nervous system?

the part of the nervous system responsible for control of the bodily functions not consciously directed, such as breathing, the heartbeat, and digestive processes.

What are the components of the ANS?

Brain & spinal cord

What are the two major efferent pathways of the ANS?

- Sympathetic, 'fight or flight' (whole body or discrete)
- Parasympathetic 'rest and digest' (discrete only)

How is sympathetic (fight or flight) stimulation activated?

- Exercise, excitement, emergency, embarrassment

What are the whole body and discrete effects of the SNS?

whole body: pupil dilation, increased heart rate, blood vessels dilate, increased lung expansion, glucose released into blood stream

Discrete: reproductive system

How is parasympathetic (rest and digest) stimulation activated?

digestion, defecation and diuresis

What are the discrete effects of the PNS?

pupils constrict, heart rate decreases, increased blood flow, enzymes and bile released, contraction/relaxation of sphincter, reproductive organs

What does the SNS and PNS working together allow for?

Rapid and precise control of tissue function

How is the ANS organised?

- Preganglionic neuron in CNS synapses with postganglionic neurone (peripheral ganglion) that transfers signal to target cell
- Both sympathetic and parasympathetic pathways have this organisation except adrenal medulla within SNS

What fibres are preganglionic neurons made of?

cholinergic
- Release Ach as their primary neurotransmitter which activates nicotinic Ach receptors on postsynaptic cell

What are some characteristics of preganglionic neurons of SNS?

- Short
- Cholinergic
- Run from thoracic and lumbar spinal cord

What are some characteristics of preganglionic neurons PNS?

- Long
- Cholinergic
- Run from brainstem and sacral spinal cord

What are some characteristics of SNS postganglionic neurons?

- Long
- Adrenergic
- Target tissue expresses alpha and beta-adrenergic receptors

What are some characteristics of PNS postganglionic neurons?

- Short
- Cholinergic
- Target tissues express muscarinic Ach receptors

Which nerve carries 80% of total PNS outflow?

Vagus nerve

What do each of the central components of the ANS do?

Spinal cord (lateral horn) - mediates autonomic reflexes and receives sensory afferent and brainstem input

Brainstem nuclei - mediates autonomic reflexes

What does the hypothalamus do?

Regulates some ANS output: feeding, thermoregulation, circadian rhythms (sleep/wake), water balance, sex drive, reproduction

What does the forebrain do?

controls complex cognitive, emotional, sensory, and motor functions

What do visceral afferents do?

sensory input from visceral afferent neurons takes priority over cortical functions

What are the two principal transmitters in the ANS and which receptors do they act on?

Ach and noradrenaline
- Act on nAChR, mAChR, alpha and beta-adrenoreceptors

What are the two classes of receptors involved in mediating the effects of ACh?

- Nicotinic (pre to postganglionic communication)
- Muscarinic (organs innovated by PNS)

What are the 5 subtypes of muscarinic receptors?

M1, M2, M3, M4, M5

Where are M2 receptors found and what do they do?

- Abundant in nodal and atrial tissue of the heart
- Activates GIRK beta-gamma subunit potassium channels and inhibit L-type calcium channels
- Gi coupled
- Activate potassium channel in pacemaker, slowing heart rate and decreasing contractility

Where are M1 and M3 receptors found and what do they do?

- Located on smooth muscle and gland cells
- Gg coupled receptor
- Downstream effects increase Ca2+
- Stimulate contraction of smooth muscle
- Stimulate secretion from exocrine glands

What are cholinergic drugs?

Agents that influence the activity of cholinergic receptors
Most mimic or block the actions of acetylcholine

What are the muscarinic antagonists?

Muscarinic antagonists block the action of acetylcholine at muscarinic receptors. They are also known as anticholinergic drugs, antimuscarinic drugs, or parasympatholytic drugs. (e.g. atropine)

What are cholinomimetic drugs?

Drugs acting indirectly to enhance cholinergic transmission, inhibit cholinesterase (e.g. physostigmine), effect all transmission including CNS

Where are noradrenalin receptors found?

found on tissues responding to postganglionic sympathetic neurons (smooth muscle, cardiac muscle, some glands)

What are the subtypes of adrenoreceptors and what do they do?

- Alpha & beta, vary in expression and function
- Beta 1, heart activation increases contractility
- Beta 2, bronchi activation promotes relaxation
- Alpha 1, blood vessel activation promotes constriction
- Alpha 2, kidney activation promotes vasoconstriction

How does the activation of beta 1 adrenoreceptors increase contractility of the cardiac muscle?

- Activation of beta 1 in heart increases cAMP, activating PKA which causes phosphorylation of L-type voltage-gated calcium channels
- Increases open time
- Increases contractility of heart muscle