Physiology Flashcards
Which part of the brain is involved in thermoregulation?
Hypothalamus
Outline the composition of intracellular fluid
Cytoplasm: high in K+, low in Na+ and Cl-
Outline the composition of extracellular fluid
Interstitial fluid and plasma; Low K+, high Cl- and Na+
Define ‘osmolarity’
Number of osmoles of solute per litre of solution (Osm/L)
Define ‘osmolality’
Osmoles of solute per kg of solvent (Osm/kg)
Define ‘colloid’
Large molecular weight particles present in solution
What is the ‘Donnan effect’?
If cell doesn’t do anything to control osmolarity –> higher solutes inside –> water flow inwards –> lysis/rupture
Define ‘tonicity’
Actual effect of solution on living cell
What is tonicity influenced by?
By solutes which can’t cross membrane
Where is sodium absorbed in the kidney?
Distal convoluted tubule regulated by aldosterone
Where is water reabsorbed in the kidney?
Collecting duct, regulated by ADH
Describe ‘hyponatraemia’
Decrease in extracellular osmolarity as total body water increases and there is decrease in plasma electrolytes - often caused by overhydration
Describe ‘hypernatraemia’
Increase in extracellular osmolarity as total body water decreases so there is increase in plasma electrolytes, often due to dehydration
Define ‘buffer system’
Substances present in body fluids and limit pH change by ability to accept or donate hydrogen ions
Define ‘buffer’
Solution which can maintain a constant pH if solution is diluted or strong acids/bases added - consists of weak acid and it’s conjugated base, or weak base and it’s conjugate acid
Describe the phosphate buffer system (include equation)
Present in intracellular fluid (cytoplasm) only:
H+ + HPO42- H2PO4-
Describe the haemoglobin buffer system
Present in RBCs only:
H+ + Hb HHb
Describe amino acid buffers
Proteins accept or donate proton (present in ICF and ECF)
Describe the carbonic acid-bicarbonate buffer system (include equation)
Present in ECF:
CO2 + H2O H2CO3 H+ + HCO3-
Describe respiratory regulation of pH
Alter rate/depth of respiration to retain or eliminate CO2 –> changes are rapid
Describe renal regulation of pH
Excretion or conservation of bicarbonate/hydrogen ions –> changes are slow
What should serum pH be?
7.35-7.45
State the equation to calculate pH
pH = -log10[H+]
Define ‘acidemia’
pH less than 7.35
Define ‘alkalemia’
pH greater than 7.45
What can affect serum pH?
Bicarbonate rise/drop and CO2 rise/drop
What is the cause of respiratory acid-base disorders?
Abnormal respiratory function –> rise /fall in CO2 in ECF
What is the cause of metabolic acid-base disorders?
Generation of acids (organic or fixed) which affects concentration of bicarbonate ions in ECF
Explain how to interpret arterial blood gases
- Look at the pH to see if primary problem is acidosis or alkalosis
- Check the CO2 levels (respiratory indicator)
- Check the HCO3- (metabolic indicator)
- Decide which is the primary disorder (respiratory or metabolic); whichever is concurrent with the change in pH (carbon dioxide is acidic and bicarbonate is alkali)
Describe ‘paracrine signalling’
Molecules act locally and include neural communication systems
How does the Na+/K+ pump contribute to establish resting membrane potential?
3 Na+ ions in for 2 K+ out –> negative inside, positive outside
Describe voltage-sensitive Na+ channels
Activation gate: closed at rest, opens on depolarisation (fast)
Inactivation gate: open at rest and closes in response to depolarisation (close is slow)
Describe voltage-sensitive K+ channels
Closed at rest, open on depolarisation (slightly more slowly than Na+ activation gate) –> stays open throughout depolarisation
Describe a normal action potential curve
Resting (-70mV) –> depolarisation (Na+ activation gate opens, influx) –> threshold potential –> action potential –> repolarisation (Na+ activation gate closes, K+ channel opens) –> hyperpolarisation (K+ channel overshoots) –> Na+/K+ pump re-establishes resting membrane potential
What is the ‘absolute refractory period’?
Cannot open voltage-gated Na+ channels regardless of size of stimulus
What is the ‘relative refractory period’?
Difficulty in producing another action potential during hyperpolarisation
Describe the mechanism of action of local anaesthetics
Bind to open voltage-gated sodium channels –> prevents them from responding by re-opening –> no action potentials generated
Why do axons with greater diameter conduct faster?
Cytoplasmic resistance decreases with increased diameter
Describe Aα axons
Motor neurones; thick myelin and large diameter –> fast conduction
Describe Aβ axons
Mechanical touch/pressure receptors so thick myelin
Describe Aδ axons
Pain receptor so thick myelin to allow sudden response
Describe C axons
Slow pain receptor, thin diameter and no myelin (for things such as itch)
What are the most common excitatory neurotransmitters in the nervous system?
Glutamate
What are the most common inhibitory neurotransmitters in the nervous system?
GABA and glycine
Describe how excitatory post-synaptic potentials are created
Glutamate-gated channels cause depolarisation on post-synaptic neurone
Describe how inhibitory post-synaptic potentials are created
GABA/Glycine-gated channels cause net influx of Cl- –> hyperpolarisation
What are axosecretory synapses?
Axon secretes directly into bloodstream
What are axoaxonic synapses?
Axon terminal secretes into another axon
What are axodendritic synapses?
Axon terminal ends on a dendritic spine
What are axoextracellular synapses?
Axon with no connection secretes into ECF
What are axosomatic synapses?
Axon terminal ends on soma
What are axosynaptic synapses?
Axon terminal ends on another axon terminal
What type of receptor binds Ach?
Nicotinic
What does an ionotropic response involve?
Opening of ligand-gated ion channels (fast response)
What does a metabotropic response involve?
Where a ligand activates a receptor which then activates G proteins –> effects enzymes
Outline 3 ionotropic receptors
Nicotinic receptors, glutamate receptors, GABAa receptors
Describe nicotinic receptors
Activated by binding of 2 ACh molecules causing Na+ to flow into post-synaptic cell
Describe G protein-coupled receptors
7 transmembrane segments and involve: G-protein receptor, G-protein, enzyme and second messengers
What are the 3 main types of second messenger?
Hydrophilic water-soluble, hydrophobic lipid-soluble, gases
Name 4 sensory skin receptors
Pucinian corpuscle, Meissner corpuscles, Merkel cells and Ruffini endings
What do Meissner corpuscles do?
Register light touch (rapidly adapting)
What do Merkel cells do?
Register pressure texture (slow adapting)
What do Pacinian corpuscles do?
Register vibration (rapidly adapting)
What do Ruffiini endings do?
Register skin stretching (slow adapting)
What do parasympathetic afferents detect?
Physiological information
What do sympathetic afferents detect?
Pathophysiological information e.g. pain
What are the parasympathetic cranial nerves?
Oculomotor, facial, glossopharyngeal and vagus (III, VII, IX, X)
Where does the sympathetic nervous system run?
Thoracolumbar (T1-L2)
How does the adrenal medulla act as a modified post-ganglionic cell?
From thoracic spinal cord, sympathetic preganglionic fibres project directly to adrenal medulla cells –> secrete adrenaline and noradrenaline into blood
What is the myenteric plexus?
In small intestine between circular and longitudinal muscle layers –> controls motility
What is the submucosal plexus?
In intestines: located between submucosa and circular muscle layer; controls secretion and muscle function of mucosae
What nervous input goes to the enteric nervous system?
Extrinsic efferent information from vagal preganglionic fibres and sympathetic post-ganglionic fibres
What do nicotinic receptors respond to?
ACh
What do muscarinic receptors respond to?
ACh and Bethanechol
What neurotransmitters are used in the autonomic nervous system?
ACh between pre and post-ganglionic, then noradrenaline/ACh at effector
How are muscarinic receptors targeted clinically?
Antagonists: anti-secretory, anti-spasmodics ad bronchodilators
Agonists: stimulate gut and bladder function
What neurotransmitter do adrenoreceptors respond to?
Noradrenaline
What do alpha 1 adrenoreceptors do?
Agonist: vasoconstriction and inhibition of GI and bladder sphincters
Antagonist: vasodilation (treat hypertension)
What do beta 1 adrenoreceptors do?
Agonist: increase HR and force
Antagonist: decrease HR (beta blockers)
What do beta 2 adrenoreceptors do?
Agonist: bronchodilation and vasodilation
Antagonist: asthma
What is the resting membrane potential?
-70mv
What is the threshold potential?
-55mV
What membrane potential does an action potential peak at?
+30mV
What do all GPCRs respond to?
Noradrenaline
