PPP Flashcards
What is nebulin?
Molecule that extends from Z band along the length of one thin actin filament
What is titin?
Associated with myosin filaments extending from Z disk to M line
What is concentric contraction?
Contraction stage with an increase in the interdigitation of the filaments
What is eccentric contraction?
Stretched stage where I and H bands are wide. Thick and thin filaments do not interact
How is contraction of skeletal muscle initiated?
ACh binds to nicotinic receptor at motor end plate; depolarisation spreads into T-tubules –> DHP is activated –> RyR are linked and activated –> release of Ca2+ from sarcoplasmic reticulum; Ca2+ binds to troponin –> change in tropomyosin allowing myosin heads to attach –> contraction
How is extracellular space defined?
Plasma + interstitial space
How is total body water distributed?
Plasma space (5% bw; 3.5 L) Interstitial space (15% bw; 10.5 L) Intracellular space (40% bw; 28 L)
What is the amount of CSF in the body?
Around 150 ml
What substances are used to measure fluid compartments?
Plasma volume: albumin, evans blue, labeled inulin
ECS: 24Na, sucrose
TBW: 3H20
What is the difference between osmolarity and osmolality?
Osmolarity: 1 osmole per liter
Osmolality: 1 osmole per kg
What is the osmolarity of plasma?
290 mosmol/l
What is crystalloid osmotic pressure?
Due to small diffusible ions
What is the ionic composition of plasma and intracellular compartment?
Na+: 140 mM and 10 mM K+: 4 mM and 120/140 mM Ca2+: 2 mM and around 100 nM Cl-: 110 mM bicarbonate: 24 mM
Which are the plasma proteins?
Albumin: oncotic pressure of around 25 mmHg
Alpha, beta and gamma globulins
Fibrinogen
What is the count of RBCs and Hb?
RBCs: 5.5/4.8 x 10^12 per litre
Hb: 160/140 g per litre
What is the total WBCC?
4-11 x 10^9 per litre
Lymphocytes (20-40%)
Monocytes (2-8%)
Granulocytes: neutrophils (50-70%), eosinophils, basophils
What is the total number of platelets?
150-400 x 10^9 per litre
What is the normal MCV?
85 fL
What are the average pressures in the pulmonary and systemic circulation?
Pulmonary: 16 mmHg
Systemic: 92 mmHg
What is Fick’s law?
Rate of diffusion depends on: 1. Area 2. Difference in concentrations 3. Distance over which it has to travel How easily it diffuses depends on: 1. Temperature 2. Solubility 3. Square root of molecular weight
What is Darcy’s law?
Flow = (P1-P2)/R
What is Poiseuille’s law?
R = 8VL/pir^4
What is the Fahraeus-Lindqvist effect?
Axial streaming due to laminar flow reduces viscosity of blood
How is Rtotal calculated in series and in parallel?
Series: Rtotal = R1 + R2 +…
Parallel: 1/Rtotal = 1/R1 + 1/R2 +…
How do you calculate MABP?
MABP = CO*TPR
What is the definition of voltage?
A measure of the electrical work done to separate charges across the membrane
What is the equilibrium potential?
When the force of the concentration gradient of K+ out of the cell is matched by the electrical force pulling K+ back into the cell
What is the Nerst equation for monovalent ions?
E = 58 (mV) x log [Cout]/[Cin]
What are the equilibrium potentials of sodium and postassium?
Sodium: +50 mV
Potassium: -90 mV
How do you calculate the driving force on the ion out of the cell?
Vm - Eeq
What is the Goldman Hodgkin Katz equation?
Calculates membrane potential taking into account permeabilities of ions
Where are cardiac t-tubules absent?
Atria, neonatal and avian hearts
How long is the cardiac AP?
200-400 ms
Why is the cardiac AP so long?
Prevents tetany, protects against re-entering arrhythmias
What does cardiac muscle require to initiate contraction?
Calcium influx
What is the difference in the mechanisms of calcium release in skeletal, cardiac and smooth muscle?
Skeletal: depolarization-induced calcium release (L-type calcium channels/DHP act as plug on RyR)
Cardiac: Ca-induced Ca-release
Smooth: IP3
How is calcium removed from the sarcoplasm in cardiac muscle cells?
Through SERCA and sarcolemma Na/Ca exchanger
What is the explanation of the length-tension relationship in cardiac muscle?
- Overlap of thick and thin filaments (only accounts for 20%)
- Increased calcium affinity to troponin C upon increased sarcomere length
What is the Frank Starling law of the heart?
CO is directly related to filling pressure; peak systolic pressure is directly related to resting fibre length
How is the force-frequency relationship in a failing heart?
Negative: force decreases with increasing frequency; due to decreased action of SERCA and increased action of Na/Ca exchanger
Which are the smooth muscle containing organs?
Blood vessels, GI tract, bladder, ureters, urethra, uterus, respiratory system, vas deferens and corpus cavernosum, iris and ciliary body
What are dense bodies?
Structures in SMCs that anchor actin filaments
Which are the vasoconstrictors of vascular smooth muscle?
Noradrenaline (from symp nerves)
Histamine (locally released from veins), PGF, TXA2
Adrenaline, angiotensin II, vasopressin (hormones)
Pressure, moderate cold
Which are the vasodilators of vascular smooth muscle?
VIP, substance P, CGRP, ACh (ANS nerves)
PGE2, PGI2, NO, EDHF, histamine (arterioles)
Adrenaline (some organs), ANP
Flow, heat
How is vascular smooth muscle contraction mediated?
Adrenaline/angiotensin II or other vasoconstrictors –> activate alpha 1 receptors:
- Phospholipase C –> IP3 and DAG –> calcium release from SR + Ca and Na influx through receptor gated channel
- Rho kinase –> calcium sensitisation
Stretch –> stretch activated channel –> sodium influx –> membrane depolarisation –> opening of voltage gated calcium channels (VGCC)
How does NO-mediated vasodilation occur?
Endothelial cells secrete NO –> activation of guanylate cyclase –> cGMP:
- Stimulation of SERCA and PMCA (plasma membrane Ca ATPase)
- Calcium desensitisation
- Opening of K+ channels –> membrane hyperpolarisation –> closing of VGCC
How does cAMP-mediated vasodilation occur?
Adrenaline, adenosine or prostacyclin –> beta1 activation –> increase in cAMP:
- stimulates SERCA and PMCA
- Opening of K+ channels –> membrane hyperpolarisation –> closing of VGCC
What are the mechanisms of the crossbridge cycle in SM and its regulation?
Myosin light chain kinase + calmodulin + calcium –> active complex:
1. myosin –> phosphorylated myosin –> crossbridge cycle
Regulation by myosin phosphatase:
- Inhibited by agonists via rho kinase –> Ca sensitisation
- Activated by NO via cGMP –> Ca desensitisation
What are latch bridges?
Form when myosin is dephosphorylated while still bound to actin –> cycle very slowly and thus maintain force
What is the AP upstroke and repolarisation in smooth muscle due to?
Upstroke: voltage gated calcium channels influx
Repolarisation: K+ outflow
What is the difference between unitary and multi-unit smooth muscle?
Unitary: not all cells have synaptic input, excitation is spread through gap junctions
Multi-unit: each muscle cell has synaptic input (iris, ciliary body, piloerector muscles)
Which receptors are present in the sympathetic and parasympathetic pathways?
Preganglionic onto postganglionic: ACh onto nicotinic
Postganglionic onto effector:
1. Sympathetic: NA onto alpha or beta (except sweat glands –> ACh onto muscarinic)
2. Parasympathetic: ACh onto muscarinic
What are NA and Adrenaline derived from?
Tyrosine + tyrosine hydroxulase –> DOPA
DOPA + DOPA decarboxylase –> dopamine
dopamine + dopamine beta-hydroxylase –> noradrenaline
How and why is NA stored?
Unprotected monoamines (NA, serotonin, dopamine) are metabolised by monoamine oxidase (MAO); thus, NA is taken into vesicles via vesicular monoamine transporter (VMAT)
What is the action of reserpine?
Blocks VMAT
What is the function of alpha 2 receptors in NA signalling?
Located on the presynaptic membrane and provide negative feedback mechanism to prevent further release of NA
What is the action of cocaine?
Blocks uptake 1 channels preventing NA reuptake –> more NA is available for signalling
What is the action of clonidine and its uses?
alpha2 receptor agonist –> inhibits NA release
Uses: hypertension and tachycardia
How is NA inactivated?
- Taken up presynaptically by uptake 1 channels –> MAO
2. Diffuses away and is taken up by extrasynaptic uptake (uptake 2) –> COMT –> MAO in liver and gut –> VMA in urine
What are the actions of salbutamol and salmeterol?
beta2 agonists –> bronchodilation (asthma) and uterine relaxation
What are the actions and uses of propanolol?
non-selective beta antagonist; used for hypertension, angina
What are the actions and uses of prazosin and tamsulosin?
Alpha adrenoreceptor antagonist –> benign prostatic hypertrophy
What are the effects of alpha1 stimulation on the following:
- Vascular smooth muscle
- Longitudinal muscle of GI tract
- Anal sphincter
- Urinary sphincter
- Uterine muscle
- Radial muscle
- Salivary glands
- Glycogen metabolism
- Vas deferens
- Vascular smooth muscle: contraction
- Longitudinal muscle of GI tract: relaxation
- Anal sphincter: contraction
- Urinary sphincter: contraction
- Uterine muscle: contraction
- Radial muscle: contraction
- Salivary glands: increased secretion
- Glycogen metabolism: increase
- Vas deferens: contraction
What are the effects of beta1 stimulation?
Increased heart rate and force of contraction
What are the effects of beta2 stimulation?
Relaxation of bronchial smooth muscle and vascular smooth muscle
Skeletal muscle, coronary and hepatic arteriole vasodilation
Uterine smooth muscle relaxation
Glycogen mobilisation in the liver
How do adrenaline and noradrenaline sympathomimetics differ in their action?
Noradrenaline: more potent on alpha receptors, least on beta2
Adrenaline: more potent on beta receptors, used also for anaphylactic shock (im or sc)
Both used for acute hypotension and cardiac arrest (iv)
Which are alpha-selective sympathomimetics?
phenylephrine (alpha1): acute hypotension
clonidine (alpha2): hypertension, migraine
Which are beta-selective sympathomimetics?
Isoprenaline (beta): heart block
Salbutamol: asthma, premature labor
Dobutamine: cardiogenic shock
What are labetalol and carvedilol?
non-selective adrenergic receptor antagonists
What are propanolol and timolol?
beta-selective antagonists
What are metaprolol and atenolol?
beta1-subtype selective antagonists
What are the structures of muscarinic and nicotinic receptors?
Muscarinic:
-GPCR
-5 subtypes: M2 (cardiac) –> Galphai/o leads to decrease in cAMP; M3 (smooth muscle, glandular) –> increase in IP3 and DAG
Nicotinic: nonselective cation channel, causes rapid cell depolarisation –> 5 subunits and 2 subtypes
How does the baroreceptor reflex work?
Arterial stretch sensed by afferent nerves of vagus nerve (aortic arch) and glossopharyngeal nerve (carotids) –> signal to the NTS in brain stem:
1. increase PNS drive to heart –> decrease heart rate and CO
2. decrease SNS –> decreased TPR
since BP = CO*TPR –> BP decreases
What are the parasympathetic effects on the eye?
Accommodation for near vision –> contraction of ciliary muscle allows lens to relax
Pupil constriction –> contraction of sphincter pupillae muscle in the iris (pupil constriction)
Mediated by CN III (oculomotor nerve)
What are the mechanisms of cholinergic neurotransmission?
Choline acetyltransferase: Acetyl CoA + choline --> acetylcholine Storage in vesicles Acetylcholinesterase: ACh --> choline + acetate --> reuptake mechanism
Why is ecothiopate given for closed angle glaucoma?
long-lasting cholinesterase inhibitor:
pupillary constriction increases outflow of acqueous humour –> decreased intraocular pressure
What is the action of botulinum toxin?
Binds to and degrades SNAP-25 –> prevents exocytosis of ACh and other NTs
How is salivary secretion controlled?
Afferents from smell, higher brain centres to hypothalamus and from trigeminal nerve (tongue) to brain stem:
- Parasympathetic efferents: CN IX to parotid and VII to sublingual and submandibular
- Sympathetic: through thoracic nerves I and II