intended learning outcomes - all Flashcards

Question

Describe the involvement of troponin and tropomyosin in skeletal muscle contraction

Answer 1

troponin T - binds to a single molecule of tropomyosin troponin C - binds Ca2+ troponin I - binds to actin and inhibits contraction tropomyosin - the heads of the heavy chains each possess a binding site for actin and a site for binding and hydrolysing ATP

Answer 2

' stiffness of death' begins 3-4 hours after death and completes in approx 12 hours. an increase in intracellular calcium ion concentration lets the regulatory proteins move aside, allowing actin to bind myosin cross-bridges that were already charged with ATP. dead cells cannot produce ATP, so actin and myosin, once bound, cannot detach

Answer 3

skeletal muscle - Action potential travels down T-tubules. Ca2+ release channel opens, releasing calcium from the sarcoplasmic reticulum (SR). Calcium binds to troponin, triggering contraction. calcium is pumped back into SR → muscle relaxes. cardiac muscle - Action potential activates L-type calcium channels in T-tubules. Extracellular calcium enters the cell, triggering Ryanodine receptor (RyR2) to release more calcium from the SR. Calcium binds to troponin, allowing contraction.Calcium is pumped back into SR and out of the cell via Na-Ca (sodium-calcium exchanger) → muscle relaxes.

Answer 4

the process that links a nerve signal to muscle contraction (action potential > muscle contraction) 1. an action potential arriving at a terminal button of the NMJ stimulates release of Ach, which diffuses across the cleft and triggers an action potential in the muscle fibre 2. the action potential moves across the surface membrane and into the muscle fibres interior through the T tubules. an action potential in the T tubules triggers release of calcium from the SR into the cytosol 3. calcium binds to troponin on thin filaments 4. calcium binding to troponin causes tropomyosin to change shape, physically moving it away from its blocking position; this uncovers the binding sites on actin for the myosin cross-bridges 5. myosin cross-bridges attach to actin at the exposed binding sites 6. the binding triggers the cross bridge to bend, pulling the thin filament over the thick filament toward the centre of the sarcomere. this power stroke is powered by energy provided by ATP 7. after the power stroke, the cross bridge detaches from actin. if calcium is still present, the cycle returns to step 5 8. when action potentials stop, calcium is taken up by the SR. with no calcium on troponin, tropomyosin moves back to its original position, blocking myosin cross-bridge binding sires on actin contraction stops and the thin filaments passively slide back to their original relaxed positions.

Answer 5

T-tubules - penetrate all the way through the muscle fibre, from one side to the other SR - sarcoplasmic reticulum - the intracellular store of calcium

Answer 6

A nerve impulse reaches the neuromuscular junction, releasing acetylcholine (ACh). ACh binds to receptors on the muscle cell membrane (sarcolemma), generating an action potential The action potential travels across the sarcolemma and into the T-tubules The action potential activates voltage-sensitive receptors (DHP receptors) in the T-tubules. This triggers the release of calcium (Ca²⁺) from the sarcoplasmic reticulum (SR) into the muscle fiber’s cytoplasm. The released calcium ions bind to troponin, a protein on the actin filaments. This causes tropomyosin to shift and expose myosin-binding sites on actin. With the myosin-binding sites exposed, myosin heads can attach to actin, forming cross-bridges. The myosin heads then pivot, pulling actin filaments toward the center of the sarcomere - this causes muscle contraction. After the nerve signal stops, calcium is actively pumped back into the SR by calcium pumps. As calcium levels drop, troponin and tropomyosin return to their original positions, blocking myosin-binding sites on actin. The muscle relaxes.

Answer 7

actin troponin tropomyosin myosin

Answer 8

sympathetic and parasympathetic divisions of the ANS often work simultaneously in a reciprocal and complementary manner maintaining homeostasis sympathetic - orchestrates the stress response and energy consumption. associated with 'fight or flight' reactions, but also has very important ongoing activity parasympathetic - regulates many functions, some of which are restorative and energy conserving, 'rest and digest' skin - thermoregulation by controlling contraction and relaxation of smooth muscle vasculature liver/pancreas - metabolism of glucose and lipids lungs - ventilation to control partial pressures and pH heart & vasculature - blood pressure by contraction and relaxation of smooth muscle in the vasculature kidneys - osmoregulation (water and electrolyte balance), acid-base balance, blood pressure regulation homeostasis generally involves a negative feedback loop which has three parts; a sensor, a comparator/integrator (in the CNS, initiates an effector response via efferent neurons) and an effector

Answer 9

a) cell bodies arise in the central nervous system, project axons which leave the CNS and synapse at pre- and post-vertebral ganglia b) cell bodies arise in ganglia c) collections of cell bodies d) chain of nerve cell clusters that run alongside the spinal cord. sympathetic NS e) clusters of nerve cells located in front of the spinal column. sympathetic NS.

Answer 10

sympathetic - pre-ganglionic neurons = acetylcholine > nicotinic Ach receptor. post-ganglionic neurons = noradrenaline > adrenoceptor (⍺1,⍺2, beta1, beta2) parasympathetic - pre-ganglionic neurons = acetylcholine > nicotinic Ach receptor. post-ganglionic neurons = acetylcholine > muscarinic Ach receptor.

Answer 11

cholinergic - acetylcholine. parasympathetic cholinoceptor - Ach is the endogenous agonist of nicotinic/muscarinic Ach receptors. nAchR > ligand-gated ion channel. mAchR > G-protein coupled receptor adrenergic - adrenaline/noradrenaline. sympathetic. adrenoceptor - noradrenaline and adrenaline are the endogenous agonists. G-protein coupled receptors. NANC - sympathetic > ATP. neuropeptide Y. parasympathetic > nitric oxide. vasoactive intestinal peptide.

Answer 12

sympathetic: increased vascular tone = vasoconstriction 1. ATP produces a fast contraction of the smooth muscle 2. noradrenaline produces a moderately fast response 3. neuropeptide Y produces a slow response pupil dilation - ⍺1 - noradrenaline airway relaxation - β2 - noradrenaline increased rate and force of heart contraction - β1 - noradrenaline sweat gland secretion - mAchR - acetylcholine penile ejaculation - ⍺1 - noradrenaline Parasympathetic: decreased vascular tone = vasodilation 1. acetylcholine and nitric oxide produce a rapid relaxation 2. vasoactive intestinal peptide can produce a slow, delayed response pupil contraction - mAchR - acetylcholine airway contraction - mAchR - acetylcholine decreased heart rate - mAchR - acetylcholine penile erection - mAchR - acetylcholine

Answer 13

sympathetic: short myelinated pre-ganglionic neuron pre-ganglioinc fibres synapse in pre- and para-vertebral ganglia long unmyelinated post-ganglionic neurons pupil dilation - ⍺1 - noradrenaline airway relaxation - β2 - noradrenaline increased rate and force of heart contraction - β1 - noradrenaline sweat gland secretion - mAchR - acetylcholine penile ejaculation - ⍺1 - noradrenaline parasympathetic: long myelinated pre-ganglioinc neurons pre-ganglionic fibres synapse in or on target tissues/organs short unmyelinated post-ganglionic neurons pupil contraction - mAchR - acetylcholine airway contraction - mAchR - acetylcholine decreased heart rate - mAchR - acetylcholine penile erection - mAchR - acetylcholine

Answer 14

a branch of the peripheral nervous system consists of the skeletal muscle and their neural control elements > RESPONSIBLE FOR MOTOR CONTROL OF SKELETAL MUSCLE voluntary motor neurons of the somatic NS - upper motor neurons. lower motor neurons. upper motor neurons - arise in the cerebral cortex > central nervous system in the brain. uses glutamate as a neurotransmitter lower motor neurons - arise from the spinal cord > axons synapse directly on skeletal muscle (force generation). uses acetylcholine as a neurotransmitter. CONTROL IS FACILITATED BY UPPER MOTOR NEURONS WHICH SYNAPSE ON AND DRIVE LOWER MOTOR NEURONS WHICH ACT AS THE FINAL COMMON PATHWAY IN INITIATING SKELETAL MUSCLE CONTRACTION

Answer 15

lower motor neurons exit the spinal cord in spinal nerves, and are organised into motor units with skeletal muscle fibres. provide both motor and sensory supply to skeletal muscle, and sensory input from skin and visceral receptors 30 spinal nerves which innervate muscles roughly at the spinal segment.

Answer 16

motor unit > ⍺-motor neuorn and all of the skeletal muscle it innervates motor pool > single muscle innervated by group of ⍺-motor neurons

Answer 17

motor unit recruitment changes in the frequency of action potentials generated

Answer 18

motor units vary in size smaller motor units control finer movements and are innervated by smaller ⍺-motor neurons larger motor units control postural muscles and are innervated by larger ⍺-motor neurons

Answer 19

red muscle: slow twitch. slow myosin ATPase activity. high fatigue resistance. high oxidative capacity. high myoglobin. low glycolytic capacity. white muscle: fast twitch. fast myosin ATPase activity. low fatigue resistance. low oxidative capacity. low myoglobin. high glycolytic capacity.

Answer 20

starts with slow motor units, then, fast, fatigue-resistant units, finally, fast, fatiguable units

Answer 21

two types of muscle fibres; 1. extrafusal - bulk of skeletal muscle fibres that create force generation and are innervated by ⍺-motor neuron. 2. intrafusal - the remaining specialised fibres (muscle spindles) that are innervated by 𝛄-motorneuron and sensory afferents sensory innervation: afferent information (travels upto the spinal cord where it synapses) provided by either the group 1a afferents or the group II afferents motor innervation: 𝛄-motorneuron generates contraction

Answer 22

a) knee jerk. muscle is stretched and group 1a afferent fibres in the muscle spindle start firing. these synapse on ⍺-motorneurons in the spinal cord (the ⍺-motorneurons innervate the same muscle from which the group 1a afferent relayed the sensory information). ⍺-motorneuron induces contraction of skeletal muscle. muscle returns to resting length and firing frequency of group 1a decreases. THE REFLEX STIMULATES IN THE SPINAL CORD, THE MOTOR NEURONS TO THE EXTENSOR MUSCLE, AND, INHIBITS THE MOTOR NEURONS TO THE FLEXOR MUSCLE. b) clasp knife. muscle contracts and the extrafusal fibres shorten, and this stimulates the golgi tendon organ. group 1b afferents start firing and send sensory information to the inhibitory interneurons they synapse on, in the spinal cord. inhibitory interneurons synapse on the ⍺-motorneurons. muscle returns to resting lrngth and firing frequency of group 1b decreases. synergistic muscles also relax and antagonistic muslces contract. THE REFLEX INHIBITS IN THE SPINAL CORD, THE MOROT NEURONS TO THE EXTENSOR MUSCLE, AND, STIMULATES THE MOTOR NEURONS TO THE FLEXOR MUSCLE. c) stubbing toe. when something painful/noxious is detected, there are multiple afferent fibres that are activated which then synapse on multiple interneurons in the spinal cord. on the same side as the painful/noxious stimuli, flexors are contracted and extensors are relaxed. on the opposite side as the painful/noxious stimuli, flexors are relaxed and extensors are contracted. IN THE LEG THAT FEELS THE PAIN, THE REFLEX INHIBITS IN THE SPINAL CORD, THE MOTOR NEURONS TO THE EXTENSOR MUSCLE, AND, STIMULATES THE MOTOR NEURONS TO THE FLEXOR MUSCLE. IN THE OPPOSITE LEG, THE REFLEX STIMULATES IN THE SPINAL CORD, THE MOTOR NEURONS TO THE EXTENSOR MUSCLE, AND, INHIBITS THE MOTOR NEURONS TO THE FLEXOR MUSCLE.

Answer 23

vasculature - controls diameter, regulates flow and pressure airways - controls diameter, regulates flow and resistance urinary system - propulsion of urine into ureters, bladder tone, tone of internal sphincter of bladder gastrointestinal tract - controls tone, motility, opening/closing of sphincters male reproductive tract - secretion, propulsion of semen female reproductive tract - propulsion (fallopian tubes), partuition (uterus) skin - pilli erection

Answer 24

tonic - multi-unit. electrical isolation of cells allows finer motor control. function individually. e.g. iris and vas deferens phasic - unitary. gap junctions permit coordinated contraction. function as a syncytium. e.g. stomach, urinary bladder and bronchioles

Answer 25

individual muscle fibres are relatively small, spindle shaped, and possess one nucleus

Answer 26

smooth muscle relies on sliding filament mechanism generated during actin-myosin cross-bridge formation to facilitate contraction. 1. driven by a rise in intracellular calcium concentration which binds to calmodulin (Ca2+ is released from sarcoplasmic reticulum, or an influx across the plasma membrane) 2. Ca2+-calmodulin complex activated myosin light chain kinase (MLCK) 3. myosin light chain is phosphorylated on the myosin head 4. phosphorylation of myosin head 'cocks' it and increases its ATPase activity readying it to interact with actin to form a cross-bridge calmodulin: a multifuncitonal Ca2+ binding protein present in the cytoplasm of all eukaryotic cells.

Answer 27

pharmacomechanical coupling: the process by which an agent causes a change in smooth muscle tone without a change in membrane potential. involves the production of intracellular second messengers that either contract or relax, the muscle (IP3 > causes contraction. cGMP and cAMP > causes relaxation) electromechanical coupling: the opening of plasma membrane voltage-activated L-type Ca2+ channels in response to depolarisation with, or, without action potential generation.

Answer 28

sliding filament mechanism actin-myosin cross-bridge formation

Answer 29

innervated by the autonomic nervous system arterial smooth muscle - sympathetic innervation with noradrenaline other smooth muscle - sympathetic and parasympathetic innervation with noradrenaline and acetylcholine

Answer 30

the primary action of organic nitrates is to induce venodilation to reduce venous pressure and the venous return to the heart which reduces work of the heart by Starlings law to overall reduce oxygen demand. nitrate dilates collateral and increases blood flow to ischaemic myocardium. organic nitrates act directly on the smooth muscle cell to increase nitric oxide production causing relaxation and therefore vasodilation where they act on veins to reduce preload and oxygen demand in the myocardium, secondary action on the coronary collaterals to improve oxygen delivery to the ischaemic myocardium

Answer 31

increase in intracellular calcium concentration by release from SR or by opening of L-type Ca2+ channels intracellular calcium binds to calmodulin forming a Ca2+-calmodulin complex which activated MLCK to phosphorylate MLC which causes contraction. cGMP activated protein kinase G which activates additional MLCP to dephosphorylate MLCp which causes relaxation

Answer 32

open Katp channels in the smooth muscle cell membrane and hyperpolarise the smooth muscle cell can be used in severe hypertension alongside beta blocker and diuretics

Answer 33

vasodilating substances cause an increase in intracellular calcium concentration in an endothelial cell which binds to calmodulin forming a calcium-calmodulin complex. L-arginine and O2 bind with endothelial nitric oxide synthase to form nitric oxide and citrulline. nitric oxide enters the smooth muscle cell which with the aid of guanylate cyclase catalyses the formation of cGMP from GTP which activates protein kinase G causing relaxation. protein kinase G: stimulates MLCP stimulates plasma membrane Ca2+ ATPase stimulates sarcoplasmic.endoplasmic reticulum Ca2+ATPase activates K+ channels that cause hyperpolarisation and inactivate Ca2+ channels.

Answer 34

act at L-type Ca2+ channels on vasclar smooth muscle and in cardiac myocytes block calcium channels so there is no increase in intracellular calcium ion concentration which leads to relaxation of the vascular smooth muscle.

Answer 35

⍺1 adrenoceptors are the first part of the signalling cascade that leads to smooth muscle contraction following activation of the sympathetic nervous system ⍺1 antagonists prevent this signalling cascade and leads to vasodilation

Answer 36

blood transportation network. blood carries nutrients, oxygen and waste products to and from cells.

Answer 37

pulmonary circulation > between the heart and the lungs. deoxygenated blood enters the lung capillaries and then exits oxygenated through the diffusion of O2 in the alveolus. systemic circulation > between the heart and all organs and tissues. oxygenated blood is distributed to the brain, skin, kidneys, muscles, liver and then back to the heart deoxygenated.

Answer 38

located within the middle mediastinum situated pbliquely, with 2/3rds of the heart left to the mid-sternal line, and 1/3rd to the right sits within the pericardium

Answer 39

the pericardium > fibrous and serous the heart wall > the epicardium - outer layer. the myocardium - middle layer, cardiac muscle. the endocardium - inner layer. the purkinje fibres - distribute excitatory activity for ventricular contraction. atrioventricular valves semilunar valves

Answer 40

deoxygenated blood flow: vena cava > right atrium > tricuspid valve > right ventricle > pulmonary valve > pulmonary artery > lungs oxygenated blood flow: lungs > pulmonary vein > left atrium > mitral valve (bicuspid) > left ventricle > aortic valve > aorta during diastole which is when the heart muscles relax as it fills with blood, the AV valves open during ventricular diastole due to relaxed papillary muscles. during systole which is when the heart muscles contract and blood is pumped out, AV valves close during ventricular systole due to contraction of papillary muscles creating tension of chorae tendinae the pulmonary valve is between the right ventricle and the pulmonary trunk the aortic valve is between the left ventricle and aorta semilunar valves prevent backflow of blood into the ventricles conducting system of the heart: generates and transmits impulses to produce coordinated contractions excitation signal is created by the sinoatrial node. the wave of excitation spreads across the atria, causing them to contract. upon reaching the atrioventricular node, the signal is delayed. signal is conducted into the bundle of His, down the intraventricular septum. the bundle of His and the purkinje fibres spread the wave of impulses along the ventricles, causing them to contract.

Answer 41

arteries of the heart supply the heart with oxygenated blood. left and right coronary arteries emerge from the aortic sinus of the ascending aorta. veins drain the heart of deoxygenated blood. drain into the coronary sinus which then empties into the right atrium blood vessel structure: 1. tunica intima - single layer of cells 2. tunica media - smooth muscle 3. tunica adventitia - outer connective tissue arteries vs veins: share the same three layers. arteries have thicker walls and smaller lumen due to higher blood pressure. veins often contain valves.

Answer 42

contractile cells - normally do not initiate action potentials autorhythmic cells - initiate or conduct action potentials

Answer 43

cardiac autorhythmic cells display pacemaker activity, they cyclically initiate action potentials which then spread through the heart to trigger contraction without any nervous stimulation. autorhythmic cells do not have a resting membrane potential. the cells membrane slow drift to threshold is called the pacemaker potential.

Answer 44

1. the sinoatrial node 2. the atrioventricular node 3. the bundle of His (atrioventricular bundle) 4. purkinje fibres

Answer 45

SA node - 70-80 action potentials per minute AV node - 40-60 action potentials per minute Bundle of His and purkinje fibres - 20-40 action potentials per minute atrial and ventricular myocardium - 0 action potentials per minute

Answer 46

cycle of voltage changes across cardiac myocytes occurs in five distinct phases; 1. depolarisation 2. early repolarisation 3. plateau phase 4. late repolarisation 5. resting potential

Answer 47

the long duration of the cardiac action potential is primarily due to the plateau phase, caused by the balance of calcium influx and potassium efflux, which prolongs the depolarisation. The long refractory period ensures that the heart cannot be re-stimulated before it has fully relaxed, preventing dangerous continuous contractions and allowing proper filling and pumping of blood.

Answer 48

prevention of tetany and ensures proper heart function prevents premature contraction and allows full heart relaxation The long plateau makes sure the heart muscle contracts long enough to pump blood effectively, while the long refractory period makes sure the heart has time to relax and refill before the next beat

Answer 49

limb leads I, II, III are bipolar leads lead I > right arm to left arm lead II > right arm to left leg lead III > left arm to left leg

Answer 50

P wave = atrial depolarisation moving towards the recording electrode QRS complex = ventricular depolarisation and atria repolarisation. T wave = ventricular repolarisation moving in a direction opposite to that of depolarisation, accounts for the usually observed upward deflection.

Answer 51

an ECG is not a direct recording of the actual electrical activity of the heart.

Answer 52

CO is the volume of blood pumped by each ventricle per minute CO =HR x SV = l/min SV = the volume of blood ejecter per contraction

Answer 53

young adult at rest = 5 l/min young adult exercising = 23 l/min marathoner = 30 l/min

Answer 54

CO is controlled according to physiological requirements - via control of HR and SV 1. intrinsic control - varying the initial length of the cardiac muscle fibres, which in turn depends upon EDV 2. extrinsic control - varying the extent of sympathetic stimulation 3. end diastolic volume - an increase in EDV increases SV > as more blood returns to the heart, the heart pumps out more.

Answer 55

an increase in tension = an increase in length cardiac muscle does not normally operate within the descending limb of the length-tension curve degree of diastolic filling causes muscle fibres to vary in length before contraction. increased EDV, the more the heart is stretched, the longer the initial cardiac fibre length before contraction, resulting in greater force on the subsequent cardiac contraction, a greater SV

Answer 56

the amount of blood that fills the hearts ventricles at the end of diastole the volume of blood in the ventricles before the heart contracts

Answer 57

the resistance the heart must overcome to pump blood out of the ventricles.

Answer 58

increase in arterial pressure = higher cardiac workload decrease in arterial pressure = lower cardiac workload

Answer 59

contractility is the hearts ability to contract with force dP/dt is a measure of how quickly the pressure inside the heart increases during contraction

Answer 60

extrinsic control - sympathetic stimulation and adrenaline - enhance the hearts contractility due to increased Ca2+ entry triggered by noradrenaline/adrenaline. increased inward Ca2+ influx during the plateau phase enhances the intracellular calcium ion concentration store. Ca2+ is required for excitation-contraction coupling in cardiac muscle cells. increase the rate of relaxation of cardiac muscle cells by stimulating Ca2+ pumps to take up more Ca2+ from the cytoplasm more rapidly and therefore shortening systole.

Answer 61

Increased sympathetic activity causes the heart to work harder, leading to increased ventricular work and higher cardiac output. This is useful during times of stress or exercise when the body needs more oxygen and nutrients delivered through the blood

Answer 62

arteries - low resistance vessels conducting blood to the various organs with little loss in pressure. act as pressure resevoirs for maintaining blood flow between ventricular contractions. several hundred. thick, highly elastic walls. large radii. passageway from heart to organs. serve as pressure resevoirs. arterioles - makor sites of resistance to blood flow. responsible for the pattern of blood flow distribution. participate in the regulation of arterial blood pressure. half a million. highly muscular, well-innervated walls. small radii. primary resistance vessels. determine distribution of cardiac output. capillaries - site of exchange between blood and tissues. ten billion. thin walled. large total cross-sectional area. site of exchange. determine distribution of extracellular fluid between plasma and interstitial fluid. veins - low resistance vessels for blood to flow back to the heart. their capacity for blood is adjusted to facilitate flow. several hundred. thin walled. highly distensible. large radii. passageway to heart from organs. serve as blood resevoir.

Answer 63

adventitial layer - connective tissue medial layer - smooth muscle cells intimal layer - endothelial cells

Answer 64

elastic artery: 5% endothelium. 25% smooth muscle. 40% elastic tissue. 30% connective tissue. arteriole: 10% endothelium. 60% smooth muscle. 10% elastic tissue. 20% connective tissue. capillary: 95% endothelium. 0% smooth muscle. 0% elastic tissue. 50% connective tissue. venule: 20% endothelium. 20% smooth muscle. 0% elastic tissue. 60% connective tissue.

Answer 65

aorta: internal radius = 12mm wall thickness = 2mm medium artery: internal radius = 2mm wall thickness = 1mm arteriole: internal radius = 15µm wall thickness = 20µm true capillary: internal radius = 3µm wall thickness = 1µm venule: internal radius = 10µm wall thickness = 2µm vein: internal radius = 2.5mm wall thickness = 0.5mm vena cava: internal radius = 15mm wall thickness = 1.5mm

Answer 66

blood flow = volume per unit time = l/min pressure = ΔP (mmHg)

Answer 67

a measure of how difficult it is for blood to flow between two points at any given pressure difference a measure of the friction impeding flow F=ΔP/R resistance is proportional to 1/r^4 dependent on 3 factors; 1. viscosity of the blood, 2. vessel length, 3. vessel radius

Answer 68

resistance is proportional to 1/r^4 flow is proportional to r^4

Answer 69

the arteries maintain a certain level of pressure to keep blood flowing between heartbeats

Answer 70

an increase in resistance causes a decrease in blood flow

Answer 71

as resistance decreases, blood flow increases

Answer 72

pulse pressure = end systolic volume - end diastolic volume

Answer 73

pressure gradient: increase = flow increases decrease = flow decreases radius: increase = flow increases decrease = flow decreases viscosity: increase = flow decreases decrease = flow increases

Answer 74

mean arterial pressure = diastolic blood pressure + 1/3(pulse pressure)

Answer 75

blood viscosity blood vessel length blood vessel radius - most important

Answer 76

blood flow rate stays the same throughout the circulatory system total cross-sectional area is small in arteries and veins, but is very large in capillaries velocity of flow is fastest in arteries and slowest in capillaries

Answer 77

as the small radius of arterioles offers considerable resistance to blood flow which causes a marked drop in mean pressure as blood flows through arterioles. this pressure gradient helps drive blood from the heart to the tissue capillary beds

Answer 78

arteriolar walls include a thick layer of smooth muscle that is richly innervated by nerves of the sympathetic nervous system

Answer 79

smooth muscle is also sensitive to many local chemical changes and certain circulating hormones

Answer 80

arteriolar smooth muscle displays a state of partial constriction which is vascular tone 1. myogenic activity 2. sympathetic activity tonic activity makes it possible to either decrease or increase contractile activity any changes in contractility of arteriolar smooth muscle will substantially change resistance to flow in these vessels

Answer 81

i) contraction. decreased radius, increased resistance. decreased local blood flow. increased contraction of smooth muscle. increase in resistance decreased flow through the vessel ii) relaxation. increased radius, decreased resistance. increased local blood flow. decreased contraction of smooth muscle decrease in resistance increased flow through the vessel

Answer 82

tachycardia - increased activity in the sympathetic nerves to the heart to increase heart rate bradycardia - increased activity in the parasympathetic nerves to the heart to decrease heart rate

Answer 83

parasympathetic: the vagus nerve releases acetylcholine to muscarinic receptors alter the activity of the cAMP second messenger pathway in innervated cardiac cells Ach is coupled to an inhibitory G-protein that reduces activity of the cAMP pathway decreases heart rate through 2 effects on pacemaker tissue - hyperpolarisation of the SA node membrane so it takes longer to reach threshold - decreases the rate of spontaneous depolarisation (Ach increases K+ permeability by G-protein-coupled inwardly-rectifying potassium channels) decreases the AV nodes excitability which prolongs transmission of impulses to the ventricles shortens the plateau phase of the action potential in atrial cotractile cells, weakening atrial contraction has little effect on ventricular contraction parasympathetic activity arises in the cardioinhibitory centre of the medulla neurotransduction through the vagus nerve mediates inhibitory input Ach increases SA node permeability to K+ (slow closure of K+ channels) and so increased leakage of +'ve charge. SA node hyperpolarises between contraction cycles resulting in fewer action potentials at the SA node, does not alter AV node function heart rate decreases sympathetic: releases noradrenaline to beta1 adrenergic receptors alter the activity of the cAMP second messenger pathway in innervated cardiac cells NorAd is coupled to a stimulatory G-protein that accelerates activity of the cAMP pathway speedsup heart rate through its effect on pacemaker tissue (tachcardia) - speeds up depolarisation, so threshold is reached more rapidly (NorAd augments funny channels, If, and transient-type Ca2+ channels, T) reduces AV nodal delay by increasing conduction velocity speeds up spread of action potential throughout the specialised conduction pathway increased contractile strength of the atrial and ventricular contractile cells - heart beats more forcefully and squeezes out more blood - increase Ca2+ permeability through prolonged opening of L-typed Ca2+ channels speeds up relaxation sympathetic activity arises in the cardioacceleratory centre of the medulla motor neurons linking to T1-T5 level of the spinal cord synapse with ganglionic neurons located in cervical and upper thoracic symoathetic chain ganglia. postganglionic fibres innervate the SA and AV node to raise HR and CO NorAd accelerates closure of K+ channels so reducing K+ permeability. SA and AV node membrane potential moves closer to threshold due to accumulation of +'ve charge in the cell between depolarisation cycles. increase in Na+ and T-type Ca2+ channel activity further accelerates depolarisation and raises action potential frequency heart rate increases

Answer 84

the resistance the heart must overcome to pump blood out of the ventricles.

Answer 85

increase arterial pressure = increases cardiac workload decrease arterial pressure = decreases cardiac workload

Answer 86

short term control - mediated by the baroreceptor reflex - neural control long term control - renin-angiotensin-aldosterone system - hormonal control neural control negative feedback loop of stretch-sensitive baroreceptors acting as the sensors (afferents), cardiovascular control centre in the medulla oblongata acting as the integrator, and autonomic neurons acting as the effectors (efferents)

Answer 87

increased BP increase in BP activates stretch receptors in the carotid sinus and impulses are transmitted to the glossopharyngeal nerve and then to nuclei tractus solitarii causing stimulation, this stimulation inhibits sympathetic activity causing a reduction in smooth muscle contraction leading to vasodilation and a fall in blood pressure

Answer 88

arterial baroreceptors afferent nerve fibres relay information to the brain about blood pressure are ideally located stretch receptors located at the carotid sinus and aortic arch cardiopulmonary baroreceptors afferent fibres of four types - myelinated veno-arterial mechanoreceptors, non-myelinated mechanoreceptors, coronary artery baroreceptors, chemosensors located in the heart and pulmonary artery

Answer 89

hypertension = BP of 140/90mmHg angiotensin-converting enzyme inhibitor angiotensin-II receptor blocker calcium channel blocker thiazide-like diuretic

Answer 90

a decrease in renal perfusion pressure (a decrease in effective circulating volume) causes a decrease in stretch on afferent arterioles and an increases in renin, as well as a rise in sympathetic activity and a decrease in NaCl concentration renin is produced by juxtaglomerular cells in the kidney, renin cleaves angiotensinogen to angiotensin I which travels thorugh the blood stream, when it reaches the lungs ACE enzymes convert it to angiotensin II which is a vasoconstrictor peptide that stimulates thirst and ADH release in the hypothalamus and the release of aldosterone from the adrenal cortex, aldosterone increases Na+ absorption which increases water uptake to increase the blood volume and therefore increases bloop pressure.

Answer 91

a) blocks ACE in the lungs from converting angiotensin I into angtiotensin II resulting in a decrease in circulating blood volume and therefore decreases blood pressure. used as a first line treatment in hypertension with type two diabetes and without type 2 diabetes but over 55 years of age and not of a black African or African-Caribbean family origin b) blocking of angiotensin II causes a decrease in veno-and atrioconstriction and a subsequent decrease in blood pressure. used as a first line treatment in hypertension with type two diabetes and without type 2 diabetes but over 55 years of age and not of a black African or African-Caribbean family origin

Answer 92

an increase in mean arterial pressure increases carotid sinus firing frequency

Answer 93

increased BP parasympathetic activation slows the heart to reduce BP vasodilation occurs to lower BP the heart > increased sympathetic drive, increased noradrenaline release from postsynaptic neurons , binds to β1 adrenoceptors on the myocardium, increased chronotropy, increased dromotropy, increased inotorpy, decreased lusitropy, increased cardiac output, increased arterial BP. the vasculature >increased sympathetic drive, increased noradrenaline release from postsynaptic neurons, binds to ⍺1 adrenoceptors on the myocardium, increased vasoconstriction, increased total peripheral resistance, increased arterial BP. decreased BP sympathetic activation increases heart rate and contractility to raise BP vasoconstriction to increase resistance and raise BP the heart >increased parasympathetic drive, increased acetylcholine release from postsynaptic neurons, binds to muscarinic M2 receptors on the myocardium, decresed chronotropy, decreased dromotropy, decreased inotorpy, increased lusitropy, decreased cardiac output, decreased arterial BP the vasculature > increased parasympathetic drive, increased acetylcholine release from postsynaptic neurons, binds to muscarinic M3 receptors on the myocardium, increased vasodilation by endothelium dependent mechanism, decreased total peripheral resistance, decreased arterial BP

Answer 94

1. embryonic - establishes basic lung structure as a template for further growth 2. pseudoglandular - establishes the branched network of gas conducting airway 3. canalicular - formation of the blood-gas barrier 4. saccular - formation of the respiratory acinus > the zone of gas exchange 5. alveolar - formation of the alveolus and high surface area for gas exchange

Answer 95

tidal volume - the air inhaled/exhaled in a normal breath inspiratory reserve volume - extra air that can be inhaled after a normal breath expiratory reserve volume - extra air that can be exhaled after a normal breath residual volume - air that remains in lungs after full exhalation - measured by spirometry functional residual capacity - air left in lungs after normal exhalation - measured by plethysmography vital capacity - max air that can be exhaled after deep inhalation total lung capacity - max air lungs can holr

Answer 96

gas follows partial pressure not concentration gradients partial pressures tells the direction of movement of gas gas moves from high partial pressure to low partial pressure both within and between phases

Answer 97

spirometry plethysmography obstructive lung diseases - asthma, COPD restrictive lung diseases - pulmonary fibrosis

Answer 98

branch generation 1 >16 conductive zone, conducting airways. trachea > mainstream bronchi > terminal bronchioles branch generation 17 >23 respiratory zone, alveolar air spaces. alveolus > respiratory bronchioles > alveolar ducts > alveolar sacs

Answer 99

Gas exchange across the blood-gas barrier happens by diffusion, where gases move from high partial pressure to low partial pressure: Oxygen (O₂) moves from the alveoli (high O₂) into the blood (low O₂) to be delivered to the body. Carbon dioxide (CO₂) moves from the blood (high CO₂) into the alveoli (low CO₂) to be exhaled. The process is affected by: Barrier thickness (thicker barriers slow diffusion), Surface area (larger surface area improves gas exchange), and Gas solubility (CO₂ diffuses faster than O₂).

Answer 100

airway restriction reduced lung compliance

Answer 101

quiet breathing - during inspiration the diaphragm and external intercostal muscles work, during expiration no active muscles as elastic recoil of the lungs is sufficient forced breathing - during inspiration the diaphragm, external intercostals, sternoceliromastoid and scalenes work, during expiration the abdominal muscles and internal intercostal muscles push air out of the lungs.

Answer 102

oxygen content - determined by the amount of haemoglobin and oxygen in the blood oxygen saturation - the proportion in percentage of oxygen oxygen carrying capacity of haemoglobin is 1.34x15 = 20mls O2/100ml of blood

Answer 103

normal p50 = 27mmHg at pH7.4 and pCO2 of 40mmHg left-shift p50 = increased Hb-O2 affinity, reduced O2 off-loading to tissues right-shift p50 = decreased Hb-O2 affinity, raised O2 offloading to tissues