Cardiovascular Physiology

Question 1

Describe the anatomy of the heart.

Answer 1

myocardial synctium - all atrial cells and ventricular cells are coupled, linked by AV nodes. the connection between cells are known as intercalated disks. electrical activation of the heart leads to coupling.

Question 2

Describe the sacromere and the sacroplasmic reticulum.

Answer 2

sacromere is the contractile unit of the myocardial cell, made of thick filaments of actin, troponin, and tropomyosin. it runs from Z line to Z line.

the sacroplasmic reticulum holds and releases calcium for excitation-contraction coupling. the approximation to t-tubules (sacrolemmal invaginations), known as dyad.

Question 3

Describe the function of chambers and valves.

Answer 3

there are four chambers, two atria and two ventricles, and two systems, the pulmonary and systemic.

valves prevent backflow into the atria and ventricles. there are atrioventricular valves, and semilunar valves. in the AV valves, there are tricuspid and bicuspid (mitral) valves, which prevent backflow to the atria. prolapse is prevented by the chordae tendinae. semilunar valves are the pulmonary valves and the aortic valves, which prevent backflow into the ventricles.

Question 4

Describe the difference between regular heart sounds and murmurs.

Answer 4

the heart has two sounds, the first as the AV valves close which signifies the beginning of systole, and the second which occurs when SL valves close at the beginning of ventricular diastole.

heart murmurs are abnormal heart sounds that are most often indicative of valve problems.

Question 5

Describe the features of cardiac muscle.

Answer 5

intercalated disks at the ends of cells to maintain cell-to-cell adhesion.

gap junctions present at the intercalated disks, for low resistance paths that allow for the spread of action potentials. they account for the observation of the heart as an electrical syncytium.

t-tubulus is continuous within the cell membrane and carry action potentials to the cell interior. it forms dyads with the SR

Question 6

Describe the intrinsic conduction system.

Answer 6

it is the path of blood flow through the heart. it consists of pacemaker cells and conduction pathways, and coordinates the contraction of the atria and ventricles.

Question 7

Explain the steps in excitation-contraction coupling in cardiac muscle

Answer 7

sinoatrial (SA) node (pacemaker) generates impulses. the impulses pause at the AV node. the AV bundle connects the atria to the ventricles. the bundle branches conducts the impulses through the interventricular septum. the purkinjie fibres depolarise the contractile cells of both ventricles.

Question 8

What are the four cardiac properties?

Answer 8

auto-rhythmicity - ability to initiate a heart beat continuously and regularly without external stimulation

excitability - the ability to respond to a stimulus by generating a propogated action potential

conductivity - the ability to conduct excitation

contractility - the ability to contract in response to stimulation

Question 9

Describe the features of an autorhythmic cell (pacemaker cell).

Answer 9

the SA node is normally the pacemaker. the AV node and his-purkinje systems are latent pacemakers that may override the SA node if supressed. they are smaller than contractile cells and don’t contain many myofibrils. they have no organised sacromere structure, meaning they don’t contribute to the contractile force of the heart.

Question 10

Describe the action potential pathway of cardiac muscle cells.

Answer 10

Na+, Ca2+ channels closed, K+ open to keep TMP stable. Rapid Na+ influx as channel opens. K+ channels open slowly, followed by influx of Ca2+ balanced by K+ efflux. Ca2+ channels close but delayed K+ rectifier channels open to return TMP.

Question 11

Describe initiation in contractile cells.

Answer 11

action potential via pacemaker cells to conduction fibers,

Question 12

Describe the process of excitation-contraction coupling in contractile cells.

Answer 12

starts with CICR (Ca2+ induced, Ca2+ released). AP spreads along sacrolemma. t-tubules contain voltage gated Ca2+ channels which open upon depolarisation, causing Ca2+ influx into cell which opens ryanodine receptors Ca2+ release channels. release causes Ca2+ spark, multiple sparks from a Ca2+ signal/

Question 13

Describe the process of contraction in contractile cells.

Answer 13

same as skeletal muscle. strength varies, response is graded and low levels of cytosolic Ca2+ will not activate as many myosin actin interactions and the vise versa.

Question 14

Describe the process of relaxation in contractile cells.

Answer 14

Ca2+ transported back into the SR, and transported out by facilitated Na+/Ca2+ exchanger. as Ca2+ levels drop, myosin/actin interactions are stopped and the sacromere lengthens.

Question 15

What features does the phases of a contractile cell have that a pacemaker cell does not?

Answer 15

effective refractory period and relative refractory period.

Question 16

What is the cardiac cycle?

Answer 16

it is the sequence of events as blood enters the atria, leave the ventricles then starts over. synchronising this is the intrinsic electrical conduction system. influencing rate (chronotrophy and dromotrophy) is done by the SNS.

Question 17

Describe electrical conduction in the cardiac cycle.

Answer 17

it is initiated by the sino-atrial node which is myogenic at 70-80 APs per min. depolarisation is spread through atria via gap junctions, and internodal pathways to the AV node. there is a fibrous connective tissue matrix in the heart which prevents the further spread of APs to the ventricles. a slight delay at the AV node occurs due to slower formation of action potentials, which allows further emptying of the atria.

Question 18

Describe the role of APs in the cardiac cycle.

Answer 18

they travel down the AV bundle which splits into left and right AV bundles (bundle branches) and then into conduction myofibres (purkinje cells). purkinje cells are larger in diameter and conduct impulse rapidly, which causes the cells at apex to contract nearly simultaneously which is good for ventricular ejection.

Question 19

Define systole and diastole.

Answer 19

systole is the period of contraction, diastole is the period of relaxation.

Question 20

Identify and describe the phases of the cardiac cycle.

Answer 20

at rest, both atria and ventricles are in diastole, while blood is filling both atria and ventricles due to low pressure conditions.

at atrial systole, ventricular filling is complete

at isovolumetric ventricular contraction, there is an increased pressure in the ventricles which cause AV valves to close. the atria goes back to diastole and there is no blood flow as semilunar valves are also closed.

during ventricular ejection, the intraventricular pressure overcomes aortic pressure. semilunar valves open and blood is ejected.

during isovolumetric ventricular relaxation, intraventricular pressure drops below aortic pressure and semilunar valves close. pressure still hasn’t dropped enouyghj to open AV valves so volume remains the same.

Question 21

Identify the steps in the conducting system of the heart.

Answer 21

SA node depolarises.

electrical activity goes to AV node via internodal pathways

depolarisation spreads slowly across atria, conduction through AV node slows

depolarisation moves rapidly through ventricular conducting system to the apex of the heart

depolarisation wave spreads upwards from the apex.

Question 22

Describe the features of cardiac output.

Answer 22

left side of heart is systemic blood flow and right side is pulmonary blood flow. output = heart rate x stroke volume. usually 5L/min, but during exercise can increase up to 20-25L/min

Question 23

What is blood pressure and how is it measured?

Answer 23

blood pressure measures the range of the force pushing against the vessel walls, and is measured as arterial pressure.

Question 24

What is systolic and diastolic blood pressure?

Answer 24

systolic bp measures bp during the contraction of arteries, and diasolic bp measures bp during the relaxation of arteries.

Question 25

What factors affect blood pressure in blood vessels?

Answer 25

resistance and driving force for fluid flow.

Question 26

What are the differences in pressure across the circulatory system?

Answer 26

systemic pressures are usually higher and pulmonary pressures are usually lower

Question 27

What is preload and afterload in relation to stroke volume?

Answer 27

preload is the degree of stretch of cardiac muscles before they contract, or the end diastolic volume which is related to right atrial pressure.

afterload is the pressure that must be overcome for ventricles to eject blood. hypertension increases afterload resulting in increased end systolic volume and reduced systolic volume.

Question 28

What is the Frank Sterling law?

Answer 28

within physiological limits, the heart pumps all the blood that returns to it by way of the veins. +ve intropy shifts the curve up resulting in a greater stroke volume, and vise-versa

Question 29

Define chronotropic, dromotropic and inotropic.

Answer 29

chronotropic means it changes heart rate.

dromotropic means it affects the conduction speed (mag of delay) in AV node and subsequently the rate of electrical impulses.

inotropic means it changes the force of the heart’s contractions.

Question 30

How does the ANS influence pacemaker cells?

Answer 30

sympathetic activity has increased chronotropic, dromotropic and inotropic effects. norepinephrine and epinephrine increase If channel activity, binding to B1 adrenergic receptors which activate cAMP and increase If channel open time. this causes more rapid pacemaker potential, faster rate of APs, and increased Ca2+ current.

parasympathetic activity has decreased chronotropic, dromotropic and inotropic effects. Ach binds to muscarnic receptors, which increases K+ permeability and decreases Ca2+ permeability which hyperpolarises the membrane. a longer time to threshold results in a slower rate of APs.

Question 31

Explain the role of homeostasis in the cardiac system.

Answer 31

baroreceptors tell the brain how much stretch is occurring in the blood vessels. a normal set point is determined by APs/min. highyer or lower normal than set point can be recognised by the brain and regulated through the ANS.

Question 32

Explain the process of extrinsic innervation.

Answer 32

ANS modifies heartbeat, and cardiac centres are located in the medulla oblongata. cardioaccelatory centre innervates SA and Av nodes, heart muscle, and coronary arteries through sympathetic neurons. cardioinhibitory centre inhibits SA and Av nodes through parasympathetic fibres in the vagus nerves.

Question 33

Explain how the ANS is regulated in the cardiac system.

Answer 33

sympathetic nervous system is activated by emotional or physical stressors, releasing norepinephrine which causes pacemaker cells to fire more rapidly, and increases contractility.

parasympathetic opposes the sympathetic effects, releasing Ach which hyperpolarises pacemaker cells by opening K+ channels.

heart at rest exhibits vagal tone (parasympathetic)