The Heart

Question 1

anatomy

Answer 1

made of cardiac muscle surrounded by a protective fluid filled sac = pericardium
- reduces friction between heart and surrounding tissues, shields from infection

Question 2

right atrium

Answer 2

receives doxygenated systemic venous return

Question 3

right ventricle

Answer 3

pushes blood to pulmonary circulation for oxygenation

Question 4

left atrium

Answer 4

recievs oxygenated blood through pulmonary circulation

Question 5

left ventricle

Answer 5

pumps oxygenated blood under high pressure to head and body

Question 6

valves

Answer 6

prevent back flow during cardiac cycle
atrioventricular valvues (mitral and tricuspid) connected to cardiac wall by chordae tendinae and papillary muscles
semilunar valves (aortic and pulmonary) have small fibrous nodules, come closely together to fill triangluar opening
vavles control unidirectional flow of blood during cardiac cycle

Question 7

3 layer of heart walls

Answer 7

epicardium
myocardium
endocardium

Question 8

epicardium layer

Answer 8

protects heart

involved in production of pericardium fluid

Question 9

myocardium layer

Answer 9

straited muscle
main tissue of heart wall
made of cardiac cells encased in collagen fibres

Question 10

endocardium layer

Answer 10

internal layer
covers heart valves
vavles are continuous with endocardium
constists of smooth muscle and elastic fibres

Question 11

heart consists of …

Answer 11

contractile cells - majority of atrial and ventircular tissues
action potenitals leads to contraction and generation of force/pressure
conducting cells (SAN, atrial internodal tracts, AVN, bundle of His and purkinje system) - rapidly spread action potentials

Question 12

electrophysiology of cardiac cells

Answer 12

excitation of myocytes triggers excitation-contraction coupling
propagation of action potentials must be carfeully timed to syncchronise ventricular contraction and optimise ejection of blood.
thick myocardium contains muscle fibre cells extensively branched and connected to one another by intercalated disks
action potential propagates cell to cell

Question 13

myocardial cell structure

Answer 13

intercalated disks - junction from cell to cell = part of sarcolemma (excitable plams membrane of muscle cell)
contains 2 important structures for cardiac muscle contraction
1 - gap junctions - link cell to cell, form channels, allows depolarising event to travel to its neighbour in a wave like pattern = syncytium
2 - desmosomes - anchors fibres together
undulating double membrane, cell boundaries can be identified as Z lines

Question 14

t tubules

Answer 14

sarcolemms forms deel invaginations
enable current to be relayed to cell core releasing calcium - gives co ordinated action results in large instantaneous force produced by sarcoplasmic reticulum calcium release near all sarcomeres simultaneously

Question 15

sarcomeres

Answer 15

basic contracile unit of muscle cell, repeating unit between Z lines, cardiac muscle is striated and composed of sarcomeres with thick and thin areas
thick - myosin, globular heads have actin binding sites and ATPase activity
thin - actin, tropomyosin and troponin
after depolarisation, cross bridges form between myosin and actin and break so thick and thin filaments move past each other so Z lines move closer together
this uses ATP, due to cross bridge cycling, muscle fibres produce tension
titin and other proteins form a scaffold for myofibrils and anchor them to cell membrane to maintain integrity as tension is created

Question 16

cardiac cycle - depolarisation

Answer 16

cells of SA node spontaneously depolarise to fire action potentials at regular instrinsic rate - 60-100 times per min
can be altered by sympathetic or parasympathetic innveration
cardiac cells electrically coupled through gap junctions conduct cell to cell through right and left atrial muscle (atrial systole)
0.1 seconds later the signal arrives at AV node
AV ring stops current travelling in wrong direction = ring of non conductive tissue
AV node known as secondary pacemaker if SA node fails AV node can pick up signal and act as primary
AV node —- down septum —- up side of ventricles to His-purkinje fibre system in muscle of ventricles - leading to ventircular systole going upwards = effective emptying

Question 17

primary pacemaker

Answer 17

SA node

Question 18

sequence

Answer 18

a - atrial systole
b - isovolumetric ventricular contraction
c - rapid ventricular ejection
d - reduced ventricular ejection
e - isovolumetric ventricular relaxation
f - rapid ventricular filling
g- reduced ventricular filling

Question 19

atrial systole

Answer 19

depolarisation of atria
following stimulation of SAN, contraction of atria causes increase in atrial pressure
as ventricles relax and mitral/tricuspid valves open, ventricles further fill with blood from atria

Question 20

isovolumetric ventricular contraction

Answer 20

volume = same
following electrical activation via purkinje fibres, ventricles contract (systole)
pressure increases, when ventricular pressure exceeds atrial pressure, mitral and tricuspid valves close
producing first heart sound = S1
pressure signif increases but volume stays the same

Question 21

rapid ventricular ejection

Answer 21

pressure continues to rise until it exceeds aortic pressure
semilunar valves open
rapid ejection of blood driven by pressure gradient between artery and ventricle
most of stroke volume is ejected in this phase
ventricular volume falls dramatically and arterial pressure rises due to large volume received
atrial filling starts and pressure slowly increases

Question 22

reduced ventricular ejection

Answer 22

ventricles begin to repolarise and pressure falls as no longer contracting
as semilunar valves are still open, blood continues to be ejected but at reduced rate and ventricular volume falls
arterial volume also falling as blood moves into arterial tree - smaller arteries
atrial pressure continues to increase as blood returns to the heart

Question 23

isovolumetric ventricular relaxation

Answer 23

begins after ventricles fully repolarise
ventricles relax and pressure decreases
when pressure falls below arterial, semilunar valves close = 2nd sound S2
all valves closed
ventricular volume = constant

Question 24

rapid ventricular filling

Answer 24

ventricular pressure falls below atrial - mitral and tricuspid valves open, ventricles begin to fill
volume increases rapidly
pressure remains low
= S3

Question 25

reduced ventricular filling

Answer 25

longest phase
includes last portion of ventricular filling
phase A and G blend into one

Question 26

ECG

Answer 26

depolarisation and repolarisation events of cardiac cycle detected b electrodes - picking up magnetic field
display of electrical activity used clinically to identify pathology with aberrant trace

Question 27

waves of ECG

Answer 27

P wave
PR interval
QRS complex
T wave

Question 28

P wave

Answer 28

depolarisation of atria, duration of P wave = atrial conduction time, repolarisation of atria masked by QRS complex

Question 29

PR interval

Answer 29

AV node conduction, reflects inital depol of atria to that of ventricles

Question 30

QRS complex

Answer 30

depolarisation of ventricles

Question 31

T wave

Answer 31

repolarisation of ventricles

Question 32

lines on ECG

Answer 32

records summed electrical activity, doesnt record +ve/-ve
described as electrical vector
vector moves towards positive electrode = positive deflection on trace
moves towards negative electrode = negative deflection
moves at right angles to axis = no deflection ——– isoelectric line