heart structure and function

Question 1

what does the heart consist off- chambers and valves

Answer 1

chambers consist of a left and right atria and ventricle. intertribal and intraventricular sections- separate atria and ventricle.

Question 2

where is the heart located

Answer 2

it is located posterior to the sternum, level with the 3rd coastal cartilage down to 5th costal space, approximately 7.5cm to the left of midline. it sits within the mediastinum- an area in chest between lungs

Question 3

what surrounds the mediastinum

Answer 3

this is surrounded by a pericardium (visceral/epicardial- serous membrane, outer surface of heart, direct contact with and parietal- fibrous membrane over top of viscrel) with 15-20ml of pericardial fluid in between

Question 4

valves of the heart

Answer 4

valves between atrium and ventricle- atrioventricular valves (tricuspid/miral and bicuspid). chord tendineae- fibrous CT hold onto valves, these fibres originate from parts of the muscle wall of heart by papillary muscles. semi lunar valves (aortic and pulmonary). fossa avails- closed foreman oval

Question 5

how does blood flow in the heart- pulmonary

Answer 5

the RA receives blood from superior (upper body) and inferior (lower body) vena cava. blood passes through the tricuspid valve to the right ventricle, from the right ventricle blood is pumped by pulmonary artery (via the pulmonary valve) to the lungs- where co2 is removed from blood and O2 is picked up. the pulmonary vein returns blood to the LA

Question 6

how does blood flow in the heart- systemic

Answer 6

from the LA blood passes through the mitral valve to the left ventricle- as this contract the miral valve closes (due to increased pressure) the aortic valves open allowing blood to leave the heart via the aorta, when the cycle of Dumont is complete the aortic valve closes preventing blood from returning into the heart

Question 7

cardiac muscle function

Answer 7

this heart is a muscle pump. actin and myosin as in skeletal muscle.

Question 8

cardiac muscle structure

Answer 8

muscle cells are connected by inhercalacted discs or gap junctions- allows for ions to be transferred and molecules to move from one muscle cell to another- because of this the heart muscle can be seen as 1 muscle. auto rhythmic fibres, inherent rhythmical activity, self excitable. contains lots of mitochondria-

Question 9

cardiac muscle- 2 muscle networks

Answer 9

cardiac muscle is made up of 2 independent interconnecting network of muscle fibres each syncytium contracts as a unit. when a single muscle cell is stimulated the whole syncytium contracts as a unit. when a single muscle cell is stimulated the whole sanctum contracts. the syncytial are electrically insulated to prevent simultaneous contractions

Question 10

contraction of cardiac muscle- depolarisation

Answer 10

same resting potential as skeletal muscle (-90mV)
AP in adjacent fibres passes via gap junction (intercalated discs) and opens the Na+ channel- rapid inflow of Na= rapid depolarisation
AP lasts 0.3 secs

Question 11

contraction of cardiac muscle- plateau

Answer 11

there is a plateau because as Na+ is being pumped out the cell Ca++ slowly enters cell balancing loss of Na+(membrane potential is 0mV) the K+ remains in cell therefore repolarisation cannot occur

Question 12

contraction of cardiac muscle- repolorization

Answer 12

the ca++ channels slowly close,
K+ channels open- K+ leaves the cell, resting membrane potential is restored
the mechanisms of contraction are the same as skeletal muscle- sliding filament theory

Question 13

contraction of cardiac muscle- refractory period

Answer 13

it is the time interval before another contraction can take place- ensures heart beats in a coordinated fashion, it lasts longer than contraction, allows muscle fibres to relax before next contraction, allows pumping mechanisms to occur

Question 14

co-ordination of cardiac cycle

Answer 14

the AP needs to be co-ordinated for the heart to act as an effective pump, chambers need to beat in a sequence, pacemakers (SA nodes) and conduction pathways

Question 15

rate of SAN

Answer 15

inherent rate of 100 Aps per minute- influence of neural and hormonal supply- slows heart beat down. this is slowed to around 75 by vagus nerve

Question 16

what is the cardiac cycle

Answer 16

this is all the events associated with one heartbeat. in a normal cycle the atria contract while ventricles relax followed by atrial relaxation and ventricular conduction contraction is called systole, relaxation is called diastole

Question 17

cardiac cycle- relaxation period

Answer 17

when the cardiac cycle begins all 4 chambers are relaxed - in diastole. it could be said fro right at at the end of cardiac cycle as well

Question 18

cardiac cycle- atria systole and ventricular filling

Answer 18

atria contracting forcing a small amount of blood (20-25 mL) into the ventricles through AV valves. at the end of each ventricle contains its end diastolic volume (130mL- 70% through passive flow) lasts about 100 msec. aortic and pulmonary valves remain shut, the atria then enter a state of diastole

Question 19

cardiac cycle- ventricular systole

Answer 19

near the end of atrial systole, the ventricle depolarise and ventricular contraction begins, ventricle systole lasts approx 270msec, AV pushed closed by blood, all valves are now closed (0.05 sec), isovolumetric contraction occurs- no change in shape, ventricular ejection occurs when pressure in ventricles opens aortic and pulmonary valves, ventricular pressure drops and SL valves close

Question 20

stroke volume

Answer 20

amount of blood ejected in one ventricular systole- 70-80ml

Question 21

what is end systolic volume

Answer 21

amount of blood left in after contraction- about 50ml

Question 22

cardiac cycle- ventricular diastole

Answer 22

lasts about 430msec, all valves are closed, isovolumetric relaxation, pressure drops in ventricles compared to atria, AV valve opens blood pours from atria into ventricles passively, rapid ventricular filling (up to 3/4 of capacity

Question 23

what is cardiac output

Answer 23

the total blood volume passing through the lungs and systemic circulation in one minute. close to your total blood volume, CO increases with demand for oxygen

Question 24

CO equation

Answer 24

SV * HR

Question 25

factors that govern stroke volume- preload

Answer 25

a bigger preload (stretch) on cardiac muscle fibres prior to contraction increases their force of contraction. frank Sterling law- the more the heart is filled in a diastole, the greater the stretch and the greater the force of systole

Question 26

factors that govern stroke volume- contractility

Answer 26

the strength of contraction after preload, positive isotropic substances- promote contractility (drugs or internal systems), negative- prevents contractility (beta blockers or stimulation of parasympathetic system)

Question 27

factors that govern stroke volume- after load

Answer 27

the pressure in blood vessels that need to be exceeded, increased after load results in reduced SV because more blood remains in ventricles at the end of systole

Question 28

blood supply to heart

Answer 28

via coronary arteries- requires large oxygen supply

Question 29

main coronary artery- right and left coronary

Answer 29

right coronary- supplies right atria and ventricle via right marginal artery also supplies SA and AV node
left coronary- supplies left atrium and ventricle, and intraventricualr septum- has 2 branches left anterior depending (LAD) and left circumflex