heart structure and function Flashcards
what does the heart consist off- chambers and valves
chambers consist of a left and right atria and ventricle. intertribal and intraventricular sections- separate atria and ventricle.
where is the heart located
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
what surrounds the mediastinum
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
valves of the heart
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
how does blood flow in the heart- pulmonary
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
how does blood flow in the heart- systemic
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
cardiac muscle function
this heart is a muscle pump. actin and myosin as in skeletal muscle.
cardiac muscle structure
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-
cardiac muscle- 2 muscle networks
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
contraction of cardiac muscle- depolarisation
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
contraction of cardiac muscle- plateau
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
contraction of cardiac muscle- repolorization
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
contraction of cardiac muscle- refractory period
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
co-ordination of cardiac cycle
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
rate of SAN
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
what is the cardiac cycle
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
cardiac cycle- relaxation period
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
cardiac cycle- atria systole and ventricular filling
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
cardiac cycle- ventricular systole
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
stroke volume
amount of blood ejected in one ventricular systole- 70-80ml
what is end systolic volume
amount of blood left in after contraction- about 50ml
cardiac cycle- ventricular diastole
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
what is cardiac output
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
CO equation
SV * HR
factors that govern stroke volume- preload
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
factors that govern stroke volume- contractility
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)
factors that govern stroke volume- after load
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
blood supply to heart
via coronary arteries- requires large oxygen supply
main coronary artery- right and left coronary
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
