the heart as a pump Flashcards
what does the cvs consist of
- the heart
- blood
- blood vessels of vascular system
what are the major cardiovascular functions
- delivery
- removal
- transport
- maintenance
- prevention
where is the heart located
the pericardium -
a fluid called membranous sac
what is the epicardium
the covering of the heart itself, the interlining of the pericardium is continuous with it
what are walls of the heart composed of
cardiac muscle cells (the myocardium)
what is the endocardium
the inner surface of walls that is in contact with blood
layers of the heart wall
outer layer - epicardium
middle layer - myocardium
inner layer - endocardium
FUNCTION of epicardium
serves as lubricative outer covering
function of myocardium
provides muscular contractions that eject blood from the heart chambers
function of endocardium
serves as protective inner lining of the chambers and valves
what does the AV valve do
prevents flow from the ventricles back into the atrium
name of right and left AV valve
right - tricuspid valve
left - mitral valve
what does the pulmonary valve do
prevents the back flow from the pulmonary trunk into the right ventricle
what does the aortic valve do
prevents the flow back from the aorta into the left ventricle
what is the cardiac cycle
the electrical and mechanical changes that occur in the heart during and following a single heart beat
what are two two phases of the cardiac cycle
- the contraction phase (systole)
- the relaxation (filling) phase (diastole)
what does alternation of contraction and relaxation allow
movement into and within the heart
always following the path of least resistance (pressure)
what is cardiac eject fraction
the amount of blood ejected (LV)/min
formula:
stroke volume (left ventricle contraction) / EDV x 100
how to calculate stroke volume
(end diastolic volume (EDV) minus end systolic volume (ESV) ) / EDV
what does EF depend on
- volume
- heart chamber dimensions
- ventricular heart rate
- valve function
- preload and after load
what is preload
the pressure of the blood on the ventricles at the end of diastole
what is afterload
the pressure in the wall of the left ventricle during ejection
where does the depolarisation stimulus for the normal heartbeat originate
the sinoatrial node
what causes the depolarisation stimulus
a collection of pacemaker cells which fire spontaneously
they exhibit automaticity
what type of cells are pacemaker cells
myocytes NOT nerve cells
where do nerve cells stop
at the SA node
do other cells in the heart exhibit spontaneous automaticity
yes
but in normal conditions the pacemaker cells are those in which show the highest rhythm
(why in healthy normal hearts depolarisation originates from the SA)
control of heart rhythm
- pacemaker generates wave of signals to contract
- signals delayed at AV node
- signal pass to heart apex
- signal spreads through ventricles
what acts as cardiac pacemaker
the SA node
what is the normal sinus rhythm
60-100 bpm
what does depolarisation trigger
depolarisation of atrial myocardium
where does the sinus rhythm conduct more rapidly
through AV node
through His bundles and Purkinje fibres
what modulates the frequency of heartbeat, HR and force of contraction
the ans
do hearts without nervous and endocrine inputs still beat
yes
where is the capability of generating rhythmic sponaneous action pontentials most developed
in a small number of cells in the SA node
can other areas start rhythmic spontaneous action potentials
yes but their rates are lower than that of the SA
as a result, the entire system is normaly driven by the SA node
are cardiac myocytes electrically excitable
yes
what is the resting intracellular voltage of myocardial cells
its negative, -90mV
(SA node is -40mV)
what is the resting state of the heart (sodium, potassium)
K+ inside the cell
and
Na+ outside the cell
when does an action potential occur
when Na+ enters the cell and sets up a depolarising current
what does stimulation of a single muscle fibre cause
electrical activity to spread across the myocardium
are myocardium cells nerve cells
NO
contraction of cardiac muscle steps
- electrical excitation
- calcium entry (Na+/K+)
- Mechanical contraction
can after load and preload affect contraction of cardiac muscle
yes
