Body fluids and Circulation 2 Flashcards
what is heart
Heart, the mesodermally derived organ, is situated in the thoracic
cavity, in between the two lungs, slightly tilted to the left. It has the size of
a clenched fist.
It is protected by a double walled membranous bag,
pericardium, enclosing the pericardial fluid.
Our heart has four
chambers, two relatively small upper chambers called atria and two larger
lower chambers called ventricles
what are septa present between the heart.
Septa are thick muscular walls present in the heart to divide the heart into different chambers.
A thin, muscular wall called the interatrial septum separates the right and the left atria, whereas a thick-walled,
the inter-ventricular septum, separates the left and the right ventricles
(Figure 18.2). The atrium and the ventricle of the same side are also
separated by a thick fibrous tissue called the atrio-ventricular septum.
what are the valves in the heart
The opening between
the right atrium and the right ventricle is guarded by a valve formed of
three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid
or mitral valve guards the opening between the left atrium and the left
ventricle.
The openings of the right and the left ventricles into the
pulmonary artery and the aorta respectively are provided with the
semilunar valves( crescent shaped valves) called pulomnary valve and aortic valve respectively.
The valves in the heart allows the flow of blood only in
one direction, i.e., from the atria to the ventricles and from the ventricles
to the pulmonary artery or aorta. These valves prevent any backward
flow
the walls of ventricles are thicker than atria.
The entire heart is made of cardiac muscles. The walls of ventricles
are much thicker than that of the atria.
what are chordae tendinae
papillary muslces are pillar shaped uscles present on ventricular walls.
the chordae tendinae are cartilaginous structures which connect the papillary muscles to the walves. their function is to hold the valves in place and regulate their function
explain the components of the heart conducting system
A specialised cardiac musculature
called the nodal tissue is also distributed in the heart (Figure 18.2). A
patch of this tissue is present in the right upper corner of the right atrium
called the sino-atrial node (SAN). Another mass of this tissue is seen in
the lower left corner of the right atrium close to the atrio-ventricular septum
called the atrio-ventricular node (AVN). A bundle of nodal fibres, atrioventricular bundle (AV bundle) continues from the AVN which passes
through the atrio-ventricular septa to emerge on the top of the interventricular septum and immediately divides into a right and left bundle.
These branches give rise to minute fibres throughout the ventricular
musculature of the respective sides and are called purkinje fibres. These
fibres alongwith right and left bundles are known as bundle of His.
explain the process of heart’s conducting system
sinoatrial node gets stimulated by the entry of blood into the right atrium due to which is generated an actiona potential( electrical impulse).
The av node gets stimulated by the electrical impulse from sa node and sends electrical signals through bundle of his through atri-ventricular bundle.
The signal passes through the bundle of his into right and left bundles and finally purkinje fibres which cause the contraction of the ventricales to pump blood thorugh artery.
why is sino atrial node called pacemaker
The
nodal musculature has the ability to generate action potentials without
any external stimuli, i.e., it is autoexcitable. However, the number of action
potentials that could be generated in a minute vary at different parts of
the nodal system. The SAN can generate the maximum number of action
potentials, i.e., 70-75 min–1
, and is responsible for initiating and
maintaining the rhythmic contractile activity of the heart. Therefore, it is
called the pacemaker. Our heart normally beats 70-75 times in a minute
(average 72 beats min–1).
list the stages of cardiac cycle
=joint diastole
-atrial systole
-ventricular systole
-joint diastole
explain joint systole
To begin with, all the
four chambers of heart are in a relaxed state, i.e., they are in joint diastole.
As they are in a relaxed state, blood from the pulmonary
veins and vena cava flows into the left and right atria. The semilunar valves are closed at this
stage. The SAN now generates an action potential which stimulates both
the atria to undergo a simultaneous contraction – the atrial systole.
Pressure in atria increase causing the opening of the both biscuspid and tricuspid valves
explain atrial systole
- the atria contract to release blood into the ventricles.
-the pressure in ventricles increase as a result of which semiulunar valves open(not req) - the action potential system The
action potential is conducted to the ventricular side by the AVN and AV
bundle from where the bundle of His transmits it through the entire
ventricular musculature. This causes the ventricular muscles to contract,
(ventricular systole)
explan ventricular systole
. Ventricular systole increases the ventricular pressure causing the closure of tricuspid and bicuspid valves due to
attempted backflow of blood into the atria. As the ventricular pressure
increases further, the semilunar valves guarding the pulmonary artery
(right side) and the aorta (left side) are forced open, allowing the blood in
the ventricles to flow through these vessels into the circulatory pathways.
The ventricles now relax (ventricular diastole) and the ventricular pressure
falls causing the closure of semilunar valves which prevents the backflow
of blood into the ventricles.
explain 2nd joint diastole
As the ventricular pressure declines further,
the tricuspid and bicuspid valves are pushed open by the pressure in the
atria exerted by the blood which was being emptied into them by the
veins. The blood now once again moves freely to the ventricles. The
ventricles and atria are now again in a relaxed (joint diastole) state, as
earlier. Soon the SAN generates a new action potential and the events
described above are repeated in that sequence and the process continues.
what is the cardiac cyle
Carduiac cylce is the series of pressure changes within the heart which involves the pumping and receing of blood.
It involves the diastole and systole of atria and ventricless
what is stroke volume?
what is cardiac output?
As mentioned earlier, the heart beats 72 times per minute,
i.e., that many cardiac cycles are performed per minute. From this it could
be deduced that the duration of a cardiac cycle is 0.8 seconds. During a
cardiac cycle, each ventricle pumps out approximately 70 mL of blood
which is called the stroke volume. The stroke volume multiplied by the
heart rate (no. of beats per min.) gives the cardiac output. Therefore, the
cardiac output can be defined as the volume of blood pumped out by each
ventricle per minute and averages 5000 mL or 5 litres in a healthy individual.
The body has the ability to alter the stroke volume as well as the heart rate
and thereby the cardiac output. For example, the cardiac output of an
athlete will be much higher than that of an ordinary man
