The Heart
Anatomy:
Chambers:
Right & left atrium: Receive blood
Right & left ventricle: pump blood away
Right side of the heart receives
deoxygenated blood
Left side of the heart receives oxygenated
blood
Vessels:
Superior & inferior vena cava: receives blood and drains to the
right atrium
Pulmonary trunk: splits into pulmonary arteries & carries
deoxygenated blood to the lungs
Pulmonary veins: deliver oxygenated blood from the lungs to
the left atrium
Aorta: delivers oxygenated blood to systemic circulation
Valves:
Prevents the back flow of blood
Right AV valve (tricuspid): between the right atrium & right
ventricle
Left AV valve (bicuspid/mitral): between the left atrium & left
ventricle
Pulmonary semilunar valve: between the right ventricle &
pulmonary trunk
Aortic semilunar valve: between the left ventricle & the aorta
Internal structures:
Coronary sinus: returns deoxygenated to the right
atrium
Fossa ovalis: former location of the foramen ovale in a
fetus to bypass blood circulation to the lungs.
Papillary muscle: in the ventricles of the heart that
contract and open the valves
Chordae tendoneae: anchor the papillary muscle to the
valves
Septum: separates the two sides of the heart
Cardiac muscle contraction:
1. Depolarizaton: Fast voltage Na channels open
that allows the entry of a lot of Na changing the
charge from -90 to +30
2. Plateau: The depolarization triggers voltage
gated K channels and K leaves the cell slightly
changing the membrane potential. Slower Ca
channels open & Ca enters the sarcolemma.
The cell remains polarized
3. Repolarization: Ca channels close, K channels
remain open & K moves back into the cell
Ca binds to troponin to begin the cross
bridge cycle for muscle contraction
Cardiac vs skeletal muscle:
Cardiac has a longer refractory
peroid
Cardiac has a longer action
potential
Cardiac cannot reach tetany
Conduction system:
1. Sinoatrial node: located in the posterior wall of the right
atrium. This is also called the pacemaker because this is
where conduction begins, action potential is created here
and spreads through gap junctions, moves to the
2. Atrioventricular node: located in the floor of the right
atrium, between the AV valve and the opening of the
coronary sinus moves to the
3. AV bundle: extends from the AV node through the septum
divides into the
4. Left & right bundles: which move to the
5. Purkinje fibers: extend from the left & right bundles and
continue through the walls of the ventricles and then the
cycle starts over. Autonomic control:
The heart is regulated by the medulla
Receives info from baroreceptors
and chemoreceptors in the blood
vessels & right atrium
This doesn't initiate the heartbeat, just
regulates
ECG: Electrocardiogram - electrical signals collected
from the heart
The cardiac cycle:
1. Atrial contraction & ventricular filling:
Atria contract & ventricles relax
Less atrial pressure & less arterial truck
pressure
AV valve opens and semilunar closes
2. Isovolumetric contraction:
Atria relax
Greater atrial pressure & less arterial
trunk pressure
AV valves closed & semilunar valves
close
3. Ventricular ejection:
Atria relax & ventricles contract
Greater atrial pressure & greater arterial
trunk pressure
AV valves closed & semilunar open
4. Isovolumetric relaxation:
Atria relax & ventricles relax
Greater atrial pressure & less arterial trunk
pressure
AV valves closed & semilunar closed
5. Atrial relaxation & ventricular filling
Atria relax & ventricles relax
Less atrial pressure & arterial trunk pressure
AV valves open & semilunar valves close
: shows the electoral changes of atrial depolarizationP wave
: shows the ventricular depolarizationQRS complex
: shows the ventricular repolarizationT wave
: associated with the atrial plateau when cardiac
muscles contract
P-Q segment
: ventricular plateau when cardiac muscles
contract
S-T segment
: beins at the at the P wave to the beginning of
QRS complex. Its the time required to transmit an action
potential through the conduction system
P-R interval
: begins at the QRS complex & extends to the
end of the T wave. Its the time thats required for the action
potential to occur in the ventricles
Q-T interval
Clinical terms:
amount of blood that is pumped by a single
ventricle
Cardiac output:
volume of blood ejected by one beatStroke volume:
number of beats per minuteHeart rate:
amount of blood remaining in the
ventricle at rest
End diastolic volume:
blood remaining in a ventricle at the end
of contraction
End systolic volume:
volume of blood returned to the heart from the
great veins
Venous return:
stretch of the heart wall due to the load of the cardiac
muscle
Preload:
resistance in arteries to the ejection of blood by the
ventricles & is the pressure of blood that has to be exceeded
before blood is ejected from the chamber
Afterload:
states that the as volume of blood entering
the heart increases there is a greater preload
Frank-Starling Law:
Blood vessels:
: carry blood away from the heartArteries
: carry blood away from the heartVeins
:3 layers
Tunica externa: areolar connective tissue
Tunica media: smooth muscle, thickest layer
Tunica interna: endothelium
3 layers:
Tunica externa: areolar connective tissue,
thickest layer
Tunica media: smooth muscle
Tunica interna: endothelium
Narrower lumen than veins
Thicker than
Retains shape without blood
More elastic and collagen that veins
Higher blood pressure
Wider than artery lumen
Thinner than artery
Doesn't retain shape without blood
Lower blood pressure
Arterioles
Venuole:
Diameter <100 micrometers
Have all 3 tunics
Capillaries:
Connect arterioles to venuoles
Slightly larger than erythrocytes
Allow exchange of materials between blood
and tissues
Diameter range from .3 mm-10 micrometers
Fewer than six layers of smooth muscle in tunica
media
