Summary
Aorta pre-experimental summary/samenvatting
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2 ChambersRight: Blood from system circulation
Left: blood from pulmonary circulation
During a cardiac cycle atria receives blood in relaxing state diastole. Then contract in systole to move
blood to the ventricles.
Roughly cube shaped with an atrial appendage, known as auricle.
Sa node located in posterior aspect of the right atrium, next to the superior vena cava- which is
group of pacemaker cells which spontaneously depolarize to create an action potential. The cardiac
action potential then spreads across both atria causing them to contract. Av node is between atria
and ventricle.
Function
There are no atrial inlet valves to interrupt blood flow during atrial systole. The atrial systole
contractions are incomplete and thus do not contract to the extent that would block flow from the
veins through the atria into the ventricles. During atrial systole, blood not only empties from the
atria to the ventricles, but blood continues to flow uninterrupted from the veins right through the
atria into the ventricles. The atrial contractions must be gentle enough so that the force of
contractions does not exert significant back pressure that would impede venous flow. The ‘let go’ of
the atria must be timed so that they relax before the start of ventricular contraction, to be able to
accept venous flow without interruption.
Structure
Left and right atria are separated by a fibromuscular wall known as the atrial septum. Atria are
separated from the ventricles with atrioventricular septum. These are fitted with valves, in contrast
to the atrial septum. Left atrium has a thicker myocardial wall: has higher pressure.
The right atrium has a shallow depression known as the sulcus terminalis. It makes the point of
fusion between the venous part of the right atrium and the true right atrium. Also provides marks
for crista terminalis which serves as the origin for pectinate muscles.
The venous part is smooth, vestibular part is rigid. Right side has no electrical field stimulation.
- Outer layer: epicardium: protects for contact.
- Middle layer: parietal pericardium: attaches the outer layer, creates a fluid-filled layer which
helps lubricate the heart.
- Inner layer: endocardium: separates the muscle from the blood it is pumping within the
chambers of the heart. In between middle-inner layer lays cardiac muscle.
Cardiac muscle is arranged in sheets of cells. Which are connected, when cells meet, a specialized
junction called an intercalated disc locks the two cells into place. Also gap junctions are present
which can pass the impuls to contract to connected cells. Striated light and dark bands under
microscope. These bands are created by highly organized sarcomeres. Actin-myosin, tropomyosin
prevents myosin from binding troponin, holds tropomyosin in its place. When calcium binds to
troponin, myosin can bind to actin to contract.
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