D. Heart Chambers and Valves OH-122

Force blood out of the heart into the arteries.
- The atrium and ventricle on the right side are separated from those on the left by a septum.

The atrium on each side communicates with its corresponding ventricle through an opening called the atrioventricular orifice which is guarded by an A-V valve.
OH- Structure of the Heart: Anterior External View Grooves on the surface of the heart mark the divisions between its chambers and also contain the major coronary arteries

Deepest is the coronary sulcus which encircles the heart between the atrial and ventricular portions.
The anterior and posterior interventricular sulci indicate the location of the septum that separates the right and left ventricles.

Right Atrium OH-122 and T96
- Receives blood from the superior and inferior vena cavae. 14097

The return blood is low in O₂ from the body.
Also receives blood from the coronary sinus.
The right atrium and right ventricle are guarded by a large tricuspid valve. 13993-13994

Valve permits blood to move from the right atrium into the right ventricle and prevents it from passing in the opposite direction.
Chordae Tendineae 13996

Are attached to the cusps of the valve.
- Originate from small mounds of muscle tissue--papillary muscle--which project inward from the wall of the ventricle.
- When the tricuspid valve closes the chordae tendineae and papillary muscles prevent the cusps from swinging into the atrium.
The right ventricle has much thinner walls than the left ventricle.
- Pumps blood a relatively short distance to the lungs against relatively low resistance to blood flow.
- When the right ventricles constricts, blood in the chamber is subjected to increasing pressure and the tricuspid valve closes passively.

As a result, the only exit is through the pulmonary trunk which divides to form the right and left pulmonary arteries.
- At the base of this trunk is the pulmonary semilunar valve which consists of three cusps.
  - This valve opens when the right ventricle contracts.
  - When the right ventricular muscles relax, blood begins to back up causing the semilunar valve to close.

The left atrium receives blood from four pulmonary veins (two form the right lung and two from the left lung).
Blood then passes from the left atrium into the atrioventricular orifice which consists of two leaflets and is named the bicuspid or mitral valve. 51919

Prevents blood from flowing back the left atrium from the left ventricle.
- When the left ventricle contracts, the bicuspid valve closes and the only exit for theblood is through the aorta.
Branches of the aorta distribute blood to all parts of the body.
At the base of the aorta is an aortic semilunar valve that consists of three cusps.
It opens and allows blood to leave the left ventricle.
- When the ventricular muscles relax, this valve closes and prevents blood from backing up into the ventricle.
Heart Valves 14914 Play

At their proximal ends, the pulmonary trunk and aorta are surrounded by rings of dense fibrous connective tissue.
- These rings are continuous with others that encircle the atrioventricular orifices.
Provide firm attachments for the heart valves and for various muscle fibers.
Also prevent the outlets of the atria and ventricles from dilating during myocardial contraction.
The fibrous rings together with other masses of dense fibrous connective tissue in the upper portion of the ventricular septum, constitute the skeleton of the heart.