Ch 12

The atria are smaller than the ventricles, and their walls are thinner and less muscular.

Atria are often called receiving chambers because blood enters the heart through veins that open into these upper cavities.

The second heart sound is caused by the closing of both the semilunar valves when the ventricles undergo diastole - relax.

Blood Flow Through the Heart

Arteries and veins carry blood in opposite directions - arteries away from the heart, veins toward the heart.

Capillaries need to be thin-walled because this is where the exchange of material between the blood and the tissues takes place.

The first, or lub, sound is caused by the vibration adn abrupt closure of the atrioventicular valves as the ventricles contract.

Closure of the atrioventricular valves prevents blood from rushing back up into the atria during contraction of the ventricles.

The pericardium is composed of a serous membrane.

Covering Sac, or Pericardium

Eventually, blood is pumped from the heart into arteries that exit from the ventricles; therefore, the ventricles are sometimes referred to as the discharging chambers of the heart

Each chamber of the heart is lined by a thin layer of very smooth tissue called the endocardium.

The heart is positioned in the thoracic cavity between the sternum in front and the bodies of the thoracic vertebrae behind.

Heart Chambers

Once filled, the two ventricles contract - ventricular systole - and force blood out of the heart.

Heart Valves

The endocardium is the inner most layer of the heart, and the epicardium is the outer most layer of the heart and is also called the viceral pericardium.

Inflammation of this lining is referred to as endocarditis.

The inner layer id the pericardium is called the visceral pericardium or epicardium.

It covers the heart the way an apple skin covers an apple.

The outer layer of pericardium is called the parietal pericardium.

It fits around the heart like a loose-fitting sack, allowing enough room for the heart to beat.

The heart has a covering and a lining.

Its covering, called the pericardium, consists of two layers of fibrous tissue with a small space in between them.

The right atrioventricular valve is the tricuspid valve locatev between the right atrium and ventricle.

The atrioventricular valves prevent backflow of blood into the atria when the ventricles contract.

Heart Sounds

The first heart sound is the closing of the tricuspid and mitral valve.

Heart - Location, Size, and Position

The heart is located between the lungs in the lower portion of the mediastinum.

About two thirds of the mass of the heart is to the left of this line and one third is to the right.

The heart is located mostly to the left of the mid-line of the sternum.

Heart Action

The heart serves as a muscular pumping device for distributing blood to all parts of the body.

The ventricles, like the atria, contract together; therefore, the two semilunar valves open and close at the same time.

The heart valves are arrange within the tricuspid and pulmonary semilunar valves at the right side of the heart.

The two valves that separate the atrial chambers above from the ventricles below are called atrioventricular (AV) valves.

The left atrioventricular (AV) valve is the bicuspid valve, or mitral valve, located between the left atrium and ventricle.

This first sound is of longer duration and lower pitch than the second.

The pause between this first sound and the dup, or second, sound is shorter than that after the second sound and the lub dup of the next systole.

A number of stringlike structures called chordae tendineae attach the atrioventricular valves to the wall of the ventricles.

The semilunar (SL) valves are located between the two ventricular chambers and the large arteries that carry blood away from the heart when contraction occurs.

The pericardium surrounding the heart has an outer layer called perital pericardium and has an inner layer called the epicardium.

The two pericardial layers slide against each other without friction when the heart beats because these are serous membranes with moist, not dry, surface.

The arteries and veins are composed of these layers of tissue.

There is a difference in thickness in these vessels because the arteries carry blood under higher pressure.

Contraction of the heart is called systole, and the relaxation is called diastole.

When the heart beats - that is, when it contracts - the atria contracts first - atrial systole - forcing blood into the ventricles.