The Heart

The Heart Intro - Valves

Advanced Anatomy

• About the size of a fist, the heart lies in the thoracic cavity in the mediastinum.  

• The heart tilts toward the left: two thirds of it extends to the left of the body’s midline. 

• The broadest part of the heart (the base) is at the upper right; the pointed end (the apex) is at the lower left

• The point of maximum impulse (where the strongest beat can be felt or heard) is located at the apex.

• The great vessels enter and leave the heart at the base.

Multiple Choice

The base of the heart is at the

• Top

• Bottom

Multiple Choice

The name of the structure where the point of maximum impulse is located is

• Mediastinum

• base

• Apex

Pericardium

•A double-walled sac called the pericardium surrounds the heart; it is anchored to surrounding structures by ligaments and tissue.

• The pericardium has two layers: the outermost is the fibrous pericardium (a loose-fitting sac of strong connective tissue); the serous pericardium covers the heart’s surface.

Layers

• The serous pericardium also has two layers. At the heart’s base, it folds back on itself to form the parietal layer (which lines the inside of the fibrous pericardium) and the visceral layer (which covers the heart’s surface).  

• The pericardial cavity exists between these two layers; it contains a small amount of serous fluid that helps prevent friction as the heart beats.

The Heart Wall

• ​The endocardium lines the chambers, covers the valves, and continues into the vessels; it consists of a thin layer of squamous epithelial cells.

• The myocardium, composed of cardiac muscle, forms the middle layer. It is the thickest of the three layers and performs the work of the heart.

• The epicardium, which consists of a thin layer of squamous epithelial cells, covers the heart’s surface. The epicardium is the visceral layer of the serous pericardium.

Multiple Choice

The pericardium is a

• Single Membrane

• A double layered sac

Multiple Select

Which of the following are layers of the heart wall?

• Parietal Layer

• Endocardium

• Visceral Layer

• Epicardium

• Myocardium

Chambers (Atria)

• The heart contains four hollow chambers: atria (upper chambers) and ventricles (lower chambers).

• Atria serve as reservoirs, receiving blood from the body or lungs; they are separated by the interatrial septum. 

• The walls of the atria are not as thick as the walls of the ventricles because the atria move blood only a short distance (from the atria to the ventricles).

Chambers(Ventricles)

• Ventricles receive blood from the atria and pump it to the lungs (right ventricle) or the body (left ventricle); they are separated by the interventricular septum.

• Because the ventricles pump blood, they must generate more force than the atria. Therefore, the walls of ventricles are thicker than those of the atria. (Because the left ventricle must generate force to push blood throughout the body, its walls are thicker than those of the right ventricle.)

• The great vessels (superior and inferior vena cava, the pulmonary artery, four pulmonary veins, and aorta) transport blood to and from the heart.

• Strands of fibrous connective tissue (chordae tendineae) extend from conical papillary muscles on the floor of the ventricle to the valve cusps. Papillary muscles contract with the ventricles, pulling on the chordae tendineae and anchoring the valve cusps in the proper position.

​Other Heart Structures

Multiple Choice

Which ventricle has the thickest walls?

• Left Atrium

• Right Atrium

• Left Ventricle

• Right Ventricle

The Valves

• Each of the heart’s four valves are formed by two or three flaps of tissue called cusps or leaflets.

• Two atrioventricular (AV) valves regulate flow between atria and ventricles; two semilunar valves regulate flow between ventricles and great arteries.

The Valves

• The right AV valve—also called the tricuspid valve (because it has three leaflets)—prevents backflow from the right ventricle to the right atrium.

• The left AV valve—also called the bicuspid valve (because it has two leaflets) or the mitral valve—prevents backflow from the left ventricle to the left atrium.

The Valves

• Semilunar valves are the pulmonary and aortic valves: The pulmonary valve prevents backflow from the pulmonary artery to the right ventricle; the aortic valve prevents backflow from the aorta to the left ventricle

Multiple Choice

The valves are made of structures called

• Cusps

• Semilunars

• Bicuspids

Skeleton of the Heart

• A semi-rigid, fibrous, connective tissue called the skeleton of the heart encircles each valve.

• The skeleton supports the heart and keeps the valves from stretching; it also provides insulation between the atria and the ventricles, preventing electrical impulses from reaching the ventricles other than through a normal conduction pathway.

Multiple Select

Which are functions of the skeleton?

• Support

• Insulation

• prevents valves from stretching

• Makes the heart rigid.