Circulatory System

Location and projection of heart• 5 inch, cone shaped

• 3.5 inches wide, 2.5 inches thick

• Rests on diaphragm in the mediastinum

• 2/3 on left of midline

• Apex (pointed side of heart) is anteriorly, inferiorly, and to the left

• Base (large side of heart) is posteriorly, superiorly, and to the right

Location and projection continued

• Anterior surface is deep to the sternum and ribs

• Inferior surface rests on diaphragm and is between the apex and right border

• Right border

1.faces right lung

2. extends from inferior surface to base

• Left border

1. faces left lung

2. extends from base to apex

Structure and function of the heart

• Pericardium

1. surrounds and protects

2. confines the heart to midiastinum, while

allowing for movement

3. Fiberous pericardium

a. superficial layer

b. dense, irregular connective tissue

c. rests on and is attached to diaphragm

d. provides protection, anchors heart

Structure and function continued

4. serous pericardium

a. forms a double layer around heart

b. parietal layer is fused with fiberous

pericardium

c. visceral layer attaches to surface of

the heart

Structure and function continued

• Pericardial cavity

1. space between parietal and visceral layer

of the serous pericardium

2. Pericardial fluid

a. secretion of pericardial cells

b. located in pericardial cavity

c. reduces friction of the membrane as

the heart moves

Layers of the heart wall

• Epicardium

1. thin, transparent outermost layer

2. gives heart its smooth texture• Myocardium

1. middle layer

2. composed of cardiac muscle tissue• Endocardium

1. innermost layer

2. provides a smooth lining for heart

chambers

Chambers of the heart

• Atria (upper chambers)• Ventricles (lower chambers)• Auricles

a. on anterior surface of atria

b. slightly increase volume of atria• Suci

a. grooves that contain coronary blood

vessels

b. each marks boundaries of heart chambers

Chambers of the heart continued• Right atrium

a. forms right border of heartb. recieves blood from three veins: Superior vena cava, inferior vena

cava, and Coronary sinus• Separated from left atrium by interatrial septum• Tricuspid valve

a. allows blood to flow from right atria to to right ventricleb. consists of three cusps

Chambers of the heart continued

• Right ventricle

a. forms most of anterior surface

b. Trabeculae Carneae

1. raised bundles of cardiac muscle

2. convey part of the conduction system

of the heart

c. Chordae tendineae

1. attach to cusps of tricuspid valves

2. attach to trabeculae Carneae

Chambers of the heart continued

• Right ventricle continued

d. separated from left ventricle by

interventricular septum

e. Blood enters pulmonary semilunar

valve into pulmonary trunk of right

and left pulmonary arteries

Chambers of the heart continued

• Left atria

1. Forms most of the base of the heart

2. receives blood from the lungs through

pulmonary veins

3. blood passes into left ventricle through

the bicuspid valve

Chambers of the heart continued

• Left ventricle

1. forms apex of heart

2. Also contains trabeculae carneae

3. Blood passes from left ventricle through

aortic semilunar valve into ascending

aorta

4. Some blood flows into Coronary arteries

5. Remainder of blood flows into arch of the

aorta and descending aorta

Myocardial thickness and function

• Atria are thin walled because they deliver blood to adjacent ventricles

• Left ventricle has largest wall because it pumps blood to the body

• Even though the right ventricle pumps the same amount of blood simultaneously as the left ventricle, the lungs offer little resistance so its wall is much smaller

Operation of heart valves• Atrioventricular valves

1. bicuspid and tricuspid valves2. when opened pointed end of cusps project into ventricle3. They open when ventricular pressure is less than atrial pressure4. When ventricles contract, they drive the cusps upward until they close5. Chordae Tendinae prevent cusps from everting

Operation of heart valves continued

• Semilunar valves

1. Allow ejection of blood into arteries but

prevents backflow

2. Consists of three crescent shaped cusps

3. When ventricles contract valves open

4. pressure from backflow causes them to

close

Circulation of blood

• Systemic circulation

1. Left side of heart

2. Receives blood from lungs

3. pumps blood through arteries to all parts

of body

4. Arteries give rise to arterioles, which lead

to systemic capillaries

5. Blood flows through one capillary and

enters a venule

6. Venules carries blood to veins and back to heart

Circulation of Blood Continued

• Pulmonary circulation

1. Right side of heart

2. Blood ejected from right ventricle flows

into pulmonary arteries

3. Blood flows through pulmonary veins to

left atria

Circulation of blood continued

• Coronary circulation

1. Blood can not diffuse through all layers of

the heart

2. Small amount of blood flows through

coronary arteries which branch from

ascending aorta

3. High aortic pressure pushes blood

through arteries, into capillaries, and into

coronary veins when the heart is at rest

Conduction system of the heart

• Autorhythmic cells

1. Cardiac muscle fibers that are self

excitable

2. allows heart to be removed for transplants

3. act as pacemakers

4. form the conduction system ( the route for

(propagating action potentials)

Components of conduction system

• Sinoatrial (SA) node

1. begins cardiac excitation

2. located in right atria

• Ateroventricular (AV) node

1. receives action potential from SA node

2. Located in septum of atria

Components of conduction system continued

• AV bundle or bundle of his1. only electrical connection of atria and ventricles2. Potential enters left and right branches that lead to apex of the heart

• Purkinje Fibers1. Conduct action potential through ventricular myocardium2. causes ventricles to contract about .20 seconds after atria