Anatomy

Chapter 11 – The Cardiovascular System – Part I

The Cardiovascular SystemThe major function of the cardiovascular system is transportation. Blood is the transport vehicle, the system carries oxygen, nutrients, cell wastes, hormones, and other substances vital for body homeostasis. The force to move the blood around the body is provided by the beating heart.

The cardiovascular system can be compared to a muscular pump equipped with one-way valves and a system of large and small tubes within which the blood travels.

• Mediastinum• Apex• Base

Location of the heart within the thorax.

Gross anatomy of the heart

Coverings and walls of the heart:The heart is enclosed by a double sac of serous membrane, the pericardium. The epicardium or visceral pericardium fits tight against the external surface of the heart, actually part of the heart wall. Parietal pericardium is found on the superficial face of the heart. The myocardium consists of thick bundles of cardiac muscle twisted and whorled into ring-like arrangements. The myocardium is the actual layer that contracts. The endocardium is the thin, glistening sheet of endothelium that lines the heart chambers.

The heart walls are composed of three layers.

• Epicardium• Myocardium• Endocardium Heart walls and coverings

Frontal Section of Heart showing interior chambers and valves

Chambers and Associated Great Vessels:

The heart contains four hollow chambers or cavities. • Atria• Ventricles• Interventricular septum• Superior and inferior venae cavae• Pulmonary arteries• Pulmonary veins• Aorta

Oxygen poor blood circulates from the tissues back to the right atrium via the systemic veins. The second circuit, from the left side of the heart and back to the right side of the heart is the systemic circulation. It supplies oxygen and nutrient rich blood to all the body organs.

Valves: the heart is equipped with four valves. The valves allow the blood to flow in only one direction through the heart chambers.

•Atrioventricular (AV) valves•Mitral or bicuspid valve •Tricuspid valve•Chordae tendineae

Chordae tendineae – anchor the valve cusps to the walls of the ventricles. Papillary muscles anchor the cusps against the force of the blood.

Semilunar valves: Semilunar valves guard the bases of the two large arteries leaving the ventricular chambers. Both have three leaflets that fit tightly together when the valves are closed.

These valves are known as the pulmonary and aortic valves, and are forced open and flattened against the walls of the arteries as the ventricles contract.

When the ventricles relax, the blood begins to flow backwards toward the heart, the leaflets fill with blood, closing the valves. This prevents the arterial blood from reentering the heart.

The valves operate at different times. The AV valves open during heart relaxation and close when the ventricles are contracting. Semilunar valves close during heart relaxation and are forced open during ventricular contraction.

Operation of the heart valves:

Heart valve replacement:

Types of replacement heart valves.

A valve being replaced in the

heart. Heart valves are simple devices. When damaged or severely deformed the valves can hamper cardiac function. The heart may have to contract more vigorously than normal. Faulty valves can be replaced with synthetic valves or a valve taken form the heart of a pig.

Cardiac circulation:

The blood contained in the heart does not nourish the myocardium. The blood that oxygenates and nourishes the heart is provided by the coronary arteries.

The coronary arteries branch from the base of the aorta and encircle the heart in the atrioventricular groove at the junction of the atria and ventricles.

Cardiac veins drain the myocardium and empty into an enlarged vessel on the backside of the heart called the coronary sinus, which in turn empties into the right atrium.

Homeostatic imbalances:

Endocarditis

Angina Pectoris

Myocardial infarction

Congestive Heart FailurePulmonary Edema

• Ischemia• Murmur• Fibillation

Physiology of the Heart

In one day, the heart pushes the body’s 6 quarts of blood through the blood vessels over 1000 times. That is 6000 quarts of blood each day.

Cardiac muscles contract spontaneously and independently and in a regular and continuous way.

Intrinsic conduction system of the heart.

Nerves of the autonomic nervous system are the brakes and accelerators. Intrinsic conduction system or nodal system – built into heart tissue, sets basic rhythm.

• Sinoatrial (SA) Node -• Atrioventricular (AV) node • Atrioventricular bundle• Purkinje fibers

Artificial pacemaker in the heart.

Electrocardiography:A clinical procedure for mapping the electrical activity of the heart.

P wave – small, signals the depolarization of the atria immediately before they contract. QRS complex – large, results from the depolarization of the ventricles; precedes the contraction of the ventricles. T wave – results from currents flowing during repolarization of the ventricles.

• Bradycardia – lower, less than 60 beat per min. • Tachycardia - rapid heart beat, over 100 beats per min.

Cardiac Cycle and Heart SoundsIn the healthy heart, the atria contract simultaneously, when they relax, the ventricular contraction begins. The cardiac cycle refers to the events of one complete heartbeat. The atria and then ventricles contract and relax 75 times per minute, lasting 0.8 seconds.

Systole – contractionDiastole – relaxation

Most of the pumping work is done by the ventricles.

• Mid-to-late diastole• Ventricular systole• Early diastole

• Heart sounds – “Lub” (AV valves),“Dub” (SL valves)

Cardiac Output (CO)- amount of blood pumped out each side of the heart in 1 minute.

• Stroke volume (SV)• Factors modifying basic heart rate• Neural (ANS) controls• Sympathetic • Parasympathetic