Physiotherapy Lecture 1: Structure and Function of CardioVascular System (CVS)

Cardiovascular System (CVS)

• The CVS is a closed system that includes the heart, blood vessels, and blood.

Structure of the Heart

• The heart is a muscle that weighs around 300g and beats around 100,000 times a day, and around 3 billion times in a lifetime.
• It is surrounded by a sac of fluid contained within the pericardium.
• The heart has three layers: the pericardium, the myocardium (heart muscle), and the endocardium (innermost layer).

The Pericardium

• The pericardium is a sac of fluid that surrounds the heart.

The Endocardium

• The endocardium is a very fine layer of squamous epithelium resting on a thin layer of connective tissue.
• It lines the myocardium and valves and provides protection to the valves and heart chambers.
• If damaged, it can lead to thrombus formation.

The Myocardium (Heart Muscle)

• The myocardium is cardiac muscle that is striated like skeletal muscle but has features of smooth muscle.
• Muscle fibers are aligned in a way that when they contract, the chambers get smaller.
• Mitochondria are much larger (10x the size compared to skeletal muscle) and contain about 5000 mitochondria per cell.
• The left ventricle is thicker than the right ventricle.

Action Potential Initiation

• Action potential is initiated within the heart by autorhythmic cells that create minimal contraction.
• These cells spontaneously generate action potentials, acting as either pacemaker cells or conducting fibers.
• The basic rate is 80-100 bpm, but it can be reduced to 60-80 bpm by parasympathetic nervous system.

Valves

• Valves have three leaflets except the bicuspid, which has two leaflets.
• Atrioventricular valves are located between the chordae tendinae and papillary muscles.
• Semilunar valves are located in the aorta and pulmonary artery.

Action of Valves

• Atrioventricular valve action: chordae tendinae prevent valve cusps from billowing into the atria.
• Semilunar valve action: cusps are up during systole, and down during diastole.

Heart Muscle Contraction Mechanisms

• The heart muscle contraction mechanism has two phases: diastole and systole.
• Diastole is the phase when the heart muscle relaxes and allows the chambers to fill with blood.
• Systole is the phase when the heart muscle contracts and pumps blood from the chambers into the arteries.

Mechanical Events

• Diastole comprises three phases: isovolumetric ventricular relaxation, ventricular filling, and ventricular filling with atrial contraction.
• Systole comprises two phases: isovolumetric ventricular contraction and ventricular contraction with atrial relaxation.

The Coronary Circulation

• The coronary circulation is the heart's blood supply.
• It includes the left and right coronary arteries, which arise from the aortic sinus above the aortic semilunar valve.
• Coronary sinus is the cardiac vein that returns blood to the right atrium.

Vasculature

• Arteries/arterioles carry blood away from the heart.
• Veins/venules carry blood to the heart.
• Capillaries are the site of exchange of gases and nutrients with the tissues.

Arterial System

• Arteries contain large amounts of elastic and fibrous tissue.
• As arteries become smaller, the amount of elastic tissue decreases, and smooth muscle increases.
• The arterial system behaves as a pressure reservoir when stretched, and the elastic forces are stored until diastole.

Capillaries

• Capillaries are the smallest and thinnest-walled vessels (5-10 micrometers in diameter and 0.5 micrometers in wall thickness).
• They are the primary site for material exchange.

Venous System

• Veins serve as a volume reservoir for the ventricles of the heart.
• Walls are thinner than arterioles, with very little smooth muscle.
• Valves are present in peripheral veins but not in central veins.

Valves in Veins

• Valves serve to prevent blood from going backwards.
• They are assisted by the surrounding muscles acting as a pump.