
288 BIOLOGY
higher, it shows hypertension. High blood pressure leads to heart diseases
and also affects vital organs like brain and kidney.
Coronary Artery Disease (CAD): Coronary Artery Disease, often referred
to as atherosclerosis, affects the vessels that supply blood to the heart
muscle. It is caused by deposits of calcium, fat, cholesterol and fibrous
tissues, which makes the lumen of arteries narrower.
Angina: It is also called ‘angina pectoris’. A symptom of acute chest pain
appears when no enough oxygen is reaching the heart muscle. Angina
can occur in men and women of any age but it is more common among
the middle-aged and elderly. It occurs due to conditions that affect the
blood flow.
Heart Failure: Heart failure means the state of heart when it is not pumping
blood effectively enough to meet the needs of the body. It is sometimes
called congestive heart failure because congestion of the lungs is one of
the main symptoms of this disease. Heart failure is not the same as cardiac
arrest (when the heart stops beating) or a heart attack (when the heart
muscle is suddenly damaged by an inadequate blood supply).
SUMMARY
Vertebrates circulate blood, a fluid connective tissue, in their body, to transport essential
substances to the cells and to carry waste substances from there. Another fluid, lymph
(tissue fluid) is also used for the transport of certain substances.
Blood comprises of a fluid matrix, plasma and formed elements. Red blood cells (RBCs,
erythrocytes), white blood cells (WBCs, leucocytes) and platelets (thrombocytes) constitute
the formed elements. Blood of humans are grouped into A, B, AB and O systems based
on the presence or absence of two surface antigens, A, B on the RBCs. Another blood
grouping is also done based on the presence or absence of another antigen called Rhesus
factor (Rh) on the surface of RBCs. The spaces between cells in the tissues contain a fluid
derived from blood called tissue fluid. This fluid called lymph is almost similar to blood
except for the protein content and the formed elements.
All vertebrates and a few invertebrates have a closed circulatory system. Our circulatory
system consists of a muscular pumping organ, heart, a network of vessels and a fluid, blood.
Heart has two atria and two ventricles. Cardiac musculature is auto-excitable. Sino-atrial node
(SAN) generates the maximum number of action protentials per minute (70-75/min) and
therefore, it sets the pace of the activities of the heart. Hence it is called the Pacemaker. The
action potential causes the atria and then the ventricles to undergo contraction (systole) followed
by their relaxation (diastole). The systole forces the blood to move from the atria to the ventricles
and to the pulmonary artery and the aorta. The cardiac cycle is formed by sequential events in
the heart which is cyclically repeated and is called the cardiac cycle. A healthy person shows 72
such cycles per minute. About 70 mL of blood is pumped out by each ventricle during a
cardiac cycle and it is called the stroke or beat volume. Volume of blood pumped out by each
ventricle of heart per minute is called the cardiac output and it is equal to the product of stroke
volume and heart rate (approx 5 litres). The electrical activity of the heart can be recorded from