Blood and Circulation Overview

Blood and Circulation

• Blood is a special connective tissue with a fluid matrix (plasma) and formed elements.
• Plasma (55% of blood) is a straw-colored, viscous fluid mainly composed of water (90-92%) and proteins (6-8%). Major proteins include fibrinogen, globulins, and albumins.
• Formed elements (45% of blood) include erythrocytes (red blood cells), leucocytes (white blood cells), and platelets.

Erythrocytes (Red Blood Cells)

• Abundant cells in blood (5-5.5 million per mm³).
• Biconcave disc shape, without a nucleus in mammals.
• Contain hemoglobin, an iron-containing protein, which gives blood its color and facilitates oxygen transport.
• Average lifespan of 120 days.
• Destroyed in the spleen.

Leucocytes (White Blood Cells)

• Colorless due to lack of hemoglobin.
• Nucleated cells.
• Average count is 6000-8000 per mm³.
• Types: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
• Important in the body's defense mechanisms, particularly phagocytic cells like neutrophils and monocytes.

Platelets

• Cell fragments, also called thrombocytes.
• Essential for blood clotting.
• Produced in bone marrow.

Blood Groups

• ABO blood grouping is based on the presence or absence of antigens (A and B) on the RBCs and corresponding antibodies in the plasma.
• Rh blood grouping is based on the presence or absence of Rh antigen on the RBCs.
• Compatibility is crucial for blood transfusions.
• O is universal donor.
• AB is universal recipient.

Lymph (Tissue Fluid)

• Fluid released from capillaries into spaces between cells.
• Contains minerals like plasma.
• Important for exchange of nutrients and gases.
• Lymphatic system collects this fluid and drains it back to the major veins carrying lymphocytes.

Circulatory Pathways

• Open circulatory systems in arthropods and mollusks. Blood pumped by the heart flows into open spaces (sinuses) in the body.
• Closed circulatory systems in annelids and chordates. Blood is circulated through a closed system of blood vessels.
• Fish have a two-chambered heart.
• Amphibians and reptiles (except crocodiles) have a three-chambered heart.
• Crocodiles, birds, and mammals have a four-chambered heart.
• The heart in humans is a four-chambered muscular organ, protected by a double-walled pericardium.
• Contains right and left atria, and right and left ventricles.
• Heart valves (atrioventricular valves - tricuspid and bicuspid, semilunar) ensure unidirectional blood flow.
• The heart's function is regulated by specialized cardiac muscle (nodal tissue - SAN and AVN).

Cardiac Cycle

• Sequence of events that occur during one complete heartbeat.
• Systole - contraction phase.
• Diastole - relaxation phase.
• Cardiac output - amount of blood pumped by each ventricle per minute.
• Stroke volume - amount of blood pumped out by each ventricle with each heartbeat.
• Pulse rate - measures the number of heartbeats per minute.

Regulation of Cardiac Activity

• Intrinsic regulation (myogenic).
• Extrinsic regulation by nerves and hormones.

Disorders of the Circulatory System

• Hypertension (high blood pressure)
• Coronary artery disease (narrowing of coronary vessels)
• Angina (chest pain).
• Heart failure (inadequate pumping of blood).