JNTU Pharm. D I Year HUMAN ANATOMY AND PHYSIOLOGY Previous Question Paper (February/March - 2023 - R08)

Blood is a specialized connective tissue consisting of formed elements suspended in a liquid matrix called plasma. It constitutes approximately 7-8% of total body weight, with a volume of about 5 liters in an average adult.

Composition of Blood:

1. Plasma (55%): A straw-colored fluid composed of 90-92% water, 7-8% proteins (albumin, globulins, fibrinogen), and 1-2% inorganic salts, nutrients, hormones, and waste products.
2. Formed Elements (45%):
   • Erythrocytes (RBCs): Biconcave, non-nucleated cells containing hemoglobin for oxygen transport.
   • Leukocytes (WBCs): Nucleated cells involved in immunity, categorized into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
   • Thrombocytes (Platelets): Cell fragments essential for blood clotting and hemostasis.

Functions of Blood:

• Transportation: Delivers oxygen, nutrients, hormones, and enzymes to tissues and transports metabolic waste (CO2, urea) to excretory organs.
• Regulation: Maintains body temperature, pH balance (via buffers), and osmotic pressure.
• Protection: Leukocytes provide defense against pathogens through phagocytosis and antibody production; platelets initiate clotting to prevent blood loss.

Disorders of Blood Components:

• Erythrocyte Disorders: Anemia (deficiency in RBCs or hemoglobin, e.g., iron-deficiency, sickle cell) and Polycythemia (excessive RBC production).
• Leukocyte Disorders: Leukopenia (low WBC count) and Leukemia (malignant proliferation of abnormal WBCs).
• Platelet/Clotting Disorders: Thrombocytopenia (low platelet count leading to bleeding) and Hemophilia (genetic inability to form proper clots).

A cardiac cycle is the sequence of coordinated electrical and mechanical events that occur in the heart from the beginning of one heartbeat to the beginning of the next. It involves the rhythmic contraction (systole) and relaxation (diastole) of the atria and ventricles, ensuring the continuous circulation of blood throughout the body. At an average heart rate of 75 beats per minute, one complete cardiac cycle lasts approximately 0.8 seconds.

The events of the cardiac cycle are divided into the following phases:

1. Atrial Systole (0.1 seconds): The SA node triggers atrial depolarization, causing the atria to contract. This forces the remaining 20-30% of blood into the ventricles. The AV valves are open, and the semilunar valves are closed.
2. Ventricular Systole (0.3 seconds): This phase is subdivided into two parts:
   • Isovolumetric Contraction: Ventricles begin to contract, causing a rapid rise in pressure that closes the AV valves (producing the first heart sound, S1). All valves are closed, and ventricular volume remains constant.
   • Ventricular Ejection: Once ventricular pressure exceeds the pressure in the aorta and pulmonary artery, the semilunar valves open, and blood is ejected into the systemic and pulmonary circulations.
3. Ventricular Diastole (0.4 seconds): This phase is subdivided into two parts:
   • Isovolumetric Relaxation: As the ventricles relax, pressure drops. The semilunar valves close (producing the second heart sound, S2) to prevent backflow. All valves are closed, and volume remains constant.
   • Ventricular Filling: When ventricular pressure falls below atrial pressure, the AV valves open. Blood flows passively from the atria into the ventricles, accounting for about 70-80% of ventricular filling before the next atrial systole begins.