PROPERTIES OF BLOOD
- Color: Blood is red in color. Arterial blood is scarlet red because it contains more oxygen and venous blood is purple red because of more carbon dioxide.
- Volume: Average volume of blood in a normal adult is 5 L. In a newborn baby, the volume is 450 ml. It increases during growth and reaches 5 L at the time of puberty. In females, it is slightly less and is about 4.5 L. It is about 8% of the body weight in a normal young healthy adult, weighing about 70 kg.
- Reaction and pH: Blood is slightly alkaline and its pH in normal conditions is 7.4.
- Specific gravity:
Specific gravity of total blood : 1.052 to 1.061
Specific gravity blood cells : 1.092 to 1.101
Specific gravity of plasma : 1.022 to 1.026
- Viscosity: Blood is five times more viscous than water. It is mainly due to red blood cells and plasma proteins.
COMPOSITION OF BLOOD
Blood contains the blood cells which are called formed elements and the liquid portion known as plasma.
Three types of cells are present in the blood:
- Red blood cells or erythrocytes
- White blood cells or leukocytes
- Platelets or thrombocytes.
FUNCTIONS OF BLOOD
1. NUTRITIVE FUNCTION
Nutritive substances like glucose, amino acids, lipids and vitamins derived from digested food are absorbed from gastrointestinal tract and carried by blood to different parts of the body for growth and production of energy.
2. RESPIRATORY FUNCTION
Transport of respiratory gases is done by the blood. It carries oxygen from alveoli of lungs to different tissues and carbon dioxide from tissues to alveoli.
3. EXCRETORY FUNCTION
Waste products formed in the tissues during various metabolic activities are removed by blood and carried to the excretory organs like kidney, skin, liver, etc. for excretion.
4. TRANSPORT OF HORMONES AND ENZYMES
Hormones which are secreted by ductless (endocrine) glands are released directly into the blood. The blood transports these hormones to their target organs/tissues. Blood also transports enzymes.
5. REGULATION OF WATER BALANCE
Water content of the blood is freely interchangeable with interstitial fluid. This helps in the regulation of water content of the body.
6. REGULATION OF ACID-BASE BALANCE
Plasma proteins and hemoglobin act as buffers and help in the regulation of acid-base balance.
7. REGULATION OF BODY TEMPERATURE
Because of the high specific heat of blood, it is responsible for maintaining the thermoregulatory mechanism in the body, i.e. the balance between heat loss and heat gain in the body.
8. STORAGE FUNCTION
Water and some important substances like proteins, glucose, sodium and potassium are constantly required by the tissues. Blood serves as a readymade source for these substances. And, these substances are taken from blood during the conditions like starvation, fluid loss, electrolyte loss, etc.
9. DEFENSIVE FUNCTION
Blood plays an important role in the defense of the body. The white blood cells are responsible for this function. Neutrophils and monocytes engulf the bacteria by phagocytosis. Lymphocytes are involved in development of immunity. Eosinophils are responsible for detoxification, disintegration and removal of foreign proteins.
Essentials of Medical Physiology, 6th Edition By K Sembulingam