NEET Biology Notes Structural Organisation in Animals Blood
Blood
Blood is red coloured liquid connective tissue, softest in the body. It is heavier than water and salty in taste. In an adult person, the volume of blood is about 5-6 L. It is slightly alkaline having 7.3-7A pH of blood in arteries is more than in veins. The study of blood is called haematology. It is composed of two main component, i.e. blood plasma (watery fluid) and blood cells (floating bodies).
- Blood Plasma
- It is pale yellow, transparent fluid, which constitutes about 60% volume of the blood. It is slightly alkaline, non-living, intercellular substance.
- Water forms about 90-92% of the plasma and solids form about 8% of the plasma. Solid part of plasma consists of 7% organic substances (proteins i. e. albumin, globulin and fibrinogen) and 1% inorganic substances (bicarbonates and chloride salts of Na, K and Ca).
- Blood Cells (Blood Corpuscles)
Blood cells are also known as blood corpuscles. These form about 40-45% volume of the blood. These are of three types, i.e. RBCs (Red Blood Corpuscles) i.e. erythrocytes, WBCs (White Blood Corpuscles), i.e. leucocytes and blood platelets (thrombocytes).
- Red Blood Corpuscles (RBCs)
These are most abundant cells present in the human body. RBCs of vertebrates are nucleated (except mammals) whereas, RBCs of mammals are non-nucleated (except camel).
Salamander has the largest RBCs (about 80 pm in diameter). Musk deer (Tragupus javanicus) has the smallest RBCs (1.5 pm).
RBCs in mammals are biconcave and circular, however RBCs of camel and llamas are oval.
The number of RBCs are counted by instrument called haemocytometer.
A normal adult man and woman have 5 and 4.5 million RBCs per cubic mm of blood respectively. Life span of RBC is about 120 days. Bone marrow is the main site for formation of RBC, i.e. called erythropoiesis. Haemoglobin (Hb) is a purple coloured conjugated protein present in the cytoplasm of RBC. It gives red colour to it and acts as respiratory pigment (or oxygen carrying pigment). 100 mL of blood of a normal man and woman contains about 15 g and 13 g of haemoglobin respectively. An abnormal rise in RBCs count is called polycythemia and decrease is called erythrocytopenia. Decrease in total count of RBCs leads to anaemia.
- Functions of RBCs
- Haemoglobin of RBCs readily combines with oxygen to form oxyhaemoglobin. In the tissues, oxyhaemoglobin readily gives up its oxygen, which is used for oxidation of food.
- RBCs transport C02, that combines with NH2 group of Hb to form carbamino haemoglobin. Hb which act as acid-base buffer, maintains the pH of blood.
- White Blood Corpuscles (WBCs)
These are nucleated, colourless cells and are also called as leucocytes. They are bigger than RBCs (12-20 pm) in size, but less in number. In blood 5,000 to 10,000 per cubic millimetre WBCs are present. Rise in WBCs count is called leucocytosis, while decrease in WBCs count is called leukopenia. WBCs are of two main types, i.e. agranulocytes and granulocytes.
Blood Platelets
These are protoplasmic disc found in mammalian blood, also called thrombocytes. These are non-nucleated and colourless. They are oval to round in shape often stellate and much smaller than both RBCs and WBCs. They are fewer than RBCs and more than WBCs in number (about 2-5 lacs/cu mm). Life span of blood platelets is about a week.
Common Functions of Blood
- It transports different materials of body like 02, CO2 hormones, etc., between various parts.
- It maintains the normal temperature of body.
- It regulates the amount of salts, acids, bases and water etc. in the tissue fluid.
- The leucocytes play important role in defence by production of toxins and antibodies, act as soldiers of the body.
- It helps in rapid healing of wounds and injuries by coagulation.
Muscular Tissues
Study of muscles is called Myology. Muscular tissues are mesodermal in origin except iris and ciliary body of eyes which are ectodermal in origin. They contribute most of the total weight of body (about 40%-50%).The muscle cells are always elongated, slender and spindle-shaped, fibre like cells. These are of three types, i.e. striated, non-striated and cardiac muscles.
