Blood is needed to keep us alive. Blood is a constantly circulating fluid providing the body nutrition, oxygen. It also removes cellular waste from the body. Blood is mostly liquid, with numerous cells and proteins suspended in it, making blood thicker than water. Blood also fights with infections and carries hormones around the body. The average person has about 5 litres of blood.
Composition of Blood
Blood is the composition of plasma and blood cells. Plasma makes up 55 % of blood content. The other 45 % consists mainly of red blood cells and platelets.
Plasma: Plasma is a yellowish fluid that contains proteins that help blood to clot and perform other functions. Plasma is 92 % water, and the contents of the remaining 8 % include carbon dioxide, glucose, hormones, vitamins, proteins, fats, etc.
Types of Blood Cells
Red blood cells: Red blood cells (RBCs) also called erythrocytes are shaped like slightly indented, flattened disks and transport oxygen to and from the lungs. RBCs contain hemoglobin, a protein that contains iron, carries oxygen. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the different body parts.The life span of RBC is about 4 months and the body makes new RBCs to replace those that die or are lost from the body. Our body produces around 2 million blood cells every second. RBCs are made in the inside part of bones called the bone marrow.
White blood cells: White blood cells (WBCs) also called leukocytes, are a key part of the immune system. The immune system helps the body defend itself against infection. White blood cells make up less than 1% of blood content. Some types of WBCs make antibodies, which are special proteins that recognize foreign materials and help the body get rid of them.Life span of white blood cells vary from hours to years. Higher and lower levels of white blood cells can indicate disease.
Platelets: Platelets also called thrombocytes, are tiny oval-shaped cells that help in the clotting process. Platelets interact with proteins called clotting factors to control bleeding inside our bodies and on our skin.There should be between 150,000 and 400,000 platelets per microlitre of blood. Life span of platelets is about 9 days in the blood and being replaced by new platelets made by the bone marrow.
Circulation of Blood
Blood is circulated through blood vessels (arteries and veins) that carry blood away from and toward the heart. The heart pumps blood throughout our body, carrying oxygen to each cell. After delivering the oxygen, the blood returns to the heart. The heart then sends the blood to the lungs to pick up more oxygen. This cycle goes on.
Two types of blood vessels carry blood throughout our body:
• Arteries carry oxygenated blood (blood that has gotten oxygen from the lungs) from the heart to the rest of the body.
• Blood then travels through veins back to the heart and lungs, so it can get more oxygen to send back to the body via the arteries.
Functions of Blood
Blood performs many functions that are essential for survival, including:
• Supply of oxygen to cells and tissues
• Supply of essential nutrients like amino acids, fatty acids, and glucose to cells
• Removal of waste materials, like carbon dioxide, lactic acid and urea
• Regulation of body temperature and acidity (pH) levels
• Transport hormones from one part of the body to another and transmit messages of tissue damage
• Protect the body from infection by the circulation of white blood cells and detect foreign materials by antibodies
• Coagulation or blood clotting enable by blood to stop bleeding from broken blood vessels
Blood Type or Group
Blood groups are categorized on the base of presence and absence of certain antibodies in the blood. Not everyone has the same antibodies. Rhesus (Rh) factor is a protein found on the surface of red blood cells. If your blood is positive, you have this protein. If it's negative, you don't.
Human can have one of these eight different blood types:
• A negative
• A positive
• B negative
• B positive
• O negative
• O positive
• AB negative
• AB positive
Blood group O (negative) is an universal donor and Blood group AB (positive) is an universal receiver.
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