Endocrine System
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2.42 Where does earwax come from? – Sebaceous glands and ceruminous glands, specialised sweat glands, located in the ear canal produce this wax-like secretion. Earwax, called cerumen, protects the ear from infection and traps debris or small insects that enter the ear. It also helps prevent the ear drum from drying out. Usually the wax moves outward, moving anything it trapped along with it.
3. THE Circulatory System
What is Circulatory System?
3.1. Your circulatory system includes the cardiovascular system and the lymphatic system. The cardiovascular system, which consists of the heart (cardio), blood, and blood vessels (-vascular), transports life-giving blood carrying oxygen, nutrients, antibodies, and infection-fighting cells to each cell in your body. It also helps rid the body of wastes. In addition to blood, your body has fluid lymph that circulates throughout it. The lymphatic system is a drainage subsystem for the larger circulatory system and is active in fighting disease.
Composition of Blood
3.2. Blood consists of various specialised cells and a fluid called plasma. The yellowish plasma contains water, nutrients, wastes, and other materials. The cells found in blood include red blood cells, which carry oxygen; white blood cells, which protect the body against disease; and platelets, which initiate the process of blood clotting. Blood cells are made in the marrow, a soft fatty substance that fills the hollow parts of bones.
3.3 Red Blood Cells – These consist mainly of haemoglobin, an oxygen-carrying protein that gives them their red colour. Oxygen is picked up by the red blood cells in the lungs. As blood is pumped around the body, oxygen is dropped off wherever it is needed by other body cells and tissues.
3.4 White Blood Cells – White blood cells, fewer than red, are an integral component of the immune system and help defend the body against infection and disease. White cells help in destroying most of the harmful microorganisms (germs) that enter the body and help us to stay strong and healthy. Some cannot be destroyed as they carry poison. To make the poison-carrying germs harmless, the white cells produce an anti-toxin (anti-poison) which turns the poison harmless.
3.5 Platelets – Platelets are a round or oval disc-like structures 2-4 mm in diameter in the blood ranging from 1,50,000 to 4,50,000/ul and play an important role in coagulation (clotting) that helps stop bleeding. They live for about 8-10 days only.
The Blood Vessels
3.6 The 1,00,000 km blood vessels of the circulatory system form a continuous system supplying oxygenated blood to the body’s 100 trillion cells, tissues and organs. There are three types of blood vessels. Arteries are the thick-walled vessels that carry blood from the heart to all parts of the body. Veins, which have thinner walls, carry blood back to the heart from all parts of the body. Veins also contain tiny valves that prevent blood from flowing downward from the pull of gravity. Capillaries, which are the smallest of the blood vessels, link the arteries to the veins. The wall of a capillary is only one cell thick, which allows oxygen and nutrients to leave the bloodstream easily and be taken up by the body’s cells. Because of their small diameter, blood cells must pass through capillaries in single file. No cell in the body is more than a few cells away from a capillary.
