Endocrine System
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3.15 The lymphatic system is also a part of the body’s immune system. In addition to the lymph fluid and vessels, this system includes the lymph glands, the thymus gland, the spleen and the tonsils. For information about the role of the lymphatic system in fighting disease, refer to the section on The Immune System.
What is a Pacemaker?
3.16 Two small groups of cells in the wall of the heart set the pace for cardiac contraction. They are the heart’s natural pacemaker. Sometimes disease causes these cells to become slow in their initiation of the contraction. If medication does not help, doctors can insert an electronic, artificial pacemaker near the heart. This pacemaker is battery-operated, and wires from it send a small electric impulse to the heart at regular intervals.
How does Blood Clot?
3.17 The body has a special way of mending itself. When a blood vessel is cut, platelets are triggered off to produce a clotting substance, which sticks to the edges of the cut. This joins with other clotting substances to form thread-like strands, which get tangled together, trapping blood cells between them. They then release chemicals which react with plasma proteins to form a blood clot. The blood makes a kind of crust, called a “scab” over the cut. The drying scab also keeps germs out of the body until the cut has healed. That is why we should never pick and remove a scab. After some time when the skin underneath has healed, the scab falls off by itself.
4. the Respiratory System
What is Respiratory System?
4.1 Out of different gases in the air only oxygen is important to life and the body. If the brain cells do not get enough oxygen even for a few minutes, they begin to die and the brain gets damaged and the heart stops beating. We live only when we take sufficient oxygen. Every breath we take provides essential oxygen to our body cells which produce the waste product carbon dioxide. The respiratory system includes the cone-shaped 13 cm long tube pharynx (throat), the larynx (voice box), the 13 cm long and about 2.5 cm dia tube trachea (windpipe) and the lungs.
Oral and Nasal Cavities
4.2 Normally, the air enters the body through the nostrils. Tiny hairs in the nose help filter out dust and dirt and thus protect us from many breathing problems. But when the nose is blocked, we can breathe through the oral cavity (mouth), which though is less healthier than through the nose. There are also very tiny hairs in the windpipe, which move like grass in the wind. These tiny hairs help in carrying the trapped debris in the mucus back to the throat, which can be discarded by coughing or swallowing. The cells in the nasal cavity warm and moisten the air before it enters the lungs. The cells lining the nasal cavity and the windpipe secrete a sticky liquid called mucus, which traps any dust, dirt, bacteria and viruses breathed in.
The Epiglottis
4.3 Both nasal and oral cavities meet at the throat. The air from the nose or mouth passes through the throat to the voice box where the vocal cords are located. The voice box is attached to the windpipe as well as the foodpipe. When a person swallows, the epiglottis (a special protective flap) closes the opening to the windpipe preventing foods or liquids from entering the lungs. But if by chance food enters the windpipe, it can be brought back to the throat by coughing and then swallowing properly.
The Lungs
4.4 A right and a left lung are located in the chest cavity. They have a spongy appearance resembling a plastic bag with lots of bubble like holes. The lungs are the only organ in the body that can float by themselves. Below the lungs is a sheet of large muscle tissue, the diaphragm, which separates the chest cavity from the abdominal cavity. It is the dome-shaped chief muscle in the respiratory process. The two tubes known as bronchi connect the windpipe to each lung. The bronchi are subdivided many times forming smaller and smaller passages, the smallest of which is known as bronchioles. At the end of each bronchiole is a cluster of tiny air sacs or pockets called the alveoli, which look like a bunch of grapes. Both lungs contain about 300 million alveoli with a large surface area. If all the alveoli could be spread flat, they would cover an area equal to the size of a tennis court. The walls of the alveoli are covered with tiny capillaries through which blood can easily pass into the blood stream. Oxygen passes from the alveoli into these capillaries for delivery to the body‘s cells. Simultaneously, carbon dioxide in the blood stream moves from the capillaries into the alveoli, where it is expelled from the lungs. This simultaneous exchange of the gases is called respiration. Some air always stays in the lungs. Otherwise the lungs would collapse.
Breathing
4.5 Air moves into and out of the lungs with every breath. When a person inhales, the dome-shaped diaphragm contracts, flattens and moves downwards, the rib muscles expand and enlarge the chest cavity upwards and outwards, oxygen-rich air rushes into the lungs, and the alveoli expand as they fill with air and lungs increase in size. When a person exhales, the diaphragm relaxes, becomes dome-shaped again and moves upwards and the rib muscles relax, the chest cavity becomes smaller, and carbon-dioxide-rich air is pushed out of the lungs, which become smaller. The muscles in the abdominal wall also contract to push the abdominal organs upwards against the diaphragm thereby aiding to push the air out of the lungs. This respiration process is automatic and is regulated by the respiratory control centre in the brain stem. In an adult the respiration rate is about 12-20 times a minute. Exercise increases the respiration speed, as our body cells are working hard and need more oxygen. Faster and deeper breathing allows oxygen to be pumped into the blood stream more swiftly from the lungs.
4.6 Why do People Yawn? — Even when people breathe normally, not all the alveoli are filled with oxygen-rich air. That means that some blood may pass through the lungs without getting sufficient oxygen. It is thought that this low blood-oxygen concentration triggers a yawn reflex. Yawning causes a person to take a deep breath, which makes more oxygen available to the alveoli and increases the blood-oxygen concentration.
5 tHE Immune SYSTEM
What is Immune System?
5.1 Immune system is the capability of the body to fight against any alien viral, bacterial, fungal or cellular attack. You constantly come in contact with many pathogens like bacteria and viruses that have the potential to make you ill. When the body’s non-specific defences are unable to overcome an invading organism, the body’s immune system goes to work. Rather than being an organ system, it works by using components of the lymphatic and circulatory systems. Nature has developed this highly complex and wonderous inborn defence mechanism to fight against any viral, fungal, bacterial or cellular attack. Nature has gifted the body to develop antibodies for shooting away or resisting infections by foreign bodies through this strong immune system.
Immune System Categories
5.2 The immune system can be broadly divided into three categories: –
(i) Innate or Natural Immunity – This is something that everyone is born with and is a general protection that human beings have. Innate immunity includes the external barrier – the skin – and mucous membranes (those that line the throat, nose and gastrointestinal tract) which are the first line of defence. If the outer defensive wall is broken, be it a cut or gash, the skin attempts to heal it quickly and special immune cells on the skin attack invading germs. Another form of natural immunity is “passive” or “borrowed” immunity. Despite being naturally present in the body, it traces its source outside the body. For example, antibodies (defensive proteins) present in mother’s milk provide an infant with temporary immunity to diseases that the mother had been exposed to. This can help protect the infant against infection during early years of childhood.
(ii) Adaptive or Acquired Immunity – This is something that individuals develop over the years. When our body gets infected, it induces antibodies on its own or sometimes with the help of medication and vaccination to fight the infection. It is most likely that the same infection will not recur. This is due to the memories these antibodies have. That is why if you have chicken pox in your childhood, chances are you will not get it when you are an adult. In other words, the antibodies induced during the first infection restart their fight if the same virus enters the body again. But then what about viruses that cause the regular cough, cold and fever? How do they recur inspite of having been cured by the antibodies before? That is because viruses are very smart! They tend to mutate and every time they enter the body, they do so in a somewhat new form. That stops the previous antibodies from recognising and fighting against them.
(iii) Artificial Immunity – This is similar to adaptive immunity, though of course, it is a little more permanent in nature. This immunity develops with the help of single or multiple vaccinations. Each dose develops a certain amount of antibodies in the system that help fight various infections and in due course create a permanent wall against them. Diseases like influenza, diphtheria and small pox fall in this category.
Immune System and Natural Environment
5.3 A person’s immunity level is much lower than normal when one is very young and when one is very old. In babies, it is yet to develop fully. In old people it stops developing and resistance power weakens. Also being over-protective and seriously limiting one’s exposure to natural surroundings leads to underdevelopment of immunity cells. The more a person is exposed to the natural environment, the more he develops his or her resistance power. Research reveals that children who are very active in outdoor activities are far more comfortable with their surroundings and have a stronger immune system than those who stay indoors all the time.
Immune System and Diet
5.4 Everyone’s immune system is different. Some people never seem to get infections, whereas others seem to be sick all the time. From genes to basic body metabolism, to lifestyle, to stress and most importantly to diet – all these have a cumulative effect on developing or debilitating the immune system as the case may be. But at the end of the day, it is the basics that matter. A good nourishing plant-based balanced diet, healthy lifestyle, regular exercise, stress management, and adequate relaxation and sleep are essential requisites for a fighting-fit immune system as well as a healthy disease-free body. Foods rich in antioxidant vitamins A, C and E, certain minerals like selenium and zinc, essential fats and probiotics greatly help improve the immunity. Other important nutrients that help improve response include vitamin B6, pantothenic acid, iron, folic acid, magnesium and copper.
