Category Zoology

The immune system can go wrong when harmless substances that we swallow, breathe in, or touch are targeted by our body’s defences. This overreaction is called an allergy. The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis — a potentially life-threatening emergency. While most allergies can’t be cured, treatments can help relieve your allergy symptoms.

Allergens

Substances that trigger an allergic reaction are called allergens. An allergen is a substance that can cause an allergic reaction. In some people, the immune system recognizes allergens as foreign or dangerous. As a result, the immune system reacts by making a type of antibody called IgE to defend against the allergen. This reaction leads to allergy symptoms. Common allergens include nuts, pollen from flowers, and animal fur.

Automatic response

Common allergic reactions are sneezing, coughing, or red, itchy skin. Reactions are sometimes severe enough to cause breathing problems and be life-threatening. Some types of allergies, including allergies to foods and insect stings, can trigger a severe reaction known as anaphylaxis. A life-threatening medical emergency, anaphylaxis can cause you to go into shock. 

The best way to manage an allergy is to avoid the allergen, but this is not always possible. In these cases, medical treatment can help.

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The body’s collective defence measures are known as the immune system. This works by identifying and targeting pathogens. Over time, the body remembers some germs and gives immunity so the same diseases do not return.

Antibodies

The body makes weapons called antibodies. These defensive chemical proteins attach themselves to invaders to identify them as enemies for white blood cells to eat.

Armies of antibodies

When the body recognizes a pathogen, about 10,000 trillion antibodies are released into the bloodstream and attach themselves to the known germs.

• Firstly, the antibodies neutralise the virus, meaning that it is no longer capable of infecting the host cell.
• Secondly, many antibodies can work together, causing virus particles to stick together in a process called agglutination. Agglutinated viruses make an easier target for immune cells than single viral particles.
• A third mechanism used by antibodies to eradicate viruses, is the activation of phagocytes. A virus-bound antibody binds to receptors, called Fc receptors, on the surface of phagocytic cells and triggers a mechanism known as phagocytosis, by which the cell engulfs and destroys the virus.
• Finally, antibodies can also activate the complement system, which opsonises and promotes phagocytosis of viruses. Complement can also damage the envelope (phospholipid bilayer) that is present on some types of virus.

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Bacteria, viruses, and other pathogens face huge resistance from the human body. The first line of defence is the skin and the linings of the eyes, mouth, nose, throat, and stomach.

Inner defences

Pathogens can enter the body through the food we eat or the air we breathe. To stop germs gaining access, internal passageways are lined with protective fluids, such as saliva, mucus and tears.

Tears

Salty tears form to wash away eye pathogens. Foreign bodies that enter the eye are washed out by tears. Moreover, tears contain a substance called lysozyme, which has an antibacterial action, and works to prevent invasion and infection by microbes. Tears contain components that heal damage to the surface of the eye.

Mucus

The nose is lined with sticky mucus to trap germs. When a sickness-causing agent like a virus or bacteria enters your body, the cells that produce mucus kick into a higher gear and pump out more of the slimy stuff, which then picks up the germs. Mucus usually clears itself out of the body as we’ve discussed, but sometimes it needs a little help. Coughing and blowing your nose are the best ways to help mucus fight the good fight.

Saliva

This slimy substance has chemicals to kill mouth bacteria. In addition to keeping your mouth healthy, saliva may contain indicators of health concerns as well. Since it shares many properties with blood, the use of saliva to detect and diagnose oral diseases and other diseases that could affect your general health is being studied. Researchers have reported promising results in the use of saliva for the diagnosis of breast cancer, oral cancers, gum disease and viral hepatitis. Saliva is already used for rapid HIV testing.

Wax

Ears contain thick wax to deter invaders. Earwax also acts as a filter. It prevents harmful things like bugs, sand and dirt from getting into our ears and to the ear drum. It’s also antimicrobial. Earwax has substances in it that prevent infections from entering the body. 

Skin

The body’s outer covering is a barrier against infection. If skin is injured, the blood supply to the skin increases in order to deliver various substances to the wound so it is better protected from infections and can heal faster. Later on, new cells are produced to form new skin and blood vessels. Depending on how deep the wound is, it heals with or without a scar.

Blood

Different types of white blood cells unite to attack invaders. A lymphocyte is a type of white blood cell that is part of the immune system. There are two main types of lymphocytes: B cells and T cells. The B cells produce antibodies that are used to attack invading bacteria, viruses, and toxins. The T cells destroy the body’s own cells that have themselves been taken over by viruses or become cancerous.

Stomach

Powerful acid in the stomach destroys germs in food. The hydrochloric acid in the gastric juice breaks down the food and the digestive enzymes split up the proteins. The acidic gastric juice also kills bacteria. 

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Every day the human body comes under attack from a range of microscopic invaders that cause disease. All kinds of defensive measures are in place to stop them. Skin and membranes form physical barriers. Fluids such as saliva, tears, and mucus provide chemical warfare. If these lines are passed, the immune system fights back. Armies of special cells target and destroy enemy attackers to make the body healthy again.

Body invaders

Pathogens are bacteria and viruses that cause disease. Most bacteria are simple and harmless, and some are helpful, such as those that live in the gut to help with digestion. However, some bacteria invade and damage body tissues. Viruses are chemical packages much smaller than bacteria that take control or body cells and multiply, causing illness and disease.

Bacteria

Bacteria are simple single-celled organisms that can multiply rapidly. A few can cause serious diseases by invading the body, and some release poisons called toxins.

• Bacilli: These rod-shaped bacteria often live harmlessly in the gut. Other bacilli cause illness, such as bladder infections and typhoid.
• Spirlla: Small spiral-shaped bacteria, called spirlla, come from uncooked shellfish or stale water. These cause stomach upsets and diarrhoea.

Viruses

Viruses reproduce by invading a body cell. The hijacked cell is turned into a factory where more viruses are produced. These are then released to infect more and more cells.

• Adenovirus: This virus can infect lungs to produce coughs, eyes to give conjunctivitis, and the digestive system to trigger diarrhea.
• Influenza: There are three main types of influenza virus. Types A and B can cause flu, especially in the winter. Type C usually causes a milder respiratory illness.

Fungi, protists, and parasites

Although most fungi grow in soil or rotting food, some live on or inside humans. Protists are simple organisms, some of which cause human disease. Parasites are other living things that live on or in our bodies.

• Athlete’s foot: This fungus, called Trichophyton, grows as a network of threads in damp skin, especially between the toes, it causes an itchy infection.
• Plasmodia: Single-celled plasmodia live inside mosquitoes. A mosquito bite can bring plasmodia into the human bloodstream where they infect red blood cells.
• Tapeworm: This parasite may live inside the intestines but not cause any symptoms. Tapeworms enter the body via undercooked or raw meat that contains tapeworm larvae.

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The network of lymph vessels carries the lymph fluid through tiny, bean-like glands called lymph nodes. As lymph flows through the spongy tissue of the node, cells called lymphocytes and macrophages identify germs and attack them. The lymph nodes also work like a filter to clean the lymph. The cleaned fluid then flows out of the node and continues to the bloodstream.

There are two kinds of lymphocytes — B-lymphocytes (or B-cells) and T-lymphocytes (or T-cells).

B-cells make antibodies that attach to germs and let your immune system know they need to be killed off.
T-cells have a couple of jobs. Some destroy germs, while others keep track of immune cells. They let your body know when to make more of certain kinds and less of others.

Lymph fluid also carries protein, waste, cellular debris (what’s left after a cell dies), bacteria, viruses, and excess fat that are filtered by the lymphatic system before it’s dumped back into the bloodstream.

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Tonsils

Deep inside the throat, the tonsils help to destroy germs that come into the body through the nose and mouth. Each tonsil is composed of tissue similar to lymph nodes, covered by pink mucosa (like on the adjacent mouth lining). Running through the mucosa of each tonsil are pits, called crypts.

The tonsils are part of the lymphatic system, which helps to fight infections.

Left subclavian vein

This drains blood from the left arm and collects lymph from the left side of the body and the lower half of the right side.

Right subclavian vein

This drains blood from the right arm and collects lymph from the upper half of the right side of the body.

Thoracic duct

The thoracic duct is the largest lymphatic vessel in the human body. Around 75% of the lymph from the entire body (aside from the right upper limb, right breast, right lung and right side of the head and neck) passes through the thoracic duct. Lymph drains into the left subclavian vein through this tube.

Ribcage

Rib cage, in vertebrate anatomy, basketlike skeletal structure that forms the chest, or thorax, and is made up of the ribs and their corresponding attachments to the sternum (breastbone) and the vertebral column.  Red bone marrow in the ribs produces white blood cells.

Spleen

The largest organ in the lymphatic system, the spleen produces cells that help to fight infection. The spleen plays multiple supporting roles in the body. It acts as a filter for blood as part of the immune system. Old red blood cells are recycled in the spleen, and platelets and white blood cells are stored there. The spleen also helps fight certain kinds of bacteria that cause pneumonia and meningitis.

Cysterna chyli

This collects lymph from the lower half of the body before it goes up into the thoracic duct. It is an elongated, sac-like structure formed by the junction of a variable number of lumbar, intestinal, liver and descending intercostal lymphatic trunks. It extends 5-7 cm in the caudocephalad axis.

Lymph node

Lymph nodes are small lumps of tissue that contain white blood cells, which fight infection. They filter lymph fluid, which is composed of fluid and waste products from your body tissues. Lymph nodes also help activate your immune system if you have an infection. Lymph is processed and cleaned as it passes through lymph nodes.

Inguinal nodes

Lymph from the legs passes through these nodes. Lymph nodes are part of the body’s lymphatic system, which helps maintain fluid balance in the bloodstream, filters waste, and plays an important role in immune defense.

Lymph vessels

These tubes drain and transport lymph from body tissues. One of the main structural features of lymph vessels is their valves, which are semilunar structures attached to opposite sides of the lymphatic endothelium. Valves are found in larger lymph vessels and collecting vessels and are absent in the lymphatic capillaries. 

Flowing fluid

The lymphatic system consists of a network of vessels (green), nodes, and organs, including the tonsils, spleen, and thymus gland. Unlike the vessels in the blood circulation system, lymphatics have no pump. Instead, lymph is pushed through the system by the movement of the surrounding muscles. Lymph eventually drains into two tubes, or ducts, in the chest, which carry the fluid back to the bloodstream.

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