Nonspecific immunity

Non-specific immunity is programmed genetically in the human body from birth. The non-specific defences that are present from birth include:

• mechanical barriers

• inflammation

• phagocytosis

Mechanical barriers

These are barriers such as the skin and mucous membrane that line the tubes of the respiratory, digestive, urinary and reproductive systems. As long as these barriers remain unbroken, many pathogens are unable to penetrate them.

The respiratory system is lined with mucous-secreting cells to help remove micro-organisms from the respiratory tract. The highly acidic environment in the stomach can help to kill pathogens, along with the production of saliva which has an antimicrobial effect. Urine helps to deter the growth of micro-organisms in the genito-urinary tract. The pH of the vagina protects against the multiplication and growth of microbes.

Chemicals

Chemicals are liberated by different cells that play an important role in immunity. There are many different types of chemicals involved in immunity including interferons, complements and histamine.

Interferons

These are proteins produced by cells infected by viruses. Interferon forms antiviral proteins to help protect uninfected cells and inhibit viral growth. There are three types of human interferon:

• alpha (from white blood cells)

• beta (from fibroblasts)

Complements

Complements are proteins found in blood that combine to create substances that phagocytise (ingest) bacteria.

Histamine

This is a chemical released by a variety of tissue cells. This includes mast cells, basophils (a type of white blood cell) and platelets. The release of histamine causes vasodilation to bring more blood to the area of injury or infection. It also increases vascular permeability to allow fluid to enter the damaged area and dilute the toxins released.

Inflammation

Inflammation is a sequence of events involving chemical and cellular activation that destroys pathogens and aids in the repair of tissues. It is a tissue response and symptoms include localised redness, swelling, heat and pain. The major actions that occur during an inflammation response include the following:

• The blood vessels dilate, resulting in an increase in blood volume (hyperaemia) to the affected area.

• Capillary permeability increases, causing tissues to become red, swollen, warm and painful.

• White blood cells invade the area and help to control pathogens by phagocytosis.

• In the case of bacterial infections, pus may form.

• Body fluids collect in the inflamed tissues. These fluids contain fibrinogen and other blood factors that promote clotting.

• Fibroblasts may appear and a connective tissue sac may be formed around the injured tissues.

• Phagocytic cells remove dead cells and other debris from the site of inflammation.

• New cells are formed by cellular reproduction to replace dead injured ones.

Phagocytosis

Neutrophils and monocytes are the most active phagocytic cells of the blood. Neutrophils are able to engulf and ingest smaller particles while monocytes can phagocytise larger ones. Moncoytes give rise to macrophages (large scavenger cells) which become fixed in various tissues and attached at the inner walls of the blood and lymphatic vessels.

Macrophage detects bacteria

Macrophage detects bacteria

Macrophage surrounds bacteria

Macrophage engulfs bacteria and digests them

Macrophage surrounds bacteria

Macrophage engulfs bacteria and digests them

Fig 6.7 Phagocytosis

Fever

An individual is said to have a fever if their body temperature is maintained above 37.28°C (99°F). The increase in temperature during a fever tends to inhibit some viruses and bacteria. It also speeds up the body's metabolism and, thereby, increases the activity of defence cells.

5 Common Skin Problems Answered

5 Common Skin Problems Answered

Our skin may just feel like a mere shield that protects us from the world outside. But, the fact is, its more than just the mask that keeps your insides in. It is a very unique and remarkable complex organ that reflects our general health.

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