Question

What immune system obstacles would bacteria encounter as they make initial contact with the skin of a hand and then enter the body through a cut in the skin? Discuss these obstacles in the order that the bacteria would encounter them.

Answer 1

First line of defence

Skin as a first line physical barrier preventing the microbes entering into the body they secrete swet from sabaceous glands their secretions consisting of high salt concentration prevent bacteria to enter the skin

If the skin is cut then the blood produces a clot formation which seals the wound and prevents microbes from entering.

The surfaces of the body the skin, digestive system, and the lining of the nose are covered by a community of microbes called the normal body flora. They help to protect a host from becoming infected with more harmful micro-organisms by acting as a physical barrier.

The normal body flora colonises these linings which reduces the area available for pathogens to attach to and become established. It also means that the harmful microbes have to compete with the normal body flora for nutrients. The average human gut contains around 1 kg of these good bacteria which is equivalent to one bag of sugar.

The respiratory system – the nose and passageways leading to the lungs – is lined with cells that produce sticky fluid called mucus that traps invading microbes and dust. Tiny hairs called cilia move in a wave-like motion and waft the microbes and dust particles up to the throat, where they are either coughed or sneezed out or swallowed and then passed out of the body in faeces.

The body produces several antimicrobial substances that kill or stop microbes from growing. For example the enzymes in tears and saliva break down bacteria.

The stomach produces acid which destroys many of the microbes that enter the body in food and drink.

Urine as it flows through the urinary system flushes microbes out of the bladder and urethra.

Second line of defence

If microbes do manage to get inside the body then the second line of defence is activated. This is also non-specific as it stops any type of microbe. Phagocytes are a type of white blood cell that move by amoeboid action. They send out pseudopodia which allows them to surround invading microbes and engulf them. Phagocytes release digestive enzymes which break down the trapped microbes before they can do any harm. This process is called phagocytosis.