Page 168 - 84 human physiolofy part-1

Chapter 9

• Mucociliary escalator

The mucociliary clearance of the respiratory tract is an important defense mechanism against
foreign debris and inhaled pathogens. The cilia that lines the upper and lower airways are lined with a
thin layer of mucus. These beat rapidly to propel particles that are trapped in the mucus layer to the
pharynx. Defective mucociliary clearance predisposes our respiratory tracts to recurrent infections.
These cilial defects may be either congenital or acquired by infection, toxins or drugs.

Chemical Defenses

• Tears, saliva

Tears and saliva contain lysozyme, an antiseptic enzyme that attacks cell walls of bacteria and
breaks them down.

• Stomach acids

Glands in the stomach lining produce hydrocloric acid. This acid kills most invading organisms
that are swallowed and take up residence there.

Non-specific responses to infection - 2nd line of defense

We are born with built in nonspecific defenses that all respond in the same way to invading
pathogens. The outermost defense our body has is our skin. The sebaceous glands produce sweat and
sebum, which contain ANTISEPTIC properties which protect. This bacteria-killing substance called
LYZOSOME is also found in tears and saliva. Acidic urine in the urinary tract and friendly bacteria in
the genital tract prevent the multiplying of harmful organisms in these areas. Most invading organisms
in the stomach are killed by gland production of hydrochloric acid. These are a few examples of how
the outer defenses protect us. All outer defenses work together as the body's first line of defense.

Inflammatory response

Any break in the skin will allow bacteria to enter the body. These foreign microbes will cause
swelling and reddening at the site of injury. This reaction by the body is called an inflammatory
reaction or inflammatory response.

Swelling, redness, heat, and pain

Inflammation is characterized by the following quintet: swelling (tumor), redness (rubor), heat
(calor), pain (dolor) and dysfunction of the organs involved (functio laesa). When an injury occurs, a
capillary and several tissue cells are apt to rupture, releasing histamine and kinins. These cause the
capillaries to dilate, become more permeable, and leak fluid into these tissues. Dilation and fluid
leaking into the tissues causes swelling, redness, and heat. The swelling and kinins stimulate nerve
endings, causing pain. If there has been a break in the skin due to the injury, invading microbes may
enter. A common cause of inflammation after surgery is serous fluid. This is a mixture of plamsa,
lymph and interstitial fluids .seeping from the damaged cells and vessels. If enough serous fluid

168 | Human Physiology