0.4 Non-specific responses against disease

Syllabus

• The body's external defence mechanisms against pathogens include features of the:

  • skin

  • digestive tract

  • urogenital tract

  • respiratory system

  • the ear

  • the eye

• Pathogens that enter the body are targeted by non-specific immune responses of inflammation & fever.

Non-specific defences

• Body's first line of defence against pathogens.

• Not directed at a particular/specific pathogen.

• Work against all pathogens in the same way.

• Can be classified into external and internal.

External defences: skin

• Effective barrier covering all outside of the body.

• Prevents entry of pathogens into the body.

• Sebum produced by the sebaceous glands in the skin contains substances that inhibit the growth of bacteria. Also helps to keep the skin from drying out and cracking.

• Sweat secreted onto the skin contains lysozymes which is a substance that kills pathogens.

• Contains harmless and useful bacteria that occupy the skin surface and prevent pathogens from gaining space on the skin.

External defences: mucous membranes

• Body contains cavities that open to the outside such as mouth, nose and urethra.

• These cavities are lined with mucus membranes.

• Mucus membranes secrete mucus which inhibits the entry of pathogens into the body by trapping them in their sticky fluid.

External defences: hair

• Found in the nose and ears.

• Help to trap larger pathogens and prevent them from gaining entry to the body.

• Hair in the nasal cavity also helps to slow air movement to trap pathogens.

External defences: cilia

• Tiny finger-like projections from cells.

• Waft in the same direction to (with move mucus (with trapped pathogens) to the throat where it can be swallowed.

External defences: acids

• Stomach juices contain hydrochloric acid that kills pathogens.

• Vagina has acidic secretions that kill pathogens.

• Sweat is slightly acidic to prevent the growth of pathogens.

External defences: lysozyme

• Enzyme that kills bacteria.

• Found in sweat, tears, saliva, nasal cavity and cerumen.

External defences: cerumen

• Found in the ear (earwax).

• Provides a physical barrier to pathogens entering the body.

External defences: flushing action of body fluids

• Urine, sweat, saliva and tears help to flush and remove pathogens from the body.

Protective reflexes

• Automatic, involuntary response to a stimulus.

• Help to protect against pathogens.

• reflexes help to protect against infection

4 reflexes against infection

1. Sneezing

2. Coughing

3. Vomiting

4. Diarrhoea

Reflexes: sneezing

irritation of the walls of the nasal cavity can stimulate a sneeze. This forceful expulsion of air from the lungs carries mucus out of body which may carry pathogens.

Reflexes: coughing

irritation of the bronchi or bronchioles can cause coughing. This will forcefully remove mucus from the lungs which may carry pathogens.

Reflexes: vomiting

contraction of the muscles of the abdomen and diaphragm expels the contents of the stomach. Stimulus can be excessive stretching of the stomach or bacterial toxins.

Reflexes: diarrhoea

caused by irritation of the small or large intestine by a pathogen. Irritation causes increased contractions of the muscles in the wall of the intestines. This will move the pathogen more quickly through the intestines.

Internal non-specific defences

If pathogens get past the external defences then the internal non-specifc responses is the next line of defence.

Cells included in internal non-specific defences

• phagocytes

• Leukocytes

• Macrophages

Internal non-specific defences: leukocytes

• Several different types

• Leave the blood capillaries and migrate to site of infection/injury.

• Will either engulf and digest bacteria or secrete substances that destroy bacteria.

Internal non-specific defences: macrophages

• Develop from leucocytes.

• Some remain fixed in place and destroy pathogens that come past.

• Other move around looking for pathogens to destroy.

Internal non-specific defences: phagocytes

• are a type of white blood cells that can engulf and digest micro organisms

• Two types: leukocytes and macrophages

Function of the inflammatory response

• reduce the spread of pathogens

• Destroy and prevent entry of additional pathogens

• Remove damaged tissue and cell debris

• Begin repair of damaged tissue

Signs of the inflammatory response

• redness

• Heat

• Swelling

• Pain

Main events in the inflammatory response PART 1

• Damage to tissue stimulates mast cell (type of WBC) to release histamine, heparin and other chemicals into the area.

• A clot of fluid forms around the damaged area to slow the spread of pathogens

Inflammatory response: histamine

• causes vasodilation of the blood vessels which leads to increased blood flow to the area = redness/heat.

• It also causes increased permeability of the capillaries. Fluid is lost from the capillaries = swelling.

Inflammatory response: heparin

• prevents blood from clotting in the immediate area. This ensures adequate amounts of blood carrying phagocytes will flow to area.

Main events in the inflammatory response PART 2

• Complement system proteins and other chemicals released by the mast cells will attract macrophages and leucocytes(mainly neutrophils) to the area. They will engulf and destroy the pathogens by phagocytosis.

• Changes in the tissues will stimulate the pain receptors causing the person to feel pain.

• Leucocytes (mainly neutrophils) will die as they fill with bacteria / debris = yellow fluid called pus forms.

• When the response is successful in removing the pathogen = tissue repair and healing will occur via mitosis.

Flow chart of inflammatory response

Fever

• During the course of an infection a person may experience an increase in body temperature.

• A body temperature above 37.2 degrees Celsius is considered having a

  temperature (febrile).

How a fever can assist the body in fighting pathogens

• Interfering with viral replication

• Inhibit growth and reproduction of some bacteria

• Increasing production of killer T cells which speeds up the specific mediated immune response.

• Increases heart rate and blood flow which enable lymphocytes to reach sites of infection quicker.

• Increase metabolic activity which assists tissue repair.

How a fever occurs

• Macrophages are attracted to the infected area by release of chemicals from the mast cells.

• Macrophages engulf and destroy pathogens. • Macrophages secretes cytokines/chemicals that produce chemical pyrogen(interleukin 1).

• Pyrogen (interleukin 1) is released into the bloodstream. • Alters the body thermostat to make the body think it is cooler than it actually is.

• Hypothalamus responds by initiating vasoconstriction and shivering.

• Body temperature rises = fever.

Fever mechanism flow chart

Lymphatic system

• Is an important part of the body's internal defence against pathogens.

• Consists of lymph nodes.

• All lymph will pass through a lymph nodes before entering back into the blood circulation.

Lymph nodes function

• remove debris and pathogens from the lymph and are thus sometimes referred to as the “filters of the lymph”

Bacteria in lymph

• Any bacteria that infects the interstitial fluid are taken up by the lymphatic capillaries and transported to a lymph node.

Lymph nodes contain..

• contains lymphoid tissue

• Cells are arranged in a network of fibres - this helps to trap pathogens

Lymphatic system: macrophages

• macrophages in the lymph node will destroy the foreign particles by phagocytosis

Lymphatic system: when an infection occurs

• the formation of lymphocytes increases and more macrophages rush to the area to kill pathogens

• This results in the lymph nodes becoming swollen and sore