4.1.4(Primary defences against disease)

Define the term primary defences

• Defences which prevent pathogens from entering the body

State and explain whether primary defences are specific or non-specific

• They are non-specific, as they will prevent the entrance of any pathogen into the body

State the 5 methods of disease primary defences

• The skin

• Blood clotting

• Mucous membranes

• Coughing and Sneezing

• Inflammation

Describe the process of keratinisation

• Keratinocytes migrate out to the surface of the skin.

• As they migrate, they dry out and the cytoplasm is replaced by the protein keratin

• By the time that the cells reach the surface, they are no longer alive

• This process takes about 30 days to complete

Describe the process of blood clotting

• If the blood vessel is damaged, collagen fibres in the blood vessel wall become exposed to blood

• Platelets from the blood rapidly stick to the collagen fibres

• Platelets then release clotting factors, and in the presence of Ca2+ and vitamin K, Prothrombin is converted to Thrombin

• Thrombin acts as an enzyme and catalyses the reaction of converting soluble fibrinogen into insoluble fibrin

• Fibrin forms a network of fibres that traps blood cells, platelets and debris to help form a clot

Describe how a scab forms and how the skin under it is repaired

• A scab forms from the clot drying

• While the clot is drying, the edges of the skin are drawn together

• Under the scab, out layer skin cells divide by mitosis and migrate to the edges of the wound

• New blood vessels grow in the skin

• The skin the contracts to bring the cut together

• collagen is deposited in the wound to help this process

Describe where the mucous membrane is needed

• The mucous membrane is needed in areas of the body where there are exchange surfaces which are are thinner and less protected from pathogens

• Such as the airways, lungs, the digestive system

Describe how the mucous membrane works

• The epithelial layer contains goblet cells which secret mucus.

• There are also extra secreting glands under the epithelium

• The epithelium also has cilia which are able to move in a coordinated fashion and waft the layer of mucus along.

• Pathogens and dust are trapped in the mucus and wafted away by the ciliated epithelium

Describe how inflammation happen

• Mast cells detect the presence of micro organisms in the tissue which release histamine

• Histamine causes vasodilation and make the capillaries more permeable to white blood cells and some proteins

• Blood plasma and phagocytic white blood cells leave the blood and enter tissue fluid

• This leads to increased production of tissue fluid, which causes swelling

Explain how swelling can be helpful to fight off pathogens

• swelling isolates any pathogens that may have entered the damaged tissue

• Excess tissue fluid from the swelling can go is drained into the lymphatic system where lymphocytes are stored

• This can lead to pathogens coming into contact with more lymphocytes and initiating specific immune responses

Describe and explain how expulsive reflexes help against fighting pathogens

• Areas that are prone to attack are sensitive and respond to the irritation that may be caused by the presence of microorganisms or the toxins that they release

• These reflexes include coughing sneezing and vomiting. which are all attempts to expel foreign objects from the body which also includes pathogens

State a few other examples of primary defences

• Eyes produce tears which contain hydrolytic enzymes that kill pathogens

• Ear canal is lines with wax which traps pathogens

• The female reproductive system is protected by a mucus plug in the cervix

• The skin is also a chemical barrier, it produces oils which inhibit the growth of pathogens and also sweat contains hydrolytic enzymes which kill pathogens