Primary Non-specific Defences in Animals

How do non-specific defences work?

The body has a number of barriers to prevent the entry of pathogens.

Name the primary non-specific defences against pathogens in animals

• Skin

• Blood clotting

• Wound repair

• Inflammation

• Expulsive reflexes

• Mucous membranes

Skin

- The outer layer of cells is the epidermis. It acts as a barrier.

- Sebum is an oily substance that prevents the growth of pathogens

- Evaporation of sweat from the skin leaves behind a salt residue

- Skin flora (healthy microorganisms) try to outcompete any pathogens

Blood Clotting & Wound Repair

1. Tissue becomes damaged

2. Platelets are released

3. These platelets release substances via a cascade of events, resulting in the formation of fibrin

4. Fibrin forms a mesh of fibres in which platelets and blood cells get trapped.

5. This dries to form a scab, which prevents bleeding

Inflammation

A condition in which the body reacts to injury, irritation, or infection.

Is inflammation a local response?

Yes

In inflammation, what happens when a tissue is damaged?

Mast cells detect an infection, and they release histamines and cytokines

What do cytokines do?

They attract more phagocytes to the infected area so they can dispose of the pathogens by phagocytosis

What does histamine do?

Arterioles dilate, so there is increased blood flow to the area

This causes localised heat and redness

The increase in temperature helps prevent the pathogens from reproducing

What does histamine do to capillaries?

The capillaries become more leaky, allowing for more tissue fluid to form.

This brings more white blood cells to the area, an also causes more fluid to enter into the lymphatic system.

The Lymphatic System

- Excess tissue fluid is drained into the lymphatic system

- Pathogens will enter the lymph and be transported to the lymph nodes

- Lymph nodes swell to produce phagocytes and lymphocytes

Mucous Membranes

Airways and the digestive system are exposed and lined with mucous secreting cells (goblet cells).

How do mucous membranes prevent pathogens from entering?

- Mucus in the airways (trachea, bronchi and bronchioles) trap the particles (virus, bacteria, pollen etc) that we breathed in

- The particles are then moved towards the back of the throat by cilia

- Cilia are small hair-like structures on the surface of cells that beat and move in a coordinated manner to shift material along the epithelial cell

Expulsive Reflex

Cough or sneeze

How do expulsive reflexes prevent pathogens from entering?

- When a pathogen irritates the lining of an airway it can trigger an expulsive reflex

- This expelled air contains secretions from the respiratory tract along with the foreign particles that have entered

Other Primary Defences

- Stomach acid

- Antibodies in tears

- Wax in ears and nose

- Acidic conditions in uterus

Lysozymes

Antimicrobial enzymes that breakdown the cell wall of bacteria.

Where are lysozymes found?

Tears