4.1.4: Primary defences against pathoogens

Question 1

What is the BOdy’s min primary defence?

Answer 1

• The skin
• the outer layer is called the epidermis.
• It consists of many layers.
• Most of these are called keratinocytes.

Question 2

Describe the process of keratinisation.

Answer 2

• Keratinocytes produced by cells at the base of the epidermis.
• 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 cells reach the surface they are dead.
• Keratinised layer acts as an effective barrier to pathogens.

Question 3

What happens when there is damage to the skin that opens the body to infection?

Answer 3

-The body must prevent excess blood loss by forming a clot, making a temporary seal to prevent infection and repairing the skin.

Question 4

What does clotting involve?

Answer 4

• Calcium ions and at least 12 factors known as clotting factors.
• Clotting factors activate an enzyme cascade.

Question 5

What releases clotting factors?

Answer 5

Platelets and damaged tissue.

Question 6

Describe the formation of a scab after a clot forms.

Answer 6

• Clot forms
• Clot begins to dry out and form a scab.
• As the scab shrinks, it draws the sides of the cut together making a temporary seal under which the skin is repaired.

Question 7

Describe the process of skin repair under a scab.

Answer 7

• Deposition of fibrous collagen under scab.
• Stem cells in the epidermis then divide by mitosis and form new cells.
• New cells migrate to the edges of the cut and differentiate to form new skin.
• New blood vessels grow to supply oxygen and nutrients to the new tissues.
• Scab released when new skin is completed.

Question 8

Why are the airways, lungs and the digestive system at risk of infection?

Answer 8

• Exchange surfaces tend to be thinner and are less well protected from pathogens.
• The air and food we take in may harbour harmful microorganisms.

Question 9

What are exchange surfaces protected by?

Answer 9

• Mucous membranes.
• Epithelial layer contains goblet cells (mucus secreting cells)
• Extra mucus secreting glands under epithelium.

Question 10

How is mucus act as a primary defence?

Answer 10

• In airways, mucus lines the passages and traps any pathogens that may be in the air.
• ciliated cells waft the mucus to the top of the trachea.
• Mucus enters the oesophagus.
• Mucus swallowed and passes down digestive system.
• Pathogens killed by acidity of the stomach.

Question 11

How are coughs and sneezes primary defences?

Answer 11

• Irritation caused by presence of microorganisms or the toxins they release.
• reflex could include cough, sneeze or vomiting.
• sudden expulsion of air carries away with it the microorganism causing irritation.

Question 12

How can the presence of a microorganism lead to inflammation?

Answer 12

• Presence of microorganism in tissue detected by mast cells.
• Mast cells release histamine.
• Histamines cause vasodilation which makes capillary walls more permeable to white blood cells and proteins.
• Blood cells and phagocytic WBC leave the blood and enter the tissue fluid.
• This leads to an increased production of tissue fluid which causes the swelling (oedema)

Question 13

What happens to

Answer 13

• Excess tissue fluid is drained into the lymphatic system where lymphocytes are stored.
• This can lead to pathogens coming into contact with the lymphocytes and initiating a specific immune response.

Question 14

How are eyes a primary defence?

Answer 14

-protected by antibodies and enzymes in the tear fluid.

Question 15

How is the wax in the ear canal a primary defence?

Answer 15

-It traps pathogens

Question 16

What is the female reproductive system protected by?

Answer 16

• A mucus plug in the cervix.

- Relatively acidic conditions.