primary non-specific defence against pathogens

Question 1

Keeping pathogens out

Answer 1

two lines of defense against pathogens

Primary non-specific defence

always present/ rapidly activated

Defend against all pathogens in the same way

Specific immune response

Specific to each pathogen it encounters

Slower to respond

Question 2

Skin

Answer 2

Covers the body and prevents the entry of pathogens

Outer layer of skin contains keratin(tough fibrous protein)

Surface of skin is dry <– consists of layer of hardened dead cells

Sweat evaporates leaving salt behind

pH on the skin surface slightly acidic <– fatty acids secreted

Skin harbours healthy microorganisms that outcompete pathogens for space on its surface

Question 3

Sebum

Answer 3

Oily/waxy substance

Produced by sebaceous glands

Coats and protects skin with antimicrobial properties

Question 4

HCl

Answer 4

Secreted by parietal cells of stomach

Kills bacteria ingested with food

Mucus secreted along length of gut to protect against acid, enzymes and pathogens

Question 5

Mucous membranes

Answer 5

Line in the gut, respiratory system & reproductive system

Epithelial cells interspersed with goblet cells that secrete mucus

Sticky/slimy

Made up of glycoprotein molecules

Pathogens and dusts trapped in mucus, cilia beat to move the mucus along, to be removed

Contains lysosomes which destroy bacterial and fungal cell walls

Contains phagocytes which remove pathogens

Question 6

Expulsive reflexes e.g. sneezing, coughing

Answer 6

Occurs when pathogens irritate lining of the airway

Eject pathogens from the upper airway tract

Allows transmission of pathogens between hosts

Vomiting and diarrhoea expel gut contents and remove pathogens in this way

Question 7

Lysozymes

Answer 7

Secreted into the body fluids

Act as an antibacterial agent by breaking down bacterial and fungal cell walls

e.g. tears, sweat, urine, acid in the stomach, breastmilk, mucus and blood

Question 8

stages of Blood clotting

Answer 8

1. Walls of the blood vessel is damaged, blood is exposed to collagen fibers
2. Platelets stick to the exposed collagen fibres forming a plug to stop bleeding
3. Platelets become activated and release clotting factors
4. Through a complex cascade, clotting factors convert prothrombin(inactive plasma protein) into active thrombin,Process requires calcium, vitamin k
5. Thrombin catalyses the conversion of inactive, soluble fibrinogen into active, insoluble fibrin
6. Fibrin forms a fibrous mesh that traps red blood cells and strengths the platelet plug, forming a clot
7. Blood clot eventually resorbed

Question 9

Blood clotting

Answer 9

When skin/ mucous membrane are injured, pathogens can enter the body. Blood will clot rapidly to seal the wound

Platelets meet collagen in the skin/ the wall of the damaged blood vessel –> adhere & begin to secrete several substances like

 -enzyme that triggers a cascade of reactions that results in the formation of a blood clot 

 -serotonin – make the smooth muscle in the walls of the blood vessels contract, reduce the supply of blood to that area 

Clot dries out to form a scab(tough, hard), keeps pathogens out

Circulating anticoagulants such as heparin normally prevent blood from clotting

Question 10

Wound repair

Answer 10

Platelets secrete growth factors –> stimulate stem cells

Formation of new blood vessels

Production of collagen fibres which are deposited

Formation of granulation tissue that fills the wound

Stem cells divide by mitosis and migrate over new tissue

Wound contraction by contractile cells

Death of unwanted cells

Once epidermis has reached normal thickness, scrab sloughs off