C.3.2 - Defence against disease

Receptors

Integral membrane proteins

Ligand

Hormones, neurotransmitters, proteins, peptides, ions etc. that bind to a receptor and creates a change within the cell

Antigens

Ligands on viruses that allow endocytosis (the virus is englufed by a cell and can change the function), typically glycoproteins

Why do viruses need to be internalised 

In order to take over the function of the cell to produce more viruses 

Innate immune system

Kills pathogens that don’t belong to the body - autoimmune disease causes it to attack the body

Adaptive immune system

Recognises pathogens and knows how to destroy them, relied on when the innate immune system is overrun 

Pathogen types

• Viruses

• Bacteria

• Protozoa

• Fungi

Skin layers

1. Epidermis

2. Dermis

3. Hypodermis

Mucous membrane functions 

Secrete mucous to trap pathogens 

Blood clotting

Collagen exposure at a wound attracts platelets, creating a platelet plug to temporarily block the blood flow. Fibrinogen also attracts and exposure turns fibrinogen into fibrin, which layers and holds the platelets in place.

Blood clotting functions

• Prevents excessive blood loss

• Seals open wounds to pathogens

Fibrinogen to fibrin mechanism

Exposure to chemicals outside the blood vessel turns polar fibrinogen into non-polar fibrin, so fibrinogen within the blood vessel doesn’t randomly clot. 

Clotting factors pathway 

Clotting factors, Prothrombin → thrombin, fibrinogen → fibrin 

Antigen-antibody binding

Antigens and antibodies fit the lock-and-key model, so they can bind to specific sites

Antibodies

Y-shaped proteins that bind to specific antigens - can collect them in a large cluster for easier neutralisation. Binding site forms the “stem” of the Y-shape.

Phagocytosis

Phagocytes engulf virus-infected cells (recognised by Fc-region, which is different from person to person because it depends on DNA)

Antibody production not triggered by pathogens

Blood types: type A produces anti-B antibodies, type B produces anti-A antigens, type AB produces none and type O produces both anti-A and B.

Autoimmune disease exp.

Diabetes

Antibody production 

Phagocytes engulf viruses and pass antigens to the T-helper cell, which then finds the B-cell with a matching antibody. The T-cell binds to the B-cell. Cytokines diffuse from the T-cell to the B-cell, activating it, and the B-cell now starts to produce antobodies for that specific pathogen.  

B-cell division

Activated B-cell divides, producing more cells that can produce the same antibodies 

Memory cells

Differentiated B-cells that are long-lives and remember the specific pathogen