Topic 11- Animal Physiology

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11.1 - Defence Against Infectious Diseases

11.1.1: Describe the process of blood clotting

Clotting prevents the body from losing too much blood and prevents pathogens from entering the body; maintains blood pressure.

Process begins by releasing platelets (cell fragments that circulate bloodstream w/ red and white blood cells). The clotting factors, released from platelets, activate prothrombin to become thrombin. This leads to catyalysing conversion of soluble fibrinogen into insoluble fibrin. Fibrinogen is found in bloodstream. Red blood cells are trapped in fibrin, preventing flow. Once platelets reach it, they will produce sticky extensions and connect. As they contract, liquid is forced out; clot is formed.

11.1.2: Outline the principle of challenge and response

Challenge and Response

The principle means that immunity to a specific pathogen is only encountered in the body The response begins when the immune system recognizes the antigens on the pathogen and begins taking steps to fight it. The white blood cells recognize the antigen, engulf it, then reform antigen on cell membrane. The cell goes to lymph nodes, where B-cells are found. The white blood cells locate B-cell that corresponds to antigen, and present them to each other. It is possible for more than one B-cell to be required (polyclonal response). All these B-cells will start cloning to form different types of plasma cell, making different antibodies to fight all of the antigens on the pathogen.

Clonal Selection

This process involves identifying the B-cell that corresponds to the antigen. The B-cell will clone itself to make plasma cells, which in turn produce and excrete appropriate antibodies. T killer cells (cytotoxic cells) are also formed to detect and destroy infected cells.

Memory Cells

The body's memory cells allow for long-term protection against diseases. They are produced from B-cells after clonal selection, so the corresponding pathogen must attack the body before immunity can be formed.

11.1.3: Define active and passive immunity

Active Immunity- due to production of antibodies by organism itself after body's defence mechanisms have been stimulated y antigens

Passive Immunity- when antibodies are acquired from another organism in which active immunity has been stimulated

Natural Immunity- due to infection

Artificial Immunity- due to inoculation with a vaccine

11.1.4: Explain antibody production

Immune systems make huge range of antibodies but they cannot remain in body all at once. B-cells are stored, which can then begin producing antibodies if necessary; process takes only a few days.

The first stage is when the macrophages (white blood cells) encounter antigen. They take it in, attach it to the MHC proteins in plasma membrane. The helper T-cells recognize antigens using receptors on their membranes, and bind to the macrophage that carries it. The macrophage passes on a signal that causes the helper T-cell to be activated.

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