3.5.3 Responses in the Human [D] The Defence System Objectives – What you will need to know from this section The Immune System Outline the Defence System including skin/mucous membranes of breathing, reproduction and digestive systems Outline the nature & role of Phagocytic white blood cells. Outline the Specific Defence System, including antigen/antibody response Define the term: Induced Immunity Explain the terms: Vaccination & Immunisation

An Immune System Immunity is the ability of an organism to resist infection. Pathogens are micro-organisms [microbes] that cause disease. The human body is designed to protect itself from foreign cells or invaders, and we have two lines of defence ‑ general and specific.

Our General Defence System consists of: Skin, Mucous membranes, Platelets and White blood cells.

General defence system consists of: Ø Barrier to entry: the skin and mucous membrane lining of the respiratory, digestive and reproductive tract. Ø The skin, acting as a structural barrier, secretes chemicals from the sebaceous glands that harm or kill bacteria. Ø  The respiratory and digestive tracts as well as other organs of the body secrete mucus and/or further chemicals that may remove foreign particles.

Composition of Blood Solids Liquid Plasma Red Blood Cells White Blood Cells Platelets

LEARNING CHECK What is Immunity? What are pathogens? List the parts of our General defence system. List the composition of blood. Give one function for each part named.

Our Specific Defence System involves : an antigen-antibody response, involving speciliased white blood cells, called lymphocytes and monocytes [macrophages]. 1. Lymphocytes - Stored in lymphatic system (spleen, lymph nodes, tonsils, adenoids & thymus gland), have large nucleus and make antibodies. (25% of white cells) lymphocyte 2. Monocytes – digest bacteria, have kidney shaped nucleus & live for 6-9 days (5% of white cells)

Monocytes -- [Macrophages] Ø  Monocytes are phagocytic white blood cells – also called macrophages Ø  These engulf bacteria and viruses upon contact. “Eating” germ Germ Monocyte Ø  Others secrete chemicals that stimulate general defence and cause fever to destroy microbes at high temperatures.

Monocyte engulfs an invader Monocyte engulfs a bacterium

LEARNING CHECK What is meant by a “specific defence system”? Name two types of White cell involved in this system. What is a lymphocyte? What is a Monocyte? What does “engulf” mean? Can you name an animals that engulfs its prey?

Specific defence system: Induced Immunity LYMPHATIC SYSTEM Ø Organs specific to the immune system: the spleen, thymus and lymph nodes. Ø Lymph and blood vessels contain cells called lymphocytes and monocytes – both are produced in the bone marrow and they respond to antigens.

Ø Antigens are any foreign molecules capable of triggering an antibody response. Germ (antigen) Antibody An antibody is a protein, made by a lymphocyte, which sticks to an antigen and marks it for destruction by other defence cells [monocytes]. “Eating” germ monocyte Ø Antigens may be found in bacterial cell walls, viral coats, foreign cells or produced in cancerous cells.

The lymphatic system consists of: • Lymphatic vessels that that return excess tissue fluid to the blood circulatory system. . • Lymph tissue [lymph nodes] that assist in fighting infection in the body.  

Three functions of the lymphatic system 1. Drainage – returns leaked fluid to the blood. 2. Transport – lipids (fats) are absorbed from the small intestine and carried to the skin or other organs for storage. 3. Defence – filters blood. Germs that invade the body will enter the blood or tissue fluid and eventually get filtered through the lymph and lymph nodes, where white cells attack and destroy them. Swollen glands are lymph nodes that are actively fighting germs. LYMPHATIC SYSTEM

Induced immunity is immunity due to antibody production. There are two types --‑ active and passive. Active immunity develops after an infection or after vaccination (immunisation). It provides long lasting protection. Passive immunity involves antibodies that we get from elsewhere, e.g. in the womb, or from mother’s milk. Mother’s antibodies

Active immunity A vaccine is a dead microbe that is injected into the body and triggers antibodies but does not cause the disease. If the real germ ever attacks you, the antibodies are present to remove it before it can cause the disease and do damage. You are then said to be immune to that disease. Passive immunity Passive immunity involves antibodies that we get from elsewhere. Since these are not produced by the body's own cells, it provides only short-lived protection.

LEARNING CHECK Give 3 functions of the Lymphatic system. Distinguish between an antigen and an antibody. What is Induced immunity? Distinguish between active and passive induced immunity. What ia a vaccine? Explain how vaccination gives us immunity.