6: Immunity - PowerPoint Presentation

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6: Immunity

Lesson Objectives:Describe the different forms of immunity in the body. (AO1: D)Describe what is meant by ‘phagocytosis’ and how it acts as a defence mechanism. (AO2: C)Explain the role of lysosomes in phagocytosis. (AO1: A)

Keywords: lymphocytes, immunity, antigen,

humoral

, responseSlide2

One of these things is not like the others…..

What do these pictures have in common?

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Barriers that help prevent the entry of pathogens into the body:A protective covering - the skin.Epithelia covered in mucus

- In the lungs pathogens are trapped by the mucus and pushed back in the trachea by the goblet cells into the stomach.Hydrochloric acid in stomach - low pH destroys the enzymes of the bacteria.Barriers to EntryAO1Slide4

There are two main types of white blood cell that protect your bodies from pathogens. Slide5

What are the main defence mechanisms of the body?

Defence mechanismsNon-specificResponse is immediate and the same for all pathogensSpecificResponse is slower and specific to each pathogenPhysical BarrierE.g. Skin

Phagocytosis

Cell-mediate response

T Lymphocytes

Humoral

response

B Lymphocytes

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Phagocytosis – In Greek phagein means ‘to devour’,

kytos means ‘cell’ and osis means ‘process’Bacteria are far too large to cross a cell membrane by diffusion or active transport. So they have to be engulfed by cells in the form of vesicles (fluid-filled cavity). This process is called phagocytosis . This type of white blood cell carried is called a phagocyte.Phagocytosis causes inflammation at the site of infection. This swollen are contains a mixture of dead pathogens and phagocytes, this is pus. The inflammation is caused by the release of histamine. Histamine causes dilation of the blood vessels, increasing the flow of blood, increasing the number of phagocytes to the area. PhagocytosisAO1Slide7

Phagocytosis

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Chemical products of the pathogen attract the phagocyte to move towards it.

The phagocyte attaches itself to the surface of the pathogen.The phagocyte engulfs the pathogen to form a vesicle, known as a phagosome.Lysosomes move towards the vesicle and fuse with it. Enzymes within the lysosome break down the pathogen. The process is the same as the digestion of food in the intestine, namely hydrolysis of insoluble molecules into smaller soluble ones.The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm everything else is discharged. PhagocytosisAO1Slide10
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Questions

What is a lysosome and what is inside it?An enzyme called lysozyme breaks down the cell walls of bacteria. Among other places, it is found in tears. Suggest a reason why this is so.What purpose does the phagosome have?PhagocytosisAO2/3Slide13

Lymphocytes are already present in the body, approximately 10million different types.Lymphocytes should be able to differentiate between own body cells and foreign bodies.

So ‘antigens’, proteins on the cell-surface membrane help the lymphocytes to differentiate between self and foreign cells. LymphocytesAO1Slide14

Immune responses that are specific to individual forms of infection are slower to act at first but provide long term immunity. This uses a type of white blood cell called a

lymphocyte and there are two types:B lymphocytes (B cells) are associated with humoral immunity (will be covered in lesson).T lymphocytes (T cells) are associated with cell-mediated immunity. LymphocytesAO1Slide15

Cell-mediated immunityT lymphocytes

are the white blood cell that responds to foreign or infected cells. This includes bacteria, viruses and cancer cells as well as transplanted tissues as they are genetically different. T lymphocytes can distinguish these cells from your own cells because:Phagocytes that have engulfed and broken down a pathogen present some of the pathogens antigens on their own cell-surface membrane.body cells invaded by a virus also manage to present some of the viral antigens on their cell- surface membrane as a sign of distress.Cancer cells likewise present antigens on their surface.These are called antigen-presenting cells as they present the antigens of other cells on their cell-surface membrane.Causes and symptomsAO1Slide16

As T lymphocytes will only respond to antigens that are attached to a

body cell (rather than those in body fluids or on a bacteria), this type of response is called cell-mediated immunity. The stages in the response of T lymphocytes to a infection are as follows:Causes and symptomsAO1Slide17

Pathogens invade body cells are taken in by phagocytosis.

The body cell or phagocyte presents antigens from the pathogen on its cell-surface membrane.Receptors (proteins) on certain T helper cells fit exactly onto these antigens.This activates other T cells to divide rapidly by mitosis and form a clone.The cloned T cells:Develop into T memory cells that enable a rapid response to future infections from the same pathogen.Stimulate phagocytes to engulf pathogens by phagocytosisStimulate B lymphocytes to divide.Kill infected cellsSlide18

Types of T cellT Helper

cells release cytokines which attract new macrophages to the infected area and stimulate phagocytosis as well as stimulating B cell division.T killer cells destroy virally infected cells and cancer cells by crating a protein that causes holes in the infected cells membrane. This makes the membrane freely preamble and the cell dies. This process is called lysis. T memory cells are clones of the original T lymphocyte that live in the body for many years and are present in great numbers causing a quick response to secondary infection by the same pathogen. Causes and symptomsAO1