Immune systemImmune system By the end of the lesson you should

be able to Outline the stages in phagocytosis. Describe how antibodies work and

how they are specific.

First lines of defenceFirst lines of defence

skin prevents entry

tears antibacterial enzymes

saliva antibacterial enzymes

stomach acid low pH kills harmful microbes

mucus linings traps dirt and microbes

“good” gut bacteria out compete bad

PathogensPathogens = disease causing micro-organisms

bacteria virus fungi, protozoa, parasite, prion

Second lines of defenceSecond lines of defence Involves white blood cells

Non-specific response invading pathogens are

targeted by macrophages Specific response

lymphocytes produce chemicals called antibodies that target specific pathogens

PhagocytesPhagocytes

PhagocytesPhagocytes Monocytes and macrophagesMonocytes and macrophages

Provide a non-specific Provide a non-specific response to infectionresponse to infection

http://www.microbelibrary.org/images/tterry/anim/phago053.html

PhagocytosisPhagocytosis Stages in phagocytosis

1. Phagocyte detects chemicals released by a foreign intruder (e.g. bacteria)

2. Phagocyte moves up the concentration gradient towards the intruder

3. The phagocyte adheres to the foreign cell and engulfs it in a vacuole by an infolding of the cell membrane.

4. Lysosomes (organelles which are rich in digestive enzymes & found in the phagocytes cytoplasm) fuse with the vacuole & release their contents into it.

PhagocytosisPhagocytosis5. The bacterium is digested by the

enzymes, and the breakdown products are absorbed by the phagocyte.

During infection, hundreds of phagocytes are needed.

Pus is dead bacteria and phagocytes!

link to phagocytosis

PusPus

An accumulation of : - dead phagocytes destroyed

bacteria dead cells

LymphocyteLymphocyte

LymphocytesLymphocytesProvide a specific immune response toinfectious diseases.

There are 2 types: -- T-cells - B-cells

They produce antibodies.

AntigensAntigens

all cells have surface markers called antigens.

body can recognise these as self or non-self (foreign)

Specific responseSpecific response Lymphocytes detect presence of

foreign antigens

Stimulated to produce specific proteins called antibodies.

antibodies combine with their specific antigen (like a lock and key)

this renders the pathogen harmless. = primary response

ImmunityImmunity

= the bodies ability to resist infection

can be natural or acquired

Immunological memoryImmunological memory after an infection is fought off some

lymphocytes become memory cells.

if same pathogen returns memory cells stimulate the produce the specific antibody very rapidly.

the infection is fought off before symptoms appear = secondary response

vaccines can stimulate same response

Immune systemImmune system

Can you Outline the stages in phagocytosis. Describe how antibodies work and

how they are specific.

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