ATAR Human Biology - Immune System

bacteria

- living organisms; live independently

- contains both RNA and DNA

- reproduced via binnary fission (asexual reproduction where a single organism splits into two identical daughter cells)

virus

- non-living organisms (need a host to survive)

- contains either DNA or RNA

- reproduced by making copies of the host cells

bacteria (structure)

- prokaryotes (no nucleus or membrane bound organelles)

- has a cell wall made up of a carbohydrate-protein complex

transmission of bacteria

- direct contact

- in water droplet

- touching infected surfaces

virus (structure)

- coating of protein to protect the DNA or RNA

- lipid-protein envelope

- no cell wall, nucleus, or membrane-bound organelles (bc they are non-living)

transmission of a virus

- person to person via body fluid,

- environment to person,

- animal to person

transmission methods - direct

actually touching the infected person

transmission methods - indirect

touching an object the infected person has touched. No human to human contact.

transmission methods - ingestion

food or drink that is contaminated with pathogens

transmission methods - body fluids

blood or body fluids from an infected person come into contact with the mucous membranes or bloodstream of an uninfected person

transmission methods - droplets

tiny droplets containing pathogens are emitted from infected person by breathing, talking, sneezing, or coughing, then they are taken in by uninfected people or eating

transmission methods - airborne

exhaled droplets can evaporate and be inhaled by others

transmission methods - vectors

animals (e.g. insects, ticks or mites) transfer pathogens by contaminating food or water or biting uninfected people

vectors vs contagious

contagious means passed directly from one person to another. vectors means passed via intermediate hosts of the pathogen

external defenses - skin

a waterproof barrier that prevents pathogens from entering our internal body

external defenses - sebum

an oily secretion (from hair follicles on the skin) that is slightly acidic, creating a hostile environment that can kill pathogens

external defenses - sweat

a secretion of water, salt and fatty acid (from sweat glands on the skin) that prevents the growth of pathogens

external defenses - mucus membrane

- secretes mucus onto the outer lining of the digestive tract, preventing pathogens from entering the body

external defenses - saliva

saliva contains lysozyme; an enzyme that creates a flushing action, preventing pathogens from entering the internal body

stomach acid

stomach acid contains enzymes that creates a hostile environment for pathogens, killing many of them

uthera

flushing action prevents bacterial growth and eliminates pathogens

tears

tears contains lysozyme; an enzyme that creates a flushing action, preventing pathogens from entering the internal body

cilia

small, hair-like structures that moves pathogen to the throat to be coughed out

phagocytosis

1. the phagocyte is chemically attracted to a foreign antigen on the surface of a pathogen.

2. the phagocyte engulfs the pathogen via endocytosis, forming a vacuole

3. a lysosome binds to the vacuole and releases digestive enzyme, breaking down the pathogen into harmless, soluble debris

4. this is removed from the phagocyte by exocytosis

inflammation response

1. when there is tissue damage - mast cells release histamine & heparin into the tissue fluid

2. heparin prevents clotting in the immediate area of injury. clots instead from around it, slowing the spread of pathogens to healthy tissues

3. histamine stimulates vasodilation & attracts phagocytes to the area, promoting phagocytosis. Macrophages consume the pathogens

4. the dead phagocytes and tissue fluid forms pus; a yellow liquid. new cells are produced by mitosis to repair the damaged tissues

role of histamine in the inflammation response

- causes vasodilation (blood vessels widen), which increases blood flow to the area → redness and heat

- makes blood vessels more permeable, allowing WBC, proteins, and fluid to leave the blood and enter the tissue → swelling.

- attracts phagocytes to the area, allowing phagocytosis to occur

- triggers itching and sometimes pain

role of heparin in inflammation response

- acts as an anticoagulant (prevents blood from clotting too quickly at the site).

- this helps keep blood flowing to the injured or infected area, making sure immune cells and nutrients can reach the tissue.

define inflammation & 3 purposes

Inflammation is a response to any tissue damage; its purpose it to:

1. Reduce spread, destroy and prevent entry of pathogens

2. Remove damaged tissue and cell debris

3. Begin repair of damaged tissue

4 signs of inflammation

The four signs of inflammation are; redness, swelling, heat and pain

define fever & 2 purposes

- A fever is a temporary increase in the body's thermostat, stimulated by the release of pyrogens.

This causes the body to activate heat production mechanisms (e.g. vasoconstriction, shivering), which helps to:

1. inhibit the growth of pathogens

2. increase the rate of chemical reactions

process of a fever

1. Infection detected → White blood cells release pyrogens, triggering the hypothalamus to raise the body's thermostat

2. Thermoreceptors detect that body temperature is lower than the set point. The body feels cold and vasoconstriction/shivering occur to raise temperature

3. When the infection is under control, the hypothalamus resets the set point to normal.

The body then feels hot and activates cooling mechanisms such as vasodilation and sweating

benefits of a fever

1. high temperatures can inhibit growth of bacteria and viruses.

2. high temperatures can increase the rate of chemical reactions, helping repair body cells faster.

b-cells

- produced & mature in the bone marrow.

- end up in lymphoid tissues (lymph nodes, spleen, tonsils, thymus) after maturation.

t-cells

- produced in bone marrow but mature in the thymus

antibody mediated response

1. When a non-self antigen enters the body, the antigen presenting cells (APCs): detect, engulf and digest them. Small parts of pathogen move to the cell surface and present these to lymphocytes.

2. B-cells & helper T-cells recognise the antigen.

3. T-cell produces cytokines to activate B-cells. B-cells enlarge and divides via mitosis

4. Most of these cells become plasma cells, which start secreting specific antibodies that match the antigen. These antibodies travel in the bloodstream and bind to the pathogen's antigens.

5. The remaining cells become memory B cells, which spread to all body tissues and stay there long term to allow for a faster response if the pathogen were to invade the body again.

primary response

- plasma cells secrete antibodies into bloodsteam

- Fairly slow - once it reaches a peak, it begins to decline quite quickly.

- Leaves the immune system with a memory cell of that particular antigen.

- Still likely to get sick - not enough antibodies are produced quick enough to deal with infection.

secondary response

- Response is faster due to activity of memory cells.

- plasma cells are formed very quickly, antibody levels in blood plasma rise rapidly and remain in the body for longer.

- response is so quick, the pathogen has little opportunity to have any noticeable effect on the body - no illness results.

cell mediated response

1. When a non-self-antigen enters the body, the antigen presenting cells (APCs) detect, engulf and digest them. small parts of pathogen move to the cell surface, and present these to lymphocytes.

2. T-cells recongises the antigen

3. T-cells become sensitised, they enlarge and divide via mitosis. This creates a large clone of identical T-cells, which specialises into three main types: Killer, helper and suppressor.

4. Some of these T-cells also become memory cells; which spread to all body tissues and stay there after the infection, to allow for a faster response if the pathogen were to invade the body again.

killer t-cells

travels directly to the site of infection, binds to the antigen & secretes a toxic substance that causes it to break down

helper t-cells

stimulates other T-cells to promote action & attracts macrophages to the site of infection to engulf and destroy pathogens via phagocytosis

suppressor t-cells

secretes a substance that stops the activity of T-cells after infection is controlled to prevent overreaction

what are antibodies?

-globular proteins produced in response to a non-self-antigen

- secreted by B lymphocytes.

- combine with antigens at specific sites to create an antigen-antibody complex

what are the six ways antibodies work? (IDRBBC)

1. immobilise viruses, bacteria and other foreign substances via agglutination

2. dissolve harmful organisms

3. react with soluble harmful substances to make them insoluble

4. bind to forgein enzymes to inactivate them by inhibiting reactions with other cells

5. bind to the surface of viruses & prevent them from entering cells

6. coat bacteria so it is easily consumed by phagocytes