unit 3 - diseases and immunity

pathogen

disease causing microorganism

infectious diseases

are caused by invasion of pathogens in the form of viruses and bacteria can be transmitted from one host to another

disease

any harmful deviation from the normal structure or functional state of an organism, generally associated with certain signs and symptoms and differing in nature from physical injury.

infectious

communicable/transmissible

bacteria structure

• bacteria is living and can live inside or outside of the body

• there are good bacteria in the body in the stomach to help digestion and absorption of food.

• they are unicellular

• rod, spherical or spiral shaped

• lack of nucleus, DNA that is free in the cytoplasm

• cell wall

• capsule

• flagella

pathogenic action of bacteria

• bacteria divide rapidly via most binary fusion

• they can communicate with each other by chemical signalling and acts as one organism

• pathogenic bacteria either releases toxins in the host, damage cells and tissues by breaking them down for food, or induce an allergic response

treatment of bacteria

bacteria can be treated with antibiotics as antibiotics aim to attack and kill living microorganisms, and bacteria is living.

viruses structure

• not living and need a host to survive

• spherical with spikes

• some beneficial viruses present in our gut, skin and blood that can kill undesirable bacteria and more dangerous viruses

• they are smaller than bacteria

• consist of genetic material, protein coat and a layer of fat

• can also assume different shapes such as spacecraft, spirals, cylinders and ball shapes

pathogenic action of viruses

• entry of the virus into the host cell

• can replicate the viral genome producing new viral proteins

• those proteins assemble into new viruses and are then released from the host cell ready to infect new/other cells

treatment of viruses

• cant be treated with antibiotics as they are not living

• antiviral meds and vaccines

• hand washing and cleaning surfaces to destroy lipid layer of viruses outside the body

transmission of pathogens

• direct and indirect contact

• transfer of bodily fluids

• vectors

• contaminated food and water

direct contact

actual physical contact e.g. skin infections, conjunctivitis and STDs

how to avoid: covering skin, avoiding physical contact, physical contraceptives

indirect contact

touching an object that has been touched by an infected individual or airborne and droplets of pathogen

how to avoid: covering nose and mouth, washing hands regularly and sanitising

transfer of bodily fluids

transfer of pathogens via blood or other bodily fluids from an infected person to mucous membranes or bloodstream of an uninfected person

fluids = semen, blood, saliva

mucous membranes in the = nose, mouth, throat and genitals

vectors

the transfer of pathogens via another animal (mites, ticks, mosquitos)

can be direct (a bite), or indirect (fruit flies contaminating food and then eating the fruit)

contaminated food and water

the ingestion of contaminated food and drinks due to the lack of hygiene

e.g. salmonella food poisoning

mechanisms of protection

skin, digestive tract, urogenital tract, respiratory system, ears and eyes

skin

the skin is an impervious layer that does not allow things to enter the body, acting as a physical barrier.

oils on the skin prevent pathogenic organisms from entering the body also

digestive tract

acidic juices that kill many microorganisms

urogenital tract

acidic secretions of the vagina to inhibit the growth of pathogens, urine flow also prevents bacteria growth due to its acidic nature inhibiting pathogen growth also

respiratory system

mucous layer traps microorganisms, hair and mucous prevent them from entering acting as filters, sneezing/coughing, mouth cavity has mucous membrane to trap microorganisms and is cleansed constantly by saliva

ear

cerumen/ear wax inhibits bacteria growth

eyes

tears cleanse the eye and have chemical that inhibit bacteria growth

non-specific immunity

phagocytes and inflammation

carries out the same way every time and defends the body from pathogens the same every time no matter the pathogen.

phagocytes

type of white blood cell that performs phagocytosis - where phagocytes engulf and destroy pathogens in blood and in tissues

2 types of phagocytes

neutrophils - immediate response, get to the site first to engulf pathogens

macrophages - also engulf pathogens and do a lot of the heavy lifting as they are actually capable of displaying antigens, help with the body’s immunity to these responses.

stages of phagocytosis

• the pathogen releases chemical that act as signals attracting phagocytes to the area of infection (this relies on a chemical or physical change in the body to occur)

• the phagocyte will then arrive and recognise the foreign body, binding to it and triggering phagocyte to engulf the pathogen

• this forms a phagosome (vesicle containing the pathogen in the phagocyte)

• lysosomes, then fuse with phagosomes creating phagolysosomes

• the pathogen is then broken down and cleaned up by enzymes

inflammation

a response to any damage to tissues in the body - it is localised to an area and is non-specific

why inflammation occurs

• slows down the speed of pathogens and prevent entry of additional pathogens

• removes damaged tissue and cell debris and repair damage - speeds up healing

process of inflammation

• Stimulus (physical or chemical change) = specialised mast cells are activated

• Mast cells release histamine and heparin

• Histamine causes blood vessels to dilate to increase blood flow and the permeability of the capillaries to allow for immune response cells to get to affected area/tissue

• More fluid enters the area = heat, redness and swelling

• Heparin prevents clotting in the immediate area to allow for blood flow, and a clot forms around the area to slow the spread of the pathogen

• Chemicals from this attract phagocytes = engulfing of pathogens and debris (phagocytosis)

• Pain receptors are stimulated due to fluid, redness and swelling = person feels pain in the area

• Phagocytes then die and form pus to get rid of the engulfed material

• Mitosis occurs to repair damaged tissue and mast cells cease to release signal for infection

4 signs of inflammation

pain, swelling, redness, and heat

fever

when core temp raises above 38 degrees Celsius

stages of fever

• macrophages that respond to and ingest pathogens produce a chemical called interleukin-1, and bacteria/pathogen itself releases pyrogens/toxins into the blood

• these in the blood causes the body to think that it is cooler than it really is

• thermoreceptors in the hypothalamus detect this ‘low’ core temp, and it responds through homeostatic processes to raise the internal body temp beyond 38 degrees

fever benefit in immunity

• increased metabolic rate = speed up of tissue repair

• increase HR and blood flow = gets more lymphocytes and phagocytes to reach the site of infection

• high temp can inhibit the growth of some pathogens/ kill some pathogens

• the heat increases the effect of killer t cells and speed up the immune response

• increase the effect of interferon protein which inhibits viral replication

specific defence

defences directed towards a particular pathogen, can be naturally or artificially

the immune response

a homeostatic mechanism

when microorganisms invade the body, the immune response helps restore the internal environment back to normal

2 types of responses: antibody mediated/humoral immunity, cell mediated

lymphocytes

white blood cells

b and t

b- mature in the bone marrow and involved in antibody mediated response

t- mature in the thymus and end up in lymphoid tissue, involved in cell mediated response

antigens

substances capable of causing an immune response, triggering both antibody and cell mediated responses

include:

• carbs, protein, lipids

• whole part of pathogen

• tissues from transplants

• allergens

self antigens- produced by the own body and do not cause an immune response

non-self-antigens - foreign and cause an immune response

they markers on the outside of the pathogen that allow antibodies t identify and attach to, in order to destroy the pathogen

antibodies

produced in response to a non-self antigen

produced by plasma cells - clones of b cells

specific to type of antigens

active sites of antibody and antigen attach to cause an antigen-antibody complex

Antigen presenting cells

macrophages, dendritic cells, an undifferentiated b cells

detect non-self antigens on the tissue, engulf the pathogen, produce small fragments on the surface of the cell, and present the antigen to t and b cells which are able to respond and further initiate responses.

antibody mediated immunity

involves the production and release of antibodies into the blood and lymph, will provide resistance to viruses, bacteria, and bacterial toxins before these microorganisms enter the body’s cells.

actions of antibodies once a antigen-antibody complex is made

• precipitation (soluble antigens become insoluble)

• agglutination (causes the clumping of antigens)

• neutralisation (masks the dangerous parts of the antigen)

• inflammation (release histamine, increasing immune cell mobility)

• complement (complement proteins perforates the cell membrane)

= phagocytosis

steps to antibody mediated immunity

1. non-self antigen enters the blood or lymph, a macrophage engulfs it, and a specific b cell will encounter the antigen on the macrophages surface (antigen presenting cell)

2. antigen presenting cells also present to a helper t cell, releasing cytokines

3. antigens then bind to a receptor on the membrane of a specific b cell and cytokines travel to the b cell. this activates the b cell (sensitising it and enlarges)

4. b cells then swell, divide and form groups of cells called clones. most of them become plasma cells which secrete specific antibodies around the body (through the blood and extracellular) in order to reach the site of the invading pathogen

5. the antibodies then combine with antigens to form antigen-antibody complex

6. depending on the antibody and antigen, a response of either:

• agglutination

• precipitation

• neutralisation

• inflammation

or

• complement.. will occur

7. levels then decline as body’s internal conditions are restored

8. the remaining clones of b cells become memory b cells which remain in the lymphoid tissue. these will then spread around the body so that if the antigen is presented to the body again a more immediate and effective immune response can then occur - secondary response

9. plasma cells will then form more rapidly and immunity will be achieved as the person will not feel symptoms.

helper t cells

killer t cells

memory t cells

suppressor t cell