Infection / Immunity plus Vaccine Extended Response

What are pathogens?

Disease causing organisms

What are infectious diseases

diseases spread from one person to another (aka communicable disease)

How does the human body protect from invading organisms

Body has internal defences if pathogen gets past external defences
Invaders may cause disease if they overcome body’s defences

What are some examples of pathogens

Bacteria Viruses , fungi and parasites

What are the characteristics of Bacteria

Prokaryotes
Microscopic
Dna floats freely in Cytoplasm
DNA may be in strands or also in the form of circular plasmid
Classified based on shape

What prokaryote mean?

Unicellular organisms with simple internal structure

Are bacteria harmful to people?

Some of them as most bacteria are harmless and beneficial (commensal bacteria)
The harmful ones are called pathogenic bacteria

What are pathogenic bacteria

Bacteria that is harmful and will produce toxins, multiply and damage tissues or induce allergic responses

what are commensal bacteria

bacteria that live normally on or in humans
(can be pathogenic in the wrong loc)

What are the characteristics of Viruses

Smaller than bacteria (needs electron microscope to be seen
All contain genetic material (DNA OR RNA)
Genetic material surrounded by a protein coat
Some have an external lipid envelope

How do viruses reproduce?

Since they are not living they need a host
-Infects living cells and inject DNA/RNA into cells DNA and informs the cell to make more copies → damages, changes or kills host cell
- The type of cell they invade will determine the symptoms

What are bacteriophages

viruses that invade bacteria

what are the two categories in pathogen transmission?

Contagious , Vectors

What is the definition of contagious

Passed directly from one person to another

What is the definitions of Vectors

Intermediate hosts of the pathogen (eg Mosquitoes)

What are the types of pathogen transmission?

Contact, Ingestion, Body fluids, Droplets , Air borne and vectors

How are pathogens transmitted through contact

Spread of pathogen by physical contact (stis)
Direct → Physical touch with the infected person
Indirect → Touching a surface / object the infected person has prev touched

How are pathogens transmitted through ingestion

food or drink that is contaminated with pathogens eg Salmonella
(indirect)

How are pathogens transmitted through body fluid

Blood or body fluids from an infected person come into contact with muscous membranes or blood stream of an uninfected person
direct (mostly intercouse
Indirect (needles)

How are pathogens transmitted through droplets

tiny droplets containing pathogen are emitted from infect person by breathing talking, sneezing or coughing and then they are taking in by uninfected people by breathing/ eating
eg covid

How are pathogens transmitted airborne?

Exhaled droplets can evaporate and be inhaled by others (measles)
(indirect)

How are pathogens transmitted through vectors

animals (mosquitoes , ticks) transfer pathogens by contaminating food/ water or biting uninfected people (malaria, lyme disease)
-indirect

What are the types of defences against disease?

Non - Specific and Specific

what is the definition of non specific defense?

Works against all pathogens the same way (internal and external

what is the definition of specific defense?

Directed at a particular pathogen

What parts of the body are part of the external non-specific defence

Skin
Mucous Membranes
Hairs
Cilia
Acids
Lysozymes
Cerumen
Flushing Action

how is skin apart of the external non specific defense

Protective barrier outside of body also contains harmless bacteria, sebum and sweat

what is harmless bacterias role in non specific defence externally on the skin

Harmless bacteria (commensals) → Pathogens find it hard to become established on skin

what is Sebums role in non specific defence externally on the skin

Sebum → Produced by oil glands in skin → contains substances that kill some pathogenic bacteria

what is Sweat role in non specific defence externally on the skin

Sweat → secreted onto skin, contains salts and fatty acids that prevent growth of microorganisms

What is the role of mucous membranes in external non specific defence

Line body cavities that open to exterior
- Secrete mucous → inhibits entry of microorganisms to organs of body (digestive urinary, reproductive and respiratory this way)

What does hair do in non specific defense externally?

Found in nose cavity and ears → traps large particles

What does cilia do in non specific defense externally?

tiny hair like projections from epithelial cells that have a beating motion
- Moves mucous containing foreign particles / microorganisms towards thraot to be coughed up or swallowed
→ nasal cavity , trachea, bronchia

What does acids do in non specific defense externally?

kills many bacteria and reduces growth of microorganisms (stomach juice, vagina , sweat and urine)

What does lysozyme do in non specific defense externally?

enzyme that kills bacteria (found in tear, saliva, swear , sebum)

What does cerumen do in non specific defense externally?

(ear wax) → protects outer ear against infection (slightly acidic and contains lysozymes

What does the flushing action do in non specific defense externally?

urine, tears, sweat, saliva → prevents bacterial growth

What are types of protective reflexes

Sneezing , Coughing , Vomiting and diarrhoea

What is the protective reflex of sneezing?

Stimulated by irritation of walls of nasal cavity
- Caused by noxious fumes and dust particles
- Forceful expulsion of air from lungs carries mucous, foreign particles out through nose/ mouth

What is the protective reflex of coughing

Stimulated by irritation in lower respiratory tract (carina, bronchi and bronchioles)
- Air is forced from lungs to try and remove irritant
- Air drives mucous up trachea towards throat / mouth

What is the protective reflex of vomiting

psychological stimuli, excessive stretching of stomach , bacterial toxins
→ caused by contraction of muscles of abdomen and diaphragm (not contraction of stomach) that expels stomach contents

What is the protective reflex of diarrhoea?

irritation of small / large intestines by bacteria, viruses, protozoans
→ Causes increase peristalsis of intestines, moves contents quickly → no time for water to be reabsorbed = watery faeces

What range of internal non specific defences exist to counterattack the pathogen

Phagocytic cells
Inflammatory response
Fever

What are the types of phagocytic cells

leucocytes
phagocytes
Monocytes and Macrophages
Neutrophils
Dendritic cells

what are leucocytes?

white blood cells, many types

what are phagocytes?

white blood cells (leucocytes) that engulf and digest microorganisms and cell debris (phagocytosis)
- Attempt to eliminate pathogens before infection occurs

What are monocytes and macrophages

when tissues are infected or inflamed - monocytes leave the bloodstream and enter tissues
- Differentiate into macrophages (large phagocytic cells)
- Some move through tissue searching for pathogens
- Others fixed in place

What are neutrophils

most abundant leucocyte
first cells to move into tissue to deal with infection
- Important for killing pathogens inside cells
- Short life span - Make up most of the pus that forms during an infection

what are dendritic cells

slightly different to macrophages and neutrophils as they don’t just phagocytose
Detects, engulf and process foreign particles (antigen presenting cells)
Used with the specific immune response

What is the definition of inflammation

response to any damage to tissues

What is the purpose of the inflammatory response

Reduce spread of pathogens
Destroy and prevent entry of additional pathogens
Remove damaged tissue and cell debris
Begin repair of damaged tissue

What are the four signs of inflammation

redness, swelling , heat and pain

What are mast cells

specialized leucocytes present in most tissues - stimulate and coordinate inflammation by releasing chemicals (when stimulating by mechanical or chemicals change)

What does histamine do?

Increases blood flow through area (vasodilation) and causes walls of capillaries to be more permeable
→ increased amount of fluid escapes from the blood capillaries into tissues (causes the heat/redness and escape of fluid causes swelling)

What does heparin do?

prevents clotting in immediate area of injury
- clot forms around damaged area and slows spread of pathogen in healthy tissues

What is the 1st step for the inflammatory response

1.Chemicals (complement proteins) released by mast cells attract phagocytes to the area to consume pathogens and cell debris

What is the 2nd step for the inflammatory response

Abnormal conditions in tissue simulate pain receptors causing pain to be felt

What is the 3rd step for the inflammatory response

Phagocytes filled with bacteria, debris and dead cells begin to die

What is the 4th step for the inflammatory response

Dead phagocytes + tissue fluid forms pus

What is the 5th step for the inflammatory response

New cells are produced by mitosis and repair of the damaged tissue takes place

What is a fever?

During an infection white blood cells release a substance called pyrogens which acts directly on the hypothalamus to regulate temperature

What does a fever cause

Causes an elevation of body temp (hypothal resets the body thermostat to higher lvl)
-Causes person to feel cold (body uses thermoregulation responses to bring body temp up)

What are homeostasis mechanisms to counteract fever and bring down body temp

Vasoconstriction
Shivering

What is vasoconstriction

Reduces heat loss through the skin via radiation/ convection

What is shivering

increases heat production as the skeletal muscle cells are performing a higher rate of cell respiration as they oscillate

How does a fever inhibit growth of some bacteria and viruses

B and V are temperature sensitive
-Heat speeds up rate of chemical reactions which may help body cells to repair themselves more quickly during a disease

When does the fever stop

When the body temp reaches “crisis” which the fever breaks
-Normal body temp “set point” is restored
Homeostatic mechs kick in to bring body temp down

What does the lymphatic system consist of (non specific defense)

Network of lymph capillaries joined to larger lymph vessels
-Lymph nodes, located along length of some lymph vessels

What does the lymphatic system main function

collect the fluid that escapes from blood capillaries and return it to circulatory system.
(also important for internal defense against pathogens)

what does lymph contain

Lymph entering lymph nodes contains cell debris, foreign particles and microorganisms

How is the lymphatic system defend against pathogens (internal non specific)

- Each lymph node contains lymphoid tissue
- Larger particles (bacteria) trapped in meshwork of fibres as lymph flows through spaces in nodes
- Macrophages destroy these particles via phagocytosis
- When infections occur, formation lymphocytes increases and lymph nodes can become swollen / sore

What is specific defenses

Directed towards a particular pathogen
- Involves production of antibodies that are effective against specific pathogens and identification and destruction of specific pathogens
- Can be produced when a person is infected or is vaccinated

What is the homeostatic mechanism?

Deals with the invasion and restores internal environment to normal conditions. It has two parts:
Humoral and Cell mediated

What is the humoral part of the homeostatic mechanism

Production of antibodies circulating in the bloodstream and lymph to attack pathogens

What is the cell mediated response part of homeostatic mechanism

Forms special lymphocytes that are involved int he intracellular phase of infections

What does both antibody mediated (humoral) and cell mediated immunity have in common

both involve lymphoid tissue (found in lymph nodes, spleen)
- Most lymphoid tissue composed of two types of lymphocytes (b and t cells)

what is the b cells and t cell table so cool

What are antigens

Any substance capable of causing specific immune response → trigger thebody to produce specific antibodies
There are three types

What are the three types of antigens

large molecules
Self antigens
Non Self antigens

What are large molecules (antigens)

Can be proteins , carbohydrates . lipids or nucleic acids, egg white , toxins

What are self antigens (antigens)

Large molecule produces in a person’s own body (do not normally cause an immune response)

What is a non self antigen (antigen)

foreign compounds that do trigger an immune response

what are antibodies

Y- shaped specialised protein that is produced in response to a non-self antigen
-Belong to a group of proteins call immunoglobins
-Antibody produced can combine with antigen to form an antigen-antibody complex

-lock and key model where antigens are specific to an antibody due to specific shape of binding site

Therefore, every entigen has its own specific antibody

How is the antibody site unique?

Through a complex of process of gene restructuring, each antibody’s binding site is unique. Up to a theoretical one million trillion antibodies are possible.

What is antibody mediated immunity?

Production and release of antibodies into blood and lymph
- Gives resistance to viruses, bacteria and bacterial toxins before these microorganisms / substances enter the body’s cells
- Lymphoid tissue contains 1000s of type B cells → each responsive to specific antigen

What do antigen presenting cells do?

When a non- self antigen enters the body, the antigen presenting cells (can be macrophages, b cells and dendritic cells)
- Detect the presence of the antigen
-Engulf and digest the pathogen
-Small parts of the pathogen move to cell surface
→ Antigen presenting cell will present antigen directly to B lymphocyte and help T lymphocyte

What does the T lymphocyte then do? (Antibody meditated immunity)

The T lymphocyte will then produce substances (cytokines) that also act to activate B- cells

What happens when antigen activates specific B- cells

THey enlarge and divide into groups of cells (clone)
Becomes two clones → Plasma cells , Memory Cells

What are Plasma cells (clones of B cells)

Most clones become plasma cells → Secrete specific antibodies that attach to active site of the antigen. (Circulate through blood and lymph)

What are memory cells (clones of B cells)

other B cells become memory cells which spread to all body tissues (allows response to occur more rapidly, should antigen invade body again

What is the primary response (antibody mediated immunity)

Primary response - First exposure to an antigen
- As plasma cells secrete antibodies, level increases in blood plasma
- Fairly slow, often taking days to build up large amounts of antibodies
- One it reaches a peak, it begins to decline quite quickly
- Leaves the immune system with a memory of that particular antigen
- Still likely to get sick (symptoms) as not enough antibodies produced fast enough to deal with infection

What is the secondary response (antibody mediated immunity)

Secondary exposure - Subsequent exposure to the same antigen
- Response is faster due to presence and activity of memory cells
- Plasma cells are formed very quickly and antibody levels in blood plasma rise rapidly and remain in body for longer
- Therefore response is so quick, the pathogen has little opportunity to exert any noticable effect on body thus no illness results

What do antibodies and antigens combine to make

All antibodies combine with the antigen for which they are specific to form an antigen-antibody complex

What may antibodies do?

-Combine with foreign enzymes / bacterial toxins or inactivate them by inhibiting reaction with other cells or compounds
-Bind to surface of viruses and prevent them from entering cells
-Coat bacteria so its more easily consumed by phagocytes
-Cause particles such as bacteria, viruses or foreign blood to agglutinate
- Dissolve organisms
- React with soluble substances to make them insoluble

What is cell mediated immunity

Provides resistance to the intracellular phase of bacterial/ viral infection, fungi and parasites, rejection of transplants and cancer cells
- T cells are involved int his process

What are T cells

Occur in different areas of lymphoid tissue to B cells
T cells like B cells only respond to one particular antigen
-When virus/ bacterium enters body, antigen presenting cells present the fragments to Helper T cells that are programmed for that antigen
→ Thus they become activated/ sensitized

What do activated T cells do

Enlarge and divide making a clone
→ Some cells of clone remain in lymphoid tissue as memory cells

What happens to the t cells that do not become memory cells

they develop further producing 3 types of t cells

wat are the three types of t cells that get developed further

killer t cells (cytotoxic)
Helper t cells
Supressor T cells

what are killer T cells (cytotoxic)

Migrate to site of infection, deal with antigen, attach to invading cells and secret substance that destroys antigen ( and infected cell)