Immunity

Question 1

What is immunity

Answer 1

Body has a wide range of defence mechanisms against pathogens
Body has non-specific and specific defence mechanisms

Question 2

What is non-specific mechanisms

Answer 2

Mechanisms that protect the body against a wide range of dangers
Usually present from birth
Sometimes termed innare

Question 3

What are specific mechanisms

Answer 3

Mechanisms directed against one specific invader
The body learns and remembers specific antigens building a immunological memory
Sometimes termed adaptive

Question 4

What is an antigen

Answer 4

Anything that stimulates an immune response

Question 5

What are the non specific defences

Answer 5

Epithelial barriers
Phagocytosis
Natural anti microbial substances
Inflammatory response
Immunological surveillance

Question 6

Describe the epithelial barriers

Answer 6

Consists of skin and mucous membranes
Healthy, intact skin is a barrier against pathogens
Examples of this are nose hair and cilia
Epithelial secretions e.g. oral are anti-bacterial and often acidic, containing antibodies and enzymes
Sebum and sweat contain antibacterial and anti fungal properties
The one way flow of urine from the bladder minimises the risk of infection ascending through the urethra into the bladder

Question 7

Describe the anti microbial substances

Answer 7

Saliva - washes away food debris to prevent bacterial growth, contains antibodies, lysosome and buffers to neutralise bacterial acids that promote dental decay
Lysosome- an anti-bacterial enzymes present in tears
Hydrocholic acid - present in gastric juice
Antibodies- protective proteins inactivate bacteria are found coating membranes exposed to external environment
Interferons - chemicals are produced by different cells which have been invaded and activate immune cells to prevent viral replication

Question 8

Describe phagocytosis

Answer 8

Neutrophils and macrophages are phagocytic cells
Phagocytes migrate to sites of inflammation and infection as they are attracted to chemicals that are released by invading microbes
Phagocytes attack, digest and destroy foreign cells, damaged cells and debris
They may also release a chemical which is toxic to invading microbes into the interstitial fluid
The chemicals released alert the immune system to presence of a threat

Question 9

Describe the inflammatory response

Answer 9

Purpose - to isolate, inactivate and remove both the causative agent and damaged tissue so healing can occur
Signs of inflammation are redness, heat, swelling and pain
Extremes of temp, pH, trauma and foreign bodies can trigger the response
What happens - increased blood flow, accumulation of tissue fluid, migration of leukocytes, increased core temperature, pain and suppuration (pus form )

Question 10

What substances are released in inflammatory response

Answer 10

Histamine ( from mast cells and basophils )
Serotonin ( from platelets, mast cells & basophils )
Prostaglandins ( most cells )
Heparin ( liver and mast cells )
Bradykinin ( tissues and blood )

Question 11

Describe increased blood flow in inflammatory response

Answer 11

Arterioles dilate, capillaries expand
Provides more oxygen and nutrients to the area
Responsible for the increased temperature, swelling and redness
Caused by local release of histamine and serotonin

Question 12

Describe accumulation of tissue fluid in inflammatory response

Answer 12

Fluid leaves blood vessels and moves into interstitial space
Caused by increased blood flow and histamine, serotonin and prostaglandins making capillary walls more permeable

Question 13

Describe migration of leukocytes in the inflammatory response

Answer 13

Loss of fluid from the blood thickens it
Slowing flow and allowing the normally fast-flowing white blood cells to make contact with and adhere to the vessel wall
Neutrophils adhere to the blood vessel lining and enters the tissues for phagocytosis
Macrophages begin phagocytosis after 24 hours

Question 14

Describe increased core temperature in inflammatory response

Answer 14

Inhibiting the growth and division of microbes while promoting the activity of phagocytes

Question 15

Describe pain in inflammatory response

Answer 15

Encourages protection
Local swelling compresses sensory nerve endings

Question 16

Describe suppuration in inflammatory response

Answer 16

Collection of material- dead phagocytes, dead cells, fibrin, inflammatory exudate and living and dead microbes

Question 17

Describe immunological surveillance

Answer 17

Natural killer cells - a type of non selective lymphocyte
They patrol the body searching for abnormal host cells
Cells that have been infected with a virus or mutated cells that might become malignant, frequently display unusual markers on their cell membranes which are recognised by NK cells
Having detected an abnormal cell, the NK cell immediately kills it

Question 18

What is specific immunity

Answer 18

When non specific defences are overwhelmed the immune system is activated
It involves T lymphocytes and B lymphocytes
Specificity means targeted to one antigen
Memory means a memory is created of each immuno- response, so if it is encountered again the response if faster and more powerful
Tolerance means doesn’t attack its own cells

Question 19

Describe lymphocytes in specific immunity

Answer 19

Make up 20-30 % of circulating WBCs
Most of them are found in lymphatic tissues rather than in the bloodstream
Lymphocytes include- NK cells, T cells and B cells
Each individual T and B cell carries antigen recognition molecules allowing only response to one antigen
The range of antigen recognition molecules is genetically determined

Question 20

Describe T cells in specific immunity

Answer 20

Produced in bone marrow
Migrate to the thymus gland and mature under the influence of the hormone thymus in
The T cell becomes specialised
The T cell becomes fully activated when they encounter infective connective tissues
The T cell are then fully mature and continue circulating the bloodstream and lymphoid organs
Mature T cells have been programmed to recognise only one type of antigen

Question 21

Describe B cells in specific immunity

Answer 21

Produced in bone marrow
And also matured in bone marrow
They produce antibodies which are proteins that bind to and destroy antigens
Each B cell targets one specific antigen

Question 22

What are the two immune responses

Answer 22

Cell mediated and antibody mediated

Question 23

Describe the cell mediated response

Answer 23

When T cells encounter the antigen for the 1st time and become sensitised to it
T cells can’t detect free antigen in body fluids
To recognise & be activated by antigen, the T cell must be presented with it on the membrane of another cell
These cells are called antigen- presenting cells ( APCs )
Many different cell types present antigen to T cells and so important in activating immune system

Question 24

What are the 4 types of T cells

Answer 24

Cytotoxic, helper, regulatory and memory

Question 25

Describe cytotoxic T cells

Answer 25

Inactivate anything carrying antigens by releasing powerful toxins
Main function is to destroy abnormal body cells which are infected or cancerous

Question 26

Describe helper T cells

Answer 26

Most common of T cells
Essential for cell mediated and antibody mediated immunity
Produce cytokines ( interleukins and interferons ) to support and promote CD8 cells and macrophages
Stimulates B cells to produce antibodies

Question 27

Describe regulatory T cells

Answer 27

These cells act as brakes, turning off activated T and B cells
This limits the powerful and potentially damaging effects of the immune response
Regulatory T cells are involved in immunological tolerance ; they help prevent the development of autoimmunity and protect the fetus in pregnancy

Question 28

Describe memory T cells

Answer 28

Respond rapidly to subsequent encounters with the same antigen

Question 29

Describe the antibody mediated immunity

Answer 29

B cells recognise and bind antigens particles directly without APCs
B cells make antibodies
Some of these antibodies are released into the bloodstream for distribution around the body but each B cell also display the antibody that it makes on its cell membrane called antigen receptors
Helper T cells the enable the B cell to enlarge and proliferating making memory B cells and plasma cells

Question 30

Describe antibodies

Answer 30

Antibodies belong to a group of glycoproteins known as immunoglobulins
Bind to antigens, labelling them as targets for other defence cells such as cytotoxic T cells and macrophages
Bind to bacterial toxins, neutralising them

Question 31

Describe the classification of antibodies

Answer 31

According to the structure and location of their heavy chains
They have two chains made of amino acids
They have two light chains made of polypeptides
The chains are linked by disulphide bonds making the antibodies a Y shape or a T shape

Question 32

Describe the complement system

Answer 32

A system of about 20 proteins found in the blood and tissues, it is activated by the presence of immune complexes and by foreign sugars on bacterial cell walls
Complement:
Binds to and damages, bacterial cell walls, destroying the microbe
Binds to bacterial cell walls, stimulating phagocytosis by neutrophils and macrophages
Attracts phagocytic cells e.g. neutrophils into an area of infection

Question 33

Describe the acquired immunity

Answer 33

The immune response to an antigen following the 1st exposure is called primary response which is a slow and delayed rise in antibody levels, produces memory cells for future infection
Second and subsequent exposures give rise to a secondary response, which is much faster and more powerful because of memory cells

Question 34

Describe active immunity

Answer 34

The individual has responded to an antigen and produced their own antibodies, lymphocytes are activated and the memory cells formed provide long-lasting resistance

Question 35

Describe passive immunity

Answer 35

The individual is given antibodies produced by someone else
The antibodies break down with time,so passive immunity is relatively brief

Question 36

Describe natural immunity

Answer 36

The body may be stimulated to produce its own antibodies by either having the disease or having a sub clinical infection
Acquired before birth by the passage of maternal antibodies across the placenta to the fetus and to the baby in breast milk

Question 37

Describe artificial immunity

Answer 37

In response to the administration of dead or live artificially weakened pathogens ( vaccines) or deactivated toxins
Ready- made antibodies, in human or animal serum are injected into the recipient

Question 38

Describe anti D immunoglobulin

Answer 38

If the mother is rhesus - and the fetus is rhesus +, and their blood mixes, the mother will mount an immune response to the rhesus antigens on the fetal blood cells as mother’s immune system recognises them as foreign bodies
These antibodies made by the mother can pass through the placenta and destroy the fetal RBCs in the fetal circulation
This can cause fetal anaemia, fetal hydrops or jaundice
Administering anti D immunoglobulin can help prevent this

Question 39

Describe the lymphatic system and immunity

Answer 39

Maintains the fluid balance by returning tissue fluid into the venous blood stream
Contains lymphoid structures which contain lymphocytes e.g. tonsils, thymus, spleen and bone marrow
Lymph nodes filter lymphatic fluid ( lymph) as it passes through them
Organic material is destroyed in the lymph nodes by antibodies & macrophages via phagocytosis
Fluid may pass through several nodes before being filtered
Activated T and B cells multiply in lymph nodes

Question 40

Describe tonsils

Answer 40

Located in a protective ring under the mucous membranes in the mouth and back of the throat
This ring is called the pharyngeal lymphoid ring
This helps protect against bacteria that may invade tissues in the area around the openings between the nasal and oral cavities

Question 41

Describe the thymus

Answer 41

Immature lymphocytes are matured in the fetal thymus
Begins secreting a group of hormones and other regulators that enable lymphocytes to develop into mature T cells