Defences of the body to pathogens and parasites

1) Primary defence:

Physical barriers-prevent pathogens entering the body

e.g. coughing/sneezing/vomiting, skin (epithelia/keratin), nose hairs, cilia in trachea, blood clotting, lysosome (mucus layer in eye), eyelashes

2) Secondary defence:

Body reacts to the presence of any pathogen (mainly phagocytosis)

e.g. antimicrobial substances, inflammation (confines and destroys microorganisms and repairs tissues), fever (inhibits microbial growth and speeds up body reactions to aid repair)

3) Tertiary defence:

Carried out by lymphocytes once the pathogen has been identified by the immune system

Non-specific immune response:
(Doesn't matter what pathogen enters)

A physical,chemical and cellular defences that prevent microorganisms from entering the body

Specific immune response:

A response to a specific pathogen, involving the action of lymphocytes and the production of antibodies

The immune response

Define= The production of antibodies due to the introduction of a pathogen into the body. Involves:

1. Antigen presentation
2. Clonal selection (choosing the right shape antibody)
3. Clonal expansion (mitosis
4. Antibody production

Antigen= A foreign substance (usually a protein) to which lymphocytes respond

Antibody= An immunoglobulin (a specialized immune protein) produced because of the introduction of an antigen into the body, which posses the remarkable ability to combine with the very antigen that triggered its production. 

Structure:

Binding site= Bind attach to antigen
Disulphide bridge= Hold shape/ tertiary structure
Constant region= Attach/bind to phagocyte 
Hinge region= Allow molecule to bend/flex/bind with more than one pathogen 

How do they work?

1. Neutralisation-Antibodies covering the pathogen binding sites prevent the pathogen from binding to a host cell and entering the cell.

2. Agglutination-A large antibody can bind many pathogens together. The group of pathogens is too large to enter a host system.

Primary immune response:

• Involves naive B and T lymphocytes (but not the memory)
• Much slower and smaller than the secondary response

Secondary immune response:

• Much larger response (more antibodies secreted)
• Involves the B and T memory cells 
• Much faster due to the memory cells

Phagocytosis

1. The surface of the bacterium becomes coated with proteins called opsinins
2. Antibodies attach themselves to antigens on the surface of the bacterium
3. The bacterium produces chemicals that attract the neutrophils towards it. (An example of chemotaxis)
4. Proteins found in the host's plasma attach themselves to the antibodies that are attached to the bacterial antigens
5. Neutrophils attach to the opsinins coating the bacteria
6. Neutrophils engulf the bacterium to form a vesicle called a phagosome
7. Lysosomes move towards the vesicle and fuse with it, forming a phagolysosome
8. The enzymes within the lysosome digest the bacterium (They may also be toxins and chemicals such as hydrogen peroxide and free radicals in the lysosome that kill the bacteria)
9. The soluble products from digestion of the bacterium are absorbed into the cytoplasm of the neutrophil and may be used by that cell

White blood cells (WBC)

Phagocytes (Left branch):

1) Neutrophil

• Engulf through phagocytosis then die shortly after forming pus

2) Monocyte

Mature in the tissues to form:

1. Macrophages

• Accumulate and reside in organs
• Perform antigen presentation

2. Dendritic cells

• Perform antigen presentation

Lymphocytes (Right branch):

1) T cells

Involved in the cell-mediated response can be divided into:

1. Helper

• Activates T+B cells by releasing chemical messengers (cytokins) after binding to antigen.
• Also release toxic chemicals

2. Killer

• Produce toxic chemicals (e.g, hydrogen peroxide) after binding to a pathogen terminating it.

3. Memory

• Long-living cells
• Are the immunological memory
• Can differentiate into T-killer cells if reinfected

2) B cells

Involved in humoral response can be divided into:

1. Plasma

• Produce antibodies specific to the antigens on the pathogen

2. Memory

• Are the immunologial memory
• Can differentiate into B-plasma cells

Infectious diseases

Pathogen= An infectious agent that causes disease
Disease=When an organism suffers from an abnormal condition and its effectiveness is reduced
Infectious disease=A disease caused by a pathogen that can be transmitted
Non-infectious disease=A disease with a cause other than a pathogen, including genetic disorders and cancer

Cholera:

Causative agent= Vibrio Cholerae (there are many strains)

Affects= Small intestine wall (secreted choleragen damages the epithelium)

Symptoms= Severe diarrhoea, dehydration, weakness

Method of transmission= Waterborne, Lack of food sanitation, Due to human waste getting into the water supply 

Method of diagnosis= Microscopic analysis of faeces

Prevention and control:
Social=Awareness and education
Economic=Improve sewage control, provide chlorinated water 
Biological=Short-term vaccination, antibiotics for severe cases

Cure?= Salts and glucose given intravenously to rehydrate them

Measles:

Causative agent= Morbillivirus

Affects=Respiratory passages, lymph nodes, conjunctiva

Symptoms=Cough, chest cold, conjunctivitis, rash and fever (+child blindness)

Method of transmission=Airborne droplets (therefore highly infectious)

Method of diagnosis=Blood test, Saliva test

Prevention and control:

Social=Surveillance, encourage breast feeding

Economic=Provide vaccination

Biological=MMR Vaccination (need 93% immunity to prevent transmission), rarely affects <8yrs due to passive immunity

TB:

Causative agent= Mycobacterium Tuberculosis

Symptoms= Coughing blood, raking cough, chest pain, fever + sweating, weight loss (can cause meningitis/hunchback)

Affects=Macrophages, primarily in lungs, secondary in lymph nodes, bones and gut (Only 1 in 10 of those who have it become activated)

Method of transmission= Airborne (coughing/sneezing), uncooked meat, unpasteurised milk

Method of diagnosis=Sputum, Chest x-ray

Prevention and control:
Social= Prevent overcrowding, pasteurise milk, Destroy TB cattle
Economic= Contact tracing
Biological=Treated with drugs (6 month course of combination antibiotics), BCG vaccination

Global distribution=More prevelant in developing countries and poorly ventilated areas, becoming more of a problem due to worldwide travel

Cure?= Antibiotics

Malaria:

Causative agent= Plasmodium falciparum/vivax/ovale (many strains, some drug resistant, with different antigens that can conceal themselves within the cell)

Affects= Hepatocytes, Erthrocytes, brain

Symptoms= Fever, anaemia, headaches, shivering, muscle pain, sweating

Method of transmission= Vector (female anopheles mosquito)

Method of diagnosis= Blood test

Prevention:

1. Prevent reproduction of vector=Draining stagnant water or, cover it with oil, spray it with chemicals
2. Avoid being bitten by vector=nets, insect repellent, clothes
3. Stop parasite infecting us=Anti-malarial drugs 

Control= Vaccine development too slow to keep up with the different strains of the protoctist.

Global distribution= 90% of malaria deaths in sub-saharan Africa

HIV/AIDS:

Causative agent= Human immunodeficiency virus

Affects= T-helper lymphocytes, brain cells, doesn't kill you but makes you more vulnerable to other diseases

Symptoms:
HIV=flu-like
AIDS=opportunistic diseases, TB, pneumonia

Method of transmission= Unprotected sexual intercourse with an HIV positive person, sharing of contaminated needles, placenta, breast milk

Method of diagnosis= Blood test

Prevention and control:
Social=Education, public health measures, free condom programmes, contact tracing 
Economic=Widespread testing and blood donor screening can't be afforded in developed countries, needle exchange
Biological=Drug resistance, Blood donor screening

Global distribution=First reported in USA, Mainly now in sub-saharan Africa (34 million cases)

Cure?= No known cure but drug therapy can slow it down

Smallpox:

Causative agent= Variola

Method of transmission=Direct contact with infected bodily fluids

Symptoms= Visible marks on the skin

Cure?= 1977 smallpox became the first major disease to be eliminated from the globe due to the vaccination (the World Health Organization offered $1000 to the first person to report an active smallpox case)

The Lymphatic system

What is the lymphatic system?

Is a system where tissue fluid that does not re-enter the blood capillary can enter and be transported to then re-join the blood in the veins nearer the heart. 

How is the tissue fluid transported?

Blind ending lymph vessels, containing lymph (which contains the tissue fluid), are compressed due to body movements which therefore moves the lymph along and is directed by the semi-lunar valves.

What are lymph nodes?

At intervals along the lymph vessels are lymph nodes. These lymph nodes contain huge numbers of macrophages (phagocytes) and lymphocytes which produce antibodies in response to any bacteria, virus or other foreign material.

Tissue fluid

What is tissue fluid?

Is plasma that has leaked from capillaries.

How does it form?

There are gaps in between the endothelial cells of the capillaries. The small molecules in plasma are forced out through gaps by high Hydrostatic Pressure (due to blood pressure)

Compared to blood:
Composition:
(Identical except...)

• No red blood cells
• No platelets
• Fewer white blood cells
• No large plasma proteins

Other differences:

• Tissue fluid has lower hydrostatic pressure 
• Tissue fluid has higher water potential
• Tissue fluid is not contained in vessels

Compared to Lymphatic fluid:

Composition:

(Lymph has these differences...)

• More white blood cells
• More globular proteins (antibodies)
• Less glucose
• Fewer amino acids 
• More triglycerides (absorbed in ileum)

Other differences:

• Lymphatic fluid is contained in vessels

Blood Vessels

Artery:

Contains:

• Endothelium intima
• Thick Tunica Media (with smooth muscle and elastic fibres), to deal with the high pressure blood and allows the arteries to recoil
• Has a relatively thick tunica externa
• Relatively smaller lumen
• Has high pressure pulsitile blood

Function=To carry high pressure blood away from the heart 

Capillary:

Contains:

• Endothelium made up of 1 layer thick squamous epithelium (thin walls)
• 1 RBC thick lumen
• Average blood pressure

Function=Exchange vessel to the organs

Vein:

Contains:

• Endothelium intima
• Relatively thinner Tunica media
• Thinner tunica externa
• Valves, prevent the backflow of blood aiding its return (if valves fail to close then it can result in varicose veins or the build up of blood)
• Very large lumen
• Very low blood pressure

Function=Carry blood to the heart

Arterioles:

Function=Are able to contract forcing blood to go through a seperate tube straight into the venules. Also connect the arteries to the capillaries.

Venules:

Function=Connects veins to the capillaries

Components of the blood

45% cells:

There are 3 cell types:

1. Erythrocytes
2. Leukocytes
3. Platelets

1. Erthrocytes 

• Contain haemoglobin (which have 4 haem groups)
• Quaternary protein
• Carries 4O2 molecules
• High SA:Volume ratio
• Only live 120 days due to lack of nucleus

2. Leukocytes

Can be split further into 2:

1. Granulocytes
2. Agranulocytes

1. Granulocytes:

There are 3 types of granulocytes:

1) Neutrophil

• Has a multi-lobed nucleus 
• Involved in phagocytosis

2) Basophil

• Histamine
• Heparin

3) Eosinophil

• Anti-histamine

2. Agranulocytes

There are 2 types of agranulocytes:

1) Monocytes

• Mature in tissues to become macrophages
• Involved in phagocytosis

2) Lymphocytes

• Release antibodies during the immune response

55% plasma:

This can be broken down into 3 main components:

1. Water (used as a solvent for the dissolved chemicals)
2. Hormones (insulin, glycogen)
3. Plasma proteins (antibodies, clotting proteins, enzymes)

It is also made up of inorganic ions (e.g. sodium ions), Glucose (source of energy for cells), Amino acids (allow cells to make proteins), urea (Excretory waste being transported to the kidney) and some dissolved gases (e.g. O2, CO2, N2).

Serum is the name given to plasma without the plasma proteins