Health, Disease and the Development of Medicines

Health and Disease

Health is defined as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity (World Health Organisation).

Communicable Diseases are caused by a disease-causing organism called pathogens, such as viruses, bacteria, fungi and protists (viruses are not true organisms as they have no cellular structure), and are passed from one infected person to another. Non-Communicable Diseases cannot be passed from one person to another because they are caused by a problem in the body, such as genetic faults or a result of lifestyle. The presence of one disease often leads to a higher susceptibility to other diseases due to a weakened immune system which makes it easier for pathogens to attack the body, and the body’s natural barriers may be damaged.

Name	Pathogen	Effect	Spread	Prevention
Cholera	Bacteria	Causes severe diarrhoea	Contaminated Water	Good hygiene and sanitation
Tuberculosis	Bacteria	Damages lungs, resulting in blood-specked mucus, fever and weight loss	Airborne – droplets from sneezes	Catch droplets with tissue, or wash hands after sneezing
Chalara Ash Dieback	Fungi	Causes lesions on trunk and branches, leaf loss and dieback of crown	Airborne – spores carried by wind	Removing infected trees and planting different species
Malaria	Protists	Multiplies in red blood cells and liver cells then lyses, causing fever and weakness	Carries by vector of mosquitos	Control spread of mosquitos e.g. mosquito nets
HIV (STI)	Virus	Destruction of white blood cells often leads to AIDS	Contact with bodily fluids	Using a condom during sex
Chlamydia (STI)	Bacterium	Infertility in men and women	Contact with bodily fluids	Avoiding unprotected sexual contact
Ebola	Virus	Breakdown of blood vessels and kidney and liver cells causing haemorrhage fever	Contact with bodily fluids	Isolated patients in sterile conditions
Ulcers	Bacteria	Heliobacteria lead to development of sore ulcers in stomach lining	Oral route through mouth	Clean water supplies and good practise of hygiene

All viruses contain genetic material in a protein coat, or capsid. They can only replicate by entering and taking over a living cell. There are two lifecycles a virus can take.

During the lytic cycle, the virus particle attaches to the host cell receptor
The nucleic acid of the virus moves across the cell membrane into the host cell
The virus uses proteins and enzymes in the host cell to replicate its genetic material and to synthesise the components of new viruses
New viruses are assembled, and the formed viruses lyse out of the cell, rupturing it and causing it to die. If this happens throughout a tissue it can cause disease
When a virus first transfers its nucleic acid into the cell, it can follow the lysogenic cycle
Its genetic material is incorporated into the genome of the host cell. The material is replicates as the host cell divides, but is dormant
A trigger will cause the viral genetic material to leave the genome and enter the lytic cycle

Plant Diseases

Defence	Explanation
Cuticle	Most leaves have a waxy cuticle which makes the leaf tougher to eat and more difficult for pathogens to enter. Also, water cannot collect on it
Trichomes	Hairs or thorns make is difficult to pathogens to reach the lead surface. Some produce substances that deter herbivores
Bark	Contains substances that are poisonous to herbivores; dark colour indicates poison
Cell Walls	Made of cellulose that form a barrier against pathogens
Lectins	Bind to carbohydrates and interferes with reactions involving carbohydrates in animals
Poison	To repel herbivores it releases substances when attacked
Aspirin	Developed from chemicals in bark and leaves of willow trees to relieve pain and fever

Distribution Analysis uses cameras on drones to see patterns in plant disease to determine causes, such as mineral deficiency, flooding, wind-carried disease or pests. Visible symptoms such as lesions can also indicate disease. Diagnosis is the best method of identifying plant disease, detecting antigens or pathogen DNA. Soil samples can show mineral deficiency.

Human Disease Prevention

Defence	Explanation
Skin	Thick layer covering the body means that pathogens can only enter through wounds
Lysozyme	Secreted in tears, mucus and saliva; enzyme that breaks down bacterial walls
Mucus	Produced by cells lining openings to trap pathogens and dust
Ciliated Cell	Specialised cells use cilia move mucus away from the digestive system
HCl(aq)	Found in the stomach to reduce pH and kill most pathogens

The immune system protects the body against infection when pathogens get through the physical barriers and chemical defences of the body
All cells and viruses have antigens on their surfaces. The immune system use antigens to identify foreign bodies
White blood cells called lymphocytes have antibodies on their surface. A lymphocyte with antibodies on its surface that perfectly matches the antigen will attach to it to deactivate it
The lymphocyte is activated and will divide continuously to create many more clones
Some of the lymphocytes secrete antibodies which enter the blood to kill all of the pathogens
In this way the secondary response will produce more of the antibody in a shorter time as memory lymphocytes will remain in the blood, creating immunity
Immunisation follows this process in a controlled way. A weak or inactive form of the pathogen is introduced by injection during a vaccination. This will cause a primary response, and the production of memory lymphocytes. If the same pathogen attacks, it will trigger a secondary response and is likely not to have an effect. Vaccines have been very successful in almost removing some diseases
Very rarely people may react badly to vaccinations, with effects such as fits or high temperatures, meaning the child is not given the vaccine. However, if 95% of their peers have the vaccine, they have what is known as herd immunity as they are unlikely to be exposed to that pathogen if so many others are immune to it

Antibiotics and the Development of Medicines

Antibiotics are substances which kill or weaken bacteria, which stops them from growing or reproducing. They only treat bacterial infections by inhibiting cell processes but not the host organism.

There are many stages to developing a new medicine:

Discovery, such as Alexander Fleming seeing a zone of clearance around mould
Testing on Cells and Tissues: shows that medicine can enter cells without damaging them and have required effect
Animal Testing: test that the drug works on a whole body and that it is not toxic
Small Group: a small clinical trial on healthy people, to check that it is safe and side effects are small
Trials: must be double-blind trials (neither doctors nor patients know who has the drug) with placebos to see if drugs are actually effective
Larger Group: using people with the disease, to check the dose and effects on more people

CORE PRACTICAL: Antibiotics

A – Use aseptic technique to pour agar plate into petri dish sterilised by autoclave. Ensure that the base of the Petri dish is covered, and the surface is smooth

B – Remove the cap of the bacterial culture and flame the neck of the bottle to remove contamination. Insert a sterile pipette and draw up a small amount of culture

C – Flame the neck again and replace cap to reduce contamination

D – Add a few drops of culture onto the agar

E – Inoculate a spreader by passing it through a roaring flame. Spread the drops of culture across the agar then disinfect it

F – Split the petri dish using a marker so you can tell which is the control and which contains antibiotics

G – Sterile forceps and place sterile filter paper on control section

H – Place antibiotic discs on other sections, then tape down and incubate

I – After it has grown, measure the zone of clearance around each disc and calculate area. Draw a graph of cross-sectional area against concentration of antibiotic

Monoclonal Antibodies

To make monoclonal antibodies, take a particular antigen and inject it into a mouse
The mouse produces lymphocytes with antibodies with matching shape to the antigen
Cancer cells are grown on a culture medium
The lymphocytes cannot divide once it has started to produce antibodies, and therefore a lymphocyte from the mouse is fused with a myeloma (cancer) cell
This makes a hybridoma call which can divide and make antibodies against this antigen

Monoclonal antibodies can be made to match any protein, from hormones to enzymes. Monoclonal antibodies can be used in medical diagnosis by making antibodies slightly radioactive. When attached to cancer cells, the radioactivity can be detected, indicating its position. Also, people with cancer can have monoclonal antibodies attached to cancer drugs to reduce the amount needed and to reduce the risk of damaging healthy cells, which is guaranteed when using chemotherapy or radiotherapy.

In a pregnancy test, monoclonal antibodies against hormone hCG, produced by pregnant women, are used
Urine is applied at the bottom and travels up the test strip
Immobilised antibodies will attach to the hormone causing it to leave the dye, causing a stain
In the control window, immobilised antibodies specific to the antibodies from the reaction zone means that a second strip is left behind

Non-Communicable Disease

Some non-communicable diseases are caused by faulty alleles of genes, while most occur as a result of malnutrition – receiving too little or too much of certain nutrients from food consumed. Scurvy is caused by a deficiency of Vitamic C, Anaemia is caused by Iron deficiency and Vitamic D deficiency causes rickets.

Consuming alcohol is a decision we make, but ethanol, found in alcoholic drinks, is a drug as it affects the way the body works. When broken down in the liver, ethanol consumption can cause cirrhosis, which can result in death.

Tobacco smoke contains many harmful substances that damage the lungs when breathed in. Some of the substances can damage the artery lining and cause the build up of fat in the artery wall at the site of damage, making the artery narrower. A blood clot may block the artery, or block the artery in another part of the body, causing a heart attack or stroke. This is a key cause of cardiovascular disease.

There is a strong positive correlation between cardiovascular disease and visceral fat. Therefore BMI and waist to hip ratio are often good indicators of risk of cardiovascular disease. Poor diet and less exercise leads to increased likelihood of developing cardiovascular disease.