B2: Keeping Healthy

B2: Keeping Healthy

1. Health and Disease

   • Disease
     • A condition that damages cells and destroys the normal structures or functioning of the organism.
     • Causes
       • Organism becomes infected by a pathogen
         • Pathogen - A type of microorganism that causes disease E.G. Bacteria, Viruses etc
       • A mutation (change) in the organism's genes
   • Communicable
     • A disease (infectious) that can spread between organisms, which is caused by pathogens infecting the organism.
   • Non - Communicable
     • Cannot be passed from one organism to another E.G. Cancer. They last a long time and progress slowly and are associated with genetic mutations, lifestyle and environmental factors.
   • Autoimmune
     • The body's immune system recognises the body's own cells as foreign, and attacks them.

2. Diseases are Transmitted in Different Ways

   • Water
     • Some pathogens are picked up by drinking/bathing in dirty water E.G. Cholera which causes diarrhoea and dehydration. Spread when drinking water is contaminated
   • Air
     • Some pathogens are carried in the air E.G. diseases that causes Chalara Ash Dieback in trees. Transmitted from infected plants, by the wind.
   • On Surfaces
     • Some pathogens are picked up by touching contaminated surfaces E.G Athlete's foot
   • Body fluids
     • Some pathogens are spread by fluids such as blood (E.G. sharing needles to injects drugs), breast milks or through unprotected sex.
   • Animal Vectors
     • Animals that spread disease are called vectors E.G. Malaria.
   • Food
     • Some pathogens are picked up by eating contaminated food E.G. Salmonella (raw meat).

3. Defending Against Pathogens

   • Defence System
     • The human body has got features that stop bad stuff entering the blood. These are defences that aren't produced in response to a particular pathogen.
   • Physical Defences
     • 1
       • The respiratory tract is lined with mucus and cilia and the mucus traps particles that contains pathogens; the cilia takes the mucus up to the back of the throat where it is swallowed.
     • 2
       • Skin acts as barrier to pathogens and if cut, pathogens could enter the bloodstream
     • 3
       • Platelets in blood clump together to close the wound, knows a blood clotting. Blood clots stop you loosing too much blood and prevents microorganisms from entering the blood.
         • Pathogens - Tiny fragments of cells, contain lots of different substances and have proteins on their surface which help them stick together.
   • Chemical Defences
     • 1
       • Eyes (tears) produce an enzyme called lysozyme, which breaks down bacteria on surface of eye.
     • 2
       • Saliva contains molecules which kill pathogens that enter the mouth, so they don't reach the stomach.
     • 3
       • Stomach produces hydrochloric acid, which kills pathogens
   • Microbial Defences
     • 1
       • Some pathogens make it past the saliva and the acid in the stomach by entering the gut.
     • 2
       • They compete with the bacteria that naturally live in the gut

4. Human Immune System

   • Attacking Pathogens
     • White blood cells travel around in your blood, constantly patrolling for pathogens. Every cell has molecules on called antigens. White blood cells have special receptors in their membrane,, helping them to identify antigens on pathogens. In a healthy person, white blood cells recognise antigens on pathogens as foreign and when they come across them the immune system is triggered to destroy any invading pathogens.
     • 1. Consuming them
       • Some white blood cells have a flexible cell membrane and contain lots of enzymes, which enables them to engulf and digest the foreign cells
     • 2. Producing Antitoxins
       • Some pathogens cause problems for the body by the toxins they produce. Some white blood cells also produce antitoxins which counteract these toxins and so limit the damage done by the pathogens.

5. Developing New Medicines

   • Preclinical Testing
     • Drugs are tested on cultured human cells (cells that have been grown in the lab), then they test it on live animals. This is used to test that the drug is effective and safe.
   • Clinical Testing
     • Then it's tested on human volunteers (clinical trial). First it is tested on healthy volunteers to make sure it's safe, then is tested on people who have the disease to test its effectiveness and safety. For many clinical tests, patients are randomly put into 2 groups, one is given the new drug and the other is given a placebo (a look alike to the drug but doesn't do anything) to allow the placebo effect to work. Clinical trials may be blind (patient doesn't know if they have the real drug or placebo) and sometimes it is double-blinded (patient nor doctor knows). Sometimes they are open-labelled (doctor and patient know which one they're taking).