Biology Unit 1 What is disease?

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Single factor diseases ­ single cause such as an infective agent e.g. malaria
Multifactorial diseases ­ cardiovascular disease that has many causes, depend on lifestyle
Communicable diseases ­ are infectious and caused by infection with another organism such as bacteria,
viruses and fungi. Can be passed from one person to another. Fungi are eukaryotic, bacteria are prokaryotic,
viruses are noncellular (akaryotic)
Noncommunicable diseases ­ are not infectious or caused by an infective agent so they cannot be passed
from person to another. Diseases can be inherited e.g. cystic fibrosis or contracted due to lifestyle e.g. heart
Pathogen ­ diseasecausing organisms, transmitted by airborne/droplet, contaminated food or water or direct
contact. Causes disease by damaging cells and producing toxins.
Viruses ­ smaller than bacteria, noncellular causes small pox, rabies, HIV, influenza, measles.
Fungal infections ­ fungi are eukaryotic, cause infections such as thrush, ringworm and athlete's foot.
Bacterial infections ­ CHOLERA. Causes are a water/food borne infectious disease. Person suffers from
severe diarrhoea transmitted by ingesting water/food contaminated by faecal material containing the pathogen.
Toxic protein released by cholera bacteria into small intestine, damages carrier proteins in plasma membrane
of epithelial cell lining in small intestine. Large release of chloride ions into gut lumen therefore water potential
will decrease, water is leaving by osmosis.
Oral Rehydration Solutions (ORS) ­ excessive fluid loss in cholera diseases, dehydration therefore could be
fatal and needs to be treated quickly. Drinking water is ineffective as water is not absorbed from intestine and
is being lost from cells. Drinking water does not replace electrolytes (ions) that are lost from cells. Contains
sodium, glucose and water leading to increased uptake of sodium and glucose into epithelial cells by making
use of the sodiumglucose cotransport proteins. Combination of glucose and sodium lowers water potential
inside cells, water following from the lumen by osmosis. ORS is effective because
The disease is caused by loss of salts via damage to carrier proteins for chloride ions this damage
is lowering the water potential in the gut water to leave by osmosis. The excessive water in the gut is
causing diarrhoea.
Symptoms are relieved when sodium and glucose are taken up by cotransport proteins into intestinal
cells lowering the water potential so water is able to be reabsorbed into the lumen by osmosis
leading to less diarrhoea.
Improving oral rehydration solutions:
Early rehydration solutions were tested with different amounts of glucose and sodium
High glucose content lowers water potential in the lumen and begins to draw water out of epithelial
cells making dehydration worse
Starch was tested instead of glucose it is a large, insoluble molecule with no osmotic effect. It is
broken down gradually in the small intestine by amylase and maltase into glucose monomers. Partly
digested starch makes the solution more viscous as smaller molecules are more soluble.
Rehydration solution developed that releases glucose at an optimum rate so it is taken up as it is
produced without affecting water potential.
Testing new drugs:
1. Small number of healthy people given small amount of drug to test for side effects. Dose gradually
increased in a series of trials (6 months)
2. Given to larger number of people with condition it is designed to treat. Check if drug works and
assess safety issues (2 years)
3. Large scale trial of many thousands of patients, given a dummy drug (placebo that is a pill or solution
made up in exactly the same way except without drug). Done as a doubleblind trial and can take
many years.
4. Successful drug published in scientific journal, published only if it is scientifically worthy. Peer review
where other scientists critically review findings and challenge for inaccuracy or if it is misleading.
Replication possible to see if same results achieved, drug given license and monitored over years for
longterm effects.
Defence against disease ­ first line of defence are barriers such as nasal passages (mucus), eyes, trachea
(cilia propel mucus to the throat where it is swallowed and goblet cells produce sticky mucus to trap microbes

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and foreign particles), stomach acid (pH 12 destroys most bacteria and toxins due to acid from gastric
glands), bladder and skin.
The immune system:
nonspecific response: present from birth, effective against specific pathogens
specific response: slow, only effective against specific pathogens, response faster after reinfection
white blood cells (leukocytes) such as phagocytes forming part of nonspecific system with platelets
which involve blood clotting. Lymphocytes involved in specific immune response (B cells, T cells).
Plasma the liquid that transports blood cells around body.…read more

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antigens. These do not correspond to memory cells from any previous infections, the body reacts to the
organism as though it is a new infection and produces a primary response = slower, symptoms develop
Antibodies proteins synthesised by B cells, they react and bind with them precisely to form an
antigenantibody complex. They are specific each antigen has its own individual antibody. Variety is present
because they are proteins each antibody has a specific tertiary structure complementary to one antigen.…read more

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WHAT IS DISEASE?…read more


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