Circulation disorders
Blood carries oxygen and food to every cell. A circulation disorder happens when blood flow is wrong in amount, place or path.
- Thrombus: a clot that forms inside a vessel and blocks it.
- Embolus: a clot, air bubble or fat drop that travels in blood and blocks a smaller vessel elsewhere.
- Ischaemia: too little blood to a part. Cells starve, hurt and can die (infarction, for example a heart attack or stroke).
- Haemorrhage: bleeding out of vessels.
- Oedema: fluid collects in the tissue, which swells.
- Hypertension: blood pressure stays too high.
Inflammation
Inflammation is the body's response to injury or germs. It brings blood, fluid and white cells to the place. Its five classic signs: redness, heat, swelling, pain and loss of function.
- Acute: starts fast, lasts days (a sprain, a boil).
- Chronic: lasts weeks to years (long-term arthritis, a long-term infection like TB).
It is useful at first because it clears the cause and starts repair. If it goes on too long, it harms the body's own tissue.
Infection
Infection means germs (bacteria, viruses, fungi, parasites) enter the body, grow and cause harm.
The chain: germ â way out of a source â way of spreading â way in â a person who can be infected. Break any link and the chain stops.
- Ways of spreading: touch, droplets from cough and sneeze, contaminated food and water, insect bites, blood and body fluids.
- Breaking the chain: hand washing, clean water, masks, vaccines, mosquito control, safe food.
- An infected person is not always ill: the body's defence may keep the germ in check.
Immune abnormalities
The immune system should attack harmful things and spare the body. Faults come in four kinds:
- Too weak (immunodeficiency): infections come again and again, for example in HIV or after some medicines.
- Too strong (allergy or hypersensitivity): a harmless thing like pollen, dust or a food sets off a big reaction.
- Against the self (autoimmune disease): defender cells attack the body's own cells, for example type 1 diabetes or rheumatoid arthritis.
- Against a transplant: the body rejects a donated organ unless medicines calm it.
Tumours
A tumour (neoplasm) is a lump of cells that divide without the normal controls.
- Benign: grows slowly, stays in one place, usually does not spread. Removal often cures it.
- Malignant (cancer): grows fast, invades nearby tissue and spreads (metastasis) through blood and lymph.
Risk factors: tobacco, some viruses, too much sun, some chemicals, family history and age. Early detection (a lump, a mole that changes, a long cough or blood in stool) saves lives.
Metabolic disorders
Metabolism is all the chemical work the body does with food. A metabolic disorder means this chemistry goes wrong.
- Diabetes: blood sugar stays high because insulin is low or not working.
- Gout: uric acid builds up and forms crystals in joints.
- Obesity and high cholesterol: too much fat stored or in the blood.
- Thyroid problems: too fast or too slow body chemistry.
- Inborn errors: a missing enzyme from birth, for example PKU.
Heredity and congenital anomalies
Hereditary diseases pass from parents to children through genes (haemophilia, sickle cell disease, thalassaemia). Congenital means "present at birth": it may be genetic or caused before birth, for example by infection, alcohol, some medicines, or lack of folic acid in the mother.
- Single-gene disease: one changed gene (cystic fibrosis).
- Chromosome disease: extra or missing chromosome (Down syndrome).
- Structural defect: a part did not form properly (cleft lip, heart hole).
Not all congenital problems are inherited, and not all inherited diseases show at birth.
Try it
Predict then check. In the last step of the 3D, before you pick a cause, say aloud what will happen to the cells: turn grey, red, green, orange or purple? Then pick and check. For each, say which of the seven causes it is.
At home: press a finger hard on your fingernail for 3 seconds, then let go. The pale spot turns pink again in about 2 seconds. That return is blood flow. Slow return can mean poor circulation.
Key formulas and definitions
- Seven basic causes: circulation ¡ inflammation ¡ infection ¡ immune ¡ tumour ¡ metabolic ¡ heredity/congenital
- Signs of inflammation: redness ¡ heat ¡ swelling ¡ pain ¡ loss of function
- Chain of infection: germ â source â spread â entry â person at risk
- Benign tumour: slow, stays put ¡ Malignant tumour: fast, invades and spreads (metastasis)
- Immune faults: too weak ¡ too strong ¡ against self ¡ against a transplant
Worked examples
1. A leg is swollen, red, hot and painful after a sprain. Which basic process is this?
Inflammation: it shows redness, heat, swelling and pain, the classic signs.
2. A person eats peanuts and gets a rash and a swollen face within minutes. Name the process.
An immune abnormality of the "too strong" kind: allergy (hypersensitivity). The peanut is harmless but the body over-reacts.
3. A tumour starts with 1 cell that doubles every day. How many cells after 6 days? What makes it malignant?
1 â 2 â 4 â 8 â 16 â 32 â 64, so 64 cells after 6 days. It is malignant if it invades nearby tissue and can spread to other parts.
4. A child is born with sickle cell disease although both parents look healthy. Is it hereditary or congenital?
Both: it is present at birth (congenital) and it comes from genes the parents carry (hereditary). The parents can be healthy carriers.
Common mistakes
- Thinking inflammation always means infection. A sprain is inflamed with no germ at all.
- Using "congenital" and "hereditary" as the same. Congenital means present at birth, and the cause need not be genes.
- Thinking every tumour is cancer. Benign tumours do not spread.
- Thinking allergy is an infection. It is an immune reaction to a harmless thing and it does not spread from person to person.