Non-infectious Disease and Disorders

Module 8 averages about 25–26 marks a year (2020–2025). Homeostasis is the most heavily examined part (about 7 marks a year), followed by epidemiology (about 6) and technologies and disorders (about 6). Causes and effects and prevention are smaller but appear most years.

The syllabus has five inquiry questions:

• Homeostasis: negative feedback (temperature and glucose); the nervous and endocrine systems; adaptations of endotherms; how plants maintain water balance.
• Causes and effects: genetic, environmental, nutritional and cancer-related non-infectious diseases; incidence, prevalence and mortality.
• Epidemiology: patterns of a non-infectious disease (such as lung cancer); treatments, benefits and costs; types of epidemiological study.
• Prevention: educational programs and campaigns, genetic engineering, and how well current prevention methods work.
• Technologies and disorders: hearing loss, visual disorders and kidney failure, and the technologies used to treat them.

Homeostasis is keeping the internal environment (temperature, blood glucose, water and salt levels) within narrow tolerance limits despite changes outside. Enzymes and cells only work well within these limits.

Negative feedback

Most homeostasis uses negative feedback: a change triggers a response that reverses the change.

1. Stimulus: a variable moves away from its set point.
2. Receptor: detects the change.
3. Control centre: compares with the set point and sends signals (often the hypothalamus).
4. Effector: a muscle or gland responds.
5. Response: returns the variable towards the set point, and the stimulus is reduced.

Positive feedback amplifies a change instead (eg oxytocin in childbirth) and is not used to maintain homeostasis.

Temperature

Thermoreceptors in the skin and hypothalamus detect changes; the hypothalamus is the control centre.

Vasodilation sends more blood to the skin surface so more heat is lost by radiation; sweat absorbs heat as it evaporates.

Blood glucose

The pancreas (islets of Langerhans) is both receptor and control centre.

• Glucose too high (after a meal): beta cells release insulin. Body cells take up more glucose, and the liver and muscles store it as glycogen. Glucose falls.
• Glucose too low (fasting, exercise): alpha cells release glucagon. The liver breaks glycogen down to glucose and makes new glucose. Glucose rises.

In type 1 diabetes, the immune system destroys beta cells so no insulin is made; in type 2, cells stop responding properly to insulin, strongly linked to lifestyle.

Nervous and endocrine systems

The hypothalamus links the two: it detects changes and signals the pituitary, which releases hormones that control other glands. Water balance is an example: when blood is too concentrated, the posterior pituitary releases ADH, so the kidneys reabsorb more water.

Adaptations of endotherms

Endotherms (mammals, birds) generate heat internally to keep a constant body temperature; ectotherms rely on outside heat. Australian examples help in exam answers.

• Structural: fur, feathers and fat for insulation; large ears with many blood vessels to lose heat (bilbies); countercurrent heat exchange in the legs of birds; a small surface-area-to-volume ratio in cold climates.
• Physiological: sweating, panting, licking forearms so evaporation cools the blood vessels (red kangaroos), torpor to save energy (some small marsupials and birds), producing concentrated urine (hopping mice).
• Behavioural: being nocturnal, sheltering in burrows by day, huddling, basking or seeking shade.

Water balance in plants

Plants lose water through transpiration, mostly through stomata. Adaptations to arid or salty conditions:

• Structural: thick waxy cuticle; sunken stomata or stomata in hairy pits that trap humid air; small, needle-like leaves or leaves reduced to phyllodes (many wattles); eucalypt leaves that hang vertically to avoid the midday sun; deep or wide roots.
• Physiological: stomata close in hot, dry conditions (triggered by the hormone abscisic acid); CAM plants open stomata only at night; mangroves exclude salt at the roots or excrete it through salt glands.
• Life cycle: some plants survive drought as seeds or drop their leaves.

A common practical uses a potometer or weighs potted plants under different conditions (wind, humidity, light) to measure the rate of water loss.

A non-infectious disease is not caused by a pathogen and cannot be passed from person to person.

Cancer develops when mutations accumulate in proto-oncogenes (which then push cells to keep dividing) and tumour-suppressor genes (which normally stop damaged cells dividing). Many cancers have both genetic and environmental causes: melanoma is linked to UV exposure and family history.

Measuring disease

• Incidence: new cases in a period, usually given per 100 000 people per year.
• Prevalence: all existing cases at one time, often given as a percentage.
• Mortality rate: deaths from the disease in a period, per 100 000 people.

Worked example: rates

A town of 48 000 people has 1 200 residents living with a condition. During one year, 84 new cases are diagnosed and 30 people die of it. Using the whole population:

Some studies use only the population at risk (people who do not already have the disease) for incidence. Here that gives 179 per 100 000. Follow whatever the question says.

Epidemiology studies the patterns, causes and effects of disease in populations. It identifies risk factors, tests treatments and guides public health spending.

Types of study

• Descriptive: records who gets the disease, where and when (age, sex, location, trends over time). It generates hypotheses but cannot show cause.
• Analytical, case-control: compares people who have the disease with similar people who do not, looking back at past exposures. Quick and cheap, but relies on memory.
• Analytical, cohort: follows a large group over time and compares those exposed and not exposed to a factor. Strong evidence but slow and expensive.
• Intervention (experimental): randomised controlled trials test a treatment or prevention method against a control or placebo, ideally double-blind.

Lung cancer as the example

Doll and Hill's 1950 case-control study found lung cancer patients were far more likely to be smokers. Their cohort study of British doctors, starting in 1951, followed smokers and non-smokers for decades and showed a dose-response: the more cigarettes per day, the higher the death rate from lung cancer.

Evidence that a link is causal (not just a correlation) includes a strong association, a dose-response relationship, consistent results in many populations, exposure coming before the disease, and a biological mechanism (carcinogens in smoke damage DNA).

Worked example: relative risk

In a cohort study, 6 000 smokers and 10 000 non-smokers are followed for 15 years. 90 smokers and 12 non-smokers develop lung cancer.

Smokers in this study were 12.5 times as likely to develop lung cancer. Compare risks, not raw numbers, when group sizes differ.

Treatment and management

Lung cancer treatment includes surgery, radiotherapy, chemotherapy, targeted drugs and immunotherapy. Benefits are longer survival and better quality of life; costs include side effects, financial cost to patients and the health system, and lost work. Evaluate treatments by survival data, side effects and cost.

Judging a study

Larger samples, randomisation, control groups, matching groups for confounding variables (age, diet, occupation) and long follow-up all improve validity and reliability. A correlation alone never proves causation.

• Education and campaigns: Slip! Slop! Slap! (from the early 1980s, later expanded into the SunSmart program) has been linked to lower melanoma rates in younger Australians; Quit campaigns and graphic warnings reduced smoking.
• Laws and policy: tobacco plain packaging (Australia was first in the world, in 2012), smoking bans, taxes, and food labelling.
• Screening: catches disease early or before it starts, eg the national bowel, breast and cervical screening programs and newborn heel-prick tests for conditions such as cystic fibrosis.
• Vaccination: the HPV vaccine (school program from 2007) prevents most cervical cancers.
• Genetic engineering: gene therapy to correct faulty genes, genetic screening of embryos in IVF, and GM foods such as golden rice to prevent nutritional deficiency.

To evaluate a prevention method, use data on incidence or mortality before and after it was introduced, its cost compared with the cost of treatment, how many people it reaches, and limitations (such as people ignoring the message, or other factors changing at the same time).

Hearing loss

• Conductive loss: sound cannot reach the cochlea properly (blocked canal, damaged eardrum or ossicles).
• Sensorineural loss: damage to the cochlear hair cells or auditory nerve (ageing, loud noise).

A cochlear implant has an external microphone and processor that turns sound into electrical signals, which are sent to electrodes in the cochlea. These stimulate the auditory nerve directly, bypassing damaged hair cells. It was developed in Australia by Graeme Clark. It needs surgery, an intact auditory nerve and time to learn to interpret the sounds, which do not sound like natural hearing.

Visual disorders

• Myopia (short-sightedness): the eyeball is too long or the lens too strong, so distant images focus in front of the retina. Corrected with a concave (diverging) lens.
• Hyperopia (long-sightedness): images of near objects focus behind the retina. Corrected with a convex (converging) lens.
• Cataracts: the lens clouds; it is surgically replaced with an artificial lens.
• Laser surgery (eg LASIK) reshapes the cornea to change its focusing power. It removes the need for glasses for many people but carries surgical risks and is not suitable for everyone.

Kidney failure

The kidneys filter wastes such as urea from the blood and control water and salt balance. When they fail:

• Haemodialysis: blood passes through a machine where it flows past dialysis fluid on the other side of a partially permeable membrane. Wastes diffuse out down their concentration gradient; the fluid flows the opposite way (countercurrent) to keep the gradient steep. It takes several hours, about three times a week.
• Peritoneal dialysis: fluid is placed in the abdomen and the peritoneum acts as the membrane. It can be done at home.
• Kidney transplant: restores function but needs a matched donor and lifelong immunosuppressant drugs.

• Describing negative feedback without naming the receptor, control centre and effector.
• Confusing glucagon (hormone) with glycogen (storage carbohydrate).
• Saying sweat "cools you down" without mentioning evaporation absorbing heat.
• Swapping incidence and prevalence, or forgetting the time period and "per 100 000".
• Claiming a correlation proves cause.
• Saying a cochlear implant amplifies sound (that is a hearing aid) or restores normal hearing.
• Correcting myopia with a convex lens.

• Explain a feedback loop: stimulus → receptor → control centre → effector → response, then say how the response reduces the stimulus. A flow diagram is acceptable if labelled.
• Compare the nervous and endocrine systems feature by feature.
• Epidemiology data: describe trends with numbers, calculate rates or relative risk where asked, and comment on sample size, controls and confounding variables.
• Evaluate a prevention program or technology: benefits, limitations and a clear judgement supported by data.
• For technology questions, link the device to the specific part of the organ that has failed and explain how it bypasses or replaces it.

• Module 5: genetic diseases follow the inheritance patterns from Module 5; insulin and ADH are polypeptides.
• Module 6: mutations in proto-oncogenes and tumour-suppressor genes cause cancer; UV and chemical carcinogens are mutagens; gene therapy and GM foods come from genetic technologies.
• Module 7: incidence, prevalence and study designs are shared with infectious disease; fever resets the temperature set point; the HPV vaccine prevents a cancer caused by an infection.