Technologies and Disorders

In short: Technologies help people with disorders of hearing, sight and the kidneys. Hearing aids and cochlear implants treat hearing loss, lenses and surgery correct sight problems, and dialysis or a kidney transplant replaces failed kidneys.

Starting point: what you already know

Sound is a wave of vibrations. Light refracts through lenses (Year 10 physics).
The kidneys filter blood and control water balance (see Homeostasis).
Disorders can be genetic, environmental or caused by ageing (see the previous chapter).

Hearing

How we hear. Sound waves enter the outer ear and make the eardrum vibrate. Three tiny bones in the middle ear (hammer, anvil and stirrup) pass the vibrations to the cochlea in the inner ear. Inside the cochlea, fluid moves tiny hair cells, which send signals along the auditory nerve to the brain.

Hearing loss.

Conductive loss: sound cannot reach the inner ear, from blocked ear canals, infections like glue ear, or damage to the eardrum or bones.
Sensorineural loss: damage to the hair cells or the nerve, from loud noise, ageing or genetics. It is usually permanent.

Hearing loss from noise is common in Australia. Being near sounds above about 85 decibels for long periods (loud concerts, power tools, headphones turned up) damages hair cells.

Technology	How it works	Best for	Limitations
Hearing aid	A microphone picks up sound, an amplifier makes it louder and a speaker sends it into the ear	Mild to moderate loss, when hair cells still work	Cannot help if hair cells are badly damaged. Background noise is also louder
Bone conduction implant	Sends vibrations through the skull bone straight to the cochlea	Conductive loss	Needs a working cochlea
Cochlear implant	An outside microphone and processor send signals to electrodes inside the cochlea, which stimulate the auditory nerve directly	Severe sensorineural loss	Needs surgery. Sound is different from natural hearing and takes time to learn

Vision

How we see. Light passes through the cornea and lens, which bend (refract) it to focus an image on the retina at the back of the eye. The retina has light-sensitive rods (dim light) and cones (colour). Signals travel along the optic nerve to the brain.

Disorder	What happens	Technology
Myopia (short-sightedness)	Eyeball too long, so distant objects focus in front of the retina	Concave (diverging) lenses, or laser surgery to flatten the cornea
Hyperopia (long-sightedness)	Eyeball too short, so near objects focus behind the retina	Convex (converging) lenses
Cataracts	Lens becomes cloudy, often with age or UV exposure	Surgery replaces the lens with a plastic one. The Fred Hollows Foundation has done this for millions of people in low income countries
Glaucoma	Raised pressure in the eye damages the optic nerve	Eye drops, laser, surgery

Myopia is rising fast among young people around the world. Spending more time outdoors in daylight in childhood lowers the risk.

The kidneys

The kidneys filter about 180 litres of blood plasma a day through about a million tiny filters called nephrons. They remove urea and extra salts and water, and return useful substances like glucose to the blood.

Kidney failure can be caused by diabetes, high blood pressure, infection or genetic disease. Wastes then build up in the blood, which can be fatal.

Technology	How it works	Limitations
Haemodialysis	Blood flows from an arm into a machine. On one side of a partially permeable membrane is the blood, and on the other is dialysis fluid. Urea and extra salts diffuse out of the blood into the fluid. The cleaned blood returns to the body	About 4 hours, 3 times a week. Tiring, and diet is restricted
Peritoneal dialysis	Dialysis fluid is put into the abdomen. The lining of the abdomen acts as the membrane	Can be done at home, but has an infection risk
Kidney transplant	A healthy kidney from a donor replaces the failed one	Donors are scarce. Patients need immunosuppressant drugs for life so their immune system does not reject it

Technologies and disorders

Hearing

Conductive loss
Sensorineural loss
Hearing aid: louder
Cochlear implant: stimulates nerve

Vision

Myopia: concave lens
Hyperopia: convex lens
Cataract: replace lens
Glaucoma: pressure

Kidneys

Nephrons filter
Dialysis: diffusion across membrane
Transplant: needs immunosuppressants

Year 11Evaluating a technology

HSC questions often ask you to evaluate how well a technology helps a disorder. Use this structure:

Explain the normal function of the organ.
Explain what goes wrong in the disorder.
Explain how the technology works and which part of the problem it fixes.
Give its effectiveness and limitations (cost, access, surgery risk, how close to normal function it gets).

Example. Cochlear implants are very effective for severe sensorineural loss in young children, who can often learn spoken language if they receive the implant early. But they do not restore natural hearing, and there are debates within the Deaf community about cultural identity and the use of sign language.

More eye problems.

Presbyopia: after about 45, the lens gets stiffer and cannot change shape enough to focus on close objects, so people need reading glasses (convex lenses).
Astigmatism: the cornea is curved unevenly, so some parts of the image are blurred. Special (cylindrical) lenses or laser surgery correct it.
LASIK uses a laser to reshape the cornea so light focuses on the retina.
Glaucoma drops lower the fluid pressure, which slows further damage to the optic nerve (damage already done cannot be reversed).

Matching the person to the technology. A young sportsperson with myopia may suit contact lenses or LASIK instead of glasses. An older person with long sight and cataracts may need cataract surgery and then convex reading glasses.

Loud music and high notes. Hair cells near the start of the cochlea detect high pitches, and they are damaged first by loud noise.

Bionic eyes and cochlear implants both skip the damaged sense cells and use electrodes to send signals straight to the nerve.

Year 12Disorders across Australia

Health technologies are not shared equally. Aboriginal and Torres Strait Islander children have some of the highest rates of otitis media (middle ear infection) in the world, which causes conductive hearing loss and affects learning at school. Programs that run hearing checks in schools and communities, and treat infections early, have shown real gains.

Rates of kidney failure are also much higher in many remote communities, often linked to diabetes. Purple House, an Aboriginal-run organisation, set up dialysis in remote communities so patients can be treated on Country instead of moving hundreds of kilometres away from family. Good evaluations include access and equity, not just how a device works.

Why the flows run opposite ways. In dialysis, blood and fluid flow in opposite directions (countercurrent). The blood always meets fresher fluid with even less urea, so a concentration gradient is kept along the whole membrane and more urea diffuses out.

Transplant or dialysis? A transplant gives near-normal kidney function and freedom from the machine, but needs a donor, surgery and lifelong immunosuppressants (raising infection risk). Dialysis is available sooner but takes many hours a week.

Quick summary

Conductive hearing loss blocks sound reaching the inner ear. Sensorineural loss damages hair cells or the nerve.
Hearing aids make sound louder. Cochlear implants stimulate the auditory nerve directly.
Myopia is corrected with concave lenses, hyperopia with convex lenses. Cataracts are fixed by replacing the lens.
The kidneys filter blood in nephrons. Dialysis removes urea by diffusion across a membrane. Transplants need immunosuppressant drugs.
Evaluate a technology by its effectiveness, limitations, cost and access.

Quiz

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Try 3 questions now

Which part of the ear contains the hair cells that detect sound?
1. A Eardrum
2. B Middle ear bones
3. C Cochlea
4. D Outer ear
Show answer
C: Cochlea
Hair cells are in the cochlea.
Who led the team that developed the cochlear implant in Australia?
1. A Graeme Clark
2. B Fred Hollows
3. C Howard Florey
4. D Ian Frazer
Show answer
A: Graeme Clark
Professor Graeme Clark in Melbourne.
Hearing loss caused by damaged hair cells is
1. A conductive
2. B sensorineural
3. C infectious
4. D temporary
Show answer
B: sensorineural
Damage to hair cells or the nerve is sensorineural.

Starting point: what you already know

Hearing

Vision

The kidneys

Quick summary

Quiz

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