Welcome to the final module of HSC Biology on Non-Infectious Diseases! This module touches upon previous topics within the course like heredity and biotechnology while introducing some completely new concepts like homeostasis and epidemiology. The syllabus can be broken down into five main points we will explore in this study guide to build a general understanding of this module including homeostasis, the types of non-infectious diseases, epidemiology, and how technologies can help disorders. If you’re keen to start exploring the fascinating world of non-infectious diseases, then this article is for you!
Concept #1 - Homeostasis
Homeostasis refers to the maintenance of a relatively stable internal environment despite changes in the external environment, like how your body can regulate its temperature to keep you warm when it’s cold.
This works through a mechanism called a negative feedback loop, a system that counteracts changes in the body. It follows something called the stimulus-response model:
- Stimulus: A change in environment
- Receptors: Cells and nerves that sense the change and sends signal to control centre
- Control centre: Often the brain or an endocrine gland that receives the information from the receptors and sends signals to effectors
- Effectors: Organs that act to offset the change in environment
- Response: Neutralises the original stimulus
In the HSC, the two main negative feedback loops explored are for body temperature regulation and blood glucose regulation as seen below:
Mechanisms That Maintain Homeostasis
Animals have many adaptations (features that aid in survival) that help them maintain homeostasis, which can be categorised into three main groups:
Behavioural Adaptations:
- Seeking shelter: When it gets too hot, animals may seek shade, and when it gets too cold, they may look for areas with greater insulation such as caves
- Nocturnal activity: Some animals sleep during daytime and wake at night to avoid the heat during the day
- Migration: Some animals travel to different geographical locations to avoid seasonal temperature changes
Structural Adaptations:
- Colour: Animals in cold climates might have a darker coat to better absorb heat, while those in hot climates may be lighter in colour to repel heat
- Insulation: Some animals have fur or feathers that insulate hot air while blocking cold air from reaching the skin, some animals also have thick layers of fat called blubber that help insulate heat
- Surface area to volume ratio: Greater surface area to volume ratio means greater susceptibility to heat loss, so animals in hot environments might have long, thin extremities to diffuse heat faster, while animals in cold environments tend to be more compact and round to conserve heat
Physiological Adaptation:
- Metabolic activity: Metabolic activity produces heat, so in colder temperatures, animals may increase their metabolic rate by shivering to release more heat
- Sweating: When sweat gets evaporated, it takes heat along with it, allowing for faster cooling
- Blood vessels: Vasodilation (widening of blood vessels) for greater heat dispersion when hot, and vasoconstriction (narrowing of blood vessels) to minimise heat dispersion when cold
- Counter-current exchange: Blood vessels carrying warm blood from the body’s core are adjacent to vessels with cold blood returning from the extremities, allowing for heat exchange between the vessels
Concept #2 - Types of Non-Infectious Diseases
There are four main types of non-infectious diseases covered in the HSC, but first of all, what are non-infectious diseases? Hopefully you remember from Module 7 that a disease is a health condition that abnormally affects the structure or function of the body. However, unlike infectious diseases, non-infectious diseases are not caused by pathogens, and hence cannot be spread from one person to another.
Genetic Disease:
A type of disease caused by an abnormal change in the DNA sequence (i.e. a mutation). Since they are genetic, they can be inherited by offspring.
(E.g. Cystic fibrosis, sickle cell anemia, Huntington’s disease)
Environmental Disease:
Diseases that are a result of exposure to harmful factors in the environment like toxins or contaminants.
(E.g. Asbestosis, lead poisoning)
Nutritional Disease:
A disease that arises from inadequate dietary intake or inability for the body to absorb nutrients, hence failing to provide the body with enough nutrients for it to function.
(E.g. Scurvy, Rickets)
Cancer:
A disease characterised by rapid and uncontrolled cell division.
(E.g. Melanoma, leukemia)
Concept #3 - Epidemiology
With all these diseases, we need to find ways to determine their causes so that we can effectively prevent and treat them. This is where epidemiology comes in, epidemiology is the scientific study of disease and health within a population.
Epidemiological studies examine data such as the incidence, prevalence, and mortality rate to determine the cause of a disease in order to find treatments and prevention.
Key Terms
Incidence: The number of new cases of a disease within a specific time period
Prevalence: The number of current cases in a population. This includes both new and pre-existing instances of the disease.
Mortality: The number of deaths within a population
Types of Studies
Descriptive Studies:
Aims to collect a wide range of data on diseases in populations in terms of what kind of people are affected (age, sex, occupation), the location and its characteristics, and the point in time or duration of the outbreak, to identify trends and create hypotheses.
Analytical Studies:
Studies that aim to actually test hypotheses on what potential risk factors may lead to certain diseases.
Cohort Studies:
Following a group of people exposed to the hypothesised risk factor and a control group then observing how many people from each group developed the disease.
Case-Control Studies:
Following a group of people with the disease and a control group to find common potential risk factors.
Experimental Studies:
Aims to observe health outcomes by manipulating variables, for example testing a treatment to determine its effectiveness.
Features of a Good Epidemiological Study
- Correct selection of design based on research goal
- Large sample size for a better reflection of the whole population
- Diverse sample size (people of different age, sex, family history, occupation, lifestyle etc.) to minimise bias
- A suitable duration, long enough for results to be valid
- Valid method of measurement, should results be qualitative (eg. surveys) or quantitative (eg. medical tests)?
Concept #4 - Prevention of Non-infectious Diseases
What are some possible methods of preventing non-infectious diseases?
Educational Programs / Campaigns:
Raising awareness and educating the public on ways to prevent infectious diseases such as putting sunscreen on to reduce the risk of melanoma
- Advantages: Easy and inexpensive to implement
- Disadvantages: Does not work for non-preventable diseases like genetic diseases
Population Screening:
Getting tested regularly for diseases like cancer so that early detection can lead to better treatment outcomes.
- Advantages: People are more likely to recover from diseases when detected early
- Disadvantages: Not a cure, not accessible to everyone, expensive
Gene Therapy:
Editing a person’s DNA to cure genetic diseases.
- Advantages: Can potentially completely cure someone from a genetic disease
- Disadvantages: Very risky and difficult to carry out, not accessible, expensive
Genetic Screening:
Testing done before or early in pregnancy to identify if the parents are carriers of a disorder that may be passed onto the offspring.
- Advantages: Parents will know the risk of their child inheriting genetic disorders and make more informed decisions, potentially lower incidence of genetic diseases
- Disadvantages: Not a cure, not accessible to everyone, expensive
Preimplantation Genetic Testing:
Testing embryos for a genetic disease, allowing couples wanting to use assisted reproductive technologies like IVF to choose healthy embryos.
- Advantages: Can lower the incidence of genetic disorders
- Disadvantages: Ethical considerations, not a cure, not accessible to everyone, expensive
Genetically Engineered Food:
Using biotechnology such as recombinant DNA to produce more nutritionally dense food to tackle nutritional diseases.
- Advantages: Reduction in incidence, can potentially cure nutritional deficiencies
- Disadvantages: Requires community cooperation, potential environmental impacts that come with biotechnology, expensive
Concept #5 - Technologies and Disorders
In this topic we will explore the structure and function of the ears, the eyes, and the kidneys, as well as potential disorders related to these organs. Furthermore, we will learn about the different technologies that help with managing these disorders.
The Ears
How Do They Work?
First, sound waves travel into the ear, causing the eardrum to vibrate. These vibrations get sent through three small bones in the middle of the ear called the ossicles, which then beats against a thin membrane called the oval window which is attached to a fluid filled chamber called the cochlea. The mechanical energy from the beating of the oval window travels through the fluid of the cochlea, stimulating tiny hair-like structures that line the inside of it, which convert the mechanical energy into electrical signals. These electrical signals get sent through the auditory nerve and into the brain, allowing it to interpret these signals as sound.
Auditory Disorders
Conductive Hearing Loss:
Hearing loss due to damage or obstruction in the outer or middle ear, making it difficult for sound waves to reach the cochlea
Sensorineural Hearing Loss:
Damage to the inner ear or auditory nerve, meaning sound waves are unable to be converted from mechanical energy into electrical signals
Technologies
Hearing aids:
Made up of a microphone that receives sound, which is then made louder by the amplifier and played through a speaker into the ears.
- Advantages: Makes sound louder so that people with conductive hearing loss can hear more clearly, improves communication, can be put on and taken off
- Disadvantages: Expensive, sound quality may not be as good as regular hearing, requires batteries, may get lost, does not work for sensorineural hearing loss
Bone Conduction Implants:
A microphone detects sound waves which are converted into vibrations by a sound processor, and are then sent to a subdermal implant that vibrates the temporal bone, conducting the waves into the cochlea to be processed into sound.
- Advantages: Bypasses outer and middle ear so people with conductive hearing issues such as damaged eardrums or ossicles can still hear, improves communication
- Disadvantages: Expensive, invasive (due to implantation surgery), lowered sound quality, requires batteries, does not work for sensorineural hearing loss
Cochlear Implants:
A microphone picks up sound waves which are converted into electrical signals that are sent directly to the auditory nerve.
- Advantages: Bypasses the whole ear which is good for people with sensorineural hearing loss, improves communication
- Disadvantages: Expensive, invasive, lowered sound quality, requires batteries
The Eyes
How do they work?
The eyes take in light from the surroundings which get sent to the brain where it is processed into vision. When light enters the eyes, it passes through the lens which refracts (bends) the rays so that they converge and focus on the retina at the back of the eye, which converts the light into an electrochemical signal that gets sent via the optic nerve into the brain where it gets processed into sight.
Visual Disorders
Myopia:
A disorder that makes it difficult to see objects that are far away. It occurs when the light that enters the eye converges too soon, and does not focus onto the retina, causing objects in the distance to appear blurry. It is usually a result of the lens or cornea being too round or the eye being too long.
Hyperopia:
Essentially the opposite of myopia, a disorder that makes it difficult to see objects that are close up. It occurs when light does not get refracted enough, and converges after the retina, causing objects that are too close to seem blurry. It is usually caused by the lens or cornea not being round enough or the eye being too short.
Cataracts:
This occurs when proteins accumulate in the lens, causing it to become cloudy and more opaque. This blocks light from entering the eyes, hence obstructing vision.
Technologies
Spectacles:
Otherwise known as glasses, spectacles can be either concave (refracts light inwards) or convex (refracts light outwards). People with myopia can wear concave lenses to correct the convergence of light, making the light rays converge further into the eye, while people with hyperopia can wear convex lenses to make the light rays converge sooner.
- Advantages: Allows for clearer vision when worn, usually affordable, can be worn or taken off with ease
- Disadvantages: Not permanent as they stop working when they are not worn, can get damaged or lost, may be uncomfortable to wear
LASIK Surgery:
LASIK surgery uses a laser to reshape the cornea of the eye, making it refract the light at the correct spot for people with myopia or hyperopia.
- Advantages: Permanent correction of vision, painless, quick recovery time
- Disadvantages: Expensive, invasive, could cause complications such as infections
Cataract Surgery:
Cataracts can be fixed through a surgery in which the cloudy lens is replaced by an artificial lens.
- Advantages: Permanent fix, minimal discomfort, short recovery time
- Disadvantages: Expensive, invasive, risk of complications such as infections
The Kidneys
How do they work?
The kidneys help filter the blood through tiny structures called nephrons. It removes waste from the blood which then gets excreted through urine, and helps keep salt and water levels balanced in the body as well as regulate blood pressure.
Kidney Failure
Kidney failure refers to the loss of kidney function, and can be a result of issues like hypertension and diabetes. Kidney failure can be fatal, and the best way of dealing with it is by getting a kidney transplant. However, this may not always be a viable option, hence technologies, namely dialysis, can be used instead.
Technologies
Haemodialysis:
This works by extracting blood from the body through a tube, which then gets passed through a dialyser machine. Inside, dialysate fluid (fluid with equal concentration of solutes as blood, such as glucose and salt, but no urea) runs parallel to the blood in the opposite direction, separated from the blood by a semi permeable membrane. This allows the waste from the blood to diffuse down the concentration gradient into the dialysate fluid, hence cleaning the blood and returning it back to the body.
- Advantages: Helps remove waste and excess water from blood to replace kidney function, buys time for a kidney transplant, available in most hospitals, can also be done at home
- Disadvantages: Does not cure kidney failure, time consuming, expensive, not accessible for everyone, patients must remain in the same place while haemodialysis is occurring
Conclusion
This concludes the HSC Biology Module 8 guide on non-infectious diseases! If you’re interested in learning more about HSC Biology or even other HSC or preliminary subjects, consider joining us at Project Academy for a Three Week Trial.
Good luck on your exams, you got this!
