HSC Bio Mod 8: Non-Infectious Diseases PDF

1. Homeostasis ============== - Inquiry question: How is an organism's internal environment maintained in response to a changing external environment? - Construct and interpret negative feedback loops that show homeostasis by using a range of sources, including but not limited to:...

1. Homeostasis ============== - Inquiry question: How is an organism's internal environment maintained in response to a changing external environment? - Construct and interpret negative feedback loops that show homeostasis by using a range of sources, including but not limited to: - - - Investigate the various mechanisms used by organisms to maintain their internal environment within tolerance limits, including: - - - - Homeostasis is defined as ***"The coordinating systems that work to maintain a relatively constant internal environment, regardless of external environmental conditions"*** - It allows for functioning and survival of cells as enzymes can operate efficiently - Some conditions that the body maintains at a stable level are: - - - - - - - - Maintaining a **stable state** means keeping internal conditions as close as possible to the **optimum conditions** - - Two stages are involved in maintaining homeostasis - - Detecting Change ---------------- 1. **Stimulus** - 2. **Receptor** - **Stimulus** **Receptor** ---------------------------------------- ----------------- Pain, pressure, gravity, touch Mechanereportor Light Photoreceptor Chemicals Chemoreceptor Temperature change heat Thermoreceptor Detects external stimulus Exteroceptor Detects internal/physiological changes Interoceptor Osmotic pressure (water) Osmoreceptor 3. **Control centre** - 4. **Effector** - 5. **Response** - - There are two main types of feedback mechanisms found in the body: - - - Most homeostatic processes are **negative** feedback mechanisms Feedback Systems ---------------- ### Negative Feedback Mechanisms ***"Change happens → Counteract Change"*** - Negative feedback is the most common form of feedback mechanism in the body - - It involves the counteraction of changes from the stable state and the maintenance of a constant environment +-----------------------------------+-----------------------------------+ |  | **Aldosterone feedback loop** | | | | | | - On adrenal glands | | | | | | - Nephron (in the kidney) | | | | | | | | | | | | - Stimulates the reabsorption | | | of water in kidneys → | | | maintenance of blood pressure | | | by increasing blood volume | | | | | | - Regulate blood pressure, | | | electrolyte balance and blood | | | volume in the body → ensure | | | that appropriate levels of | | | sodium and potassium are | | | maintained for proper | | | physiological functioning | | | | | | - Blood Pressure decreases | | | aldosterones are released → | | | stimulate the reabsorption of | | | of sodium ions | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | ### Positive Feedback Mechanisms | | | | | | ***"Change happens → Make the | | | change happen more"*** | | | | | | - They involve moving the | | | system away from the state of | | | equilibrium (the stable | | | state) | | | | | | - - | | +-----------------------------------+-----------------------------------+ Glucose Regulation ------------------ - Blood glucose concentration is tightly regulated in a negative feedback system mediated by the **pancreas** - The stable state for blood glucose is 4-7mM - - - - - - - In the pancreas, α and β-cells collect in functional endocrine groups called Islets of Langerhans  - Islets of Langerhans have 2 main cells: - - - - - - - **Insulin** (from β-cells) and **glucagon** (from α -cells) are both peptide hormones with opposing actions - - - The failure of these hormones to enact their function can lead to: - - Investigate the various mechanisms used by organisms to maintain their internal environment within tolerance limits, including: - Trends and patterns in behavioural , structural and physiological adaptations in endotherms that assist in maintaining homeostasis - Internal coordination system that allow homeostasis to be maintained, including hormones and neural pathways - Mechanisms in plants that allow water balance to be maintained Thermoregulation ---------------- - Thermoregulation ***"The process of controlling one's body temperature"*** - - This is achieved through **physiological, structural and behavioural** adaptations. - Animals can be either - - - - - - - - - -  ### Humans - Humans are **endotherms**, and thus have many homeostatic thermoregulatory mechanisms to assist in thermoregulation - The **hypothalamus** is a region of the brain that **controls body temperature** - - - If our body temperature is **too cold**, we need to warm up. How is this achieved? **Physiological** Blood vessels near the skin contacts, called vasoconstriction. This means less warm blood is exposed to the cold skin, reducing heat loss through conduction ------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------- Shivering produces a lot of heat through respiration by making the muscles twitch **Behavioural** Seeking shelter shields the body from exposure to the cold, allowing for improved heat retention Curling into a ball reduces the surface area of your body exposed to the cold, creating a warmer core - If the body temperature is **too hot**, we need to cool down. How is this achieved? **Physiological** Blood vessels near the skin open, called vasodilation. This means more warm blood is exposed to the cool skin, increasing heat loss through conduction ------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------- The production of sweat from sweat glands on the skin leaves a layer of water on the skin, facilitating evaporative cooling **Behavioural** Seeking shade removes the body from radiating heat of the sun, allowing your body to cool down Decreasing the desire to move decreases the heat production that results from cellular respiration ### +-----------------------------------+-----------------------------------+ | ### Desert Endotherm | | | | | | #### Mitchell's Hopping Mouse | | | | | | - **Structural** | | | | | | - | | | | | | - **Behavioural** | | | | | | - | | | | | | - **Physiological** | | | | | | - - | | +-----------------------------------+-----------------------------------+ ### +-----------------------------------+-----------------------------------+ | ### Alpine Endotherm |  | | | | | #### Mountain Pygmy Possum | | | | | | - **Structural** | | | | | | - | | | | | | - **Behavioural** | | | | | | - - | | | | | | - **Physiological** | | | | | | - - | | +-----------------------------------+-----------------------------------+ Internal Coordination Systems ----------------------------- - They key systems that allow homeostasis to be maintained are the **endocrine system and the nervous systems** - - The body **detects** and **responds** to signals from their internal and external environments, usually relying on negative feedback mechanisms to maintain homeostasis - When the body detects a stimulus, receptor cells pass this information on to other cells by **releasing signalling molecules** - - The signal can be passed through many cells before reaching the effector cell - - ### The Endocrine System - The endocrine system is composed of various tissues and glands which produce **hormones** - Hormones regulates almost every aspect of homeostasis in most animals and plants - - **Hormones** are: ***"Signalling molecules that are secreted by specialised glands or cells"*** - Hormones can be transported by a simple diffusion or through the **circulatory system** - Compared to nervous responses, hormone responses are generally - - - - A single hormone can trigger multiple physiological responses from multiple cell types - For example, release of adrenaline acts on: - - - - - - - - +-----------------------------------+-----------------------------------+ |  | - The hypothalamus and the | | | pituitary gland **regulate | | | the release of many other | | | hormones** in humans. | | | Together, they are called the | | | **hypothalamic pituitary | | | axis** | | | | | | - | +-----------------------------------+-----------------------------------+ ### Nervous System - The nervous system is made up of **many nerve cell pathways** - - Compared to the endocrine system, the nervous system is - - - +-----------------------------------+-----------------------------------+ | - A neuron (nerve cell) is a | | | specialised cell that allows | | | for rapid transmission of | | | information between cells | | | | | | - A neuron is composed of three | | | parts: | | | | | | - - - | | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | - Signals are transmitted |  | | across gaps between 2 neurons | | | called synapses | | +-----------------------------------+-----------------------------------+ - Functionally, there are three types of neurons **Neuron** **Description** ------------------------- --------------------------------------------------------------------------------------------------- Afferent/sensory neuron Collect information from sensory stimuli and transmit impulses towards the central nervous system Interneuron Link afferent and efferent neurons Efferent/motor neuron Transmit information away from the central nervous system to an effector muscle/gland - Neural pathways are highly specific with high speed conduction of signals along nerve fibres - They require more energy than hormonal responses as neurons use active transport to **produce an [action potential] (or electrical impulse)** - -  +-----------------------------------------------------------------------+ | **Action potential** = electrical impulse that is produced by | | depolarisation | | | | **Depolarisation** = shift in electrical charge inside and outside | | the cell caused by opening of Na+ channels | | | | **Threshold** = level of depolarisation which neuron must reach to | | release action potential | | | | - Limit that must be reached before we have the successful release | | of the action potential | | | | **Repolarisation** = when the cell returns to original electron | | charge distribution due to Na+ channel closure | | | | - K+ channel opens during repolarisation and K+ exits → helps to | | correct all charge distribution → return to resting membrane | | potential | | | | **Resting membrane potential** = normal electrical change | | distribution | | | | **Membrane potential** = difference in electrical charge distribution | | inside/outside cell → dictates the release of the electrical impulse | | | | - Starts negative → one side of the cell is less positively charged | | compared to the other | | | | - Low amount of sodium inside → high amount of sodium outside → bc | | there is a large difference between the inside and the outside of | | the cell, the membrane potential is negative | | | | - Sodium channels open → amount of sodium/positive charge inside | | and outside are the same → charge distribution is altered → | | membrane potential increases | | | | - K+ channel → facilitates | | | | **Hyperpolarization** = state wherein the cell is unable to | | depolarisation before returning back to resting membrane potential | | | | - Drops lower than what it started off with → too much K+ leaks out | | → dramatically different (inside and outside) → cannot restart | | the repolarization process because we are lower than the resting | | membrane potential | | | | - Na+ channel lets things in | | | | - K+ lets things out | | | | | | | | - Irl example: Kicking a knee → if we kick it again, the leg won\'t | | move because of the above graph\^ | +-----------------------------------------------------------------------+ - In vertebrates, the nervous system consists of the **central nervous system (CNS) and the peripheral nervous system (PNS)** - - The PNS can be further divided into the somatic nervous system and autonomic nervous system - - - The autonomic nervous system is made up of the sympathetic, parasympathetic and enteric nervous systems **Structure** **Function** -------------------------------- ----------------------------------------------------------------------------------------------------------------- Sympathetic nervous system Increases energy use, prepares the body for a 'fight or flight' response by increasing heart rate and metabolic Parasympathetic nervous system Conserves energy, increases digestion, slows heart rate Enteric nervous system Found within the wall of the gut, coordinates digestive functions - Neurons never touch. Instead, dendrites and axons get very close, **forming a gap called a synapse** - Communication occurs by the **release of neurotransmitters**, signalling molecules that **traverse the synapse by diffusion** - - Water Balance in Plants ----------------------- - Plants have **simpler** mechanisms to achieve homeostasis than animals - - **NOTE:** Phototropism refers to the growth of an organism (usually plants) in response to light - In addition to maintaining water balance, **plants need to remove metabolic wastes such as oxygen and carbon dioxide**. They also need to maintain concentrations of nutrients within cells ### Stomata - Plants have stomata which are small non-specific excretory pores found on the surface of leaves - Stomata are generally found on the underside of leaves and range in size depending on the species of plant - - - Stomata allow for transpiration to occur. Transpiration is: ***"The loss of water from plants by evaporation"*** - Transpiration occurs when the **guard cells are swollen, which causes the stomata to open** - - - +-----------------------------------+-----------------------------------+ | - Plants can regulate the size |  | | of their stomata to conserve | | | water | | | | | | - - - | | | | | | - The stoma will remain closed | | | until it receives a supply of | | | water | | +-----------------------------------+-----------------------------------+ Structural Adaptations ---------------------- ### Water Balance in Plants +-----------------------------------+-----------------------------------+ | Plant type | Description | +===================================+===================================+ | Hydrophytes | - Adapted for water loss | | | | | - Live in freshwater and | - Have extremely high number of | | receive a constant supply of | stomata on their upper | | water | epidermis to maximise water | | | loss and prevent tissue | | | flooding | | | | | | - Large leaves to maximise | | | surface area for | | | transpiration and | | | photosynthesis | +-----------------------------------+-----------------------------------+ | Mesophytes | - Average number of stomata on | | | the underside of their leaves | | - Live on land and receive | to maximise photosynthesis | | regular and adequate water | and removal of excess water | | supply | | | | - Not adapted for water | | | conservation, but can close | | | their stomata to regulate | | | water loss when necessary | +-----------------------------------+-----------------------------------+ | Xerophytes | - Adapted for water | | | conservation | | - Live in conditions and | | | receive inadequate water | - Have very few stomata located | | supply | within depressions and | | | surrounded by stomatal hairs | | - Like australian plants | which help to maintain a | | | humid microclimate | | | | | | - Often have small leaves with | | | thick waxy cuticles to | | | prevent transpiration | +-----------------------------------+-----------------------------------+ #### Hydrophytes -- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Water lilies have a large number of stomata on the upper epidermis to maximise water loss and prevent tissue flooding. Their large, flat leaves also maximise their exposure to sunlight to increase photosynthetic activity. -- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- #### #### Mesophytes ------------------------ -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  Pansies are terrestrial plants and receive a regular supply of water. They have a regular number of stomata on the lower epidermis to regulate water balance. These stomata will close to conserve water when required. ------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- #### #### Xerophytes +-----------------------------------+-----------------------------------+ | | Eucalyptus leaves hang vertically | | | to minimise exposure to sunlight. | | | This prevents water loss through | | | transpiration. | +===================================+===================================+ |  | Marram grasses have leaves that | | | roll up in response to hot and | | | dry conditions.The hairs on the | | | inner surface of the leaf trap | | | moisture and provide a humid | | | environment, preventing | | | transpiration and water loss. | +-----------------------------------+-----------------------------------+ | | Desert plants and plants living | | | at high altitudes have fine hairs | | | covering their leaves which gives | | | them a white, reflective | | | appearance. This can be observed | | | in the edelweiss flower. | | | | | | The reflective hairs cools the | | | surface of the leaf and prevents | | | evaporative water loss | +-----------------------------------+-----------------------------------+ |  | Succulents store water in their | | | leaves and stems. | | | | | | Cacti exhibit a complete loss of | | | leaves and their stems are | | | responsible for photosynthesis. | | | They are often spherical in | | | shape, reducing their SA:V. This | | | minimises their exposure to | | | sunlight to facilitate water | | | conservation. | +-----------------------------------+-----------------------------------+ 2. Causes and Effects ===================== - - - - - - - Investigate the treatment/management, and possible future directions for further research, of a non-infectious disease using an example from one of the non-infectious diseases categories listed above [[Causes And Effects]](https://www.conquerhsc.com/hsc-biology-notes-module-8-non-infectious-disease) Genetic Diseases ---------------- - Genetic diseases are caused by abnormalities in the genome - Most genetic diseases are **hereditary, meaning they are passed from parent to offspring** - - Any genetic material in a cell can be the cause of genetic disease - - - ### Down Syndrome - Down syndrome is caused by a **trisomy mutation in chromosome 21** (trisomy-21) - - Trisomy occurs due to **nondisjunction of chromosomes** during either anaphase step of meiosis - -  +-----------------------------------+-----------------------------------+ | | - Older mothers are more at | | | risk at having a baby with | | | Down syndrome | | | | | | - | | | | | | - Symptoms of Down syndrome | | | include: | | | | | | - - - - - - | +-----------------------------------+-----------------------------------+ - Down syndrome, along with most genetic diseases, is **incurable**. Thus, the emphasis is placed on **management** - Early intervention by various healthcare professionals is important to **improve quality of life**. - - - - ### Cystic Fibrosis - Cystic fibrosis (CF) is caused by a **mutation on the CFTR** (cystic fibrosis transmembrane conductance regulator) **gene** on chromosome 7 (somatic chromosome) - It is an **autosomal recessive disease** - - The CFTR gene codes for an integral transmembrane channel, particularly cells in the respiratory and gastrointestinal systems - - This allows for the **cellular surface to become hydrated**, allowing any extracellular mucus and it contents to be easily swept and removed from the body  +-----------------------------------+-----------------------------------+ | | - People with CF either fail to | | | make the CFTR protein or make | | | a dysfunctional form. Sodium | | | and chloride ions can't be | | | transported out of the cell | | | and thus **accumulate in the | | | intracellular environment** | | | | | | - | | | | | | - In the respiratory system, | | | the cilia (small hairs) on | | | the surface of the cells | | | lining the airways are | | | **unable to clear the sticky | | | mucus** | | | | | | - | +-----------------------------------+-----------------------------------+ - People with Cystic Fibrosis may experience +-----------------------------------+-----------------------------------+ | - Coughing | - Small stature | | | | | - Shortness of breath | - Late onset puberty | | | | | - Respiratory infections | - Reflex | | | | | - Excessive appetite | - Constipation | | | | | - Anorexia | - Fatigue | | | | | - Poor weight gain | - Sinusitis | +-----------------------------------+-----------------------------------+ - Cystic fibrosis is screened for within 2 months after birth using a heel-prick test. - - Physiotherapy helps clear the build up of sticky mucus in the lungs. Inhaled medications as well as intermittent positive pressure breathing (IPPB) machines help with ventilation - If symptoms are severe, a lung transplant is performed. The cells in the transplanted lung will have **normal copies of the CFTR gene**, alleviating respiratory symptoms and extending life expectancy - - Environmental Exposure ---------------------- - Diseases caused by environmental exposures are diverse and varied. Some examples include - - - - - - - - ### Hypersensitivity and Allergic reactions - Hypersensitivity reactions occur when the **immune system malfunctions and reacts to harmless antigens** - - There are four types depending on the antigens and the immune mechanisms involved - - - - - Type I hypersensitivity reactions occur **rapidly** (within minutes) when the immune system responds inappropriately to **harmless environmental antigens (allergens)** - Common allergens include : - - - - - - The severity of the allergic reaction depends on the individual and the antigen - - Allergic reactions are mediated by an antibody (IgE) produced by plasma cells secreted into the blood.  - Upon **first exposure**, the antigen binds to receptors on B-cells, causing them to mature into plasma cells - The plasma cells secrete IgE. One end of IgE binds to the receptors on the surface of mast cells - - There are no symptoms experienced upon primary exposure - Upon **secondary exposure**, the antigen binds to IgE on the mast cells, bridging two adjacent IgE molecules - - Histamine has the following actions - - - - - This causes white blood cells to fluid and extravasate - - - The patient may also find it difficult to breathe due to swelling of the mucosal lining of the airways - **Note:** Extravasation means to move out of blood cells - Allergic reactions can be treated with aniti-histamines and steroids. - - - EpiPens are intramuscular adrenaline injections. Adrenaline causes: - - - - **Note:** The effects of adrenaline (from an EpiPen) are not permanent - the patient must be taken to hospital for emergency treatment  ### Type I diabetes - Type I diabetes mellitus is an auto-immune disease that affects (BETA)-cells in the pancreas - - It is hypothesised that an environmental insult, like viral infection, causes the immune system to recognise (BETA)-cells and their associated antigens as foreign, leading to immune attack - - Signs and symptoms of type I diabetes include: - - - - - - - - +-----------------------------------+-----------------------------------+ | | - Diabetics have to frequently | | | test their blood glucose to | | | make sure it remains within | | | normal limits | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ |  | - Type I diabetes is treated | | | with **exogenous insulin.** | | | Manual administration of | | | insulin replaces the role of | | | (BETA)-cells in glucose | | | management | | | | | | - Electronic pumps include an | | | embedded sensor that | | | continuously measures blood | | | glucose | | | | | | - | | | | | | - Insulin pumps are usually | | | attached to the waist. They | | | will administer insulin when | | | glucose increases too high | | | | | | - | +-----------------------------------+-----------------------------------+ ### Asbestosis - Asbestos is a fibrous material commonly used as an insulant in the late 1800s - **Shards of asbestos are released when the material is agitated**. If these shards are inhaled over a long period of time, asbestosis develops - These sharp asbestos fibres are microscopic and can be released into the air when agitated - When asbestos fibres enter the lungs, **an inflammatory reaction begins**. Neutrophils and macrophages will initially try to phagocytose these fibres - - Successful eradication of the fibres leads to macrophages **initiating tissue** repair. This scars the lungs and makes them stiff - +-----------------------------------+-----------------------------------+ | This is a cytological image of | | | several macrophages | | | (unsuccessfully) attempting to | | | phagocytose an asbestos fibre | | | | | | At the top, several macrophages | | | have fused cytoplasms in an | | | attempt to make themselves bigger | | | and stronger to digest the fibre | | +-----------------------------------+-----------------------------------+ ------------------------ ----------------------------------------------------------------------------------------------  Inflamed lung tissue in asbestosis scars over, forming non-functional portions of stiff lung ------------------------ ---------------------------------------------------------------------------------------------- +-----------------------------------+-----------------------------------+ | The constant inflammation can | | | cause asbestosis to **transform | | | into mesothelioma, a type of lung | | | cancer** | | | | | | More than 80% of mesothelioma | | | cases are caused by asbestosis | | +-----------------------------------+-----------------------------------+ Nutritional Diseases -------------------- - Nutritional diseases are caused by unsuitable intake of nutrients - There are two major categorisations - - - - - **Note:** The word "malnutrition" means both under- and overnutrition, but it is commonly used to solely refer to undernutrition ### S**c**urvy - Scurvy is a disease of undernutrition caused by **prolonged vitamin C deficiency** - - - Signs and symptoms include - - - - +-----------------------------------+-----------------------------------+ |  | This patient has gum disease | | | secondary to scurvy | | | | | | Gums are almost completely made | | | of collagen, so in scurvy the | | | gyms become unable to repair them | | | self due to lack of vitamin C | +-----------------------------------+-----------------------------------+ - Risk factors for scurvy include - - - - - - - ### Obesity - Obesity is a disease of overnutrition caused by **chronic positive energy balance.** - +-----------------------------------+-----------------------------------+ | | - Energy balance compares | | | energy intake (through diet) | | | with energy expenditure | | | | | | - - | | | | | | | | | | | | - **NOTE:** Positive energy | | | balance means there is more | | | intake than is expenditure | +-----------------------------------+-----------------------------------+ - Obesity predisposes patients to other non-infectious diseases like: +-----------------------------------+-----------------------------------+ | - - - | - - - | +-----------------------------------+-----------------------------------+ ------------------------ -----------------------------------------------------------------------  This patient has a BMI of 53. They would be considered severely obese ------------------------ ----------------------------------------------------------------------- +-----------------------------------+-----------------------------------+ | | - Obesity is often screened | | | using the body mass index | | | (BMI) | | | | | | - However it is a very coarse | | | measurement and is usually | | | **only used as a screening | | | tool** | | | | | | - | +-----------------------------------+-----------------------------------+ - Waist circumference is a **more accurate measurement of obesity** - - - ----------------------- ----------------------------------------------------------------------------------------------  Everyone has fat, but visceral fat is more associated with obesity and worse health outcomes ----------------------- ---------------------------------------------------------------------------------------------- #### Obesity - Treatment and Management - **[Prevention is always better than treatment]**. Patients should always be counselled on decreasing food intake and increasing physical activity to prevent obesity - **Lifestyle and dietary** **changes** are the first-line treatment for all cases of overweight and obesity - - - Pharmacological therapy can be used to assist with weight loss if lifestyle changes along are not sufficient - - - - Psychological therapy can also be helpful in **motivating patients to lose weight and increasing self esteem by changing unhelpful perspectives** of body image and weight loss - For morbidly obese patients, **bariatric surgery** can be considered - - - +-----------------------------------+-----------------------------------+ | | - A gastric band reduces the | | | size of the stomach by | | | tightening a part of the | | | stomach. This reduces the | | | size of the stomach and | | | decreases appetite by | | | increasing the feeling | | | satiety and fullness | +-----------------------------------+-----------------------------------+ - All pharmacotherapies and surgical interventions have side effects that may not be desired - - - #### Obesity - Future Directions - Many emerging treatments are being researched for obesity, many of them new pharmacotherapeutic agents - - Other promising treatments are more surgical nature - - +-----------------------------------+-----------------------------------+ | Current research is looking into |  | | gastrointestinal liners. | | | | | | A duodenal bypass liner allows | | | the food to completely bypass the | | | stomach and duodenum (small | | | intestine) by using a thin | | | plastic tube. This prevents the | | | food from contacting the | | | absorptive intestinal lining, | | | thus decreasing total nutrient | | | intake. | | +-----------------------------------+-----------------------------------+ ### Starvation - Starvation is a disease of undernutrition caused by **chronic negative energy balance** - The causes starvation are highly diverse, including: - - - - - - Just like obesity, starvation also increases the risk of many non-infectious diseases such as: - - - - - ----------------------------------------------------------------------------------------------------------------------------------- -- This man was rescued from a Viet Cong concentration camp during the Vietnam War. He shows clear signs cachexia, or bodily wasting ----------------------------------------------------------------------------------------------------------------------------------- -- - When food intake is stopped, the body first adopts a **fasting state** - - Once all the body's energy stores are exhausted, the body will then break down proteins for energy to sustain function. This is called **starvation** - +-----------------------------------+-----------------------------------+ |  | - When there is no protein | | | intake (such as in | | | starvation), the belly and | | | the feet may become swollen. | | | This disease is called | | | kwashiorkor. | | | | | | - The lack of proteins means | | | that the body is **unable to | | | establish an appropriate | | | concentration gradient in the | | | tissues** | | | | | | - This leads to fluid retention | | | as water flows via osmosis | | | into areas of protein | | | deficiency | +-----------------------------------+-----------------------------------+ Cancer ------ - Cancer is an umbrella term for a class of diseases which involves the **replication and proliferation of genetically damaged cells** - - **Tumours** can benign or malignant, and they are classed as **cancer when they are classified as being malignant** - - - There are three different mechanisms of malignancy: - - - - - - -- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- This is a benign tumour demonstrating expansile growth. The tumour is also clearly circumscribed (with clear borders) and is not invading or infiltrating into the surrounding tissue - it is simply pushing surrounding tissue away. -- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  Notice that the melanoma is infiltrating into the dermis below. The melanoma does not have clear borders, like the previously shown benign tumour, and is ignoring normal skin architecture. ------------------------ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- - Genetic damage which disrupts the cell cycle punctuates carcinogenesis. There are 4 types of genes that are affected in cancer - - - - - - - - - Mutations in these genes can either be - - - - - - - Some risk factors cancer are modifiable, such as smoking habits, exposure to carcinogens, diet and exercise - The symptoms and effects on the organism depend on where the cancer is found +-----------------------------------+-----------------------------------+ | - - - - | - - - - | | | | | - - - - | - - - - - | | | | | - - - | | +-----------------------------------+-----------------------------------+ ### Host Response - The body has a number of preventative measures to stop cells from turning cancerous - - - - - The immune system is built to **recognise abnormal body cells** if our genetic protections fail - - - Advanced cancers either **evade immune detection, or turn off immune surveillance**. This allows them to grow unchecked and cause damage ### Treatment and Management - Generally, drugs target some pathological process that is present in abnormal cells, and not present in normal cells - - Every cancer is different, even within the same patient. This means that each cancer will have its own susceptibilities and drug targets that will/will not be effective - - Breast cancer involves the cells of the breast, such as: - - - - - Breast tissue is hormonally sensitive - the cells have many receptors for various hormones which modulate milk production and breast development - - Most breast cancers will be treated with a combination of: - - - - - - -- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Radiotherapy involves shooting multiple beams of radiation from different angles to deliver as much radiation to the cancer as possible, whilst minimising radiation dose to surrounding tissues -- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- - When a breast cancer is diagnosed, a sample of the cancer is taken to perform receptor status testing - - The most significant receptors are: - - - - - Breast cancers which are hormone receptor positive (PR+, ER+ or ER+/ER+) can be treated using hormone blockers. These cancers have a better prognosis - - HER2+ breast cancers are more aggressive, but the HER2 receptor can be used as a drug target to treat the cancer - - The breast cancer with the worst prognosis has no usable receptor targets (ER-/PR-/HER2-). They are called **triple-negative cancers** - - - In triple-negative cancer, combination chemotherapy can be used by this comes with many side effects - - 3. Epidemiology =============== **Inquiry question:** Why are epidemiological studies used? - - - - - - [[Epidemiology]](https://www.conquerhsc.com/hsc-biology-notes-module-8-epidemiology) - Epidemiology is: ***"The study of the distribution, pattern and cause of diseases in a population"*** - These studies can be done for both infectious and non-infectious diseases but it is used more widely for non-infectious diseases - - - What useful data can we extract using epidemiological study? - - - - So, epidemiology is: - - - - - Epidemiological studies occur in two steps: 1. - - - 2. - - - Epidemiological studies answer research questions. A research question can be structured using **PICO** **P**opulation What is the population you are interested in ------------------ ----------------------------------------------------------------- **I**ntervention What is the exposure/treatment/disease you are looking to study **C**ontrol What are you going to compare the intervention to **O**utcome What are you going to be measuring the two populations - For example: ***"What effect does commencing pack-a-day smoking in a group of non-smokers have on the incidence of lung cancer?"*** - **Note:** The control is omitted as it is implied in the question what the control group is - Once a research question has been established, the next step to designing a study is deciding who will be in it. This is called **sampling** - - The better the sample represents the general population (or your population of interest), the better your results will be - - - **Note:** power is the mathematical strength of a statistic obtained from experimentation - The correct study design must be chosen to match your question. - - First hand investigations Second hand investigations ------------- -------------------------------------------------------- ----------------------------------------------- Accuracy How close the results are to the "golden value" How consistent the source is to other sources Reliability How consistent the results are between repetitions How trustworthy the source is Validity How well the experiment measures a particular variable How relevant the source is to your research  1 Systematic review and meta analysis Collects data from many papers and combines their results giving a consensus result ------------------------ --- ------------------------------------- -------------------------------------------------------------------------------------------------------------------------- 2 Randomised controlled trial Same as below but the population is split randomly to eliminate bias 3 Non-randomised controlled trial Split population into a treatment group and a control group, and observe what happens when treatment is used 4 Cohort Study Compares data between individuals with a particular risk factor to those without, and follows them for a number of years 5 Case control study Compares data and risk factors between individuals with the condition to individuals without 6 Cross sectional study Gathers data on a set of variables of interest from a population at a single point of time 7 Case report A detailed report of a number of individual cases +-----------------+-----------------+-----------------+-----------------+ | Study design | Characteristics | Advantages | Disadvantages | +=================+=================+=================+=================+ | Case control | Samples | Can highlight a | People might | | study | individuals | factor which is | not remember | | | with a disease | more prevalent | things | | | and individuals | in a group with | correctly when | | | without a | the disease | asked to recall | | | disease | | exposures | | | | | | | | Patients are | | | | | asked about | | | | | previous | | | | | exposure they | | | | | have had in | | | | | their lifetime | | | | | or in recent | | | | | history | | | +-----------------+-----------------+-----------------+-----------------+ | Cohort study | Samples | Gives more | Difficult, time | | | individuals | reliable | consuming, | | | with a specific | results | expensive | | | exposure and | | | | | individuals | | | | | without a | | | | | specific | | | | | exposure | | | | | | | | | | Patients are | | | | | then observed | | | | | after a survey | | | | | for a length of | | | | | time | | | +-----------------+-----------------+-----------------+-----------------+ | Randomised | Involves | Golden standard | Difficult to | | controlled | recruiting | for reliability | recruit | | trial | volunteers and | | volunteers | | | randomly | | willing to | | | allocating them | | subject | | | into two | | themselves to | | | groups: | | experimentation | | | | | | | | 1. Receives | | | | | 'treatment' | | | | | | | | | | 2. Left as a | | | | | control/tre | | | | | ated | | | | | as a | | | | | placebo | | | +-----------------+-----------------+-----------------+-----------------+ Sources of Bias --------------- - Bias occurs when there is a systematic error (error exists within the design of the experiment ) or human error - Human error is usually unintentional or accidental. Bias occurs when there is a systematic error - that is. - Minimising bias is key to a good epidemiological study - Common types of bias: - - - - - - - - Confounding Factors ------------------- - The aim of an epidemiological study can be simplified to: A -\> B - - Causation can be difficult to conclude due to the presence of a confounding factor. - A confounding factor is: ***\"A variable outside of the study design which influences both the*** ***independent variable (A) and the dependent variable (B)\"*** - An example: In this study, there was thought to be a causative link between physical inactivity and heart disease. However, age may be causing both. - ### Examples of Epidemiological Studies #### Doll\'s Case study. - Doll performed a case control study to establish a relationship between lung cancer and smoking. - Case group Patients with lung cancer in London hospitals --------------- ------------------------------------------------------------------------------------------- Control group A random sample of patients from the same hospitals with something other than lung cancer - **What conclusion can we make from these results?** - - **What were the advantages of Dolls case control study** - - - - **What was wrong with Dolls case study** - - - - - - #### Hills Cohort Study - Hill performed a cohort study to assess the potential effects of smoking on health and disease. - Case group English doctors who were smokers --------------- -------------------------------------- Control group English doctors who were not smokers - Results: Number of daily cigarettes Lung cancer deaths (n) Lung cancer deaths (%) ---------------------------- ------------------------ ------------------------ 0 (non smoker) 3 2% 1 - 14 22 16% 15 - 24 54 40% \> 25 57 42% Total 136 100% - **What conclusion can we make from these results?** - - **What was good about Hill\'s case study?** - - - - **What was wrong with Hill's cohort study** - - - - - #### PEAK\'s Randomised Controlled Trial - Let\'s try designing our own epidemiological study to demonstrate a causative relationship between smoking and lung cancer. We will design a randomised controlled trial to produce the highest quality evidence. - What are our treatment and control groups? Treatment group Smoke a pack a day (20 cigarettes) from the start date of the study ----------------- --------------------------------------------------------------------- Control group Continue to be a non-smoker - We will split the population perfectly evenly and randomly into these two groups. - What are we measuring? - - - What do we hypothesise? - - - In practicality, what problems would we run into? +-----------------------------------+-----------------------------------+ | Sampling | - Where would we be recruiting | | | our patients from? | | | | | | - How do we get a perfect | | | sample like this in the real | | | world | +===================================+===================================+ | Treatment | - How ethical is it to make a | | | group of people starting | | | smoking for the sake of | | | science, especially if we | | | have a reasonable suspicion | | | that it causes lung cancer | | | | | | - Will every single patient | | | comply 100% with the | | | experiment? Will some smoke | | | more/less | +-----------------------------------+-----------------------------------+ | Measurement and follow-up | - How do we plan to get these | | | patients back every 2 years | | | to be measured | | | | | | - How do we detect lung cancer | | | | | | - Currently X-rays can | | | reasonably do this, but X | | | rays cause cancer as well | | | | | | - What if a patient dies due to | | | unforeseen circumstances, or | | | leaves? | | | | | | - The loss to follow up | | | introduces bias | +-----------------------------------+-----------------------------------+ - So although randomised controlled trials are considered the gold standard for epidemiological study, **this study design is inappropriate** for the scientific question we are trying to answer. - - - - - - - - State of Obesity in Australia ----------------------------- - Australia is fast becoming a fatter country. - - According to WHO data, the prevalence of overweight/obesity in Australia was: - Data from the Australian Institute for Health and Welfare (2014) breaks down this statistic: +-----------------------------------+-----------------------------------+ |  | - The trends that can be seen | | | in this graph include: | | | | | | - - | | | | | | - - - | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | | - A confidence interval shows | | | the area in **which the study | | | is 95% confident the true | | | value lies in.** | | | | | | - | | | | | | - What trend do you notice from | | | the graph? | | | | | | - | +-----------------------------------+-----------------------------------+ - This graph, from the AlHW 2018 report \"Australia\'s Health\", shows the prevalence of overweight and obesity in adults - The trends that can be seen in the graph include: - - - - - - - - The following graph shows the trends of overweight/obesity for children: - The trends that can be seen in this graph include: - - - - - - - The key trends in overweight and obesity in Australia are: - - - - - - Diseases caused by environmental exposure - The Australian Institute of Health and Welfare released a report called Cancer in Australia (2019)\" which outlines the main statistics concerning cancer. - Over 1 million people alive in Australia have lived or are living with cancer. - - The risk factors for cancer are plentiful. This graph shows the burden of specific risk factors in DALYs.  - **NOTE:** DALY stands for disability-adjusted life years, and is a measure of how many years of life a disability takes from you - The trends that can be seen in this graph include: - - - - - - +-----------------------------------+-----------------------------------+ | - These graphs show the | | | survival rates of melanoma, | | | prostate and lung cancer | | | stratified to cancer stage at | | | diagnosis | | | | | | - - - | | +-----------------------------------+-----------------------------------+ ------------------------ --  ------------------------ -- - The trends that can be seen from these graphs include: - - - - - - - The following graph summarises the incidence of all cancers per 100,000 people.  - The trends that can be seen from this graph include: - - - - - The following table summarises data about the 10 most common cancers at principal diagnosis, stratified to sex - The trends that can be seen in the graph include: - - - - - - - The key trends in cancer in Australia are: - - - - - - 4. Prevention ============= **Inquiry question:** How can non-infectious diseases be prevented? - - - [[Prevention]](https://www.conquerhsc.com/hsc-biology-notes-module-8-non-infectious-disease-prevention) Preventative Healthcare ----------------------- - Preventative healthcare focuses on population-level educational programs and health campaigns to improve health. There are three main levels of prevention - - - - - - ### Primary Prevention - Primary prevention involves protecting individuals from disease BEFORE it develops. - - - Health promotion and educational campaigns make up the majority of primary prevention. - - - In Australia, there are many well-known primary prevention programs. - - - - +-----------------------------------+-----------------------------------+ | - Plain packaging with very |  | | graphic, of a nationwide | | | primary prevention campaign | | | to reduce smoking. The | | | graphic nature of the | | | packaging serves to | | | discourage - some smokers | | | avoid specific images on | | | their smokes because they are | | | so graphic | | +-----------------------------------+-----------------------------------+ ### Secondary Prevention - The earlier a problem is discovered and addressed, the better the outcomes. This rings true for healthcare as well. - Secondary prevention focuses on **screening, the practice of doing routine checks to attempt to diagnose disease early** and address it before it becomes a bigger problem. - - **Note:** S for \"secondary\", S for \"screening" - Australians are not well known for regularly visiting a doctor for a check up. However, this practice is important to help screen for many diseases, including but not limited to: - - - - - - All of these diseases (and others) do not require anything more than a medical history, a physical exam and a blood test. - Breast screening is a well-known phenomenon. There are 2 main components to breast screening in Australia: - - - - - - +-----------------------+-----------------------+-----------------------+ | - In a mammogram, | |  | | pressed flat and | | | | an X-ray is | | | | taken. The above | | | | Image shows an | | | | abnormal | | | | mammogram, with | | | | an unidentified | | | | opacity. | | | +-----------------------+-----------------------+-----------------------+ +-----------------------------------+-----------------------------------+ | - Women are encouraged from | | | puberty to regularly examine | | | their own breasts by | | | massaging them, becoming | | | familiar with their usual | | | texture and observing them in | | | the mirror | | +-----------------------------------+-----------------------------------+ ### Tertiary Prevention - Tertiary prevention focuses on **preventing further progression of an already-present disease**, and fixing any damage done so far - - A big part of tertiary prevention is routine visits to an appropriate health care professional, ensuring that compliance to preventative treatment is appropriate. - Diabetes (type I and II) has many long term complications, such as: - - - - - - If a patient is diagnosed with diabetes, we need to treat in order to prevent these complications - Management of diabetes is usually overseen by a GP who will refer the patient to various health services like: - - - - - - Although no problems may be currently present to lead the patient to see these professionals, the preventative aspect is just as important ------------------------ -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  This is a patient with a severe diabetic foot ulcer. Patients who do not regularly visit a podiatrist are at risk of developing a diabetic foot ulcer (in extreme cases) gangrene that may warrant having a foot amputation ------------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Gene Therapy ------------ +-----------------------------------+-----------------------------------+ | - Gene therapy is a **new | | | method of treating disease | | | using genes and | | | recombination**, instead of | | | traditional medicines | | | | | | - | | +-----------------------------------+-----------------------------------+ - This technique is done by extracting the damaging DNA from a host cell, then injecting healthy DNA into that host cell - This is usually done via a **viral vector**, as viruses infect hosts by injecting DNA into somatic cells to replicate viral proteins - - The injected DNA then triggers the production of required proteins, thus curing (or providing a good means of management of) the genetic disease ### Cystic Fibrosis - Cystic fibrosis is caused by a **mutation to the CTFR gene** - - The CTFR protein produced from this gene regulates mucus production, swear and digestive processes - Cystic fibrosis can be treated by **somatic gene therapy** - Cystic fibrosis can be treated by using **viral vector** containing copies of a healthy CTFR gene. - - - - #### Limitations - **Creating the genetically modified viruses is expensive and time consuming** - Treatment is slow, as it relies on gradually replacing the faulty genes with functional ones - The treatment **lasts for a relatively short period of time** - - - - There is also a risk that the viral vector will become pathogenic - - - **[Liposomes]** are another form of gene therapy. It is a genetic material encased in a **phospholipid vesicle**. They are able to administer genes using endocytosis - 5. Technologies and Disorders ============================= **Inquiry question:** How can technologies be used to assist people who experience disorders? - - - - - - - - - [[Technologies And Disorders]](https://www.conquerhsc.com/hsc-biology-notes-module-8-technologies-and-disorders) - Anatomy of the Ear ------------------ - The ear is a sensory organ responsible for detecting **auditory stimuli** from the environment - It is divided into three regions - - - - - -  ### External Ear Structure Description Function ------------------- ------------------------------------------------------------------------------------------ -------------------------------------------------------------------------------------------------------------------------------------- Pinna Visible part of the ear, composed of cartilage and skin Channels sound down the ear canal, helps determine direction of sound and protects ear Ear canal Tube leading from the pinna to the tympanic membrane Channels sound wave to tympanic membrane, produces a waxy substance to protect and lubricate the ear Tympanic membrane A sensitive membrane otherwise known as the eardrum, divides the external and middle ear Vibrates with the same frequency as the sound wave that hits it, provides an airtight protection between the external and middle ear *Sound collected in the pinna → passes into external acoustic meatus → causes vibration in tympanic membrane* ### Middle Ear  Structure Description Function -------------- ---------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Ear ossicles Three small bones in the middle ear: malleus, incus and stapes Transfers vibrations from the tympanic membrane to the middle of the ear to the oval window and reduces the level of vibration on the tympanic membrane. It also amplifies the force of vibrations to the oval window Oval window Thin membrane that divides the middle and inner ear Receives the vibrations of the tympanic membrane from the ossicles at a much greater force. Bulges in and out, transferring vibrations of the oval window to the fluid in the inner ear Round window Located below the oval window Terminates the cochlear canals. It also acts as a valve to relieve pressure build up in the fluid filled cochlear *Sound collected in the pinna → passes into external acoustic meatus → causes vibration in tympanic membrane → ossicles amplify force of vibration to the oval window → force of vibration transferred to fluid of inner ear* ### Internal Ear Structure Description Function ---------------- ----------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------- Cochlea Has a snail-shell appearance, it has a long tube of liquid wound around itself Fluid within the cochlea transfers vibrations to the hairs in the Organ of Corti Organ of Corti Lies within the cochlea, containing millions of receptor hair cells attached to nerves. Each hair cell detects sounds of specific frequencies Transforms mechanical energy (vibration of sound waves) into an electrical signal Auditory nerve A bundle of nerve fibres bound together Transports electrical signals to the brain to be interpreted *Sound collected in the pinna → passes into external acoustic meatus → causes vibration in tympanic membrane → ossicles amplify force of vibration to the oval window → force of vibration transferred to fluid of inner ear → fluid in cochlea transfer vibrations to stereocilia in organ of corti → transforms mechanical energy which can be passed through auditory nerve and into the brain* Physiology of the Ear --------------------- ### Sound - Sound is produced when there is a vibration of particles. Therefore, a **medium** is required for sound to propagate - A medium is: ***"Any material through which the energy of sound waves travels"*** - - Sound travels through different media as a **compression** wave ------------------------ ----------------------------------------------------------------------------------  Notice the compression of air molecules, owing to sound being a compression wave ------------------------ ---------------------------------------------------------------------------------- +-----------------------------------+-----------------------------------+ | - Sound waves have frequencies | | | and amplitudes | | | | | | - - | | | | | | - The **frequency** determines | | | the **pitch** of the sound | | | | | | - - | | | | | | | | | | | | - The **amplitude** determines | | | the **volume** of the sound | | | | | | - - | | +-----------------------------------+-----------------------------------+ ### Hearing 1. Sound is funnelled into the ear canal by the **pinna** 2. It travels down the ear canal and causes **tympanic membrane** to vibrate - 3. The tympanic membrane transmits these vibrations to the ossicles - - 4. In the inner ear, vibration of the oval window by the stapes causes a compression wave in the fluid of the cochlea 5. The compression wave bends the stereocilia of hair cells, causing a nervous impulse to travel from the hair cells through the auditory nerve to the brain - - The cochlea is a coiled tube lined with many hair cells. These hair cells, together with the basilar and tectorial membranes are collectively called the **Organ of Corti** - - The further along the tube of the cochlea, the lower frequency (lower pitch) the sound is detected +-----------------------------------+-----------------------------------+ |  | Pitch is mapped to the cochleas | | | length | | | | | | The further in through the | | | cochlea, the lower the detected | | | pitch will be | +-----------------------------------+-----------------------------------+ +-----------------------------------+-----------------------------------+ | | This diagram shows the cochlea in | | | traverse cross-section, focusing | | | on the Organ of Corti | | | | | | As the fluid in the cochlea | | | vibrates, the tectorial membrane | | | vibrates. This bends the | | | stereocilia of the hair cells and | | | leads to the perception of sound | +-----------------------------------+-----------------------------------+ Disorders of the Ear -------------------- ### Conductive Hearing Loss - Conductive hearing loss is when sound is not conducted efficiently **through the outer and middle ear** - - - There are several reasons for conductive hearing loss, including: - - - - Treatment involves addressing the cause of the problem - - - - In cases where the conductive problem cannot be fixed, such as [otosclerosis] (thickening of the ossicles), a **bone conduction hearing aid** can be used to increase the volume of sounds - ### Sensorineural Hearing Loss - Sensorineural hearing loss involves the **inner ear or the nervous circuitry** that lead to the perception of sound - - There are several reasons for sensorial inaugural hearing loss, including: - - - - - - Sensorineural hearing loss is a permanent and untreatable, but it can be managed with a **cochlear impact** - - - - ### Mixed hearing loss - Combination of sensorial and conductive hearing loss ### Auditory Processing Disorders - When the brain has problems processing information contained in sound - Brain's inability to recognise and interpret sound - - Problems when transmitting information from the cochlea to the brain +-----------------+-----------------+-----------------+-----------------+ | | **Conventional | **Bone | **Cochlear | | | hearing aids** | conduction | implants** | | | | hearing implant | | | | | (MOST | | | | | EFFECTIVE)** | | +=================+=================+=================+=================+ | Mechanism | Amplifies sound | Captures sound | Captures sound | | | and plays this | and causes | and converts it | | | directly to the | vibration of | into electrical | | | ear | the bones of | impulses which | | | | the skill to | are used to | | | | vibrate the | directly | | | | round window | stimulate | | | | and cochlea | auditory nerves | +-----------------+-----------------+-----------------+-----------------+ | Indication | Moderate | Only for | Mostly used for | | | conductive | conductive | sensorineural | | | hearing loss | hearing loss | loss | | | | | | | | Minor | | Can be used for | | | sensorineural | | very severe | | | hearing | | conductive | | | | | hearing loss | +-----------------+-----------------+-----------------+-----------------+ | Appearance | Can be | Surgery hides | Surgery hides | | | unsightly and | most of the | most of the | | | obvious | implant inside | implant inside | | | | the head | the head | +-----------------+-----------------+-----------------+-----------------+ | Sound quality | Minimal loss of | Minimal to | Significant | | | sound quality | little loss of | loss of sound | | | | sound quality | quality and | | | | | clarity | +-----------------+-----------------+-----------------+-----------------+ | Reception | Some can cancel | | Highly distance | | limitations | out background | | reliant and | | | noise | | captures a lot | | | | | of background | | | | | noise | +-----------------+-----------------+-----------------+-----------------+ | Cost | Relatively | Expensive due | Expensive due | | | cheap | to surgery | to surgery | +-----------------+-----------------+-----------------+-----------------+ ---------------------------------------------------------------------------------------------------------------------------------------- ------------------------ Conventional hearing aids are essentially a microphone connected to an amplifying earpiece. They are relatively simple in construction  ---------------------------------------------------------------------------------------------------------------------------------------- ------------------------ -- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Bone conduction implants are contained within the bone of the skull. Sounds are captured by the receiver cause the implant to vibrate the bones of the skill to facilitate hearing -- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ ----------------------------------------------- ------------------------ Bone conduction implants are usually discrete  ----------------------------------------------- ------------------------ -- ------------------------------------------------------------------------------------------------------------------------------------------------------- Insertion of cochlear implant involves surgery to place electrodes into the cochlea. This electrode is then used to directly stimulate sensory nerves -- ------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------- ----------------------- They are similar to a conventional hearing aid, which can be unsightly to some patients  ----------------------------------------------------------------------------------------- ----------------------- Anatomy of the Eye ------------------ - The eye is a sensory organ responsible for detecting visual stimuli from the environment - Each eye has many photoreceptors called rods and cones which allow for night vision and colour vision respectively. - +-----------------------+-----------------------+-----------------------+ | Structure | Description | Function | +=======================+=======================+=======================+ | Conjunctiva | Transparent membrane | Lubricates and | | | covering the sclera | nourishes the eye | +-----------------------+-----------------------+-----------------------+ | Cornea | A sensitive, | Refracts light, | | | tran