Notes

Homeostasis describes all of the processes that happen in a cell or organism to maintain (keep) conditions optimal. This is needed to respond to changes in the internal and external environment.

Because humans are organisms that live in a changing environment, it is important to regulate our body’s internal conditions to ensure that our enzymes and cells function well.
If conditions are not optimal, then our enzymes can denature, reducing their ability to catalyse metabolic reactions.

Conditions that need to be regulated are:
Urea concentration
Internal body temperature
Blood sugar levels
Water levels
Carbon dioxide levels

Control systems are made up of three part coordination centre (receives and processes information arriving from receptor cells) recpetor cells (detect changes in the environment) effector (muscles or glands that carry out responses to stimuli)

The body's negative feedback loop: When our internal conditions are optimal, the body does not need to respond. If an internal condition changes and is no longer optimal, the body works to counteract (reverse) the change and return conditions to the optimum. This process is called negative feedback and needs all of the components of the nervous system to work together.

Thermoregulation (Control of Body Temperature)
Our body temperature needs to be kept as close to 37°C as possible. Receptors detect temperature changes and relay the information to the central nervous system (CNS). The CNS then allows effectors (muscles or glands) to respond.There's receptors in the thermoregulatory centre in the brain called hypothalamus which moniters internal body temp as blood flows through the brain. Receptors on the surface of your skin which moniters temp at surface of body.
*When it is too hot: Sweat is released from sweat glands under the skin. Hair erector muscle relaxes causing hairs to lie flat. Blood vessels dilate to allow more blood to enter capillaries that pass close to the skin surface (vasodilation).
*When it is too cold: Muscle contractions increase, causing shivering. Hair erector muscle contracts so hairs stand on end trapping an insulating layer of air around the body (goose bumps). Blood vessels constrict to reduce blood flow in capillaries (vasoconstriction).

*sweating: sweat glands (in the middle layer of skin called the dermis) releases sweat which covers the outer layer of the skin (epidermis). Heat energy from the body is transferred to the water in the sweat and when it has enough energy it evaporates which takes the heat energy with it which lowers the average temp of the body.
*shivering: when we are cold our muscles start to contract automatically. this makes us shiver. this needs energy which is generated through repiration which produces heat and warms us up.
(When it is too hot, sweat glands release sweat. Heat energy from the body is transferred to the water in sweat. As the water evaporates, it takes the heat energy with it. This lowers the average temperature of the body.)

Glucose is fuel for respiration, which is the chemical reaction that releases energy in many living cells
The optimal glucose level in humans is between 6-8 mmol/dm3.
Too little glucose: glucose is important for respiration which releases energy. if not enough, an organism cant produced enough energy. as blood flows through the pancreas, the low conc of blood glucose is detected. this triggers the pancreas to release glucagon into the bloodstream. this is detected by the liver and it converts stores of glycogen back into glucose which can be released into the bloodstream. this process continues until the pancreas detects a normal blood glucose conc.
Too much glucose: has a negative impact on osmosis by affecting conc gradients. Pancreas releases glucagon is too little glucose and insulin if too much glucose.Excess glucose in the body is coverted into glycogen. as blood flows through the pancreas, the high conc of blood glucose is detected. this triggers the pancreas to release insulin into the bloodstream. this is detected by the liver and muscle tissues which take in excess glucose and converts it into glycogen (which is a form of glucose that is insoluble and can be stored for later use) this process continues until the pancreas detects a normal blood glucose conc.

Diabetes sufferers are not able to control their blood glucose levels. There are two types:
In type 1 diabetes, the pancreas cells in the body either produce little or no insulin. This develops during childhood. the cause of it is the immune cells attack the pancreas cells. treatment is to inject insulin when blood glucose levels are too high and can diet and exercise to steady the blood glucose levels.

In type 2 diabetes, sufferers can still produce insulin, but their body no longer responds to it. develops later on in life. old age and being overweight are seen as primary risk factors. treatment: Because the body no longer responds to insulin, injections are an ineffective method of treatment. Instead, type 2 diabetics control their blood glucose levels by managing their diet and doing regular exercise.

Water levels in the body must be kept relatively constant to control the amount of water and ions diffusing in and out of cells. Some factors that disrupt the balance is illness result in dehydration, eating too much salt result in blood ion conc too high, exhaling results in water in the lungs leaving, sweating results in water ions and urea being lost in sweat. kidneys control water and ion levels in the blood. it filters the blood and produces urine to remove unwanted substances like urea and excess water from the body.

Urea needs to be removed from the body because it is toxic. When there is too much urea in the bloodstream, it can harm cells and tissues. urea is formed from the digestion of proteins results in excess in amino acids which cant be stored in the body. in the liver the amino acids undergo a process called demination and the waste producst is ammonia which is converted into urea and excreted from the body as urine.

Each kidney contains millions of very small structures called nephrons. There are two stages in the process of urine production. These stages happen in every nephron. Ultrafiltration: the blood capillaries form a knotted cluster called the glomelarus in the bowman's capsule. the blood is filtered and water, urea and salts move into the nephron tube. Blood cells and proteins remain in the blood as they are too big to move across the capillary walls. Selective reabsorption, useful substances (like glucose and some water) are reabsorbed from the tubule into the bloodstream. This leaves urea, excess salts and excess water to form urine which is excreted.

The volume of urine produced depends on the internal conditions. The volume of water in the blood is monitored by the hypothalamus in the brain. if the body has too much water it responds by the hypothalamus triggers the pituitary gland to stop the release of ADH which reduces the permiability of the kidney tubules so there is less water reabsorbed back into the bloodstream so large volume of dilute urine. if the body has too little water it responds by the hypothalamus triggers the pituitary gland to release ADH which increases the permeability of the kidney tubules so there is more water reabsorbed back into the bloodstream so small volume of concentrated urine.

Dialysis is one possible treatment for kidney failure. It is an essential treatment for people whose kidneys cannot keep the concentrations of urea and salt at an optimum level to ensure that tissue damage does not occur.A dialysis machine is designed to replicate the kidney’s function: The patient is linked up to the dialysis machine and their blood flows into the machine. The machine contains a fluid that is designed to have the optimum concentrations of salts (e.g. sodium and potassium ions) and glucose, as would be found in a healthy person’s blood.The patient's blood passes over a partially permeable membrane in the machine that is designed to replicate the kidney tubules.The dialysis fluid is on the other side of this membrane. A concentration gradient is established, allowing excess ions and urea to diffuse from an area of high concentration in the patient’s blood to an area of low concentration in the dialysis fluid.
Advantages:Life-saving process. More time to find a donor kidney
Disadvantages:Each session lasts 3-4 hours and is needed 3x a week. Increases risk of blood clots and infections
Expensive process.

patients receiving a donor kidney have to take immunosuppressant drugs for the rest of their lives which prevents the immune system from destroying the foreign cells of the transplanted kidney. most kidney transplant are from a close family as antigens wont be recognised as foreign and have a higher chance of being a tissue match and also from people who have recently died, provided that they are a tissue match and have registered onto the organ donor register.
Advantages: Don't need dialysis. Cheaper than dialysis in the long-run. Disadvantages: Kidney may be rejected Long waiting lists. Often have to take immunosuppressant drugs. This can result in patients becoming more prone to other infections