B3 Keeping internal conditions constant

The internal conditions of your body have to be controlled to maintain a constant internal environment. 

Keeping the conditions within a narrow range is called homeostasis.

These include your body temperature, your water and ion balance and your blood sugar levels.

Urea is produced by your liver as excess amino acids are broken down, and is removed by your kidneys into the urine.

If the concentrations of your body fluids change, water will move into or out of your cells by osmosis. This could damage or destroy the cells.

Homeostasis: the maintenance of constant internal body conditions. 

The kidneys filter the blood, excreting substances you do not want and keeping those the body needs.

A healthy kidney produces urine by:

• filtering the blood
• reabsorbing all the sugar
• reabsorbing the dissolved ions needed by the body
• reabsorbing as much water as the body needs
• releasing urea, excess ions and water in the urine

Large molecules such as protein cannot be filtered.

Urea is made in the liver by the breakdown of amino acids. It is poisonous, and removed from the blood by the kidneys during filtration. 

People suffering from kidney failure may be treated by regular sessions on a kidney dialysis machine or by having a kidney transplant.

A dialysis machine carries out the same job as the kidneys. The blood flows between partially permeable membranes.

The dialysis fluid contains the same concentration of useful subtsnaces that the patient's blood does e.g. glucose and mineral ions.

This means that these substances do not diffuse out of the blood so they do not need to be reabsorbed.

Urea diffuses out from the blood into the dialysis fluid.

Dialysis restores the concentration of substances in the blood back to normal, but needs to be carried out at regular intervals.

DIAGRAM:

A diseased kidney can be replaced by a healthy donor kidney.

To try and prevent rejection of the donor kidney, the tissue types of the donor and the recipient are matched as closely as possible.

Immunosuppressant drugs are also used.

Dialysis vs Transplants:

• with a transplant, you are free from the restrictions of dialysis, e.g. diet
• risk of rejection, you have to take medicine every day and have regular check-ups
• you may never get a donor
• dialysis is more readily available
• long term dialysis is more expensive than a transplant

Your body temperature is monitored and controlled by the thermoregulatory centre in your brain.

Your body temperature must be kept as the level at which enzymes work best.

If the core temperature rises:

• blood vessels near the surface of the skin dilate, allowing more blood to flow through the skin capillaries. Energy is transferred by radiation and the skin cools.
• Sweat glands produce more sweat. Its water evaporates from the skin's surface. The energy required for the water to evaporates comes from the skin's surface, which cools.

If the core temperature falls:

• blood vessels near the surface of the skin constrict and less blood flows through the skin capillaries. Less energy is radiated.
• We "shiver". Muscles contract quickly, which requires respiration, and some of the energy warms the blood. 

DIAGRAM:

When deciding the best course of treatment for patients with kidney failure, the doctors need to consider:

• the general health of the patient
• how long the patient has been on dialysis
• the total cost of treatment, the long term costs of dialysis against an expensive operation followed by treatment with immunosuppressant drugs
• the risks of a transplant operation e.. anaesthetics, infection
• availability of donor kidneys

Extreme temperature can be very dangerous for survival because the body's enzymes do not work properly.

Small children have a very large surface area to volume ratio. This means they transfer energy to their surroundings very quickly in cold conditions and dehydrate very quickly in hot conditions.

If the body temperature is too low the respiratory enzymes work too slowly and too little energy is released. If the body is dehydrated, it overheats and the enzymes denature.

Elderly people suffer from hypothermia in cold conditions because they do not move around much to release energy from respiration in the muscles. 

Your blood glucose concentration is monitored and controlled by your pancreas.

The pancreas produces the hormone insulin, which allows glucose to move from the blood into the cells.

In type 1 diabetes, the blood glucose may rise to fatally high levels because the pancreas does not secrete enough insulin. It can be treated by injections of insulin before meals.

Insulin reduces blood glucose concentration.

Glucagon increases blood glucose concentration.

If the level gets too low, receptors in the pancreas detect the low level.

The pancreas releases glucagon, another hormone.

The glucagon causes glycogen in the liver to be converted back into glucose and released back into the blood.

glucose = a sugar found in the blood  

glycogen = a storage carbohydrate found in the liver and muscles  

glucagon = a hormone

Type 1 diabetes is traditionally treated with human insulin produced by genetically engineered bacteria.

The diabetic has to inject before meals every day of their life.

Type 2 diabetes is heated by careful attention to diet and taking more exercise.

New methods of treating and possibly curing Type 1 diabetes include:

• pancreas transplants
• transplanting pancreas cells
• using embryonic stem cells to produce insulin secreting cells
• using adult stem cells from diabetic patients
• genetically engineering pancreas cells to make them work properly