Biology (B3) - Homeostasis

This set of notes is for homeostasis, AQA, GCSE biology (B3). In this topic there are 7 sub-topics which are as follows:

Staying in Balance          The Role of the Kidneys          Treatment with Dialysis        Kidney Transplants          Controlling Body Temperature          Controlling Blood Glucose          Treating Diabetes

HideShow resource information

Staying in Balance

Our bodies are taking in substances through breathing and what we eat and drink, we also make substances through chemical reactions. However, if there is a build up of these substances they could damage cells or interfere with reactions.

To stop this we excrete these products through sweating, breathing, faeces and urine.

The proceess of keeping everything balanced is homestasis.

An example of homeostasis is keeping water levels balanced. 

if we have to much water our cells can swell and possibly burst, if we have too little they will shrink and function less efficiently, also, it makes it more difficult for other substances to move around.

Many things affect the movement of water like ions. If there isn't a right concerntration of ions then the water may move into or out of our cells through osmosis.

1 of 7

The Role of the Kidneys

Proteins are digested into amino acids which pass easily through the gut wall into the blood to be taken where needed. However the blood can only hold so much so any excess amino acids must be excreted. 

They are removed by the liver which breaks them down into urea, which is toxic in high doses so to remove the urea from the blood, which is the job of the kidney.

You have two kidneys and each one is made up of over one million tubules which filter the blood and remove unneeded substances, like urea.

There is a small capillary network at the start of each tubule and each cell that lines it have very leaky membranes which allows the small molecules dissolved in the plasma to be filtered from the blood. This leaves the cells and large molecules inn the blood vessel.

Glucose in the tubule are absorbed back into the capillary because it is needed for respiration. This is to make sure there is the right balance of water and ions.

The fluid that has remained in the tubule is now urine which goes into the bladder to be excreted. 

2 of 7

Treatment with Dialysis

Kidneys can fail to work properly through an accident or a disease, if both kidneys fail, the concerntration of urea will increase and the amount of water and ions won't stay balanced.

Many things can cause kidney diseas like infection, diabetes, long-term high blood pressure or blockage of the tubbes by hard lumps called kidney stones, but only a small portion of these will go on to get kidney failure.

The treatment for this is dependant on the problem, if someone has kidneystones, the stones can be broken up using ultrasound, but for some cases haemodialysis is used.

For this, needles are inserted into blood vessels and blood flows from the patient through a tube into a filter called the dialyser and back into the patient.

The dialyser has a partially permeable membrane separating the blood from the dialysing fluid which contains glucose and useful minerals similar to those in normal plasma.

The glucose and minerals will diffuse into the blood if the blood has a low concerntration of these and if the blood has a high concerntration, they will difuse into the dialysing fluid. Waste products will diffuse out of the blood as the dialysing fluid has none of these. 

3 of 7

Kidney Transplants

Another way of treating kidney failure is using a transplant.

Usually, the old kidneys are left in place, unless they are innfected and the new kidneys are attatched in the abdomen. The patient must be as healthy as possible before the operation as the body is under strain during it. Only one kidney is transplanted as only one is needed.

Unfortunately, finding the right donor is hard as ever cell has an antigen on the surface which define your tissue type and depend on your genes.Your immune system will produce antibodies to attack antigens that don't match your cells. Therefore you need to have as good a match as possible which is why many people find donors from family members.

No matter how good the kidney match the immune system will always attack so to slow the process the patient must take immunosupprssant drugs for the rest of their lives. On average a kidney will last about eight years.

4 of 7

Controlling Body Temperature

Your central core body temperature mkust always be kept at 37 degrees celcius.

The thermoregulatory centre in your brain detects the change of temperature through the temperature of the blood flowing through the brain and the receptors in your skin detect changes in your skin temperature.

If you core temperature is too high, nerve impulses are sent to the blood vessels to dilate (open wider) so more flood flows nearer the skin surface. The heat is lost from the skin by radiation and you may start to sweat.

Sweat goes onto the surface of the skin and evapourates becoming water vapour, this requires energy which is taken from the skin, cooling it down. As the skin temperature goes down, so does the rate of sweating. Unfortunately, sweatig cause the loss of water and some ions which have to be replaced through food or water.

If the core temperature gets too low, nerve impulses are sent to the blood vessels to constict (narrow) reducing the flow from the surface therefore the amount of lost heat. Also the energy from respiration cause muscles to have small rapid contractions (shiver) and also provides heat to warm body tissues.

5 of 7

Controlling Blood Glucose

If there was too much glucose in the blood, it would cause a loss of water through osmosis. The body has to take glucose out of the blood, therefore, for respiration or to be stored.

The control of how much glucose there is in your body is controlled by the pancreas.

If the concerntration is too high, the pancreas releases a hormone called insulin which cause cells, especially in the liver and muscles, to take glucose from the blood, lowering the concerntration. The muscles use glucose for respiration and the liver stores it as glycogen.

If the concerntration gets too low, the pancreas produces glucagon which stimulates the liver to release stored glucose into the blood, therefore lifting the concerntration.

Diabetes is when you cannot control your glucose levels. Symptons for this is finding glucose in your urine, tiredness and constant thirst. If glucose levels are too high it can lead to a coma or death so it is imerativ to be treated. 

Type 1 diabetes is where the pancreas produces no insulin so glucose levels rise to dangerous levels after eating, the treatment is injections, a controlled diet and exercise.

6 of 7

Treating Diabetes

Diabetes can cause blindness and kidney failure so it is important to be treated.

Insulin is usually injected because if swallow, it would be broken down in the stomach as it is a protein. There are two forms of it, one is fasting acting and taken just before eating food and the other is slow acting and injected once a day. many patients take a both.

The correct dose is calculated using blood test when they need an innjection which is done using a pinprick of blood measured on a blood glucose meter.

Another method is insulin pumps which continually supply insuling just under the skin.

INSULIN INJECTIONS ADVANTAGES: 1. Discreet 2. Cheaper equipment DISADVANTAGES: 1. Greater chance of high or low concerntration of glucose 2. Uses more insulin.

INSULIN PUMP ADVANTAGES: 1. Better control of glucose concerntration 2. Uses less insulin. DISADVANTAGES: 1. Must be worn always 2. Expensive equipment.

7 of 7


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Homeostasis resources »