AQA B3 Topic 3. Homeostasis

Transcription

1 AQA B3 Topic 3 Homeostasis

2 Removal of waste & water control (osmoregulation) Key words: Excretion the removal of waste products from the body eg. carbon dioxide & urea Homeostasis the maintaining of a constant internal environment Internal conditions have to be kept within a narrow range of values so the cells can function properly. This is homeostasis. Examples of homeostasis: removal of waste products water & ion concentration body temperature (thermoregulation) blood glucose levels Waste products have to be removed from the body so levels do not become toxic. Waste product Why is it produced? How is it removed? Carbon dioxide Urea Produced through aerobic respiration Produced in the liver when excess amino acids are broken down Through the lungs when we breathe out (exhale) The kidneys remove it from the blood and make urine which is temporarily stored in the bladder What happens if the water or ion content is wrong? Too much water may & leave the cells damaging them. Ions are lost from the body via sweating & urine Ions are gained via eating & drinking

3 Key words: Water control the kidney Urea produced from the breakdown of amino acids toxic Urine mixture of water, excess ions and urea created in the kidney & stored in the bladder Selective reabsorption when the kidney takes back different amounts of water and ions into the blood depending on the bodys demand for them A healthy kidney produces urine by: Water is lost from the body via Exhaling Sweating Urine Water is gained via Drinking Eating 1. Filtering the blood glucose, amino acids, mineral ions, urea & water move from the blood to kidney tubles by diffusion. Proteins & red blood cells are too large to be filtered out the blood. 2. Reabsorbtion all the sugar via active transport 3. Selective reabsorbtion the dissolved ions needed by the body via active transport 4. Selective reabsorbtion as much water as the body needs is selectively reabsorbed by osmosis 5. Releasing urea, excess ions and water as urine Little drunk & hot day = little dark yellow, concentrated urine Lots drunk & cool day = lots of dilute, almost colourless urine.

4 Kidney failure dialysis If a persons kidney stops working properly there are 2 options: 1) Dialysis 2) Kidney transplant Dialysis Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels and has to be carried out at regular intervals. Advantages Available to all kidney patients (no shortage) No need for immune suppressant drugs In a dialysis machine a person s blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of useful substances as the blood. This ensures that glucose and useful mineral ions are not lost. Urea passes out from the blood into the dialysis fluid. Disadvantages Patient must limit their salt and protein intake between dialysis sessions Expensive for the NHS Regular dialysis sessions (8hrs) impacts on the patient s lifestyle

5 Kidney failure kidney transplant Key words: Antigen proteins on the surface of cells which identify a cell as self or foreign to the body Antibody protein used in the immune response to fight off foreign cells Kidney transplant A diseases kidney is replaced by a healthy donor kidney. Organ rejection is a problem as the antigens on the surface of the donor kidney are recognised by the immune system as foreign and can be attacked by the patients antibodies To reduce the chances of this happening 2 precautions are taken: 1) Immune suppressant drugs are give 2) A donor kidney with a similar tissue type is used Advantages Patients can lead a more normal life without having to watch what they eat and drink Cheaper for the NHS overall Disadvantages Must take immune suppressant drugs which increase the risk of infection Shortage of organ donors Kidney only lasts 8 9 years on average Any operation carries risks

6 Temperature control thermoregulation Body temperature is monitored and controlled by the thermoregulatory centre in the brain. This centre has receptors which are sensitive to the temperature of the blood. Receptors in the skin also send impulses to the thermoregulatory centre about the skin temperature. Consequences of your core body temperature raising too high: Enzymes are denatured so can no longer catalyse reactions in your cells. Consequences of your core body temperature dropping too low: Enzyme reaction rate is slowed. Not enough energy is released & cells begin to die

7 Temperature control thermoregulation Responses to decreased body temperature: Increased body temperature Responses to increased body temperature: 1. Vasoconstriction narrowing of blood vessels in the skin. Blood flow through the skin is reduced, therefore heat loss is decreased. Body temperature increases. 2. Shivering tiny muscles under the skin contracting and relaxing very quickly. The muscle cells release heat. 3. Body hair rises away from the skin, trapping a layer of air next to it, insulating the body. Erector muscles contracting. Decreased body temperature 1. Vasodilatation widening of blood vessels. Blood flow is increased and more heat is lost through the skin. Nerve impulses pass along the nerves from the thermoregulatory centre to the muscles in the walls of blood cells, stimulating contraction and causing them to narrow. When the muscles relax the blood vessels widen. 2. Sweat is produced. Heat from the body evaporates the water in sweat. when it is hot more water is lost so more has to be taken in. 3. Body hair lies flat against the skin, preventing air becoming trapped next to it.

8 Blood glucose control Blood glucose concentration is controlled by the release of hormones from the pancreas Insulin Hormone released from the pancreas when blood glucose levels have increased. Allows glucose to move from the blood to the cells where it is used or stored as glycogen in the liver. Glycogen Hormone released from the pancreas when blood glucose levels fall. Causes glycogen stored in the liver to be converted into glucose and released into the blood

9 Problems with blood glucose control diabetes Diabetes is a disease where a persons blood glucose concentrations are not controlled properly because of either a lack of insulin (type 1) or cells not responding to insulin (type 2) Type 1 Diabetes 1. Pancreas does NOT produce any or enough insulin 2. Inject insulin daily (into the fat layer beneath the skin) traditionally this was from pigs, but now we use genetically engineered human insulin as it is more effective. 3. Exercise and diet are used to help lower blood glucose levels too Type 2 Diabetes 1. Cells respond less well to insulin (they become resistant) 2. Risk factors of developing it are: 1. High fat diets 2. Lack of exercise 3. Getting older 4. Obesity 3. Control by changes in diet and exercise eg. eating a balanced diet with fewer carbohydrates Losing weight Regular exercise