Homeostasis

Glossary Maintain – keep up. Constant – the same. Internal – inside the body. Environment – surroundings of the body.

What is Homeostasis? Body cells work best if they have the correct Temperature Water levels Glucose concentration Your body has mechanisms to keep the cells in a constant environment.

What is Homeostasis? The maintenance of a constant environment in the body is called Homeostasis

Controlling body temperature All mammals maintain a constant body temperature. Human beings have a body temperature of about 37 º C. E.g. If your body is in a hot environment your body temperature is 37 º C If your body is in a cold environment your body temperature is still 37 º C

What mechanisms are there to cool the body down? Sweating When your body is hot, sweat glands are stimulated to release sweat. The liquid sweat turns into a gas (it evaporates) To do this, it needs heat. It gets that heat from your skin. As your skin loses heat, it cools down.

What mechanisms are there to cool the body down? Vasodilation Your blood carries most of the heat energy around your body. There are capillaries underneath your skin that can be filled with blood if you get too hot. This brings the blood closer to the surface of the skin so more heat can be lost. This is why you look red when you are hot!

If the temperature rises, the blood vessel dilates (gets bigger). This means more heat is lost from the surface of the skin

What mechanisms are there to warm the body up? Vasoconstriction This is the opposite of vasodilation The capillaries underneath your skin get constricted (shut off). This takes the blood away from the surface of the skin so less heat can be lost.

If the temperature falls, the blood vessel constricts (gets shut off). This means less heat is lost from the surface of the skin

What mechanisms are there to warm the body up? Piloerection This is when the hairs on your skin “stand up” . It is sometimes called “goose bumps” or “chicken skin”! The hairs trap a layer of air next to the skin which is then warmed by the body heat The air becomes an insulating layer.

Controlling Glucose levels Your cells also need an exact level of glucose in the blood. Excess glucose gets turned into glycogen in the liver This is regulated by 2 hormones (chemicals) from the pancreas called: Insulin Glucagon

If there is too much glucose in the blood, Insulin converts some of it to glycogen Glycogen Insulin Glucose in the blood

If there is not enough glucose in the blood, Glucagon converts some glycogen into glucose. Glycogen Glucagon Glucose in the blood

Diabetes Some people do not produce enough insulin. When they eat food, the glucose levels in their blood cannot be reduced. This condition is known as DIABETES. Diabetics sometimes have to inject insulin into their blood. They have to be careful of their diet.

Time Glucose Concentration Meal eaten Insulin is produced and glucose levels fall to normal again. Glucose levels rise after a meal. Normal

Time Glucose Concentration Meal eaten Insulin is not produced so glucose levels stay high Glucose levels rise after a meal. Diabetic

The glucose in the blood increases. Glycogen Insulin Glucose in the blood But there is no insulin to convert it into glycogen. Glucose concentration rises to dangerous levels.

Controlling water levels The control of water levels is carried out by the KIDNEYS. It is closely linked to the excretion of urea. Urea is a waste product that is made when the LIVER breaks down proteins that are not needed by the body. Urea contains the element Nitrogen.

The kidneys The kidneys “clean” the blood of waste products and control how much water is kept in the body. The waste products and water make up urine which is excreted via the ureter. “ Dirty” blood enters the kidney through the renal artery. Then, several things happen to clean the blood...

Blood enters the tubule area in a capillary. The capillary forms a small “knot” near the kidney tubule. The blood is filtered so all the small particles go into the tubule. The capillary then carries on to run next to the tubule. 1. Filtration Kidney tube Capillary

The kidney tubule now contains lots of blood components including: Glucose: Ions: Water: Urea: Kidney tube

2. Reabsorb sugar The body needs to have sugar in the blood for cells to use in respiration. So all the sugar is reabsorbed back into the capillary.

3. Reabsorb ions Water and ions are the next to be absorbed. It depends on how much is needed by the body.

4. Reabsorb water Water and ions are the next to be absorbed. It depends on how much is needed by the body.

Reabsorbing water If you have too little water in your blood, you will produce very concentrated urine. (very little water in it=dark yellow) If you have too much water in your blood, you will produce very dilute urine. (lots of water in it=light yellow)

5. Excrete the waste Everything that is left in the kidney tubule is waste: All the urea Excess water This waste is called urine. It is excreted via the ureter and is stored in the bladder. The “clean” blood leaves the kidney in the renal vein. Renal vein

Summary of urine production Urea is a waste product made in the LIVER Water content of the body is controlled in the KIDNEYS Urea, water and other waste makes up URINE . Urine travels down the URETER and is stored in the BLADDER Urine is excreted through the URETHRA .

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Homeostasis

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Homeostasis