Flashcards · Biology
Homeostasis
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What is homeostasis?
The regulation of the conditions inside the body, so that they stay constant.
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What is the normal body temperature?
About 37 °C.
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Name three conditions that are controlled.
Body temperature, blood glucose concentration and water content.
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Why does temperature need to be constant?
The enzymes in the body work best at about 37 °C.
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Why does water content need to be constant?
So that cells do not swell or shrink by osmosis.
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What are the three parts of a control system?
A receptor, a coordination centre and an effector.
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What does a receptor do?
Detects a change in a condition.
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What does a coordination centre do?
Receives information and decides on the response.
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What does an effector do?
Carries out the response.
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What is negative feedback?
A response that reverses the change, and so returns the condition to normal.
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Give an example of an internal change.
Eating a meal, or exercising.
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Give an example of an external change.
A hot or cold day.
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Name two types of effector.
Muscles and glands.
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Which tissue sends impulses in nervous control?
Neurones.
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How does hormonal control differ from nervous control?
It is slower, and it usually lasts for longer.
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Common mistake about homeostasis?
Thinking a condition is held at one exact value. It is kept within narrow limits.
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What is thermoregulation?
The control of body temperature.
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What is osmoregulation?
The control of the water content of the body.
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What is the optimum temperature of human enzymes?
About 37 °C.
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What happens to enzymes when it is too cold?
They work more slowly, because there are fewer collisions.
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What happens to enzymes when it is too hot?
They are denatured, and stop working.
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Is denaturing reversible?
No, the enzyme does not return to its shape when it cools.
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What is denaturing?
A change in the shape of the enzyme, including the active site.
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Why do animal cells burst in pure water?
Water enters by osmosis, and they have no cell wall.
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What happens to a red blood cell in a concentrated solution?
Water leaves by osmosis, and it shrinks.
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What happens to a red blood cell in a dilute solution?
Water enters by osmosis, and it swells and may burst.
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What does a partially permeable membrane do?
Lets some substances pass, but not others.
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Which membrane controls what enters an animal cell?
The cell surface membrane.
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How do you calculate percentage change?
Change divided by the original value, multiplied by 100.
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Why does a high temperature stop an enzyme working?
The active site changes shape, so the substrate no longer fits.
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Which organ controls the water content of the blood?
The kidney.
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Common mistake about enzymes and temperature?
Saying that enzymes are killed. They are not alive, so they are denatured.
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What is the outer layer of the skin?
The epidermis.
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What does the dermis contain?
Sweat glands, hair follicles, blood vessels and receptors.
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Which part of the brain controls body temperature?
The hypothalamus.
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What does the hypothalamus monitor?
The temperature of the blood.
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How does sweat cool the body?
As it evaporates, it takes heat from the skin.
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What is shivering?
Rapid contractions of the muscles that release heat.
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Where does the heat in shivering come from?
Respiration in the muscle cells.
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What do the hairs do when the body is cold?
They stand up and trap a layer of air.
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What do the hairs do when the body is hot?
They lie flat.
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What happens to sweating when it is cold?
The glands release little or no sweat.
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What is the role of the epidermis?
A barrier that stops pathogens getting in and water leaving.
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What is the role of the fat layer?
Stores energy and insulates the body.
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Which receptors send information to the hypothalamus?
Temperature receptors in the skin.
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Name the effectors in thermoregulation.
Sweat glands, muscles and blood vessels in the skin.
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What type of control is thermoregulation?
Negative feedback.
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Common mistake about shivering?
Saying that it cools the body. It releases heat and warms the body.
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What is vasodilation?
The widening of the blood vessels in the skin.
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What is vasoconstriction?
The narrowing of the blood vessels in the skin.
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When does vasodilation happen?
When the body is too hot.
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When does vasoconstriction happen?
When the body is too cold.
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What does vasodilation do to heat loss?
Increases it.
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What does vasoconstriction do to heat loss?
Reduces it.
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What makes the vessels change diameter?
Muscles in the vessel walls, controlled by impulses from the hypothalamus.
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Where is heat lost from?
The blood close to the surface of the skin.
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What colour is the skin in vasodilation?
Redder.
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What colour is the skin in vasoconstriction?
Paler.
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Which part of the brain controls the response?
The hypothalamus.
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What is the normal body temperature?
About 37 °C.
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Name two other responses when too hot.
More sweat, and the hairs lie flat.
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Name two other responses when too cold.
Shivering, and the hairs stand up.
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Does the blood vessel move towards the skin?
No, it changes in diameter.
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Common mistake about vasoconstriction?
Saying that it warms the skin. It makes the skin cooler, because less blood reaches it.
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What is the normal blood glucose concentration?
About 5 mmol per dm³.
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Which hormone lowers the blood glucose?
Insulin.
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Where is insulin made?
In the pancreas.
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What does insulin do?
Makes cells take up glucose from the blood.
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What does the liver do with the extra glucose?
Converts it to glycogen, which it stores.
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What is glycogen?
A storage carbohydrate made from glucose.
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What detects the high glucose?
Cells in the pancreas.
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What is the effect of insulin on the blood glucose?
It falls.
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Name two types of cell that take up glucose.
Liver cells and muscle cells.
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Why does the blood glucose rise after a meal?
Carbohydrate is digested to glucose, which is absorbed.
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What happens to insulin release when the glucose falls to normal?
Less insulin is released.
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What type of control is this?
Negative feedback.
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What carries insulin around the body?
The blood.
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Why is a high blood glucose harmful?
Water leaves the cells by osmosis, and tissues are damaged.
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What are the units of blood glucose?
mmol per dm³.
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Common mistake about insulin?
Saying it makes glucose. It makes cells take up glucose, and convert it to glycogen.
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Which hormone raises the blood glucose?
Glucagon.
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Where is glucagon made?
In the pancreas.
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When is glucagon released?
When the blood glucose concentration is too low.
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Where does glucagon act?
On the liver.
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What does glucagon make the liver do?
Convert glycogen into glucose, and release it.
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What do insulin and glucagon have in common?
Both are made in the pancreas, and both act on the liver.
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How do insulin and glucagon differ?
They have opposite effects on the blood glucose.
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What happens to glucagon release when the glucose rises to normal?
Less glucagon is released.
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When might glucose fall?
Between meals, or during exercise.
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What stores glucose in the liver?
Glycogen.
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Why does the glucose fall during exercise?
Muscle cells use glucose for respiration.
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What is negative feedback?
A response that reverses a change.
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What would happen without glucagon?
The blood glucose could fall too low, and cells would run out of fuel.
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What detects a low glucose?
Cells in the pancreas.
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Which organ cannot store much glucose?
The brain, so it depends on the blood supply.
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Common mistake about glucagon?
Confusing it with glycogen. Glucagon is the hormone, and glycogen is the store.
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What is diabetes?
A condition in which the blood glucose concentration is not controlled.
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What is the cause of type 1 diabetes?
The pancreas does not produce enough insulin.
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What destroys the insulin-making cells in type 1?
The immune system.
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How is type 1 diabetes controlled?
Insulin injections, diet and exercise.
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Why is insulin injected?
It is a protein, so it would be digested if taken by mouth.
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What is the cause of type 2 diabetes?
The body cells no longer respond to insulin.
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What is the main risk factor for type 2 diabetes?
Obesity.
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How is type 2 diabetes controlled?
Diet, exercise and weight loss, sometimes tablets or insulin.
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Which type usually starts in childhood?
Type 1.
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Which type can often be prevented?
Type 2, by a healthy lifestyle.
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Name two symptoms of diabetes.
Thirst and frequent urination.
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Name an effect of high glucose over many years.
Damage to blood vessels, nerves, kidneys and eyes.
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Which type is not caused by lifestyle?
Type 1.
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What does an insulin pump do?
Delivers insulin under the skin.
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What happens to the blood glucose after a meal in diabetes?
It rises higher, and falls back more slowly.
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Common mistake about diabetes?
Saying that type 2 has no insulin. In type 2 the cells do not respond to it.
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What is the BMI equation?
Mass in kilograms divided by height in metres squared.
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What is a healthy BMI?
18.5 to 24.9.
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What BMI is obese?
30 or more.
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What BMI is underweight?
Below 18.5.
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What is the waist to hip ratio?
The waist circumference divided by the hip circumference.
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What does a high ratio show?
More fat is stored around the abdomen, and there is a higher risk.
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What ratio is high for a man?
Above about 0.90.
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What ratio is high for a woman?
Above about 0.85.
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What is the correlation between BMI and type 2 diabetes?
Positive: the risk rises as the BMI rises.
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Does a correlation prove a cause?
No.
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Name a limit of BMI.
It does not distinguish muscle from fat.
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Why does obesity increase the risk of type 2?
Excess fat can make cells less sensitive to insulin.
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Name a confounding factor.
Diet, lack of exercise or genetics.
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What units must height be in for BMI?
Metres.
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Can weight loss help type 2 diabetes?
Yes, it can improve control.
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Common mistake in the BMI calculation?
Forgetting to square the height, or using centimetres.