Homeostasis Flashcards Preview

A2 Biology Unit 5 > Homeostasis > Flashcards

Flashcards in Homeostasis Deck (37):

What is homeostasis?

Homeostasis is the maintenance of a constant internal environment in organisms.
It involves maintaining the chemical make up, volume and other features of blood and tissue fluid within restricted limits.


Why is homeostasis so important?

Enzymes that control biochemical reactions in cells need to be a certain pH and temp to function- maintaining = reactions at a constant and predictable rate.
Changes to the water potential of blood may cause cells to shrink and expand- maintain blood glucose concentration.
Organisms that are able to have a constant internal environment have a larger geographical range as they are more independent of the external environment.


The control of any self regulating system involves a series of stages that feature:

- the set point, which is the desired level, or norm at which the system operates. This is monitored by...
- receptor, which detects any deviation from the set point and informs the...
- controller, which coordinates information from various receptors and sends instructions to an appropriate...
- effector, which brings about the changes needed to return the system to the set point. This return to normality creates a...
- feedback loop, which informs the receptor of changes to the system brought about by the effector.


Methods of gaining heat include:

- production of heat by the metabolism of food during respiration.
- gain of heat from the environment by conduction (eg ground), convection (eg surrounding air or water) and radiaton.


Methods of losing heat include:

- evaporation of water eg sweating.
- loss of heat to the environment by conduction


What are endotherms?

Animals that derive heat from metabolic activities that take place within their bodies.


What are ectotherms?

Animals that derive heat from sources outside their body.


Give examples of how ectotherms control their body temperature.

Exposing themselves to the sun.
Taking shelter.
Gaining warmth from the ground.
Generating metabolic heat.
Colour variation.


Give examples of how mammals and birds have adapted for living in cold environments.

Layer of fat.
Small surface area to volume ratio.


What mechanisms do animals have to quickly respond to cold conditions?

Vasoconstriction- the diameter of the arterioles near the surface of the skin is made smaller. This reduces the volume of blood reaching the skin through capillaries & beneath layer of insulating fat to reduce heat loss.
Shivering- contractions produce metabolic heat.
Raising of hair- traps a layer of insulating hair.
Increased metabolic rate.
Decrease in sweating.
Behavioural mechanisms.


Rapid response to lose heat in hot environments:

Vasodilation: diameter of arterioles near surface become larger (radiates away).
Increased sweating
Lowering of body hair.
Behavioural mechanisms.


Within the hypothalamus there is a thermoregulatory centre consisting of two parts:

- a heat gain centre, which is activated by a fall in blood temperature- it controls the mechanisms that increase blood temp.
- a heat loss centre, which is activated by a rise in blood temperature- it controls the mechanisms that decrease blood temp.


Hormones are different chemically but all have certain characteristics in common. Hormones are:

- Produced by glands, which secrete the hormone directly into the blood (endocrine glands).
- Carried in the plasma to target cells- which have receptors on their cell surface membranes that are complementary to the hormone.
- Are effective in very small quantities, but often have wide spread and long lasting effects.


What is the second messenger model?

- The hormone (e.g adrenaline) is the first messenger, it binds to specific receptors on the cell surface membrane of target cells to form a hormone receptor complex.
- This activates an enzyme inside the cell that converts ATP to cyclic ATP which acts as a second messenger.
- This then activates other enzymes that in turn convert glycogen to glucose.


What is the pancreas?

A large gland that is situated in the upper abdomen, behind the stomach.
It produces the enzymes (protease, amylase and lipase) for digestion and hormones (insulin and glucagon) for regulating blood glucose.


What two types are there of islets of Langerhans?

a cells which produce the hormone glucagon.
B cells which produce the hormone insulin.


What happens if blood glucose levels change?

If the levels fall too low, the cells are deprived of energy and die- brain cells are especially sensitive in this respect as they can only respire glucose.
If the levels rise too high- it lowers the water potential of the blood and creates osmotic problems that can cause dehydration and be equally dangerous.


What three sources does blood glucose come from?

- Directly from the diet (break down of carbohydrates).
- From the break down of glycogen (glycogenolysis) stored in liver and muscle cells.
- From gluconeogenesis which is the production of new glucose from sources other than carbohydrate eg the liver can make glucose from glycerol and amino acids.


How do B cells respond do when they detect a rise in blood glucose level?

By secreting the hormone insulin directly into the blood plasma.


Almost all body cells have glycoprotein receptors on their cell surface membranes that bind with insulin molecules. When it combines with the receptors, insulin brings about...

- a change in the tertiary structure of the glucose transport protein channels, causing them to change shape and open, allowing more glucose into the cells.
- an increase in the number of carrier molecules on the cell surface membrane.
- activation of the enzymes that convert glucose to glycogen and fat.


In what ways are blood glucose levels lowered?

- by increasing the rate of absorption of glucose into cells , especially in muscle cells.
- by increasing the respiratory rate of cells, which therefore use up more glucose, thus increasing their uptake of blood glucose.
- by increasing the rate of conversion of glucose into glycogen (glycogenesis) in the cells of liver and muscles.
- by increasing the rate of conversion of glucose to fat.


How is the lowering of blood glucose an example of negative feedback?

The lowering of blood glucose causes the B cells to reduce their secretion of insulin.


What do a cells do when they detect a fall in blood glucose?

They respond by secreting the hormone glucagon directly into the blood plasma.


Only the cells of the liver have receptors that bind to glucagon, so only river cells respond. They do this by:

- activating an enzyme that converts glucagon to glucose .
- Increasing the conversion of amino acids and glycerol into glucose (gluconeogenesis).


How is the raising of blood glucose an example of negative feedback?

The raising of blood glucose levels causes the a cells to reduce the secretion of glucagon


Adrenaline raises the blood glucose by:

Activating an enzyme that causes the breakdown of glycogen to glucose in the liver.
Inactivating an enzyme that synthesises glycogen from glucose.


Why is insulin and glucagon thought to work antagonistically?

Insulin lowers the blood glucose level whereas glucagon increases it.


What is diabetes?

Diabetes mellitus is a condition where blood glucose concentration can’t be controlled properly.


What is type I diabetes?

The β cells in the islets of Langerhans don’t produce any insulin. After eating, the blood glucose rises and stays high (hyperglycaemia) and can result in death if untreated.
The kidneys cannot reabsorb all the glucose so some is excreted in urine.
Type I diabetes can be treated regularly with injections of carefully controlled amounts of insulin.
Eating regularly and controlling simple carbohydrates helps to avoid sudden rises.


What is type II diabetes?

Type II diabetes is usually found in older people that are overweight/ obese.
It occurs when the β cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin.
Cell’s don’t respond properly because the insulin on their membranes don’t work properly because the insulin receptors on their membranes don’t work properly, so the cells don’t take up enough glucose.
So the blood glucose concentration is therefore higher than normal.
It can be treated by controlling simple carbohydrate intake and losing weight.
Glucose lowering tablets can be taken if diet and weight loss don’t work.


Symptoms of Diabetes Causes: Thirst

Increased glucose conc. in the blood causes cells to become dehydrated as it reduces the water potential of the blood, causing chemical receptors to detect this change triggering the brain to ‘tell’ you you’re thirsty.


Symptoms of Diabetes Causes: Frequent urination

High conc of glucose causes there to be an osmotic difference that resists the reabsorption of water in the kidneys, causing more urine to be produced.


Symptoms of Diabetes Causes: Poor eyesight

Water diffuses out of ocular tissues via osmosis down a concentration gradient as the blood as a high glucose content, causing the tissue to become dehydrated and shrivel, pulling away from the lens of the eye. This means your eyes cannot focus properly.


Symptoms of Diabetes Causes: Weight loss

Due to the lack of glucose the body must use alternate respiratory substrates, such as muscle tissue and fat leading to weight loss


Symptoms of Diabetes Causes: Tiredness

Glucose isn’t being absorbed by cells so it can’t be used in cellular respiration. And so the rate of respiration falls and less ATP is produced, less energy is released


State one difference between type I and type II diabetes.

Type I is caused by an inability to produce insulin.
Type II is caused by receptors on body cells losing their responsiveness to insulin.


State one difference between the main ways of treating type I and type II diabetes.

Type I is controlled by the injection of insulin.
Type II is controlled by regulating the intake of carbohydrate in the diet and matching this to the amount of exercise taken.