Homoeostasis-The control of blood glucose concentration

Define the second messenger

A substance that carries the message of the hormone inside the cell which brings about a response.

State the three main things that glucagon does to increase the blood glucose concentration

Activates enzymes that break down glycogen to form glucose. Activates enzymes that make glucose from glycerol and fatty acid. Decrease the rate of respiration of glucose in cells.

Role of glucagon

Activates enzymes that breakdown glycogen into glucose. Activates enzymes that makes glucose from amino acids and glycerol.

State the three main roles of adrenaline

Activates glycogenolysis Inhibits glycogenesis Activates glucagon secretion and inhibits insulin secretion

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase.

Adenylate cyclase activated and cAMP, the second messenger is produced. This activates enzymes in the cell so glycogenolysis occurs and glycogenesis is inhibited.

describe the role of adenylate cyclase, cyclic AMP and protein kinase in the second message model.

Adenylate cyclase converts ATP into cAMP. cAMP activates an enzyme called protein kinase A. Protein kinase A activates a cascade that breaks down glycogen to form glucose.

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase.

Adenylate cyclase within the plasma membrane is activated. cAMP produced. The second messenger produced. Activates enzymes in cell so glycogenolysis and gluconeogenesis occurs whilst glycogenesis inhibited.

Name the enzymes and chemical signals involved in the second messenger model

Adenylate cylase, cyclic AMP, protein kinase A.

What gland is the hormone adrenaline secreted from?

Adrenal glands

Explain the stages involved in the action of adrenaline (linked to blood glucose concentration)

Adrenaline binds to receptors on the cell surface membranes of liver cells. It activates glycogenolysis and inhibits glycogenesis Adrenaline also activates glucagon secretion and inhibits insulin secretion to increase blood glucose concentration making more glucose availablee for muscles to respire.

What triggers the release of adrenaline?

Adrenaline is secreted from the adrenal glands when the blood glucose concentration is too low

Which cells produce glucagon?

Alpha cells

What roles do the α cells of the Islets of Langerhans play in regulating blood glucose concentration?

Alpha cells secrete glucagon into the blood

What is a negative correlation?

As one parameter increases the other decreases

What are the actions which glucagon binding to protein receptors brings about?

Attach to receptors on the surfaces of target cells. Activate enzymes involved in the conversion of glycogen to glucose. Activate enzymes involved in the conversion of glycerol and amino acids into glucose. Cells respire more.

Which cells produce insulin?

Beta cells

Describe the role of the hormone glucagon in the control of blood sugar concentration.

Binds to specific receptor on liver cells. This results in the activation of enzymes in liver that catalyse the hydrolysis of glycogen. Facilitated diffusion of glucose out of liver cells. This increases blood glucose levels.

Why does blood sugar levels and temperature need to be controlled?

Blood sugar levels are controlled to provide cells with a constant supply of energy. Internal body temperature is controlled to maintain a temperature at which enzymes work best.

Glucose enters a cell through glucose-transporter proteins. Explain why glucose can only enter a cell in this way.

Cell surface membrane has a phospholipid bilayer. Glucose is not lipid-soluble.Transporter spans the membrane.Glucose must enter by facilitated diffusion.

2 examples of positive feedback

Childbirth (oxytocin) apple ripening (ethylene)

Examples of external heat input

Conduction,convection and radiation

What is the second messenger?

Cyclic adenosine monophosphate (cAMP)

What triggers the release of glucagon?

Decrease in blood glucose concentration in the blood

What is meant by negative feedback?

Departure from normal level causes changes to restore to norm to reverse departure.

Stages of negative feedback

Departure from normal. receptor. co-ordinator. effector. response. return to normal.

Negative feedback

Departure from original level causes changes to restore systems to their original level (within certain limits)

Suggest one way in which the insulin receptors might be abnormal.

Different tertiary structure due to different sequence of amino acids

What are the main factors that influence blood glucose concentration?

Eating (rises) and exercise (falls)

How does increased rate of sweating help reduce blood temperature?

Evaporation of sweat cools the skin and hence the blood.

4 ways in which heat is lost from the body

Evaporation,conduction,convection,radiation

Scientists made an artificial gene which codes for insulin. They put the gene into a virus which was then injected into rats with type I diabetes. The virus was harmless to the rats but carried the gene into the cells of the rats. The treated rats produced insulin for up to 8 months and showed no side-effects. The scientists measured the blood glucose concentrations of the rats at regular intervals. While the rats were producing the insulin, their blood glucose concentrations were normal. Research workers have suggested that treating diabetes in humans by this method of gene therapy would be better than injecting insulin. Evaluate this suggestion.

For; Avoids pain of injections. Longer lasting as permanent new cells will contain and express gene. Less need to measure blood sugar. Less restriction on diet. Rats are different to humans. May have side effects on humans. Longer term effects of treatment not known, it may have caused effects after 8 months. insulin may be rejected by the body.

When insulin binds to receptors on liver cells, it leads to the formation of glycogen from glucose. This lowers the concentration of glucose in liver cells. Explain how the formation of glycogen in liver cells leads to a lowering of blood glucose concentration

Formation of glycogen causes glucose concentration in liver cells to fall below that in blood plasma. This creates a glucose concentration gradient and as a result glucose leaves blood by facilitated diffusion via carrier proteins.

Explain how glucagon works to bring about a response

Glucagon binds to specific receptors on the cell membranes of liver cells. Glucagon activates enzymes in liver cells that break down glycogen into glucose. Glucagon also acitvates enzymes that are invovled in the formation of glucose from glyceorl and amino acids. Glucagon also decreases the rate of respiration of glucose in cells.

Explain how the kidneys normally prevent glucose appearing in the urine of a non-diabetic person.

Glucose is reabsorbed into the blood from proximal tubule by active transport.

Diabetic people who do not control their blood glucose concentration may become unconscious and go into a coma. A doctor may inject a diabetic person who is in a coma with glucagon. Explain how the glucagon would affect the person's blood glucose concentration.

Glycogen is converted to glucose (glycogenolysis) by activating enzymes. Gluconeogenesis is also activated.

explain the benefit of having separate mechanisms for different departures from the original level

Homeostasis involves multiple negative feedback mechanisms for each thing being controlled.This is because having more than one mechanism gives more control over changes in your internal environment. Having multiple negative feedback mechanisms means you can actively increase OR decrease a level so it returns to normal.

Explain how hormones work to bring about a response

Hormones attach to receptor proteins that are on the cell surface of target cells which leads to reactions that activates enzymes.

Why are responses produced by hormones slower and longer lasting than responses produced by nervous impulses.

Hormones travel via the blood stream and they aren't broken down as quickly as neuortransimitters

What are most processes in the body controlled by?

Hormones which are secreted by glands and are usually transported to their target organs by the bloodstream.

Suggest the effect on cells if blood sugar level was to rise.

If blood glucose levels are too high the water potential of blood is reduced so much so that water molecules diffuse out of cells into the blood by osmosis causing the cells to shrivel up and die.

Suggest the effect on cells if blood sugar level was to fall.

If blood glucose levels are too low cells are unable to function properly because theres an insufficient amount of glucose for respiration to provide energy.

Why is it important to maintain the right blood pH?

If blood pH is too high or too low the enzyme becomes denatured. The hydrogen bonds holding its 3D shape break changing the shape of the active site. The enzyme becomes disfunctional because the substrate can no longer bind to it hence the metabolic reactions are less efficient.

Why is it important to maintain the right core body temperature?

If temperature is too high enzymes denature and no longer work as catalysts. This means metabolic reactions are less efficient.If temperature is too low enzyme activity is reduced , slowing the rate of metabolic reactions.

What would happen if you only have one negative feedback mechansim?

If you had only one negative feedback mechanism then you would only be able to actively change a level in one direction so it reutrns to normal. This means a slower response and less control

Explain the role of the liver in glycogenolysis

In glycogenolysis the liver converts glycogen into glucose

Explain the role of the liver in gluconeogenisis

In th eliver glucose is made from non-carbohydrates

What triggers the release of insulin?

Increase in blood glucose concentration in the blood

What are the four actions which insulin binding to insulin receptors brings about?

Increased absorption of glucose into target cells by stimulating these cells to add more carrier proteins. increased rate of respiration of glucose (muscle cells). increased glycogenesis in liver to increase glucose uptake. Increase the rate of glucose uptake in adipose tissue by stimulating fat synthesis.

State three main things that insulin does to lower the blood glucose concentration

Increases the number of glucose channels on the membranes of liver and muscle cells to increase their permeability to glucose. Activates enzymes that convert glucose to glycogen. Increase the rate of respiration by glucose particualry in muscle cells.

Role of insulin

Increases the rate at which liver muscle and fat cells absorb glucose by facilitated diffusion. Activates enzymes in the liver to convert glucose into glycogen

Describe how insulin leads to lowering of the concentration of glucose in blood.

Insulin binds to receptor on target cell membrane.This leads to more transport proteins for glucose. More glucose enters cells from blood which lowers conc. in blood. Insulin causes increase in activity of enzymes that convert glucose to glycogen. Insulin leads to higher metabolic rate in target cells, so more respiration occurs.

Explain how insulin leads to lowering of the concentration of glucose in blood.

Insulin binds to specific insulin receptors on target cell membranes of target cells. This binding causes vesicles containing glucose channel proteins to jonin the cell surface membrane. More transport proteins on the cell surface membrane. increases the rate of facilitated diffusion of cells. More glucose enters cell which lowers blood glucose concentration. Insulin causes increase in activity of enzymes that convert glucose to glycogen. Stimulates fat formation from glucose. Insulin also leads to higher metabolic rate in target cells.

Explain how insulin works to bring about a response

Insulin binds to specific receptors on the cell surface membranes of liver and muscle cells. It increases the permeability of muscle cell membrane to glucose so the cells take up more glucose. It does this by increasing the number of channel proteins in the cell membranes. Insulin activates enzymes in liver and muscle cells that convert glucose to glycogen. The cells are able to store gylcogen in their in their cytoplasm as an energy source. Insulin also increases the rate of respiration of glucose especially n muscle cells

Explain the main roles of insulin

Insulin: Attaches to receptors on the surfaces of target cells. Controls the uptake of glucose by regulating the inclusions of channel proteins in ther surface membrane of target cells. Activates enzymes involved in the conversion of glucose to glycogen.

Why isn't positive feedback and example of homoeostasis?

It does keep internal environment constant

Why isn't positive feedback involved in homeostasis?P

It doesn't keep thee internal environment stable

Which cells are the only cells that have glucagon receptors?

Liver cells

Which cells are especially affected in terms of increasing the rate of glucose absorption?

Liver cells, muscle cells and adipose tissue cells

Explain what triggers the release of adrenaline

Low blood glucose concentration e.g. when stressed or exercising.

It is important that mammals maintain a constant core temperature.Explain why.

Maintain optimum temperature for enzymes. If temperature rises above optimum, enzyme activity falls because enzymes denature. If temperature falls below normal, then low kinetic energy so fewer enzyme-substrate collisions. Keeping a constant core temperature maintains high metabolic rate.

Homeostasis (MACIEDEC)

Maintaining a constant internal environment (within restricted limits) despite external conditions

Glucose enters a cell through glucose-transporter proteins. Explain why glucose can only enter a cell in this way.

Membrane has lipid/hydrophobic bilayer and glucose is not lipid-soluble.Transporter spans the membrane. Transporter has water filled channel. Transporter channels allow glucose to cross the membrane by facilitated diffusion. These channels have a specific shape that glucose are complemntary to.

2 examples of internal heat input in the body

Metabolism and muscle contractions

Negative feedback restores systems to their original level.

Negative feedback restores systems to their original level.

The release of a substance called dopamine in some areas of the brain increases the desire to eat. Scientists measured increases in the release of dopamine in the brains of rats given different concentrations of sucrose solution to drink. Sucrose stimulates taste receptors on the tongue. The graph shows their results. Each point is the result for one rat.The scientists concluded that drinking a sucrose solution had a positive feedback effect on the rats' desire to eat. HOW do these data support this conclusion?

Positive correlation between sucrose and dopamine concentrations because the higher the concentration of sucrose the more dopamine is released. Dopamine makes them want to drink more sucrose. This is positive feedback because drinking the sucrose leads to wanting to drink even more.

State the difference between positive and negative feedback

Positive feedback involves amplification whilst negative feed back involves stabilization.

What is positive feedback useful for?

Positive feedback is useful to rapidly activate something

What is positive feedback?

Positive feedback mechanisms amplify a change from the normal level.

State the importance of maintaining a stable blood glucose concentration

Provides cells with a constant supply of energy It affects the water potential of blood

The insulin receptor protein binds to insulin molecules but not to the molecules of any other substance. Explain why.

Receptor has specific tertiary structure complementary to insulin.

Explain the general stages involved in negative feedback, and why these are used in homeostatic mechanisms

Receptors detects when a level is too high or too low. This information is communicated via the nervous system or the hormonal system to effectors. The effectors respond to couteract that change bringing the level back to normal. These stages are used to keep things around a normal level

What do homeostatic systems involve?

Receptors, a communication system and effectors

Scientists investigated the control of blood glucose concentration in mice. They kept a group of normal mice without food for 48 hours. After 48 hours, the blood glucose concentrations of the mice were the same as at the start of the experiment.Explain how the normal mice prevented their blood glucose concentration falling when they had noteaten for 48 hours

Release of glucagon leads to formation of glucose in liver cells from non-carbohydrates such as amino acids and fatty acids

When blood glucose levels are too high how can glucose be transported into the cell

Skeletal and cardiac muscle contain a channel protein called GLUT4 which is a glucose transporter. When insulin levels are low GLUT4 is stored in a vesicle in the cytoplasm of cells. When insulin binds to receptors on the cell surface membrane it triggers the movement of GLUT4 to the membrane. Glucose can be transported into the cell through GLUT4 channel protein by facilitated diffusion.

Limitation of having one negative feedback mechansims

Slower response and less control.

What is the importance of maintaining a stable core temperature and stable blood pH in relation to enzyme activity.

Temperature and pH affect enzyme activity and enzymes control the rate of metabolic reactions.

Positive feedback

The amplification of a response to a stimulus

Glycogenolysis

The breaking down of glycogen into glucose.

Glycogenesis

The formation of glycogen from glucose which occurs in the liver

The girl who took part in this investigation was being successfully treated with insulin. The graph shows that on some occasions, the concentration of glucose in her blood was very high. WSuggest why.

The girl may have eaten something that contained lots of carbohydrate. The glucose was absorbed from intestine into blood but the glucose ws not taken up from the blood and insulin did not convert the glucose to glycogen.

What is the benefit of having separate negative feedback mechanisms controlling departures in different directions from the original state?

The possession of separate mechanisms involving negative feedback, controls departures in different directions from the original state, giving a greater degree of control.

what is Glycogenolysis

The process of breaking down glycogen into glucose

what is Gluconeogensis

The process of forming glucose from non carbohydrates.

what is Glycogenesis

The process of forming gylcogen from glucose

Gluconeogenesis

The synthesis of glucose from non-carbohydrates such as amino acids and glycerol.

What roles do the β cells of the Islets of Langerhans play in regulating blood glucose concentration?

They release insulin into blood

Three ways in which water leaves our body

Through the lungs, through the skins, through the kidneys.

How do the hormones involved in bringing about adjustments to blood glucose concentration travel to their target organ

Travel through the blood

The kidney removes various substances from the blood plasma. The clearance value for a substance is the volume of blood cleared of that substance by the kidney in one minute. Explain how the activity of the kidney results in this clearance value for glucose.

Ultrafiltration, out of blood plasma and into the renal capsule. Hydrostatic pressure. At PCT all the glucose is reabsorbed by active transport.

Internal conditions that are controlled in the body

Water content, ion content, blood glucose levels, temperature.

Name the internal conditions that are controlled by the body

Water content, ion content, blood sugar levels, and temperature.

Types of hormones

Water soluble and lipid soluble

Technicians in a hospital laboratory tested urine and blood samples from a girl with diabetes at intervals over a one-year period. Each time the technicians tested her urine, they also measured her blood glucose concentration. Their results are shown in the graph.Use the graph to evaluate the use of the urine test as a measure of blood glucose concentration.

What correlation does the graph show? How large is the range, and is there overlap? What type of scale is used on the graph. Is it an arbitrary scale?

Explain the role of the pancreas, specifically the alpha and bet cells of the Islets of Langerhans, in regulating blood glucose concentration.

When the blood glucose concentration rise the pancreas detects the blood glucose is too high and so beta cells are the receptors and secrete insulin and alpha cells stop secreting glucagon. When blood glucose falls the pancreas detects the fall and alpha cells secrete glucagon whilst beta cells stop secreting insulin.

Benefit of having multiple negative feedback mechanisms

You can actively increase or decrease a level so it turns back to normal. If you only had one negative feedback mechanism you would only be able to actively change a level in one direction so it returns to normal.

The factors that influence blood glucose concentration

bgc increases after eating food that contains carbohydrate bgc decreases after exercising as glucose is being used in respiration to release energy.

Explain the general stages involved in negative feedback (the 5 c's)

conditions in the body change from set point change detected by receptors corrective mechanism activated as a result conditions return to set point corrective mechanism switched off

Explain the role of the liver in glycogenesis.

converts glucose into glycogen

Explain how the presence of abnormal insulin receptors results in a high blood glucose concentration.

insulin unable to attach to receptors so reduced of glucose into liver cells because there are no GLUT4 channel ptoeins for glucose transport;