Blood Glucose Concentration

What is homeostasis?

The maintenance of the internal environment in a constant state within an organism, despite external changes

What internal conditions need to be kept within a narrow range?

Temperature, pH, water potential, blood glucose concentration

Why is it important to maintain the right blood glucose concentration?

Cells need glucose for respiration to produce ATP and it also affects water potential of the blood

What happens if blood glucose concentration is too high?

Water potential decreases and water molecules move out of the cells into the blood by osmosis

What can happen to cells when blood glucose is too high?

They crenate (shrivel up)

What happens to cells if blood glucose concentration is too low?

Cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide ATP

What is negative feedback?

A process that brings about a reversal of any change in conditions

What happens when the norm is restored?

The response is inhibited

What happens when there’s a change in a factor?

Receptors detect the rise/fall

Effectors bring about a response

Factor returns to set point/norm

Why does homeostasis involve multiple negative feedback mechanisms

Having more than one mechanism gives more control over changes in your

What is positive feedback?

A process that increases any change detected by the receptors

Why does positive feedback not lead to homeostasis?

Because it doesn’t keep your internal environment stable

What is positive feedback used for?

To rapidly activate processes in the body

What is blood glucose concentration regulated by?

Negative feedback / homeostasis

What do blood glucose concentrations vary depending on?

Food intake and energy requirements

What two hormones are glucose levels regulated by?

Insulin and glucagon

Where is insulin and glucagon produced?

Alpha and beta islet cells

Where are alpha and beta islet cells found?

In the pancreas

What are alpha and beta islet cells surrounded by?

Blood capillaries, cells that secrete enzymes, containing tubules in the centre

What hormone is involved in a rise in blood glucose concentration?

Insulin

What hormone is involved in a decrease in blood glucose concentration?

Glucagon

What is a rise in blood glucose detected by?

B cells in the islet of langerhans

What do the B cells do when they detect this increase?

Secrete insulin into the blood

What is the insulin detected by?

Receptors on liver and muscle cells (effector)

What do the liver and muscle cells do (increase in blood glucose)?

Remove glucose from the blood and convert the glucose to glycogen so glucose concentration falls

What is a fall in glucose concentration detected by?

Alpha cells in the islets of langerhans

What do the a cells do?

They secrete glucagon into the blood

What is glucagon detected by?

Receptors on liver cells

What do the liver cells do (decrease in blood glucose)?

Convert glycogen to glucose and release glucose into the blood so glucose concentration rises

What is it called when glucose concentration is too high?

Hyperglycaemia

What do B cells do when blood glucose levels are too high?

Release insulin

What do a cells do when blood glucose levels are too high?

Stop producing glucagon

How does insulin lower blood glucose concentration?

By binding to receptor proteins found on the plasma membrane of liver and muscle cells

What happens within cells when insulin binds to receptor proteins on liver and muscle cells?

1. More glucose transport proteins on cell surface membrane

2. More glucose can therefore enter the cell

3. More glucose converted to glycogen

4. More glucose used in respiration

Why does glycogen not affect the cells water potential?

It’s insoluble

What is it called when blood glucose falls too low?

Hypoglycaemia

What do a cells do when blood glucose levels are too low?

Detect this and release glucagon

What do B cells do when blood glucose levels are too low?

Stop releasing insulin

What does glucagon do in hypoglycaemia?

Binds to receptors on the plasma membrane of liver cells to convert the stored glycogen into glucose

How does the glucose get from the liver cells into the blood?

Diffusion

What do target cells do in hypoglycaemia?

They take up less glucose

What happens to the rate of respiration in hypoglycaemia?

Decreases

What is used instead of respiration in hypoglycaemia?

Lipids or amino acids instead

What does glucagon activate?

Enzymes that are involved in the formation of glucose from non-carbohydrates

What are glucose transporters an example of?

Channel proteins

What do glucose transporters do?

Allow glucose to be transported across a plasma membrane

Which cells contain GLUT4?

Skeletal and cardiac muscle cells

Where is GLUT4 stored when insulin levels are low?

Stored in vesicles in the cell cytoplasm

How does GLUT4 move to the membrane of the cell?

When insulin binds to the receptors on the plasma membrane

How does glucose enter the cell?

Through the GLUT4 protein by facilitated diffusion

What is glucose?

A monosaccharide used in respiration (respiratory substrate). A hexose sugar (C6H12O6)

What is glycogen?

A glucose polysaccharide. Branched. Used for energy storage

What bonds is glycogen made up of?

1,4 and 1,6 glycosidic bonds

What is glucagon?

A protein hormone released by alpha islet of langerhans cells in the pancreas. Bind to complimentary receptors on the plasma membrane

What is glycogenesis?

The process of glucose being converted to glycogen by condensation reactions

What is glycogenolysis?

The conversion of stored glycogen into glucose (splitting of glycogen) by hydrolysis reaction

Gluconeogenesis

The production of a new glucose from non-carbohydrates

What examples of non-carbohydrates are used in gluconeogenesis?

Amino acids and glycerol

What is glycolysis?

The splitting of glucose to form x2 pyruvate, results in the net production of 2 ATP molecules

Where is adrenaline secreted from?

The adrenal glands

What is adrenaline?

A hormone

When is adrenaline secreted?

• There’s a low concentration of glucose in your blood

• You’re stressed

• You’re exercising

What does adrenaline bind to?

Receptors in the plasma membrane of liver cells

What does adrenaline do?

• Activates glycogenolysis

• Inhibits glycogenesis

What does adrenaline do to insulin and glucagon?

Activates glucagon secretion and inhibits insulin secretion

How does adrenaline get the body ready for action?

By making more glucose available for muscles to respire

Where do adrenaline and glucagon activate glycogenolysis?

Inside a cell

What are adrenaline and glucagon examples of?

First messengers (hormones)

What do first messengers do?

Bind to hormone receptors, activates an enzyme on the inside of the plasma membrane, causes a chemical to be produced.

What is the second messenger?

A chemical

What is the second messenger activated by adrenaline and glucagon called?

Cyclic AMP (cAMP)

How is cAMP produced?

1. Adrenaline and glucagon are the first messenger

2. They are unable to enter the target cell

3. Adrenaline or glucagon bind to their complimentary receptor proteins in the target cell membrane

4. Activates the enzyme adenylate cyclase

5. Adenylate cyclase converts ATP to cyclic AMP

What enzyme converts ATP to cyclic AMP?

Adenylate cyclase

What does cAMP do?

Activates a protein called protein kinase A

What does protein kinase A cause?

A cascade of enzyme reactions within the cell, causes glycogen to be broken down into glucose (glycogenolysis)

What is diabetes?

A disease where the body is no longer able to control its blood glucose concentration

What are the two types of diabetes?

Type 1 and type 2

What is type 1 diabetes?

Autoimmune disease where b cells of the pancreas are attacked by the immune system so can’t produce insulin

What happens to the glucose in type 1 diabetes?

The kidneys can’t re absorb it all so it’s excreted in the urine

What is needed for someone with type 1 diabetes?

Regular monitoring of blood glucose concentration and regular insulin injections

When is type 2 diabetes acquired?

Later in life

What is type 2 diabetes?

B cells don’t produce enough insulin or target cells are less responsive to insulin

Why does this happen? (type 2 diabetes)

Because insulin receptors on plasma membranes aren’t working properly

What are risk factors for type 2 diabetes?

Lack of exercise, obesity, poor diet, family history, ethnic origin

How can type 2 diabetes be controlled?

Diet, losing weight and regular exercise. Glucose lowering medication if necessary

What health problems is type 2 diabetes linked to?

Visual impairment, kidney failure

What diet do health advisers recommend we have to reduce the risk of type 2 diabetes?

• Low in fat sugar and salt

• Whole grains, fruit, veg

• Regular exercise

• Lose weight if necessary

What is the NHS’s ‘change for life’ campaign for?

To educate people on how to have a healthier diet and lifestyle

How do health advisors challenge the food industry?

• To reduce the advertising of junk food

• To improve nutritional value of their products

• To use clearer labelling on products

How have food companies responded to criticism?

Using sugar alternatives to sweeten food and drink, and reducing the sugar, fat, salt content of products

How is diabetes tested by a doctor?

Urine sample to check glucose concentration (should be between 0 and 0.8mM)