Organisms response - Blood glucose

By what system are blood glucose levels controlled?

Homeostasis

What do levels of glucose in the blood effect?

- Water potential

- Blood pressure

- Availability of respiratory substrates

What happens to the brain if blood glucose becomes too low?

Cells become damaged and rapidly die as they cannot respire

What happens to blood pressure if glucose levels become too high?

1. Water potential of blood decreases

2. Water moves in

3. This increases the volume of blood

4. This causes blood pressure to rise

How can glucose enter the bloodstream?

- Absorption from the gut following digestion

- Hydrolysis of glycogen stores

- Converting non-carbs such as lipids and proteins into glucose

Why does the amount of glucose gained from meals vary?

It is dependent on the carb content of the meal

What are the hormones that regulate blood glucose levels?

- Insulin

- Glucagon

Where is insulin and glucagon secreted?

Pancreas

What tissue in the pancreas secrete insulin and glucagon?

Islets of Langerhans

What are the two types of cells in the islets of Langerhan?

Alpha cells and beta cells

What do alpha cells produce?

Glucagon

What do beta cells produce?

Insulin

Describe the role of the alpha and beta cells?

They act as receptors and also initiate response to blood glucose levels

What cells act as the targets/effectors that respond to insulin?

Liver, muscle and fat cells

How do alpha and beta cells respond to high blood glucose?

Beta starts to secrete insulin and alpha stops secreting glucagon

Describe the secretion of insulin.

1. High blood glucose is detected by beta cells in the pancreas

2. Glucose is absorbed into the beta cells via carrier proteins

3. This causes insulin containing vesicles to move towards the cell surface

4. The vesicles release the insulin into the capillaries

5. Insulin circulates the body, stimulating the uptake of glucose by muscle, fat and liver cells

How do the effector cells uptake glucose from the blood?

1. Insulin binds to specific receptors on the membrane of the target/effector cells

2. These cells possess some glucose transported proteins in their surface membranes

3. The binding of insulin stimulates the cells to add more glucose transporter molecules to the surface membrane

4. Increased permeability to glucose so rate of facilitated diffusion increases

What does glucose stimulate in the liver?

Glycogenesis

Describe the action of glycogenesis in the liver.

1. Glucose enters the liver cell

2. It is converted to glucose phosphate by an enzyme

3. Another enzyme then converts this into glycogen

4. This lowers glucose conc in the liver so more glucose moves in from the bloodstream

How do the alpha and beta cells respond to low blood glucose?

Beta cells stop secreting insulin and alpha cells start secreting glucagon

What cells act as the targets/effectors that respond to glucagon?

Liver and muscle cells

How do effector cells respond to the production of glucagon?

They begin the second messenger model which breaks down the glucagon in the cells into glucose to return to the blood stream and raise blood sugar

What is the second messenger model?

The binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane which then produces a chemical known as a 2nd messenger

Describe the second messenger model.

1. Glucagon binds to the surface membrane of liver and muscle cells

2. This causes a change in a receptor that activates a G protein

3. This G protein activates the enzyme adenylyl cyclase

4. Active adenylyl cyclase catalyses the conversion of ATP to cyclic AMP or cAMP

5. cAMP binds to protein kinase A enzymes and activates them

6. These enzymes catalyse the breakdown of glucagon to glucose (glycogenolysis)

What is an enzyme cascade?

An enzyme chain which works like a set of dominos, if stopped anywhere in the process the cascade is compromised. The second messenger model is an example of this

What is the first and second messeger?

Glucagon and then cAMP

How does adrenaline affect blood glucose?

It increases the concentration of blood glucose

What cells act as the targets/effectors that respond to adrenaline?

Liver cells

How does adrenaline increase glucose concentration?

It binds to a specific receptor on liver cells which activate the second messenger model

What is the second messenger model for adrenaline?

1. Adrenaline binds to the surface membrane of liver cells

2. This causes a change in a receptor that activates a G protein

3. This G protein activates the enzyme adenylyl cyclase

4. Active adenylyl cyclase catalyses the conversion of ATP to cyclic AMP or cAMP

5. cAMP binds to protein kinase A enzymes and activates them

6. These enzymes catalyse the breakdown of glucagon to glucose (glycogenolysis)

What does adrenaline stimulate in muscle cells?

During exercise, it stimulates the breakdown of glycogen that is stored in them so they can be used for respiration

How does the liver help convert between glycogen and glucose?

The binding of insulin and glucagon stimulates three processes in the liver:

- Glycogenolysis

- Glycogenesis

- Gluconeogenesis

Summarise glycogenesis.

- Synthesis of glycogen from glucose

- Triggered by insulin as a result of high blood glucose

- Removes glucose from blood stream

Summarise glycogenolysis.

- Breakdown of glycogen to glucose

- Triggered by glucagon as a result of low blood glucose

- Returns glucose to blood stream

Summarise gluconeogenesis.

- Synthesis of glucose from non-carb molecules by activating enzymes in liver

- Triggered by glucagon as a result of low blood glucose

- Adds glucose to blood stream

In what order are the other non-carb molecules used in gluconeogenesis?

1. Lipids (fats)

2. Proteins