Objectives

Explain how hormones work

Outline the role of the pancreas as an endocrinegland

Explain how blood glucose concentration is regulated with reference to insulin, glucagon and adrenaline

Hormone Regulation Hormones are

regulated by negative feedback.

Regulation of blood sugar is a good example of this.

How do hormones work?

Hormones are proteins that are produced in (endocrine) glands and secreted into the blood

Carried in the blood plasma to target cells

These cells have complementary receptors to the specific hormone

Adrenaline and glucagon follow the second messenger model of action

The pancreas Is both an endocrine

and exocrine gland Exocrine function -

secretes digestive enzymes into the pancreatic duct

Endocrine function - secretes hormones (insulin and glucagon) directly into the blood

Secretion of enzymes (exocrine function)

Pancreatic cells surround small tubules which drain into the pancreatic duct

Pancreatic cells produce pancreatic juice which is made up of; Amylase (a

carbohydrase) Trypsinogen (an inactive

protease) Lipase

Secretion of hormones (endocrine function)

Hormones are secreted from the cells in the islets of Langerhans

α cells manufacture and secrete the hormone glucagon

βcells manufacture and secrete the hormone insulin

These are released directly into the blood

Control of blood glucose The natural sources of blood glucose are:

1. Directly from the diet – glucose enters blood when carbohydrates are broken down

2. Breakdown of glycogen (Glycogenolysis )

3. Gluconeogenesis – production of new glucose from sources other than carbohydrates

Control of blood glucose

Is a negative feedback process

The normal blood glucose level is 90mg per 100ml of blood

If the blood glucose levels get too high or too low, then the changes are detected by the α and βcells in the islets of Langerhans

Insulin and the β cells of the pancreas

*Act as Receptors that detect rise in blood glucose level

*When rise is detected they secrete insulin into the blood plasma

*Insulin binds to glycoprotein receptors on cell surface of most body cells (notably excluding Red Blood Cells)

http://www.medbio.info/horn/time%203-4/insulin's%20mechanism%20of%20action.htm

When bound the following can happen:1) Modifies the tertiary structure of glucose carrier protein channels so that they allow more glucose into cells 2) Increase number of glucose carrier proteins in cell -surface membrane3) Activate enzymes that convert glucose to glycogen and fat

This results in:

1)More glucose absorbed into cells

2)Increases respiratory rate of cells so more glucose is used up so more glucose is absorbed

3)Increasing rate of conversion of glucose to glycogen (glycogenesis) in the liver and muscles

4)Increasing conversion of glucose to fat

http://www.youtube.com/watch?v=X0ezy1t6N08

Glucagon and the α cells of the pancreas

*Act as Receptors that detect fall in blood glucose level

*When fall is detected they secrete hormone glucagon into the blood plasma

*glucagon binds to glycoprotein receptors on LIVER cells only

When bound the following happens:a)An enzyme is activated that converts glycogen to glucose

b)There is an increase in the conversion of amino acids and glycerol into glucose GLUCONEOGENESIS)

This results in:An increase in blood glucose levels

The role of adrenalineThere are a number of other hormones that increase blood sugar levels. The most well known is adrenaline

• Produced in adrenal glands (above kidneys)

•It raises blood glucose by:

Activating an enzyme that causes breakdown of glycogen to glucose in the liver

Inactivating an enzyme that synthesises glycogen from glucose

Hormone interaction in regulating blood glucose

Uses negative feedback as both hormones work to keep blood glucose at around 90mg per 100ml of blood.

They are said to work antagonistically

Task

The exam questions