Objectives Describe the structure of the pancreas

Outline the role of the pancreas as an endocrine and exocrine gland

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

The Liver

What does endocrine and exocrine mean?

Endocrine means a gland without a duct – i.e. it secretes hormones DIRECTLY into the blood

Exocrine means a gland with a duct – i.e. it secretes hormones into a tube

The pancreas- 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 Sodium

hydrogencarbonate

Questions…..

Why is an inactive protease released?

How is it activated?

Why is sodium hydrogen carbonate released?

Secretion of hormones (endocrine function)

Hormones are secreted from the cells in the islets of Langerhans

α (alpha)cells produce and secrete the hormone glucagon

βcells produce and secrete the hormone insulin

These are released directly into the blood

nucleus rough endoplasm ic re ticu lum cell m em brane beta ce ll secretory vesic le

a lpha ce ll secretory vesicle m itochondrian x 30000

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 β cells in the islets of Langerhans

Card sort activity

Glucose ( monosaccharide)

Glucagon (hormone that increases blood glucose levels)

Glycogen (storage molecule of glucose)

Glycogenesis (glycogen synthesis)

Gluconeogenesis (conversion of amino acids and fats into glucose

Glycogenolysis (glycogen converted to glucose

Blood Sugar level Rises

Detected by B Cells of Islet of Langerhans in pancreas.

Insulin released into the blood. Binds to receptors on liver and

muscle cells.

Glucose transport proteins open and glucose enters the

cells.

Enzymes are stimulated to

convert glucose into glycogen

Glucose is converted into triglycerides.

Rate of respiration is increased.

Blood sugar level falls

Control of blood glucose: A Second Messenger System

1. Insulin binds to receptors in the muscle and liver.

2. Adenylate cyclase (enzyme) is activated which converts ATP to cAMP.

3. cAMP acts as a second messenger and activates a series of reactions.

If blood glucose levels rise… GLUT4 receptors/ glucose

channelshttp://www.youtube.com/watch?v=FkkK5lTmBYQ

Blood Sugar level FallsDetected by A Cells of Islet of

Langerhans in pancreas.

Glucagon released into the blood. Glucagon binds to receptors on liver

cells only.

Glucose enters the blood.

Glycogenolysis: Glycogen broken down into soluble glucose.

Gluconeogenesis: Glycerol and amino acids are converted into glucose.

Blood sugar level rises

Why do hepatocytes have specialised receptors for both insulin

and glucagon? Hepatocytes contain a store of glycogen, when

there is excess glucose in the blood, the cells absorb glucose and make more glycogen-therefore they need to respond to insulin.

However when there is insufficient glucose in the blood the cells break down glycogen and release glucose into the blood therefore they need also must respond to glucagon.

How is the ultrastructure of alpha and beta cells in the islets of Langerhans

specialised to manafacture and secrete hormones?

Will have many:

-Ribosomes & RER for protein synthesis

-Golgi apparatus (hormone prep and packaging into vesicles)

-Secretory vesicles

-mitochondria (ATP for active processes in the cell)