PANCREAS AS AN ENDOCRINE GLAND - 2

Dr. Sumera Gul

Associate Professor

Department of Physiology

Learning objectives

At the end of the lecture the students should be able to:

• Explain the mechanism of secretion of Insulin

• Discuss the factors affecting the secretion of Insulin

• Explain the relationship of insulin in switching between carbohydrate and lipid metabolism

Insulin

• Cell?

• Type?

• Receptor location?

• Receptor type?

• Mechanism of action?

Insulin

• Cell? B cell of Islet of Langerhans

• Type? peptide

• Receptor location? Cell membrane

• Receptor type? Enzyme linked receptor

• Mechanism of action? Activation of tyrosine kinases and IRS

Secretion of Insulin

Control of Insulin secretion• Increased Blood Glucose Stimulates Insulin

Secretion.

• At the normal fasting level of blood glucose of 80 to 90 mg/100 ml, the rate of insulin secretion is minimal on the order of 25 ng/min/kg of body weight.

Control of Insulin secretion

• 1. The concentration of insulin in plasma increases almost 10-fold within 3 to 5 minutes after acute elevation of the blood glucose.

• This increase in insulin concentration decreases about halfway back toward normal in another 5 to 10 minutes.

• 2. Beginning at about 15 minutes, insulin secretion rises a second time and reaches a new plateau in 2 to 3 hours

• Amino acids:

• The most potent of these amino acids are arginine and lysine.

• Amino acids strongly potentiate the glucose stimulus for insulin secretion.

Effect of Amino Acids

• Gastrin,

• Secretin,

• Cholecystokinin,

• Glucagon like peptide–1 (GLP-1),

• Glucose-dependent insulinotropic peptide (GIP)

Effect of Gastrointestinal hormones

Incretins

GLP-1 and GIP,

they enhance the rate of insulin release from the pancreatic beta cells in presence of glucose

inhibit glucagon secretion from the alpha cells

Effect of Gastrointestinal hormones

• Other hormones that either directly increase insulin secretion or potentiate the glucose stimulus for insulin secretion

• Include:

• Glucagon, • growth hormone,• cortisol, • progesterone and estrogen.

• Parasympathetic stimulation increase insulin secretion during hyperglycemic conditions

• Sympathetic nerve stimulation may increase glucagon secretion and decrease insulin secretion during hypoglycemia

Control of Insulin secretion

Witch between CHO and Fat metabolism

Hyperglycemia

Insulin secretion

And use of Glucose

Decreased glucose levels

Glucagon

Lipolysis

Spare glucose

utilization

Witch between CHO and Fat metabolism

Prolonged Hypoglycemia

GH

Cortisol

Use of Fats

Spare glucose

utilization

Increases Blood

glucose

Witch between CHO and Fat metabolism

Stress

Fear

Severe Hypoglycemia

Epinephrine

Lipolysis

Glycogenolysis

Increases Blood glucose