Endocrine PhysiologyPANCREAS

Dr. Meg-angela Christi M. Amores

Pancreas

• Digestive function• Secretes two important hormones– Insulin– Glucagon * important in regulation of glucose

• amylin, somatostatin, and pancreatic polypeptide

Physiologic Anatomy

• Two major types of tissues:a. Acini- secrete digestive juices into the duodenumb. Islets of Langerhans -secrete insulin and glucagon

directly into the blood• Islet of Langerhans– 1 to 2 million islets – alpha, beta, and delta cells

Physiologic Anatomy

• Beta cells– constituting about 60% of all the cells of the islets– secrete insulin and amylin

• Alpha cells– about 25% of the total cells– secrete glucagon

• Delta cells– about 10% of the total cells– secrete somatostatin

Insulin and Its Metabolic Effects

• Insulin is a hormone associated with energy abundance– insulin is secreted in great quantity when there is

great abundance of energy-giving foods in the diet (carbohydrates)

– stored as glycogen mainly in the liver and muscles– converted into fats and stored in the adipose

tissue– promoting amino acid uptake by cells and

conversion of these amino acid into protein

Effect of Insulin on Carbohydrate Metabolism

Insulin Promotes Muscle Glucose Uptake and Metabolism

• muscle tissue depends not on glucose for its energy but on fatty acids

• normal resting muscle membrane is only slightly permeable to glucose except when the muscle fiber is stimulated by insulin

Insulin Promotes Muscle Glucose Uptake and Metabolism

• two conditions the muscles do use large amounts of glucose

• Heavy exercise – more permeable to glucose• Few hours after meal - pancreas is secreting large

quantities of insulin

Storage of Glycogen in Muscle

• stored in the form of muscle glycogen instead of being used for energy

• can later be used for energy by the muscle• useful for short periods of extreme energy use

by the muscles and even to provide spurts of anaerobic energy

Quantitative Effect of Insulin to Facilitate Glucose Transport Through the Muscle Cell

Membrane• lower curve labeled "control" shows the

concentration of free glucose demonstrating that the glucose concentration remained almost zero despite increased extracellular glucose

• the curve labeled "insulin" demonstrates that the intracellular glucose concentration rose to as high as 400 mg/100 ml when insulin was added

Insulin Promotes Liver Uptake, Storage, and Use of Glucose

• cause most of the glucose absorbed after a meal to be stored almost immediately in the liver in the form of glycogen

• when food is not available, insulin secretion decreases rapidly and the liver glycogen is split back into glucose, which is released back into the blood

Insulin Promotes Conversion of Excess Glucose into Fatty Acids and Inhibits Gluconeogenesis in

the Liver

• insulin promotes the conversion of all this excess glucose into fatty acids

• fatty acids are subsequently packaged as triglycerides in very-low-density lipoproteins and transported in this form to the adipose tissue and deposited as fat.

• Insulin also inhibits gluconeogenesis

Lack of Effect of Insulin on Glucose Uptake and Usage by the Brain

• Brain does not need insulin for glucose uptake• Brain cells are permeable to glucose• Glucose is the main form of energy of the

brain cells• Have difficulty in using other substrates such

as fats

Effect of Insulin on Fat Metabolism

Insulin Promotes Fat Synthesis and Storage

• insulin increases the utilization of glucose which automatically decreases the utilization of fat, thus functioning as a fat sparer

• insulin promotes fatty acid synthesis– when more carbohydrates are ingested than can

be used for immediate energy• Insulin promotes storage of fat in the adipose

cells

Effect of Insulin on Protein Metabolism and on Growth

• Insulin promotes protein synthesis and storage• Lack of insulin causes protein depletion and

increased plasma amino acids• Insulin and Growth Hormone interact

synergistically to promote growth

Mechanism of Insulin Secretion

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

– If the blood glucose concentration is suddenly increased to a level two to three times normal and kept at this high level thereafter, insulin secretion increases markedly

Glucagon and Its Functions

• hormone secreted by the alpha cells when the blood glucose concentration falls

• functions is to increase the blood glucose concentration, an effect that is exactly the opposite that of insulin.

Effects of Glucagon on Glucose Metabolism

• Glucagon causes glycogenolysis and increased blood glucose

• glucagon increases gluconeogenesis• activates adipose cell lipase, making increased

quantities of fatty acids available for energy• inhibits the storage of triglycerides in the liver

Regulation of Glucagon Secretion

• Increased blood glucose inhibits glucagon secretion

• Increased blood amino acids stimulate glucagon secretion

• exercise stimulates glucagon secretion

Somatostatin and its Function

• Secreted by the delta cells• all factors related to the ingestion of food

stimulate somatostatin secretion– increased blood glucose – increased amino acids– increased fatty acids– increased concentrations of several of the

gastrointestinal hormones

Somatostatin and its Function

• depress the secretion of both insulin and glucagon

• decreases the motility of the stomach, duodenum, and gallbladder.

• decreases both secretion and absorption in the gastrointestinal tract

Summary of Blood Glucose Regulation

1. The liver functions as an important blood glucose buffer system

2. Both insulin and glucagon function as important feedback control systems for maintaining a normal blood glucose concentration

3. In severe hypoglycemia, a direct effect of low blood glucose on the hypothalamus stimulates the sympathetic nervous system

4. Over a period of hours and days, both growth hormone and cortisol are secreted in response to prolonged hypoglycemia, and they both decrease the rate of glucose utilization by most cells of the body, converting instead to greater amounts of fat utilization

Diabetes Mellitus

• Is a syndrome of impaired carbohydrate, fat, and protein metabolism caused by either lack of insulin secretion or decreased sensitivity of the tissues to insulin

• Type I diabetes, also called insulin-dependent diabetes mellitus (IDDM)

• Type II diabetes, also called non-insulin-dependent diabetes mellitus (NIDDM)

Diabetes Mellitus