A and P II

Glucose Metabolism

120 grams of glucose / day = 480 calories

Saccharides

• Glucose is the primary monsaccaride in the body (one sugar)

• There are dissaccarides like fructose, sucrose, galactose

• Starches and glycogen are polysaccarides

How is sugar made/absorbed?

• Amylase-(pancreatic and salivary)breaks starches into dia+trisaccharides

• Lactase,maltase,sucrase-enzymes in small intestine that break up dissaccharides into small glucose

• Then absorbed and transported in blood

Where does it go after it is absorbed?

The Pancreas

• Organ (5 inches) consists of head, body & tail• Has both an exocrine & an endocrine function

– acinar cells produce digestive enzymes– endocrine cells (Islets of Langerhans) produce hormones

Cell Organization in Pancreas

• Exocrine acinar cells surround a small duct• Endocrine cells secrete near a capillary

Histology of the Pancreas

• 1 to 2 million pancreatic islets

• Contains 4 types of endocrine cells

Cell Types in the Pancreatic Islets

• Alpha cells (20%) produce glucagon

• Beta cells (70%) produce insulin

• Delta cells (5%) produce somatostatin

Regulation of Glucagon & Insulin Secretion

• Low blood glucose stimulates release of glucagon

• High blood glucose stimulates secretion of insulin

Insulin• Released in response to rising blood glucose

levels

• Decreases glucose levels by promoting:– The rapid up-take of glucose by cells– Storage of glucose (stored as glycogen in the

liver)– Promotes the use of glucose by most body tissues– Promotes the conversion of excess glucose to fat– Inhibits gluconeogenesis from protein

= “hypoglycemic effect”

Insulin

Insulin

Cell Use of Glucose for ATP

production

Glucagon

• Released from alpha cells in pancreas in response to decreasing blood glucose levels

• Increases blood glucose levels by promoting:

– Glycogenolysis of liver glycogen– Gluconeogenesis in liver cells– Mobilizes fatty acids for energy

= “hyperglycemic effect”

• It is important to maintain blood glucose levels within a narrow range

• Glucose is the only nutrient that the brain, retina & germinal epithelia of the gonads can use

• The liver acts as an important “buffering mechanism”• Insulin & glucagon function in opposite directions• Insulin is more important day-to-day• Glucagon is usually only present in times of stress

Pathologies of Blood Glucose Regulation

1. Diabetes mellitus– Decreased insulin secretion from the beta cells– 2 types: Type I (juvenile)

Type II (adult onset)

2. Hyperinsulinism- too much insulin e.g tumour

Diabetes Mellitus

• Type I– Hereditary predisposition to autoimmune disease of beta cells– Or destruction of beta cells (ie: viral infection)

• Type II– Degeneration or suppression of the beta cells– Precipitated by factors such as obesity, stress, pregnancy,

menopause

• Pathogenesis– Altered glucose, fat & protein metabolism

• Signs– Glucose in urine– Dehydration– Acidosis

• Symptoms– Polyuria, Polydipsia & Polyphagia– Loss of weight– Lack of energy– Acetone breath– Rapid deep breathing

• Diabetic coma can be fatal & results from severe dehydration & acidosis

• Treatable…..Yes

Regulation of Glucose Metabolism During Exercise

• Glucagon secretion increases during exercise to promote liver glycogen breakdown (glycogenolysis)

• Epinephrine and Norepinephrine further increase glycogenolysis

• Cortisol levels also increase during exercise for protein catabolism for later gluconeogenesis.

• Growth Hormone mobilizes free fatty acids• Thyroxine promotes glucose catabolism

Regulation of Glucose Metabolism During Exercise

• Glucose must not only be delivered to the cells, it must also be taken up by them. That job relies on insulin.

• Exercise may enhance insulin’s binding to receptors on the muscle fiber.

• Up-regulation (receptors) occurs with insulin after 4 weeks of exercise to increase its sensitivity (diabetic importance).

If glucose is Not available

• First use exogenous blood sugar (in blood)

• Then break up glycogen in liver etc

• Then break up fatty acids from triglycerides (fat stores) etc which produce ketones as a by produce

• Also work on proteins then to try to convert to energy the body can use

• Stage 1 – postparandial – All tissues utilize glucose

• Stage 2 – postabsorptive • KEY – Maintain blood glucose

– Glycogenolysis– Glucogneogenesis– Lactate– Pyruvate– Glycerol– Spare glucose by metabolizing fat

• Stage 3- Early starvation– Gluconeogenesis

• Stave 4 – Intermediate starvation – gluconeogenesis– Ketone bodies

• Stage 5 – Starvation

Reading

• sugar metabolism of Endocrine section Saladin

• Look in your Caroline book as well on endocrine disorders

• Note:

Normal blood sugar is 4.0-6.0 mmol/L