REGULATION OF BLOOD GLUCOSE LEVEL

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Regulation of Blood Glucose Level :

Regulation of Blood Glucose Level

INTRODUCTION:

INTRODUCTION Blood sugar concentration, or glucose level, refers to the amount of glucose present in the blood of a human. Normally, in mammals the blood glucose level is maintained at a reference range between about 3.6 and 5.8 mM ( mmol /l).60- It is tightly regulated as a part of metabolic homeostasis.

INTRODUCTION…..:

INTRODUCTION….. There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels: catabolic hormones (such as glucagon, growth hormone, cortisol and catecholamines) which increase blood glucose; and one anabolic hormone (insulin), which decreases blood glucose

INTRODUCTION…..:

INTRODUCTION….. liver is the predominant tissue responding to signals that indicate reduced or elevated blood glucose levels. Low blood glucose triggers release of glucagon from pancreatic α-cells. High blood glucose triggers release of insulin from pancreatic β-cells .

Roles of Insulin and Glucagon in Regulating Blood Glucose:

Roles of Insulin and Glucagon in Regulating Blood Glucose Figure 13.9

Glucagon….:

Glucagon…. Glucagon binding to its' receptors on the surface of liver cells triggers an increase in cAMP production leading to an increased rate of glycogenolysis by activating glycogen phosphorylase via the PKA-mediated cascade. This is the same response hepatocytes have to epinephrine release. The resultant increased levels of G6P in hepatocytes is hydrolyzed to free glucose, by glucose-6-phosphatase, which then diffuses to the blood.

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The glucose enters extrahepatic cells where it is re-phosphorylated by hexokinase. Since muscle and brain cells lack glucose-6-phosphatase, the glucose-6-phosphate product of hexokinase is retained and oxidized by these tissues.

Glucagon…..:

Glucagon…..

INSULIN:

INSULIN insulin stimulates extrahepatic uptake of glucose from the blood and inhibits glycogenolysis in extrahepatic cells and conversely stimulates glycogen synthesis. As the glucose enters hepatocytes it binds to and inhibits glycogen phosphorylase activity. The binding of free glucose stimulates the de-phosphorylation of phosphorylase thereby, inactivating it.

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When blood glucose levels are low, the liver does not compete with other tissues for glucose . Conversely, when blood glucose levels are high extrahepatic needs are satisfied and the liver takes up glucose for conversion into glycogen for future needs.

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Under conditions of high blood glucose, liver glucose levels will be high and the activity of glucokinase will be elevated. The G6P produced by glucokinase is rapidly converted to G1P by phosphoglucomutase, where it can then be incorporated into glycogen.

Regulation of Glucose Metabolism During Exercise:

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. Thyroxine promotes glucose catabolism

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Hormone Tissue of Origin Metabolic Effect Effect on Blood Glucose insulin Pancreatic beta cells 1) Enhances entry of glucose into cells; 2) Enhances storage of glucose as glycogen , or conversion to fatty acids; 3) Enhances synthesis of fatty acids and proteins; 4) Suppresses breakdown of proteins into amino acids, of adipose tissue into free fatty acids. Lowers somatostatin Pancreatic D Cells 1) Suppresses glucagon release from α cells (acts locally); 2) Suppresses release of Insulin, Pituitary tropic hormones, gastrin and secretin Raises glucagon Pancreatic alpha cells 1) Enhances release of glucose from glycogen; 2) Enhances synthesis of glucose from amino acids Raises epinephrine Adrenal medulla 1) Enhances release of glucose from glycogen ; 2) Enhances release of fatty acids from adipose tissue. Raises cortisol Adrenal cortex 1) Enhances gluconeogenesis ; 2) Antagonizes Insulin. Raises ACTH Anterior pituitary 1) Enhances release of cortisol ; 2) Enhances release of fatty acids from adipose tissue. inhibiting uptake by extrahepatic tissues . Raises Growth hormone Anterior pituitar Antagonizes Insulin, inhibiting uptake by extrahepatic tissues. Raises thyroxine thyroid 1) Enhances release of glucose from glycogen; 2) Enhances absorption of sugars from intestine Raises

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