Veterinary Physiology-III

BLOOD GLUCOSE

• The normal blood glucose concentration varies from 62 to 120 mg/dl in dogs, cats,horses and pigs; in cows, sheep and goats it varies from 42 to 80 mg/dl; adult ruminants have lower level than newborn ruminants.
• The normal blood level is termed euglycaemia; when the blood glucose level is increased it is hyperglycemia and a decreased level is hypoglycaemia.

Control of blood glucose

• There are two major sources of blood glucose
  • Dietarycarbohydrates – absorbed from intestine
  • Synthesisof glucose in liver – from glucogenic substances – glycogen, glucogenic aminoacids, glycerol and propionate in ruminants, 

Role of Liver

• Liver is the major organ involved in regulating blood glucose. After a carbohydrate meal, the increase in blood glucose is prevented by liver by converting glucose to glycogen and fatty acids. Liver can store glycogen up to 10 to 15% of its weight. During decrease in blood glucose level, liver glycogen is broken down to glucose and released into circulation.

Role of Hormones

• The only hormone that produces hypoglycaemia is insulin
• All other hormones – glucagon, growth hormone, cortisol and epinephrine have hyperglycaemic effect.
• When insulin effect is removed by pancreatectomy, IGF-I sustains weak insulin activity (but not sufficient to maintain life).
• Glucagon and epinephrine promotes glycogenolysis while insulin has antagonistic effect of glycogenesis. Molar ratio of insulin: glucagon rather than the absolute concentration is the determining factor of glycogen breakdown or synthesis. Glucagon stimulates gluconeogenesis from amino acids.

Glucose tolerance test

• The capacity of the body’s control mechanisms to regulate blood glucose level canbe evaluated by oral glucose tolerance test.
• About1 to 2 g of glucose / kg weight is given orally and blood samples are collected 30 min intervals for 120 or 240 min.
• In normal dogs, blood glucose level should reach close to 160 mg/dl in 30 to 60min and the level should reach the baseline normal values by 120 to 180 min.
• In horses, by 120 min, the glucose level should reach 175 mg/dl which should return to normal by 360 min.