Integration of Metabolism, Diabetes, Fasting, and Starvation Flashcards
The integration of energy metabolism across organ systems is controlled primarily by the actions of the pancreatic hormones
Insulin and Glucagon
When food is available in abundance, responding changes in the circulating levels of these hormones allow the body to store energy in the forms of
Glycogen and FAs
Represents the most common disruption that occurs in this complex system of hormones, enzymes, and metabolites in humans
Diabetes Mellitus
There are two fundamental sorts of diabetes, type 1 is known as
Insulin-dependent diabetes (IDDM)
Type 2 diabetes is classified as
Insulin-independent diabetes (NIDDM)
A polypeptide hormone produced by the B- cells of the Islets of Langerhans, clusters of cells that comprise about 1% of the pancreas
Insulin
Insulin is one of the most important hormones coordinating the utilization of
Fuel
The metabolic effect of insulin are
Anabolic
Composed of 51 amino acids arranged in two polypeptide chains, designated A and B (proteolytically processed from a single primary translation product)
Insulin
These A and B polypeptide chains are linked together by two
Disulfide bridges
The insulin molecule also contains an intra-molecular disulfide bridge between amino acid residues
6 and 11
The B-cells of the pancreas release both the mature insulin and the processing by-product
C-peptide
Human insulin has the same potency as pig insulin, which is similar in structure to the human hormone and has been used in the past for treatment of
Diabetes
Insulin secretion by the B-
cells of the Islets of Langerhans of the pancreas is closely coordinated with the release of
Glucagon by a-cells
The most important glucose-sensing cells in the body
Pancreatic Beta-cells
Ingestion of glucose or a carbohydrate-rich meal leads to a rise in blood glucose, which is a signal for increased
Insulin secretion
Causes a transient rise in plasma amino acids levels, which in turn induces the immediate secretion of insulin
Ingestion of protein
Insulin secretion is stimulated by the gastric peptides
-release following the ingestion of food
Secretin and Incretins
Cause an anticipatory rise in insulin levels in the portal vein before there is an actual rise in blood glucose
Secretin and Incretins
This may account for the fact that the same amount of glucose given orally induces a much greater secretion of insulin than if given intravenously
The anticipatory rise
Decreased when there is a scarcity of dietary fuels, and also during periods of trauma
Synthesis and release of insulin
Trauma effects on insulin secretion are mediated primarily by
Epinephrine
Has a direct effect on energy metabolism, causing a rapid mobilization of energy-yielding fuels, including glucose from the liver and fatty acids from adipose tissue, via a receptor and signal transduction mechanism
Epinephrine
Able to override the normal glucose-stimulated release of insulin
Epinephrine
Thus, in emergency situations, the sympathetic nervous system largely replaces plasma glucose concentration as the controlling influence over
Insulin secretion
Glucose transport into most insulin responsive tissues, for example, skeletal muscle and adipocytes, increases in the presence of
Insulin
Promotes the recruitment of glucose transporters from a pool in intracellular vesicles to the cell membrane
Insulin
Depends on both the abundance of glucose transporters and their activation, probably by phosphorylation of transporters in the membrane
Glucose Transport
Hepatocytes, erythrocytes, the nervous system, and the cornea have
Insulin-dependent glucose transport
In the liver, brain, cornea, intestinal mucosa, renal tubes and the red blood cells, glucose transport is not sensitive to
Insulin
Leads to significant changes in carbohydrate metabolism, including increased glycolysis, increased glycogen synthesis, and decreased gluconeogenesis
Intravenous administration of insulin
Adipose tissue metabolism patterns respond within minutes to the administration of
Insulin
This results in a marked increase in
FA synthesis
Insulin decreases the level of circulating fatty acids by inhibiting the activity of
Hormone-sensitive lipase
Insulin acts primarily by countering the stimulation of adenylyl cyclase by
Epinephrine and Glucagon