Endocrinology - Glucose homeostasis... Flashcards
Glucose is the sole source of energy for the ________.
brain
What is the range for normal blood glucose?
70-120 mg/dl
What are the exogenous sources of glucose?
intestinal absorption
What are the endogenous sources of glucose?
glycogenolysis and gluconeogenesis
Post-prandially, how long does glucose provide fuel for and for what?
fuel for 4-8 hours of cell metabolism
In the fasted state, what sources maintain normoglycemia?
The endogenous sources
What is glycogenolysis?
breakdown of hepatic glycogen stores into glucose
When are the hepatic glycogen stores exhausted during fasting?
after 2-3 days of fasting
When glycogen stores are depleted in fasted patients, what takes over to maintain normoglycemia?
gluconeogenesis
What is gluconeogenesis?
The formation of glucose from precursors
What are the precurosors for gluconeogenesis?
Amino acids, glycerol, and lactate
Where does gluconeogenesis occur?
Mainly in the liver, but it can also occur in the kidney
Aside from the exogenous and endogenous sources of glucose, what is also required for normoglycemia?
hepatic function/hepatic blood supply and a functioning endocrine system
What does insulin do?
Promote the cellular uptake of glucose, AA, FA, and electrolytes
Promotes the storage of glucose as glycogen
Inhibits lipolysis and subsequent release of FFA into circulation
Inhibits gluconeogenesis and glycogenolysis
Hypoglycemia is when BG falls below what level?
70 mg/dl
What is the normal response to hypoglycemia?
There is a stimulation of a release of diabetogenic hormones - glucagon, cortisol, catecholamines, and growth hormone (unimportantly progesterone and thyroxine too)
What is the net effect of the diabetogenic hormones?
Promote gluconeogenesis and glycogenolysis, decrease peripheral glucose use, and shut down insulin secretion
What is the net result of the effect of diabetogenic hormones?
to normalize blood glucose levels
What hormones increase BG?
cortisol, epinehrine, glucagon, and growth hormone
What hormone decreases BG?
insulin
What can cause hypoglycemia?
Lack of intestinal absorption, lack of hepatic production, endocrine disorders, increased glucose utilization, and miscellaneous
What can cause lack of intestinal absorption of glucose?
severe malnutrition/starvation and severe intestinal disease
What can cause lack of hepatic production of glucose?
Portosystemic shunts, hepatic failure, and glycogen storage diseases
What are the sub-categories of endocrine disorders can cause hypoglycemia?
Lack of diabetogenic hormones or too much insulin
What endocrine disorders can cause lack of diabetogenic hormones?
hypoadrenocorticism - cortisol deficiency
What endocrine disorders can cause the production of too much insulin?
iatrogenic and insulinoma
What can cause increased glucose utilization?
sepsis, pollycythemia, and extreme exertion
What miscellaneous causes can lead to hypoglycemia?
Juvenile hypoglycemia, xylitol toxicity, paraneoplastic, and artifact
What is the pneumonic to remember the eitiologies for hypoglycemia?
SHIN SPLATS - Sepsis, Hunting dog hypoglycemia, Insulin overdose/iatrogenic, Neoplasia, Spurious, Puppy or polycythemia, Liver disease, Addison’s disease, Toxin, and Storage diseases
What is the first area affected by hypoglycemia?
the cerebral cortex
Clinical signs from hypoglycemia in the brain result from what?
Neuroglycopenia and sympathoadrenal stimulation
What is neuroglycopenia?
lack of glucose to the brain
What is sympathoadrenal stimulation?
The release of epinephrine as a result of hypoglycemia
What are the clinical signs of neuroglycopenia?
weakness, lethargy, behavioral change, ataxia, seizures, and coma
What are the clinical signs associated with sympathoadrenal stimulation?
Think of someone that is hangry - muscle tremors, nervousness, restlessness, and hunger
What is an insulinoma?
A tumor of pancreatic beta cells that autonomously secretes insulin
Insulinomas are common in _____, uncommon in ______, and rare in _______.
ferrets, dogs, and cats
What breed of dog is over-represented in insulinomas? Age of diagnosis?
Large breeds are over-represented and average age is 9-10 years
Are the majority of insulinomas benign or malignant?
malignant
What is the behaviorof insulinomas?
Chronic, insidious onset - at the time of diagnosis a majority of them metastasize
How may patients with insulinomas present?
They may have severe hypoglycemia with relatively mild clinical signs
How are insulinomas diagnosed?
By demonstrating high insulin with concurrent low glucose - you must measure insulin when BG is low (i.e. prior to stabilization of the patient)
If BG is <50 mg/dl and insulin is above the reference range, what is the likelihood that the cause is due to an insulinoma?
a high probability
If BG is <50 mg/dl and insulin is low, what is the chance that an insulinoma is the cause?
it should be ruled out
If the insulin:glucose ratio is greater than 30, what should you suspect?
hyperinsulinemia
What is the recommended emergency therapy for hypoglycemia?
IV catheter, 50% dextrose solution, and Administer glucose slowly over 10 minutes
Why do we want to treat for clinical signs associated with hypoglycemia and not the number?
Because if the reason for hypoglycemia is due to an insulinoma, the increase in BG will promote insulin release ultimately worsening the hypoglycemia
What some alternative options to using glucose to treat hypoglycemia?
glucagon and dexmedetomidine CRI
Why would you want to give dexmedetomidine to treat hypoglycemia?
it antagonizes insulin
When is hyperglycemia a normal finding?
2-4 hours post prandial - it is mild
What are the etiologies of hyperglycemia?
Too much of one (or more) hormones that raise BG, deficiency in hormone that decreases BG, and miscellaneous
What hormones can cause hyperglycemia if they are in excess?
cortisol, growth hormone, epinephrine, glucagon, and progesterone
True or False: If there is excess of a hormone, hyperglycemia is not usually the sole clinical presentation.
TRUE
When is therapy for hyperglycemia indicated?
Usually only if diabetes develops as a complication of the primary endocrine disease
What are the sources of stress hyperglycemia?
Catecholamine release and glucocorticoids
What is the renal threshold for glucose in dogs?
180 mg/dl
What is the renal threshold for glucose in cats?
280 mg/dl
What disease process that is due to low insulin can cause hyperglycemia?
Diabetes mellitus
What is the pathophysiology of insulin deficiency in diabetes mellitus?
There is decreased tissue utilization of glucose, increaed hepatic glycogenolysis and gluconeogenesis, and then the glucose from the liver accumulates in the circulation resulting in hyperglycemia
How does hyperglycemia in diabetes mellitus patients lead to glucosuria?
The high glucose levels exceeds renal tubular reabsorptive abilities
How does hyperglycemia in diabetes mellitus patients lead to polyuria?
It causes osmotic diuresis
Why does polydipsia follow polyuria in diabetes mellitus patients?
it is a compensatory mechanism to prevent dehydration
Why does polyphagia occur in the face of hyperglycemia in diabetes mellitus patients?
Normally, the satiety center inhibits the feeding center after a meal. In order to do this, the satiety center requires insulin for glucose transport. When insulin is defficent, glucose does not enter the satiety center and therefore fails to inhibit the feeding center. Polyphagia is the result
What are the clinical signs of diabetes mellitus?
polyuria, polydipsia, polyphagia, and weight loss
How is diabetes mellitus diagnosed?
Resting hyperglycemia with glucosuria in an animal with compatible clinical signs
