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51 terms

Regulation of Blood Glucose by the Endocrine System

M1 Winter
Is glucose concentration regulated or controlled?
The availability of ATP is kept as constant as possible by regulating the concentration of glucose (the predominant
source or substrate for the production of ATP) in the blood.

Blood glucose concentration is regulated at a level of 80 mg/dl with an "acceptable" range of 60-115 mg/dl.
What cells secrete Insulin?
Beta cells of pancreatic islet cells. Proteins
What cells secrete Glucagon?
Alpha cells of pancreatic islet. Peptide
What cells secrete epinephrine?
Adrenal medulla. Amine
What cells secrete growth hormone?
Anterior pituitary. Protein
What cells secrete cortisol?
Adrenal cortex. Steroid.
Is movement of glucose across SGLT1 receptor passive?
No. It is secondary active transport.
Where can GLUT2 receptors be found?
They can be found in liver and beta-cells of pancreas.
Where can GLUT3 receptors be found?
Where can GLUT4 receptors be found?
Adipose tissue, striated muscle cells.
What are the main targets of insulin?
Liver, adipose, and muscle.
What is the stimuli for insulin secretion?
Food intake and digestion, increased plasma substrate concentration of glucose
What is the inhibitor of insulin secretion?
Epinephrine and somatostatin
What is the gross response on the target cells of insulin?
Insulin alters the function of its target cells via a fixed receptor system. Major anabolic hormone of the body, major effect is substrate storage.
What effect does insulin have on plasma substrates?
Decreases plasma concentration of glucose, fatty, acids, keto-acids, and amino acids.

Stimulates K+ uptake into muscle; decreases [K+] in the plasma.
What effects do other hormones have on insulin?
Some support. e.g. amino acid uptake and protein synthesis by growth hormone.

Most oppose. Glucagon, epinephrine, GH, cortisol are counter-regulatory hormones of insulin.
How is release of insulin biphasic?
Rapid initial release of already stored insulin followed by a slower release as increased synthesis produces more insulin.
What endocrine cell releases glucagon?
Alpha islet cells of the pancreas
What are the main target cells of glucagon?
Liver (primary)
Adipose tissue (at higher concentrations)
What is the gross response of the target cells for glucagon?
Binds to membrane receptors and activates second messengers which alter enzyme activity.

One of the major substrate mobilizers. Increases hepatic glycogenolysis and gluconeogenesis; adipose fate mobilization and hepatic ketogenesis.
What are the stimulators for release of glucagon?
Decrease in blood glucose
What are the inhibitors for release of gluagon?
High plasma glucose, insulin, somatostatin
What effect does glucagon have on plasma substrate concentration?
Increases plasma glucose, fatty acids, and ketone bodies.
What effects do other hormones have on the actions of glucagon?
Epinephrine and cortisol support its activity.

All of the actions of glucagon are opposed by insulin.
What effect does glucagon have on the secretion of insulin?
Glucagon increases the secretion of insulin.
What endocrine cells release epinephrine?
Chromaffin cells of the adrenal medulla

Tyrosine derivative synthesized, stored, and secreted by the chromaffin cells of the adrenal medulla.
What is the stimulus for epinephrine secretion?
Stimulation by sympathetic pre-ganglionic neurons
What are the inhibitors of epinephrine secretion?
None that act directly
What are the main target cells of epinephrine?
Liver, skeletal muscle, adipose tissues
What is the gross response of the target cells of epinephrine?
Major substrate mobilizer.

Stimulates glycogenolysis in liver and muscle, gluconeogenesis in liver, and liplolysis in adipose tissue.

Binds to adrenergic receptors in cell membrane.
What effects do other hormones have on the actions of epinephrine?
Actions on the liver are supported by glucagon.

Actions on adipose cells are supported by glucagon, cortisol, and GH.

Cortisol has a permissive effect on the synthesis of epinephrine.
What are the effects of epinephrine on plasma substrate concentrations?
Increases plasma glucose, lactic acid, and fatty acid.

Inhibits insulin secretion and stimulates glucagon.
What endocrine cells release GH?
Anterior pituitary.

Specifically, the somatotrophs (acidophils)
What is the stimulus of release of GH?
GHRH from the hypothalamus (release influenced by sleep, stress, low plasma [glucose] and low [fatty acid])

What are the inhibitors of release of GH?
GHIH, somatostatin, somatomedin (IGF).

There is a diurnal secretion cycle with concentration highest early in sleep.
What are the main target cells of GH?
Liver, muscle, and adipose tissue
What is the gross response of the target cells of GH?
Increases uses of fats, while conserving glucose and protein.

Inhibits the glucose uptake of muscle, lipid, and other tissues.

Stimulates adipose lipolysis, muscle amino acid uptake, and proteogenesis.

Stimulates hepatic glycogenolysis, gluconeogenesis, and ketogenesis.

Stimulates release of IGF-1 from the liver which promotes growth.

Mechanism of action: Binds to membrane receptor, activates second messenger systems, alters enzyme activity.
What effect does GH have on plasma substrate concentrations?
Produces hyperglycemia, hyperlipidemia, and lowers plasma amino acid levels.
What effects do other hormones have on the actions of GH?
Antagonizes insulin's effects on cardbohydrate and fat metabolism.

Supports effects of glucagon, epinephrine, and cortisol with carbohydrate and fat metabolism.

Effects on amino acid uptake and protein synthesis parallel insulin's actions.
What endocrine cells secrete cortisol?
Steroid that is released from the zona fasciculata of the adrenal gland.
What stimulates release of cortisol?
ACTH from anterior pituitary (released in response to CRH from the hypothalamus in response to stress and hypoglycemia)

Exhibits a diurnal rhythm with highest concentration present at the end of sleep.
What inhibits release of cortisol?
None direct
What are the main target cells of cortisol?
Liver, adipose tissue, muscle, many other tissues are affected.
What is the gross response of the target cells of cortisol?
Essential for response to stress, including mobilizaton of substrate.

Primary actions are catabolic. In absence of cortisol death occurs quickly.

Stimulates proteolysis in muscle (and other tissues) and hepatic gluconeogenesis and glycogenesis. Decreases glucose utilizaton of muscle and fat; facilitates fat mobilization.

Enters cell nucleus and alters gene transcription and hence enzyme production.
What effect does cortisol have on plasma substrate concentrations?
Produces hyperglycemia, hyperaminoacidemia, hyperlipidemia.

Increases hepatic glycogen stores.
What effects do other hormones have on the actions of cortisol?
Opposes insulin's actions.

Acts permissively with gluagon and epinephrine to mobilize substrate.
Do alanine levels increase due to the effects of cortisol?
No. Even though cortisol increases proteolysis and aminoacidemia, cortisol also stimulates alanine in gluconeogenesis.
Does cortisol increase or decrease cell sensitivity to insulin?
Decreases the sensitivity to insulin.

Decreases glucose use and inceases glucose production.
What cells secrete leptin?
Adipose cells. The greater the mass of adipose cells, the greater the concentration of leptin.
Where does leptin act?
Leptin goes to the hypothalamus.

The hypothalamus has receptors for leptin. When these neurons are stimulated, they generate neural signals that reduce the urge to eat (satiety signals).

--> Blood glucose does not increase further. Increased blood glucose is BAD.
What is the neuroendocrine system?
Controls feeding and energy expenditure.

Involves hypothalamic neurons with receptors for two hormones: insulin and leptin. These neurons also measure blood glucose.

Peripheral tissues such as the liver are controlled by parasympathetic activity in the vagus nerve.