Hormonal Regulation of Blood Glucose

Hormonal Regulation of Blood Glucose

• Insulin, glucagon, and epinephrine are key hormones that regulate blood glucose levels.
• Insulin is secreted by the pancreas in response to high blood glucose levels and promotes glucose uptake into cells for energy production and storage as glycogen.
• Glucagon is secreted by the pancreas in response to low blood glucose levels and stimulates the breakdown of glycogen in the liver, releasing glucose into the bloodstream.
• Epinephrine (adrenaline) is secreted by the adrenal medulla in response to stress and promotes the breakdown of glycogen in the liver and muscle, raising blood glucose levels for immediate energy needs.

Hormonal Levels before and after Meals

• Prior to a meal, blood glucose levels are relatively low, leading to glucagon secretion, promoting glucose release from the liver.
• Following a meal, blood glucose levels rise, triggering insulin secretion, promoting glucose uptake into cells and storage.

Mammalian Nutrition Hormones

• Insulin, glucagon, and epinephrine play critical roles in regulating nutrient intake and utilization.
• Insulin promotes glucose uptake, anabolic processes like protein synthesis and fat storage.
• Glucagon promotes glucose release and catabolic processes like protein and fat breakdown.
• Epinephrine stimulates the mobilization of energy stores, promoting both glucose release and fat breakdown, supporting the "fight or flight" response.

Antidiuretic Hormone (ADH) / Vasopressin

• ADH, also known as vasopressin, is synthesized in the hypothalamus and released by the posterior pituitary gland.
• ADH plays a crucial role in regulating water balance by promoting reabsorption of water in the kidneys, concentrating urine and reducing water loss.
• ADH acts via a secondary messenger system involving cAMP, leading to the insertion of aquaporin-2 (AQP-2) channels into the apical membrane of collecting duct cells, increasing water permeability.

Endocrine System

• The endocrine system is composed of glands that secrete hormones, chemical messengers that regulate various bodily functions.
• The endocrine system plays a vital role in maintaining homeostasis, growth, and development, and coordinating responses to stress and environmental changes.
• Hormones are classified based on their chemical structure, with steroid hormones derived from cholesterol, amine hormones derived from amino acids, and peptide/protein hormones composed of amino acids.

Insulin Synthesis and Processing

• Insulin is a peptide hormone synthesized in pancreatic beta cells.
• Insulin is synthesized as a precursor molecule called preproinsulin, which undergoes processing in the endoplasmic reticulum (ER) and Golgi apparatus to form mature insulin.
• The proinsulin molecule contains three regions: A, B, and C.
• In the Golgi, the C-peptide is cleaved from proinsulin, resulting in mature insulin and C-peptide, which are packaged and stored in secretory vesicles.
• Insulin secretion is triggered by depolarization of the cell membrane, leading to exocytosis of vesicles, releasing insulin into the bloodstream.

Hypothalamus and Pituitary Gland

• The hypothalamus is a brain region that controls the pituitary gland, a key endocrine organ.
• The posterior pituitary gland releases hormones synthesized in the hypothalamus, including ADH and oxytocin.
• The anterior pituitary gland releases hormones that are regulated by hypothalamic releasing and inhibiting hormones.

Adrenal Gland

• The adrenal gland is an endocrine organ located above the kidneys.
• The adrenal gland has two primary components: the adrenal cortex and the adrenal medulla.
• The adrenal cortex produces steroid hormones like cortisol, aldosterone, and androgens.
• The adrenal medulla secretes catecholamines like epinephrine (adrenaline) and norepinephrine (noradrenaline).

HPA Axis

• The hypothalamic-pituitary-adrenal (HPA) axis is a complex neuroendocrine system regulating stress responses.
• The HPA axis involves the hypothalamus, pituitary gland, and adrenal cortex.
• In response to stress, the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary to secrete adrenocorticotropic hormone (ACTH).
• ACTH acts on the adrenal cortex, promoting the release of glucocorticoids, primarily cortisol, which helps regulate stress response by suppressing inflammation, increasing blood glucose levels, and mobilizing energy stores.

Mammalian Stress Response

• The mammalian stress response is a complex physiological and psychological reaction to threatening stimuli.
• The stress response involves both the nervous system and the endocrine system.
• The sympathetic nervous system, controlled by the locus coeruleus, releases epinephrine and norepinephrine, causing rapid physiological responses, including increased heart rate, blood pressure, and glucose levels.
• The HPA axis releases cortisol, which acts over a longer time scale to regulate the stress response and restore homeostasis.
• The immune system also plays a role in the stress response, with immune cells releasing cytokines that influence the HPA axis and contribute to inflammation.
• Glucocorticoids, particularly cortisol, act as negative feedback on the HPA axis, controlling the duration and intensity of the stress response.