Hormones | Medical Science Optional Notes for UPSC PDF Download

Hormones serve as chemical messengers and are produced by specialized cells within endocrine glands. These messengers, which can be composed of proteins, lipids, or amines, play a crucial role in regulating physiological activities by exerting specific effects on target cells. Hormones are typically released into the bloodstream, allowing them to circulate throughout the body and reach their target cells. Importantly, once their actions are completed, hormones undergo disintegration or are otherwise cleared from the circulation. This precise and regulated system enables hormones to exert specific and time-sensitive influences on the functions of target cells and tissues in the body.

Characteristics of Hormones

• Source of Secretion: Hormones are secreted by endocrine cells, which are specialized cells found in endocrine glands.
• Nature as Chemical Messengers: Hormones function as chemical messengers in the body.
• Circulation in Body Fluids: They are chemical signals that circulate in the body fluids, typically in the bloodstream.
• Regulation of Target Cells: Hormones regulate the behavior of target cells by interacting with specific receptors.
• Non-Enzymatic Action: Unlike enzymes, hormones do not catalyze any biochemical reactions.
• On-Demand Secretion: Hormones are secreted only when needed; they are not stored in large quantities prior to use.
• Proteinaceous or Non-Proteinaceous: Hormones may be proteinaceous (proteins or peptides) or non-proteinaceous (amino acids or steroids) in nature.
• Regulation by Nervous System: The secretion of hormones is often regulated by the nervous system through feedback mechanisms.
• Long-Term Effects: Hormones typically cause long-term effects, such as changes in behavior, growth, and other physiological processes.
• Stimulatory or Inhibitory Effects: Hormones function to stimulate or inhibit the activities of target organs.
• Minute Quantities: They are active in minute quantities, exerting significant effects even at low concentrations.
• Low Molecular Weight Compounds: Hormones are mostly low molecular weight compounds.
• Water Solubility: Most hormones are water-soluble, facilitating their transport in the aqueous environment of the bloodstream.
• Species Specific: Hormones often exhibit specificity for particular species.
• Formation of Hormone-Receptor Complex: Hormones usually activate target cells by forming a complex with specific hormone receptors on the surface of or within the target cells.

Pancreas

Diabetic coma

Other conditions that can cause unconsciousness in a person with diabetes are 

• Stroke 
• uremic encephalopathy 
• Alcohol 
• Drug overdose 
• Head injury 
• Seizure

Biosynthesis and secretion of Insulin

• Genetic Origin: The gene responsible for insulin is situated on the short arm of chromosome 11 in humans.
• Synthesis in B Cells: Insulin is synthesized within the rough endoplasmic reticulum of pancreatic beta cells (B cells).
• Transport to Golgi Apparatus: After synthesis, insulin is transported to the Golgi apparatus, a cellular organelle.
• Packaging into Granules: Within the Golgi apparatus, insulin is packaged into membrane-bound granules.
• Microtubule-Mediated Movement: These granules, containing insulin, move toward the plasma membrane with the assistance of microtubules.
• Exocytosis: Upon reaching the plasma membrane, the granules undergo exocytosis, a process where their contents, including insulin, are expelled from the cell into the extracellular space.
• Basal Lamina Crossing: Insulin then crosses the basal lamina of the pancreatic beta cell.
• Capillary Interaction: Subsequently, insulin traverses a neighboring capillary, interacting with the fenestrated endothelium of the capillary.
• Entry into the Bloodstream: Insulin finally enters the bloodstream, where it can be transported to various target tissues and organs to regulate glucose metabolism and other physiological processes.

This highly regulated and intricate process ensures the controlled release of insulin into the bloodstream, allowing it to perform its vital role in maintaining glucose homeostasis in the body.

Metabolism

• The half-life of insulin in the circulation in humans is about 5 min.
• Insulin binds to insulin receptors, and some is internalized.
• It is destroyed by proteases in the endosomes formed by the endocytotic process.

Insulin mechanism of action

Effects of Insulin deficiency

Diabetes Presentation

• The feeding area of the hypothalamus is not inhibited and thus satiety is not sensed so food intake is increased.
• Excretion of the osmotically active glucose molecules entails the loss of large amounts of water (osmotic diuresis)
• The resultant dehydration activates the mechanisms regulating water intake, leading to polydipsia.

Pancreas-Repeats