In human metabolism, which one of the following hormones is essential for the uptake of glucose by most body cells and for lowering blood glucose levels?

Introduction / Context:
Regulation of blood glucose is a core topic in human physiology and is essential for maintaining energy supply to cells. Several hormones influence blood glucose, but only one is directly responsible for promoting glucose uptake into most body cells and for lowering elevated blood sugar. Understanding this hormone is also important for recognising the pathophysiology of diabetes mellitus. This question asks you to identify that hormone from among several endocrine candidates.

Given Data / Assumptions:
• The hormone must be essential for uptake of glucose by cells and for lowering blood glucose levels.• The options include GH, TSH, insulin, cortisol, and glucagon.• We assume standard physiological roles for these hormones.• We focus specifically on the hormone that drives glucose into cells in an insulin dependent manner.

Concept / Approach:
Insulin is a peptide hormone produced by beta cells of the pancreatic islets. It facilitates the uptake of glucose into many tissues, especially muscle and adipose tissue, by promoting the insertion of glucose transporters into cell membranes. It also stimulates glycogen synthesis in liver and muscle and inhibits gluconeogenesis, thereby lowering blood glucose levels. Growth hormone, cortisol, and glucagon all tend to raise blood glucose under various conditions, and TSH regulates thyroid function rather than glucose uptake. Therefore, the correct answer is insulin.

Step-by-Step Solution:
Step 1: Identify the key requirement: the hormone must promote glucose uptake into cells and reduce blood sugar.Step 2: Recall that insulin is secreted after meals when blood glucose rises.Step 3: Remember that insulin stimulates target tissues to increase glucose uptake and glycogen storage.Step 4: Recognise that GH and cortisol are counter regulatory hormones that can increase blood glucose by stimulating gluconeogenesis or reducing glucose uptake.Step 5: Note that glucagon also raises blood glucose by promoting glycogen breakdown and gluconeogenesis in the liver.Step 6: Conclude that among the options, only insulin fits the description in the question.

Verification / Alternative check:
Clinical features of insulin deficiency in Type 1 diabetes include hyperglycaemia, glucosuria, and weight loss, which clearly show that without insulin, cells fail to take up glucose effectively. Treatment with insulin injections lowers blood glucose and reverses these symptoms. Conversely, excess insulin or overdose can cause hypoglycaemia because too much glucose is driven into cells. These clinical observations confirm that insulin is the central hormone responsible for glucose uptake and lowering of blood sugar, unlike GH, TSH, cortisol, or glucagon.

Why Other Options Are Wrong:
Growth hormone primarily stimulates growth of bones and tissues and in high amounts can actually reduce glucose uptake in some tissues, leading to increased blood glucose. Thyroid stimulating hormone acts on the thyroid gland to regulate secretion of thyroid hormones and does not directly govern glucose uptake into cells. Cortisol is a glucocorticoid that increases blood glucose during stress by promoting gluconeogenesis and protein breakdown. Glucagon is a pancreatic hormone that raises blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver. None of these directly serve as the main hormone that lowers blood glucose; that role is played by insulin.

Common Pitfalls:
Students sometimes assume that any hormone with a role in metabolism might be responsible for glucose uptake, which can lead them to choose GH or cortisol. Others may forget that glucagon has effects opposite to insulin. To avoid errors, remember the simple opposition: insulin lowers blood glucose and promotes storage, while glucagon, cortisol, and GH are generally counter regulatory and tend to raise glucose levels. TSH belongs to the thyroid axis and is not a glucose regulating hormone. This framework makes it easy to pick insulin in questions like this.

Final Answer:
The hormone essential for cellular uptake of glucose and for lowering blood sugar is Insulin, which promotes glucose uptake by cells and lowers blood sugar.