Peptide Hormones

An overview of peptide hormones, their functions, and significance in human physiology.

Peptide hormones are a class of hormones that are composed of amino acids and are characterized by their peptide bonds. These hormones play crucial roles in regulating a variety of physiological processes in the body, including metabolism, growth, and reproduction.

Structure and Synthesis

Peptide hormones are synthesized in the endoplasmic reticulum of cells as larger precursor molecules known as preprohormones. These precursors undergo cleavage to form prohormones, which are further processed in the Golgi apparatus to produce the active hormone. The final active peptide hormone is then stored in secretory vesicles until it is released into the bloodstream in response to specific stimuli.

Mechanism of Action

Peptide hormones exert their effects by binding to specific receptors on the surface of target cells. These receptors are typically G protein-coupled receptors or tyrosine kinase receptors. Upon binding, a cascade of intracellular signaling pathways is activated, leading to the desired physiological response. Unlike steroid hormones, peptide hormones do not enter the cell but instead act through second messenger systems such as cyclic AMP (cAMP) or calcium ions.

Examples of Peptide Hormones

• Insulin: A hormone produced by the beta cells of the pancreas, insulin is crucial for regulating blood glucose levels by facilitating the uptake of glucose into cells.
• Glucagon: Also produced by the pancreas, glucagon works antagonistically to insulin by promoting the release of glucose from the liver into the bloodstream.
• Adrenocorticotropic hormone (ACTH): Secreted by the anterior pituitary gland, ACTH stimulates the production of cortisol from the adrenal cortex.
• Oxytocin: Produced by the hypothalamus and released by the posterior pituitary gland, oxytocin is involved in childbirth and lactation.
• Antidiuretic hormone (ADH): Also known as vasopressin, ADH is important for regulating water balance in the body by increasing water reabsorption in the kidneys.

Clinical Significance

Peptide hormones are critical in maintaining homeostasis, and their dysregulation can lead to various endocrine disorders. For example, insufficient production of insulin results in diabetes mellitus, while excessive secretion of growth hormone can cause acromegaly.

Research and Therapeutic Use

Peptide hormones are not only important in physiology but also have therapeutic applications. Synthetic analogs of peptide hormones are used in the treatment of various conditions. For instance, synthetic insulin is a mainstay in the management of diabetes, and synthetic oxytocin is used to induce labor.

Also see

• Endocrine system
• Hormone
• Protein hormone
• Steroid hormone
• Neurotransmitter