Medical Biochemistry 2: Hormones Biosynthesis and Mechanism

Hormones: Biosynthesis, Metabolism, and Mechanism of Action

What are Hormones?

• Hormones are chemical messengers produced by endocrine glands and secreted into the bloodstream to coordinate certain body functions.

Classes of Hormones

• Hormones can be classified based on their solubility and chemical structure.

Target Cells

• Target cells contain specific receptors (binding site) for a particular hormone.

Hormone Receptors

• There are two types of hormone receptors: cell surface receptors and intracellular receptors.
• Cell surface receptors are located on the plasma membrane and generate second messengers that alter the activity of other molecules within the cell.
• Intracellular receptors are located in the cytoplasm or nucleus and alter transcriptional activity of responsive genes.

Hormones with Cell Membrane Receptors

• Water-soluble hormones have a hormone-binding site located on the external portion of a specific cell-surface receptor.
• Hormones exert their action by binding to target cell receptor proteins, leading to a signal that is conveyed to the interior of the cell.
• Amplification of hormone activity is achieved by activation of a cascade of chemical reactions.

Hormones with Intracellular Receptors

• Lipid-soluble (steroid) hormones diffuse easily through the lipid bilayer of cell membranes and bind to receptors in the cytoplasm or nucleus.
• Binding causes a change in affinity of the receptor for binding sites on DNA in the cell nucleus, leading to changes in gene expression.
• Onset of action of lipid-soluble hormones is slow compared to water-soluble hormones, and there is no amplification cascade.

Regulation of Hormone Secretion

• Three types of stimuli stimulate the synthesis and release of hormones.
• Regulation of hormone secretion normally maintains homeostasis and prevents overproduction or underproduction of a particular hormone.
• Negative feedback is the most common mechanism, which reverses the direction of a change in a physiological system.
• Positive feedback amplifies physiological changes, leading to more hormone release.

Hormone Clearance

• Hormones are cleared from the plasma in several ways.

This quiz covers the biosynthesis, metabolism, and mechanism of action of hormones, including their classification, production, and function in the human body.