5.1 Endocrine glands and hormone classification

2 min read•august 7, 2024

The endocrine system is a complex network of glands that produce hormones. These chemical messengers regulate various bodily functions by traveling through the bloodstream to target cells. Understanding the different types of glands and signaling mechanisms is crucial for grasping how the body maintains balance.

Hormones come in different forms, each with unique characteristics. are water-soluble and bind to cell surface receptors, while are lipid-soluble and work inside cells. Amine and have diverse properties and functions, contributing to the system's versatility.

Endocrine System Components

Glands and Signaling Mechanisms

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Endocrine glands secrete hormones directly into the bloodstream
- Lack ducts to transport secretions
- Examples include the , , and
Exocrine glands secrete substances through ducts onto epithelial surfaces
- Have ducts to transport secretions
- Examples include sweat glands, salivary glands, and mammary glands
Hormones act as chemical messengers that regulate physiological processes
- Produced by endocrine glands and released into the bloodstream
- Bind to specific receptors on target cells to elicit a response
occurs when a cell secretes a substance that binds to receptors on the same cell
- Allows for self-regulation of cellular functions
- Examples include immune cells and cancer cells
involves the release of substances that affect nearby cells
- Substances diffuse through the extracellular fluid to reach target cells
- Examples include neurotransmitters and local inflammatory mediators
involves the release of hormones into the bloodstream
- Hormones travel throughout the body to reach distant target cells
- Enables systemic regulation of physiological processes

Hormone Types and Characteristics

Peptide hormones are composed of amino acids
- Water-soluble and cannot cross cell membranes
- Bind to cell surface receptors and activate second messenger systems
- Examples include , , and
Steroid hormones are derived from cholesterol
- Lipid-soluble and can cross cell membranes
- Bind to intracellular receptors and directly influence gene expression
- Examples include , , and
are derived from amino acids
- Include catecholamines ( and ) and
- Catecholamines are water-soluble and bind to cell surface receptors
- Thyroid hormones are lipid-soluble and bind to intracellular receptors
Lipid-derived hormones are derived from lipids other than cholesterol
- Include and
- Act locally as paracrine or autocrine signaling molecules
- Involved in inflammation, pain sensation, and smooth muscle contraction