Overview
This lecture introduces the endocrine system, focusing on its structure, how hormones are released and act in the body, and the differences between amino acid-based and steroid-based hormones.
Introduction to the Endocrine System
- The endocrine system is made up of glands that secrete hormones and the hormones themselves.
- Endocrine glands are scattered throughout the body and affect many diverse processes.
- Major endocrine glands include the hypothalamus, pituitary, pineal, adrenal, thyroid, thymus, pancreas, ovaries, and testes.
- Each gland is surrounded by rich blood supply, allowing rapid hormone entry into the bloodstream.
Hormones and Target Cells
- Hormones are released by glands, enter the blood, and are carried throughout the body.
- Only cells with specific receptors for a hormone (target cells) are affected by that hormone.
- Example: Insulin, from the pancreas, binds to receptors mainly on muscle and fat cells, allowing glucose to enter.
Types of Hormones: Amino Acid-Based vs. Steroid-Based
- Most hormones are amino acid-based (protein-based) and water soluble (polar).
- Amino acid-based hormones dissolve easily in blood but cannot cross cell membranes; they bind to cell surface receptors.
- Steroid hormones are lipid-based (non-polar) and must bind to carrier proteins to travel in blood.
- Steroid hormones cross cell membranes easily and bind to internal cell receptors.
Hormone Actions on Target Cells
- Hormone binding can alter cell membrane permeability.
- Hormones can stimulate or inhibit enzyme or protein production.
- Hormones can activate or deactivate enzymes.
- Hormones can trigger mitosis, leading to changes in cell activity or function.
Key Terms & Definitions
- Endocrine System — Body system composed of glands that secrete hormones into the blood.
- Hormone — Chemical messenger produced by glands and carried by the blood to target organs.
- Target Cell — Cell with receptors specific for a particular hormone.
- Amino Acid-Based Hormone — Water-soluble hormone made from amino acids or proteins.
- Steroid Hormone — Lipid-soluble hormone derived from cholesterol.
- Receptor — Protein on or within a cell that binds a specific hormone.
- Carrier Protein — Blood protein that transports non-polar hormones.
Action Items / Next Steps
- Review the posted learning outcomes and self-assess your understanding.
- Pause at review slides in the lecture and answer all practice questions.
- Access and review the Canvas site for course materials and module one.
Hormones made out of amino acids (amino acid-based hormones) act on cells by binding to receptors on the cell surface (the cell membrane).
Because these hormones are water-soluble and polar, they cannot cross the non-polar phospholipid bilayer of the cell membrane. Instead, they bind to specific receptors located on the outside of the target cell's membrane, which then triggers a response inside the cell.