Overview
This lecture covers the types of hormones in the endocrine system and the two primary mechanisms by which hormones affect their target cells.
Hormone Basics
- The endocrine system communicates via hormones to regulate body functions and maintain homeostasis.
- Hormones are chemical messengers secreted into the bloodstream by glands.
- There are three basic groups of hormones: amino acid derivatives, peptide hormones, and lipid derivatives (steroid hormones).
Types of Hormones
- Amino acid derivatives are small molecules made from amino acids like tyrosine and tryptophan; example: melatonin.
- Peptide hormones are chains of amino acids; examples: thyroid-stimulating hormone, oxytocin, prolactin.
- Lipid derivatives or steroid hormones are lipophilic, circulate in blood bound to carrier proteins, and last longer in circulation.
Hormone Mechanisms of Action
- Non-steroid hormones (amino acid and peptide hormones) cannot enter target cells directly; they bind to cell surface receptors.
- Binding triggers an intracellular signaling cascade, often involving a G-protein and production of cyclic AMP (cAMP) as a second messenger.
- cAMP initiates a cascade of enzymatic changes resulting in the hormone's effect on the cell.
- Hormones using cAMP second messenger include ACTH, calcitonin, epinephrine, glucagon, parathyroid hormone, and ADH.
Steroid Hormone Action
- Steroid hormones are lipophilic and can cross cell membranes to bind internal receptors.
- These hormones can directly affect gene activity in the nucleus, increasing mRNA and protein production.
- Examples include testosterone, estrogen, progesterone, aldosterone, and calcitriol.
Key Terms & Definitions
- Endocrine system — body system using hormones for long-distance communication and homeostasis.
- Hormone — chemical messenger secreted by glands into the bloodstream.
- Amino acid derivatives — hormones made from amino acids, e.g., melatonin.
- Peptide hormone — hormone made from amino acid chains, e.g., oxytocin.
- Lipid derivative/steroid hormone — hormone derived from lipids, able to cross cell membranes.
- G-protein — intracellular protein linked to hormone receptors, initiates signaling cascade.
- cAMP (cyclic AMP) — second messenger molecule triggering cellular responses.
- Second messenger — molecule relaying signals inside the cell after hormone binds receptor.
Action Items / Next Steps
- Review examples of each hormone type and their mechanisms.
- Study the steps of cAMP second messenger pathway and steroid hormone gene activation.
- Prepare for questions on hormone classification and signaling mechanisms.