Hormones
- Hormones are broadly classified as water-soluble or lipid-soluble.
- Hormones are chemical messengers released by cells and carried in blood to influence target cells somewhere else.
- Messenger function means a hormone does not usually build tissue directly; it tells target cells which activities to increase or decrease.
- Blood transport allows one endocrine gland to coordinate many distant organs at the same time.
- Target response requires a receptor, so a hormone in the blood is ignored by cells that lack the matching receptor.
- Water-soluble hormones dissolve well in plasma and usually cannot cross the lipid-rich plasma membrane by simple diffusion.
- Protein hormones are water-soluble chains of amino acids that often act through receptors on the cell surface.
- Polypeptide hormones are shorter amino acid chains, and many endocrine signals belong to this group.
- Amino acid-derived hormones come from individual amino acids and can be water-soluble or lipid-soluble depending on the molecule.
- Insulin is a water-soluble hormone that helps many cells take up and store nutrients after eating.
- Glucagon is a water-soluble hormone that helps raise blood glucose during fasting.
- Follicle-stimulating hormone (FSH) is a pituitary hormone involved in ovarian follicle growth and sperm production.
- Lipid-soluble hormones dissolve in lipids and can usually cross the plasma membrane more easily than water-soluble hormones.
- Steroid hormones are lipid-soluble hormones made from cholesterol.
- Progesterone is a steroid hormone important for reproductive cycling and pregnancy support.
- Estradiol is an estrogen steroid hormone important for many female reproductive and systemic effects.
- Testosterone is an androgen steroid hormone important for male reproductive function and many systemic effects.
- Cell-surface receptors sit in the plasma membrane and detect water-soluble hormones outside the cell.
- Signal transduction means a receptor converts hormone binding into intracellular events that change cell behavior.
- G protein-linked receptors are membrane receptors that activate internal signaling proteins after a hormone binds.
- Epinephrine can act through G protein-linked receptors to produce rapid stress responses.
- Thyroid-stimulating hormone (TSH) can act through G protein-linked receptors on thyroid follicular cells.
- Serotonin can act through G protein-linked receptors in some target tissues.
- Messenger signaling can use a small intracellular molecule made after receptor activation to carry the message deeper into the cell.
- Amplification occurs because one hormone-receptor event can generate many second messenger molecules.
- Catalytic receptors are receptors that have enzyme activity or activate enzymes when a hormone binds.
- Protein kinases are enzymes that add phosphate groups to proteins, often changing those proteins' activity.
- Phosphorylation means adding a phosphate group to a target protein as a way to turn signaling pathways on or off.
- Growth hormone uses catalytic receptor signaling to affect growth and metabolism.
- Cytosol is the fluid portion of the cell outside the nucleus where some lipid-soluble hormone receptors are located.
- The nucleus is the cell compartment that contains genetic material and controls gene expression.
- Hormone-receptor complexes form when lipid-soluble hormones bind intracellular receptors.
- Transcription means copying genetic instructions into messenger ribonucleic acid so proteins can later be made.
- Gene regulation explains why steroid and thyroid hormones often have slower but longer-lasting effects than many water-soluble hormones.
- Clinical reasoning depends on hormone class because receptor location predicts onset, duration, and mechanism of action.
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