Overview
This lecture covered the structure, function, and hormone regulation of the endocrine system, focusing on its organs, hormone types, mechanisms of action, feedback regulation, and major disorders.
Prefixes & Key Concepts
- Indo = inside; Exo = outside; Hyper = above; Hypo = below.
- Endocrine glands secrete hormones directly into body fluids; exocrine glands use ducts.
- Endocrine and nervous systems coordinate to maintain homeostasis.
Structure & Function of the Endocrine System
- Endocrine glands are anatomically unconnected and widely distributed.
- Major glands: pituitary, thyroid, parathyroid, adrenal, pineal, pancreas, ovaries, testes.
- Hormones act on target cells with specific receptors.
Types of Hormones & Glands
- Endocrine glands: ductless, secrete internal hormones (e.g., thyroid).
- Exocrine glands: secrete to surfaces via ducts (e.g., sweat glands).
- Paracrine: acts on nearby cells; Autocrine: acts on same cell type.
Comparison: Nervous vs. Endocrine System
- Nervous: fast, short-lived, local effects via neurotransmitters.
- Endocrine: slower, longer-lasting, effects throughout body via hormones.
- Both systems use receptor-based chemical signaling.
Hormone Action & Regulation
- Up-regulation: more receptors in response to low hormone.
- Down-regulation: fewer receptors in response to high hormone.
- Steroid hormones: lipid-soluble, derived from cholesterol, affect gene expression.
- Nonsteroid hormones: water-soluble, include amines, peptides, proteins, glycoproteins.
Mechanisms of Hormone Action
- Steroid hormones pass cell membranes, bind intracellular receptors, alter gene transcription.
- Nonsteroid hormones bind cell membrane receptors, use second messengers (e.g., cyclic AMP) for signal transduction.
- Protein kinases activated via phosphorylation lead to hormone effects.
Hormone Regulation & Feedback
- Negative feedback most common; stabilizes hormone levels.
- Three negative feedback methods: hypothalamus→pituitary→glands, nervous system direct control, blood substance concentration.
- Positive feedback is rare (e.g., oxytocin in labor, milk ejection).
Major Endocrine Glands & Hormones
- Pituitary: anterior (GH, prolactin, TSH, ACTH, FSH, LH), posterior (ADH/vasopressin, oxytocin).
- Thyroid: T3, T4 (metabolism), calcitonin (lowers blood calcium).
- Parathyroid: PTH (raises blood calcium).
- Adrenal cortex: aldosterone (sodium/water balance), cortisol (stress, metabolism), androgens.
- Adrenal medulla: epinephrine/norepinephrine (fight-or-flight).
- Pancreas: insulin (lowers blood glucose), glucagon (raises blood glucose), somatostatin (inhibits both).
Disorders & Diseases
- Hypopituitary dwarfism: GH deficiency in childhood.
- Gigantism, acromegaly: excess GH.
- Hyperthyroidism, hypothyroidism, Graves disease, goiter: thyroid disorders.
- Addison’s disease: adrenal insufficiency; Cushing’s syndrome: cortisol excess.
- Diabetes mellitus: insulin deficiency/resistance (type 1/type 2).
Hormone Abuse & Medical Uses
- Steroid abuse: muscle strength, harmful side effects.
- Erythropoietin (EPO): increases red blood cells, dangerous in sports.
Stress Response
- General adaptation syndrome: alarm (fight-or-flight, epinephrine), resistance (cortisol), exhaustion.
- Stress hormones mobilize energy, increase BP, suppress immune system.
Lifespan Changes
- Endocrine gland size and function decrease with age.
- Changes in hormone levels can lead to conditions like osteoporosis and insulin resistance.
Key Terms & Definitions
- Homeostasis — Stable internal body environment.
- Hormone — Chemical messenger secreted by endocrine glands.
- Target Cell — Cell with receptor for a specific hormone.
- Steroid Hormone — Lipid-soluble hormone derived from cholesterol.
- Second Messenger — Intracellular signaling molecule (e.g., cyclic AMP).
- Negative Feedback — Mechanism that maintains equilibrium by reversing a change.
- Tropic Hormone — Hormone that stimulates other endocrine glands.
Action Items / Next Steps
- Review hormone pathways (e.g., hypothalamus→pituitary→gland).
- Memorize hormone names, sources, and functions.
- Know symptoms of major endocrine disorders for exams.
- Study the comparison chart between nervous and endocrine systems.
- Prepare for a half-life calculation question on the exam.