Major Endocrine Glands and Functions
Hypothalamus-Pituitary Axis
- The hypothalamus produces releasing and inhibiting hormones that control the anterior pituitary. It also produces ADH and oxytocin, which are stored in the posterior pituitary.
- The anterior pituitary secretes six major hormones: GH, TSH, ACTH, FSH, LH, and prolactin. Remember the acronym "Go To A Fun Location Please".
- The posterior pituitary releases ADH (antidiuretic hormone) for water retention and oxytocin for uterine contractions and milk ejection.
Memory Aid: Pituitary Hormones
FLAT PEG: FSH, LH, ACTH, TSH, Prolactin, Endorphins, Growth Hormone (Anterior Pituitary)
Posterior Pituitary: "ADH and Oxytocin - Always Delivering Happiness and Oxytocin"
Key Points
- Negative feedback loops regulate most endocrine functions
- The hypothalamus is the master control center linking nervous and endocrine systems
Thyroid and Parathyroid Glands
- The thyroid gland produces T3 (triiodothyronine) and T4 (thyroxine) which regulate metabolism, and calcitonin which lowers blood calcium levels.
- The parathyroid glands (four small glands behind the thyroid) secrete parathyroid hormone (PTH) which increases blood calcium by promoting bone resorption and kidney calcium retention.
Calcium Regulation Comparison
| Hormone | Source | Effect on Calcium | Mechanism |
|---|
| Calcitonin | Thyroid | Decreases | Inhibits bone breakdown |
| PTH | Parathyroid | Increases | Promotes bone breakdown, kidney retention |
Important Alert: Post-thyroidectomy patients are at risk for hypocalcemia due to accidental parathyroid removal - monitor for Chvostek's and Trousseau's signs!
Adrenal Glands
- The adrenal cortex produces three types of hormones: mineralocorticoids (aldosterone), glucocorticoids (cortisol), and sex hormones (androgens).
- The adrenal medulla secretes catecholamines (epinephrine and norepinephrine) as part of the sympathetic nervous system response.
Memory Aid: Adrenal Cortex Layers
"Salt, Sugar, Sex" from outside to inside:
- Zona Glomerulosa → Mineralocorticoids (Salt/Aldosterone)
- Zona Fasciculata → Glucocorticoids (Sugar/Cortisol)
- Zona Reticularis → Sex hormones (Androgens)
Pancreas (Endocrine Function)
- The islets of Langerhans contain alpha cells (produce glucagon) and beta cells (produce insulin) that regulate blood glucose levels.
- Insulin lowers blood glucose by promoting cellular uptake and glycogen storage, while glucagon raises blood glucose by promoting glycogenolysis and gluconeogenesis.
Clinical Scenario
A patient with Type 1 diabetes forgot their morning insulin. Blood glucose is 350 mg/dL. The pancreatic beta cells are unable to produce insulin, so glucose cannot enter cells for energy, leading to hyperglycemia and potential diabetic ketoacidosis.
Study Tips and Memory Aids
Endocrine System Memory Aids
- Steroid vs Non-steroid hormones: "Steroids are Lipid Lovers" - they cross cell membranes easily
- Cortisol functions: "The 4 S's" - Sugar (gluconeogenesis), Salt (sodium retention), Sex (suppresses reproduction), Stress response
- Thyroid hormone effects: "Thyroid Makes Everything Fast" - metabolism, heart rate, growth, mental activity
Common Pitfalls: Don't confuse the adrenal cortex (produces cortisol) with the adrenal medulla (produces epinephrine). Cortex = Chronic stress response, Medulla = Acute stress response.
Quick Check Questions
- ☐ Can you name the six anterior pituitary hormones?
- ☐ Do you understand the difference between negative and positive feedback?
- ☐ Can you explain how calcium homeostasis is maintained?
- ☐ Do you know which hormones are water-soluble vs lipid-soluble?