Hormone Mechanisms
Hormones are chemical messengers secreted into the bloodstream to act on target organs. Control mechanisms: negative feedback (most common), positive feedback (e.g., LH surge at ovulation). Hormone types: peptide (insulin, ADH), steroid (cortisol, aldosterone), amine (thyroid hormones, epinephrine).
Pituitary Gland
"Master gland" — anterior pituitary: TSH, ACTH, GH, FSH, LH, Prolactin. Posterior pituitary: stores/releases ADH (water retention) and Oxytocin (uterine contraction, lactation). ADH dysfunction: excess = SIADH (hyponatremia); deficiency = Diabetes Insipidus (hypernatremia, polyuria).
Thyroid & Adrenal Glands
Thyroid: T3/T4 regulate metabolism. Hypothyroidism: weight gain, cold intolerance, bradycardia. Hyperthyroidism: weight loss, heat intolerance, tachycardia. Adrenal cortex: Cortisol (stress response), Aldosterone (Na+/K+ balance). Cushing's: excess cortisol. Addison's: adrenal insufficiency.
Pancreatic Hormones
Beta cells: Insulin — lowers blood glucose. Alpha cells: Glucagon — raises blood glucose. C-peptide: marker of endogenous insulin production (low in Type 1 DM).
Important Notes
- Thyroid storm: life-threatening hyperthyroid crisis — high fever, extreme tachycardia, altered LOC.
- Addisonian crisis: adrenal insufficiency emergency — treat with IV hydrocortisone and IV fluids immediately.
Clinical Tips
- Never abruptly stop exogenous corticosteroids — adrenal suppression means the adrenal gland cannot respond to stress without tapering.
Summary
The endocrine system coordinates homeostasis through hormone signaling. Nurses must recognize clinical presentations of hormonal excess and deficiency to identify emergencies.
