The endocrine system is a network of glands producing hormones that regulate metabolism, growth, reproduction, and mood. Major glands include the pituitary (the "master gland" controlling other endocrine organs), thyroid (producing T3 and T4 to regulate metabolism), parathyroid (controlling calcium via PTH), adrenal glands (producing cortisol, aldosterone, and adrenaline), and the pancreas (producing insulin and glucagon). Diabetes mellitus results from insulin problems: Type 1 is an autoimmune destruction of insulin-producing beta cells requiring lifelong insulin, while Type 2 involves insulin resistance and relative deficiency and is initially managed with metformin and lifestyle changes. Both can lead to acute complications such as diabetic ketoacidosis (DKA, mainly in Type 1) and hyperosmolar hyperglycemic state (HHS, mainly in Type 2). Chronic complications include diabetic neuropathy, nephropathy, and retinopathy. HbA1c testing reflects average blood sugar over 2–3 months (normal below 5.7%; diabetes at 6.5% or higher).
Thyroid disorders are common and well-defined. Hypothyroidism (underactive thyroid, most often caused by Hashimoto's thyroiditis) causes fatigue, weight gain, and cold sensitivity, treated with levothyroxine. Hyperthyroidism (overactive thyroid, most often caused by Graves' disease) causes weight loss, rapid heart rate, and heat intolerance, treated with antithyroid drugs, radioactive iodine, or surgery. Other endocrine disorders include Cushing's syndrome (excess cortisol causing weight gain and high blood sugar), Addison's disease (adrenal insufficiency requiring lifelong hormone replacement), pheochromocytoma (a catecholamine-secreting adrenal tumor producing episodic hypertension), diabetes insipidus, hyperparathyroidism, acromegaly (excess growth hormone in adults), PCOS, and gestational diabetes. Metabolic syndrome, defined by central obesity, high triglycerides, low HDL, hypertension, and high fasting glucose, raises the risk of cardiovascular disease and Type 2 diabetes.
The nervous system includes the central nervous system (brain and spinal cord) and the peripheral nervous system, transmitting signals through neurons. Common neurological conditions include stroke (ischemic from a clot or hemorrhagic from a ruptured vessel, identified by the FAST mnemonic: Face drooping, Arm weakness, Speech difficulty, Time to call emergency services), transient ischemic attacks (TIAs, "mini-strokes"), seizures and epilepsy, Parkinson's disease (loss of dopamine-producing neurons causing tremor and rigidity), multiple sclerosis (autoimmune attack on myelin), Alzheimer's disease and other dementias, meningitis (inflammation of the meninges), encephalitis, migraine headaches, peripheral neuropathy, and amyotrophic lateral sclerosis (ALS). The musculoskeletal system supports and moves the body; common disorders include osteoarthritis (wear-and-tear cartilage breakdown), rheumatoid arthritis (autoimmune joint inflammation), gout (uric acid crystal deposition), herniated discs, sciatica, scoliosis, carpal tunnel syndrome, fibromyalgia, osteoporosis (low bone density diagnosed by DEXA scan), and fractures. Ligaments connect bone to bone (injured in sprains), while tendons connect muscle to bone (injured in strains and tendinitis).