Lesson 11

The Endocrine System

The endocrine system communicates through hormones — chemical messengers secreted into the bloodstream to act on distant target organs. The nine major endocrine glands regulate metabolism, growth, reproduction, stress response, and fluid balance. Endocrinology covers diabetes mellitus, thyroid disorders, adrenal disease, and pituitary tumors.

55 min3 sections5 objectives

Learning Objectives

1Identify the major endocrine glands and their hormones
2Describe feedback mechanisms controlling hormone secretion
3Identify combining forms for endocrine structures
4Recognize common endocrine disorders
5Differentiate hypo- from hyper- endocrine conditions

1Major Endocrine Glands

Pituitary Gland (hypophysis): "Master gland"; controlled by hypothalamus via releasing/inhibiting hormones

Anterior: GH, TSH, ACTH, FSH, LH, Prolactin

Posterior: ADH (vasopressin), Oxytocin

Thyroid Gland: Located at base of neck; regulated by TSH

T3 (triiodothyronine) and T4 (thyroxine): Regulate metabolism, growth

Calcitonin: Lowers blood calcium

Parathyroid Glands (4 tiny glands behind thyroid):

PTH (parathyroid hormone): Raises blood calcium (opposes calcitonin)

Adrenal Glands (suprarenal; atop each kidney):

Cortex: Glucocorticoids (cortisol — stress), mineralocorticoids (aldosterone — Na/K), sex hormones

Medulla: Epinephrine (adrenaline) + norepinephrine → fight or flight

Pancreas (endocrine portion): Islets of Langerhans

Beta cells: Insulin (lowers glucose)

Alpha cells: Glucagon (raises glucose)

Pineal Gland: Melatonin → circadian rhythms

Thymus: Thymosin → T lymphocyte maturation (mainly during childhood)

2Diabetes Mellitus

Type 1 DM (5–10%): Autoimmune destruction of beta cells → absolute insulin deficiency

Requires insulin injections; onset usually in childhood

DKA (Diabetic Ketoacidosis): Emergency; very high glucose, ketones, acidosis

Type 2 DM (90–95%): Insulin resistance + progressive beta cell dysfunction

Risk factors: Obesity, inactivity, family history

Treatment: Lifestyle, metformin, other oral agents, insulin if needed

HHS (Hyperosmolar Hyperglycemic State): Emergency in type 2

Gestational DM: During pregnancy; ↑risk of type 2 later

Complications ("MRNO"):

Microvascular: Retinopathy, nephropathy, neuropathy

Macrovascular: CAD, stroke, PVD

A1C (glycated hemoglobin): Reflects average glucose over 3 months; goal <7% for most

3Thyroid Disorders

Hypothyroidism: Low thyroid hormone

Hashimoto's thyroiditis (autoimmune): Most common cause in developed countries

Symptoms: Weight gain, fatigue, cold intolerance, bradycardia, constipation, myxedema

Treatment: Levothyroxine (synthetic T4)

Hyperthyroidism: Excess thyroid hormone

Graves' disease (autoimmune): Most common cause; exophthalmos (bulging eyes) characteristic

Thyroid storm: Emergency; extremely high T4 → high fever, tachycardia, heart failure

Symptoms: Weight loss, heat intolerance, tachycardia, anxiety, tremor

Treatment: Methimazole, radioactive iodine, surgery

Goiter: Enlarged thyroid gland (can occur in hypo or hyper)

Thyroid Cancer: Papillary (most common, good prognosis), follicular, medullary, anaplastic

Clinical Connections

►Over 422 million people worldwide have diabetes; by 2030 it will be the 7th leading cause of death
►Thyroid disorders are 5–8× more common in women than men
►Cushing's syndrome (excess cortisol) can be iatrogenic — caused by long-term steroid medications

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