Overview
This lecture covers the major endocrine glands, focusing on the pituitary (anterior and posterior), thyroid, and parathyroid glands, their hormones, and regulatory mechanisms.
Hypothalamus & Pituitary Gland
- The hypothalamus, a brain structure, controls the pituitary gland and monitors body conditions like stress, temperature, water, sugar, and calcium levels.
- The pituitary gland is divided into anterior (front) and posterior (back), with the anterior pituitary producing several hormones.
- The hypothalamus releases "releasing" or "inhibiting" hormones to regulate pituitary hormone secretion.
Anterior Pituitary Hormones
- Growth hormone (GH, somatotropin) stimulates cell division, protein synthesis, cartilage growth, and fat catabolism; regulated by growth hormone releasing hormone (GHRH) and somatostatin.
- Hyposecretion of GH causes pituitary dwarfism in children; hypersecretion causes gigantism in children and acromegaly in adults.
- Prolactin promotes milk production in mammary glands; regulated by prolactin releasing hormone and positive feedback from breastfeeding.
- Luteinizing hormone (LH) stimulates sex hormone (estrogen, testosterone) production in gonads; follicle-stimulating hormone (FSH) stimulates sperm and egg maturation.
- Thyroid stimulating hormone (TSH, thyrotropin) prompts the thyroid gland to release T3 and T4, raising metabolic rate.
- Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to release glucocorticoids (mainly cortisol), increasing glucose, fat, and protein metabolism and suppressing inflammation during stress.
Posterior Pituitary Hormones
- The posterior pituitary stores and releases oxytocin and antidiuretic hormone (ADH), both produced by the hypothalamus.
- ADH (vasopressin) decreases urine output to conserve water when blood becomes concentrated; inhibited by diuretics and alcohol.
- Oxytocin causes uterine contractions during labor and milk ejection during breastfeeding; regulated by positive feedback.
Thyroid & Parathyroid Glands
- The thyroid gland produces T3 and T4, which regulate basal metabolic rate and require iodine for synthesis.
- Hypothyroidism leads to cretinism in infants and myxedema in adults; common causes include iodine deficiency and autoimmune disease (Hashimoto's).
- Hyperthyroidism causes heat intolerance, weight loss, restlessness, and is often due to Graves disease.
- Calcitonin from the thyroid lowers blood calcium by inhibiting osteoclasts and promoting bone deposition.
- Parathyroid hormone (PTH) raises blood calcium by stimulating osteoclasts, increasing intestinal absorption (via vitamin D), and increasing kidney reabsorption.
Calcium Balance
- Hypocalcemia causes overactive nerves/muscle cramps and weak heart contractions.
- Hypercalcemia leads to weak muscle responses and risk of over-contraction of the heart.
Key Terms & Definitions
- Anterior Pituitary — front part of pituitary, produces many key hormones.
- Posterior Pituitary — stores/releases hypothalamic hormones.
- Growth Hormone (GH) — stimulates body growth and metabolism.
- Prolactin — promotes milk production.
- Luteinizing Hormone (LH) — stimulates sex hormone production.
- Follicle-Stimulating Hormone (FSH) — stimulates egg/sperm production.
- Thyroid Stimulating Hormone (TSH) — stimulates thyroid hormone release.
- Adrenocorticotropic Hormone (ACTH) — stimulates adrenal cortex.
- Antidiuretic Hormone (ADH) — conserves body water.
- Oxytocin — causes labor contractions and milk release.
- Thyroxine (T4), Triiodothyronine (T3) — thyroid hormones for metabolic rate.
- Calcitonin — lowers blood calcium.
- Parathyroid Hormone (PTH) — raises blood calcium.
Action Items / Next Steps
- Draw hormone regulatory flowcharts for key anterior pituitary hormones.
- Review symptoms and causes of hormone hypo/hypersecretion.
- Read textbook sections on thyroid and calcium disorders.