Functions and Structure of the Endocrine System
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TOPIC 02: Structure and Function of the Endocrine Glands

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Thyroid and Parathyroid Glands
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Lesson Splash, Page 1
Splash
Lesson Overview, Page 2
Overview
Topic 01: Introduction, Page 3
Mechanisms of Hormonal Regulation
Topic 01: General Functions, Page 4
Mechanisms of Hormonal Regulation
Topic 01: Mechanisms of Hormonal Regulation, Page 5
Mechanisms of Hormonal Regulation
Topic 01: Regulation of Hormone Release, Page 6
Mechanisms of Hormonal Regulation
Topic 01: Hormone Receptors, Page 7
Mechanisms of Hormonal Regulation
Topic 01: Check Your Understanding, Page 8
Mechanisms of Hormonal Regulation
Topic 01: Review, Page 9
Mechanisms of Hormonal Regulation
Topic 02: Introduction, Page 10
Structure and Function of the Endocrine Glands
Topic 02: Hypothalamic-Pituitary Axis, Page 11
Structure and Function of the Endocrine Glands
Topic 02: Thyroid and Parathyroid Glands, Page 12
Structure and Function of the Endocrine Glands
Topic 02: Check Your Understanding, Page 13
Structure and Function of the Endocrine Glands
Topic 02: Review, Page 14
Structure and Function of the Endocrine Glands
Lesson Summary, Page 15
Lesson Summary
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Thyroid and Parathyroid Glands

The thyroid gland, located in the neck just below the larynx, produces hormones that control the rates of metabolic processes throughout the body. 

The four parathyroid glands are located near the posterior side of the thyroid and function to control serum calcium levels.

Thyroid hormone (TH) is regulated through a negative-feedback loop involving the hypothalamus, the anterior pituitary, and the thyroid gland. This loop is initiated by Thyrotropin-releasing hormone (TRH), which is synthesized and stored within the hypothalamus.
 
The primary effects of TSH on the thyroid gland include: 
• An immediate increase in the release of stored thyroid hormones
• An increase in iodide uptake and oxidation
• An increase in thyroid hormone synthesis
• An increase in the synthesis and secretion of prostaglandins by the thyroid
 
The parathyroid glands produce parathyroid hormone (PTH), which is the single most important factor in the regulation of serum calcium concentration. The overall effect of PTH secretion is to increase serum calcium concentration and decrease the concentration of serum phosphate.
Select each item to learn more.
Endocrine Pancreas
The pancreas is both an endocrine gland that produces hormones and an exocrine gland that produces digestive enzymes.
Adrenal Glands
The adrenal glands are paired pyramid-shaped organs located behind the peritoneum and close to the upper pole of each kidney.
 
The adrenal cortex:
  1. The glucocorticoids are steroid hormones and have metabolic, neurologic, anti-inflammatory, immunosuppressive, and growth-suppressing effects. They are released under stress conditions.
  2. Mineralocorticoid steroids directly affect ion transport by epithelial cells, causing sodium retention and potassium and hydrogen loss. Aldosterone is the most potent of the naturally occurring mineralocorticoids and acts to conserve sodium by increasing the activity of the sodium pump of the epithelial cells in the nephron.
  3. Adrenal estrogens and androgens. The healthy adrenal cortex secretes small amounts of estrogen and androgens.
 
The adrenal medulla store and secrete the catecholamines epinephrine (adrenaline) and norepinephrine.
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