Adrenal Glands Overview

Adrenal Glands

• Adrenal glands are located at the superior poles of the kidneys.
• Each adrenal gland is composed of two parts: adrenal medulla (20%) and adrenal cortex (80%).

Adrenal Cortex

• Secretes corticosteroids:
  • Glucocorticoids: Cortisol, corticosterone
  • Mineralocorticoids: Aldosterone
• Zona Glomerulosa: Outermost layer of the adrenal cortex.
  • Secretes Aldosterone.
  • Controlled by the renin-angiotensin system and plasma potassium levels.
• Zona Faciculata: Middle layer of the adrenal cortex.
  • Secretes cortisol, corticosterone and small amounts of adrenal androgens and estrogens.
  • Controlled by the hypothalamic-pituitary axis via ACTH.
• Zona Reticularis: Innermost layer of the adrenal cortex.
  • secretes adrenal androgens (dehydroepiandrosterone and androstenedione), small amounts of estrogens and glucocorticoids.
  • Controlled by ACTH and cortical androgen-stimulating hormone.

Adrenal Medulla

• Secretes non-steroid hormones:
  • Epinephrine (adrenaline)
  • Norepinephrine (noradrenaline)
  • Dopamine
• Also secretes opioid peptides (encephalin) and adrenomedullin.
• Plays a role in metabolism, blood pressure, and heart activity.
• Most circulating norepinephrine comes from noradrenergic nerve endings.
• About half of circulating dopamine comes from sympathetic ganglia.

Disorders of the Adrenal Gland

• Addison's disease: Deficiency in cortisol and aldosterone.
  • Leads to low blood glucose levels and low blood sodium levels.
  • Symptoms: fatigue, weakness, abdominal pain, weight loss, and bronzed skin.
• Cushing's syndrome: Excess cortisol.
  • Symptoms: excessive glucose production from glycogen and protein, retention of salt and water.

Parathyroid Hormone (PTH)

• Controls blood calcium levels
• Effects:
  • Removes calcium and phosphate from bone
  • Increases calcium absorption in the digestive tract
  • Causes kidneys to retain calcium and excrete phosphate.

Pancreas

• Endocrine gland: secretes hormones into the blood.
• Exocrine gland: secretes enzymes, fluids, and ions into the digestive tract.
• Islets of Langerhans: Clusters of endocrine cells scattered throughout the pancreas.
• Alpha cells: Secrete glucagon, which raises blood sugar levels.
• Beta cells: Secrete insulin, which lowers blood sugar levels.
• Delta cells: Secrete somatostatin.

Disorders of the Pancreas - Diabetes

• Type 1 diabetes: Failure of the pancreas to produce enough insulin.
  • Insulin-dependent diabetes.
  • Autoimmune disorder where the immune system attacks insulin-producing cells.
• Type 2 diabetes: Cells fail to respond adequately to insulin, even when it is present.
  • Non-insulin-dependent diabetes.
  • May have a genetic component, but lifestyle factors are major determinants.

Endocrine System

• Collection of specialized cells, tissues, and glands.
• Produces and secretes circulating chemical messenger molecules (hormones).

Hormones

• Secreted by endocrine glands.
• Endocrine glands are ductless organs that secrete their products into interstitial fluid, lymph, and blood.
• Exocrine glands: secrete products into ducts.

Characteristics of the Endocrine System

• Hormones reach nearly every living cell.
• Each hormone acts only on certain cells.
• Endocrine control is slower than nervous system control.
• The endocrine and nervous systems interact.

Classification of Hormones

• Steroid hormones: Structurally related to cholesterol, lipid-soluble.
• Non-steroid hormones: Structurally related to proteins, lipid-insoluble.

Learning Objectives

• Discuss the general functions of the endocrine system.
• Classify hormones by their chemical makeup.
• Describe the endocrine functions of the hypothalamus and pituitary.
• Discuss the hormone functions of the pancreas and adrenal glands.
• Describe the hormone functions of the thyroid and parathyroid glands.
• Discuss the hormones produced by reproductive organs.
• Describe other hormone sources and other chemical messengers.
• Discuss various disorders of the endocrine system.

Test your knowledge about the adrenal glands, their location, and their structure. Explore the functions of the adrenal cortex and medulla and learn about the hormones they secrete, including glucocorticoids and mineralocorticoids. This quiz covers the layers of the adrenal cortex and their hormonal regulation.