Miscellaneous Hormones in Medical Physiology

Diverse Hormones

• Adipose tissue, cardiac tissue, pineal gland, and gastro-intestinal tract are endocrine organs that produce diverse hormones.

Adipose Tissue as Endocrine Organ

• Adipose tissue produces adiponectin, angiotensin II, leptin, insulin-like growth factor-1, and oestrogen.
• Adipokines are a group of over 600 bioactive molecules produced by adipose tissue that act as paracrine and endocrine hormones.

Adipokines

• Adipokines regulate appetite and satiety, fat distribution, inflammation, blood pressure, hemostasis, and endothelial function.
• Examples of adipokines include adiponectin, leptin, tumor necrosis factor-alpha (TNFa), osteoprotegerin, interleukin-6 (IL-6), resistin, interleukin-1 (IL-1), monocyte chemotactic protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1).

Adiponectin

• Adiponectin is a protein hormone that regulates glucose regulation and fatty acid catabolism.
• Adiponectin is exclusively secreted from adipose tissue into the bloodstream.
• Plasma levels of adiponectin are inversely correlated with body fat percentage in adults.
• Adiponectin is associated with the suppression of various pathophysiological conditions such as type 2 diabetes, obesity, atherosclerosis, non-alcoholic fatty liver disease (NAFLD), and metabolic syndrome.

Leptin

• Leptin is a satiety hormone that regulates energy intake and energy expenditure.
• Leptin levels rise after food intake and are very sensitive to fasting conditions, with levels dropping during fasting.
• Leptin levels are directly correlated to body fat percentage.

Neuropeptide Y (NPY)

• Neuropeptide Y (NPY) is a potent orexigenic peptide found in the brain.
• NPY stimulates food intake, especially carbohydrates.

Dysfunctional Adipocytes

• Dysfunctional adipocytes alter adipokine secretion.
• Adipokine secretion can be altered by dysfunctional adipocytes.

The Heart as Endocrine Organ

• The heart produces atrial natriuretic peptide (ANP).
• ANP is part of the ADH-ANP renin-control pair.

The Gastro-Intestinal Tract as Endocrine Organ

• The stomach produces gastrin, which causes acid secretion.
• Stretching of the antrum of the stomach leads to gastrin secretion, which causes histamine release, stimulating HCl secretion.
• The small intestine produces secretin, which was the first hormone to be described.
• Secretin is produced in the epithelial lining of the Crypts of Lieberkühn in the duodenum.