Name the enzymes and hormones released by liver and pancreas. Discuss their functions in digestion of food and maintenance of blood glucose balance.

Liver: Enzymes and Hormones

While the liver doesn’t secrete digestive *enzymes* directly into the intestinal lumen, it produces bile, which contains bile salts that emulsify fats, aiding in their digestion and absorption. The liver’s primary hormonal role is related to glucose metabolism, though it doesn’t secrete classical hormones. It responds to hormonal signals like insulin and glucagon.

• Bile Salts: Facilitate the digestion and absorption of fats and fat-soluble vitamins (A, D, E, K).
• Lipoproteins (VLDL, LDL, HDL): Transport lipids in the bloodstream.
• Angiotensinogen: A precursor protein converted to angiotensin I, initiating the renin-angiotensin-aldosterone system (RAAS) for blood pressure regulation.
• Insulin-like Growth Factor 1 (IGF-1): Produced in response to growth hormone, mediating growth and metabolic effects.

Pancreas: Enzymes and Hormones

The pancreas exhibits both exocrine and endocrine functions. The exocrine pancreas secretes digestive enzymes, while the endocrine pancreas secretes hormones regulating blood glucose.

Exocrine Pancreas – Digestive Enzymes

These enzymes are secreted into the duodenum via the pancreatic duct.

• Trypsinogen: Activated to trypsin in the duodenum by enteropeptidase, then activates other proenzymes. Digests proteins.
• Chymotrypsinogen: Activated to chymotrypsin by trypsin. Digests proteins.
• Procarboxypeptidase: Activated to carboxypeptidase by trypsin. Digests proteins.
• Pancreatic Amylase: Digests carbohydrates (starch) into smaller sugars.
• Pancreatic Lipase: Digests fats into fatty acids and glycerol.
• Ribonuclease & Deoxyribonuclease: Digest RNA and DNA, respectively.

Endocrine Pancreas – Hormones

These hormones are secreted directly into the bloodstream by the Islets of Langerhans.

• Insulin (β cells): Lowers blood glucose levels by promoting glucose uptake by cells, glycogenesis (glucose to glycogen), and inhibiting gluconeogenesis (glucose production).
• Glucagon (α cells): Raises blood glucose levels by promoting glycogenolysis (glycogen to glucose) and gluconeogenesis.
• Somatostatin (δ cells): Inhibits the release of insulin and glucagon, slowing down digestion and nutrient absorption.
• Pancreatic Polypeptide (PP cells): Regulates pancreatic exocrine secretions and appetite.

Functions in Digestion of Food

The liver’s bile salts are crucial for fat digestion, allowing for efficient absorption of lipids and fat-soluble vitamins. Pancreatic enzymes collectively break down all major food components: proteins, carbohydrates, and fats. Trypsin, chymotrypsin, and carboxypeptidase work synergistically to hydrolyze proteins into peptides and amino acids. Pancreatic amylase breaks down starch into disaccharides, while pancreatic lipase breaks down triglycerides into fatty acids and glycerol. These breakdown products are then absorbed in the small intestine.

Maintenance of Blood Glucose Balance

The pancreas plays a central role in maintaining blood glucose homeostasis. After a meal, blood glucose levels rise, stimulating insulin release. Insulin facilitates glucose uptake by cells, lowering blood glucose. Between meals, blood glucose levels fall, triggering glucagon release. Glucagon stimulates the liver to release stored glucose (glycogenolysis) and produce new glucose (gluconeogenesis), raising blood glucose. Somatostatin modulates these processes, preventing excessive fluctuations. The liver acts as the primary target organ for both insulin and glucagon, storing and releasing glucose as needed.

Hormone	Effect on Blood Glucose	Mechanism of Action
Insulin	Decreases	Promotes glucose uptake, glycogenesis, inhibits gluconeogenesis
Glucagon	Increases	Promotes glycogenolysis, gluconeogenesis
Somatostatin	Modulates	Inhibits insulin and glucagon release