Diabetes and Gastrointestinal Quiz

The Digestive System Part II

• The digestive system consists of the oral cavity, salivary glands, esophagus, pancreas, gallbladder, stomach, large intestine, and small intestine.
• The digestive system structures work together to process food for absorption into the body.

Accessory Digestive Organs of the Small Intestines

• The liver's primary function is bile production.
• The gallbladder stores bile.
• The pancreas supplies most of the enzymes needed to digest chyme, alongside bicarbonate to neutralize stomach acid.

Gross Anatomy of the Liver

• The largest gland in the body, roughly 3 pounds.
• Consists of four primary lobes: right and left, quadrate, and caudate.
• The gallbladder sits in a recess on the inferior surface of the right lobe.
• Falciform ligament separates the larger right lobe from the smaller left lobe.
• It is suspended from the diaphragm and the anterior abdominal wall.
• The round ligament is a remnant of the fetal umbilical vein, aligned along the free edge of the falciform ligament.
• Lesser omentum anchors the liver to the stomach.
• The hepatic artery proper and hepatic portal vein enter the liver at the porta hepatis.
• Bile leaves the liver through left and right hepatic ducts, which fuse to form the common hepatic duct.
• The cystic duct fills/drains the gallbladder.
• The bile duct is formed by the union of the common hepatic and cystic ducts.

Microscopic Anatomy of the Liver

• Liver lobules are hexagonal, sesame-sized structural and functional units.
• Plates of hepatocytes (liver cells) filter and process nutrient-rich blood.
• Central veins are located along the longitudinal axis.
• Liver sinusoids are leaky capillaries between hepatic plates, lined with stellate (hepatic) macrophages that remove debris and old red blood cells.
• Portal triads in each corner of a lobule contain a branch of the hepatic artery (supplies O2), a branch of the hepatic portal vein (delivers nutrient-rich blood from the intestine), and a bile duct (receives bile from bile canaliculi).

The Liver

• Hepatocytes contain rough and smooth ER, Golgi apparatus, peroxisomes, and mitochondria.
• They produce approximately 900 ml of bile per day.
• Hepatocytes process bloodborne nutrients, storing glucose as glycogen and producing plasma proteins.
• They store fat-soluble vitamins and perform detoxification functions (e.g., converting ammonia to urea).
• Hepatocytes excrete bilirubin into the bile, phagocytize old red blood cells, leukocytes, and some bacteria, and synthesize most clotting factors and lipoproteins.
• The only digestive function of the liver is bile production.

Bile: Composition and enterohepatic circulation

• Bile is a yellow-green, alkaline solution containing bile salts , cholesterol derivatives and phospholipids that function in fat emulsification and absorption.
• Bilirubin, the main bile pigment from heme of hemoglobin, is broken down by bacteria in the intestine to stercobilin, which gives the brown color to feces.
• Bile also contains cholesterol, triglycerides, phospholipids, and electrolytes.
• Enterohepatic circulation is a recycling mechanism that conserves bile salts.
• Reabsorbed in the ileum, they are returned to the liver.
• 95% of secreted bile salts are recycled.

The Gallbladder

• A thin-walled muscular sac on the inferior surface of the liver.
• Stores and concentrates bile by absorbing its water and ions.
• Contains honeycomb folds that allow it to expand as it fills.
• Muscular contraction releases bile via the cystic duct into the common bile duct.

The Pancreas

• Mostly retroperitoneal, with its head encircled by the duodenum and its tail abutting the spleen.
• Contains endocrine (insulin and glucagon) and exocrine (pancreatic juice) parts.
• Acinar cells produce zymogen granules containing proenzymes.
• Ducts secrete to the duodenum via the main pancreatic duct, with smaller ducts producing water and bicarbonate (HCO3—).
• Pancreatic juice is 1200-1500ml/day and contains watery alkaline solution (pH 8) to neutralize acidic chyme from the stomach, electrolytes (primarily HCO3−), and digestive enzymes (e.g. proteases, amylase, lipases, and nucleases).
• Proteases are produced in inactive form (proenzymes) and require activation in the duodenum by enterokinase.

The Small Intestine

• The major organ of digestion and absorption.
• Includes duodenum, jejunum, and ileum.
• Extends from pyloric sphincter to ileocecal valve; ~7-13 ft during life and ~20ft in a cadaver.
• Has a small diameter of 2.5-4 cm (1.0 - 1.6 inches).
• Modifications (circular folds, villi, and microvilli) increase surface area ~ 600x to ~ 200 m2, aiding absorption.
• Blood supply from superior mesenteric artery; venous return via veins to superior mesenteric veins, then hepatic portal vein, and finally the liver.
• Nerve supply from parasympathetic innervation via the vagus nerve and sympathetic innervation from thoracic splanchnic nerves.
• The mucosa has absorptive cells synthesizing digestive enzymes (brush border enzymes), producing intestinal juice (a watery mixture of mucus that aids in chyme transport), and five main cell types (enterocytes, goblet cells, enteroendocrine cells, and paneth cells).

The Large Intestine

• Frames the small intestine on three sides, extending from the ileocecal valve to the anus.
• Much shorter than the small intestine (~1.5 vs. 6 m), but about twice its diameter (~7 cm).
• Major functions include absorbing most of the remaining water from indigestible food residues, and absorbing metabolites produced by resident bacteria.
• It also stores residues temporarily and eliminates them as semisolid feces.
• Subdivisions include: cecum, appendix, ascending colon, transverse colon, descending colon, and sigmoid colon.
• The anal canal terminates at the anus and includes the internal and external anal sphincters; they close the anus except during defecation.
• Mucus from glands in the mucosa coats the large intestine and reduces friction.
• The muscularis externa has 3 bands, called teniae coli, that run the length of the colon and form pouches called haustra, which facilitate movement of digested material.

The Liver, Gallbladder, and Pancreas

• The liver, gallbladder and pancreas function in digestion and absorption of nutrients.