Human Digestive System Overview

Digestion Overview

• Digestion begins in the mouth, with peristalsis moving food through the digestive tract to the anus.
• Cholecystokinin (CCK) is released from I-cells in the duodenum and jejunum, stimulated by fatty acids, proteins, and weak acids. It inhibits gastric activity.
• Gastrin, released from G cells in the antrum and duodenum, stimulates hydrochloric acid secretion and the growth of stomach, duodenum, and colon mucosa. Its release is stimulated by protein digestion products.
• Glucose-dependent insulinotropic polypeptide (GIP) stimulates insulin release.

Motility and Emptying

• Slow waves excite spike potentials, which are true action potentials.
• Rapid gastric emptying can cause diarrhea, hypertension, reactive hypoglycemia, and duodenal ulcers.
• Gastric emptying is regulated by factors like stomach tone, pylorus tone, and peristaltic contractions.
• Chyme must enter the duodenum at a proper rate after a meal.

Colon Cancer Stages

• Stage 1: Cancer spreads from the colon's inner lining to the muscle layer.
• Stage 2: IIa= cancer spreads through the muscle layer to the outer covering (serosa), IIb= cancer spreads through the serosa but not to nearby organs; IIc= tumor invasion and spread to nearby organs.
• Stage 3: IIIa= cancer spreads to muscle, and has spread to 1-3 nearby lymph nodes or 4-6 nearby lymph nodes; IIIb= cancer to muscle/serosa and 4-6 nearby lymph nodes; IIIc= cancer through serosa to nearby organs and 1+ nearby lymph nodes.
• Stage 4: Cancer spreads to other parts of the body through the bloodstream and lymphatic system.

Carbohydrate Absorption

• Membrane carrier (SGLUT-1): Absorbs glucose using energy from the Na+-K+ ATPase.
• Fructose (GLUT-5): Absorbed via facilitated diffusion (GLUT-5), does not require energy, but relies on a concentration gradient.

Intestinal Motility

• Peristalsis moves food in one direction (law of gut).
• Segmentation moves food in both directions (mixing movement).
• Secondary peristalsis is induced by distension.

Upper Gastrointestinal Sphincters

• Upper esophageal sphincter (UES): Prevents air from entering the esophagus.
• Lower esophageal sphincter (LES): Prevents acid reflux into the esophagus.

Sodium Absorption in the Small Intestine

• Absorption mechanisms: Sodium absorption in the SI and colon occurs via diffusion through water channels, co-transport with amino acids and glucose, co-transport with chloride, or counter-transport in exchange for hydrogen ions.
• Aldosterone: Increases sodium reabsorption and potassium secretion in the small intestine and colon.

Crypt Cell Secretion

• Mechanism: Cyclic AMP (cAMP) activates chloride channels, sodium follows the electrical gradient, and water moves along the osmotic gradient.

Secretin

• Function: A natural anti-acid.

Cirrhosis and Complications

• Definition: Chronic liver disease where healthy liver cells are replaced by scar tissue, often due to excessive alcohol intake.
• Complications: Jaundice, ascites, coma/death, esophageal varices, blood clotting abnormalities, and peripheral edema.

Autonomic Nervous System (ANS)

• Vagus stimulation: Information about how the vagus nerve stimulation plays a role in the ANS is not included in the provided text.