Human Digestive System Overview

Study Notes

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.

Description

Explore the fundamentals of digestion, including the roles of key hormones like CCK and gastrin. Learn about digestive motility, emptying processes, and the importance of chyme regulation. This quiz also touches upon the stages of colon cancer, highlighting its relevance in digestive health.