The Digestive System

The Digestive System Chapter 23 Anatomy of the Digestive System – Part 2

Pharynx • The bolus is forced into the pharynx • open area at the back of the oral cavity. • Common muscular passageway for both food, fluids, and air • Muscular contractions in the pharynx propel bolus downwards • A flap of elastic cartilage (epiglottis) prevents the bolus from entering the windpipe. • Bolus is now in the esophagus

Esophagus • Muscular tube ~10 in (25 cm) long • Collapsed when food isn’t in it • After food moves trough the laryngopharynx, it is routed into the esophagus as the epiglottis closes off the entry to the larynx.

Esophagus • Peristalsis moves the bolus down the esophagus (like an ocean wave) • A series of muscle contractions and relaxations • Food encounters the cardiac sphincter aka the lower esophageal sphincter. • Circular muscle that separates the esophagus from the stomach • When it opens, the bolus enters the stomach

Esophagus • This sphincter is reinforced by the diaphragm  helps to keep it closed when food isn’t being swallowed

Heartburn • Burning, radiating substernal pain. • Occurs when the acidic gastric juices regurgitates into the esophagus. • Symptoms are similar to those of a heart attack  often rushed to the ER! • Most likely to occur when eaten or drank a lot. Or when stomach is forced upwards  extreme obesity, pregnancy, running (stomach contents splashed upwards).

Stomach • Temporary “storage tank” • Chemical breakdown of proteins begins and food is converted to chyme • ~ 6-10 inches long • Empty  volume of 50 mL • Full  can hold up to 4L (1 gallon) of food and may extend nearly all the way to the pelvis!

Stomach • Circular, longitudinal, and oblique smooth muscle layers  • allows for stomach to churn, mix, pummel food  physically breaking it down • Move food along the digestive tract

Stomach - Regions • Cardiac region • Cardia “near the heart” • Surrounds the cardiac sphincter • Fundus • Dome-shaped part, tucked beneath the diaphragm • Superior bulge • Body • midportion

Stomach - Regions • Pyloric region • Funnel shaped region near the pyloric sphincter • Pyloric sphincter • Exit of the stomach to the small intestine

Stomach - Regions • Rugae (wrinkle, fold) • seen when stomach is empty  inward collapse to form large, longitudinal folds • Greater curvature • Convex, lateral surface • Lesser curvature • Concave, medial surface

Stomach - Regions • Lesser omentum – • Helps to keep the stomach connected to other digestive organs and the body wall • Runs from liver to lesser curvature • Greater omentum – • Helps to keep the stomach connected to other digestive organs and the body wall • Runs from greater curvature to cover the small intestine, spleen, and large intestine • Riddled with fat deposits (oment = fatty skin)

Stomach • Lining is simple columnar tissue with goblet cells  produce a protective coat of mucus • Also dotted with gastric pits (small openings) which produce gastric juice  hydrochloric acid and pepsinogen (inactive) • Release gastric juice = pepsinogen + HCl  pepsin (enzyme) • Pepsin + proteins  digestion!

Stomach • Mucous coats the inside of the stomach to protect it from HCl and pepsinogen. • Churning of food and mixing makes chyme • Contains fats, sugars, starches, vitamins, minerals, proteins, and amino acids.

Stomach • The secreted HCl makes the stomach very acidic (pH 1.5 – 3.5) • Necessary for activation and optimal activity of pepsin which digests proteins • Aids in food digestion  denatures proteins, breaks down cell walls of plant foods, kills many of the bacteria that are ingested with foods

Ulcers • When the mucus barrier is breached and underlying tissue is damaged  erosion of the stomach wall • Very painful. Usually starts 1-3 hours after eating. Relieved by eating again. • Danger  if ulcer perforates the stomach wall and stomach contents leak into the abdominal cavity • Thought to be caused by taking aspirin, ibuprofen, smoking, spicy foods, alcohol, coffee, stressed • Most recurrent ulcers are caused by Helicobacter pylori bacteria, but it is hard to prove this because it is found in most healthy people

Emesis • AKA vomiting • Many different factors may influence. Most common are extreme stretching of the stomach or intestine or the presence of irritants such as bacterial toxins, excessive alcohol, spicy foods, and certain drugs. • The diaphragm and abdominal wall muscles contract, the cardiac sphincter relaxes, and the soft palate rises to close off the nasal passages the stomach (and duodenal) contents are forced upwards through the esophagus and pharynx and out the mouth • Excessive vomiting may cause dehydration and may lead to severe disturbances in electrolyte and acid-base balance of the body.

Stomach • Food is forced out of the stomach by peristalsis through the pyloric sphincter and into the duodenum.

The Digestive System