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.