Unit 5 Notes: The Stomach

The stomach The stomach is a dilated part of the alimentary canal between the esophagus and the small intestine. It is a muscular sac. It is a J-shaped.

Stomach Size When it is expanded, the stomach measures about 10 inches by 4 inches. Its capacity holds about one quart.

The stomach The stomach is divided into four regions: The cardia, which surrounds the opening of the esophagus into the stomach. The fundus of stomach, which is the area above the level of the cardial orifice. The body of stomach, which is the largest region of the stomach. The pyloric part, which is divided into the pyloric antrum and pyloric canal and is the distal end of the stomach.

The stomach Openings: Gastroesophageal: To esophagus Pyloric: To duodenum

The stomach Sphincters The cardiac sphincter (lower esophagus sphincter) closes off the top end of the stomach. The pyloric sphincter closes off the bottom.

Where is our Stomach located? The stomach is located between the Esophagus and the Duodenum above the small intestines. The Esophagus is the passage between the mouth and the stomach. The Duodenum is the first part of the small intestines. The stomach is on the upper left quadrant of the abdomen and lies against the diaphragm. The above photo shows the Esophagus to the stomach.

Food travels through the Esophagus into the Stomach and through the small intestines.

The stomach

Stomach Anatomical Relation

(1) About The Stomach Stomach can contain up to 1.5L of food without pressure changes. Feelings of discomfort come from irritants + too much food Stomach composed of excess tissue  Folds of Tissue = Rugae Folds allow the stomach to expand Folds also contain secretion glands Food sits in the stomach for 3-4 hours Depends on Amount & Type of food

Color Atlas of Physiology 5th Ed. - A. Despopoulos

(2) Dig. In The Stomach Mechanical Digestion: Chemical Digestion: Peristaltic churning of stomach muscle breaks apart bolus. Triggered by release of serotonin from rugae Chemical Digestion: Gastric Juice contains enzymes and acid that breaks down bolus.

Stomach Process: 3 phase Cephalic- Sense of smell and sight, as well as thinking about food sends a message to the brain indicating that the stomach is hungry. Gastric- Food enters the stomach and stretches and sends impulses to the brain, then the gastrin begins secreting. Intestinal- Food enters the small intestines and is digested.

pH video

(3) Release of Gastric Juice Gastrin (hormone) released from G-Cells within Rugae: Triggered by smell + taste of food Triggered by increase in pH Gastrin stimulates release of HCl = Decreasing pH: Proteins & Carbohydrates Metabolized Small & Large Intestine stimulated

Description The stomach is an expanded J-shaped organ in the upper left region of the abdominal cavity. It is continuous with the esophagus superiorly and empties into the duodenum of the small intestine inferiorly. It continues the mechanical and chemical digestion of the bolus. After the bolus has been completely processed in the stomach, the product is called chyme.

(4) Gastric Juice Contains… HCl = Hydrochloric Acid Pepsin = Enzyme = Breaks down protein Rennin = Enzyme = Breaks down protein Muccin = Mucus = Lubricate Food Mass

(5) Protein Metabolism Proteins take a lot of Gastric Juice to Metabolize. Breaking Down Proteins releases H+ ions. Decreases pH of stomach. G-Cells stop releasing gastrin  HCl stopped.

(6) Leaving The Stomach The mass leaving the stomach is called “Chyme”: Mostly liquid  Liquids leave first! Solids are left behind until broken down Approximately 3mL of food leaves at one time…. Food Exits the Pyloric Sphincter Chyme dumped into Small Intestine

When empty, the stomach collapses inward, throwing its mucosa into large, longitudinal folds called rugae (roo’ge).

Gastric emptying Solid food remains in the stomach until it has been broken down into small particles (diameter of !1mm) and suspended in chyme. The chyme then passes to the duodenum. The time required for 50% of the ingested volume to leave the stomach varies, for instance: 10—20 min for water and 1–4 hours for solids (carbohydrates, proteins, fats). Color Atlas of Physiology 5th Ed. - A. Despopoulos

Indigestible substances Indigestible substances (bone, fiber, foreign bodies) do not leave the stomach during the digestive phase. Special contraction waves called migrating motor complexes (MMC) pass through the stomach and small intestine roughly every 1.5 hours during the ensuing interdigestive phase, as determined by an intrinsic “biological clock”. These peristaltic waves transport indigestible substances from the stomach and bacteria from the small intestine to the large intestine. Color Atlas of Physiology 5th Ed. - A. Despopoulos

Mechanical Digestion The walls of stomach have several layers of smooth muscle. There are three layers of muscle, when food is present, these muscles work together to churn the content of stomach. You have probably heard your stomach “growl” when it has been empty for some times. These sounds are made by the contraction of smooth muscles that form the walls of stomach. Modern Biology - Postlethwait , Hopson

Chemical Digestion Gastric enzymes: Gastric fluid carries out chemical digestion in the stomach. Gastric enzymes: Pepsin splits complex protein molecules into shorter chains of amino acids. Hydrochloric acid in the stomach not only ensure the low pH, but also dissolves minerals and kills bacteria that enter the stomach along with food. Modern Biology - Postlethwait , Hopson

Gastrectomy About half of the patients subjected to total gastrectomy experience weight loss. Malabsorption, particularly fat malabsorption, is a common feature after total gastrectomy. This may be due to shortened intestinal transit time and small bowel bacterial overgrowth, but is less often due to diarrhea or pancreatic exocrine insufficiency. http://link.springer.com/article/10.1007%2FBF01656593?LI=true

Total and subtotal In a total gastrectomy, the intestine is joined to the end of the esophagus, whilst In a partial (or sub-total) gastrectomy the intestine is joined to the remaining healthy stomach. Life after Gastrectomy and Oesophagectomy

sub

Total

Common After-Effects of Gastrectomy Prolonged period of recovery. Reduces size of the food reservoir – this can lead to reduced food intake and weight loss. Vitamin B12 not available from diet – so B12 will be needed by injection. No stomach acid means that the stomach is more susceptible to infections. Rapid movement of food to small intestine – this causes ‘dumping syndrome’. Dumping Syndrome It is caused by rapid movement of food into the intestine. This process creates insulin which then makes the blood sugar level too low, causing some or all of: • sweatiness • dizziness • light-headedness • nausea • weakness and fatigue • fast heart rate Refined sugar can cause worse symptoms - to prevent dumping, try to take some fibre with refined sugar. If symptoms of dumping occur, a little sugary food improves symptoms quickly.

Health Problems Many problems can occur if there are issues with your digestive system: Ulcers Gastritis Gastroenteritis Gastroesophageal reflux Stomach Cancer Black Stool

Causes Ulcers-affects is the nerves that is around it. It becomes agitated and causes pain. Gastritis-  inflammation, irritation, or erosion of the lining of the stomach Gastroenteritis- causes irritation and inflammation of the stomach and intestines Gastroesophageal reflux (GERD)-affects the lower esophageal sphincter Stomach Cancer- disease in which stomach cells become cancerous Black Stool- darkening or blackness of stool

Review Video

Comparison between different animals