The Digestive System

1.Digestion The mechanical and chemical breakdown of food into molecules that can be absorbed across the lining of the small intestine and into the bloodstream as nutrients for the body.

2,3 Mechanical Digestion Mechanical digestion breaks food up into small pieces that are more accessible to digestive enzymes. It includes the chewing of teeth, the churning of food in the stomach and peristalsis throughout the entire digestive process.

4,5,6 Chemical Digestion Chemical digestion refers to the action of the digestive enzymes. The various digestive juices contain enzymes that digest particular types of food. Examples: Salivary amylase: breaks starch down into maltose Pepsin: breaks proteins down into amino acids

7,8,9. Flow chart of Digestion: Salivary Glands Mouth Pharnyx Esophagus Pancreas Liver Gallbladder Large Intestine Stomach Small Intestine Rectum Anus

10-13 Mouth Food enters the mouth, where it is mechanically digested. The teeth, the palate (roof of mouth) and the tongue break the food down into small pieces. The Salivary Glands secrete Salivary Amylase into the mouth that begins the chemical digestion of carbohydrates. Carbohydrates are broken down into simple sugars. (glucose) Food leaves the mouth in a bolus (moist, ball of food)

CLEFT PALATE

CLEFT PALATE

CLEFT PALATE: BEFORE AND AFTER

14,15 Pharynx Food (bolus) travels through the throat “pharynx” on the way to the esophagus. There is a flap of tissue called the epiglottis that prevents food from going down the trachea. Pharynx

16-20 Esophagus The esophagus is a muscular tube that joins the pharynx with the stomach. Swallowing pushes the bolus into the esophagus. Rhythmical contractions called peristalsis pushes food through the esophagus to the stomach. When the bolus reaches the end of the esophagus it goes through the cardiac sphincter into the stomach. This is the sphincter muscle that prevents the acidic contents of the stomach from entering the esophagus.

21,22 Heartburn Normally, the cardiac sphincter prevents the acidic contents of the stomach from entering the esophagus. Sometimes, heartburn, which feels like a burning pain rising up into the throat, occurs when some of the contents of the stomach escape into the esophagus.

23-31 Stomach The stomach is a thick walled “J” shaped organ that lies underneath the diaphragm muscle. The stomach stores food and starts the digestion of proteins. The wall of the stomach has three muscular layers and contains deep folds called “rugae”. The muscular walls of the stomach churn, mixing the contents. Gastric glands secrete gastric juice into the stomach. Gastric Juice contains HCl acid and a digestive enzyme called pepsin. Pepsin digests protein and breaks in down into amino acids. Normally the stomach empties in 2-6 hours. When food leaves the stomach it is semisolid mixture called chyme.

Lap band

Gastric bypass

(Inside walls of stomach) Rugae (Inside walls of stomach)

32-34 ULCER Normally the wall of the stomach is protected by a thick layer of mucus, but if chance, Hydrochloric Acid penetrates this mucus, an ulcer can form. An ulcer is an open sore in the stomach wall caused by gradual breakdown of the mucus membrane that lines the stomach The most frequent cause of an ulcer is an infection caused by the bacterium helicobacter pylori.

35-38 Small Intestine The small intestine is named for its small diameter. (In comparison to the large intestine) The small intestine averages about 10 feet in length. The small intestine receives secretions from the pancreas and liver. The primary function of the small intestine is absorption.

Note the area in which the liver and pancreas secrete into the Duodenum of the small intestine.

The digestive tract

39-41 Three parts of the small intestine: Duodenum (du”o-de’num): The first 25 cm of the small intestine. This part receives the pancreatic secretions and bile from the liver. Jejunum (je-joo’num): The next 3 feet of the small intestine. This part contains the villi. (fingerlike extensions that absorb nutrients) Ileum: (il’e-um): The last 6-7 feet of the small intestine. This part also contains villi to absorb nutrients from the digestive system to the circulatory system.

42-45 Villi The wall of the small intestine is made up of fingerlike extensions called villi. The epithelial cells of each villi have extensions called microvilli. The large number of villi and their microvilli increase the surface area of the small intestine to provide more area for absorption. The surface area of the small intestine is equal to a tennis court.

villi

46-49 Large Intestine Includes the cecum, colon, rectum and anal canal. Larger in diameter than the small intestine The cecum (se’kum): is the first portion of the large intestine. This is where the small intestine attaches to the large intestine. The appendix is a small projection from the cecum.

Superior to the cecum the large intestine is termed the ascending colon. At the level of the liver, the large intestine bends sharply and becomes the transverse colon, it travels across where it bends again and becomes the descending colon. 50,51

At the lower region of the large intestine, the descending colon turns in to form an S shaped bend known as the sigmoid colon. The last 20 cm of the large intestine is known as the rectum, which ends in the anal canal, which opens at the anus. (The out shoot) 52,53

The large intestine absorbs water and electrolytes. It prepares and stores non-digestible material (feces) Feces contain bile pigments and large quantities of bacteria (E-coli) The E-coli bacteria live off of the fecal matter. When they break down this material, they emit odorous molecules that cause the characteristic fecal odor. Some of the vitamins (Vitamin K and some B vitamins) and amino acids are produced by the E-coli bacteria and absorbed by the intestinal lining. The E-coli bacteria are beneficial for humans in this matter. 54-59

60,61 APPENDIX The appendix is a fingerlike extension of the cecum of the large intestine. The appendix can become infected, resulting in appendicitis, a very painful condition in which the fluid content of the appendix can increase to the point that it bursts.

62-64 Diarrhea & Constipation Two common everyday complaints associated with the large intestine are diarrhea and constipation. In diarrhea, too little water is absorbed by the large intestine. In constipation, too much water is absorbed by the large intestine.

Diarrhea The major causes of diarrhea are infection of the lower tract and nervous stimulation. In the case of infection, such as food poisoning caused by eating contaminated food, the intestinal wall becomes irritated and peristalsis increases. Lack of water absorption is a protective measure by the body, and diarrhea serves to rid the body of the infectious organisms. When a person is under stress, the Nervous System sometimes stimulates the intestinal wall, resulting in diarrhea. Loss of water due to diarrhea may lead to dehydration, a serious condition in which the body tissues lose their normal water content. 65-69

Constipation & Hemorrhoids 70-73 When a person is constipated, the feces are dry and hard. Chronic constipation is associated with the development of hemorrhoids. Hemorrhoids are masses of tissue within the anal canal that contain blood vessels. Internal hemorrhoids are normal. It is when the hemorrhoids descend through the anal canal that they become painful and irritated.

Severe Grade 3 Hemorrhoids

Accessory Organs: 74-75 Salivary Glands Pancreas Liver Gallbladder These organs are essential to the process of digestion, but food does not actually travel into any of these organs. These organs secrete important fluids into the primary organs of digestion to speed up the chemical digestive process.

The salivary glands 76-79 The salivary glands secrete about 1 liter of saliva each day, which enters the mouth by way of their ducts. Saliva contains mucus and a digestive enzyme called salivary amylase. Salivary amylase begins the digestion of carbohydrates into simple sugars. There are three pairs of salivary glands: the sublingual glands (found underneath the tongue), the submandibular glands (lie under the tongue at the back portion of the mouth and the parotid glands which are located in front of and below the ears.

The Pancreas 80-82 The pancreas has both endocrine and exocrine functions. The exocrine functions are the ones associated with digestion. The pancreas produces pancreatic juice, which contains sodium bicarbonate, a chemical that neutralizes the HCl acid from the stomach, and digestive enzymes that break down carbohydrates, proteins and fats into simple substances small enough to be absorbed by the villi of the small intestine.

The Liver 83-88 The liver is the largest gland of the body. The liver produces bile. Bile is a yellowish green fluid. It contains bile salts that emulsify fats once bile reaches the small intestine. The liver plays many other important roles in the body. It detoxifies the blood by removing poisonous substances and metabolizing them. It stores glucose as glycogen after eating and the breakdown of glycogen to glucose between meals to maintain the blood glucose level.

Cirrhosis is a chronic disease of the liver in which the organ first becomes fatty and then the liver tissue is replaced by scar tissue. This condition is most often the result of excessive amounts of alcohol in which the liver had to break down. Cirrhosis of the Liver 89,90

The Gallbladder 91,92 The gallbladder is a pear shaped, muscular sac attached to the liver. The liver produces bile and any excess bile is stored in the gallbladder.

This is the inside of the gallbladder of a patient with gallstones. Gallstones are small, hard pellets that form in the gallbladder. Gallstones can range from a few millimeters to several centimeters in diameter. Most gallstones are formed from cholesterol.