ch+38

. The digestive system is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Food taken into the mouth is broken down into smaller pieces and the tongue rolls these pieces into balls (boluses). Sensory receptors on the tongue and the olfactory nerves contribute to the sensation of taste by picking up the aroma of the food and passing the sensation of smell on to the brain. The sight of the food also stimulates the salivary glands. Altogether, the sensations of sight, taste, and smell cause the salivary glands, located in the mouth, to produce saliva, which then pours into the mouth to soften the food. An enzyme in the saliva called amylase begins the break down of carbohydrates (starch) into simple sugars, such as maltose. Ptyalin is one of the main amylase enzymes found in the mouth; ptyalin is also secreted by the pancreas. The bolus of food, is swallowed, moving to the throat at the back of the mouth (pharynx). In the throat, rings of muscles force the food into the esophagus, the first part of the upper digestive tube. The esophagus extends from the bottom part of the throat to the upper part of the stomach. The esophagus does not take part in digestion, but moves the bolus into the stomach by peristaltic movement. There is a powerful muscle (the esophageal sphincter), at the junction of the esophagus and stomach, which acts as a valve to keep food, stomach acids, and bile from flowing back into the esophagus and mouth.
 * All the healthline links I’ve posted have illustrations (graphics, X-rays, pictures). This helps to understand better.**
 * CHAPTER 38**
 * STRUCTURE & FUNCTION OF THE DIGESTIVE SYSTEM**

Chemical digestion begins in the stomach. The stomach, a large, hollow, pouched-shaped muscular organ. Food in the stomach is broken down by the action of the gastric juice containing hydrochloric acid and a protein-digesting enzyme called pepsin. Gastric juice is secreted from the lining of the stomach walls, along with mucus, which helps to protect the stomach lining from the action of the acid. The three layers of powerful stomach muscles churn the food into a fine semiliquid paste called chyme. The chyme is periodically passed through the pyloric sphincter), which controls the passage of chyme between the stomach and the beginning of the small intestine. Gastric juice secretion initially results from the stimulation of the brain by the taste, smell of food (1st ). And again when the food enters the stomach.(2nd ) Gastric juice is needed mainly for the digestion of protein by pepsin for the break down of the large protein molecules into smaller molecules: polypeptides and peptides. These smaller molecules in turn stimulate the cells of the stomach lining to release the hormone gastrin into the bloodstream. Gastrin then circulates throughout the body, and eventually reaches the stomach, where it stimulates the cells of the stomach lining to produce more gastric juice. The more protein there is in the stomach, the more gastrin will be produced, and the greater the production of gastric juice. (3rd ). The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine. Starch is digested in two steps: First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose; then an enzyme in the lining of the small intestine (maltase) splits the maltose into glucose molecules that can be absorbed into the blood. Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body. Table sugar is another carbohydrate that must be digested to be useful. An enzyme in the lining of the small intestine digests table sugar into glucose and fructose, each of which can be absorbed from the intestinal cavity into the blood. Milk contains yet another type of sugar, lactose, which is changed into absorbable molecules by an enzyme called lactase, also found in the intestinal lining.
 * Digestion**
 * Carbohydrates.** It is recommended that about 55 to 60 percent of total daily calories be from carbohydrates. Some of our most common foods contain mostly carbohydrates. Examples are bread, potatoes, legumes, rice, spaghetti, fruits, and vegetables. Many of these foods contain both starch and fiber.


 * Protein.** Foods such as meat, eggs, and beans consist of giant molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. An enzyme in the juice of the stomach starts the digestion of swallowed protein. Further digestion of the protein is completed in the small intestine. Here, several enzymes from the pancreatic juice and the lining of the intestine carry out the breakdown of huge protein molecules into small molecules called amino acids. These small molecules can be absorbed from the hollow of the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells


 * Fats.** Fat molecules are a rich source of energy for the body. The first step in digestion of a fat such as butter is to dissolve it into the watery content of the intestinal cavity. The bile acids produced by the liver act as natural detergents to dissolve fat in water and allow the enzymes to break the large fat molecules into smaller molecules, some of which are fatty acids and cholesterol. The bile acids combine with the fatty acids and cholesterol and help these molecules to move into the cells of the mucosa. In these cells the small molecules are formed back into large molecules, most of which pass into vessels (called lymphatics) near the intestine. These small vessels carry the reformed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.


 * The small intestine**, or small bowel, is sub-divided into three sections, the duodenum, the jejunum, and the ileum. The duodenum is about 1 ft (0.3 m) long and connects with the lower portion of the stomach. When fluid food reaches the duodenum it undergoes further enzymatic digestion and is subjected to pancreatic juice, intestinal juice, and bile. **Accessory organs of digestion**
 * The liver** is located primarily in the right hypochondriac and epigastric regions of the abdomen, just beneath the diaphragm. It is the largest gland in the body. On the surface, the liver is divided into two major lobes and two smaller lobes. The functional units of the liver are lobules with sinusoids that carry blood from the periphery to the central vein of the lobule. Liver functions include the following:
 * secretion
 * synthesis of bile salts
 * synthesis of plasma protein
 * storage
 * detoxification
 * excretion
 * carbohyrate metabolism
 * lipid metabolism
 * protein metabolism
 * filtering

The large intestine extracts water from the waste products of digestion and returns some of it to the bloodstream, along with some salts.. http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd http://people.bu.edu/fgarcia/lectures/gi/index.htm http://www.nlm.nih.gov/medlineplus/digestivesystem.html
 * The pancreas** is a large gland located below the stomach that secretes pancreatic juice into the duodenum via the pancreatic duct. There are three enzymes in pancreatic juice which digest carbohydrates, lipids, and proteins. Amylase, breaks down starch into simple sugars such as maltose, maltase in intestinal juice completes the break down of maltose into glucose. Lipases in pancreatic juice break down fats into fatty acids and glycerol, while proteinases continue the breakdown of proteins into amino acids. The pancreas has both endocrine and exocrine functions. The endocrine portion consists of the islets of Langerhans, which secrete the hormones insulin and glucagon into the blood. The exocrine portion is the major part of the gland. It consists of pancreatic acinar cells that secrete digestive enzymes into tiny ducts interwoven between the cells. Pancreatic enzymes include anylase, trypsin, peptidase, and lipase. Pancreatic secretions are controlled by the hormones secretin and cholecystokinin
 * The gall bladder**, located next to the liver, secretes bile into the duodenum. Which contains bile salts and other substances that help to emulsify (dissolve) fats, which are otherwise insoluble in water Chyme passing from the duodenum next reaches the jejunum of the small intestine.. In the jejunum, the digested products of carbohydrates, fats, proteins, and most of the vitamins, minerals, and **iron** are absorbed. The inner lining of the small intestine is composed of up to five million tiny, finger-like projections called //villi//. The villi increase the rate of absorption of the nutrients into the bloodstream by extending the surface of the small intestine to about five times that of the surface area of the skin. The ileum, is smaller and thinner-walled than the jejunum, and it is the preferred site for **vitamin B**12 absorption and bile acids derived from the bile juice.
 * The large intestine**, or colon, is wider and heavier and much shorter than the small intestine. It rises up on one side of the body (the ascending colon), crosses over to the other side (the transverse colon), descends (the descending colon), forms an s-shape (the sigmoid colon), reaches the rectum, and anus, from which the waste products of digestion (feces or stool), are passed out, along with gas. The muscular rectum, about 5 in (13 cm) long, expels the feces through the anus, which has a large muscular sphincter that controls the passage of waste matter.
 * Vitamins.** Another vital part of our food that is absorbed from the small intestine is the class of chemicals we call vitamins. The two different types of vitamins are classified by the fluid in which they can be dissolved: water-soluble vitamins (all the B vitamins and vitamin C) and fat-soluble vitamins (vitamins A, D, and K).
 * Water and salt.** Most of the material absorbed from the cavity of the small intestine is water in which salt is dissolved. The salt and water come from the food and liquid we swallow and the juices secreted by the many digestive glands.
 * Intestinal Absorption**

http://www.gicare.com/pated/ecdgs46.htm
 * Gastritis**

http://www.abbysenior.com/biology/digestive_system.htm
 * A brief review of structure and functioning of GI system with Questions for review**

Refer to Table 38-4 - 38 -8 (Pg 1377 -1380)
 * Tests of Digestive function**

3 QUIZES on GI system http://digestive.healthcentersonline.com/digestivehealthbasics/?sicontent=0&sicreative=387972253&sitrackingid=3476418&WT.srch=1

Hiatal hernia http://www.healthline.com/adamcontent/hiatal-hernia
 * CHAPTER 39**
 * ALTERATIONS OF DIGESTIVE FUNCTIONS**

GERD http://www.protonix.com/heartburn_and_gerd.htm??SK=2322#gerd

http://www.mercksource.com/portal/site/mercksource/zQzmenuItemzEzConditionPagezAzconditionzEzGERD

DYSPHAGIA http://www.healthline.com/galecontent/dysphagia

pyloric obstruction http://health.howstuffworks.com/define-pyloric-stenosis.htm

http://www.healthline.com/galecontent/duodenal-obstruction

Ileus – 6 pictures gives a better understanding of the condition http://www.healthline.com/adamcontent/intestinal-obstruction

Peptic Ulcer Disease – pictures to illustrate http://www.healthline.com/adamcontent/peptic-ulcer

http://www.usnews.com/usnews/health/digestive-diseases/peptic-ulcer/ulcer.about.htm?s_kwcid=peptic%20ulcer%20disease|408524773

IBD http://www.healthline.com/galecontent/inflammatory-bowel-disease

Chron’s disease – pictures http://www.healthline.com/adamcontent/crohn's-disease

Diverticula http://www.emedicinehealth.com/diverticulosis_and_diverticulitis/article_em.htm http://health.howstuffworks.com/how-to-treat-diverticular-disease.htm

OBESITY An interesting article http://www.pedresearch.org/cgi/content/full/53/5/721 http://www.healthline.com/adamcontent/obesity