Small Intestine Home > Digestive System > Digestive System of the Lower Torso > Intestines > Small Intestine Small Intestine The small intestine is a long, highly convoluted tube in the digestive system that absorbs about 90% of the nutrients from the food we eat. It is given the name “small intestine” because it is only 1 inch in diameter, making it less than half the diameter of the large intestine. The small intestine is, however, about twice the length of the large intestine and usually measures about 10 feet in length. The small intestine winds throughout the abdominal cavity inferior to the stomach. Its many folds help it to pack all 10 feet of its length into such a small body cavity.... Move up/down/left/right: Click compass arrows Rotate image: Click and drag in any direction, anywhere in the frame Identify objects: Click on them in the image Change View Angle Full Small Intestine Description [Continued from above] . . . A thin membrane known as the mesentery extends from the posterior body wall of the abdominal cavity to surround the small intestine and anchor it in place.

Blood vessels, nerves, and lymphatic vessels pass through the mesentery to support the tissues of the small intestine and transport nutrients from food in the intestines to the rest of the body. The small intestine can be divided into 3 major regions: The duodenum is the first section of intestine that connects to the pyloric sphincter of the stomach. It is the shortest region of the small intestine, measuring only about 10 inches in length. Partially digested food, or chyme, from the stomach is mixed with bile from the liver and pancreatic juice from the pancreas to complete its digestion in the duodenum. The jejunum is the middle section of the small intestine that serves as the primary site of nutrient absorption. It measures around 3 feet in length. The ileum is the final section of the small intestine that empties into the large intestine via the ileocecal sphincter. The ileum is about 6 feet long and completes the absorption of nutrients that were missed in the jejunum. Like the rest of the gastrointestinal tract, the small intestine is made up of four layers of tissue. The mucosa forms the inner layer of epithelial tissue and is specialized for the absorption of nutrients from chyme.

Deep to the mucosa is the submucosa layer that provides blood vessels, lymphatic vessels, and nerves to support the mucosa on the surface. Several layers of smooth muscle tissue form the muscularis layer that contracts and moves the small intestines. Finally, the serosa forms the outermost layer of epithelial tissue that is continuous with the mesentery and surrounds the intestines. The interior walls of the small intestine are tightly wrinkled into projections called circular folds that greatly increase their surface area. Microscopic examination of the mucosa reveals that the mucosal cells are organized into finger-like projections known as villi, which further increase the surface area. Each square inch of mucosa contains around 20,000 villi. The cells on the surface of the mucosa also contain finger-like projections of their cell membranes known as microvilli, which further increase the surface area of the small intestine. It is estimated that there are around 130 billion microvilli per square inch in the mucosa of the small intestine. All of these wrinkles and projections help to greatly increase the amount of contact between the cells of the mucosa and chyme to maximize the absorption of vital nutrients.

The small intestine processes around 2 gallons of food, liquids, and digestive secretions every day. To ensure that the body receives enough nutrients from its food, the small intestine mixes the chyme using smooth muscle contractions called segmentations. Segmentation involves the mixing of chyme about 7 to 12 times per minute within a short segment of the small intestine so that chyme in the middle of the intestine is moved outward to the intestinal wall and contacts the mucosa. In the duodenum, segmentations help to mix chyme with bile and pancreatic juice to complete the chemical digestion of the chyme into its component nutrients. Villi and microvilli throughout the intestines sway back and forth during the segmentations to increase their contact with chyme and efficiently absorb nutrients. Once nutrients have been absorbed by the mucosa, they are passed on into tiny blood vessels and lymphatic vessels in the middle of the villi to exit through the mesentery. Fatty acids enter small lymphatic vessels called lacteals that carry them back to the blood supply. All other nutrients are carried through veins to the liver, where many nutrients are stored and converted into useful energy sources.

Chyme is slowly passed through the small intestine by waves of smooth muscle contraction known as peristalsis. Peristalsis waves begin at the stomach and pass through the duodenum, jejunum, and finally the ileum. Each wave moves the chyme a short distance, so it takes many waves of peristalsis over several hours to move chyme to the end of the ileum. Prepared by Tim Taylor, Anatomy and Physiology Instructor Digestive System - Untamed Science Untamed Science Digestive System Review The digestive system plays an important role in the absorption of nutrients into the body. It takes the food we ingest, breaks it down mechanically and chemically in the mouth and stomach. It then absorbs nutrients, fats, proteins and water in the intestines before eliminating the waste through the rectum. Major organs involved in the digestive system include the mouth, stomach, small intestine, large intestine, liver, pancreas. The main steps in the digestive system The digestive system is designed to do a few major things.

They can be grouped into four categories: Ingestion Excretion Following Food from Mouth to Anus To understand how our food is digested in the digestive system, it might be very useful to follow our food along its normal path, starting from the mouth. Imagine for just a second that you’re hungry and your eyes gaze upon a nice home cooked thanksgiving turkey dinner. Your mouth starts to water. The salivary glands in your mouth are triggered to start producing saliva, a compound that will aid in the digestion of the meal. As food enters your mouth, your teeth begin mechanically breaking down the food into small and smaller pieces. The saliva starts to chemically break it down as well. Soon, your conscious mind says, “lets swallow this food.” You swallow it and take another bite. While you’re thinking about your next bite of food, your nervous system is helping to move the bolus (the food package you swallowed), down throat. A small flap of skin called your epiglottis makes sure your food goes down your esophagus. Movements of the smooth muscles, known as peristalsis help move that bolus down your esophagus. When it reaches your stomach, a sphincter opens and dumps the food in.

Inside the stomach, cells start to secrete different acids that help increase acidity to a pH of 2. This strong acidic environment kills most bacteria and starts to chemically break apart the food. Movements of the smooth muscles in the stomach, known as peristalsis mix and churn the food up more. After the food has been well mixed and has a consistency of oatmeal, it is ready to move to the small intestine. At this stage it is known as chyme. To move into the small intestine, chyme must pass through the pyloric sphincter. From here it enters the duodenum, the first part of the small intestine. The liver mixes in bile, which helps break down fats in the food. The pancreas also secretes digestive enzymes that aid in digestion. Most of the nutrients are absorbed from the small intestine and moved into the blood stream via a system of small folds, called vili. After the food moves through the small intestine it enters the large intestine. The large intestine is named for the diameter of the cavity and not for the length. It is actually much shorter than the small intestine. The role of the large intestine is to remove any extra water from the digested material before it is finally excreted.

So there you have it – a basic rundown of what happens to the food we eat from the time we eat it, to when we excrete it. While we didn’t go into detail on all the steps, we would encourage you to explore as much as you can about each step of the process. Review our links below for more detailed explanations of the entire process. Digestive System Vocabulary Terms Anus: located at the end of the digestive system. The function of the anus is to expel feces, and unwanted semi-solid material produced during digestion. Appendix: a pouch like structure of the colon. The appendix is located near the junction of the small and large intestines. It is often referred to as the vermiform appendix or cecal appendix. The appendix is thought to be a vestigial structure in humans (an organ that has lost its original function). Today the appendix is prone to infection is often removed at the first sign of a problem. Ascending Colon: The large intestine can be divided up into different regions. The first section that takes digested material up is the ascending colon. It is smaller in caliber than the cecum, with which it is contiguous. Bile: yellowish, blue and green fluid secreted from the liver.

Bile is sometimes called gall and is stored in the gallbladder between meals. It is secreted into the duodenum to aid int eh process of digestion of lipids via emulsification. Cecum: the beginning of the large intestine. The cecum is a pouch that connects the ileum with eh ascending colon. Chyme: the name given to the partially digested food that leaves the stomach via the pyloric valve into the small intestine (duodenum). Chyme, also known as chymus has the consistency of oatmeal. Descending Colon: the region of the large intestine that moves digested material downward through the left hypochondrium and lumbar regions. Duodenum: the first section of the small intestine. This hollow, jointed tube is only about 10-12 inches long. It connects the stomach to the jejunum and is where most of the chemical digestion takes place. Epiglottis: a small flap of elastic cartilage just below the pharynx that helps direct food down the esophogus and direct air into the lungs.

Without the epiglottis, it would be difficult to Esophagus: a muscular tube that allows food to pass from the pharynx to the stomach. Through peristalsis the esophagus is able to push food from the pharynx to the stomach, even if the individual is standing on their head. Gall Bladder: a small organ that stores bile produced in the liver. It can hold about 50 mL of bile. Ileum: the last region of the small intestine. The ileum follows the other small intestine regions known as the duodenum and the jejunum. After the ileum, digestive material must pass through the ileocecal valve to get to the cecum. Jejunum: the middle section of the small intestine. It is preceded by the duodenum and followed by the ileum. Liver: a vital organ that produces chemicals necessary for digestion. In digestion it is extremely important in producing bile, which helps break down fats. Mouth: Often considered the first step in the digestive process. The chewing action of the mouth serves to mechanically break down food particles. Saliva produced here helps in chemical breakdown of food.

Pancreas: an organ that aids in both the digestive system and the endocrine system. It aids in the digestive system by producing pancreatic juices, which contain digestive enzymes, which pass through the small intestine. These juices help break down carbohydrates, protien and fat in the chyme. Peristalsis: a radially symmetrical contraction of muscles that propagate down a tube. It occurs especially in the esophagus and the stomach. This movement helps the stomach mix up and break down our food. Rectum: the last portion of the large intestine. Human rectums are about 12cm long. Saliva: a substance produced by the salivary glands that aids in digestion. Human saliva is about 98% water. The other 2% consists of electrolytes, mucus, and antibacterial compounds. Salivary Glands: an exocrine gland that produces saliva, and amylase, among others. Sigmoid Colon: a loop of the large intestine about 40 cm long. It is the closest part of the large intestine to the rectum and anus. Stomach: a muscular organ in the gastrointestinal tract that helps churn up and digest food. The stomach lies between the esophagus and the small intestine.

Smooth muscles in the stomach help to break down food mechanically via peristalsis. Transverse Colon: the longest and most movable part of the colon. It is the section of the large intestine just after the ascending colon and just before the descending colon. 1.2 The lower G.I. Tract INTRODUCTION In the previous minicourse we discovered how the stomach is involved in the digestive process. This minicourse deals with the structure and function of the intestines - both small and large. Most of the digestion and absorption of food takes place in the small intestine, whereas the large intestine is intimately involved with water and electrolyte balance as well as with the absorption of some vitamins. Understanding these important structures is a necessary prerequisite for anyone who will be involved in the treatment of patients having intestinal disorders. 1.2 The Lower G.I. Tract On completion of this minicourse you will be able to: Describe the small intestine in terms of: structure how carbohydrates, proteins and fats are digested Describe the large intestine in terms of: principal function Describe the circulation of the abdominal region. Describe the principal factors involved in normal peristalsis of the intestine.

Describe the anatomical basis for intestinal obstruction by intussusception, volvulus, and carcinoma. Describe the anatomy and physiology of the vermiform appendix. Locate on a diagram the two most common positions of the appendix. Describe the pathophysiology of acute appendicitis. Describe the physiological basis of intestinal motility and its effects on water and electrolyte balance. 1 Describe the common dysfunctions of the intestinal tract and the effects of laxatives, cathartics and antidiarrheal agents on - those dysfunctions. SECTION 1 OBJ. 1. Describe the small intestine in terms of: structure how carbohydrates, proteins, and fats are digested. The Small Intestine Structure From the pyloric portion of the stomach, a small muscular valve, the pyloric sphincter, opens into the small intestine. The small intestine, composed of three segments, is about 1 to 1 inches in diameter and approximately 20 feet long (of course this varies with age and with the state of muscular contraction or relaxation).

Although some digestion has already begun (i.e., the mouth and its salivary amylase - initiating carbohydrate digestion; the stomach's pepsin - initiating protein digestion), the majority of digestion and absorption of foodstuffs takes place chiefly in the convoluted tube of the small intestine. The first portion of the small intestine is called the duodenum. This part extends from the pyloric sphincter toward the right. Following some twisting and turning, it finally winds up on the left side of the body. This twisting and turning causes the duodenum to come near the head of the pancreas, which is one of the digestive glands from which the small intestine receives secretory enzymes (carboxy peptidase, amylase, trypsin, chymotrypsin, lipase, ribonuclease and deoxyribonuclease). It should also be noted that near the center of the duodenum are located the tubular ducts from the liver, gallbladder, and pancreas. The next part of the small intestine is called the jejunum, and the third is called the ileum. Except by close internal histological inspection, these two parts cannot be readily separated.

Together the jejunum and the ileum contribute more than 15 feet to the small intestinal length. The ileum ends by opening into the large intestine, or colon, via the ileocecal junction. The junction is located in the lower right quadrant of the abdominal cavity. At this junction is the ileocolic sphincter. It may be helpful to review how much digestion has alreadv taken place before material enters the small intestine. In summary, therefore: Region Carbohydrates Proteins Fats Mouth Salivary amylase (salivary amylase) breaks starches into monosaccharides and dextrins Stomach Some diestion may Pepsin breaks (pepsin-HCl) continue by salivary proteins into amylase peptones and proteases To small intestine To small To small intestine intestine Secretions You will reca]l that when food is sufficientlv liquified in the stoach (into chyme), it is transported to the small intestine via the pyloric sphincter. As this occurs, the presence of fats within the duodenum causes cholecystokinin and secretin to he released which will inhibit further astric activity.

While the chvme is present within the small intestine, glands within this structure begin to secrete different types of digestive enzymes called carbohydrases (amylase, proteases, and lipases or fat splitting r enzymes). The glands responsible for these enzymatic secretions are really pits (found in the mucosal layer of the small intestine) called the crypts of Lieberkuhn. Another set of glands called Brunner's glands are responsible for the secretion of mucus. Collectivey, the intestinal secretions are referred to as succus entericus. Figure 1 depicts the important anatomical relationship between the duodenum and the liver and pancreas. Secretions from each structure (liver and pancreas) empty into the duodenum. Figure 1 Bile, an olive-green liquid produced in the liver at the rate of 250-1000 ml/day, is composed of bile salts, phospholipids, cholesterol, water, and two important pigments: bilirubin and biliverdin. Bile is usually prevented from reaching the duodenum because of a muscular valve (sphincter) at the opening of the bile duct which is kept closed.

There, as bile collects within the bile duct, it will eventually back up and collect within a reservoir structure called the gallbladder. Bile contains bile salts which aid in the digestion of fats through a process called emulsification. Therefore, another action of the presence of fats within the duodenum causing the release of cholecystokinin becomes important. This hormone causes ejection of bile from the gallbladder (by causing gallbladder contraction) and opening of the valve between the common bile duct and the duodenum (sphincter of Oddi). The bile salts coat the surfaces of fat droplets. This keeps the droplets separated from each other and allows the fat-splitting lipases coming from various sources to break up the large fatty molecules. An earlier paragraph mentioned the importance of fat to hormonal regulation and secretion. The acidity of chyme is just as important. This acidity, caused by both HCl and by products of protein digestion from the stomach, will stimulate the secretion of the duodenal hormone secretin which causes secretion of bicarbonate-rich pancreatic juice to promote acid neutralization. The secretions of the pancreas are coming from the exocrine portion (not the endocrine portion, which produces insulin).

Therefore, the enzyme-rich pancreatic juice contains: pancreatic amylase - starch splitting pancreatic lipase - fat splitting pancreatic proteases - protein splitting The important proteases from the pancreas are trypsin and chymotrypsin. Like pepsin from the stomach, trypsin and chymotrypsin are first produced in an inactive form. Thus, trypsin is produced as trypsinogen, which is activated by a protease called enterokinase. Once enterokinase has converted trypsinogen to trypsin, trypsin (a protease) in turn activates another substance, chymotrypsinogen and converts it to chymotrypsin. (If you have managed to keep that straight you are doing well.) Remember that, under normal conditions, the walls of the stomach and small intestine are coated with a protective mucous film. In cases where this protection is incomplete, digestion of the gastric or duodenal wall can result. This can lead to the production of gastric or duodenal ulcers. The pancreatic secretion is under hormonal control by secretin and cholecystokinin, both of which are produced by the duodenum.

The results of the digestive process are summarized below: Carbohydrates Proteins Fats sugars amino acids glycerol fatty acids Absorption Once all this digestion has taken place, the next task for the body becomes one of absorbing these sugars, amino acids, glycerol and fatty acids. The small intestine has been especially modified for this absorptive process. The predominant modification is in the form of villi (finger-like projections) which vastly increase the surface area of the intestine. Embedded within the underlying connective tissue of each villus are an artery, a venule, and a specialized lymphatic vessel called a lacteal. Other modifications for absorption in the small intestine include the microvilli and plicae circulares, both of which further increase the intestinal surface area. The products of carbohydrate and protein digestion enter the villi of the intestinal lining and are absorbed directly into the bloodstream. From this point they are carried to the hepatic portal system of the liver. On the other hand, the end products of fat digestion (glycerol and fatty acids) are picked up by the specialized lymphatic vessels called lacteals. Food materials within the small intestine are moved along by peristaltic contractions.

These contractions are dependent upon action of the smooth involuntary musculature. Digestive Activity Mouth Stomach Small Intestine Villi Carbohydrates Salivary amylase Some digestion may Pancreatic amylase, breaks starches continue via maltase, lactase into monosacchar- salivary amylase sucrase continue to ides, disaccharides facilitate break- and dextrin down of sugars to monosaccharides: l) glucose 2) fructose 3) glactose Proteins Pepsin breaks Trypsin and chymo- Picked up by villi; proteins into trypsin degrades the then to capillaries peptones and proteins missed in then to hepatic proteses stomach. The pep- portal blood and tones and proteses finally to the liver are further broken down to amino acids Fats Bile and pancreatic Picked up by special- lipase break fats ized lymph vessels down into glycerol called lacteals and fatty acids EXERCISE 1 1. Describe the major secretions of the small intestine. 2. Briefly describe how carbohydrates, proteins, and fats are handled during the digestive process.

EXERCISE 1 DISCUSSION OBJECTIVE 1 - Answers 1. The secretions of the small intestine are called the succus entericus. Brunner's glands secrete mucus. Other glands, the crypts of Lieberkuhn, secrete the carbohydrases, proteases and lipases which are the major digestive enzymes of the small intestine. These glands are located in the mucosal layers of the small intestine. 2. Carbohydrate. About 50% of the starches are digested by amylase from the salivary glands while the starches are in the stomach. Maltose is the primary product of this action. The remaining 50% is broken down into disaccharides and monosaccharides by enzymes (carbohydrases) of the small intestine. Carbohydrates are almost completely absorbed in the jejunum. Protein. Proteins are broken down into peptides by pepsin and by the enzymes of the pancreas. These peptide fragments are further digested to free amino acids by carboxypeptidase from the intestinal villi. About 70% to 80% of the ingested protein is absorbed by the end of the jejunum.

Fats. Most fat digestion occurs in the small intestine through the action of pancreatic lipase. Bile salts secreted by the liver speed up lipid digestion by increasing the surface area (emulsification) of the r- lipid droplets accessible to the lipase. As digestion proceeds, the bile salts perform a second important function in promoting aggregation of the liberated materials into micelles of several thousand molecules. These micelles are water soluble. During their passage through the intestinal epithelial cells, the fatty acids are resynthesized into triglycerides which are released into the lacteals of the lymphatic system. SECTION 2 OBJ. 2. Describe the large intestine in terms of: a) principal function c) phases of colonic activity The Large Intestine Click here for a radiology study of the colon The large intestine, which begins at the ileocecal sphincter (ileocolic junction) and terminates at the anus, is a muscular tube approximately five feet long and two and one-half inches in diameter. The first portion of the colon is called the cecum.

The small intestine communicates with the cecum (a blind pouch) via the ileocecal sphincter, which has two important functions: 1) allows substances to pass from the small intestine to the large intestine 2) prevents substances from moving back into the small intestine Dangling down from the cecum is a small coiled tube called the vermiform appendix. An infection of this structure can lead to appendicitis. The cecum opens into the colon (large intestine). Traveling up the right lateral aspect of the abdominal cavity as the ascending colon, it reaches the liver "right turn", also called the "hepatic flexure." Continuing across the abdominal cavity, this part of the colon is called the transverse colon. It continues to the area of the spleen and turns right again to become the descending colon. At the left iliac crest the descending colon becomes contorted to form the S-shaped sigmoid colon. The tail-end of the S projects toward the midline to form the rectum. This structure lies just anterior to the sacrum and the coccyx. The last two or three centimeters of the rectum are modified into anal columns which are longitudinally arranged arteries and veins. This area is quite delicate.

An enlargement and/or inflammation of these veins is called hemorrhoids. Characteristics Distinguishing the Large and Small Intestine Large Intestine Aggregations of lymphatic tissue called Peyer's patches. Has permanent internal folds called plicae circulares. The functions of the large intestine include movement of intestinal contents, absorption of water, vitamins and electrolytes and the formation of feces. As food passes through the ileocecal sphincter, it fills the pouch- like cecum and accumulates within the ascending colon. The digested material is moved by a mechanism called haustral churning. This occurs by filling of a haustrum (out-pocket) to its maximum, followed by a haustral contraction, followed by a filling of a succeeding haustrum. Another mechanism involved in the movement of material through the large intestine is peristalsis. In addition, there is a massive peristaltic contraction, thought to occur three or four times a day, which pushes chyme (feces at this point) from the colon into the rectum. The absorption of food performed by the large intestine is minimal. By the time chyme reaches the large intestine, most of the digestion and absorption is already complete.

The chyme, after remaining within the large intestine for five to ten hours, becomes a semisolid mass called feces, which consist of: water products of bacterial decomposition mucus cell and cell fragments from the alimentary mucosa Following the action of bacteria, chyme is prepared for elimination. Bacteria normally present within the large intestine perform the following functions: Ferment carbohydrate - release hydrogen, carbon dioxide, methane gas Convert remaining proteins into amino acids Transform amino acids into simpler compounds such as: indole; skatole (some of a and c are carried off with feces and contribute to odor) Decompose bilirubin (excreted with bile) into simpler pigments giving feces its color Aids in synthesis of vitamins such as some B vitamins riboflavin, nicotinic acid, folic acid and biotin - as well as vitamin K. The large intestine plays an important role in water balance in that it absorbs a considerable quantity of water and electrolytes (particularly sodium). This absorption occurs for the most part in the cecum and ascending colon. It also absorbs products of bacterial action, including inorganic solutes as well as some vitamins.

OBJECTIVE 2 Questions Longitudinal muscle present called taeniae coli in large intestine. Large intestine has a sacculated wall. Large intestine lacks villi. Large intestine lacks lymphatic aggregation. Occurs through "haustral" contractions and slow peristalsis which moves the chyme along. This massive contraction is thought to occur three or four times per day and acts to push the feces (formerly chyme) into the rectum for elimination. The bacteria convert remaining carbohydrates, convert remaining proteins into amino acids and then convert unabsorbed amino acids into simpler compounds for elimination. Bacteria also decompose bilirubin and acid in the synthesis of several vitamins which are used either in the large intestine or elsewhere in the body (B vitamins and vitamin K). Describe the principal factors involved in normal peristalsis of the intestine. OBJECTIVE 4 Answer Most peristaltic activity of the intestine is mediated via the central nervous system through reflex arcs involving the vagus nerve. These depend on the intrinsic nerves of the intestinal wall for their effect on the smooth muscle cell. The entrance of food into the intestine slightly distends the intestine and it reflexly begins a series of contractions that result in a peristaltic wave.

The wave is propagated by the ganglion cells in the gut wall. The majority of intestinal activity is probably mediated by mechanical factors rather than hormonal. This is somewhat different from gastric motility which is influenced by gastric and duodenal secretions. SECTION 5 Describe the three types of intestinal obstruction which were presented in this minicourse. OBJECTIVE 5 Answer Intussusception - in which one segment of intestine (small or large) becomes invaginated into another segment of intestine. Volvulus - in which there is a clockwise rotation of the intestine. Carcinoma - in which the inward growth of the malignancy creates a blockage and the outward growth impinges on adjacent gastrointestinal organs and further compromises the lumen of the gut. OBJ. 6. Describe the anatomy and physiology of the vermiform appendix. OBJ. 7. Describe the two most common positions of the appendix. OBJ. 8. Describe the pathophysiology of acute appendicitis. The Appendix Hanging from the cecum is a small organ containing a large amount of lymphatic tissue. This worm-like structure, about three to five inches long, is called the vermiform appendix.

It is located just below the ileocolic junction on the posteromedial aspect of the cecum. The appendix has a mesentery of its own called the mesoappendix. It is really a portion of the mesentery attachment to the small intestine. Thus, the appendix can be considered to be freely mobile, because the mesoappendix exerts very little restraint. It is not uncommon for the lower one-third of the structure to be devoid of mesentery, thus adding to its mobility. The appendix is located in the right lower quadrant beneath McBurney's point. The end of the appendix, which is devoid of mesentery, is thus highly movable and may adopt various positions depending on its attachment to the cecum. Following is a list of the most common positions: located against pelvic wall by hanging into pelvis located in retrocecal fossa - coiled behind the cecum anterior or posterior to ileum located along lateral side of cecum The arterial supply to the appendix is via a branch of the posterior cecal artery known as the appendicular artery. The posterior cecal vein drains the appendix. The appendix has a large amount of lymphatic tissue.

Because of this, it is conjectured that this organ may be involved in the immunological process. The lymph that is drained from this structure eventually reaches the superior mesenteric nodes. The appendix, it should be remembered, is a blind tube which hangs down from the cecum. Because of this, it accumulates food and bacteria. Normally, this is not a problem. Sometimes, however, the appendiceal-cecal orifice, which is the attachment of the appendix to the cecum, becomes occluded. Because of this the structure cannot cleanse itself. Inflammation may result leading to pain in the right lower quadrant. In most instances surgery is recommended because appendicular rupture could result in peritonitis. Acute Appendicitis As describe above, obstruction of the appendiceal lumen can lead to a condition called acute appendicitis. Interference with the vascular supply to the structure, however, may be another causative factor. These two etiological factors probably cause the wall of the appendix to lose its ability to resist the invasion of bacteria which are potential pathogens. Some of the more common organisms found within the diseased appendix are various streptococci as well as the bacilli normally found in the colon.

Acute appendicitis can be classified as follows: Catarrhal - in which the submucosal and mucosal layers become involved with inflammation. Diffuse - in which mucosal layers of the catarrhal type are involved as well as the serosal and muscular layers. Gangrenous - the involvement of the structures described in diffuse appendicitis plus the added condition of necrosis. The more salient points concerning the pathophysiology of acute appendicitis are as follows: The initial event in acute appendicitis is blockage of the appendiceal-cecal orifice. This blockage most commonly is due to a fecalith (in intestinal concretion formed around a center of fecal matter) but it may in some cases be due to other causes. The lumen of the appendix ordinarily receives and expels cecal contents during the active phases of the cecum. The intestinal contents, particularly the large bowel, contain a great quantity of active normal bacterial flora that can become pathogenic under the proper conditions. The appendiceal structure is similar to the remainder of the gut in that it has a mucous-secreting lining in its lumen, submucosal lymphatic tissue and a muscular coat.

After blockage occurs, the mucosal secretion continues and accumulates in the lumen until the appendix is distended sufficiently to compromise its blood supply. The bacterial flora normally present now become pathogenic because they are not being flushed out by intestinal action and conditions are ideal for growth. The appendix is now infected. The accumulation of mucus and bacteria cause an intense inflammatory reaction, known as the "hot" appendix. If not treated, the compromised blood supply condition leads to gangrene and/or rupture of the wall of the appendix which can result in peritonitis and eventually can lead to death! OBJECTIVES 6, 7 AND 8 Questions Draw the appendix and its surrounding structures. Describe the two most common positions of the appendix. Describe the three major classes of acute appendicitis. Enumerate the basic aspects concerning the pathophysiology of acute appendicitis. OBJECTIVES 6, 7 & 8 Answers The most common positions of the appendix are hanging in pelvic region against pelvic wall coiled behind the cecum The three major classes of appendicitis are the catarrhal, diffuse and gangrenous.

The catarrhal has the least complications involving only the submucosal and mucosal layers whereas the gangrenous variety shows tissue necrosis. Blockage of appendiceal orifice Entrapment of normal intestinal bacterial flora which can become pathogenic. Mucous secretion continues and accumulation occurs because of blockage. Blood supply becomes compromised. Accumulation of mucous and bacteria cause inflammatory reaction. If not treated - rupture peritonitis - perhaps death. SECTION 7 OBJ 9. Describe the physiological basis of intestinal motility and its effects on water and electrolyte balance. OBJ. 10. Describe common dysfunctions of the intestinal tract and the effects of laxatives, cathartics and antidiarrheal agents on those dysfunctions. Motility of the Alimentary Canal Normal swallowing is accomplished by peristaltic movements. These are initiated by reflexes arising from voluntary contractions of the muscles of the pharynx. As the food bolus is pressed against the posterior pharyngeal wall the pressure in the pharynx rises and the muscles contract to seal off the larynx. The contractions of the Laryngeal muscles pushes the food bolus downward into the esophagus which has a lower pressure.

The wave of contraction thus initiated voluntarily sweeps down the esophagus, propelling the food bolus along. This reflex is subserved by the voluntary system in the mouth, pharynx and upper one-third of the esophagus. The contraction wave in the lower two-thirds of the esophagus is an autonomic reflex (parasympathetic - vagus). During this process the larynx is elevated against the epiglottis and the posterior wall of the pharynx moves forward to complete sealing off the laryngeal opening. The soft palate is also reflexively elevated and comes in apposition to the advancing posterior pharyngeal wall to seal off the nose. Dysphagia (difficulty in swallowing) may result from a defect or disorder in any part of the above mechanisms. Mechanical obstruction may also interfere with propelling the food bolus. Emotional conflicts in a patient may also interfere with the function of this system. The motility of the lower esophagus may be altered by disease processes in the muscular wall or diseases that interfere with the intrinsic nervous system (diseases that either paralyze it or erode it so that there are breaks in its continuity).

As food bolus enters the stomach, a small amount is propelled on through the stomach into the duodenum. This apparently acts as a signal for the pyloric sphincter to close. During the quiescent phases, the pyloric sphincter is relaxed. It contracts in response to acidic stomach contents reaching the duodenum. The remainder of the ingested food enters the stomach, which dilates progressively to accommodate the food. There now follows a period of propulsive churning movements. Next, a series of peristaltic waves begins near the pyloric end of the stomach and continues over the duodenal wall. These waves also begin to extend up onto the body of the stomach. They continue until the stomach is empty, at which point all activity ceases. Except when there is a very large intake of food, most of the passage of food and churning action takes place along the lesser curvature. The lesser curvature, called magenstrasse (great street), is the area of most of the gastric activity. Recall the prominence of ulcers along the lesser curvature. Gastric emptying is retarded when the duodenum receives low pH solutions or hypertonic solutions of sugar, sodium chloride or fats.

Gastric emptying is accelerated, however, by the administration of alkaline solutions. Vigorous peristaltic activity of the stomach is associated with normal hunger. Nausea is accompanied by a cessation of gastric activity and simultaneous sustained contraction of the duodenum. That the reactions of nausea and hunger are mediated by the central nervous system is evidenced by the fact that they both occur in the gastrectomized patient. Motility of the intestinal tract may vary from a hypermotive phase to a hypomotile phase to a complete cessation of activity. These changes in normal colonic function may be induced by emotional stress, humoral agents, defective innervation (both motor and sensory), diseases in other systems and intrinsic disease of the colon itself. The colon has two main functions, the absorption of water and crystalloids and the storage of fecal material until it can be evacuated. The material that enters the colon from the ileum is a highly fluid mass. Most of the activity of the colon is a slow, phasic, kneading type of contraction which facilitates absorption. At periodic intervals, usually after a meal, a period of mass peristalsis occurs which moves the colonic contents into the rectum.

Interference with intestinal motility will interfere with the normal functions of the colon, especially the function of water resorption. This causes a highly fluid fecal mass which fills and distends the rectum and causes the defecation reflex to occur. Dysfunction of the colon may also cause excessively long retention of the fecal material, resulting in constipation. Dysfunction of the colon upsets the transfer of water across the various membranes. Here also the passage of water is by passive osmotic diffusion and depends on the various other osmotic pressures exerted across the membrane. Abnormal activity of the colon (either hyper or hypo) affects this diffusion process in several ways. It affects the passage of water across the intestinal mucosa, from the interstitial fluid of the colon and alters the exchange of fluid across the capillary beds of the colon. The loss of large amounts of fluid in diarrhea causes a shifting of the water and electrolyte balance in the various compartments of the body. Fluid lost into the lumen of the gut due to dysfunction of the mucosa and muscularis layers is drawn from the interstitial spaces of the colon, which upsets the fluid exchange at the capillary bed.

This causes fluid to leave the plasma and enter the interstitial spaces of the colon. Recall that ionic transfer is also passive and occurs in the direction of fluid flow. Therefore, loss of fluid into the lumen of the colon causes both water and electrolytes to leave the blood and enter the tissue spaces to be ultimately lost across the colonic membranes into the lumen. As the blood electrolyte supply is depleted, other water and electrolyte stores in the body begin to release fluid and ions into the plasma in an attempt to restore equilibrium. Nausea is an unpleasant sensation. It is usually somewhat ill- defined in extent but located in the epigastric region. It is a painless sensation and may be accompanied by a desire to vomit. The nauseous phase is often followed by vomiting, but not necessarily so. It may be accompanied by hypersalivation and an unpleasant taste sensation. Nausea is accompanied by cessation of gastric phasic contractions and there is a simultaneous sustained contraction or spasm of the duodenum. The gastroduodenal motor patterns are probably only peripheral manifestations of a disturbance arising in the brain.

Some causes of vomiting are: stimulation of the gag reflex areas in the oral pharynx infections of the stomach brainstem tumors drugs Vomiting, or emesis, is the expulsion of the material in the stomach and upper intestinal tract through the mouth. It is a complex reflex action coordinated through the medulla. It is usually preceded by an increase in salivation, sweating and by an increased heart rate and feelings of nausea. These signs are characteristic of a general discharge of the autonomic nervous system. Emesis begins with a deep inhalation, closure of the glottis and elevation of the soft palate. The abdominal and thoracic muscles are contracted, raising the intraabdominal pressure, and this is transmitted to the stomach. The gastroesophageal sphincter relaxes and the increased abdominal pressure pushes the stomach contents into the esophagus. When the pressure is sufficiently great, the contents in the esophagus are forced through the hypopharyngeal sphincter to the mouth. Vomiting is accompanied by strong contractions of the upper part of the small intestine. This tends to force some of the contents of the intestine back into the stomach. Input into the vomiting center (of the medulla) is from receptors throughout the body.

The primary stimuli are tactile stimuli of the back of the throat, e.g., a finger thrust into the throat, gross distention of the stomach or duodenum increased pressure in the skull, rotating movements of the head producing dizziness, and excruciating pain. Some chemical agents, e.g., copper sulfate, also induce vomiting. Such chemicals act on chemoreceptors in the brain or parts of the G.I. tract. Too much vomiting can lead to excessive loss of fluid and salts from the body and can cause severe upset of the acid-base balance. Gastroenteritis Food poisoning due to an infection or intoxication usually does not cause major pathological changes in the tissues. Those due to infections by Salmonella typhosa, causing typhoid fever, lead to a great increase in monocytes. There is particular involvement of the lymphatic tissue of the intestinal tract, principally Peyer's patches in the terminal ileum, which may lead to ulceration and necrosis. Erosion of adjacent blood vessels may cause intestinal hemorrhage. Lesions are usually confined to mucosa and submucosa, but may penetrate the other layers, leading to perforation.

Healing of the intestinal lesions usually does not give rise to appreciable scarring or stricture formation. Nonbacterial gastroenteritis is thought to be caused by viruses. It does not usually present any significant pathological changes. Certain drugs which stimulate gastrointestinal peristalsis are used as cathartics. Physicians seldom prescribe these drugs, since the indications for their use are limited. More commonly, the health professional is faced with the problem of misuse of these drugs due to their easy accessibility in the form of over-the-counter preparations. A cathartic is an agent which causes an increased elimination of fecal material from the bowel - three types are: irritant - increases G.I. motility bulk - increases water content of stools (or decreases water reabsorption) surface active - makes feces slippery Drugs which harden the stools are referred to an antidiarrheal agents. These mainly act to decrease fecal transit time, allowing for a greater reabsorption of water, and thus hardening of the stools. EXERCISE 7 OBJECTIVES 9 & 10 Questions What effect would prolonged vomiting have on: a. digestion b.

water balance in the body Describe the interrelationships of intestinal (large and small) motility and water and electrolyte balance. Describe the effects of each of the following agents on intestinal motility: a. cathartics b. antidiarrheal agents EXERCISE 7 DISCUSSION OBJECTIVES 9 & 10 Answers a. Along with the water loss would be a loss of saliva and gastric juice. These are acidic, so this loss could result in increased alkalinity (higher pH) of remaining fluids which would affect body functions. b. Water balance would be affected because as the fluid in the stomach was expelled, more water would diffuse from the extracellular fluid to replace it. This results in dehydration. Chyme entering the duodenum from the stomach is almost isotonic. In the small intestine, Wa+ and other ions derived from the diet and gastrointestinal secretions are actively transported across the intestinal membranes. In addition, monosaccharides and amino acids are actively transported. These active transport mechanisms make the blood plasma hypertonic to the lumen contents. Since the passage of water is by passive diffusion, water moves from gut to the plasma in an attempt to restore equilibrium.

If the gut contents become hypertonic, there is a net movement of water into the lumen of the gut. Gut motility greatly affects absorption process. Hyperactivity of the gut decreases the time available for absorption of salts, monosaccharides and amino acids, thus leaving large quantities of water in the gut. Hyperactivity may also create a hypertonic solution in the feces, thus drawing more water out of the plasma. Students: Read this paragraph carefully, in light of what you have read! Are there any typographical errors? Some cathartic agents increase the fecal transit time, thus decreasing the water reabsorption. Antidiarrheal agents harden the stools, usually by a mechanism involving a decrease in fecal transit time, which allows more water to be reabsorbed from the fecal matter. XI. Splanchnology. 2g. The Small Intestine. Gray, Henry. 1918. Anatomy of the Human Body. Aggregated lymphatic nodules. FIG. 1062 An intestinal gland from the human intestine.

(Flemming.) ( See enlarged image ) The circular folds (plicæ circulares [Kerkringi]; valvulæ conniventes; valves of Kerkring) are large valvular flaps projecting into the lumen of the bowel. They are composed of reduplications of the mucous membrane, the two layers of the fold being bound together by submucous tissue; unlike the folds in the stomach, they are permanent, and are not obliterated when the intestine is distended. The majority extend transversely around the cylinder of the intestine for about one-half or two-thirds of its circumference, but some form complete circles, and others have a spiral direction; the latter usually extend a little more than once around the bowel, but occasionally two or three times. The larger folds are about 8 mm. in depth at their broadest part; but the greater number are of smaller size. The larger and smaller folds alternate with each other. They are not found at the commencement of the duodenum, but begin to appear about 2.5 or 5 cm. beyond the pylorus.

In the lower part of the descending portion, below the point where the bile and pancreatic ducts enter the intestine, they are very large and closely approximated. In the horizontal and ascending portions of the duodenum and upper half of the jejunum they are large and numerous, but from this point, down to the middle of the ileum, they diminish considerably in size. In the lower part of the ileum they almost entirely disappear; hence the comparative thinness of this portion of the intestine, as compared with the duodenum and jejunum. The circular folds retard the passage of the food along the intestines, and afford an increased surface for absorption. 20 FIG. 1063 Vertical section of a human aggregated lymphatic nodule, injected through its lymphatic canals. a. Villi with their chyle passages. b. Intestinal glands. c. Muscularis mucosæ. d. Cupola or apex of solitary nodule. e. Mesial zone of nodule. f. Base of nodule. g. Points of exit of the lacteals from the villi, and entrance into the true mucous membrane. h.

Retiform arrangement of the lymphatics in the mesial zone. i. Course of the latter at the base of the nodule. k. Confluence of the lymphatics opening into the vessels of the submucous tissue. l. Follicular tissue of the latter. ( See enlarged image ) The intestinal villi (villi intestinales) are highly vascular processes, projecting from the mucous membrane of the small intestine throughout its whole extent, and giving to its surface a velvety appearance. They are largest and most numerous in the duodenum and jejunum, and become fewer and smaller in the ileum. 21 FIG. 1064 Transverse section through the equatorial plane of three aggregated lymphatic nodules from the rabbit. ( See enlarged image ) Structure of the villi ( Figs. 1059, 1060 ).The essential parts of a villus are: the lacteal vessel, the bloodvessels, the epithelium, the basement membrane, and the muscular tissue of the mucosa, all being supported and held together by retiform lymphoid tissue.

22 The lacteals are in some cases double, and in some animals multiple, but usually there is a single vessel. Situated in the axis of the villus, each commences by dilated cecal extremities near to, but not quite at, the summit of the villus. The walls are composed of a single layer of endothelial cells. 23 The muscular fibers are derived from the muscularis mucosæ, and are arranged in longitudinal bundless around the lacteal vessel, extending from the base to the summit of the villus, and giving off, laterally, individual muscle cells, which are enclosed by the reticulum, and by it are attached to the basement-membrane and to the lacteal. 24 The bloodvessels (Fig. 1061) form a plexus under the basement membrane, and are enclosed in the reticular tissue. 25 These structures are surrounded by the basement membrane, which is made up of a stratum of endothelial cells, and upon this is placed a layer of columnar epithelium, the characteristics of which have been described. The retiform tissue forms a net-work (Fig.

1060) in the meshes of which a number of leucocytes are found. 26 FIG. 1065 No caption. ( See enlarged image ) FIG. 1066 No caption. ( See enlarged image ) FIG. 1067 No caption. ( See enlarged image ) FIG. 1068 No caption. ( See enlarged image ) FIG. 1069 No caption. ( See enlarged image ) FIG. 1070 Diagrams showing the arrangement and variations of the loops of the mesenteric vessels for various segments of the small intestine of average length. Nearest the duodenum the mesenteric loops are primary, the vasa recta are long and regular in distribution, and the translucent spaces (lunettes) are extensive. Toward the ileocolic junction, secondary and tertiary loops are observed, the vessels are smaller and become obscured by numerous fat-tabs. (After Monks.) ( See enlarged image ) The intestinal glands (glandulæ intestinales [Lieberkühni]; crypts of Lieberkühn) (Fig.

1062) are found in considerable numbers over every part of the mucous membrane of the small intestine. They consist of minute tubular depressions of the mucous membrane, arranged perpendicularly to the surface, upon which they open by small circular apertures. They may be seen with the aid of a lens, their orifices appearing as minute dots scattered between the villi. Their walls are thin, consisting of a basement membrane lined by columnar epithelium, and covered on their exterior by capillary vessels. 27 The duodenal glands (glandulæ duodenales [Brunneri]; Brunners glands) are limited to the duodenum (Fig. 1058), and are found in the submucous areolar tissue. They are largest and most numerous near the pylorus, forming an almost complete layer in the superior portion and upper half of the descending portions of the duodenum. They then begin to diminish in number, and practically disappear at the junction of the duodenum and jejunum.

They are small compound acinotubular glands consisting of a number of alveoli lined by short columnar epithelium and opening by a single duct on the inner surface of the intestine. 28 The solitary lymphatic nodules (noduli lymphatici solitarii; solitary glands) are found scattered throughout the mucous membrane of the small intestine, but are most numerous in the lower part of the ileum. Their free surfaces are covered with rudimentary villi, except at the summits, and each gland is surrounded by the openings of the intestinal glands. Each consists of a dense interlacing retiform tissue closely packed with lymph-corpuscles, and permeated with an abundant capillary network. The interspaces of the retiform tissue are continuous with larger lymph spaces which surround the gland, through which they communicate with the lacteal system. They are situated partly in the submucous tissue, partly in the mucous membrane, where they form slight projections of its epithelial layer (see Fig. 1082 ).

29 The aggregated lymphatic nodules (noduli lymphatici aggregati; Peyers patches; Peyers glands; agminated follicles; tonsillæ intestinales) (Fig. 1063) form circular or oval patches, from twenty to thirty in number, and varying in length from 2 to 10 cm. They are largest and most numerous in the ileum. In the lower part of the jejunum they are small, circular, and few in number. They are occasionally seen in the duodenum. They are placed lengthwise in the intestine, and are situated in the portion of the tube most distant from the attachment of the mesentery. Each patch is formed of a group of solitary lymphatic nodules covered with mucous membrane, but the patches do not, as a rule, possess villi on their free surfaces. They are best marked in the young subject, become indistinct in middle age, and sometimes disappear altogether in advanced life. They are freely supplied with bloodvessels (Fig. 1064), which form an abundant plexus around each follicle and give off fine branches permeating the lymphoid tissue in the interior of the follicle.

The lymphatic plexuses are especially abundant around these patches. 30 FIG. 1071 The myenteric plexus from the rabbit. X 50. ( See enlarged image ) FIG. 1072 The plexus of the submucosa from the rabbit. X 50. ( See enlarged image ) Vessels and Nerves.The jejunum and ileum are supplied by the superior mesenteric artery, the intestinal branches of which, having reached the attached border of the bowel, run between the serous and muscular coats, with frequent inosculations to the free border, where they also anastomose with other branches running around the opposite surface of the gut. From these vessels numerous branches are given off, which pierce the muscular coat, supplying it and forming an intricate plexus in the submucous tissue. From this plexus minute vessels pass to the glands and villi of the mucous membrane. The veins have a similar course and arrangement to the arteries. The lymphatics of the small intestine (lacteals) are arranged in two sets, those of the mucous membrane and those of the muscular coat.

The lymphatics of the villi commence in these structures in the manner described above. They form an intricate plexus in the mucous and submucous tissue, being joined by the lymphatics from the lymph spaces at the bases of the solitary nodules, and from this pass to larger vessels at the mesenteric border of the gut. The lymphatics of the muscular coat are situated to a great extent between the two layers of muscular fibers, where they form a close plexus; throughout their course they communicate freely with the lymphatics from the mucous membrane, and empty themselves in the same manner as these into the origins of the lacteal vessels at the attached border of the gut. 31 The nerves of the small intestines are derived from the plexuses of sympathetic nerves around the superior mesenteric artery. From this source they run to the myenteric plexus (Auerbachs plexus) (Fig. 1071) of nerves and ganglia situated between the circular and longitudinal muscular fibers from which the nervous branches are distributed to the muscular coats of the intestine.

From this a secondary plexus, the plexus of the submucosa (Meissners plexus) (Fig. 1072) is derived, and is formed by branches which have perforated the circular muscular fibers. This plexus lies in the submucous coat of the intestine; it also contains ganglia from which nerve fibers pass to the muscularis mucosæ and to the mucous membrane. The nerve bundles of the submucous plexus are finer than those of the myenteric plexus. 32 Note 168. Treves states that, in one hundred cases, the average length of the small intestine in the adult male was 22 feet 6 inches, and in the adult female 23 feet 4 inches: but that it varies very much, the extremes in the male being 31 feet 10 inches, and 15 feet 6 inches. He states that in the adult the length of the bowel is independent of age, height, and weight.

[ back ] Digestive System - humans, body, used, water, process, plants, type, chemical, form Digestive System Digestive system Photo by: krishnacreations The digestive system is a group of organs responsible for the conversion of food into nutrients and energy needed by the body. In humans, the digestive system consists of the mouth, esophagus, stomach, and small and large intestines. The digestive tube made up by these organs is known as the alimentary canal. Several glands—salivary glands, liver, gall bladder, and pancreas—also play a part in digestion. These glands secrete digestive juices containing enzymes that break down the food chemically into smaller molecules that are more easily absorbed by the body. The digestive system also separates and disposes of waste products ingested with the food. Ingestion Food taken into the mouth is first broken down into smaller pieces by the teeth. The tongue then rolls these pieces into balls called boluses. Together, the sensations of sight, taste, and smell of the food cause the salivary glands, located in the mouth, to produce saliva. An enzyme in the saliva called amylase begins the breakdown of carbohydrates (starch) into simple sugars.

The bolus, which is now a battered, moistened, and partially digested ball of food, is swallowed, moving to the pharynx (throat) at the back of the mouth. In the pharynx, 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. Its job is to move the bolus into the stomach. Food is moved through the esophagus (and other parts of the alimentary canal) by a wavelike muscular motion known as peristalsis (pronounced pear-i-STALL-sis). This motion consists of the alternate contraction and relaxation of the smooth muscles lining the tract. Words to Know Alimentary canal: Tube formed by the pharynx, esophagus, stomach, and intestines through which food passes. Amylase: Digestive enzyme that breaks down carbohydrates to simple sugars. Bile: Bitter, greenish liquid produced in the liver and stored in the gall bladder that dissolves fats.

Bolus: Battered, moistened, and partially digested ball of food that passes from the mouth to the stomach. Carbohydrate: A compound consisting of carbon, hydrogen, and oxygen found in plants and used as a food by humans and other animals. Chyme: Thick liquid of partially digested food passed from the stomach to the small intestine. Enzyme: Any of numerous complex proteins that are produced by living cells and spark specific biochemical reactions. Esophagitis: Commonly known as heartburn, an inflammation of the esophagus caused by gastric acids flowing back into the esophagus. Gastric juice: Digestive juice produced by the stomach wall that contains hydrochloric acid and the enzyme pepsin. Pepsin: Digestive enzyme that breaks down protein. Peristalsis: Wavelike motion of the digestive system that moves food through the system. Proteins: Large molecules that are essential to the structure and functioning of all living cells. Ulcer: Inflamed sore or lesion on the skin or a mucous membrane of the body. Villi: Fingerlike projections found in the small intestine that increase the absorption area of the intestine.

At the junction of the esophagus and stomach there is a powerful muscle—the esophageal sphincter—that acts as a valve to keep food and stomach acids from flowing back into the esophagus and mouth. Digestion in the stomach Chemical digestion begins in the stomach. The stomach is a large, hollow, pouched-shaped muscular organ. Food in the stomach is broken down by the action of gastric juice, which contains hydrochloric acid and pepsin (an enzyme that digests protein). The stomach begins its production of gastric juice while food is still in the mouth. Nerves from the cheeks and tongue are stimulated and send messages to the brain. The brain in turn sends messages to nerves in the stomach wall, stimulating the secretion of gastric juice before the arrival of food. The second signal for gastric juice production occurs when food arrives in the stomach and touches the lining. Gastric juice is secreted from the linings of the stomach walls, along with mucus that helps to protect the stomach lining from the action of the acid. Three layers of powerful stomach muscles churn food into a thick liquid called chyme (pronounced KIME).

From time to time, chyme is passed through the pyloric sphincter, the opening between the stomach and the small intestine. Digestion and absorption in the small intestine The small intestine is a long, narrow tube running from the stomach to the large intestine. The small intestine is greatly coiled and twisted. Its full length is about 20 feet (6 meters). The small intestine is subdivided into three sections: the duodenum (pronounced do-o-DEE-num), the jejunum (pronounced je-JOO-num), and the ileum (pronounced ILL-ee-um). The duodenum is about 10 inches (25 centimeters) long and connects with the lower portion of the stomach. When chyme reaches the duodenum, it is further broken down by intestinal juices and through the action of the pancreas and gall bladder. The pancreas is a large gland located below the stomach that secretes pancreatic juice into the duodenum through the pancreatic duct. There are three enzymes in pancreatic juice that break down carbohydrates, fats, and proteins. The gall bladder, located next to the liver, stores bile produced by the liver.

While bile does not contain enzymes, it contains bile salts that help to dissolve fats. The gall bladder empties bile into the duodenum when chyme enters that portion of the intestine. The jejunum is about 8.2 feet (2.5 meters) long. The digested carbohydrates, fats, proteins, and most of the vitamins, minerals, and iron are absorbed in this section. The inner lining of the small intestine is composed of up to five million tiny, fingerlike projections called villi. The villi increase the rate of absorption of nutrients into the bloodstream by greatly increasing the surface area of the small intestine. The ileum, the last section of the small intestine, is the longest, measuring 11 feet (3.4 meters). Certain vitamins and other nutrients are absorbed here. Absorption and elimination in the large intestine The large intestine is wider and heavier than the small intestine. However, it is much shorter—only about 5 feet (1.5 meters) long.

It rises up on the right side of the body (the ascending colon), crosses over to the other side underneath the stomach (the transverse colon), descends on the left side, (the descending colon), then forms an s-shape (the sigmoid colon) before reaching the rectum and anus. The muscular rectum, about 6 inches (16 centimeters) long, expels feces (stool) through the anus, which has a large muscular sphincter that controls the passage of waste matter. The large intestine removes water from the waste products of digestion and returns some of it to the bloodstream. Fecal matter contains undigested food, bacteria, and cells from the walls of the digestive tract. Millions of bacteria in the large intestine help to produce certain B vitamins and vitamin K. These vitamins are absorbed into the bloodstream along with the water. Disorders of the digestive system Among the several disorders that affect the digestive system are esophagitis (heartburn) and ulcers. Esophagitis is an inflammation of the esophagus caused by gastric acids flowing back into the esophagus. Mild cases of this condition are usually treated with commercial antacids.

Stomach ulcers are sores that form in the lining of the stomach. They may vary in size from a small sore to a deep cavity. Ulcers that form in the lining of the stomach and the duodenum are called peptic ulcers because they need stomach acid and the enzyme pepsin to form. Duodenal ulcers are the most common type. They tend to be smaller than stomach ulcers and heal more quickly. Any ulcer that heals leaves a scar. Until the early 1990s, the medical community generally believed that ulcers were caused by several factors, including stress and a poor diet. However, medical researchers soon came to believe that a certain bacterium that can live undetected in the mucous lining of the stomach was responsible. This bacterium irritated and weakened the lining, making it more susceptible to damage by stomach acids. The human digestive process. (Reproduced by permission of The Gale Group .) It is believed that about 80 percent of stomach ulcers may be caused by the bacterial infection. With this discovery, ulcer patients today are being treated with antibiotics and antacids rather than special diets or expensive medicines. Also read article about Digestive System from Wikipedia User Contributions:

Question: What name is given to the first, horseshoe-shaped section of the human intestine?
Answer: DUODENUM