Terminal Ileum - Anatomy Pictures and Information Home > Digestive System > Digestive System of the Lower Torso > Intestines > Terminal Ileum Terminal Ileum The terminal ileum is the distal end of the small intestine that intersects with the large intestine. It contains the ileocecal sphincter, a smooth muscle sphincter that controls the flow of chyme into the large intestine. Anatomy The terminal ileum is located on the right side of the abdominopelvic cavity in the umbilical and hypogastric regions. It is a tube about 1.25 to 1.5 inches (3 to 4 cm) long at the end of the ileum and terminates at the ileocecal sphincter.... 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 2D Interactive 3D Rotate & Zoom Change Anatomical System Change View Angle Full Terminal Ileum Description [Continued from above] . . .

The ileocecal sphincter is a band of smooth muscle that controls the flow of chyme from the ileum into the cecum of the large intestine. Physiology Chyme is thoroughly processed by the duodenum, jejunum, and ileum before it enters the terminal ileum. It is then stored in the hollow lumen of the terminal ileum as it awaits the opening of the ileocecal sphincter. Small masses of chyme are pushed into the cecum by waves of peristaltic contraction of the walls of the terminal ileum coordinated with the opening of the ileocecal sphincter. While the chyme is stored, Peyer’s patches lining the walls of the terminal ileum examine the contents of the chyme for any potentially dangerous pathogens. Histology The walls of the terminal ileum are made of four distinct tissue layers surrounding the hollow lumen at its center. The innermost layer, the mucosa, contains epithelial cells whose function is specialized for the absorption of nutrients from chyme in the lumen. Masses of lymphatic tissue known as Peyer’s patches dot the surface of the mucosa to detect the presence of pathogens in the chyme.

Surrounding the mucosa is the submucosa layer that contains the nerves and blood vessels, which support the other tissue layers of the terminal ileum. The muscularis layer surrounds the submucosa and contains bands of smooth muscle that contract in wave of peristalsis to move food through the terminal ileum and into the cecum. Finally, the serosa forms the outermost layer of the terminal ileum. Serosa is made of a smooth layer of simple squamous epithelial tissue and secretes a slippery liquid known as serous fluid. Serosa and serous fluid give the terminal ileum a slick, slimy surface to protect it from friction between organs and the walls of the abdominopelvic cavity. Prepared by Tim Taylor, Anatomy and Physiology Instructor The Colon (Human Anatomy): Picture, Function, Definition, Problems Human Anatomy The colon is also called the large intestine. The ileum (last part of the small intestine) connects to the cecum (first part of the colon) in the lower right abdomen. The rest of the colon is divided into four parts: • The ascending colon travels up the right side of the abdomen. • The transverse colon runs across the abdomen.

• The descending colon travels down the left abdomen. • The sigmoid colon is a short curving of the colon, just before the rectum. The colon removes water, salt, and some nutrients forming stool. Muscles line the colon's walls, squeezing its contents along. Billions of bacteria coat the colon and its contents, living in a healthy balance with the body. Colon Conditions Colitis: Inflammation of the colon. Inflammatory bowel disease or infections are the most common causes. Diverticulosis : Small weak areas in the colon's muscular wall allow the colon's lining to protrude through, forming tiny pouches called diverticuli. Diverticuli usually cause no problems, but can bleed or become inflamed or infected. Diverticulitis : When diverticuli become inflamed or infected, diverticulitis results. Abdominal pain, fever, and constipation are common symptoms. Colon bleeding (hemorrhage): Multiple potential colon problems can cause bleeding. Rapid bleeding is visible in the stool, but very slow bleeding might not be. Inflammatory bowel disease : A name for either Crohn's disease or ulcerative colitis. Both conditions can cause colon inflammation (colitis).

Crohn's disease : An inflammatory condition that usually affects the colon and intestines. Abdominal pain and diarrhea (which may be bloody) are symptoms. Ulcerative colitis : An inflammatory condition that usually affects the colon and rectum. Like Crohn's disease, bloody diarrhea is a common symptom of ulcerative colitis. Diarrhea : Stools that are frequent, loose, or watery are commonly called diarrhea. Most diarrhea is due to self-limited, mild infections of the colon or small intestine. Salmonellosis : The bacteria Salmonella can contaminate food and infect the intestine. Salmonella causes diarrhea and stomach cramps, which usually resolve without treatment. Shigellosis : The bacteria Shigella can contaminate food and invade the colon. Symptoms include fever, stomach cramps, and diarrhea, which may be bloody. Travelers' diarrhea : Many different bacteria commonly contaminate water or food in developing countries. Loose stools, sometimes with nausea and fever, are symptoms. Colon polyps : Polyps are small growths. Some of these develop into cancer, but it takes a long time. Removing them can prevent many colon cancers.

Colon cancer : Cancer of the colon affects more than 100,000 Americans each year. Most colon cancer is preventable through regular screening. Continued Colon Tests Colonoscopy : An endoscope (flexible tube with a camera on its tip) is inserted into the rectum and advanced through the colon. A doctor can examine the entire colon with a colonoscope. Virtual colonoscopy : A test in which an X-ray machine and a computer create images of the inside of the colon. If problems are found, a traditional colonoscopy is usually needed. Stool occult blood testing : A test for blood in the stool. If blood is found in the stool, a colonoscopy may be needed to look for the source. Sigmoidoscopy : An endoscope is inserted into the rectum and advanced through the left side of the colon. Sigmoidoscopy cannot be used to view the middle and right sides of the colon. Colon biopsy : During a colonoscopy, a small piece of colon tissue may be removed for testing. A colon biopsy can help diagnose cancer, infection, or inflammation. Colon Treatments Antidiarrheal agents : Various medicines can slow down diarrhea, reducing discomfort.

Reducing diarrhea does not slow down recovery for most diarrheal illnesses. Stool softeners : Over-the-counter and prescription medicines can soften the stool; stool softeners can affect constipation, but not always. Laxatives : Medicines and herbs and some salts can stimulate the bowel muscles or bring more water into the bowel to relieve constipation. Some laxatives are not safe with long term use. Enema : A term for pushing liquid into the colon through the anus. Enemas can deliver medicines to treat constipation or other colon conditions. Colonoscopy : Using tools on the tip of the endoscope, a doctor can treat certain colon conditions. Bleeding, polyps, or cancer might be treated by colonoscopy. Polypectomy : During colonoscopy, removal of a colon polyp is called polypectomy. Colon surgery : Using open or laparoscopic surgery, part or all of the colon may be removed (colectomy). This may be done for severe bleeding, cancer, or ulcerative colitis. Anti-inflammatory medicines: Various drugs can slow down immune system function, easing symptoms of inflammatory bowel disease. Antibiotics : Medicines can kill bacteria in the colon, used to cure some cases of colitis.

Antibiotics may also be used for attacks of inflammatory bowel disease. Probiotics : Microbes are important for the health of the colon. Probiotics are supplements of healthy microbes which may have benefit for some conditions like Crohn’s colitis. WebMD Image Collection Reviewed by William Blahd, MD on March 04, 2016 Sources Human Intestines | Interactive Anatomy Guide [Continued from above] . . . Gross Anatomy The intestines are located inferior to the stomach in the abdominal body cavity. They are connected to the posterior wall of the abdomen by the mesentery, a thin vascular membrane. Blood vessels of the mesentery carry oxygenated blood to support the tissues of the intestines and carry nutrient-rich venous blood away from the intestines to feed the tissues of the body. The small intestine is about 1 inch in diameter and about 10 feet long in a living body. It extends from the stomach to the large intestine and consists of 3 major regions: the duodenum, jejunum, and ileum. The duodenum receives partially digested food from the stomach, bile from the liver and gallbladder, and pancreatic juice from the pancreas.

These substances mix in the duodenum to further digest food into its most basic units. The duodenum begins to absorb nutrients from the food passing through its lumen. Food next passes into the jejunum, a longer region of intestine where the bulk of the absorption of nutrients takes place. Finally, food passes into the ileum, the longest region of the small intestine. Any last nutrients that were not absorbed in the jejunum are absorbed in the ileum before the food passes into the large intestine. The large intestine is about 2 ½ inches in diameter and about 5 feet long in a living body. It receives fecal matter from the small intestine through the ileocecal sphincter. The smooth walls of the large intestine absorb water from fecal matter. These intestinal walls also absorb vitamins released from the fermentation of feces by bacteria living in the large intestine. Our large intestine consists of 4 major regions: the cecum, colon, rectum, and anal canal. The cecum is a pouch-like dead-end passage that branches inferiorly from the end of the ileum. Fecal matter entering the large intestine from the ileum passes into the cecum before being pushed superiorly into the ascending colon.

The appendix is attached to the inferior end of the cecum and is believed to store beneficial bacteria that help break down undigested food. Fecal matter passes from the cecum into the colon, the largest region of the large intestine. The ascending colon carries feces superiorly from the cecum to the transverse colon. The transverse colon then carries feces transversely from the right side of the abdomen to the left side, where it enters the descending colon. Next, the descending colon carries the feces inferiorly to the S-shaped sigmoid colon and rectum. The rectum stores feces until they are ready to be defecated (eliminated from the body). During defecation, the anal sphincter muscles of the anal canal relax to allow feces to exit the body. Histology The innermost layer of the intestines is the mucosa. Mucosa is made of epithelial tissue containing mucus-secreting goblet cells. Mucus produced by the mucosa lubricates the interior of the intestines to prevent friction from food passing through the lumen, or hollow portion of the intestine.

The epithelial cells of the mucosa absorb the nutrients and water from digested food and transfer these substances to blood in nearby capillaries. In the small intestine, many tiny folds called villi increase the surface area of the mucosa so that the contact between food and mucosa is greatly increased, subsequently allowing more nutrients to be absorbed by the intestines. Deep to the mucosa is the submucosa layer that contains many blood vessels, nerves, and connective tissues that support the mucosa. The muscularis layer surrounds the submucosa and provides several layers of smooth muscle tissue to move the intestines. Intestinal movements such as peristalsis and segmentation help to move food through the intestine and churn the food so that it has contact with the intestinal walls. The outermost layer of the intestines is the serosa, which is made of simple squamous epithelium. The serosa forms a smooth, slimy outer layer so that the intestines do not become inflamed from contact with other organs or muscles during digestion and movement of the body.

Prepared by Tim Taylor, Anatomy and Physiology Instructor Wikijunior:Human Body/Digestive System/Small Intestine - Wikibooks, open books for an open world Wikijunior:Human Body/Digestive System/Small Intestine This is the latest reviewed version , checked on 29 October 2013. (+) Quality: minimal Jump to: navigation , search The small intestine is a part of the digestive system. It is the most important organ for the digestion of food. The small and large intestines Contents 4 How does the small intestine interact with other parts of the body? What does the small intestine look like?[ edit ] The small intestine is a long, narrow tube that is all coiled up in the lower part of our abdomen (the part of our body we usually call our "stomach"). It is over 20 feet (6 meters) long! This is the largest part of the digestive system. The only way the small intestine can fit into our bodies is by curling and looping to fit in a small space. What are the parts of the small intestine?[ edit ] The first part of the small intestine is called the duodenum . The middle part is the jejunum .

This is where most of the nutrients in food are absorbed into the blood. The last part of the small intestine is called the ileum . This part connects to the large intestine. The lining of the small intestine is covered with tiny finger-like projections called villi . They look almost like carpet. The villi help the nutrients in food to be absorbed into the blood. The villi are carpet-like fingers inside the small intestine that help absorb nutrients. What is the function of the small intestine?[ edit ] The small intestine is where most digestion takes place. Food is broken down into smaller and smaller particles. Finally, when the particles are small enough, they are absorbed into the blood. The blood carries the nutrients to all parts of the body. How does the small intestine interact with other parts of the body?[ edit ] The small intestine is connected to the stomach. Food that the stomach has begun to digest moves into the small intestine. After it moves through the small intestine, food moves on the large intestine. Like other organs, the small intestine gets oxygen from blood vessels. The blood in the small intestine also carries the nutrients from food to the rest of the body. The small intestine gets enzymes from two important glands, called the liver and the pancreas.

The liver is the largest organ in our bodies. It makes a liquid called bile that helps digest fat. The bile is stored in another organ called the gall bladder. The pancreas makes a juice that breaks down sugars and starches . Jejunum And Ileum Jejunum And Ileum Description This section is from the book " Applied Anatomy: The Construction Of The Human Body ", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body . Jejunum And Ileum The jejunum is about 8 1/2 ft. long and the ileum about 12 1/2 ft. They are bound to the spinal column by the mesentery , which extends from the left side of the body of the second lumbar vertebra to the right sacro-iliac joint . Duodenojejunal Flexure And Fossae The point of ending of the duodenum and beginning of the jejunum is marked by a sharp bend called the duodeuojejunal flexure. The beginning of the jejunum passes downward, forward, and usually toward the left.

If the transverse colon is thrown upward and the jejunum is pulled sharply to the right, a folded edge of peritoneum containing some muscular fibres is seen passing from the flexure to the parietal peritoneum. This is called the suspensory ligament or muscle of Treitz. The fossa which is behind it is the superior duodenojejunal fossa of Treitz while that below is the inferior duodenal fossa. Below the fossa runs the inferior mesenteric artery and near the left edge of the ligament runs the inferior mesenteric vein . Into the fossae, if abnormally large, the intestines may enter and produce a retroperitoneal hernia. If the constricting band, which is the ligament of Treitz, is cut, there is danger of dividing the inferior mesenteric vein (see Fig. 420). Fig. 420. - The duodenojejunal flexure and duodenal fossa; the jejunum drawn to the right. The small intestine decreases in size and thickness from its upper to its lower end. The diameter of the jejunum is about 4 cm. (1 1/2 in.

) while that of the ileum is about 3 cm. (1 1/4 in.). The walls of the jejunum are thicker, redder, and more vascular than those of the ileum and the valvulae conniventes are better developed. The ileum is thinner, narrower, paler and, particularly when diseased, the large Peyer's patches can be seen. The intestinal coils, while not constant in position , are most apt to be as follows: The commencement of the jejunum is in the upper left portion of the abdomen . The ileum is more in the right lower quadrant of the abdomen. According to Treves, the intestine from six to eleven feet from its commencement has the longest mesentery and is apt to be found in the pelvis . The lower end of the ileum is also usually found in the pelvis, and rises over its brim to join the caecum . There is no certainty, however, of finding a definite piece of the small intestine under any special point on the surface, because the varying distention and movements cause frequent changes of position.

Meckel's Diverticulum In the embryo the vitello-intestinal duct passes from the umbilicus to the lower end of the small intestine. Normally this disappears, but sometimes a portion of it remains and there is found, one to three feet above the ileocaecal valve, a finger -like projection from the side of the ileum, 5 to 7.5 cm. (2 to 3 in.) long. This is called Meckel's diverticulum, and may become the site of disease the same as the rest of the ileum. From its extremity a fibrous band may run to the umbilicus. This has been in rare instances the source of strangulation, causing intestinal obstruction. One such case has been under our care (Fig. 421). Peyer's patches (noduli lymphatici aggre-gati) are most numerous in the lower portion of the ileum. They are ulcerated in typhoid cases and are frequently the site of perforations. These patches are from 1 to 2.5 cm. (1/2 to 1 in.) wide and 2.5 to 7.5 cm. (1 to 3 in.) long.

When affected in typhoid fever they can readily be seen through the intestinal walls. By holding the intestine up against the light both Peyer's patches and the valvulae conniventes can readily be seen. The perforations in typhoid fever occur usually within three feet of the ileo-caecal valve, though occasionally they may occur, as we have seen, in the appendix, or higher up in the small intestine, or even in the large intestine. Fig. 421. - Meckel's diverticulum. (From author's sketch). Ileum Function In Humans: What Does Ileum Do In The Digestive System Home > Health FAQ 8 > Ileum Function In Humans: What Does Ileum Do In The Digestive System Published September 19, 2011 by Salina Ileum Function In Humans: What Does Ileum Do In The Digestive System Ileum is the part of the small intestine is observed in higher vertebrates including humans. The ileum is the distal part of the small intestine and is about two to four meters in length.

Ileum plays a crucial part in the digestive system by aiding in the process of absorption of vitamin B12 and bile salts. The small intestine is divided into three divisions namely the duodenum, jejunum and ileum. The ileum connects the small intestine to the large intestine. The internal environment of the ileum is maintained at 7 to 8 pH, which makes it slightly alkaline. Main Function Of Ileum In Humans The walls of the ileum comprise of folds each of which in turn have tiny finger like projections referred to as villi. Further the villi possess several smaller epithelial cells which are termed as microvilli. These microvilli play a crucial role in the absorption of various foods, which have been digested and also contribute effectively towards digesting foods that have not been digested in the upper part of the small intestine. Firstly, the villi contain a large number of capillaries which help in the absorption of fatty acids and glycerol. In addition the ileum plays a crucial role in the absorption of Vitamin B12 and other bile salts, which are then transmitted to the liver through the hepatic portal system.

Secondly, the ileum secretes protease and carbohydrate enzymes, which are responsible for the final breakdown of carbohydrates and proteins. Some of the key hormones released in the ileum include cholecystokinin, gastrin and secretin (as a part of the Diffuse NeuroEndocrine System). Finally, the longitudinal smooth muscle fibers contract regularly to propel the undigested food forward into the large intestine. This process is also referred to as peristalsis. The undigested food along with water is then propelled forward to the colon. The ileum is the part of the small intestine which is connected on one end to the jejunum and on the other hand with the caecum, by the ileocecal fold. The ileum is a short part of the small intestine which is suspended by the posterior part of the mesentery. The muscular contraction of the ileum and obstruction of the ileal opening may often result in engorgement of the ileum. The ileum plays a crucial role in preventing the back flow of undigested food into the jejunum, especially in cases of obstructive conditions.

Further, the ileum plays a vital role in maintaining the acid-base balance of the small intestine as it prevents the back flow of the undigested food. Function Of Ileum In Digestive System As a part of the small intestine, the ileum plays a crucial role in aiding the process of digestion and absorption of vital nutrients and vitamins. Though the ileum is much smaller than the jejunum, it is very vital part of the small intestine. The most important digestive function of ileum is to absorb nutrients from the chyme (i.e. bile salts). This is done through the villi located on the inner walls of the ileum. Ileum plays a vital role in the absorption of Vitamin B12. Further proteins and peptides are broken down into simpler forms like amino acids, which makes it easier for the absorption of proteins Ileum also plays a crucial role in breakdown of carbohydrates into simpler sugars and lipids into fatty acids and glycerol. This process of digestion is assisted by the various enzymes that are produced in the ileum lining. Related posts: ileum | anatomy | Britannica.com anatomy vertebrate Ileum, the final and longest segment of the small intestine .

It is specifically responsible for the absorption of vitamin B12 and the reabsorption of conjugated bile salts . The ileum is about 3.5 metres (11.5 feet) long (or about three-fifths the length of the small intestine) and extends from the jejunum (the middle section of the small intestine) to the ileocecal valve, which empties into the colon ( large intestine ). The ileum is suspended from the abdominal wall by the mesentery , a fold of serous (moisture-secreting) membrane. The small intestine contains many distinct types of cells, each of which serves a specific function. Encyclopædia Britannica, Inc. The smooth muscle of the ileum’s walls is thinner than the walls of other parts of the intestines, and its peristaltic contractions are slower. The ileum’s lining is also less permeable than that of the upper small intestine.

Small collections of lymphatic tissue ( Peyer patches ) are embedded in the ileal wall, and specific receptors for bile salts and vitamin B 12 are contained exclusively in its lining; about 95 percent of the conjugated bile salts in the intestinal contents is absorbed by the ileum. Two percent of all humans are born with a congenital ileum malformation, called Meckel diverticulum , that consists of a side channel from 1 to 12 cm (0.4 to 4.7 inches) long extending from the intestinal wall. The malformation occurs when the duct leading from the navel to the small intestine in the fetus fails to atrophy and close. A small number of cases require surgical removal because of intestinal bleeding and inflammation . Injury or disease affecting the terminal ileum produces vitamin B12 deficiency and extensive diarrhea , the latter resulting from the interference of bile salts on water absorption in the large intestine. Learn More in these related articles: How Does the Small Intestine Digest Food? | Laparoscopic.MD Digestion Intestine Your small intestine and digestion The small intestine is a long tube that is approximately 18 feet long (6 meters).

The small intestine is called small because the diameter or the width of the tube is much less than the large intestine . The parts of the small intestine include the duodenum , jejunum and the ileum. The duodenum is a segment of intestine between the stomach and the jejunum that is very active in digestion where many different enzymes mix from the stomach , liver , gallbladder and pancreas . The small intestine is the location in the body where the majority of the nutrients from ingested food are absorbed. Whereas the stomach is responsible for the churning and mechanical breakdown of food, the small intestine is very important for absorption. Digested food passes through the wall of the intestine into the blood vessels which then distribute the nutrition first to the liver and then through the rest of the body. Jejunum The jejunum is the second section of the small intestine; it is around 3 to 6 feet (average 1.5 meters) in length and lies between the duodenum and the ileum. There is no distinct demarcation between the jejunum to the ileum; however, the change from the duodenum to the jejunum is clearly marked because of the ligament of Treitz.

The mucous membrane on the inner surface of the jejunum is covered with hair-like projections termed villi. These are instrumental in the absorption of nutrients such as proteins, carbohydrates, amino acid, sugar, fatty acid particles, vitamins, minerals, electrolytes and water. It is interesting to note that the villi in the jejunum are longer than those in the duodenum and the ileum. The surface are of the jejunum is also increased due to large circular folds called plicae circulares present in the submucosa. Ileum The ileum is the final part of the small intestine. It opens into the large intestine via the ileocecal valve. The ileum is preceded by the jejunum. This section of the small intestine is approximately 6 to 12 feet (3.5 meters) long. The ileum absorbs mainly vitamin B12 , other water soluble vitamins, bile salts, and nutrients that were not absorbed in the jejunum. More specifically, the absorption of the vitamins takes place at the terminal ileum – the last part of the ileum. Removal of this portion of the ileum will necessitate supplementary vitamin B12 doses for rest of the life.

The surface area of the ileum is very large to facilitate the adsorption and absorption process. The surface consists of many tiny finger-like segments that protrude outwards. These are termed villi and are covered with epithelial cells. Capillaries in the villi transport amino acids to the liver via the hepatic portal vein. The products of fat digestion, namely fatty acid and glycerol are absorbed by lacteals. These are small lymph vessels. The digested food is pushed along the ileum by means of peristaltic muscle contractions. The undigested food and water move into the colon. There is no marked point at which the jejunum ends and the ileum begins; however there are certain differences between the two regions of the intestinal tract. There is more fat within the transparent mesenteric membrane at the ileum as compared to the jejunum. Also, the ileum is of a paler shade and has a smaller bore. Anatomical Structure: Small Intestine - MicrobeWiki Small Intestine This is a curated page . Report corrections to Microbewiki . This article is concerned with the microbes residing in one particular niche: the small intestine of the digestive tract.

Although most of the human flora (the term used for the bacteria living in the human body) is found in the colon, there are a good number of microbes found in the small intestine. The following article will discuss the different bacteria that contribute to normal functioning and diseased states of the small intestine, with a focus on that of humans. The Small Intestine (in order from stomach to the large intestine): Duodenum, Jejunum, and Ileum. [1 Contents 9 References Introduction The human body is not only made up of human cells, but is also comprised of bacterial cells. In fact, microorganisms, or microbes, are so abundant that there are about ten times as many bacteria as there are human cells; while there are 100 trillion human cells, there are 1000 trillion bacteria cells [12] . It is estimated that there are 500 to 100,000 species of bacteria living in the human body [12] . These microbes reside on the skin and mucus surfaces of human tissue, but not within tissues [10] .

Some of the bacteria in the body can be beneficial by helping the host obtain and breakdown nutrients, while others can be infectious, causing harm to the host. The microbes living in the host are known as “normal” bacteria and have been dubbed microbiota [11] . However, there are several that indeed benefit the human (a relationship of mutualism), while there are some bacteria that are harmful to the host (a parasitic relationship). Parasitic bacteria can cause many different types of disease, and are thus also considered pathogenic bacteria. As this article is looking at the small intestine, different microbial diseases of the small intestine will be reviewed. It is interesting to note that the growth of pathogenic bacteria can be controlled via means of competitive exclusion provided by the presence of useful bacteria provides [13] ; this demonstrates the importance of studying the interaction between different microorganisms in a niche, which will be covered later in this article. Description of the niche The small intestine is the site where most of the nutrient absorption occurs such as minerals, sugars, and amino acids. After food has been broken down in the stomach by strong hydrochloric acid, the pyloric sphincter opens and food get pushed into small intestine by peristalsis.

There are three major structural parts of the small intestine, duodenum, jejunum, and ileum. Throughout these sections, finger-liked structure called villi increase surface area that helps the absorption of nutrients. The concentration of bacterial activity in the small intestine is around 1 million per milliliter [28] . The microbial processes it undergoes is limited proteolysis and saccharolysis, toxin and SCFA production [25] . The lymphoid appearance of the Peyer's patch under electron microscope [15 Duodenum The duodenum is a hollowed tube that is situated between the stomach and the jejunum. The duodenum is the shortest section of the small intestine; it is 26cm long, on average. It is mostly responsible for digesting chyme, the food bolus that was created by the churning motion of the stomach. Since it doesn’t have the thick mucus lining like the stomach, the duodenum cannot tolerate the low pH introduced by the chyme.

In order to neutralize the pH, the liver secretes bile and pancreas secretes bicarbonate into the duodenum and brings the pH of duodenum up to around 5 and 6 range, a much more tolerable pH for protein and enzymes to function. Enzymes such as lipase, trypsin and chymotrypsin are also secreted into the duodenum to aid digestion. The bacterial density in this section of the small intestine reaches 101 to 103 CFU (Colony Forming Units) /mL and flourishes with gram-positive cocci and rods [2] . Jejunum The jejunum is 2.5m long, and is the site of absorption. The pH is 7-8 (slightly alkaline). The jejunum is situated right after the duodenum and it is about 10 feet long with pH between 7 and 8 [21] . Goblet cells are most numerous in jejunum, although they exist throughout small intestine. The primary functions of these cells are to secrete mucus. Mucus provides protection against pH, stress, and microorganisms by trapping them [22] .

As a result of this, the bacterial density rise to 104-107 CFU/mL and obtains various microbes such as Enterococcus faecalis , lactobacilli, diphtheroids, and the yeast Candida albicans . [25] Ileum The ileum is the last section of the small intestine. Like the jejunum, it is also around 10 feet long and its pH lies between 7 and 8. The bacterial density here is also 104-107 CFU/mL and has a microbe community similar to that of the colon. The Ileum is responsible for most of the food and liquid absorption, and the unabsorbed matter and waste products are passed into the large intestine. [21] ] One unique feature of the ileum is the dominance of Peyer’s patch, a form of lymphoid tissue. The main function of these Peyer’s patches is to provide leukocytes, part of the immune system, to fight against foreign microorganisms [1] . Image of the Paneth cell under the 1BAS 2 Image Analyzer.

[20 Protection against bacteria Functionally similar to neutrophils, the most abundant form of white blood cell in human, paneth cells on the crypt in the lumen of the small intestine provide host defense against harmful bacteria by primarily secreting antibacterial molecules defensins, or alpha-defensins when exposed to both Gram positive and negative bacteria. Defensins kills the bacteria cells by disrupting their membrane function. Defensins peptides contain hydrophobic and positively-charged regions that can interact with bacteria’s negatively phospholipids membrane by forming pores. This leads to the weakening of the membrane and causing lysis of the bacterial cell. Since most bacteria have higher concentration of negatively charged membrane than normal vertebrae cell membrane, they interact well with defensins’ positively charged regions and sparing the normal vertebrae cells that are needed for normal metabolic functions. Paneth cells also secrete lysozyme and phospholipase A2, which both have antimicrobial functions as well. With the addition of these two agents, paneth cells not only have the ability to kill bacteria, but even fungi and some enveloped viruses as well [14] .

Adjacent communities Stomach The stomach is located directly above the small intestine, and it is separated from the duodenum by the pyloric sphincter. As mentioned above, the duodenum has a neutral pH, which is needed because inside the stomach, gastric juice is secreted in order to provide the acidic environment needed to convert the inactive pepsinogen to the active pepsin. As the chyme (the semi-digested foodstuff) enters the duodenum, bile is secreted by the liver through the bile duct, to neutralize the acidic pH from the stomach. Large Intestine The colon is connected to the other end of the small intestine, at the ileum. It contains an incredibly large number of bacteria, at a concentration of 1011-1012 CFU/mL; the highest concentration found in any ecosystem. The colon contains 400 different types of species which is mostly anaerobic, gram-positive and gram-negative cells. The large intestine absorbs water, minerals, and organic acids. The microbial processes it undergoes is proteolysis, saccharolysis, toxin and SCFA production [2] .

Conditions under which the environment changes The physical conditions of the small intestine can change if there is diarrhea, ulcers, or infections. For example, one may have to take medications like antacid due to conditions such as heart burn or acid reflux into the esophagus. However, one side effect of taking such medication is the decrease of acidity of stomach acid due to neutralization of hydrochloric acid with carbonate from antacid. The result of this is that stomach cannot effectively kill the bacteria that enters the body, which increase the vulnerability of the gastrointestinal tract to bacterial infection [30] . These will be detailed in the diseases section below. Resident microbes Fluorescent image of gut bacteria . [28 Which microbes are present? The intestinal tract of human body has ten times as many microbial organisms than the rest of the body cells in the body [9] . There are up to 100,000 primarily aerobic organisms per milliliter found in the small intestine, and there are at least 500 bacterial species present inside the intestinal tract [9] .

The bacterial environment of the jejunum, the middle section of the small intestine located after the duodenum, consists mainly of gram-positive Streptococci and Lactobacilli [6] . Research done on several healthy volunteers showed the presence of Streptococci , Lactobacilli , Staphylococci , and fungi in the intestinal tract [6] . In the ileocaecal valve, Bacteroides and coliform bacteria are the dominant bacteria present there, in addition to anaerobic Lactobacilli [6] . In the ileum, the last section of the small intestine, the bacterial presence is varied, due to the “backwash contamination of the colon” [6] . Functions of flora [2] Protective • The natural flora of the small intestine protect the host by taking up space inside the small intestine. Their presence in the small intestine prevents pathogens from obtaining a foothold in the niche. • Normal bacteria stimulate the growth of the intestinal lining and the immune system of the intestine. • The natural flora of the small intestine provides competition for nutrients against pathogens, making it more difficult for pathogens to grow.

• The natural flora of the small intestine produces anti-bacterial products to eliminate competition such as pathogens. Structural • The natural flora in the small intestine makes up part of the intestinal barrier. • The natural flora of the small intestine is critical in the natural development of the immune system. Metabolic • The natural flora of the small intestine protect the host by metabolizing carcinogens in dietary foods. • The natural flora of the small intestine provide the host with synthesized vitamins, such as biotin and folate. • Help produce vitamin K, which is absorbed and used by the host. • The bacteria are important even for the muscular activity of the small intestine. Without bacteria, there is reduced muscular activity. Microbial Adventures: Vol. 1 It was a dark and churning night in the stomach of Bob. Lactobacillus lounged around in the folds of the stomach, waiting for the churning to stop. It had been churning for hours with no end in sight. Then, as suddenly as the churning started, it stopped. LB, as he was known among his fellows, stepped out from the folds and surveyed the environment. The harsh acid environment was held back by only his spore coatings. No, he decided.

This was not the place to germinate, I wouldn't last long in this environment. He decided to stay inside his spore, ready to spring forth when the moment was right. Before he could return to the safety of the fold he had been hiding under, the stomach began to undergo peristalsis, the undulating motion of the stomach rippled across the landscape throwing LB to and fro. He was thrown across the Pyloric Sphincter. There he blacked out. LB suddenly awoke to the rushing river of bile released by the gall bladder. If LB had a mouth, he would have been spitting out the bile, luckily he did not have a mouth. The bile crashed into the partially digested fat around him, causing the fat to emulsify! Around him a pool of bicarbonate began to form, causing the acids from the stomach to be neutralized. I must be in the duodenum, LB rationalized. This place is much more habitable than the stomach, but its a bit too volatile for me! LB floated along with the gentle flow of food and other spores, some of the spores eventually decided they liked this environment and decided to stay.

It wasn't his place to make judgements on other microbe's choices, so he wished them well and moved along. It wasn't long before LB arrived to find himself at a bustling city! It was the largest collection of microbes LB had ever seen. The city had looked like it had started at a center point and had expanded outward, a colony had once settled here and had eventually grew into the wonder LB saw before him. Nearby LB heard one microbe say to another "Ah, the Jejunum. You will never find a more wretched hive of scum and villainy." The words of this other microbe were very convincing, and LB decided against germinating in this town. He had overheard rumors of a place even larger and more densely packed than even the jejunum, they were whispers of the colon. LB wished to see the sight whose very description was uttered with secrecy and reverence. LB stayed packed in his spore and continued to move along, hopeful to see the colon. He traveled a long while and eventually landed in the ileum. The ileum was not the metropolis he had heard about. In fact, it was nearly the same size as the jejunum.

The conditions here were more pleasant than the duodenum and the jejunum. Doubt gripped LB, he felt the legendary metropolis slip away. LB had given up hope, LB decided that the ileum would be the place to stay to germinate, replicate, and produce lactic acid. The food was plentiful and the neighborhood was friendly. Little did he know that the metropolis he was looking for was the colon, and it was just a bit further down the tract. Fortunately for LB, this place made him happier than he would ever be if he had indeed traveled to the colon to live there. For if he had traveled to the colon, he would not have wanted to live there, it is an incredibly crowded place, more so than LB's wildest dreams. Microbial diseases of the small intestine Pathogenic bacteria in the small intestine are the cause of a variety of diseases. Specific species of bacteria are responsible, but the balance of bacterial numbers is also important. The human host thus has enzymes specialized in regulating the numbers should they get too high or low, but the small intestine is still at risk for disease.

Peptic Ulcers from Helicobacter Pylori [31] ] Helicobactor pylori under the transmission electron microgram. . [26 Peptic ulcers are sores in the lining of the stomach or the duodenum of the small intestine. They have two different causes: infection by the bacteria Helicobacter pylori (H. pylori), or long-term use of NSAIDs (nonsteroidal anti-inflammatory agents) such as aspirin. Contrary to popular belief, stress and spicy food do not cause peptic ulcers; instead, they merely exacerbate the severity of preexisting ulcers. Once an ulcer develops, abdominal discomfort is the most common symptom, and is sometimes accompanied by nausea, weight loss or poor appetite. The bacteria H. pylori is a spiral-shaped, gram-negative microaerophile proteobacterium that inhabits the stomach and duodenum. Once a person contracts H. pylori, it attacks the stomach and duodenum by targeting the protective mucus coating. Since mucus usually protects the stomach from the acid, acid can now reach the underlying sensitive lining and break it down. H.

pylori is specially adapted to the acidic environment of the stomach due to the secretion of protective neutralizing enzymes, specifically urease, and its spiral shape allows for burrowing and embedding into the intestinal lining. Contrary to popular belief, peptic ulcers are actually predominant in the duodenum rather than the stomach. Since the duodenum has a neutral pH environment, H. pylori is not limited to acidic environments; it has merely adapted to survive in the stomach, and instead changes its living conditions by regulating urease [32] . Surprisingly, H. pylori infection usually does not lead to ulcers; while 20 percent of people under 40 years old are infected, only 10 percent of people actually suffer from peptic ulcers at some point in their lives. It is believed that the bacterium is transferred through food or water, but the exact method of spreading is still unknown; as a result, prevention is very difficult, and researchers are currently working on developing a vaccine [29] . The diagnosis of H.

pylori-induced ulcers begins with first identifying a stomach ulcer by performing an endoscopy or an upper gastrointestinal series (an X-ray taken after the patient drinks barium to highlight the organs on the film). Next, H. pylori will be diagnosed through a variety of tests: blood, breath, stool and tissue sample. For the blood test, they detect the presence of antibodies to the bacteria. For the breath test, a urea solution containing a special carbon atom is ingested, and if the bacteria is present, the urea breaks down to release the carbon, which is measured. A test on the fecal matter can also be performed, which is also known as the Helicobacter pylori antigen test (HpSA). Finally, the tissue test is saved until the very end because it is the most invasive; a biopsy sample is removed with the endoscope, and either the urease test, a histology test, or a culture test is taken. Ulcer . [29 Treatment of H. pylori peptic ulcers can take the form of drugs that either target the ulcers or target the bacteria.

Those that strictly treat the ulcers both suppress acid secretion and protect the stomach lining, such as histamine receptor-2 (H2) blockers and proton pump inhibitors. Antibiotics are taken to kill the H. pylori. It is not wise to use only one type of medication; to date, it is recommended to undergo a 2-week course of triple therapy, which involves taking two antibiotics to kill the H. pylori, an acid suppressor or a stomach-lining protector. This method has been proven to be effective for over 90 percent of patients suffering from this ailment. The only downside to this treatment is that many pills have to be taken at once. There are also variations to triple therapy: dual therapy (antibiotic, acid suppressor) and quadruple therapy (two antibiotics, an acid suppressor, and a stomach-lining protector). Tropical Sprue One of the infectious disorders of the small intestine is tropical sprue. Although there is no precise definition of this disorder as of yet, some scientists define it as “malabsorption of two or more test substances of people living in the tropics" [6] .

Symptoms of tropical sprue usually include macrocytic anemia, or abnormally enlarged erythrocytes, due to a malabsorption of folate and vitamin B12 [7] . In early stages of this disease, the ileum and jejunum specifically are affected due to the malabsorption of xylose, glucose, fat, vitamin B12, and folate. After a duration of four months, the mucosa in the small intestine shows partial villous atrophy. Since the villi are the main components of the small intestine that is used for the absorption of nutrients, the absorptive qualities of the small intestine are limited in a patient with tropical sprue, leading to malabsorption of essential nutrients. Though there is no specific known cause of tropical sprue, there is little doubt that it is caused by a severe, acute gastrointestinal infection. No specific microorganism has been identified as the sole cause of tropical sprue, however. Patients with tropical sprue often have a colonization of coliform bacteria in the small intestine. Studies have shown that patients with tropical sprue in areas such as North India, Puerto Rico, Haiti, and in Europeans travelling in India contain coliform bacteria in the jejunum.

The bacteria in the intestines of the European travelers included Alcaligenes faecaelis , Enterobacter aerogenes , and the hafnia species [6] . Other patients were infested with Klebsiella pneumonia , Escherichia coli , and Enterobacter cloacae . In one study in Vellore, India, coliform bacteria were present in 29 of 33 patients with tropical sprue [6] . Additional studies in animals have shown that colonization of Enterobacteria in the small intestine causes changes in mucosal structure of the villi. Several experiments have been conducted on rabbit jejunum. Coliform bacteria are usually aerobes or facultative anaerobes, and they contain toxins that increase fluid secretion in the intestines. Another experiment conducted on rabbit jejunum has shown that Klebsiella pneumonia , when entered into the jejunum, decreases xylose absorption while shortening and blunting the villi, inhibiting absorption [6] . Similar results have been shown with a different strain of bacteria, Enterobacter cloacae , is also entered into the jejunum [6] .

The standard treatment of tropical sprue is a dosage of tetracycline and folic acid for at least six months [6] . This treatment fixes the mucosal structure of the villi of the small intestine, resolving malabsorption , resulting in patients having increased appetite and weight gain. If there is evidence of vitamin B12 malabsorption in the body during tropical sprue, a vitamin B12 replacement is added as a remedy. Though full recovery is expected, people who stay in the tropical areas where this disease is endemic, have a good chance of falling into a relapse [6] . If this disease is untreated, death eventually occurs, with the victim dying extremely malnourished. However, tropical sprue can be fatal in extremely young or old victims, even with treatment. Tropical sprue is mostly prevalent in tropical areas, however, not all of these areas have cases of tropical sprue. This may be due to dietary differences of the inhabitants in these regions. There has been a study linking the amount of long-chain unsaturated fatty acids consumed to the occurrence of tropical sprue in the population [6] .

Small Intestine Bacterial Overgrowth Small intestine bacterial overgrowth (SIBO), also known as small bowel bacterial overgrowth (SBBO), is a condition of the small intestine, defined as an increase in the number of bacteria in the upper gastrointestinal tract [9] . It can be caused by any condition that interferes with the muscular activity in the small intestine that can allow bacteria to multiply [8] . SIBO can result in villous atrophy and mucosal inflammation, altering the absorptive functions of the small intestine [9] . The main cause of SIBO is thought to be mainly bacterial. The production of enterotoxins by facultative anaerobes injures the intestinal surface while aerobic bacteria produce enzymes and metabolic products that cause epithelial injury. Symptoms of SIBO result mainly from malabsorption, and these symptoms include combinations of cramping, diarrhea, dyspepsia, and weight loss. In addition, anemia can result from malabsorption caused by occult blood loss, vitamin B12 deficiency, or both [9] . The diagnosis of SIBO usually starts with a clinical exam.

The presence of 105 or more colony units of non-pharyngeal bacteria, usually coliforms, suggest SIBO [9] . Screening tests, which include urine ladicans, serum D-lactic acid, and the glucose breath hydrogen test, are also used. The most common of these, the glucose breath hydrogen test, works as an increase in the hydrogen production in the breath after glucose consumption usually means that there is a significant small intestine bacterial fermentation of carbohydrates [9] . Treatment is usually given when the symptoms become too severe, and they usually depend on the species of bacteria involved and the severity of the symptoms. Most treatments include the use of oral antibiotics, which reduce the number of bacteria in the intestinal tract. Surgery may be needed for anatomical anomalies such as diverticula, which are pouches in the colon that provide bacteria with a safe area in which to multiply. The most popular antibiotic used is metronidazole [9] . Trimethoprim-sulfamethoxazole, aminoglycosides, spectrum penicillins, and cephlasporins are usually used against facultative anaerobes [9] .

If a patient has increased symptomatic activity, increased dosage may be administered. Sulfasalazine or corticosteroids may be used if there is an increased inflammatory response, however, dosage is based only on bacterial response [9] . A new and upcoming treatment used to combat SIBO is the use of bacterial substitution, which utilizes probiotic bacteria to replace existing bacteria, since the probiotic bacteria can eliminate pathogenic bacterial infections [9] . These probiotic bacteria have a beneficial effect on the small intestine. The probiotic bacteria commonly used are able to control the growth of pathogenic bacteria such as Salmonella typhimurium , Shigella sp , Clostridium difficile , Ampylobacter jejuni , and Escherichia coli , and in addition, are able to offer protection against Gardnerella vaginalitis , Bacteroides bivius , Candida albicans , and Chlamydia trachomatis . Lactic acid bacteria such as Lactobacillus GG and Actobacillus plantarum 299V are able to inhibit many gram-negative bacteria by removing toxic substances in the small intestine and stimulating the immune system [9] . Other Diseases Current Research and Discoveries 1.

Proliferation and Apoptosis of the Enterocyte is influenced by Bacteria Prior studies have shown that the small intestines have undergone morphological changes, such as the crypt depth and villous height, after inoculating germ-free pigs with different types of bacteria. Two gnotobiotic experiments were performed where 16 piglets were allocated into 4 types of treatment groups: Germ-Free, monoassociation with Lactobacillus fermentum , Escherichia coli , or sow feces. The piglets were reared for 14 days of age where the intestinal tissue and enterocytes were collected each day for histology, gene expression, and protein analysis. Quantitative PCR was used to measure proliferating nuclear cell antigen and it was concluded that the Escherichia coli and not the Lactobacillus fermentum helped stimulate an increase apoptosis and cell proliferation. Thus, only by the death of the receptors and commensal bacteria were the enterocyte able to have a significant turnover [3] . 2. Commensal Bacteria increase invasion of intestinal epithelium Researchers from Harvard Medical School have discovered that the bacteria in the small intestine may help promote the invasion of typhoid.

The beneficial bacteria located in the small intestine produce a compound that assist in redistributing the protein on the cell’s surface, which resides on the lining of intestine. This triggers epithelial cell trafficking of a protein, therefore serving as a receptor for the pathogenic bacteria. As a result, the cells become more susceptible to infection of Salmonella enterica serovar Typhi [4] . Streptococcus gordonii observed under Transmission electron micrograph . [27 3. Diversity of Intestinal Bacterial in Maturing Chicken Bacterial flora in the ilea and ceca of chickens are analyzed by studying 1,230 partial 16S rRNA gene sequences. Bacterial DNA was isolated using density gradient centrifugation. Studies show that the microbes that live in the ileum consist of: 68.5% Lactobacillus , 11% Clostridiaceae , 6.5% Streptococcus , and 6.5% Enterococcus . The large amount and variety of bacteria in the intestine make it difficult to distinguish the function of each one; however, overall that intestinal bacterial affect: nutrition, immune responses, pathogenesis of intestinal disease, and degradation of mucus.

The bacterial community in birds is affected by diet, age, and antibiotics. Overall, results showed that as the bacterial community started out as a stable community in the ileum and cecum. However, as the chickens matured, the bacterial community becomes more complex and increasingly differs between the ileum and cecum, which shows that each region develops its own unique set of microbes [16] . 4. Regulation of Intestinal Angiogenesis by Microbes via Paneth Cells Using three-dimensional imaging, researchers at the Washington University School of Medicine studied the impact of intestinal angiogenesis on the microbes in the small intestine of mice. Angiogenesis, the growth of new blood vessels, takes place in the complex network of blood vessels in small intestinal villi. However, the villi is also the site where gut microorganisms, or microbiota, live. This experiment studies the differences between the villi in germ-free mice and mice with Bacteroides thetaiotaomicron colonies during or after postnatal gut development – approximately a ten day period. Studies have shown that Bacteroides thetaiotaomicron is of the major microbes that reside in both mouse and human gut.

This experiment focuses on Paneth cells, which defend the host against microbes by secreting antibacterial peptides that affect the microbes in the lumen, or interior of the blood vessels. The results show that microbes function in breaking down carbohydrate polymers by facilitating lumen breakdown of dietary macromolecules so that the host does not have to cleave the various linkages in their food themselves. Symbiosis is observed since the host is able to gain more nutrients, while microbes are provided a safe niche with a plentiful carbon source [17] . 5. Microbial Symbiosis prevents Intestinal Inflammatory Disease Symbiosis between microbes and their human host can be observed by microbes preventing intestinal inflammatory disease. One of the main microbes this experiment focuses on is Bacteroides fragilis , which protects its human host against colitis, a chronic inflammation of the membrane lining the gastrointestinal tract, caused by Helicobacter hepaticus , a commensal bacterium. Although colitis is mainly affects the large intestine, in some rare cases it affects the ileum as well since it precedes the large intestine.

In order for Bacteroides fragilis to be beneficial to its host, it must express polysaccharide A, or PSA, which affects the interleukin-10-producing CD4 T cells; otherwise Helicobacter hepaticus will continue to grow and cause inflammatory disease. It is shown that purified PSA can prevent gut pathology. This experiment gives purified PSA to mice and measures the changes of the inflammatory disease. Mice without Helicobacter hepaticus had a very mild colitis, while mice with Helicobacter hepaticus developed severe colitis. When purified PSA was given to the diseased mice, they were almost completely protected against the Helicobacter hepaticus , and the disease level was reduced to match those who did not develop colitis. Thus, Bacteroides fragilis is just one example of a symbiosis relationship where a single bacterial organism promotes human health; and suggests that there are others yet to be discovered [18] . 6.

Effects of Dietary Fat Source and Antibiotics and Age on Bacterial in the Ileum of Chickens PCR with denaturing gradient gel electrophoresis (DGGE) studies how different fat sources in the diets of broiler chickens affected the microbial community in the ileum of the chickens at different ages. DGGE involves molecular fingerprinting which separates polymerase chain reaction (PCR)-generated DNA products. This experiment differs from previous experiments, which only focused on the cecum, by examining the parts of the small intestine – the jejunum and ileum, which are largely responsible for nutrient absorption. The experiment focuses only on the ileum, but notes that the same micro flora exist in both sites. In addition, instead of studying the effects of dietary carbohydrate sources, it focuses on dietary fat sources by feeding the chickens with either soy oil or lard and tallow mix and an antibiotic supplement (avilamycin and salinomycin mix). Salinomycin antibiotic inhibits the growth of C. perfringens. The results confirmed that the microbial communities were affected by both factors: the chickens’‘ dietary fat source with antibiotics as well as the age of the chickens.

As the chickens aged, there was an increase in Streptococcus alactolyticus , enterobacteria, and Clostridium perfringens . The different dietary fat sources primarily affected Lactobacillus salivarius and Clostridium perfringens . Results show that soy oil has a higher solubility which help the dispersion of antibiotics in the small intestine; thus, indirectly affects the microbial communities that live there. Clostridium perfringens , which was affected by both age and dietary fat sources, also exhibited different strains in response to the factors [19] . 7. Why the immune system doesn’t attack the small intestine Researchers from the Dana Farber Cancer Institute and Shannon Turley, PhD, recently identified a group of lymph node cells that instruct the immune system to leave healthy tissue alone. They have found that cells that are not generally thought of as part of the immune system actually help protect against microbe attacks in the intestine. Since the lymph nodes are found throughout the body, they suppress a variety of autoimmune diseases, which normally results from immune system assault on healthy tissue. In order to distinguish the normal and foreign cells, small proteins are located on the cell surface called antigens.

Thus the dendritic cells exposed the antigens of normal neighboring cells, which in-turn puts the immune system at ease. Turley discovered that dendritic cells are not essential in creating tolerance in T cells but instead tolerance is produced by stomal cells from nearby lymph nodes [24] . Conclusion A wide variety of microbes reside on the mucus surfaces of the small intestine. From these 500 bacterial species, many of these microbial communities are beneficial for the host by: aiding in nutrient absorption, stimulating growth, providing protection against pathogens, producing antibiotics, and even aiding in muscular activity of the small intestine. However, some microbes are parasitic and cause diseases. Despite the large number and diversity of microbes that inhabit the small intestine, current research and studies on the small intestine gradually provide more insight on the specific function each microbe, which can lead to the development of new drugs and treatments for diseases. References [1] Bentley-Hibbert, Dr. Stuart. Small Intestine [The small intestine is the portion of the digestive system most responsible for absorption of nutrients from food into the bloodstream. The pyloric sphincter governs the passage of partly digested food from the stomach into the duodenum. This short first]. Digital image.

MedlinePlus Medical Encyclopedia. 25 Oct. 2006. ADAM. 26 Aug. 2008 < >. [2] O'Hara, Ann M., and Fergus Shanahan. "The gut flora as a forgotten organ." European Molecular Biology Organization 7 (2006): 688-93. [3] Willing, B. P., and A.G. Van Kessel. "Enterocyte proliferation and apoptosis in the caudal small intestine is influenced by the composition of colonizing commensal bacteria in the neonatal gnotobiotic pig." Journal of Animal Science 2527th ser. 85 (2007): 3256-266. [4] Lyczak, J.B. "Commensal Bacteria Increase Invasion of Intestinal Epithelium by Salmonella enterica Serovar Typhi." INFECTION AND IMMUNITY 71 (2003): 6610-614. [5] Baker, S.J. "Tropical Sprue." British Medical Bulletin 28 (1972): 87-91.

[6] Glynn, Judith. "Tropical sprue--its aetiology and pathogenesis." Journal of the Royal Society of Medicine 79 (1986): 599-606. [7] Westgaard, Henrik. "Tropical Sprue." Current Treatment Options in Gastroenterology 7 (2004): 7-11. [8] Lee, Dennis, and Jay W. Marks. "Small Intestine Bacterial Overgrowth." MedicineNet Inc. < #tocb >. [9] Vanderhoof, Jon A., Rosemary J. Young, Nancy Murray, and Stuart S. Kaufman. "Treatment Strategies for Small Bowel Bacterial Overgrowth in Short Bowel Syndrome." Journal of Pediatric Gastroenterology & Nutrition 27 (1998): 155-60. [10] [11]Samuel Baron MD; Charles Patrick. Davis (1996). "Bacteriology": Chapter 6. Normal Flora. University of Texas Medical Branch at Galveston. [12]Sears CL (2005 Oct;11). "A dynamic partnership: celebrating our gut flora".

Anaerobe (5):247-51: 247–251. Academic Press. [13]Salminen S, Gueimonde M, Isolauri E (2005). "Probiotics that modify disease risk". J Nutr 135 (5): 1294 – 8. PMID 15867327 . [14]Wilson CL, Ouellette AJ, Satchell DP, etc: Regulation of intestinal alpha-defensin activation by the metalloproteinase matrilysin in innate host defense. Science 286:113-117, 1999. [15]Nagi/Babiuk, A. M. "Preparation, purification and characterization of bovine Peyer's patch leukocytes." PudMed Central. Apr. 1988. Canadian Veterinary Medical Association. 29 Aug. 2008 < >. [16]Lu, Jiangrang, Umelaalim Idris, Barry Harmon, Charles Hofacre, John J. Maurer, and Margie D. Lee.

‘‘Diversity and Succession of the Intestinal Bacterial Community of the Maturing Broiler Chicken.’‘ Applied and Environmental Microbiology 11th ser. 69 (2003): 6816-824. [17]Stappenbeck, Thaddeus S., Lora V. Hooper, and Jeffrey I. Gordon. ‘‘Developmental regulation of intestinal angiogenesis by indigenous microbes via Paneth cells.’‘ Proceedings of the National Academy of Sciences 99 (2002): 15450-5455. [18]Mazmanian, Sarkis K., June L. Round, and Dennis L. Kasper. ‘‘A microbial symbiosis factor prevents intestinal inflammatory disease.’‘ Nature 453 (2008): 620-25. [19]Knarreborg, Ane, Mary Alice Simon, Ricarda M. Engberg, Bent Borg Jensen, and Gerald W. Tannock.

‘‘Effects of Dietary Fat Source and Subtherapeutic Levels of Antibiotic on the Bacterial Community in the Ileum of Broiler Chickens at Various Ages.’‘ Applied and Environmental Microbiology 68 (2002): 5918-924. [20]Elmes/Stanton/Howells/Lowes. "Relation between the mucosal flora and Paneth cell population of human jejunum and ileum." PudMed Central. Nov. 1984. BMJ Group. 29 Aug. 2008 < #page >. [21]"Anatomy and Function of the Gastrointestinal Tract." University of Missouri Health Care. University of Missouri. 29 Aug. 2008 < >. [22]Gartner & Hiatt. "Jejunum." Histology Lab. University of Medicine and Dentistry of New Jersey. 29 Aug. 2008 < >. [23] "Getting To Know "Friendly Bacteria"" NCCAM, National Institutes of Health 12 (2006). [24] Turley, Shannon, and Dana Farber Cancer Institute.

"Why doesn't the Immune System attack the Small Intestine?" Bright Surf. 10 Jan. 2007. The Resource for Science Institution. 27 Aug. 2008 < > [25]Gibson, Glenn R., and Robert A. Rastall. "When We Eat, Which Bacteria Should We Be Feeding?" American Society of Microbiology May 2004: 1-8. [26]Dai, GuoFei. "Bactericidal and Morphological Effects of NE-2001, a Novel Synthetic Agent Directed against Helicobacter pylori." Pubmed Central. Aug. 2005. American Society for Microbiology (ASM). 29 Aug. 2008 < >. [27]Stinson, Murray. "Invasion and Killing of Human Endothelial Cells by Viridans Group Streptococci." Pubmed Central. May 2003. American Society for Microbiology (ASM). 29 Aug. 2008 < >. [28]Gibson/Rastall. "When We Eat, Which Bacteria Should We Be Feeding?" American Society for Microbiology.

May 2004. American Society for Microbiology (ASM). 29 Aug. 2008 < >. [29]"Peptic Ulcer." Medline Plus. National Institute of Health. 29 Aug. 2008 < >. [30]"Antacids and Heartburn." Antacid and Heartburn. Cleveland Clinic. 29 Aug. 2008 < >. [31]"H. pylori and Peptic Ulcer." National Digestive Diseases Information Clearinghouse. National Institute of Health. 29 Aug 2008 < > [32] "Regulation of Urease for Acid Habitation." George Sachs, David R. Scott, David L. Weeks, Marina Rektorscheck, and Klaus Melchers. < > Edited by Ellis Chiu, Janet Kwok, Kevin Lee, Susan Lee, Martin Tang, Adnan Vahora, students of Rachel Larsen Jejunum - Anatomy, Histology, Function, Composition | Kenhub Jejunum Contents Macroscopic anatomy The jejunum is the middle of the three parts of the small intestine .

The transition from the extraperitoneal ascending part of the duodenum to the intraperitoneal jejunum occurs at the duodenojejunal flexure (at the height of L2). The transition to the ileum is not sharply marked and only visible microscopically. The jejunum makes up about 2/5 of the total length of the small intestine (1.5 to 3.5 meters). Macroscopically noticeable are the many parallel running circular folds in the mucosa (valves of Kerckring). Like all intraperitoneal organs both the jejunum and ileum are attached to the posterior wall of the abdomen by the mesentery. By this means the entire convolute of the small intestine lies quite flexibly in the abdominal cavity however “framed” by the colon . The blood supply is carried by around 5 jejunal arteries which are interconnected with the other arteries of the small intestine by numerous arcades. The venous blood drains through the correspondent veins into the superior mesenteric vein.

The sympathetic innervation is carried by the nerves of the coeliac plexus and superior mesenteric plexus, the parasympathetic innervation by the vagus nerve (cranial nerve X). Recommended video: Mesentery Overview of the mesentery on anterior view of abdomen with greater omentum reflected and small intestine removed. Microscopic anatomy The jejunum has the typical histological pattern as the entire small intestine: mucosa, submucosa, muscularis and serosa. The mucosa is lined by simple columnar epithelium towards the lumen (lamina epithelialis). It contains enterocytes and goblet cells. Characteristic features are the crypts of Lieberkuhn and finger-like villi protruding in the intestinal lumen. Similar to the duodenum paneth cells are found deep in the crypts. The epithelial layer is followed by a connective tissue layer (lamina propria) and a muscle layer (lamina muscularis mucosae). The submucosa consists of loose connective tissue with blood vessels, lymph nodes and the Meissner’s plexus.

As usual, the muscularis has an inner circular and outer longitudinal layer of smooth musculature between which the Auerbach’s plexus lies. The entire jejunum is covered by serosa from the outside which consists of simple squamous epithelium and a connective tissue layer underneath (lamina propria serosae). Histologically the jejunum differentiates from the rest of the small intestine by the absence of Brunner’s glands (duodenum) and Peyer’s patch (ileum) however single lymphoid follicles are present. Function The main tasks of the jejunum are: cleavage of nutrients (e.g. by amylase, proteinase) absorption of lipophilic nutrients (proteins, fats, cholesterol and the fat-soluble vitamins A, D, E and K) absorption of water (about 90% of the secreted water, 6 to 8 liters/day). This induces an osmotic gradient leading to a paracellular transport of electrolytes, carbohydrates and amino acids.

Get me the rest of this article for free Create your account and you’ll be able to see the rest of this article, plus videos and a quiz to help you memorize the information, all for free. You’ll also get access to articles, videos, and quizzes about dozens of other anatomy systems. D. Drenckhahn/J. Waschke: Taschenbuch Anatomie, 1.Auflage, Urban & Fischer Verlag/Elsevier (2008), S.265-267 U. Welsch: Lehrbuch Histologie, 2.Auflage, Urban & Fischer Verlag/Elsevier (2006), S.370-378 M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Innere Organe, Thieme Verlag (2009), S.224-225 M.

Müller: Chirurgie – für Studium und Praxis 2012/13, Medizinische Verlags- und Informationsdienste (2011), S.188 Biochemie und Molekularbiologie des Menschen, Urban & Fischer Verlag/Elsevier (2009), S.876 Photo: Flickr / euthman

Question: Where in the human body is the 'Ileum'?
Answer: SMALL INTESTINE