Small+Intestines

**__Small Intestines__**
 * Functions: **
 * 1) Peristalsis
 * 2) Digestion
 * 3) Absorption

**Peristalsis:** Food from the stomach is allowed into the duodenum by a muscle called the pylorus, or pyloric sphincter, and is then pushed through the small intestine by a process of muscular-wavelike contractions called peristalsis.

The small intestines are the location where most of the digestive process takes place. A large majority of the digestive enzymes used during this process are secreted by the pancreas which enter the small intestines through the pancreatic duct. "The enzymes enter the small intestine in response to the hormone cholecystokinin, which is produced in the small intestine in response to the presence of nutrients. The hormone secretin also causes bicarbonate to be released into the small intestines to protect against the potentially harmful acids coming from the stomach" (Wikipedia).  //Three main nutrients that undergo digestion are://
 * Digestion: **
 * Proteins - Proteins are broken down into amino acids. This process starts in the stomach and then continues in the small intestines.Proteolytic enzymes, which include trypsin and chymotrypsin, are secreted by the pancreas and then cleave proteins into smaller peptides. Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products.
 * Carbohydrates - Carbohydrates are degraded into simple sugars and monosaccharides(glucose). Pancreatic amylase breaks down carbohydrates into oligosaccharides. From there brush border enzymes take control. The most important brush border enzymes are dextrinase and glucoamylase which break down oligosaccharides into smaller forms. Other brush border enzymes are maltase, sucrase and lactase.
 * Lipids(fats) - Lipids are broken down into fatty acids and glycerol. Pancreatic lipase degrades triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from the bile secreted by the liver and the gall bladder. Bile salts attach to triglycerides to help emulsify them, which aids access by pancreatic lipase. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings. The bile salts are the "middle man" that holds the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption.

 **Absorption:** The digested food can now pass into the blood stream in the walls of the intestines. The small intestines are the site where most of the nutrients for digested food is absorbed. The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue. The mucosa is covered in wrinkles or folds called plicae circulares, which are considered permanent features in the wall of the organ. "They are distinct from rugae which are considered non-permanent or temporary allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called villi. The individual epithelial cells also have finger-like projections known as microvilli. The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for the absorption of nutrients" (Wikipedia). Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries and lacteals. The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. This is called assimilation. The food that remains undigested and unabsorbed passes into the large intestine.Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:
 * Iron is absorbed in the duodenum.
 * Vitamin B12 and bile salts are absorbed in the terminal ileum.
 * <span style="font-family: 'Courier New', Courier, monospace;">Water and lipids are absorbed by passive diffusion throughout the small intestine.
 * <span style="font-family: 'Courier New', Courier, monospace;">Sodium is absorbed by active transport and glucose and amino acid co-transport.
 * <span style="font-family: 'Courier New', Courier, monospace;">Fructose is absorbed by facilitated diffusion.

<span style="font-size: 130%; font-family: 'Courier New', Courier, monospace;">**Functional Histology:** <span style="font-size: 120%; font-family: 'Courier New', Courier, monospace;">//There are three functional components to the small intestines including://
 * 1) <span style="font-family: 'Courier New', Courier, monospace;">Duodenum - serosa = normal; muscularis externa = longitudinal layers; submucosa = Brunner's glands and Meissner's plexus; mucosa: lamina propria = no Peyer's Patches; mucosa: intestinal epithelium = simple columnar
 * 2) <span style="font-family: 'Courier New', Courier, monospace;">Jejunum - serosa = normal; muscularis externa = longitudinal layers; submucosa = no Brunner's glands but have Meissner's plexus; mucosa: lamina propria = Peyer's Patches; mucosa: intestinal epithelium = simple columnar, villi very long
 * 3) <span style="font-family: 'Courier New', Courier, monospace;">Ileum - serosa = normal; muscularis externa = longitudinal layers; submucosa = no Brunner's glands but have Meissner's plexus; mucosa: lamina propria = no Peyer's Patches; mucosa: intestinal epithelium = simple columnar, villi very long

<span style="font-size: 120%; font-family: 'Courier New', Courier, monospace;">//__Three diseases__ that affect the small intestines are://
 * <span style="font-family: 'Courier New', Courier, monospace;">Small Intestine Cancer - is a cancer of the small intestine. It is relatively rare compared to other gastrointestinal malignancies such as gastric cancer (stomach cancer) and colorectal cancer. Small intestine cancer can be subdivided into duodenal cancer (the first part of the small intestine) and cancer of the jejunum and ileum (the later two parts of the small intestine). Duodenal cancer has more in common with stomach cancer, while cancer of the jejunum and ileum have more in common with colorectal[[image:crohn.jpg width="150" height="141" align="right" caption="Crohn's Disease"]] cancer.
 * <span style="font-family: 'Courier New', Courier, monospace;">Crohn's Disease - is an inflammatory disease that may affect any part of the gastrointestinal tract from mouth to anus, causing a wide variety of symptoms. It primarily causes abdominal pain, diarrhea (which may be bloody), vomiting, or weight loss, but may also cause complications outside of the gastrointestinal tract such as skin rashes, arthritis and inflammation of the eye.
 * <span style="font-family: 'Courier New', Courier, monospace;">Coeliac Disease - is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy on up. Symptoms include chronic diarrhœa, failure to thrive (in children), and fatigue, but these may be absent, and symptoms in all other organ systems have been described. A growing portion of diagnoses are being made in asymptomatic persons as a result of increased screening.

<span style="font-size: 120%; font-family: 'Courier New', Courier, monospace;">**Across** <span style="font-family: 'Courier New', Courier, monospace;">3. Carbohydrates are also known as. 5. One of the three comonpents of the small intestines categorized by having only the Meissner's plexus and no Peyer's patch. 6. Who is the best anatomy teacher? 8. Which of the three nutrients are broken down into fatty acids and glycerol. 9. The mucosa is covered in wrinkles or folds called _. 13. Bile is secreted by the liver and the. 14. The process by which absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. 16. Which of the three nutrients that undergo digestion are degraded into simple sugars? 17. In which organ does the digestive process start? 19. The individual epithelial cells also have finger-like projections known as. 20. Which of the three nutrients that undergo digestion get broken down into amino acids? 21. Upon secretion, the digestive enzymes enter the small intestines through the _. 23. One of the three comonpents of the small intestines categorized by having both the Brunner's glands and the Meissner's plexus.

<span style="font-family: 'Courier New', Courier, monospace;">1. Which enzymes are secreted by the pancreas and then cleave proteins into smaller peptides. 2. Food is pushed through the small intestine by a process of muscular-wavelike contractions called _. 4. The inner wall, or mucosa, of the small intestine is lined with _ epithelial tissue. 7. Food from the stomach is allowed into the duodenum by the action of a muscle called _. 10. Pancreatic degrades triglycerides into free fatty acids and monoglycerides. 11. A large portion of the digestive enzymes needed for digestion are secreted by which organ. 12. Which of the three functions of the small intestines is where digested food can pass into the blood stream in the walls of the intestines. 15. One of the three comonpents of the small intestines categorized by having the Meissner's plexus and Peyer's patch. 18. Site where most of the digestive process takes place. 22. These digestive enzymes enter the small intestines in response to the hormone. 24. Pancreatic amylase breaks down carbohydrates into _.
 * <span style="font-size: 120%; font-family: 'Courier New', Courier, monospace;">Down **

<span style="font-size: 60%; font-family: 'Courier New', Courier, monospace;">Answers: 1.Proteolytic 2.Peristalsis 3.Glucose 4.Simple Columnar 5.Jejunum 6.Mackes 7.Pyloric Sphincter 8.Lipids 9.Plicae Circulares 10.Lipase 11.Pancreas 12.Absorption 13.Gallbladder 14.Assimilation 15.Ileum 16.Carbohydrates 17.Stomach 18.Small Intestines 19.Microvilli 20.Proteins 21.Pancreatic Duct 22.Cholecystokinin 23.Duodenum 24.Oligosaccharides

<span style="display: block; font-size: 80%; font-family: 'Courier New', Courier, monospace; text-align: right;">__ References __ http://www.medgadget.com/archives/img/crohn.jpg http://en.wikipedia.org/wiki/Small_intestine http://en.wikipedia.org/wiki/Small_intestine_cancer http://en.wikipedia.org/wiki/Crohn%27s_disease http://en.wikipedia.org/wiki/Celiac_disease