Exam 3 Review:  Chapter 23:  Intestinal Anatomy

small intestine - The narrow, winding, longest part (~22 feet) of the gastrointestinal tract where chemical digestion is completed and where nutrients are absorbed into the blood; it extends from the pyloric sphincter to the ileocecal valve and consists of the duodenum, the jejunum, and the ileum; its wall consists of an inner simple columnar epithelium with some goblet cells, a lamina propria of loose fibrous connective tissue, a muscularis, and an outer serosa.

duodenum - The first or proximal portion of the small intestine, starting at the pyloric sphincter at the lower end of the stomach and extending to the jejunum; it is approximately one foot in length; its wall consists of an inner simple columnar epithelium with some goblet cells, a lamina propria of loose fibrous connective tissue, a muscularis, and an outer serosa; it receives bile from the liver and gall bladder via the common bile duct and pancreatic juice from the pancreatic duct; it is the main site for completion of the chemical digestion of food; it has circular folds (plicae circulares) and only a few Peyer's patches.

jejunum - The middle portion of the small intestine, starting at the duodenum and extending to the ileum; it is ~9-10 feet in length; its wall consists of an inner simple columnar epithelium with goblet cells, a lamina propria of loose fibrous connective tissue, a muscularis, and an outer serosa; it is a main site for absorption of nutrients into the bloodstream; it is larger, thicker-walled, more vascular and has more circular folds (plicae circulares) and fewer Peyer's patches than the ileum.

ileum - The final or distal portion of the small intestine, starting at the jejunum and extending to the ileocecal valve where it joins the large intestine; it is ~12 feet in length; its wall consists of an inner simple columnar epithelium with many goblet cells, a lamina propria of loose fibrous connective tissue, a muscularis, and an outer serosa; it is a site for absorption of nutrients into the bloodstream; it is smaller, thinner-walled, less vascular and has fewer circular folds (plicae circulares) and more Peyer's patches than the jejunum.

ileocecal sphincter - A thickening of the circular layer of smooth muscle at the juncture of the ileum and the large intestine which serves as a valve to control the movement of chyme from the ileum into the cecum; it is controlled by the ANS.  aka - ileocecal valve

circular folds = plicae circulares - The numerous permanent crescentic folds or pleats of mucous membrane found in the small intestine, especially in the lower part of the duodenum and the jejunum; they increase the surface area available for absorption.

 1. 

See a Lacteal within a villus below.  Lacteals convey chyle (lymph containing lipids absorbed from the meal and packaged in chylomicrons) from the intestine to the lymphatic circulation and thereby to the thoracic duct and then to the systemic blood circulation.
   3 Descending (second) part of duodenum
   4 Proximal ileum
   5 Proximal jejunum
   7 Stomach
   9 Plicae circulares of jejunum 		The mucosa M is thrown into transverse folds, the plicae circulares PC, covered with villi V. The muscularis mucosae MM lies immediately beneath the basal crypts and is difficult to see at this magnification. The vascular submucosa S extends into the plicae circularis.  Beneath it lie circular CM and longitudinal LM layers of the muscularispropria and the serosa Sr.  Peyer's patches P dominate the mucosa at the left of the field.

villi - A minute finger-like, multicellular projection arising from a mucous membrane which serve to greatly increase the surface area of the mucous membrane; in the gastrointestinal tract, they are found in the small intestine and improve the efficiency of absorption; they are lined by a simple columnar epithelium with goblet cells; the interior contains loose fibrous connective tissue, small blood vessels, a small amount of smooth muscle, small nerve fibers, and a lacteal.

segmentation - A pattern of annular contraction of the smooth muscle layers in the walls of the small intestine which temporarily seems to cut the region affected into individual compartments; this activity serves to mix the chyme within the small intestine; it is controlled by the ANS.

List:

8.  structures which increase the surface area of the small intestine.

          (1)  circular folds = plicae circulares, (2) villi, (3) microvilli

14.  the functions of the small intestine.

         (1)  complete chemical digestion of food with the combination of bile, pancreatic enzymes, and intestinal brush border enzymes
         (2)  neutralize acidic chyme from the stomach with bicarbonate ions secreted by the liver and biliary tree, the pancreatic duct, and the intestinal glands
         (3)  use segmentation contractions to mix chyme to facilitate final chemical digestion and nutrient absorption 
         (4)  absorb the majority of nutrients, electrolytes, vitamins and minerals from the chyme as well as the water ingested with the foods and the majority of the water secreted into the GI tract during digestive gland secretions
         (5)  secrete mucous to lubricate and protect the stomach and intestinal linings
         (6)  secrete CCK, VIP, and secretin (enteroendocrine substanes) to help regulate the digestive activities of the stomach, liver, gall bladder, pancreas and intestines

Diagram and Label:

3. structures of the small intestine that increase its surface area (folding) for digestion and absorption.

Plicae Circularies:  Lining epithelium covers a series of villi which are supported by a dense fibrous connective tissue support within the plica circularis
Intestinal Villus
Intestinal Epithelial Lining Cell Microvilli form a Brush Border on the Luminal Surface
Microvilli seen in an electron micrograph -- computer colorized

4.  an intestinal villus.