Cholecystokinin stimulates the secretion of the enzymatic component of pancreatic juice. The major stimulus for the release of Cholecystokinin is the presence of fatty acids and other lipids in the duodenum. Cholecystokinin also causes the sphincters of the pancreatic duct and hepatopancreatic ampulla to relax.
Parasympathetic stimulation through the vagus nerves also stimulates the secretion of pancreatic juices rich in pancreatic enzymes, and sympathetic impulses inhibit secretion. The effect of vagal stimulation on pancreatic juice secretion is greatest the cephalic and gastic phases of stomach secretion.
Large Intestine
The large intestine is the portion of the digestive tract extending from the ileocecal junction to the animus. It consists of the Cecil, colon, rectum, and anal canal. while in the colon, thyme is converted to feces the absorption of water and salts, secretion of mucus, and extensive action of water and salts, secretion of mucus, and extensive action of microorganisms are involved in the formation of feces, which the colon stores until the feces are eliminated by the process of defecation.
Anatomy and Histology of the Large Intestine
Cecum
The cecum is the proximal end of the large intestine. It is where the large and small intestine meet at the ileocecal junction. The cecum is a sac extending inferiorly about 6 cm past ileocecal junction. Attached to the cecum is a small, blind rube about 9 cm long called the vermiform appendix. The walls of the appendix contain many lymphatic nodules.
Appendicitis
Appendicitis is an inflammation of the appendix; it usually occurs because of obstruction. Secretions from the appendix cannot pass the obstruction and accumulate, causing enlargement and pain. Bacteria in the area can cause infection. Symptoms include sudden abdominal pain, particularly in the right-lower quadrant of the abdomen, along with a slight fever, loss of appetite, constipation or diarrhea,nausea, and vomiting. If the appendix bursts, the infection can spread throughout the peritoneal cavity, causing peritonitis, with life threatening results. Each year, 500000 people in the United States suffer from appendicitis. An appendectomy is removal of the appendix.
McBurney's point is located on the abdomen in the right-lower quadrant approximately one -third of the distance along a line from the anterior superior Iliad spine to umbilical.
McBurney's point is over the most common location of the attachment of the appendix to the cecum. Pain produced by applying pressure to McBurney's point is suggestive of appendicitis. However, many cases of appendicitis do not exhibit pain at McBurney's point, and other conditions can cause pain at McBurney's point.
Colon
The colon is about 1.5-1.8 m long and consists of four parts: the ascending colon, the transverse colon, the descending colon, and the signified colon. The ascending colon extends superiority from the cecum to the liver, where it turns to the left, forming the right colic flexure. The transverse colon extends from the right colic flexure to the spleen, where it turns inferiority, forming the left colic flexure. The descending colon extends from the left colic flexure to the pelvis, where it become the sigmoid colon. The sigmoid colon forms
an S-shaped tube that extends medially and then inferiorly into the pelvic cavity and ends at the rectum.
The circular muscle layer of the colon is complete, but the longitudinal muscle layer is incomplete. The longitudinal layer does not completely envelop the intestinal wall but forms three bands, called the teniae coli , that run the length of the colon.
Haustra are pouches formed in the colon wall along its length, giving the colon a puckered appearance.
The mucosal lining of the large intestine consists of simple columnar epithelium. This epithelium is not formed into folds or villi like that of the small intestine but has numerous, straight, tubular glands called crypts. The crypts are somewhat similar to the intestinal glands of the small intestine, with three cell types-absorption, goblet, and granular cells. The major difference is that, in the large intestine, goblet cells predominate and the other two cell types are greatly reduced in number.
Rectum
The rectum is a straight, muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal. The muscular tunic is relatively thick, compared with the rest of the digestive tract.
Anal Canal
The last 2-3 cm of the digestive tract is the anal canal. It begins at the inferior end of the rectum and ends at the anus, the inferior opening of the digestive tract. The smooth muscle layer of the anal canal is even thicker than that of the rectum and forms the internal anal sphincter at the superior end of the anal canal.
Skeletal muscle forms the external anal sphincter at the inferior end of the canal. The epithelium of the superior part of the anal canal is simple columnar and that of the inferior part is stratified squamous.
Hemorrhoids
Hemorrhoids are enlarged rectal veins. Enlargement is associated with increased pressure in the veins, as occurs when straining to have a bowel movement (constipation), pregnancy, and liver disease. Internal hemorrhoids are enlarged rectal veins in the anal canal. They are usually painless but often bleed following a bowel movement.The most common sign of internal hemorrhoids is blood on toilet paper. Prolapse, or extrusion, of an internal hemorrhoid through the anus can be painful. External hemorrhoids are enlarged rectal veins around the anus. The development of a blood clot in an external hemorrhoid can be painful. Treatments for hemorrhoids include increasing the bulk in the diet, taking sits baths, and using hydrocortisone suppositories. Surgery may be necessary if the condition is extreme and does not respond to other treatment.
Secretions of the Large Intestine
The mucosa of the colon has numerous goblet cells scattered along its length and numerous crypts lined almost entirely with goblet cells. Little enzymatic activity is associated with secretions of the colon because mucus is the major secretory product. Mucus lubricates the wall of the colon and help the fecal matter stick together. Tactile stimuli and irritation of the wall of the colon trigger local enteric reflexes that increase mucous secretory rate of the goblet cells.
The feces that leave the digestive tract consist of water, solid substances, microorganisms, and ploughed-off epithelial cells.
Numerous microorganisms inhibit the colon. They reproduce rapidly and ultimately constitute about 30% of the dry weight of the feces. Some bacteria in the intestine synthesize vitamin K, which is passively absorbed in the colon. Bacteria actions in the colon produce gases called Flatbush. The amount of flatus depends partly on the bacterial population in the colon and partly on the type of food consumed. For example, beans, which contain certain complex carbohydrates, are well known for their flatus-producing effect.
Movement in the Large Inteหtine
Normally, 18-24 hours are required for material to pass through the large intestine, in contrast to the 3-5 hours required for the movement of chyme through the small intestine. Simultaneous contractions of the circular muscles and tensile coli of the colon wall cause constriction and shortening of the colon, resulting in haustra formation. As the colon contradicts and bulges, it's contents are mixed. In addition, the formation of haustra proceeds toward the anus, resulting in the slow, analysed movement of colon contents. Local reflexes regulate haustra formation.
Three or four times each day, the circular muscles in large parts of the transverse and descending colon undergo several strong peristaltic contractions, called mass movements. Each mass movement contraction extends ever 20 cm of the colon and propels the colon contents a considerable distance toward the anus. Mass movements are stimulated by irritation or distention of the colon, local reflexes in the enteric plexus, and intense parasympathetic stimulation. The gastronomic and duodenocolic reflexes are local reflexes that can stimulate mass movements step 1 and 2.The gastronomic reflex is initiated in the stomach and the duodenocolic reflex in initiated in the duodenum. The though or smell of food, distention of the stomach, and the movement of chyme into the duodenum can stimulate these reflexes. Mass movements are most common about 15 minutes after breakfast. They usually persist for 10-30 minuted and then stop for perhaps half a day.
1.The though or smell of food, distortion of the stomach, and the movement of chyme into the duodenum can stimulate the gastrocolic and duodenocolic reflexes.
2. The gastrocolic and duodenocolic reflexes stimulate mass movements in the colon, which propel the contents of the colon toward the rectum.
3. Distention of the rectum by feces stimulates local defecation reflexes. These reflexes cause contraction of the colon and rectum, which move feces toward the anus.
4. Local reflexes cause relaxation of the internal anal sphincter.
5. Distortion of the rectum by faces stimulates parasympathetic reflexes. Action potentials are propagated to the defecation reflex center located in the spinal cord.
6. Action potentials stimulate contraction of the colon and rectum and relaxation of the internal anal sphincter.
7. Action potentials are propagated through ascending nerve tracts to the brain.
8. Descending nerve tracts from the brain regulate the defection reflex center.
9. Action potentials from the brain control the external anal sphincter.