Digestive System

Diagram of the Digestive System

Your Digestive System
Complete the Organize Organs activity. During all this, our rational mind is disengaged and our current concern is focused on fear, not remembering facts. Thus, thromboembolism has been presumed to be a cause of recurrent episodes of colic and weight loss. A horse will sometime freeze in bright light since it blinds them due to their extremely sensitive night vision ability. You can help your digestive system by drinking water and eating a healthy diet that includes foods rich in fiber. See if they can correctly guess which mixture it is!

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Gastrointestinal tract

Students will practice taking quizzes in order to learn the structures and functions within the digestive system. Students will discover the reasons for the bizarre and gross sounds that occur in the digestive system. Computer access to the internet. Highlight each part to see its location on the GI tract.

Open the Virtual Body Tour on the digestive system. Click on English or Spanish. Click on Digestive Tract. Begin by taking the Guided Tour. Click on the Zoom-In and move down through the system reading the notes. Complete the Organize Organs activity. Click on animation to observe movement of food from mouth toward stomach. Although inguinal hernias are common in young foals, they rarely cause clinical problems; the situation is considerably different in stallions. Similarly, if the ventral abdominal wall fails to form properly around the umbilicus, an opening remains and the potential exists for intestinal problems to develop secondary to an umbilical hernia.

The epiploic foramen, a natural opening between the portal vein, the caudal vena cava, and the caudate lobe of the liver, can be the site of intestinal incarcerations. Finally, there is a natural space between the dorsal aspect of the spleen and the left kidney. This space is bounded by the renosplenic ligament, a strong band of tissue that connects the dorsomedial aspect of the spleen with the fibrous capsule of the left kidney.

Normograde peristalsis in the left ventral colon moves ingesta toward the left dorsal colon, and the muscles in the wall of the left dorsal colon contract to move the ingesta toward the diaphragmatic flexure. There is evidence, however, that the muscles in the left ventral colon contract in a retrograde fashion, from the pelvic flexure region toward the sternal flexure. Furthermore, these contractions appear to originate from a pacemaker region in the pelvic flexure. It has been hypothesized that this pacemaker senses either the size or the consistency of the feed particles in the ingesta and then initiates the appropriate motility pattern.

If the ingesta has been digested sufficiently, it is moved in a normograde direction; if additional digestion is necessary, the ingesta is moved in a retrograde direction to retain it in the ventral colon.

This theory has been proposed to help account for the common clinical occurrence of obstruction at or near the pelvic flexure. Numerous clinical signs are associated with colic. The most common include pawing repeatedly with a front foot, looking back at the flank region, curling the upper lip and arching the neck, repeatedly raising a rear leg or kicking at the abdomen, lying down, rolling from side to side, sweating, stretching out as if to urinate, straining to defecate, distention of the abdomen, loss of appetite, depression, and decreased number of bowel movements.

It is uncommon for a horse with colic to exhibit all of these signs. Although they are reliable indicators of abdominal pain, the particular signs do not indicate which portion of the GI tract is involved or whether surgery will be needed. A diagnosis can be made and appropriate treatment begun only after thoroughly examining the horse, considering the history of any previous problems or treatments, determining which part of the intestinal tract is involved, and identifying the cause of the particular episode of colic.

In most instances, colic develops for one of four reasons: This stimulates the stretch-sensitive nerve endings located within the intestinal wall, and pain impulses are transmitted to the brain. Under such circumstances, proinflammatory mediators in the wall of the intestine decrease the threshold for painful stimuli. The list of possible conditions that cause colic is long, and it is reasonable first to determine the most likely type of disease and begin appropriate treatments and then to make a more specific diagnosis, if possible.

The history of the present colic episode and previous episodes, if any, must be considered to determine whether the horse has had repeated or similar problems or whether this episode is an isolated event. The duration of the present episode, the rate of deterioration of the horse's cardiovascular status, the severity of pain, whether feces have been passed, and the response to any treatments are important pieces of information.

The physical examination should include assessment of the cardiopulmonary and GI systems. The oral mucous membranes should be evaluated for color, moistness, and capillary refill time. The mucous membranes may become cyanotic or pale in horses with acute cardiovascular compromise and eventually hyperemic or muddy as peripheral vasodilation develops later in shock.

The membranes become dry as the horse becomes dehydrated. The heart rate increases due to pain, hemoconcentration, and hypotension; therefore, higher heart rates have been associated with more severe intestinal problems strangulating obstruction.

However, it is important to note that not all conditions requiring surgery are accompanied by a high heart rate. An important aspect of the physical examination is the response to passing a nasogastric tube. Because horses can neither regurgitate nor vomit, adynamic ileus, obstructions involving the small intestine, or distention of the stomach with gas or fluid may result in gastric rupture. If fluid reflux occurs, the volume and color of the fluid should be noted.

In healthy horses, it is common to retrieve The abdomen and thorax should be auscultated and the abdomen percussed. The abdomen should be auscultated over several areas cecum on the right, small intestine high on the left, colon lower on both the right and left. Intestinal sounds associated with episodes of pain may indicate an intraluminal obstruction eg, impaction, enterolith.

Gas sounds may indicate ileus or distention of a viscus. Fluid sounds may indicate impending diarrhea associated with colitis. A complete lack of sounds is usually associated with adynamic ileus or ischemia. Percussion helps identify a grossly distended segment of intestine cecum on right, colon on left that may need to be trocarized.

The respiratory rate may be increased due to fever, pain, acidosis, or an underlying respiratory problem. Diaphragmatic hernia is also a possible cause of colic. The most definitive part of the examination is the rectal examination. The veterinarian should develop a consistent method of palpating for the following: The intestine should be palpated for size, consistency of contents gas, fluid, or impacted ingesta , distention, edematous walls, and pain on palpation.

In healthy horses, the small intestine cannot be palpated; with small-intestinal obstruction, strangulating obstruction, or enteritis, the distended duodenum can be palpated dorsal to the base of the cecum on the right side of the abdomen, and distended loops of jejunum can be identified in the middle of the abdomen. A sample of peritoneal fluid obtained via paracentesis performed aseptically on midline often reflects the degree of intestinal damage.

The color, cell count and differential, and total protein concentration should be evaluated. Normal peritoneal fluid is clear to yellow, contains The age of the horse is important, because a number of age-related conditions cause colic. The more common of these include the following: Ultrasonographic evaluation of the abdomen may help differentiate between diseases that can be treated medically and those that require surgery.

The technique also can be applied transrectally to clarify findings noted on rectal palpation. In foals, echoes from the large colon and small intestine are commonly identified from the ventral abdominal wall, whereas only large-colon echoes are usually seen in adult horses. The large colon can be identified by its sacculated appearance. The duodenum can be identified in the tenth intercostal space and traced around the caudal aspect of the right kidney.

The jejunum is rarely identified during transabdominal ultrasonographic examination of normal adult horses, whereas the thick-walled ileum can be identified by transrectal examination. The most common abnormalities identified by ultrasonography include inguinal hernia, renosplenic entrapment of the large colon, sand colic, intussusception, enterocolitis, right dorsal colitis, and peritonitis.

Stallions with inguinal hernia have incarcerated intestine on the affected side; it is possible to identify the intestine and to obtain information concerning the thickness of its wall as well as the presence or lack of peristalsis. In horses with renosplenic entrapment of the large colon, the tail of the spleen or the left kidney cannot be imaged, or the gas-filled large colon is present in the caudodorsal aspect of the abdomen in the region of the renosplenic space.

Horses with sand colic have granular hyperechoic echoes originating from the affected portion of the colon. Very often the intestine proximal to the intussusception is distended, and the strangulated portion is thickened.

Horses with enterocolitis frequently have evidence of hyperperistalsis, thickened areas of the bowel wall, and fluid distention of the intestine. In contrast, horses with right dorsal colitis commonly have marked thickening of the wall of the right dorsal colon.

In horses with peritonitis, the peritoneal fluid may be anechoic, or there may be evidence of flocculent material and fibrin between serosal surfaces of the viscera. Horses with colic may need either medical or surgical treatments. Almost all require some form of medical treatment, but only those with certain mechanical obstructions of the intestine need surgery.

The type of medical treatment is determined by the cause of colic and the severity of the disease. In some instances, the horse may be treated medically first and the response evaluated; this is particularly appropriate if the horse is mildly painful and the cardiovascular system is functioning normally.

Ultrasonography can be used to evaluate the effectiveness of nonsurgical treatment. If necessary, surgery can be used for diagnosis as well as treatment.

If evidence of intestinal obstruction with dry ingesta is found on rectal examination, a primary aim of treatment is to rehydrate and evacuate the intestinal contents. If the horse is severely painful and has clinical signs indicating loss of fluid from the bloodstream high heart rate, prolonged capillary refill time, and discoloration of the mucous membranes , the initial aims of treatment are to relieve pain, restore tissue perfusion, and correct any abnormalities in the composition of the blood and body fluids see Table: If damage to the intestinal wall as a result of either severe inflammation or a displacement or strangulating obstruction is suspected, steps should be taken to prevent or counteract the ill effects of bacterial endotoxins that cross the damaged intestinal wall and enter the bloodstream.

Finally, if there is evidence the colic episode is caused by parasites, one aim of treatment is to eliminate the parasites. Adapted, with permission, from Zimmel DN, Management of pain and dehydration in horses with colic.

In most cases of colic, pain is mild, and analgesia is all that is needed. In these instances, the cause of colic is presumed to be spasm of intestinal muscle or excessive gas in a portion of the intestine. If, however, the pain is due to an intestinal twist or displacement, some of the stronger analgesics may mask the clinical signs that would be useful in making a diagnosis.

For these reasons, a thorough physical examination should be completed before any medications are given. However, because horses with severe colic or pain may hurt themselves and become dangerous to people nearby, analgesics often must be given first. Additionally, many horses with less severe problems may need pain relief until the other treatments have time to be effective. Medications used commonly for abdominal pain are NSAIDs that reduce the production of prostaglandins. When these drugs are used as recommended, their toxic effects on the kidneys and GI tract occur infrequently.

Clinical experience suggests that flunixin meglumine may mask the early signs of conditions that require surgery and, therefore, must be used carefully in horses with colic. Within a few minutes after administration, the horse stands quietly and is less responsive to pain. Unfortunately, the effects of xylazine are short-lived, and it inhibits intestinal muscular activity; it also decreases cardiac output and thus reduces blood flow to the tissues. Of the narcotic analgesics, butorphanol is used most often in horses with colic.

Butorphanol has few adverse effects on the GI tract or heart. However, when given in large doses, narcotics can cause excitement, and the horse may become unstable. Although pain relief usually is provided by analgesics, there are other important ways to reduce the degree of pain. For example, passing a nasogastric tube also an important part of the diagnostic evaluation may remove any fluid that has accumulated in the stomach because of an obstruction of the small intestine.

The removal of this fluid not only relieves pain from gastric distention but also prevents rupture of the stomach. Horses with displacement of the colon over the renosplenic ligament ie, left dorsal displacement of the colon may benefit from administration of phenylephrine.

This drug is given to contract the spleen and often is followed by light exercise on a lunge line in an effort to dislodge the entrapped colon.

Many horses with colic benefit from fluid therapy to prevent dehydration and maintain blood supply to the kidneys and other vital organs. The fluids may be given either through the nasogastric tube or IV, depending on the particular intestinal problem see General Concepts Regarding Fluid Needs in Dehydrated Horses.

Horses with strangulating obstruction or enteritis must be given fluids IV, because absorption of fluids from the diseased intestine is impaired and fluid may be secreted into the lumen of the intestine. The latter mechanism causes a buildup of fluid in the intestine, which must be removed from the stomach through a nasogastric tube.

This abnormal movement of body fluids into the intestine contributes to the development of circulatory shock, which is often the ultimate cause of death. In healthy horses, most of the fluid in the intestinal tract is reabsorbed in the cecum and colons.

Therefore, horses with intestinal obstructions near the pelvic flexure usually require relatively small amounts of IV fluids, whereas horses with small-intestinal obstructions need extremely large amounts.

The volume and type of fluid to be given are determined by the severity and cause of the problem. Laboratory tests to determine the degree of hemoconcentration and whether concentrations of electrolytes are abnormal are critical for accurate treatment of horses with severe colic. The balance of body fluids can be reestablished by administering IV fluids formulated to replenish the deficient electrolyte s.

In most instances, however, fluid therapy must be started before laboratory results are available, particularly when the horse is showing clinical signs of circulatory shock. When IV fluids are needed but the clinical signs are mild to moderate, the horse is usually given 8—10 L of a sterile replacement fluid that contains electrolytes in concentrations similar to those that normally exist in the blood.

This volume is administered throughout 1—2 hr, and the horse is reevaluated to determine whether additional fluids are needed. Horses in circulatory shock require much larger volumes of IV fluids, given as rapidly as possible; as much as 20 L in 1 hr may be needed to reestablish tissue perfusion.

Depending on the cause of colic, IV fluids may be needed for several days until intestinal function has returned, electrolyte concentrations are balanced, and the horse can maintain its fluid needs by drinking.

Under such circumstances, the daily IV fluid requirements may range from 30 to L. Fluids are sometimes given through the nasogastric tube as part of the treatment of impactions of the colon.

Many clinicians believe the same result can be accomplished by giving large volumes of fluids IV. If the horse will not drink voluntarily and there is no obstruction in the small intestine, hydration may be maintained by administering fluids through the tube.

Fluids or medications should not be given through the nasogastric tube if fluid reflux is being removed from the stomach, because this indicates either the stomach or the small intestine is not emptying properly. In healthy horses, the mucosal lining of the GI tract restricts enteric bacteria and their structural components eg, endotoxins, lipoproteins, nucleic acids, flagellin to the intestinal lumen.

These bacterial components exist in high concentrations in the intestinal lumen, because they are released when the bacteria die or, in some cases, when bacteria multiply rapidly. However, when this mucosal barrier is disrupted, as occurs with intestinal ischemia or inflammation, the bacterial components can move into the peritoneal cavity and then be absorbed into the systemic circulation. Based on recent research studies, equine leukocytes are most sensitive to endotoxins but also respond strongly to other components, most notably flagellin.

Most studies performed to date have focused on endotoxins, because they are assumed to be the primary triggers for the systemic inflammatory responses that occur in many horses with GI disease. These responses can include fever, depression, hypotension, reduced tissue perfusion, and coagulation abnormalities. Flunixin meglumine reduces the cellular production of prostaglandins and can help prevent some of their effects. Because flunixin can help prevent some of the early effects of endotoxemia at dosages less than the recommended dosage 1.

There is considerable controversy regarding the efficacy of plasma or serum that contains antibodies designed to neutralize endotoxin. These antibodies are directed against the components of endotoxins that are consistent among different gram-negative bacteria.

The results of clinical studies using such antibodies have been conflicting, with evidence of protection being seen in some studies and no positive effects identified in others. This apparent lack of efficacy of anti-endotoxin antibodies also may indicate that some of the systemic inflammatory responses encountered are triggered by other bacterial components. Because endotoxin itself stimulates the generation of a wide array of inflammatory substances that ultimately produce the pathophysiologic effects, neutralizing antibodies should be used as early as possible in the course of the disease.

Polymyxin B has well-documented nephrotoxicity; however, concentrations of polymyxin B that bind endotoxin are far less than those that cause toxic effects. This form of therapy should be started as early as possible in the clinical course of the disease.

In addition, fluid replacement therapy should be maintained in hypovolemic horses, and serum creatinine concentration should be closely monitored. This latter concern is especially relevant for azotemic neonatal foals, because they appear to be more susceptible to the nephrotoxic adverse effects of polymyxin B. A common cause of colic in horses is simple obstruction of the large colon by dehydrated ingesta, sometimes mixed with sand. These impactions generally develop near the pelvic flexure or in the right dorsal colon but may involve any portion of the large colon, descending colon, or cecum.

In most instances, lubricants or fecal-softening agents given through a nasogastric tube soften the impacted ingesta, allowing it to be passed.

This form of therapy can be aided by the simultaneous administration of IV fluids. Keeping the horse muzzled is advised to prevent further impaction of feed material while the obstruction is softening.

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