The digestive system

Digestive system Digestion takes place within a tube called the digestive tract, which begins with the mouth and ends with the anus. Functions of the digestive system: 1. Ingest food 2. Digest it to nutrients that can cross plasma membrane. 3. Absorb nutrients 4. Eliminate indigestible remains.

Swallowing It occurs in the pharynx which receives food from the mouth and air from the nasal cavity. Swallowing is reflex action performed automatically without conscious thought. During swallowing the soft palate moves back to close off the nasopharynx and the trachea moves up under the epiglottis to cover the glottis. The glottis is the opening to the larynx (voice box). During swallowing, food normally enters the esophagus because the air passages are blocked. Some times food goes the wrong way either into the nasal cavities or into the trachea. If the later happen coughing will most likely force the food up out of the trachea and into the pharynx again.

The esophagus: A muscular tube that passes from the pharynx through the thoracic cavity and diaghram into the abdominal cavity where it joins the stomach. It is ordinarily collapsed, but it opens and receives the bolus when swallowing.

Esophagus Peristalsis is a rhythmic contrast which pushes food along the digestive tract. No chemical digestion of food occurs. There is a sphincter (valve) between the esophagus and stomach. Relaxation of the sphincter allows the bolus to pass into the stomach, while contrast prevents the acidic contents of the stomach from backing up into the esophagus. If it happens heart burn which feels like burning pain rising up into the throat.

The accessory organs A. Pancreas: 1. Can be an endocrine gland, it secretes insulin and glucagons, hormones that help keep the blood glucose level within normal limits. 2. Can be an exocrine gland which produces pancreatic juice which contains sodium bicarbonate and digestive enzymes for all types of food. 3. Pancreatic amylase—digests starch 4. Trypsin---digest protein. 5. Lipase---digest fat.

B. The Liver Functions: 1. Detoxifies blood by removing and metabolizing poisonous substances. 2. Stores iron and fat-soluble vitamins A, D, E, K and B12 3. Makes plasma proteins, such as albumins and fibrinogen from amino acids. 4. Stores glucose as glycogen after eating and breaks down glycogen to glucose to maintain the glucose concentration of blood between eating periods. 5. Produces urea after breaking down amino acids. 6. Removes bilirubin breakdown products of hemoglobin from the blood, and excretes it into bile (a liver product) 7. Helps regulate blood cholesterol level, converting some to bile salt.

Continue Disorders: 1. Hepatitis: Inflammation of the liver. Hepatitis A---from swage-contaminated drinking water. Hepatitis B---spread by sexual contact, blood transfusion or contaminated needles. Moore contagious than AIDS. Hepatitis C---Acquired by contact with infected blood, there is no vaccine. Can lead to chronic hepatitis liver cancer and death.

Continue 2. Cirrhosis: A chronic disease. First the organ becomes fatty and liver tissue is then replaced by inactive fibrous scar tissue. It is seen in alcoholics due to malnutrition and the excessive amounts of alcohol (toxin) the liver is forced to break down. The liver has amazing generative powers and can recover if the rate of generation exceeds the rate of damage. During liver failure there may not be enough time to let the liver heal itself.

C. The gallbladder Excess bile is stored in the gallbladder. Water is reabsorbed by the gallbladder so that bile becomes thick mucus like material. When needed bile leaves the gallbladder and proceeds to the duodenum via common bile duct. The cholesterol content of bile can come out of solution and form crystals. If they grow in size they form gallstones. The passage of the stones from the gall bladder may block the common bile duct and cause obstructive jaundice. Then the gallbladder must be removed.

Imaging Modalities 1. Fluoroscopy: Upper GI------Barium meal Barium swallow Lower GI------Barium follow through Barium Enema

2. Abdominal CT Cross-sectional slices of the abdomen is imaged and viewed Image reconstruction is possible where 3D images, CT endoscopy, CT fluoroscopy can be produced

Radiograph from double-contrast upper GI showing normal duodenum.

Radiograph from double-contrast upper GI showing normal esophagus.

Stomach with normal folded lining of the stomach and normal duodenum.

Radiograph from double-contrast upper GI showing normal stomach.

Right side of the large intestine Right side of the large intestine. Air (dark) distends the bowel and barium (white) coats the inner lining.

Normal air-contrast barium enema.