Summary

In study session IV you have learnt

  • The throat is the common portion of the respiratory and digestive tracts adjoining the nasal and oral cavities. The nasal cavity opens into the upper part (nasopharynx), the oral cavity into the middle part (oropharynx), and the larynx and esophagus into the lower part (hypopharynx
  • The act of swallowing prevents the food from reaching the trachea. It includes a voluntary and an involuntary (reflex) phase. This important and complex reflex is regulated by the swallowing center (deglutition center) in the medulla (medulla oblongata) in the brain.
  • The esophagus transports the bolus from the pharynx into the stomach.
  • The inferior end of the esophagus is more constricted than the rest, forming the lower esophageal sphincter. This is not an anatomical feature but is a physiological constriction that helps close the cardiac orifice.
  • The stomach is J-shaped relatively vertical in tall people, and more horizontal in short people. The pylorus is surrounded by a thick ring of smooth muscle, the pyloric (gastroduodenal) sphincter, which regulates the passage of chyme into the duodenum.
  • The gastric glands produce 2 to 3 L of gastric juice per day (pH 1.5-2 /as low as 0.8/), consisting essentially of water, mucus, hydrochloric acid, and protein-splitting enzymes (pepsin), the stomach macerates and liquefies food chemically.
  • The speed at which substances empty from the stomach depends on their physical state and chemical composition. Liquids empty more rapidly than solids. Nutrients in the duodenum activate chemoreceptors which reflexes inhibit gastric emptying, allowing time for further digestion and absorption in the small intestine.
  • Several physiological, pathological and pharmacological factors occurring in the perioperative period may delay gastric emptying and increase the risk of inhalation of gastric contents
  • The actual digestion and absorption of nutrients takes place in the small bowel. The nutrients are broken down to easily absorbed components by pancreatic enzymes.
  • The small intestine is divided into three regions: the duodenum, jejunum, and ileum. The duodenum constitutes the first 25 cm (10 in.). It begins at the pyloric valve, arcs around the head of the pancreas and passes to the left, and ends at a sharp bend called the duodenojejunal flexure. The duodenum receives the stomach contents, pancreatic juice, and bile.
  • The pancreas is the most important digestive gland. It is an exocrine gland and secretes about 2 liters of pancreatic juice a day. The secretion and composition of pancreatic juice are regulated partly by the vagus, and partly especially by two mucosal hormones of the duodenum (secretin and cholecystokinin)..
  • The liver lies in the right upper abdominal quadrant, directly under the diaphragm. It weighs 1500-2000 g and so is the largest gland in the human body. Because it secretes bile, it is an exocrine gland. The main components of bile are bile acids, which enable the absorption of fats in the intestine by emulsifying them.
  • Within the liver, carbohydrates are stored as glycogen and are released again when needed. Fats and proteins are constantly transformed and broken down (e. g., fatty acid synthesis, amino acid breakdown, urea synthesis), and foreign substances such as medications or poisons are inactivated. The liver also takes part in the synthesis of numerous blood components (e. g., albumin, clotting factors).
  • The gallbladder is a thin-walled pear-shaped sac with a capacity of about 30-35ml. Bile is concentrated there (gallbladder bile) and when required released by way of the cystic duct into the common bile duct.
  • The common bile duct formed by the junction of the cystic duct and the common hepatic duct is also called the choledochous duct.
  • The gastrointestinal tract has a nervous system all its own called the enteric nervous system. It lies entirely in the wall of the gut, beginning in the esophagus and extending all the way to the anus.
  • Although the enteric nervous system can function on its own, independently of these extrinsic nerves stimulation by the parasympathetic and sympathetic systems can greatly enhance or inhibit gastrointestinal functions.
  • The blood vessels of the gastrointestinal system are part of a more extensive system called the splanchnic circulation.
  • A comprehensive gastrointestinal assessment includes history, physical examination and diagnostic tests that provide information about GIT function. However, bedside clinical assessment provides vital information about GIT function. It is important for nurse anesthetists to be able to perform a basic GIT assessment

Last modified: Wednesday, 16 November 2016, 9:49 AM