Gastrointestinal Tract Nursing PDF

Definitions  Digestion: breakdown large insoluble molecules into small soluble ones.  Ingestion: taking food into a living organism.  Absorption: is the movement of small and soluble food.  Egestion : getting rid of undigested materials.  overview  Food supplies the body w...

Definitions  Digestion: breakdown large insoluble molecules into small soluble ones.  Ingestion: taking food into a living organism.  Absorption: is the movement of small and soluble food.  Egestion : getting rid of undigested materials.  overview  Food supplies the body with : energy and important nutrients.  Nutrient requirements must be swallowed, processed and broken down (digestion) before it can be absorbed from the intestines.  The three-layered GI musculature ensures that the GI contents are mixed and transported.  Solid food is chewed and mixed with saliva, which lubricates it and contains enzymes. How digestive system works?  There are two types of digestion:  1-Mechanical digestion:  it is breaking down the large insoluble molecules into smaller soluble molecules to be easier swallow and to increase the surface area for the enzyme action.  This happens by:  1-teeth: by chewing in the mouth.  2-churning: in the stomach by contraction of muscles in the stomach wall.  3-Emulsification: by bile salts in the small intestine. 2-Chemical digestion 1-Mouth: food mixed with saliva. Saliva contains amylase enzyme that digests the starch into sugar maltose 2-Oesophagus 3-Stomach: Pepsin enzyme: breakdown proteins into polypeptides. Mucus: protects the stomach lining from acidity HCl: for work of pepsin, and kill the bacteria Passage of food 1-Esophagus  Passage of food  Esophagus:  It rapidly transports the food bolus to the stomach.  The lower esophageal sphincter opens only briefly to allow the food to pass.  The proximal stomach mainly serves as a food reservoir.  Its tone determines the rate at which food passes to the distal stomach., where it is further processed (chyme formation) and its proteins are partly broken down.  Chyme:  It is a semi-fluid formed in the stomach made of partly digested food and the secretions of the gastrointestinal tract.  It is initially acidic in pH and also contains salivary enzymes and gastric enzymes.  The distal stomach: including the pylorus)  It is responsible for portioning chyme delivery to the small intestine.  2- In the small intestine  Enzymes from the pancreas and small intestinal mucosa:  break down the nutrients into absorbable components.  HCO3– in pancreatic juices:  neutralizes the acidic chyme.  Bile salts in bile :  are essential for fat digestion.  Amylase : breakdown the starch into 2 glucose.  Trypsin: breakdown proteins to amino acids.  Lipase: break down lipids into 3 fatty acids and glycerol.  Bile juice: it is made in the liver and stored in the gallbladder, so gall bladder secretes the bile juice to the small intestine for emulsification. Pancreatic enzymes   The products of digestion:  Monosaccharides amino acids  Dipeptides monoglycerides  free fatty acids as well as water  and vitamins  All these products are absorbed in the small intestine.  Waste products (e.g. bilirubin) to be excreted reach the feaces via bile secreted by the liver.  3-The liver The functions of liver: 1-Metabolism and distribution of substances reabsorbed from the intestine. 2-Synthesizes plasma proteins (albumin, globulins, clotting factors).  3-Detoxifies foreign substances (biotransformation) and metabolic products (e.g., ammonia) before they are excreted. Liver regulates the blood glucose level in 3 steps:  If there is an excess glucose in the blood, the liver absorbs it and used some in respiration.  Converts some glucose into glycogen.  Excess glucose will be converted to fats and stored under the skin in the adipose tissues. Small Intestinal Function  The main function of the small intestine is:  to finish digesting the food and to absorb the accumulated breakdown products as well as water, electrolytes and vitamins. Peristaltic reflex  Outer longitudinal muscles layer contract at the head of the bolus (chyme).  Inner circular muscles contract behind the bolus.  It is the spontaneous contraction and relaxation of the smooth muscles of intestine for the movement of the food through the intestine. The large intestine  It is the last stop for water and ion absorption.  It is colonized by bacteria and contains storage areas for feces (cecum, rectum).  Function of Intestinal bacteria:  increase the activity of intestinal immune defenses (“physiological inflammation”), and their metabolic activity is useful for the host.  The bacteria synthesize vitamin K  Convert indigestible substances (e.g. cellulose) or partially digested saccharides (e.g. lactose) into absorbable short chain fatty acids and gases (methane, H2, CO2). Immune defense of GIT 1- Saliva:  It contains mucins, immunoglobulin A (IgA) and lysozyme that prevent the penetration of pathogens. 2-Gastric juice has a bactericidal effect. 3-Peyer’s patches supply the GI tract with immuno- competent lymph tissue.  Saliva 1-Mucins : 1- lubricate the food 2- making it easier to swallow 3-Keep the mouth moist to facilitate masticatory and speech-related movement. 4-Saliva has a low NaCl concentration and is hypotonic, making it suitable for rinsing of the taste receptors while eating. 5-Saliva also contains α-amylase, which starts the digestion of starches in the mouth. N.B:  The high HCO3– concentration in saliva results in a pH of around 7,  which is optimal for α-amylase-catalyzed digestion.  Saliva secretion is very dependent on the body water content.  A low content results in decreased saliva secretion—the mouth and throat become dry, thereby evoking the sensation of thirst (fluid balance).  Gastric acid:  The pH of the gastric juice decreases during peak HCl secretion.  Role of acidity in GIT:  Swallowed food buffers it to a pH of 1.4 -1.8 , which is optimal for most pepsins and gastric lipases. The low pH contributes to bactericidal effect.