Digestive function And Processes - PRECIADO IBARRA URIEL GILBERTO

Digestive function And Processes - PRECIADO IBARRA URIEL GILBERTO

1. The primary function of the digestive system is to move nutri-ents, water, and electrolytes from the external environment into the body’s internal environmen

   • To accomplish this, the system uses four basic processe
     • Digestion
       • is the chemical and mechanical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body.
     • Absorption
       • is the move-ment of substances from the lumen of the GI tract to the ex-tracellular fluid
     • Motility
       • is movement of material in the GI tract as a result of muscle contraction.
     • Secretion
       • in the GI tract has two meanings. It can mean the movement of water and ions from the ECF to the digestive tract lume
     • regulation of gi function
       • Of the four GI processes, motility and secretion are the primary regulated functions.
       • If food moves through the system too rap-idly, there will not be enough time for everything in the lumen to be digested and absorbed.
       • Secretion is regulated so that the ap-propriate digestive enzymes can break down food into an absorb-able form
         • GI Peptides Include Hormones, Neuropeptides, and Cytokines
           • Peptides secreted by cells of the digestive tract may act as hor-mones or paracrine signals
             • Integrated function: the cephalic Phase
               • Digestive processes in the body begin before food ever enters the mouth. Simply smelling, seeing, or even thinking about food can make our mouths water and our stomachs rumble.
                 • Chemical and Mechanical Digestion Begins in the Mouth
                   • Soften and moisten food
                     • The water and mucus in saliva soften and lubricate food to make it easier to swallow
                   • Digestion of starch
                     • Chemical digestion begins with the secre-tion of salivary amylase
                   • Taste
                     • Saliva dissolves food so that we can taste it.
                   • Defense
                     • The final function of saliva is defense
                 • Saliva Is an Exocrine Secretion
                   • Saliva
                     • is a complex hyposmotic fluid that contains water, ions, mucus, and proteins such as enzymes and immunoglobulins.
                       • integrated function: the gastric Phase
                         • liters of food, drink, and saliva enter the fundus of the stomach each day. The stomach has three general functions:
                           • Storage
                             • The stomach stores food and regulates its passage into the small intestine, where most digestion and absorption take place.
                           • Digestion
                             • The stomach chemically and mechanically di-gests food into the soupy mixture of uniformly small par-ticles called chyme.
                           • Defense
                             • The stomach protects the body by destroying many of the bacteria and other pathogens that are swallowed with food or trapped in airway mucus
                       • Integrated function: the intestinal phase
                         • Once chyme passes into the small intestine, the intestinal phaseof digestion begins. Chyme entering the small intestine has un-dergone relatively little chemical digestion, so its entry must be controlled to avoid overwhelming the small intestine
                           • Intestinal Secretions Promote Digestion
                             • Digestive enzymes are produced by the intestinal epithe-lium and the exocrine pancreas.
                             • Bile made in the liver and released from the gall bladder is a nonenzymatic solution that facilitates the digestion of fats.
                             • Bicarbonate secretion into the small intestine neutralizes the highly acidic chyme that enters from the stomach
                             • Mucus from intestinal goblet cells protects the epithelium and lubricates the gut’s contents.
                             • An isotonic NaCl solution mixes with mucus to help lubricate the contents of the gut
                           • The Pancreas Secretes Enzymes and Bicarbonate
                             • The pancreas is an organ that contains both types of secretory epithelium: endocrine and exocrin
                           • The Liver Secretes Bile
                             • Bile is a nonenzymatic solution secreted from hepatocytes, or liver cell
                           • Most Digestion Occurs in the Small Intestine
                             • The intestinal, pancreatic, and hepatic secretion of enzymes and bile is essential for normal digestive function
                           • Bile Salts Facilitate Fat Digestion
                             • Fats and related molecules in the Western diet include triglyc-erides, cholesterol, phospholipids, long-chain fatty acids, and the fat-soluble vitamins
                 • Swallowing Moves Food from Mouth to Stomach
                   • Swallowing, or deglutition {glutire, to swallow}, is a reflex action that pushes a bolus of food or liquid into the esophagus
           • GI hormones
             • GI hormones, like all hormones, are secreted into the blood and transported throughout the body. They act on the GI tract, on accessory organs such as the pancreas, and on distant targets, such as the brain.
           • GI hormone Families
             • The gastrointestinal hormones are usu-ally divided into three families. All the members of a family have similar amino acid sequences, and in some cases there is overlap in their ability to bind to receptors