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Digestive System
Anatomy & Physiology
| Question | Answer |
|---|---|
| digestive system | provides means to break down digested nutrients |
| nutrients are... | unusable in their original form, required for survival, and the digestive system provides a means to absorb them |
| digestive system includes organs that | ingest, mix, and propel food and add secretions and expel waste products |
| digestive system includes | upper and lower gastrointestinal tract and accessory organs |
| six main functions of the digestive system | ingestion, motility, secretion, digestion, absorption, and elimination |
| ingestion | introduction of solid and liquid nutrients into the oral cavity and the first step in the process of digesting and absorbing nutrients |
| motility | voluntary and involuntary muscular contractions that mix and move materials through the GI tracts |
| secretion | process of producing and releasing fluid products facilitating digestion (i.e. digestive enzymes, acid, bile) |
| digestion | breakdown of ingested food into smaller structures |
| two types of digestion | mechanical and chemical digestion |
| mechanical digestion | material physically broken down by chewing and mixing |
| chemical digestion | involves specific enzymes to break chemical bonds and changes large, complex molecules into smaller molecules |
| absorption | transport of digested molecules, electrolytes, vitamins, and water to move from GI tract into blood or lymph |
| elimination | expulsion of indigestible components that are not absorbed |
| two kinds of organs in the digestive system | gastrointestinal (GI) tract and accessory digestive organs |
| gastrointestinal (GI) tract function | digests and absorbs food (mouth, pharynx, esophagus, stomach, small intestine, and large intestine |
| accessory digestive organs function | teeth, tongue, gallbladder, digestive glands (salivary glands, liver, and pancreas) |
| upper GI tract organs include | oral cavity and salivary glands, pharynx, esophagus, and stomach |
| oral cavity and salivary glands | the beginning of mechanical digestion, secrete saliva from salivary glands in response to food, contain salivary amylase (enzyme initiating digestion of starch) - this mixes with ingested materials to form bolus |
| pharynx | location where bolus is moved to, where swallowing occurs and mucus is secreted here to facilitate swallowing |
| esophagus | from the pharynx, bolus is transported here to enter stomach and is lubricated by mucus secretions |
| stomach | where bolus was mixed with gastric secretions by smooth muscle contraction, secretions are produced by the epithelial cells of the stomach, and chyme is formed by the mixing |
| oral cavity has | the tongue on the inferior surface of the cavity |
| oral cavity structure | primarily from skeletal muscle with extrinsic and intrinsic muscles, has numerous projections, papillae, involved with taste, manipulates, repositions, & mixes materials & food during chewing, forms bolus occurs here, & is important in swallowing & speech |
| salivary glands | extrinsic salivary glands (parotid, submandibular, and sublingual) are here, secretion of saliva cleanses the mouth, moistens and dissolves food chemicals, and contains enzymes that begin the breakdown of starch |
| mechanical digestion - mastication | mechanically reduces bulk to facilitate swallowing, increases surface area to facilitate exposure to digestive enzymes, promotes salivation, and requires coordinated activities of teeth, lips, tongue, cheeks, and jaws |
| gross anatomy of the pharynx | funnel-shaped muscular passageway that allows the passage of food, fluids and air and is formed by the skeletal muscle pairs (superior, middle, and inferior pharyngeal constrictors) |
| gross anatomy of esophagus | flat muscular tube from pharynx to stomach |
| two components of the esophagus | superior esophageal sphincter and inferior esophageal sphincter |
| superior esophageal sphincter | contracted ring of circular skeletal muscle at superior end, area where esophagus and pharynx meet, and closed during inhalation of air |
| inferior esophageal sphincter | contracted ring of circular skeletal muscle at inferior end |
| motility: the swallowing process | swallowing takes place in three phases: voluntary phase, pharyngeal phase, and esophageal phase |
| swallowing (deglution) | moving ingested materials from oral cavity to stomach and occurs in three phases |
| voluntary phase | (occurs after ingestion), the bolus is formed as ingested materials and saliva mix and the bolus is directed posteriorly toward oropharynx |
| pharyngeal phase | involuntary reflex in which the bolus passes through the pharynx to the esophagus (through sequential contraction of pharynx muscles) |
| esophageal phase | involuntary phase - bolus passes through esophagus & stimulates sequential waves of muscular contraction (propels bolus toward stomach), sup. & inf. esophageal sphincters closed at rest, relax when bolus swallowed, & contract again to prevent reflux |
| stomach | sac in the sup. left abdominal quadrant, immediately inf. to diaphragm, chemical & mechanical digestion continuing here (digestion of protein and fat begin here), ingested materials spend 2-6 hours here, & absorption limited to small, nonpolar substances |
| gross anatomy of the stomach | muscular J-shaped organ that has greater curvature, lesser curvature, cardia, fundus, body, pylorus, and pyloric sphincter |
| greater curvature | larger convex inferolateral surface of the stomach |
| lesser curvature | smaller concave superomedial surface of the stomach |
| cardia | small superior entryway into stomach lumen from esophagus |
| cardiac orifice | where cardia meets esophagus |
| fundus | dome-shaped region superior and lateral to esophageal connection |
| body | largest region of the stomach and inferior to the cardiac orifice and extends to the pyloric orifice |
| pyloric sphincter | ring of circular smooth muscle surround orifice and regulates material into small intestine |
| gastric mixing | form of mechanical digestion, churning and mixing lead to reduction in size of swallowed particles, and changes semidigested bolus into chyme |
| gastric emptying | movement of acidic chyme from stomach into duodenum, pressure gradient moving contents toward pylorus, gradient increasing force against pyloric sphincter, sphincter opens, with entrance of small volume of chyme, sphincter closes with retropulsion |
| retropulsion | reverse flow of some contents back toward stomach |
| motility in the stomach | gastric mixing and gastric emptying |
| lower GI tract organs | continue digestive process and absorption and eliminate material that cannot be digested and absorbed |
| components of the lower GI tract organs | small intestine, accessory organs, large intestine |
| small intestine | divided into three continuous regions: duodenum, jejunum, and ileum (duodenum considered part of upper GI tract), receives chyme from stomach mixed with accessory organ secretions, and most chemical digestion and absorption here |
| accessory organs | secretions include bile and pancreatic juice, bile produced by liver, and is stored, concentrated, and released by gallbladder, and pancreatic juice with digestive enzymes secreted from pancreas |
| large intestine | continues absorption of water, electrolytes, vitamins and feces produced and eliminated through anus |
| small intestine | (most important - absorption) major organ of digestion and absorption, ingested nutrients spend at least 12 hours here, absorbs most nutrients and large percentage of water and electrolytes, vitamins absorbed here, 2-4 m long |
| gross anatomy of the small intestine | duodenum, jejunum and ileum |
| duodenum | first segment of the small intestine, originating at pyloric sphincter, arched into C-shape around head of pancreas, and receives accessory gland secretions from liver, gallbladder, and pancreas |
| jejunum | middle region of the small intestine and is the primary region for chemical digestion and nutrient absorption |
| ileum | last region of the small intestine and absorption continues here |
| chyme from the stomach contains | partially digested carbohydrates and proteins and undigested fats |
| small intestine | delivers bile, enzymes and bicarbonate from the liver and pancreas |
| peristalsis | alternating contraction sequence of inner and outer layers of the small and large intestine and propels ingested materials through tract (involuntary) |
| mixing | "back-and-forward" motion that lacks directional movement, blends ingested material with secretions |
| liver functions | accessory digestive organ in the right, upper quadrant of the abdomen that is immediately inferior to the diaphragm and has the main function of storing bile - it is the largest intestinal organ |
| liver anatomy | two partially separated lobes (right lobe is larger than the left lobe) and process bloodborne nutrients, stores fat-soluble vitamins, and performs detoxification |
| bile | secreted by the liver and contains water, bicarbonate ions, bile salts and pigments, cholesterol, lecithin, and mucin (bile salts, lecithin, and mucin help in mechanical digestion of lipids) |
| gallbladder | saclike organ attached to the inferior surface of the liver that stores, concentrates, and releases bile produced in the liver, and has a sphincter valve |
| sphincter valve | controls flow of bile into and out of the gallbladder |
| pancreas functions | has endocrine function (producing and secreting insulin and glucagon) and has exocrine function (produces pancreatic juice to assist with digestive activities) |
| pancreas anatomy | extends horizontally from left lateral edge of duodenum, wide head adjacent to duodenum curvature, central elongated body that projects toward left lateral wall, and tail, tapering as approaches the spleen |
| pancreatic juice | pancreatice amylase to digest starch, pancreatic lipase to digest fats, inactive proteases that digest proteins when activated, and nucleases for digestion of nucleic acids |
| cholecystokinin (CKK) | hormone released from small intestine in response to fatty chyme, stimulates gallbladder to strongly contract and release bile, stimulates pancreas to release pancreatic juice |
| large intestine | major function - propulsion feces 2 anus, semi wide tube shorter than sm. intestine, located n ab. pelvic cavity, absorbs water & electrolytes from remaining digested material, watery chyme compacted n2 feces, & stores feces til eliminated thru digestion |
| anatomy of large intestine | cecum, colon, rectum, and anal canal |
| cecum | first potion of the large intestine (chyme entering from ileum) |
| colon | second portion of the large intestine (forms inverted U-shaped arch and has four segments (ascending, transverse, descending, and sigmoid colon) |
| ascending colon | extends superiorly from cecum along right lateral abdominal cavity and makes 90-degree turn to left as approaches the liver |
| transverse colon | projects horizontally to left across abdominal cavity, makes 90-degree turn inferiorly and posteriorly |
| descending colon | along left side of abdominal cavity and descends vertically |
| sigmoid colon | terminates at the rectum |
| rectum | third major region of large intestine, structure connecting to sigmoid colon, muscular tube that expands to store feces |
| anal canal | last few centimeters of large intestine, terminates at the anus |
| internal anal sphincter | smooth muscle |
| external anal sphincter | skeletal muscle |
Created by:
Nicolekr
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