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Digestive System

Anatomy & Physiology

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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