 | Term | Definition |
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digestive system |
organ system that processes food, extracts nutrients from it, and eliminates the residues |
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mechanical digestion |
physical breakdown of food into smaller pieces |
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chemical digestion |
series of hydrolysisi reactions that break dietary macromolecules into their monomers |
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mesenteries |
connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall. serve as a means of holdiing the abdominal mesentery in proper relationship to each other |
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dorsal mesentery |
a sheet of tissue found at the dorsal midline of the abdominal cavity, which extends to the digestive tract. it folds around the digestive tract to form the serosa |
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ventral mesentery |
sheet of tissue that continues beyond the digestive organs. it hangs freely in the abdominal cavity or it may attach to the ventral abdominal wall |
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lesser omenum |
a ventral mesesntery that extends from the stomach to the liver. found on the right superior margin ( lesser curvature) of the stomach |
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greater omentum |
hangs from the left inferior margin of the stomach (greater curvature) and loosely covers the small intestines like an apron. It turns back on itself and forms a serous membrane around the spleen and transverse colon |
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intraperitoneal |
when an organ is enclosed by mesentery on both sides |
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retroperitoneal |
when an organ lies against the dorsal body wall and is covered by peritoneum on the ventral side only, it is said to be outside of the peritoneal cavity |
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myenteric reflexes |
aka short reflexes, an autonomic reflex that streches or chemically stimulates the digestive tract through the myenteric nerve plexus to stimulate contractions |
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vagovagal reflexes |
aka long reflexes, an autonomic reglex that acts through nerve fibers that carry sensory signals from the digestive tract to the central nervous system, and motor commands back to the digestive tract. Parasympathetic fibers of the vagus nerves are especially important in stimulating digestive motility and secretion by way of these. |
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mastication |
breaking food into peices small enough to be swallowed and exposes more area to the action of digestive enzymes. food stimulates receptors that trigger an involuntary chewing reflex. Food is manipulated by the tongue, buccinator, and orbicularis muscles. and the masseter and temporalis muscles produce the crushing action of the teeth. the lateral and medial pterygoid muscles and masseters produce side to side grinding action. |
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saliva |
moistens the mouth, digests a little starch and fat, cleanes the teeth, inhibits bacterial growth, and dissolves muscles so they can stimulate the taste buds. and aid in swallowing |
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salivary amylase |
an enzyme that begins starch digestion in the mouth. works well at a neutral pH. and is deactivated by the low pH of the stomach |
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lingual lipase |
an enzyme that is activated by stomach acid and digests fat after the food is swallowed. not active in the mouth, but is actvated by the acidity of the stomach |
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mucus |
binds and lubricates the food mass and aids in swallowing |
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lysozyme |
an enzyme that kills bacteria |
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immunoglobulin A |
an antibody that inhibits bacterial growth |
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pharyngeal constrictors |
circular muscles that downward during swallowing. consists of a deep larer of longitudinal oriented skeletal muscle, and a superficial layer of circular skeletal muscle. |
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upper esophageal sphincter |
the inferior constrictor that remains contracted when food is not being swallowed in order to exclude air from the esophagus |
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esophagus |
a straight muscular tube, begins at the cricoid cartilagem inferior to the larynx and dorsal to the trachea. the upper 1/3 is commonly composed of skeletal muscle, and the lower 1/3 is smooth muscle...this transition is because of the shift from voluntary to involuntary phases of swallowing as food bolus passes down the esophagus. |
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esophageal hiatus |
where the esophagus penetrates the diaphragm |
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cardiac orifice |
where the esophagus meet the stomach. it is named this because of its proximity to the heart. |
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lower esophageal sphincter |
a physiological sphincter that briefly slows down food before it enters the stomach . it also acts to prevent stomach contents from regurgitating into the esophagus, thus protecting the esophageal mucosa from the corrosive effect of the stomach acid. |
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esophageal glands |
glands found in the submucosa of the esophagus that secrete lubricating mucus into the lumen |
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deglutition |
complex action involving over 22 muscles in th mouth, pharynx, and esophagus, coordinated by the swallowing center |
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swallowing center |
a nucleus in the medulla oblongata and pons, which communicates with the muscles of the pharynx and esophagus by way of the trigeminal . facial, glossopharyngeal, and hypoglossal nerves |
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buccal phase |
The first phase in swallowing, the tongue collects food, presses it against the palate to form a bolus, and pushes it back into the oropharynx. the bolus stimulates the tactile receptors and activates the next phase |
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pharyngeal-esophageal phase |
food and drink are blocked from reentering the mouth or entering the nasal cavity or larynx by 1) the root of the tongue blocks the oral cavity. 2) the soft palate rises and blocks the nasopharynx, 3) the infrahyoid muscles pull the larynx up, the epiglottis covers its opening |
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peristalsis |
a wave of muscular contraction that pushes the bolus ahead of it, triggered by the bolus sliding off the epiglottis and stretching the esophagus. This is moderated partly by a short reflex through the myenteric nerve plexus |
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chyme |
digestion in the stomach produces a soupy/pasty mixture of semidigested food |
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regions of the stomach |
lesser curvature, greater curvature, cardiac region, fundic region, body, pyloric region....antrum, pyloric canal, pylorus, and pyloric sphincter |
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innervation of the stomach |
the stomach receives parasympathetic nerve fibers from the vagus nerves and sympathetic fibers from the celiac ganglia |
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circulation of the stomach |
blood is supplied by branches of the celiac trunk, and blood is drained from the stomach and intestines into the hepatic portal circulation and filters through the liver before returning to the heart |
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gastric rugae |
longitudinal wrinkles that become more apparent as the stomach empties |
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gastric pits |
gastric mucosa is pocked with depressions which are lined with the the same columnar epithelium as the surface. they are continually producing new epithelial cells |
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stomach glands |
the cardiac, pyloric, and gastric glands are all found in their relative region of the stomach |
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mucous cells |
secrete mucous, and are predominately in the cardiac and pyloric glands |
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regenerative cells |
cells that divide rapidly and produce a continued supply of new cells...they are found in the base of the pit and neck of the glands |
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parietal cells |
cells found in the upper half of the gland and sevrete HCl and intrinsic factor. |
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chief cells |
the most numerous cells which sevrete chymosin and lipase in infancy and pepsinogen throughout life. they dominate the lower half of the gastric glands |
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enteroendocrine cells |
cells that secrete hormones and paracrine messengers that regulate digestion. they are concentrated in the lower end of a gland, there are at least 8 different kinds of these cells in the stomach...each of which produces a different chemical messenger |
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