Digestion the mechanical and chemical breakdown of foods into
nutrients that cell membranes can absorb 2 Components of the
digestive system: Alimentary canal mouth, pharynx, esophagus,
stomach, small intestine, large intestine, anal canal Accessory
organs secrete products into the canal; salivary glands, liver,
pancreas, gallbladder
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Alimentary Canal Around 9 meters long Muscular tube that passes
through the ventral cavity
Salivary Glands Secrete saliva: Moistens food particles Helps
bind food particles Begins chemical digestion of carbohydrates
Dissolves food for tasting Helps cleanse mouth and teeth
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Regions of the Pharynx Nasopharynx Open to nasal cavity Passage
for air during breathing Oropharynx Behind soft palate Passage for
air and food Laryngopharynx Passage for food to the esophagus
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Swallowing Reflex 1.Food is chewed and mixed with saliva to
form a mass called a bolus. 2.Bolus is forced into the pharynx.
3.Swallowing reflex is stimulated by sensory receptors around the
pharyngeal opening. 4.Soft palate rises to prevent food from
entering the nasal cavity. 5.Hyoid bone and larynx are elevated,
and the epiglottis of the larynx closes off the top of the trachea.
6.Breathing is briefly inhibited.
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Swallowing Reflex 7.Tongue presses against the soft palate,
sealing the oral cavity off from the pharynx. 8.Longitudinal
muscles in the pharyngeal wall contract, moving the pharynx up
toward the bolus. 9.Muscles in the lower pharynx relax, and the
esophagus opens. 10.Peristalsis moves the bolus through the
esophagus.
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Swallowing Reflex
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Esophagus Straight, collapsible tube Approximately 25 cm long
Passageway from pharynx to stomach Cardiac sphincter Mucous glands
for lubrication
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Stomach Receives food from the esophagus Mixes food with
gastric juices Initiates protein digestion Performs limited
absorption of water, salts, alcohol, and lipid- soluble drugs Moves
food into the small intestine
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Gastric Secretions Gastric pits Gastric glands Goblet cells
Chief cells pepsinogen Parietal cells HCl and intrinsic factor
Gastric juice Regulated by ACh, gastrin, and cholecystokinin
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Pancreas Secretes pancreatic juice from acinar cells Mixed
gland Pancreatic duct Hepatopancreatic sphincter
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Pancreatic Secretions Pancreatic juice contains several
enzymes: Pancreatic amylase Pancreatic lipase Nucleases Trypsin,
chymotrypsin, and carboxypeptidase Bicarbonate ions Release
regulated by secretin
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Liver Carbohydrate, lipid, and protein metabolism Storage of
glycogen, iron, vitamins A, D, and B12 Blood filtering
Detoxification Secretion of bile
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Gallbladder Pear-shaped sac on the inferior liver surface
Connects to the cystic duct which feeds into the common hepatic
duct Stores bile between meals Reabsorbs water to concentrate bile
Releases bile into the small intestine Common bile duct
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Small Intestine Extends from pyloric sphincter to the large
intestine Receives secretions from the pancreas and liver Completes
digestion of nutrients in chyme and absorbs products of digestion
Mixing movements and peristalsis chyme moves through in 3-10 hours
Transports digestive residue to the large intestine
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Regions of the Small Intestine Duodenum 25 cm long Most fixed
portion of the small intestine Jejunum Ileum Jejunum and ileum are
not distinctly separate Both are mobile
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Intestinal Villi Tiny projections on the inner wall off the
small intestine Densest in the duodenum Increase surface area for
absorption Microvilli Secrete peptidases, sucrase, maltase,
lactase, intestinal lipase Capillaries absorb simple sugars, amino
acids, electrolytes, and water
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Large Intestine Ileocecal valve 1.5 meters long Proximal end
functions primarily in water and electrolyte absorption Distal end
functions primarily to store feces Little to no digestive
function
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Regions of Large Intestine Cecum Vermiform appendix Colon
Ascending colon Transverse colon Descending colon Sigmoid colon
Rectum Anal canal
Defecation Reflex Can be initiated by person (deep breath and
abdominal contraction) Forces feces into rectum Reflex involves
relaxation of the internal anal sphincter and peristaltic waves
through the descending colon Can be prevented by contraction of the
external anal sphincter
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Feces Made of materials not digested or absorbed Water
Electrolytes Mucus Bacteria 75% water Color from bile pigments
altered by bacterial action Odor from compounds produced by
bacteria