DIGESTIVE SYSTEM – ALIMENTARY CANALChapter 14
ALIMENTARY CANAL
Aka gastrointestinal (GI) tract Continuous tube open at both ends About 9m long in a cadaver; when living
shorter due to muscle tone Food is technically outside the body
MOUTH (ORAL CAVITY)
Mastication (chewing) occursas saliva mixes w/ food
Parts Lips Cheeks –walls Hard palate – anterior roof Soft palate – posterior roof Uvula – projection of soft palate Vestibule – btw lips/cheeks and teeth/gums Oral cavity proper – area w/in teeth Tongue
Attaches to 2 bones – hyoid, styloid process Lingual frenulum – secures to floor
Palatine tonsils – posterior – sides Lingual tonsils – on base of tongue
PHARYNX
Undergoes peristalsis Oropharynx – posterior to oral cavity Laryngopharynx – joins esophogus
ESOPHAGUS
Joins pharynx and stomach About 25cm long 4 tissue layers (tunics) – esophagus to large
intestineMucosa – inner
Lines lumenSurface epithelium w/ connective lamina propria and smooth muscle
Submucosa – contains blood and lymphatic vessels, nerve endings
ESOPHAGUS CONT.
Muscularis extrnaInner circular layer and outer longitudinal layer of smooth muscle
Serosa – outermost – visceral peritoneumConnected to parietal peritoneum by mesentery
Walls contain submucosal nerve plexus and myenteric nerve plexusRegulates mobility and secretory activity
of GI tract organs
STOMACH
On left side of cavity Regions
Cardiac region – around cardioesophogeal
sphincterWhere food enters
Fundus – lateral to cardiac regionBodyPyloric antrum – most activity herePylorus – terminal – around pyloric
sphincter valve
STOMACH CONT.
Length about 25cm Diameter varies
May hold about 4L of food Forms rugae (folds) when empty
Greater curvature – convex lateral surface Lesser curvature – concave medial surface
Joined to liver by lesser omentum (peritoneum) Greater omentum – hangs down to insulate,
cushion, and protect organs Contains an extra muscle layer – an oblique
layer Allows churning and mixing
STOMACH CONT.
Lining has gastric pits w/ gastric glands that secrete gastric juicesChief cells – protein enzymes –
pepsinogensParietal cells – hydrochloric
acidMucous neck cells – produce
protective mucousEnteroendocrine cells – gastrin
Chyme – processed food that enters intestine
SMALL INTESTINE
Average length 2.5-7m Extends from the pyloric
sphincter to the ileocecal valve 3 divisions
Duodenum – “12 finger lengths long” Bile duct and pancreatic duct join to form the
hepatopancreatic ampulla and enter duodenum via the duodenal papilla
Allows pancreatic enzymes and bile to enter and complete digestion
Jejunum – “empty” Ileum – “twisted intestine”
SMALL INTESTINE CONT.
Pyloric sphincter – controls movement of food into intestine
Wall modifications Microvilli – aka brush border
Tiny projections to increase surface area Villi
Fingerlike projections Contain capillaries and a
lacteal (modified lymphatic capillary) – absorbed nutrients move into capillaries
SMALL INTESTINE CONT. Circular folds – aka plica circulares
Deep folds in mucosa and submucosa layers – increase surface area
Peyer’s patches – collections of lymphatic tissue – increase toward end of small intestine to keep bacteria out of blood
LARGE INTESTINE
About 1.5m long Extends from ileocecal valve to the anus Absorbs water from indigestible food and
gets rid of wastes Subdivisions
Cecum – sac-likeAppendix – hangs from
cecumAppendicitis – build up of bacteria
LARGE INTESTINE CONT.
Colon Ascending colon – up right side
of body – turns at right colic (hepatic) flexure
Transverse colon – moves across body – turns at left colic (splenic) flexure
Descending colon – moves down left side Sigmoid colon – enters pelvis Rectum Anal canal – opens to exterior at anus
Voluntary sphincter (external anal sphincter) – skeletal muscle
Involuntary sphincter – smooth muscle
LARGE INTESTINE CONT.
Mucosa contains goblet cells – produce an alkaline mucus for lubrication
Haustra – puckering of wall due to muscle tone of teniae coli (longitudinal muscle)
ACCESSORY ORGANS – SALIVARY GLANDS
Empty into mouth Parotid glands – anterior to ears – mumps Submandibular glands – floor of mouth Sublingual glands – floor of mouth All produce saliva – mixture
Mucus – moistens and binds food into a bolus
Serous fluid – contains salivary amylase – begins starch digestion
ACCESSORY ORGANS - TEETH
1st set – deciduous teeth – baby teeth; milk teeth Should have full set by 2 years Begin to lose btw 6-12 years old
2nd set – permanent teeth – 32 Should have all but third molars (wisdom teeth)
by end of adolescence Wisdom teeth emerge btw 17-25
Types – pairs listed for top ½ of mouth Incisors (2 pr) – cutting Canines (1pr)– tearing/piercing Premolars (2 pr) and molars (3 pr) – grinding
TEETH CONT.
Parts Crown – exposed portion
Above gingiva (gum) Covered by enamel Dentin – bulk of tooth – under enamel Pulp cavity – contains blood vessels and
nerves Neck – connects crown to root Root – embedded in jawbone
Cementum – covers outer surface and attaches to periodontal membrane (holds tooth in place)
Root canal – where pulp cavity enters root
ACCESSORY ORGANS
Pancreas – produces digestion enzymesAlso produces insulin and glucagen
Liver – largest gland in body – 4 lobesLies over stomachHangs from diaphragm and abdominal wall
by falciform ligament Produces bile – leaves via the common
hepatic ductComposed of bile salts and phospholipids which aid digestion
Salts emulsify fats by breaking large globules into smaller ones
ACCESSORY ORGAN - GALLBLADDER
Small, green sac on the inferior surface of the liver
Connected to liver via the cystic duct
Stores bile until needed
Gallstones – form when bile is stored too long or too much water is removed cholesterol crystallizes
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