Digestive system – Alimentary canal

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