A&P Chapter 24 - Digestive System

• the physical and chemical breakdown of complex food into its component parts
• catabolism

• alimentary canal
• accessory organs

• mouth
• pharynx
• esophagus
• stomach
• small intestine
• large intestine

• teeth
• tongue
• salivary glands
• liver
• gallbladder
• pancreas

• (inside out)
• mucosa
• submucosa
• muscularis
• serosa

• inner lining of AC
• simple columnar w/many lymph nodes

• 2nd layer of AC
• extremely vascular membrane that binds to muscularis

• 3rd layer of AC
• skeletal muscle tissue that produces voluntary movement of swallowing
• found mostly in mouth, pharynx, esophagus

• outside lining of AC
• aka visceral peritoneum

• peritoneum
• mesentary
• mesocolon
• greater omentum
• falciform ligament

• covers all digestive organs and structures
• largest serous membrane in the body

binds small intestine together

bines large intestine to posterior body wall

• apron of fat that hangs over stomach and intestines
• many lymph nodes

attaches liver to diaphragm and anterior body wall

• controlled by hypothalamus
• 2 centers: feeding center, satiety center

• part of hypothalamus
• when active, cannot control food intake

• part of hypothalamus
• when active, will not eat

chewing, moving, swallowing, mixing

• all reactions that split the bonds in food to break into component parts
• controlled by enzymes

• aka buccal cavity
• tissue: stratified squamous non-keritinized ET
• lined with mucous membrane
• mostly mechanical digestion
• chemical digestion of starch by salivary amylase

space between teeth, lips, cheeks

food combined with saliva

• enzyme that digests starch in the mouth
• not completely digested because food is swallowed quickly
• salivary amylase is denatured by stomach acid
• produced by parotid gland

• enzyme secreted by glands in the tongue
• should digest fat but its swallowed before it occurs
• denatured in the stomach by acid

3 pair: parotid, sublingual, submandibular

• largest salivary glands
• in front of and slightly below the ears
• secretes thin, watery saliva
• produces salivary amylase

• salivary glands
• under the tongue toward front of mouth
• produces thick mucus-like saliva
• most active under stress

• salivary glands
• aka submaxillary glands
• at the junction of manible and maxilla
• contains mucus cells
• produces thick saliva

• produce 1.5qt daily
• 99.5% H20, sodium, potassium, chloride, bicarb ions
• contains amylase, lipase, lipoenzyme

kills bacteria in the mouth

• anchord by the hyoid bone
• tissue: skeletal muscle covered with mucous membrane
• covered with papillae
• 5 tastes: sweet, salt, sour, bitter, umami (savory)
• glands produce lingual lipase
• 2 muscles: extrinsic, intrinsic

divides the tongue

anchors tounge underneath

moves tongue in/out, side to side

alters size/shape of tongue during speech and swallowing

• adult: 32 permanent teeth (2123)
• children: 20 deciduous teeth (2102)

• incisors
• canine/cuspid
• premolar/bicuspid
• molars

part of tooth above gumline

1-3 projections below the gumline

• junction point of crown and root
• located at/below gumline
• composed of dentin

calcified CT

• covers dentin of the crown
• hardest substance in the body

• covers dentin of the root
• not as hard as enamel

blood vessels and nerves deep in the crown

space within the root of the tooth

hole at the base of each root where blood vessels and nerves enter/exit

tooth socket

anchor tooth

joint of tooth in socket

• aka deglutition
• process that moves bolus from mouth to esophagus
• requires saliva and mucus
• 3 stages: voluntary, pharangeal, esophageal

move bolus from mouth toward oropharynx

• bolus moves involuntarily from throat to esophagus
• soft pallet rises and closes nose
• epiglottis tips up and closes trachea

bolus moves involuntarily through esophagus into stomach

• throat
• 3 subdivisions: nasopharynx, oropharynx, laryngopharynx

• behind the nose
• passageway for air only

• behind the mouth
• passageway for air and food

• between oropharynx and trachea
• passageway for air and food

• collapsed tube directly behind trachea
• connects throat to stomach
• lined with mucus
• movement occurs through peristalsis

• contaction of the muscularis that moves food
• always strongest proximal/weakest distal

• muscular J shaped bag located on left side of abdominal cavity
• tissue: simple columnar w/ goblet cells, gastric pits, gastric glands

cells in stomach that release mucus onto surface of tissue

entrance to gastric glands

• produce gastric juice components
• 4 types of cells: chief cells, parietal cells, mucous cells, G cells

• in gastric glands
• produce pepsinogen and gastric lipase

• in gastric glands
• produce HCl and intrinsic factor

• in gastric glands
• produce mucus

• in gastric glands
• produce gastrin
• only in antrum

• series of mixing waves that occur q 20 sec
• waves mix bolus w/ gastric juice to form chyme
• mixing waves increase proximal to distal

bolus mixed with gastric juice

• stomach pH is < 2.0 (to kill bacteria/microbes)
• chemicals: HCl, gastric lipase, mucus, intrinsic factor, gastrin, pepsinogen

• chemical digestion in stomach
• kills bacteria
• denatures enzymes
• stimulates release of hormones that release bile and pancreatic juice

• chemical digestion in stomach
• enzyme that digests fat
• functions best at pH 6 or higher
• digests milk fat in infants - useless in adults

• chemical digestion in stomach
• coats stomach w/ 1" layer to prevent destruction of stomach by acid

• chemical digestion in stomach
• needed for B12 absorption

• chemical digestion in stomach
• hormone that controls stomach emptying

• chemical digestion in stomach
• pepsin: digests protein
• pepsinogen: inactive form of pepsin
• must be produced in inactive form since pepsin would eat chief cells (since cell is protein)
• becomes pepsin when it contacts HCl
• pepsin is only enzyme that will work in acid (primary structure)

3 phases: reflex (cephalic), gastric, intestinal

• gastric juice production
• begins when food is seen, smelled, thought about
• controlled by MO and hypothalamus

• gastric juice production
• controlled by hormones and ANS
• food enters stomach and stretches stomach (stretch receptors)
• raises pH (chemoreceptors)
• receptors trigger nerves that cause release of gastric juice
• stomach distends -> G cells release gastrin -> gastric juice
• constricts cardiac sphincter, relaxes pyloric sphincter (contents can exit)

• gastric juice production
• chyme enters small intestine
• causes release of 3 hormones: GIP, secretin, CCK

• gastric inhibitory peptide
• slows production of gastric juice

slows production of gastric juice

• cholecystokinin
• slows/stops stomach emptying
• causes release of bile and pancreatic juice

• forceable expulsion of stomach contents through the mouth
• vomiting center is the MO
• prolonged, excessive vomiting causes acid-base imbalance, ulcers in the esophagus, destruction of tooth enamel

• endocrine and exocrine gland
• large, long, flat
• head, body, tail
• located behind stomach along posterior wall

• endocrine portion of pancreas
• produces insulin, glucagon, somatostatin, pancreatic polypeptide

decreases BGL

increases BGL

metabolic hormones

• exocrine portion of pancreas
• produces 1.5qts of pancreatic juice daily

• made of water, salt, sodium, bicarb, enzymes
• ph 7.1 - 8.2 (slightly alkalid)
• released in response to CCK
• functions:
• --buffers acidic chyme as it enters small intestine
• --stops digestive action of pepsin (pepsin needs acid)
• --creates proper pH for digestion in small intestine
• --alkaline pH is required to keep pancreatic enzymes alive (acid would denature)

• pancreatic enzyme
• starch -> sugar

• pancreatic enzyme
• lipids -> fatty acid + glycerol

• pancreatic enzyme
• DNA -> sugar, phosphate, nitrogen base (A G C T)

• pancreatic enzyme
• RNA -> sugar, phosphate, nitrogen bases (A G C U)

• pancreatic enzyme
• inactive
• contacts enterokinsase (small intestine enzyme) -> trypsin
• breaks proteins into peptides

• pancreatic enzyme
• inactive
• contacts trypsin -> chymotrypsin
• breaks proteins into peptides

• pancreatic enzyme
• inactive
• contacts trypsin -> carboxypeptidase
• breaks peptides into amino acid

• detoxes everything in the body
• epigastric/R hypochondriac region, below diaphragm
• largest/heaviest organ
• tissue: dense irregular CT covered by peritoneum
• 2 lobes: R and L
• contains hepatic cells
• contains sinusoids

separates R and L lobes of the liver

• quadratic
• caudate

• cells in the liver that produce bile, heparin, most blood proteins
• store vitamins, minerals, glycogen (stored glucose)

• spaces in the liver
• contain kuppfer cells

• destroy bacteria
• break down toxins
• remove old blood cels

• browinsh green, slightly alkaline
• 1 qt produced daily
• composed of H20, bile salts, cholesterol, lipid, pigment (bilirubin), ions
• function: emulsification of fat

• small gobules of fat after being broken down by bile
• greater surface action for p. lipase

• sac off of R lobe of liver
• function: stores and concentrates bile by reabsorbing H20
• bile is released when CCK is present (as fat enters small intestine)

duct from liver to small intestine

duct from gallbladder to small intestine

where common bile duct and cystic duct join

• fat enters intestine
• fat in intestine: bile leaves gallbladder, enters cystic duct -> common bile duct -> intestine (sphincter is open)
• no fat in intestine: bile leaves liver -> common bile duct -> cystic duct -> gallbladder (sphincter is closed)

• 20ft long, 1" wide
• 3 parts:
• --duodenum - 1st foot
• --jejunum - next 8 feet
• --ileum - last 11 feet
• tissue: simple columnar w/ goblet cells, crypts of lieberkuhn, brunners glands, panath cells, villi/microvilli

• located throughout entire small intestine
• makes intestinal juice

• found in duodenum
• secrete alkaline fluid to help raise pH of entering chyme

• in small intestine
• secrete lysozyme to kill bacteria

fingerlike projections in small intestine that increase surface area of lining of intestion to make absorption more efficient

• peristalsis - weaker than in stomach
• segmentation

• major mechanical process of small intestine
• localized contractions in region that contains chyme
• mixes chyme with intestinal juice
• brings chyme into contact with intestinal wall for absorption
• helped by plicae circulares

• rings/bands in small intestine
• allow chyme to spiral throughout intestine

• pancreatic enzymes break down carbs, lipids, proteins
• 90% of all absorption occurs in small intestine
• drugs/alcohol absorbed in stomach
• H2O in small and large intestine

• bile salts released in duodenum reabsorbed in the ileum
• move from intestine to blood back to liver

• last 5 feet of AC
• 2.5" diameter
• tissue: simple columnar w/ goblet cells

pouches in the colon

• peristalsis - weak/insignificant
• haustral churning
• mass peristalsis

haustra fill and contract to push contents through intestine

• strong contractions that begins in transverse colon and pushes contents to the rectum
• initiated by gastrocolic reflex

• controlled by bacterial enzymes
• bacteria breaks down waste, helps absorb vitamins, minerals, H20

• anything not reabsorbed
• reabsorption greatest in cecum and ascending colon

liquid feces frequently expelled because too little water reabsorbed

• dry, hard feces that is difficult to expel
• too much water reabsorbed

• emptying the rectum
• inhale, voluntarily contract abdomen/diaphragh, push
• sphincter relaxes
• if not expelled, contents remain in sigmoid colon until next mass peristalsis