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Copyright © 2010 Pearson Education, Inc.
Pharynx
• Oropharynx and laryngopharynx
• Allow passage of food, fluids, and air
• Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors
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Esophagus
• Flat muscular tube from laryngopharynx to stomach
• Travels through the diaphragm via an opening called the esophageal hiatus
• Joins stomach at the cardiac orifice
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Esophagus
• Esophageal glands secrete mucus to lubricate and aid in bolus movement
• Muscularis: consists of skeletal muscle superiorly; smooth muscle inferiorly
• Contains upper and lower esophageal sphincters: upper and lower that act as “gateways” for food
• Lower esophageal sphincter prevents backflow of stomach contents into the esophagus
Copyright © 2010 Pearson Education, Inc. Figure 23.12a
Mucosa(contains a stratifiedsquamous epithelium)
Submucosa (areolarconnective tissue)
LumenMuscularis externa
Adventitia (fibrousconnective tissue)
(a)
• Circular layer • Longitudinal layer
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Digestive Processes: Mouth
• Ingestion
• Mechanical digestion
• Mastication is partly voluntary, partly reflexive
• Chemical digestion (salivary amylase and lingual lipase)
• Propulsion
• Deglutition (swallowing)
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Deglutition – 2 major phases
• Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups
• Buccal (oral) phase
• Voluntary contraction of the tongue
• Pharyngeal-esophageal phase
• Involuntary (sensory receptors initiate the swallowing reflex)
• Control center in the medulla and lower pons
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 1
Tongue
Trachea
Pharynx
Epiglottis
Glottis
Bolus of food
Upper esophageal sphincter is contracted. Duringthe buccal phase, the tongue presses against the hardpalate, forcing the food bolus into the oropharynxwhere the involuntary phase begins.
1
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 2
Epiglottis
Esophagus
Uvula
Bolus
The uvula and larynx rise to prevent food fromentering respiratory passageways. The tongue blocksoff the mouth. The upper esophageal sphincterrelaxes, allowing food to enter the esophagus.
2
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 3
Bolus
The constrictor muscles of the pharynx contract,forcing food into the esophagus inferiorly. The upperesophageal sphincter contracts (closes) after entry.
3
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 4
Relaxed muscles
Bolus of food
Stomach
Circular musclescontract
Longitudinal musclescontract
Gastroesophagealsphincter closed
Food is moved throughthe esophagus to thestomach by peristalsis.
4
Copyright © 2010 Pearson Education, Inc. Figure 23.13, step 5
Relaxedmuscles
Gastroesophagealsphincter opens
The gastroesophagealsphincter opens, and foodenters the stomach.
5
Copyright © 2010 Pearson Education, Inc. Figure 23.13
Tongue
Trachea
Pharynx
Epiglottis
Glottis
Bolus of food
Epiglottis
Esophagus
Uvula
Bolus
Bolus
Relaxed muscles
Circular musclescontract
Bolus of food
Longitudinal musclescontract
Stomach
Relaxedmuscles
Gastroesophagealsphincter opens
Gastroesophagealsphincter closed
Upper esophageal sphincter iscontracted. During the buccal phase, thetongue presses against the hard palate,forcing the food bolus into the oropharynxwhere the involuntary phase begins.
Food is movedthrough the esophagusto the stomach byperistalsis.
The gastroesophagealsphincter opens, and foodenters the stomach.
The uvula and larynx rise to prevent foodfrom entering respiratory passageways. Thetongue blocks off the mouth. The upperesophageal sphincter relaxes, allowing foodto enter the esophagus.
The constrictor muscles of thepharynx contract, forcing foodinto the esophagus inferiorly. Theupper esophageal sphinctercontracts (closes) after entry.
1 2
4
3
5
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The Stomach
Four Main Functions:
1. Temporary storage for ingested food
2. Mechanical breakdown of food
3. Chemical breakdown of food
4. Production of intrinsic factor, necessary for absorption of vitamin B12
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Stomach: Gross Anatomy
• Cardiac region (cardia)
• Surrounds the cardiac orifice
• Fundus
• Dome-shaped region beneath the diaphragm
• Body
• Midportion
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Stomach: Gross Anatomy
• Pyloric region: antrum, pyloric canal, and pylorus
• Pylorus is continuous with the duodenum through the pyloric valve (sphincter)
• Greater curvature
• Convex lateral surface
• Lesser curvature
• Concave medial surface
Copyright © 2010 Pearson Education, Inc. Figure 23.14a
Cardia
Esophagus
Pyloric sphincter(valve) at pylorus
Pyloriccanal
Pyloricantrum
Rugae ofmucosa
Body
Lumen
Serosa
Fundus
Lessercurvature
Greatercurvature
Muscularisexterna • Longitudinal layer • Circular layer • Oblique layer
(a)
Duodenum
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Stomach: Gross Anatomy
• Lesser omentum
• From the liver to the lesser curvature
• Greater omentum
• Drapes from greater curvature
• Anterior to the small intestine
• Protects abdominal viscera
Copyright © 2010 Pearson Education, Inc. Figure 23.30a
Falciform ligament
Liver
Gallbladder
Spleen
Stomach
Ligamentum teres
Greater omentum
Small intestine
Cecum
(a)
Copyright © 2010 Pearson Education, Inc. Figure 23.30b
Liver
Lesser omentumGallbladder
StomachDuodenum
Transverse colon
Small intestine
Cecum
Urinary bladder(b)
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Stomach: Microscopic Anatomy
• Still has four tunics
• Muscularis and mucosa are modified
• Muscularis externa
• Three layers of smooth muscle
• Inner oblique layer allows stomach to churn, mix, move, and physically break down food
Copyright © 2010 Pearson Education, Inc. Figure 23.15a
3 muscular layers•Longitudinal•Circular•Oblique
Copyright © 2010 Pearson Education, Inc.
Stomach: Microscopic Anatomy
• Mucosa
• Simple columnar epithelium composed of mucous cells
• Produce a layer of mucus that traps bicarbonate-rich fluid beneath it
• Protects the epithelial cells from acids, enzymes and abrasive materials
• Gastric pits lead into gastric glands
Copyright © 2010 Pearson Education, Inc. Figure 23.15b
(b) Enlarged view of gastric pits and gastric glands
Mucous neck cells
Parietal cell
Surface epithelium(mucous cells)
Gastric pits
Chief cell
Enteroendocrine cell
Gastric pit
Gastric gland
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Gastric Glands
• Cell types
• Mucous neck cells (secrete thin, acidic mucus)
• Parietal cells
• Chief cells
• Enteroendocrine cells
Copyright © 2010 Pearson Education, Inc. Figure 23.15c
(c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland
Pepsinogen
Mitochondria
PepsinHCl
Chief cell
Enteroendocrinecell
Parietal cell
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Gastric Gland Secretions
• Glands in the fundus and body produce most of the gastric juice
Parietal cell secretions
• HCl
• pH 1.5–3.5 denatures protein in food, activates pepsin, and kills many bacteria
• Intrinsic factor
• Glycoprotein required for absorption of vitamin B12 in small intestine
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Gastric Gland Secretions
• Chief cell secretions
• Inactive enzyme pepsinogen
• Converted to pepsin by HCl and by pepsin itself
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Homeostatic Imbalance
• Gastritis: inflammation caused by anything that breaches the mucosal barrier
• Peptic or gastric ulcers: erosion of the stomach wall
• Most are caused by Helicobacter pylori bacteria
• Cause 80% of gastric ulcers
• Treated successfully with antibiotics
Copyright © 2010 Pearson Education, Inc. Figure 23.16
Bacteria
Mucosalayer ofstomach
(a) A gastric ulcer lesion (b) H. pylori bacteria
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Digestive Processes in the Stomach
• Physical digestion
• Denaturation (breakdown) of proteins
• Enzymatic digestion of proteins by pepsin (and rennin in infants)
• Secretion of intrinsic factor required for absorption of vitamin B12
• Lack of intrinsic factor pernicious anemia
• Delivers chyme to the small intestine
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Regulation of Gastric Secretion
• Regulated by CNS and hormonal mechanisms
• Events occur in three phases:
1. Cephalic (reflex) phase: few minutes before food entry:
• sight, smell, taste or thought of food initiates gastric secretion
• Prepares the stomach to receive food
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Regulation of Gastric Secretion
2. Gastric phase: lasts for 3–4 hours after food enters the stomach (distending stomach)
• Stimulates stretch receptors
• Gastrin is released increasing gastric secretion production
• Distension and gastrin increase force of contraction
3. Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects to slow gastric activity down giving the intestine time to do its job
Copyright © 2010 Pearson Education, Inc. Figure 23.19
1 Propulsion: Peristaltic waves move from the fundus toward the pylorus.
2 3 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.
Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach.
Pyloricvalveclosed
Pyloricvalveclosed
Pyloricvalveslightlyopened
Copyright © 2010 Pearson Education, Inc.
Regulation of Gastric Emptying
• As chyme enters the duodenum in 3 ml spurts
• Receptors respond to stretch and chemical signals
• Enterogastric reflex and enterogastrones inhibit gastric secretion and duodenal filling
• Carbohydrate-rich chyme moves quickly through the duodenum
• Fatty chyme remains in the duodenum 6 hours or more
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Small Intestine: Gross Anatomy
• Major organ of digestion and absorption
• 2–4 m (7-13 ft) long; from pyloric sphincter to ileocecal valve
• Three Subdivisions
1. Duodenum – contains the bile duct and main pancreatic duct
2. Jejunum
3. Ileum
Copyright © 2010 Pearson Education, Inc. Figure 23.1
Mouth (oral cavity)Tongue
Esophagus
LiverGallbladder
Anus
DuodenumJejunumIleum
Small intestine
Parotid glandSublingual glandSubmandibulargland
Salivaryglands
Pharynx
StomachPancreas(Spleen)
Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal
Largeintestine
Copyright © 2010 Pearson Education, Inc. Figure 23.21
Jejunum
Mucosawith folds
Cystic duct
DuodenumHepatopancreaticampulla and sphincter
Gallbladder
Right and lefthepatic ducts of liver
Bile duct and sphincter
Main pancreatic ductand sphincter
PancreasTail of pancreas
Head of pancreas
Common hepatic duct
Major duodenalpapilla
Accessory pancreatic duct
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Structural Modifications
• Increase surface area of proximal part for nutrient absorption
• Circular folds (plicae circulares)
• Villi
• Microvilli
• Circular folds
• Permanent ridged
• Force chyme to slowly spiral through lumen
Copyright © 2010 Pearson Education, Inc. Figure 23.22a
Vein carrying blood tohepatic portal vessel
MusclelayersCircularfoldsVilli
(a)
Lumen
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Structural Modifications
• Villi
• Motile fingerlike extensions of the mucosa
• Villus epithelium
• Simple columnar absorptive cells (enterocytes)
• Goblet cells
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Structural Modifications
• Microvilli
• Projections (brush border) of absorptive cells
• Contain brush border enzymes which complete carbohydrate and protein digestion in the small intestine
Copyright © 2010 Pearson Education, Inc. Figure 23.22b
(b)
Absorptive cells
Lacteal
Intestinal crypt
Mucosaassociatedlymphoid tissue
MuscularismucosaeDuodenal gland Submucosa
EnteroendocrinecellsVenuleLymphatic vessel
Goblet cellBloodcapillaries
Vilus
Microvilli(brush border)
Copyright © 2010 Pearson Education, Inc.
Intestinal Juice
• Secreted in response to distension or irritation of the mucosa
• Slightly alkaline and isotonic with blood plasma
• Largely water, enzyme-poor, but contains mucus
• Facilitates transport and absorption of nutrients
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Liver
• Largest gland in the body
• Four lobes—right, left, caudate, and quadrate
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Liver
• Falciform ligament
• Separates the (larger) right and (smaller) left lobes
• Suspends liver from the diaphragm and anterior abdominal wall
• Round ligament (ligamentum teres)
• Remnant of fetal umbilical vein along free edge of falciform ligament
Copyright © 2010 Pearson Education, Inc. Figure 23.24a
SternumNipple
Liver
Right lobeof liver
Gallbladder
(a)
Bare area
Falciformligament
Left lobe of liver
Round ligament(ligamentum teres)
Copyright © 2010 Pearson Education, Inc. Figure 23.24b
Lesser omentum(in fissure)
Left lobe of liver
(b)
Porta hepatiscontaining hepaticartery (left) andhepatic portal vein(right)
Quadrate lobeof liverLigamentum teres
Gallbladder
Hepatic vein (cut)
Sulcus forinferiorvena cava
Caudate lobeof liver
Bare area
Bile duct (cut)
Right lobe ofliver
Sternum
Nipple
Liver
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Liver: Associated Structures
• Lesser omentum anchors liver to stomach
• Hepatic artery and hepatic portal vein
• Bile ducts
• Common hepatic duct leaves the liver
• Cystic duct connects to gallbladder
• Bile duct formed by the union of the above two ducts
Copyright © 2010 Pearson Education, Inc. Figure 23.21
Jejunum
Mucosawith folds
Cystic duct
DuodenumHepatopancreaticampulla and sphincter
Gallbladder
Right and lefthepatic ducts of liver
Bile duct and sphincter
Main pancreatic ductand sphincter
PancreasTail of pancreas
Head of pancreas
Common hepatic duct
Major duodenalpapilla
Accessory pancreatic duct
Copyright © 2010 Pearson Education, Inc.
Liver: Microscopic Anatomy
• Liver lobules
• Hexagonal structural and functional units
• Filter and process blood
• Composed of hepatocytes (liver cells)
• Longitudinal central vein
Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b
(a) (b)Lobule Central vein Connectivetissue septum
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Liver: Microscopic Anatomy
• Portal triad at each corner of lobule
• Bile duct receives bile from bile canaliculi
• Portal arteriole is a branch of the hepatic artery
• Hepatic venule is a branch of the hepatic portal vein
• Liver sinusoids are leaky capillaries between hepatic plates
• Kupffer cells (hepatic macrophages) in liver sinusoids
Copyright © 2010 Pearson Education, Inc. Figure 23.25c
(c)
Interlobular veins(to hepatic vein) Central vein
Sinusoids
Portal triad
Plates ofhepatocytes
Portal vein
Fenestratedlining (endothelial cells) of sinusoids
Bile duct (receivesbile from bile canaliculi)
Bile duct
Portal arteriolePortal venuleHepatic
macrophagesin sinusoid walls
Bile canaliculi
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Liver: Microscopic Anatomy
• Hepatocyte functions
• Process bloodborne nutrients
• Store fat-soluble vitamins
• Perform detoxification
• Produce ~900 ml bile per day
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Bile
• Yellow-green, alkaline solution containing
• Bile salts: function in fat emulsification and absorption
• Bilirubin: pigment formed from heme
• Cholesterol, triglycerides, phospholipids, and electrolytes
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Bile
• Enterohepatic circulation
• Recycles bile salts
• Bile salts duodenum reabsorbed from ileum hepatic portal blood liver secreted into bile
Copyright © 2010 Pearson Education, Inc.
The Gallbladder
• Thin-walled muscular sac on the ventral surface of the liver
• Stores and concentrates bile by absorbing its water and ions
• Releases bile via the cystic duct, which flows into the bile duct
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