Upload
bozica
View
24
Download
0
Embed Size (px)
DESCRIPTION
23. The Digestive System: Part B. Pharynx. Oropharynx and laryngopharynx Allow passage of food, fluids, and air Stratified squamous epithelium lining Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors. Esophagus. Flat muscular tube from laryngopharynx to stomach - PowerPoint PPT Presentation
Citation preview
PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College
C H A P T E R
Copyright © 2010 Pearson Education, Inc.
23
The Digestive System: Part B
Copyright © 2010 Pearson Education, Inc.
Pharynx
• Oropharynx and laryngopharynx
• Allow passage of food, fluids, and air
• Stratified squamous epithelium lining
• Skeletal muscle layers: inner longitudinal, outer pharyngeal constrictors
Copyright © 2010 Pearson Education, Inc.
Esophagus
• Flat muscular tube from laryngopharynx to stomach
• Pierces diaphragm at esophageal hiatus
• Joins stomach at the cardiac orifice
Copyright © 2010 Pearson Education, Inc.
Esophagus
• Esophageal mucosa contains stratified squamous epithelium
• Changes to simple columnar at the stomach
• Esophageal glands in submucosa secrete mucus to aid in bolus movement
• Muscularis: skeletal superiorly; smooth inferiorly
• Adventitia instead of serosa
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
Copyright © 2010 Pearson Education, Inc. Figure 23.12b
Mucosa(contains a stratifiedsquamous epithelium)
(b)
Copyright © 2010 Pearson Education, Inc.
Digestive Processes: Mouth
• Ingestion
• Mechanical digestion
• Mastication is partly voluntary, partly reflexive
• Chemical digestion (salivary amylase and lingual lipase)
• Propulsion
• Deglutition (swallowing)
Copyright © 2010 Pearson Education, Inc.
Deglutition
• Involves the tongue, soft palate, pharynx, esophagus, and 22 muscle groups
• Buccal phase
• Voluntary contraction of the tongue
• Pharyngeal-esophageal phase
• Involuntary
• Control center in the medulla and lower pons
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
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
Copyright © 2010 Pearson Education, Inc.
Stomach: Gross Anatomy
• Cardiac region (cardia)
• Surrounds the cardiac orifice
• Fundus
• Dome-shaped region beneath the diaphragm
• Body
• Midportion
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Stomach: Gross Anatomy
• Lesser omentum
• From the liver to the lesser curvature
• Greater omentum
• Drapes from greater curvature
• Anterior to the small intestine
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)
Copyright © 2010 Pearson Education, Inc.
Stomach: Gross Anatomy
• ANS nerve supply
• Sympathetic via splanchnic nerves and celiac plexus
• Parasympathetic via vagus nerve
• Blood supply
• Celiac trunk
• Veins of the hepatic portal system
Copyright © 2010 Pearson Education, Inc.
Stomach: Microscopic Anatomy
• 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
Mucosa
Surfaceepithelium
Lamina propria
Muscularismucosae
Oblique layer
Circular layer
Longitudinallayer
Serosa
(a) Layers of the stomach wall (l.s.)Stomach wall
Muscularis externa(contains myentericplexus)
Submucosa(contains submucosalplexus)
Copyright © 2010 Pearson Education, Inc.
Stomach: Microscopic Anatomy
• Mucosa
• Simple columnar epithelium composed of mucous cells
• Layer of mucus traps bicarbonate-rich fluid beneath it
• 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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Gastric Gland Secretions
• Chief cell secretions
• Inactive enzyme pepsinogen
• Activated to pepsin by HCl and by pepsin itself (a positive feedback mechanism)
Copyright © 2010 Pearson Education, Inc.
Gastric Gland Secretions
• Enteroendocrine cells
• Secrete chemical messengers into the lamina propria
• Paracrines
• Serotonin and histamine
• Hormones
• Somatostatin and gastrin
Copyright © 2010 Pearson Education, Inc.
Mucosal Barrier
• Layer of bicarbonate-rich mucus
• Tight junctions between epithelial cells
• Damaged epithelial cells are quickly replaced by division of stem cells
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc. Figure 23.16
Bacteria
Mucosalayer ofstomach
(a) A gastric ulcer lesion (b) H. pylori bacteria
Copyright © 2010 Pearson Education, Inc.
Digestive Processes in the Stomach
• Physical digestion
• Denaturation of proteins
• Enzymatic digestion of proteins by pepsin (and rennin in infants)
• Secretes intrinsic factor required for absorption of vitamin B12
• Lack of intrinsic factor pernicious anemia
• Delivers chyme to the small intestine
Copyright © 2010 Pearson Education, Inc.
Regulation of Gastric Secretion
• Neural and hormonal mechanisms
• Stimulatory and inhibitory events occur in three phases:
1. Cephalic (reflex) phase: few minutes prior to food entry
2. Gastric phase: 3–4 hours after food enters the stomach
Copyright © 2010 Pearson Education, Inc.
Regulation of Gastric Secretion
3. Intestinal phase: brief stimulatory effect as partially digested food enters the duodenum, followed by inhibitory effects (enterogastric reflex and enterogastrones)
Copyright © 2010 Pearson Education, Inc. Figure 23.17
Presence of lowpH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty
Distension;presence offatty, acidic,partiallydigested foodin theduodenum
Briefeffect
Intestinal(enteric)gastrinreleaseto blood
Entero-gastricreflex
Release of intestinalhormones (secretin,cholecystokinin, vasoactiveintestinal peptide)
Localreflexes
Vagalnucleiin medulla
Pyloricsphincter
Stimulate
Inhibit
1
1
2
Stomachsecretoryactivity
Sight and thoughtof food
Stomachdistensionactivatesstretchreceptors
Stimulation oftaste and smellreceptors
Food chemicals(especially peptides and caffeine) and rising pHactivate chemoreceptors
Loss ofappetite,depression
Emotionalupset
Lack ofstimulatoryimpulses toparasym-patheticcenter
Cerebralcortex
Cerebral cortexConditioned reflex
Vagovagalreflexes
Localreflexes
Medulla
G cells
Hypothalamusand medullaoblongata
Vagusnerve
Vagusnerve
Gastrinreleaseto blood
Gastrinsecretiondeclines
G cells
Overridesparasym-patheticcontrols
Sympatheticnervoussystemactivation
1
11
1
2
2
2
Stimulatory events Inhibitory events
Cephalicphase
Gastricphase
Intestinalphase
Excessiveacidity (pH <2) in stomach
Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum
Copyright © 2010 Pearson Education, Inc.
Regulation and Mechanism of HCl Secretion
• Three chemicals (ACh, histamine, and gastrin) stimulate parietal cells through second-messenger systems
• All three are necessary for maximum HCl secretion
• Antihistamines block H2 receptors and decrease HCl release
Copyright © 2010 Pearson Education, Inc. Figure 23.18
Stomach lumenChief cell
Parietal cell
Inter-stitialfluid
Carbonicanhydrase
Alkalinetide
HCO3–
Bloodcapillary
CO2
Cl–
CO2 + H2O
H2CO3
HCO3–- Cl–
antiporter
HCO3–
H+
Cl– Cl–l
K+ K+
H+
H+-K+
ATPase
HCI
Copyright © 2010 Pearson Education, Inc.
Response of the Stomach to Filling
• Stretches to accommodate incoming food
• Reflex-mediated receptive relaxation
• Coordinated by the swallowing center of the brain stem
• Gastric accommodation
• Plasticity (stress-relaxation response) of smooth muscle
Copyright © 2010 Pearson Education, Inc.
Gastric Contractile Activity
• Peristaltic waves move toward the pylorus at the rate of 3 per minute
• Basic electrical rhythm (BER) initiated by pacemaker cells (cells of Cajal)
• Distension and gastrin increase force of contraction
Copyright © 2010 Pearson Education, Inc.
Gastric Contractile Activity
• Most vigorous near the pylorus
• Chyme is either
• Delivered in ~ 3 ml spurts to the duodenum, or
• Forced backward into the stomach
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
• 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
Copyright © 2010 Pearson Education, Inc. Figure 23.20
Presence of fatty, hypertonic,acidic chyme in duodenum
Duodenal entero-endocrine cells
Chemoreceptors andstretch receptors
Enterogastrones(secretin, cholecystokinin,vasoactive intestinalpeptide)
Duodenalstimulidecline
Via shortreflexes
Via longreflexes
Entericneurons
Initial stimulus
Physiological response
Result
Contractile force andrate of stomachemptying decline
CNS centers sympathetic activity; parasympathetic activity
Stimulate
Inhibit
Secrete Target
Copyright © 2010 Pearson Education, Inc.
Small Intestine: Gross Anatomy
• Major organ of digestion and absorption
• 2–4 m long; from pyloric sphincter to ileocecal valve
• Subdivisions
1. Duodenum (retroperitoneal)
2. Jejunum (attached posteriorly by mesentery)
3. Ileum (attached posteriorly by mesentery)
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.
Duodenum
• The bile duct and main pancreatic duct
• Join at the hepatopancreatic ampulla
• Enter the duodenum at the major duodenal papilla
• Are controlled by the hepatopancreatic sphincter
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.
Structural Modifications
• Increase surface area of proximal part for nutrient absorption
• Circular folds (plicae circulares)
• Villi
• Microvilli
Copyright © 2010 Pearson Education, Inc.
Structural Modifications
• Circular folds
• Permanent (~1 cm deep)
• Force chyme to slowly spiral through lumen
Copyright © 2010 Pearson Education, Inc. Figure 23.22a
Vein carrying blood tohepatic portal vessel
MusclelayersCircularfoldsVilli
(a)
Lumen
Copyright © 2010 Pearson Education, Inc.
Structural Modifications
• Villi
• Motile fingerlike extensions (~1 mm high) of the mucosa
• Villus epithelium
• Simple columnar absorptive cells (enterocytes)
• Goblet cells
Copyright © 2010 Pearson Education, Inc.
Structural Modifications
• Microvilli
• Projections (brush border) of absorptive cells
• Bear brush border enzymes
Copyright © 2010 Pearson Education, Inc.
Intestinal Crypts
• Intestinal crypt epithelium
• Secretory cells that produce intestinal juice
• Enteroendocrine cells
• Intraepithelial lymphocytes (IELs)
• Release cytokines that kill infected cells
• Paneth cells
• Secrete antimicrobial agents (defensins and lysozyme)
• Stem cells
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.
Submucosa
• Peyer’s patches protect distal part against bacteria
• Duodenal (Brunner’s) glands of the duodenum secrete alkaline mucus
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
Copyright © 2010 Pearson Education, Inc.
Liver
• Largest gland in the body
• Four lobes—right, left, caudate, and quadrate
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Liver: Associated Structures
• Lesser omentum anchors liver to stomach
• Hepatic artery and vein at the porta hepatis
• 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 nutrient-rich blood
• Composed of plates of hepatocytes (liver cells)
• Longitudinal central vein
Copyright © 2010 Pearson Education, Inc. Figure 23.25a, b
(a) (b)Lobule Central vein Connectivetissue septum
Copyright © 2010 Pearson Education, Inc.
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
Copyright © 2010 Pearson Education, Inc.
Liver: Microscopic Anatomy
• Hepatocyte functions
• Process bloodborne nutrients
• Store fat-soluble vitamins
• Perform detoxification
• Produce ~900 ml bile per day
Copyright © 2010 Pearson Education, Inc.
Bile
• Yellow-green, alkaline solution containing
• Bile salts: cholesterol derivatives that function in fat emulsification and absorption
• Bilirubin: pigment formed from heme
• Cholesterol, neutral fats, phospholipids, and electrolytes
Copyright © 2010 Pearson Education, Inc.
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