PharynxPharynx

From the mouth, the oro- and laryngopharynx From the mouth, the oro- and laryngopharynx allow passage of:allow passage of: Food and fluids to the esophagusFood and fluids to the esophagus Air to the tracheaAir to the trachea

Lined with stratified squamous epithelium and Lined with stratified squamous epithelium and mucus glandsmucus glands

Has two skeletal muscle layersHas two skeletal muscle layers Inner longitudinal Inner longitudinal Outer pharyngeal constrictors Outer pharyngeal constrictors

EsophagusEsophagus

Muscular tube going from the laryngopharynx Muscular tube going from the laryngopharynx to the stomachto the stomach

Travels through the mediastinum and pierces Travels through the mediastinum and pierces the diaphragm the diaphragm

Joins the stomach at the cardiac orifice Joins the stomach at the cardiac orifice

Esophageal CharacteristicsEsophageal Characteristics

Esophageal mucosa – nonkeratinized stratified Esophageal mucosa – nonkeratinized stratified squamous epithelium squamous epithelium

The empty esophagus is folded longitudinally The empty esophagus is folded longitudinally and flattens when food is presentand flattens when food is present

Glands secrete mucus as a bolus (compacted Glands secrete mucus as a bolus (compacted food product) moves through the esophagusfood product) moves through the esophagus

Muscularis changes from skeletal (superiorly) Muscularis changes from skeletal (superiorly) to smooth muscle (inferiorly)to smooth muscle (inferiorly)

Digestive Processes in the MouthDigestive Processes in the Mouth

Food is ingestedFood is ingested Mechanical digestion begins (chewing)Mechanical digestion begins (chewing) Propulsion is initiated by swallowingPropulsion is initiated by swallowing Salivary amylase begins chemical breakdown Salivary amylase begins chemical breakdown

of starchof starch The pharynx and esophagus serve as conduits The pharynx and esophagus serve as conduits

to pass food from the mouth to the stomachto pass food from the mouth to the stomach

Deglutition (Swallowing)Deglutition (Swallowing)

Coordinated activity of the tongue, soft palate, Coordinated activity of the tongue, soft palate, pharynx, esophagus, and 22 separate muscle pharynx, esophagus, and 22 separate muscle groupsgroups

Buccal phase – bolus is forced into the Buccal phase – bolus is forced into the oropharynx oropharynx

Deglutition (Swallowing)Deglutition (Swallowing)

Pharyngeal-esophageal phase – controlled by the Pharyngeal-esophageal phase – controlled by the medulla and lower ponsmedulla and lower pons All routes except into the digestive tract are sealed All routes except into the digestive tract are sealed

offoff Peristalsis moves food through the pharynx to Peristalsis moves food through the pharynx to

the esophagusthe esophagus

StomachStomach Chemical breakdown of proteins begins and Chemical breakdown of proteins begins and

food is converted to chymefood is converted to chyme Cardiac region – surrounds the cardiac orificeCardiac region – surrounds the cardiac orifice Fundus – dome-shaped region beneath the Fundus – dome-shaped region beneath the

diaphragmdiaphragm Body – midportion of the stomachBody – midportion of the stomach Pyloric region – made up of the antrum and Pyloric region – made up of the antrum and

canal which terminates at the pyloruscanal which terminates at the pylorus The pylorus is continuous with the duodenum The pylorus is continuous with the duodenum

through the pyloric sphincterthrough the pyloric sphincter

StomachStomach

Greater curvature – entire extent of the convex Greater curvature – entire extent of the convex lateral surfacelateral surface

Lesser curvature – concave medial surfaceLesser curvature – concave medial surface Lesser omentum – runs from the liver to the Lesser omentum – runs from the liver to the

lesser curvaturelesser curvature Greater omentum – drapes inferiorly from the Greater omentum – drapes inferiorly from the

greater curvature to the small intestinegreater curvature to the small intestine

StomachStomach

Nerve supply – sympathetic and Nerve supply – sympathetic and parasympathetic fibers of the autonomic parasympathetic fibers of the autonomic nervous systemnervous system

Blood supply – celiac trunk, and Blood supply – celiac trunk, and corresponding veins (part of the hepatic portal corresponding veins (part of the hepatic portal system)system)

Microscopic Anatomy of the Microscopic Anatomy of the StomachStomach

Muscularis – has an additional oblique layer Muscularis – has an additional oblique layer that: that: Allows the stomach to churn, mix, and pummel Allows the stomach to churn, mix, and pummel

food physically food physically Breaks down food into smaller fragmentsBreaks down food into smaller fragments

Microscopic Anatomy of the Microscopic Anatomy of the StomachStomach

Epithelial lining is composed of:Epithelial lining is composed of: Goblet cells that produce a coat of alkaline mucusGoblet cells that produce a coat of alkaline mucus

The mucous surface layer traps a bicarbonate-rich fluid The mucous surface layer traps a bicarbonate-rich fluid beneath itbeneath it

Gastric pits contain gastric glands that secrete Gastric pits contain gastric glands that secrete gastric juice, mucus, and gastringastric juice, mucus, and gastrin

Glands of the Stomach Fundus Glands of the Stomach Fundus and Bodyand Body

Gastric glands of the fundus and body have a Gastric glands of the fundus and body have a variety of secretory cellsvariety of secretory cells Mucous neck cells – secrete acid mucusMucous neck cells – secrete acid mucus Parietal cells – secrete HCl and intrinsic factor Parietal cells – secrete HCl and intrinsic factor

Glands of the Stomach Fundus Glands of the Stomach Fundus and Bodyand Body

Chief cells – produce pepsinogen Chief cells – produce pepsinogen Pepsinogen is activated to pepsin by:Pepsinogen is activated to pepsin by:

HCl in the stomachHCl in the stomach Pepsin itself via a positive feedback mechanismPepsin itself via a positive feedback mechanism

Enteroendocrine cells – secrete gastrin, histamine, Enteroendocrine cells – secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propriasomatostatin into the lamina propria

Stomach LiningStomach Lining

The stomach is exposed to the harshest The stomach is exposed to the harshest conditions in the digestive tractconditions in the digestive tract

To keep from digesting itself, the stomach has To keep from digesting itself, the stomach has a mucosal barrier with:a mucosal barrier with: A thick coat of bicarbonate-rich mucus on the A thick coat of bicarbonate-rich mucus on the

stomach wallstomach wall Epithelial cells that are joined by tight junctionsEpithelial cells that are joined by tight junctions Gastric glands that have cells impermeable to HClGastric glands that have cells impermeable to HCl

Damaged epithelial cells are quickly replacedDamaged epithelial cells are quickly replaced

Digestion in the StomachDigestion in the Stomach

The stomach:The stomach: Holds ingested foodHolds ingested food Degrades this food both physically and chemicallyDegrades this food both physically and chemically Delivers chyme to the small intestineDelivers chyme to the small intestine Enzymatically digests proteins with pepsinEnzymatically digests proteins with pepsin Secretes intrinsic factor required for absorption of Secretes intrinsic factor required for absorption of

vitamin Bvitamin B1212

Regulation of Gastric SecretionRegulation of Gastric Secretion

Neural and hormonal mechanisms regulate the Neural and hormonal mechanisms regulate the release of gastric juicerelease of gastric juice

Stimulatory and inhibitory events occur in Stimulatory and inhibitory events occur in three phasesthree phases Cephalic (reflex) phase: prior to food entryCephalic (reflex) phase: prior to food entry Gastric phase: once food enters the stomachGastric phase: once food enters the stomach Intestinal phase: as partially digested food enters Intestinal phase: as partially digested food enters

the duodenum the duodenum

Cephalic PhaseCephalic Phase

Excitatory events include:Excitatory events include: Sight or thought of foodSight or thought of food Stimulation of taste or smell receptorsStimulation of taste or smell receptors

Inhibitory events include:Inhibitory events include: Loss of appetite or depressionLoss of appetite or depression Decrease in stimulation of the parasympathetic Decrease in stimulation of the parasympathetic

divisiondivision

Gastric PhaseGastric Phase

Excitatory events include:Excitatory events include: Stomach distension Stomach distension Activation of stretch receptors (neural activation)Activation of stretch receptors (neural activation) Activation of chemoreceptors by peptides, Activation of chemoreceptors by peptides,

caffeine, and rising pH caffeine, and rising pH Release of gastrin to the bloodRelease of gastrin to the blood

Gastric PhaseGastric Phase

Inhibitory events include:Inhibitory events include: A pH lower than 2 A pH lower than 2 Emotional upset that overrides the parasympathetic Emotional upset that overrides the parasympathetic

divisiondivision

Intestinal PhaseIntestinal Phase Excitatory phase – low pH; partially digested Excitatory phase – low pH; partially digested

food enters the duodenum and encourages food enters the duodenum and encourages gastric gland activitygastric gland activity

Inhibitory phase – distension of duodenum, Inhibitory phase – distension of duodenum, presence of fatty, acidic, or hypertonic chyme, presence of fatty, acidic, or hypertonic chyme, and/or irritants in the duodenumand/or irritants in the duodenum Initiates inhibition of local reflexes and vagal Initiates inhibition of local reflexes and vagal

nucleinuclei Closes the pyloric sphincterCloses the pyloric sphincter Releases enterogastrones that inhibit gastric Releases enterogastrones that inhibit gastric

secretionsecretion

Regulation and Mechanism of Regulation and Mechanism of HCl SecretionHCl Secretion

HCl secretion is stimulated by ACh, histamine, HCl secretion is stimulated by ACh, histamine, and gastrin through second-messenger systemsand gastrin through second-messenger systems

Antihistamines block HAntihistamines block H22 receptors and receptors and

decrease HCl releasedecrease HCl release

Response of the Stomach to Response of the Stomach to FillingFilling

Stomach pressure remains constant until about Stomach pressure remains constant until about 1L of food is ingested1L of food is ingested

Relative unchanging pressure results from Relative unchanging pressure results from reflex-mediated relaxation and plasticityreflex-mediated relaxation and plasticity

Response of the Stomach to Response of the Stomach to FillingFilling

Reflex-mediated events include:Reflex-mediated events include: Receptive relaxation – as food travels in the Receptive relaxation – as food travels in the

esophagus, stomach muscles relaxesophagus, stomach muscles relax Adaptive relaxation – the stomach dilates in Adaptive relaxation – the stomach dilates in

response to gastric fillingresponse to gastric filling Plasticity – intrinsic ability of smooth muscle Plasticity – intrinsic ability of smooth muscle

to exhibit the stress-relaxation responseto exhibit the stress-relaxation response

Gastric Contractile ActivityGastric Contractile Activity

Peristaltic waves move toward the pylorus at Peristaltic waves move toward the pylorus at the rate of 3 per minutethe rate of 3 per minute

This basic electrical rhythm (BER) is initiated This basic electrical rhythm (BER) is initiated by pacemaker cells (cells of Cajal)by pacemaker cells (cells of Cajal)

Gastric Contractile ActivityGastric Contractile Activity

Most vigorous peristalsis and mixing occurs Most vigorous peristalsis and mixing occurs near the pylorusnear the pylorus

Chyme is either:Chyme is either: Delivered in small amounts to the duodenum orDelivered in small amounts to the duodenum or Forced backward into the stomach for further Forced backward into the stomach for further

mixingmixing

Regulation of Gastric EmptyingRegulation of Gastric Emptying

Gastric emptying is regulated by:Gastric emptying is regulated by: The neural enterogastric reflexThe neural enterogastric reflex Hormonal (enterogastrone) mechanismsHormonal (enterogastrone) mechanisms

These mechanisms inhibit gastric secretion These mechanisms inhibit gastric secretion and duodenal fillingand duodenal filling

Regulation of Gastric EmptyingRegulation of Gastric Emptying

Carbohydrate-rich chyme quickly moves Carbohydrate-rich chyme quickly moves through the duodenum through the duodenum

Fat-laden chyme is digested more slowly Fat-laden chyme is digested more slowly causing food to remain in the stomach longercausing food to remain in the stomach longer

Small Intestine: Gross AnatomySmall Intestine: Gross Anatomy

Runs from pyloric sphincter to the ileocecal Runs from pyloric sphincter to the ileocecal valve valve

Has three subdivisions: duodenum, jejunum, Has three subdivisions: duodenum, jejunum, and ileumand ileum

Small Intestine: Gross AnatomySmall Intestine: Gross Anatomy

The bile duct and main pancreatic duct:The bile duct and main pancreatic duct: Join the duodenum at the hepatopancreatic ampulla Join the duodenum at the hepatopancreatic ampulla Are controlled by the sphincter of OddiAre controlled by the sphincter of Oddi

The jejunum extends from the duodenum to The jejunum extends from the duodenum to the ileumthe ileum

The ileum joins the large intestine at the The ileum joins the large intestine at the ileocecal valveileocecal valve

Small Intestine: Microscopic Small Intestine: Microscopic AnatomyAnatomy

Structural modifications of the small intestine Structural modifications of the small intestine wall increase surface areawall increase surface area Plicae circulares: deep circular folds of the mucosa Plicae circulares: deep circular folds of the mucosa

and submucosaand submucosa Villi – fingerlike extensions of the mucosaVilli – fingerlike extensions of the mucosa Microvilli – tiny projections of absorptive mucosal Microvilli – tiny projections of absorptive mucosal

cells’ plasma membranescells’ plasma membranes

Small Intestine: Histology of the Small Intestine: Histology of the WallWall

The epithelium of the mucosa is made up of:The epithelium of the mucosa is made up of: Absorptive cells and goblet cells Absorptive cells and goblet cells Enteroendocrine cells Enteroendocrine cells Interspersed T cells called intraepithelial Interspersed T cells called intraepithelial

lymphocytes (IELs)lymphocytes (IELs) IELs release cytokinesIELs release cytokines

Small Intestine: Histology of the Small Intestine: Histology of the WallWall

Cells of intestinal crypts secrete intestinal juiceCells of intestinal crypts secrete intestinal juice Peyer’s patches are found in the submucosa Peyer’s patches are found in the submucosa Brunner’s glands in the duodenum secrete Brunner’s glands in the duodenum secrete

alkaline mucus alkaline mucus

Intestinal JuiceIntestinal Juice

Secreted by intestinal glands in response to Secreted by intestinal glands in response to distension or irritation of the mucosadistension or irritation of the mucosa

Slightly alkaline and isotonic with blood Slightly alkaline and isotonic with blood plasmaplasma

Largely water, enzyme-poor, but contains Largely water, enzyme-poor, but contains mucusmucus

LiverLiver

The largest gland in the bodyThe largest gland in the body Superficially has four lobes – right, left, Superficially has four lobes – right, left,

caudate, and quadratecaudate, and quadrate The falciform ligament:The falciform ligament:

Separates the right and left lobes anteriorlySeparates the right and left lobes anteriorly Suspends the liver from the diaphragm and Suspends the liver from the diaphragm and

anterior abdominal wallanterior abdominal wall

LiverLiver

The ligamentum teres:The ligamentum teres: Is a remnant of the fetal umbilical veinIs a remnant of the fetal umbilical vein Runs along the free edge of the falciform ligamentRuns along the free edge of the falciform ligament

Liver: Associated StructuresLiver: Associated Structures

The lesser omentum anchors the liver to the The lesser omentum anchors the liver to the stomachstomach

The hepatic blood vessels enter the liver at the The hepatic blood vessels enter the liver at the porta hepatisporta hepatis

The gallbladder rests in a recess on the inferior The gallbladder rests in a recess on the inferior surface of the right lobesurface of the right lobe

Liver: Associated StructuresLiver: Associated Structures

Bile leaves the liver via:Bile leaves the liver via: Bile ducts, which fuse into the common hepatic Bile ducts, which fuse into the common hepatic

duct duct The common hepatic duct, which fuses with the The common hepatic duct, which fuses with the

cystic ductcystic duct These two ducts form the bile ductThese two ducts form the bile duct

Figure 23.24c

Liver: Microscopic AnatomyLiver: Microscopic Anatomy

Hexagonal-shaped liver lobules are the Hexagonal-shaped liver lobules are the structural and functional units of the liverstructural and functional units of the liver Composed of hepatocyte (liver cell) plates Composed of hepatocyte (liver cell) plates

radiating outward from a central veinradiating outward from a central vein Portal triads are found at each of the six corners of Portal triads are found at each of the six corners of

each liver lobuleeach liver lobule

Figure 23.24d

Liver: Microscopic AnatomyLiver: Microscopic Anatomy

Portal triads consist of a bile duct andPortal triads consist of a bile duct and Hepatic artery – supplies oxygen-rich blood to the Hepatic artery – supplies oxygen-rich blood to the

liverliver Hepatic portal vein – carries venous blood with Hepatic portal vein – carries venous blood with

nutrients from digestive visceranutrients from digestive viscera

Liver: Microscopic AnatomyLiver: Microscopic Anatomy

Liver sinusoids – enlarged, leaky capillaries Liver sinusoids – enlarged, leaky capillaries located between hepatic plateslocated between hepatic plates

Kupffer cells – hepatic macrophages found in Kupffer cells – hepatic macrophages found in liver sinusoidsliver sinusoids

Liver: Microscopic AnatomyLiver: Microscopic Anatomy

Hepatocytes’ functions include:Hepatocytes’ functions include: Production of bileProduction of bile Processing bloodborne nutrientsProcessing bloodborne nutrients Storage of fat-soluble vitaminsStorage of fat-soluble vitamins DetoxificationDetoxification

Secreted bile flows between hepatocytes Secreted bile flows between hepatocytes toward the bile ducts in the portal triads toward the bile ducts in the portal triads

Composition of BileComposition of Bile A yellow-green, alkaline solution containing A yellow-green, alkaline solution containing

bile salts, bile pigments, cholesterol, neutral bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytesfats, phospholipids, and electrolytes

Bile salts are cholesterol derivatives that:Bile salts are cholesterol derivatives that: Emulsify fatEmulsify fat Facilitate fat and cholesterol absorptionFacilitate fat and cholesterol absorption Help solubilize cholesterolHelp solubilize cholesterol

Enterohepatic circulation recycles bile salts Enterohepatic circulation recycles bile salts The chief bile pigment is bilirubin, a waste The chief bile pigment is bilirubin, a waste

product of hemeproduct of heme

The GallbladderThe Gallbladder

Thin-walled, green muscular sac on the ventral Thin-walled, green muscular sac on the ventral surface of the liversurface of the liver

Stores and concentrates bile by absorbing its Stores and concentrates bile by absorbing its water and ionswater and ions

Releases bile via the cystic duct, which flows Releases bile via the cystic duct, which flows into the bile ductinto the bile duct

Regulation of Bile ReleaseRegulation of Bile Release

Acidic, fatty chyme causes the duodenum to Acidic, fatty chyme causes the duodenum to release:release: Cholecystokinin (CCK) and secretin into the Cholecystokinin (CCK) and secretin into the

bloodstreambloodstream Bile salts and secretin transported in blood Bile salts and secretin transported in blood

stimulate the liver to produce bilestimulate the liver to produce bile Vagal stimulation causes weak contractions of Vagal stimulation causes weak contractions of

the gallbladderthe gallbladder

Regulation of Bile ReleaseRegulation of Bile Release

Cholecystokinin causes:Cholecystokinin causes: The gallbladder to contractThe gallbladder to contract The hepatopancreatic sphincter to relaxThe hepatopancreatic sphincter to relax

As a result, bile enters the duodenumAs a result, bile enters the duodenum