The Digestive SystemThe Digestive SystemA. Digestive processesA. Digestive processesB. OrganizationB. Organization 1. General histology of the GI tract1. General histology of the GI tract a. Mucosaa. Mucosa b. Submucosab. Submucosa c. Muscularisc. Muscularis d. Serosad. Serosa 2. Peritoneum2. PeritoneumC. Mouth (oral cavity)C. Mouth (oral cavity) 1. Tongue1. Tongue 2. Salivary glands2. Salivary glands a. Composition of salivaa. Composition of saliva b. Secretion of salivab. Secretion of saliva 3. Physiology of digestion in the mouth3. Physiology of digestion in the mouth a. Mechanical digestiona. Mechanical digestion b. Chemical digestionb. Chemical digestion 4. Physiology of deglutition4. Physiology of deglutitionD. EsophagusD. Esophagus 1. Histology1. Histology 2. Physiology2. PhysiologyE. StomachE. Stomach 1. Anatomy and Histology1. Anatomy and Histology 2. Physiology of digestion in the stomach2. Physiology of digestion in the stomach a. Mechanical digestiona. Mechanical digestion b. Chemical digestionb. Chemical digestion 3. Regulation of gastric secretion and motility3. Regulation of gastric secretion and motility a. Cephalic phasea. Cephalic phase b. Gastric phaseb. Gastric phase c. Intestinal phasec. Intestinal phase 4. Regulation of gastric emptying4. Regulation of gastric emptying 5. Absorption5. Absorption

F. PancreasF. Pancreas 1. Anatomy and Histology1. Anatomy and Histology 2. Pancreatic juice2. Pancreatic juice 3. Regulation of pancreatic secretions3. Regulation of pancreatic secretionsG. LiverG. Liver 1. Anatomy and Histology1. Anatomy and Histology 2. Blood supply2. Blood supply 3. Bile3. Bile 4. Regulation of bile secretion4. Regulation of bile secretion 5. Physiology of the liver5. Physiology of the liverH. GallbladderH. Gallbladder 1. Histology1. Histology 2. Physiology2. PhysiologyI. Small intestineI. Small intestine 1. Anatomy and Histology1. Anatomy and Histology 2. Intestinal juice and brush border enzymes2. Intestinal juice and brush border enzymes 3. Physiology of digestion in the small intestine 3. Physiology of digestion in the small intestine a. Mechanical digestiona. Mechanical digestion b. Chemical digestionb. Chemical digestion 4. Regulation of intestinal secretion and motility4. Regulation of intestinal secretion and motility 5. Physiology of absorption5. Physiology of absorptionJ. Large intestineJ. Large intestine 1. Anatomy and Histology1. Anatomy and Histology 2. Physiology of digestion in the large intestine 2. Physiology of digestion in the large intestine a. Mechanical digestiona. Mechanical digestion b. Chemical digestionb. Chemical digestion 3. Absorption and feces formation3. Absorption and feces formation 4. Physiology of defecation4. Physiology of defecation

Food is vital to life becauseFood is vital to life because

1. provides energy1. provides energy

2. provides building blocks2. provides building blocks

Why do we have a digestive system?Why do we have a digestive system?

Five Basic Digestive ProcessesFive Basic Digestive Processes

1. ingestion1. ingestion

2. movement of food (peristalsis)2. movement of food (peristalsis)

3. digestion3. digestion

4. absorption4. absorption

5. defecation5. defecation

Two Types of DigestionTwo Types of Digestion

1. mechanical1. mechanical

2. chemical2. chemical

Digestive System OverviewDigestive System Overview

OrganizationOrganization

1. gastrointestinal tract1. gastrointestinal tractmouthpharynxesophagusstomachsmall intestinelarge intestine

2. accessory organs2. accessory organsTeethTongueSalivary glandsLivergallbladderpancreas

General HistologyGeneral Histology

1. mucosa1. mucosa a. epitheliuma. epithelium b. lamina propriab. lamina propria c. muscularis mucosaec. muscularis mucosae2. submucosa2. submucosa (submucosal plexus)(submucosal plexus)3. muscularis3. muscularis a. inner circulara. inner circular b. outer longitudinalb. outer longitudinal c. myenteric plexusc. myenteric plexus4. serosa 4. serosa

(visceral peritoneum)(visceral peritoneum)

PeritoneumPeritoneum1. parietal 1. parietal vsvs visceral visceral

2. peritoneal cavity2. peritoneal cavity

3. mesentery3. mesentery

4. mesocolon4. mesocolon

Mouth (oral cavity)Mouth (oral cavity)

1. boundaries1. boundaries

2. hard palate 2. hard palate vsvs soft palate soft palate

3. palatoglossal arches3. palatoglossal arches

4. palatopharyngeal arches4. palatopharyngeal arches

5. epithelium5. epithelium

6. vestibule6. vestibule

7. fauces7. fauces

fauces

TongueTongue1. intrinsic muscles1. intrinsic muscles

2. extrinsic muscles2. extrinsic muscles

3. frenulum3. frenulum

4. bolus4. bolus

5. hypoglossal nerve5. hypoglossal nerve

Salivary GlandsSalivary Glands1. buccal, lingual, labial1. buccal, lingual, labial

2. paired glands2. paired glands

a. parotida. parotid

b. submandibularb. submandibular

c. sublingualc. sublingual

Saliva is composed of 99.5% water, used to Saliva is composed of 99.5% water, used to dissolve foods, and 0.5% solutes, including:dissolve foods, and 0.5% solutes, including:

1. salivary amylase1. salivary amylase

2. ions (Na, K, Cl, HCO3, HPO4)2. ions (Na, K, Cl, HCO3, HPO4)

3. mucous3. mucous

4. lysozyme 4. lysozyme

SalivationSalivation is controlled by the is controlled by the parasympathetic nervous system parasympathetic nervous system

(cranial nerves VII and IX).(cranial nerves VII and IX).

Three types of stimuli may initiate Three types of stimuli may initiate salivation:salivation:

1. psychic1. psychic

2. chemical2. chemical

3. tactile3. tactile

Physiology of Digestion in MouthPhysiology of Digestion in Mouth

1. mechanical = mastication1. mechanical = mastication

2. chemical2. chemical

salivary amylasesalivary amylase

starch -----------------------> maltosestarch -----------------------> maltose

(glu+glu)(glu+glu)

Swallowing (Deglutition)Swallowing (Deglutition)

1. voluntary (buccal) stage1. voluntary (buccal) stage

(cranial nerves V, VII, XII)(cranial nerves V, VII, XII)

2. pharyngeal-stage2. pharyngeal-stage

(deglutition reflex)(deglutition reflex)

(cranial nerves IX, X, XI)(cranial nerves IX, X, XI)

3. esophageal stage3. esophageal stage

EsophagusEsophagus1. gross anatomy1. gross anatomy

2. esophageal hiatus2. esophageal hiatus

3. mucosa3. mucosa

4. muscularis4. muscularis

5. sphincters5. sphincters

a. uppera. upper

b. lower (gastroesophageal)b. lower (gastroesophageal)

lumen

mucosasubmucosa

muscularis externa

adventitia

stratified squamous epithelium

IC

OL

Stomach AnatomyStomach Anatomy

1. location1. location

2. divisions2. divisions

3. pyloric sphincter3. pyloric sphincter

4. curvatures4. curvatures

5. rugae5. rugae

Stomach HistologyStomach Histology1. simple columnar epithelium1. simple columnar epithelium2. gastric glands2. gastric glands a. chief cellsa. chief cells (pepsinogen, gastric lipase)(pepsinogen, gastric lipase) b. parietal cellsb. parietal cells (HCl, intrinsic factor)(HCl, intrinsic factor) c. mucous neck cells (mucous)c. mucous neck cells (mucous) d. G cells (gastrin)d. G cells (gastrin)3. muscularis3. muscularis

serosa has been removed

inner oblique fibers

middle circular fibers

outer longitudinal fibers

Mechanical Digestion in the Mechanical Digestion in the StomachStomach

1. regular gentle peristaltic waves1. regular gentle peristaltic waves

2. mixing waves producing chyme2. mixing waves producing chyme

Chemical Digestion in the StomachChemical Digestion in the Stomach

1.1. pepsinogen pepsin (pH 1 - 3)pepsinogen pepsin (pH 1 - 3)

proteins peptidesproteins peptides

2. gastric lipase2. gastric lipase

3. rennin (infant only)3. rennin (infant only)

HCl

Mode of Hydrochloric Acid Mode of Hydrochloric Acid SecretionSecretion

Pepsid ACPepsid AC

ZantacZantac

Three Phases of Stomach ControlThree Phases of Stomach Control

Cephalic PhaseCephalic Phase

Gastric PhaseGastric Phase

Intestinal PhaseIntestinal Phase

Stomach Regulation-First PhaseStomach Regulation-First Phase1. cephalic phase1. cephalic phase

a. psychic stimulia. psychic stimuli

b. vagus nerveb. vagus nerve

c. increased motility and secretionc. increased motility and secretion

Stomach Regulation-Cephalic Phase

Cephalic phase

thought and anticipation of food

parasympathetic output via the vagus nerve (X)

stimulation of stomach’s enteric nervous system

PSYCHIC STIMULI

sight, taste, smell of food sound of food preparation

increased gastric secretion + increased gastric motility

Stomach Regulation-Second PhaseStomach Regulation-Second Phase2. gastric phase2. gastric phase

a. stretch receptors and a. stretch receptors and

chemoreceptorschemoreceptors

b. local parasympathetic responseb. local parasympathetic response

c. gastrinc. gastrin

Stomach Regulation-Gastric Phase

increased stretch of stomach wall

direct stimulation of stomach’s enteric nervous system

increased gastric secretion + increased gastric motility

food enters the stomach

input to brainstem

parasympathetic output via the vagus nerve (X)

increased gastrin secretion

increased pH stimulates chemoreceptors

Positive Feedback Control of Positive Feedback Control of Gastric SecretionGastric Secretion

Negative Feedback of the Gastric Phase

CONTROLLED CONDITION

RECEPTORChemoreceptors and stretch receptors

increased pH and stretch of stomach wall, and generate nerve impulses that pass to

the control centers

CONTROL CENTER

Enteric nervous system and medullary neurons generate parasympathetic impulses that pass to the effectors

EFFECTORSParietal cells of the gastric mucosa

secrete HCl and the muscularis contracts more vigorously (increased frequency and

strength of mixing waves)

RETURN TO HOMEOSTASISIn response, there is increased acidity in stomach chyme and the mixing waves

begin emptying the stomach. An empty stomach is a return to homeostasis.

Food entering stomach disrupts homeostasis by causing an increase in

gastric juice pH AND stretch (distention) of stomach wall

Stomach Regulation-Third PhaseStomach Regulation-Third Phase3. intestinal phase3. intestinal phase a. stretch receptors and a. stretch receptors and chemoreceptorschemoreceptors b. enterogastric reflexb. enterogastric reflex c. hormonesc. hormones (1) gastrin (+)(1) gastrin (+) (2) cholecystokinin (CCK) (-)(2) cholecystokinin (CCK) (-) (3) secretin (-)(3) secretin (-) (4) gastric inhibitory peptide (4) gastric inhibitory peptide (GIP) (-)(GIP) (-)

Stomach Regulation-Intestinal Phase

increased stretch of duodenal wall

direct stimulation of duodenum’s enteric

nervous system

chyme enters the duodenum

decreased stomach activity

cholecystokininsecretin

increased enteric endocrine cell activity

secretion ofenterogastric

reflex

input to brainstem

increased sympathetic output to stomach

increased stomach activity

enteric gastrindecreased parasympathetic

output from the vagus nerve (X) to stomach

NET EFFECTgastric inhibition

inhibits

inhibits inhibits

Gastric Emptying

distention of stomach

STIMULATION OF GASTRIC EMPTYING

increased gastrin secretion increased vagal activity

contraction of gastroesophageal sphincterrelaxation of pyloric sphincter

increased rate of mixing wavesincreased gastric secretion

increased rate of emptying

partially digested proteinsalcoholcaffeine

distention of duodenum

INHIBITION OF GASTRIC EMPTYING

enterogastric reflex

decreased rate of emptying

partially digested proteins, fatty acids,

glucose in duodenum

secretion of cholecystokinin and

secretin

contraction of pyloric sphincterdecreased rate of mixing waves

decreased gastric secretion

Stomach AbsorptionStomach Absorption

Accomplishments of digestion to this point in the GI tractAccomplishments of digestion to this point in the GI tractstarch maltose by salivary amylase (action stops in stomach)proteins partially digested proteins (action of pepsin)lipids partially digested fats (action of lingual and gastric lipase)creation of chyme from food, drink, saliva, and gastric juice

Stomach Absorption

1. water1. water2. electrolytes2. electrolytes3. certain drugs (aspirin)3. certain drugs (aspirin)4. alcohol4. alcohol

Accessory Organs of DigestionAccessory Organs of Digestion

PancreasPancreas

Liver Liver

GallbladderGallbladder

PancreasPancreas1. gross anatomy1. gross anatomy

2. main pancreatic duct2. main pancreatic duct

3. hepatopancreatic ampulla3. hepatopancreatic ampulla

4. accessory pancreatic duct4. accessory pancreatic duct

5. 99% exocrine5. 99% exocrine

6. 1% endocrine6. 1% endocrine

Pancreatic JuicePancreatic Juice1. sodium bicarbonate (NaHCO3)1. sodium bicarbonate (NaHCO3)

2. pancreatic amylase2. pancreatic amylase

3. pancreatic lipase and cholesterol esterase3. pancreatic lipase and cholesterol esterase

4. nucleases -- DNAse and RNAse4. nucleases -- DNAse and RNAse

5. protein-digesting enzymes5. protein-digesting enzymes

a. trypsinogen (inactive)a. trypsinogen (inactive)

b. chymotrypsinogen (inactive)b. chymotrypsinogen (inactive)

c. procarboxypeptidase (inactive)c. procarboxypeptidase (inactive)

Pancreatic Regulation-Neural Pancreatic Regulation-Neural Control and Endocrine ControlControl and Endocrine Control

1. vagus nerve1. vagus nerve

2. CCK = enzymes2. CCK = enzymes

3. secretin = NaHCO33. secretin = NaHCO3

Pancreatic Regulation

acid chyme in duodenum

ENDOCRINE CONTROL

enteroendocrine cells stimulated

increased secretion of bicarbonate ions

increased secretin increased cholecystokinin

increased secretion of enzymes

NEURAL CONTROL

psychic stimuli stretch of stomach

increased parasympathetic impulses via vagus nerve

increased pancreatic secretion

Liver AnatomyLiver Anatomy1. location1. location

2. lobes2. lobes

3. falciform ligament3. falciform ligament

4. bile4. bile

5. bile canaliculi5. bile canaliculi

6. ducts6. ducts

Liver HistologyLiver Histology1. lobule1. lobule

2. hepatocytes2. hepatocytes

3. central vein3. central vein

4. sinusoids4. sinusoids

5. flow of bile5. flow of bile

6. blood flow6. blood flow

7. portal triad7. portal triad

BileBile

1. is a detergent1. is a detergent

2. emulsification of fats2. emulsification of fats

Produced continuously at slow rate

Secretion increased in response to:

vagus nerve – psychic and gastric phases

secretin – from the duodenum during intestinal phase

Physiology of the LiverPhysiology of the Liver

1. carbohydrate metabolism 4. detoxification1. carbohydrate metabolism 4. detoxification a. glycogenesis 5. synthesis and a. glycogenesis 5. synthesis and

excretion of bile excretion of bile b. glycogenolysis 6. storageb. glycogenolysis 6. storage c. gluconeogenesis 7. phagocytosis of c. gluconeogenesis 7. phagocytosis of

RBCs RBCs2. lipid metabolism 8. activation of vitamin 2. lipid metabolism 8. activation of vitamin D D 3. protein metabolism3. protein metabolism a. deamination (-NH2)a. deamination (-NH2) b. urea formationb. urea formation c. plasma protein productionc. plasma protein production

GallbladderGallbladder

1. anatomy1. anatomy2. rugae2. rugae3. cystic duct3. cystic duct4. stores/concentrates bile4. stores/concentrates bile5. sphincter of Oddi5. sphincter of Oddi6. CCK6. CCK

Biliary TractBiliary Tractcommon hepatic duct +cystic duct = common bile duct +main pancreatic duct = ampulla of Vatersphincter of Oddi

Regulation of Bile SecretionRegulation of Bile Secretion

acid chyme in duodenum

REGULATION OF BILE SECRETION

enteroendocrine cells stimulated

cholecystokinin secretion

gallbladder contraction

relaxation of sphincter of Oddi

release of bile into duodenum

Small Intestine AnatomySmall Intestine Anatomy

1. 21 ft. x 1 in.1. 21 ft. x 1 in.2. duodenum (10 in.) 2. duodenum (10 in.) -- retroperitoneal-- retroperitoneal3. jejunum (8 ft.)3. jejunum (8 ft.) -- mesentery-- mesentery4. ileum (12 ft.)4. ileum (12 ft.) -- mesentery-- mesentery5. ileocecal sphincter5. ileocecal sphincter

Small Intestine HistologySmall Intestine Histology

1. intestinal glands1. intestinal glands

2. plicae circulares2. plicae circulares

3. villi3. villi

4. microvilli4. microvilli

5. Peyer's patches5. Peyer's patches

Intestinal Juice and Brush Intestinal Juice and Brush Border EnzymesBorder Enzymes

MaltaseMaltase

LactaseLactase

PeptidasesPeptidases

DextrinasesDextrinases

NucleosidasesNucleosidases

PhosphatasesPhosphatases

Small Intestine-Mechanical Small Intestine-Mechanical DigestionDigestion

1. segmentation1. segmentation

2. peristalsis2. peristalsis

Review of Chemical Digestion of Carbohydrates

STARCH SUCROSE LACTOSE

mouth

stomach

small intestine

salivary amylase

(absorbed into blood of villus)

MALTOSE

pancreaticamylase

brush border maltase

glucose + glucose

SUCROSE

glucose + fructose(absorbed into blood of villus)

brush border sucrase

LACTOSE

glucose + galactose(absorbed into blood of villus)

brush border lactase

Review the Chemical Digestion of ProteinsReview the Chemical Digestion of Proteins

Review the Chemical Digestion of LipidsReview the Chemical Digestion of Lipids

Regulation of small intestinal Regulation of small intestinal secretion and motilitysecretion and motility

1. local reflexes1. local reflexes

2. parasympathetic reflexes 2. parasympathetic reflexes

(vagus nerve)(vagus nerve)

3. gastrin3. gastrin

Regulation of the Small Intestine

psychic stimuli stretch of stomach

increased parasympathetic impulses via vagus nerve

increased small intestinal motility secretion

+ relaxation of ileocecal sphincter

gastroileal reflex

chemoreceptors in stomach

increased gastrin secretion

stretch of small intestine

increased enteric nervous system activity

GASTRIC PHASE

Small Intestine AbsorptionSmall Intestine Absorption

1. monosaccharides1. monosaccharides2. 2. amino acidsamino acids

hepatic portal bloodhepatic portal blood liver inferior vena cava general circulation

3. fats 3. fats triglyceridestriglycerides chylomicronschylomicrons lymph lacteals intestinal trunk thoracic duct general circulation

4. water4. water

blood capillary

lactealwith

chylomicrons

monosaccharidesamino acids

superior mesenteric vein

hepatic portal vein

thoracic duct

inferiorvena cava

lymphatic vessel

Water absorptionWater absorption

GI tract fluids/24 hoursGI tract fluids/24 hours

saliva = 1 L small intestine =saliva = 1 L small intestine =ingested liquids = 2L 8 Lingested liquids = 2L 8 Lgastric juice = 2 L large intestine =gastric juice = 2 L large intestine =bile = 1L 0.9 Lbile = 1L 0.9 Lpancreatic juice = 2 Lpancreatic juice = 2 Lintestinal juice = 1Lintestinal juice = 1Ltotal = 9 Ltotal = 9 L

0.1 L0.1 L

Ingested or secreted into GI tract Absorbed into blood

Excretedin feces

Large Intestine AnatomyLarge Intestine Anatomy

1. 5 ft. x 2.5 in.1. 5 ft. x 2.5 in.2. cecum with appendix2. cecum with appendix3. colon3. colon a. ascendinga. ascending b. transverseb. transverse c. descendingc. descending d. sigmoidd. sigmoid4. rectum4. rectum

Large Intestine Anatomy Con’tLarge Intestine Anatomy Con’t5. haustra5. haustra

6. taenia coli6. taenia coli

7. epiploic appendages7. epiploic appendages

8. anal canal8. anal canal

9. anus9. anus

10. internal anal sphincter10. internal anal sphincter

11. external anal sphincter11. external anal sphincter

Large Intestine HistologyLarge Intestine Histology

1. no plicae circulares1. no plicae circulares

2. no villi2. no villi

3. goblet cells3. goblet cells

no villi

intestinal gland

lumen

goblet cells

muscularis mucosae

submucosa

Mechanical Digestion in the Mechanical Digestion in the Large IntestineLarge Intestine

1. haustral churning1. haustral churning

2. mass peristalsis 2. mass peristalsis

(gastrocolic reflex)(gastrocolic reflex)

3. peristalsis3. peristalsis

Chemical digestion in the Chemical digestion in the large intestinelarge intestine

1. bacteria fermentation1. bacteria fermentation

2. bacteria secrete vitamin K and some 2. bacteria secrete vitamin K and some

B complex vitaminsB complex vitamins

Large Intestine AbsorptionLarge Intestine Absorption

1. simple molecules and vitamins1. simple molecules and vitamins2. most remaining water (~900 ml/day) 2. most remaining water (~900 ml/day)

Feces consists of:Feces consists of:1. water (about 100 ml/day)1. water (about 100 ml/day)2. undigested foodstuffs (plant fibers = cellulose)2. undigested foodstuffs (plant fibers = cellulose)3. bacteria3. bacteria4. products of bacterial decomposition4. products of bacterial decomposition5. sloughed epithelial cells5. sloughed epithelial cells

Defecation Reflex in the AdultDefecation Reflex in the Adult1. distention of the rectum 1. distention of the rectum

stimulates stretch receptorsstimulates stretch receptors2. sacral parasympathetic area output, 2. sacral parasympathetic area output,

causing:causing: a. contraction of the descending colon, a. contraction of the descending colon,

sigmoid colon, and rectum; andsigmoid colon, and rectum; and b. reflex relaxation of the b. reflex relaxation of the

internal anal sphincterinternal anal sphincter3. voluntary relaxation of the 3. voluntary relaxation of the

external anal sphincterexternal anal sphincter (in the infant, this is also reflexive)(in the infant, this is also reflexive)4. expulsion of feces4. expulsion of feces