The Digestive System

Objectives• Understand the major parts and functions of the

digestive tract• Learn how the digestive process is regulated• Analyze how nutrients are broken down by

secretions and enzymes of the digestive system• Appreciate how diseases of the digestive system

can affect overall nutrition• Learn some common dietary propensities for GI

problems and some remedies for digestive system pathologies

Mouth

Esophagus

Duodenum

Stomach

Fig. 2-1, p. 25

Outer longitudinal muscleInner circular muscle

Myenteric plexus

Epithelial lining

Lamina propria

Muscularis mucosaLumen

Serosa or adventitia

(outermost layer)

Submucosa

(second layer)

Duct from external exocrine gland

Submucosal plexus

Muscularis externa

(third layer)

Mucosa(innermost

layer)

Fig. 2-2, p. 26

esophagus

stomach

Small intestine

Mouth

Esophagus

Stomach

Upper GI Tract

Chronic reflux disease

GERD – gastro esophageal reflux diseaseSymptoms:

Treatments:

Antacids

Histamine H2 receptor blockers

Promotility agents

Proton pump inhibitors

Licorice

Aloe Vera

Gamma Oryzanol

Fig. 2-1, p. 25

Cystic duct

Right hepatic bile duct

Left lobe of liver

Left hepatic bile duct

Common hepatic bile duct

Common bile duct

Pancreatic duct

Pancreas

Main pancreatic duct

Duodenum

Sphincter of Oddi

Gallbladder

Right lobe of liver

Fig. 2-4a, p. 28

Hepatic plates

Lymphatic vesselPortal

vein

Bile duct

Bile canaliculi

Hepatic artery

Portal vein

Hepatic cells (hepatocytes)

Sinusoids

Central vein

Fig. 2-3, p. 27

Stomach

Bile duct from liver

Duodenum

Duct cells secrete aqueous NaHCO3 solution

Acinar cells secrete digestive enzymes

Exocrine portion of pancreas acinar and duct cells

Endocrine portion of pancreas(Islets of Langerhans)

The glandular portions of the pancreas are grossly eggagerated.

Blood

Hormones (insulin, glucogen)

Fig. 2-4b, p. 28

Lumen

Villi

Intestinal wall

Nerve plexusesSubmucosal

Myenteric

LumenVilli

Central lacteal

Blood vessels

Intestinal glands

Crypts of Lieberkühn

Mucosa

Submucosa

Muscularis

Serosa

Fig. 2-5, p. 29

Blood capillaries

Lacteal

Microvilli brush border

Tight junction

Desmosome

Cell membrane

MitochondrionRough endoplasmic reticulum

Ribosome

Golgi’s sacculeNucleus

Enterocyte Brush border

Glycocalyx

Glycocalyx

Actin filaments

Cell membrane

Myosin filaments

Terminal web

Fig. 2-6, p. 30

02CO, p. 24

Transverse colon

Cecum

Appendix

Ascending colon

Ileum

Descending colon

Tenia coli

Haustra

Sigmoid colon

Rectum

Anal sphincter

Fig. 2-7, p. 31

Table 2-1, p. 32S=stimulates I=inhibits O=no effect or information not available

Pharynx

Esophagus

Mouth

Salivary glands

Parotid

Sublingual

Submandibular/submaxillary

Saliva containingWater Electrolytes Mucus Enzymes* Antibacterial and antiviral compounds

*Main enzyme in saliva is salivary amylase, which hydrolyzes 1-4 bonds in starch Fig. 2-8, p. 34

-amylase

Lingual lipase

Mucins

Water and electrolytes

IgA

EsophagusFundus

Lower esophageal sphincter

Cardia

Rugae

PylorusPyloric sphincter

Duodenum

Pyloric portion (or antrum)

Body

Pacemaker location

Greatercurvature

Fig. 2-9, p. 35

Lumen of gland or gastric pit

Gastric epithelial mucosa

Neck or mucus cells

Bicarbonate and mucus

Peptic or chief cells

Pepsinogens

Oxyntic or parietal cells

Hydrochloric acid and intrinsic factor

Enteroendocrine (G)cell Gastrin

Stomach

Fig. 2-10, p. 36

Fig. 2-11, p. 37

Duodenum

Esophagus

No enzymatic activity

Stomach

Protein Polypeptides

Starch Dextrins

Pepsin

Salivary amylase

Fig. 2-12, p. 37

Regulation of Gastric Secretion

Both neurotransmitters and hormones: acetylcholine, gastrin, histamine –all receptor mediated to activate secretion

Histamine and Gastrin –predominantly activate acid secretion by parietal glands

Acetylcholine –activates all types of secretion in gastric glandsPepsinogen (peptic cells)Hydrochloric acid (parietal cells)Mucus (mucus cells)

PHASES OF SECRETION

Cephalic

Gastric

Intestinal

INHIBITION OF SECRETION

Fig. 2-13, p. 41

Fig. 2-13a, p. 41

Fig. 2-13b, p. 41

Fig. 2-14, p. 43

Lumen of small intestine

Triacylglycerol

Phospholipid

Cholesterol

Glycerol

3 fatty acids

2-monoacylglycerol or

2 fatty acids

Bile from liver

Micelle

Fatty acids

2-monoacylglycerol

Enterocyte

Lymphatic system lacteal

Blood capillary

Chylomicron

PhospholipidsCholesterol

Protein

Triacylglycerol synthesis

+

+

Pancreaticlipase

Fig. 2-15, p. 43

Liver

Hepatic portal vein

Gallbladder

Ileum

Jejunum

Duodenum

Bile

Bile

Bile

Bile

Bile

Bile

Bile

Fig. 2-16, p. 44

Fig. 2-17, p. 44

Fig. 2-17a, p. 44

Fig. 2-17b, p. 44

Fig. 2-18, p. 45

Fig. 2-19, p. 46

Table 2-2, p. 33

Esophagus

Stomach

Duodenum

Jejunum

Ileum

Large intestine

CalciumPhosphorusMagnesiumIronCopperSeleniumThiaminRiboflavinNiacinBiotinFolateVitamins A, D, E, and K

LipidsMonosaccharidesAmino AcidsSmall peptides

Vitamin CFolateVitamin B12

Vitamin DVitamin KMagnesiumOthers*

WaterEthyl alcoholCopperIodideFlourideMolybdenum

ThiaminRiboflavinNiacinPantothenateBiotinFolateVitamin B6

VitaminCVitamins A, D, E, and KCalciumPhosphorusMagnesiumIronZincChromiumManganeseMolybdenum

LipidsMonosaccharidesAmino AcidsSmall peptides

Bile salts and acidsSodiumChloridePotassium

Short-chain fatty acids

Water

Vitamin KBiotin

Fig. 2-20, p. 47

Diffusion

Facilitated diffusion

Active transport

Pinocytosis

Energy(ATP)

Cell membrane

Water

Small lipids

Cell membrane

Cell membrane

Cell membrane

Fig. 2-21, p. 48

DiffusionCell membrane

Water

Small lipids

Fig. 2-21a, p. 48

Facilitated diffusion Cell membrane

Fig. 2-21b, p. 48

Active transport

Energy(ATP)

Cell membrane

Fig. 2-21c, p. 48

PinocytosisCell membrane

Fig. 2-21d, p. 48