Chapter 45: Processing Food and Nutrition

The Digestive System

Fig. 41-7

Ingestion Digestion Absorption Elimination

Undigestedmaterial

Chemical digestion(enzymatic hydrolysis)

Nutrientmoleculesenter bodycells

Smallmolecules

Mechanicaldigestion

Food

Piecesof food

1 2 3 4

Fig. 41-10a

Cecum

Anus

Ascendingportion oflarge intestine

Gall-bladder

Smallintestine

Largeintestine

Smallintestine

Rectum

Pancreas

Liver

Salivary glands

TongueOral cavity

Pharynx

Esophagus

Sphincter

Stomach

Sphincter

Duodenum ofsmall intestine

Appendix

Fig. 41-10b

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Fig. 41-11-3

LarynxTrachea

Epiglottisup

Pharynx

Tongue

Glottis

Esophagus

Esophagealsphinctercontracted

Food

Tostomach

Tolungs

Epiglottisdown

Esophagealsphincterrelaxed

Glottis upand closed

Epiglottisup

Esophagealsphinctercontracted

Sphincterrelaxed

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Glottisdownand open

Fig. 41-12

Interior surfaceof stomach

Esophagus

Chief cells

Small intestine

Epithelium

Stomach

Sphincter

Parietal cell

Pepsinogen and HClare secreted.

HCl convertspepsinogen to pepsin.

Pepsin activatesmore pepsinogen.

Chief cell

Folds ofepithelialtissue

Pepsin

Sphincter

Pepsinogen

HCl

H+

Cl–

Parietal cells

Mucus cells

Gastric gland

1

2

2

3

3

1

5 µm

Fig. 41-13

Oral cavity,pharynx,esophagus

Stomach

Lumen ofsmall intes-tine

Epitheliumof smallintestine(brushborder)

Carbohydrate digestion

Polysaccharides

Smaller polysaccharides,maltose

Polysaccharides

Maltose and otherdisaccharides

Disaccharides

Protein digestion Nucleic acid digestion Fat digestion

Proteins

Small polypeptides

Pepsin

Pancreatic amylases

Salivary amylase

Disaccharidases

Monosaccharides

Small peptides

Amino acids

Amino acids

Polypeptides

Smallerpolypeptides

Pancreatic trypsin andchymotrypsin

Pancreatic carboxypeptidase

Dipeptidases, carboxypeptidase,and aminopeptidase

DNA, RNA

Pancreatic nucleases

Fat globules

NucleotidesFat droplets

Nucleosides

Nitrogenous bases,sugars, phosphates

Nucleotidases

Nucleosidasesandphosphatases

Glycerol, fattyacids, monoglycerides

Bile salts

Pancreatic lipase

(starch, glycogen) (sucrose, lactose)

Fig. 41-15a

Muscle layers

Vein carrying bloodto hepatic portal vein

Villi

Intestinal wall

Key

Nutrientabsorption

Largecircularfolds

Fig. 41-15bMicrovilli (brushborder) at apical(lumenal) surface

Key

Nutrientabsorption

Bloodcapillaries

Epithelialcells

Villi

Lymphvessel

Basal surface

LactealEpithelial cells

Lumen

Fig. 41-21

Homeostasis:90 mg glucose/100 mL blood

Stimulus:Blood glucose

level risesafter eating.

Stimulus:Blood glucose

level dropsbelow set point.