Animal Nutrition

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Chief cells secrete inactive pepsinogen, which is activated to pepsin when mixed with hydrochloric acid in the stomach.

Mucus protects the stomach lining from gastric juice.

Slide 43

The stomach and its secretions

Interior surface of stomach

Esophagus

Chief cells

Small intestine

Epithelium

Stomach

Sphincter

Parietal cell

Pepsinogen

and HCl are secreted.

HCl converts pepsinogen to

pepsin.

Pepsin activates more pepsinogen.

Chief cell

Folds of epithelial tissue

Pepsin

Sphincter

Pepsinogen

HCl

H+

Cl–

Parietal cells

Mucus cells

Gastric gland

1

2

2

3.

3

3

1

5 µm

Slide 44

Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori.

Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents.

Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine.

Slide 45

Digestion in the Small Intestine

The small intestine is the longest section of the alimentary canal.

It is the major organ of digestion and absorption.

Slide 46

Enzymatic hydrolysis in the human digestive system

Oral cavity, pharynx, esophagus

Stomach

Lumen of small

intestine

Epithelium of small intestine (brush border)

Carbohydrate digestion

Polysaccharides

Smaller polysaccharides, maltose

Polysaccharides

Maltose and other disaccharides

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

Smaller polypeptides

Pancreatic trypsin and chymotrypsin

Pancreatic carboxypeptidase

Dipeptidases, carboxypeptidase, and aminopeptidase

DNA, RNA

Pancreatic nucleases

Fat globules

Nucleotides

Fat droplets

Nucleosides

Nitrogenous bases, sugars, phosphates

Nucleotidases

Nucleosidases and phosphatases

Glycerol, fatty acids, monoglycerides

Bile salts

Pancreatic lipase

(starch, glycogen)

(sucrose, lactose)

Slide 47

The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself.

Slide 48