Animal Nutrition II (Ch. 41)

Guest lecturer: Letitia Reichart (Letty)

Keywords

• Roles of mouth, stomach, sm.&lg. Intestine in digestion

• Pepsin, pepsinogen• Villi, microvilli• Cecum• Cellulose• Cellulase

• Acid chyme• Enzymatic hydrolysis• Peristalsis

Mammalian Digestive System

• Alimentary canal

• Accessory glands– Salivary glands, pancreas, liver, gallbladder

• Food moved by peristalsis

Mouth (oral cavity)

• Mechanical– Teeth– Saliva

• Enzymatic– Salivary amylase –

breakdown of starch and glycogen

Throat (pharynx) & Esophagus

• Throat – junction to esophagus & trachea

– Epiglottis

• Esophagus – uses peristalsis to move food to stomach

Stomach

• Stores food

• Secretes gastric juices

– Acid chyme

Relaxedmuscles

Contractedmuscles

Stomach

Digestive mechanisms in stomach

• Mechanical

• Chemical

• Enzymatic

Esophagus

Stomach

Pyloricsphincter

Cardiacorifice

Liver

Gall-bladder

Pancreas

Mechanical

• Mixing and churning– Smooth muscle– Every 20 seconds

Esophagus

Stomach

Pyloricsphincter

Cardiacorifice

Chemical

• Hydrochloric acid (HCl)

• pH around 2– Also breaks food down

Enzymatic

• Pepsin– Breaks down proteins

Chief cells

Mucus cells

Parietal cells

Interior surface of stomach

Gastric gland

Why doesn’t pepsin digest stomach?

Gastric pit

Activation of pepsin

Pepsin(active enzyme)

Pepsinogen

HCl

Parietal cellChief cell

Stomach

• After mechanical and enzymatic digestion:

-Acid chyme (nutrient-rich broth)

- Pyloric sphincter to the small intestine Stomach

Pyloricsphincter

Cardiacorifice

Smallintestine

Small intestine• Most of:

– Enzymatic digestion occurs here

– Absorption of nutrients into the blood stream occurs here

Figure 41.21 p. 859 in CampbellOral cavity,pharynx,esophagus

Stomach

Lumen ofsmall intes-tine

Smaller polysac-charides, maltose

Polysaccharides Disaccharides

Carbohydrate digestion

Salivary amylase

Polysaccharides

Pancreatic amylases

Maltose and otherdisaccharides

Epitheliumof smallintestine(brushborder)

Disaccharidases

Monosaccharides

Protein digestion Nucleic acid digestion

Proteins

Fat digestion

Fat globulesDNA, RNA

Fat dropletsNucleotides

Bile salts

Pancreatic lipase

Pancreaticnucleases

Nucleotidases

Glycerol, fattyacids, glycerides

Nitrogenous bases,sugars, phosphates

Nucleosides

Nucleosidasesand phosphatases

Dipeptidases, carboxy-peptidase, and aminopeptidase

Amino acids

Amino acids

Small peptides

Pancreatic carboxypeptidase

Pancreatic trypsinand chymotrypsin

Smaller polypeptides

Polypeptides

Small polypeptides

Pepsin

Stomach

Pancreas

Liver

Gall-bladder

Duodenum ofsmall intestine

Intestinaljuice

Bile

Acid chyme

Pancreatic juice

Figure 41.19 p. 858 in Campbell

Pancreas• Secretes proteases into duodenum

Inactive form Active form

Trypsinogen Trypsin

Procarboxypeptidase Carboxypeptidase

Chymotrpsinogen Chymotrypsin

Why doesn’t the small intestine digest itself?

Pancreas

Activeproteases

Fig. 37.13

Lumen of duodenum

Membrane-boundenteropeptidase

Inactivetrypsinogen

Other inactiveproteases Active

proteases

Trypsin

Liver• Produces bile that is stored in gallbladder• Bile contain bile salts• Bile salts aids digestion and absorption of fats

Largecircularfolds

Vein carrying bloodto hepatic portalvessel

Muscle layers

Villi

Intestinal wall

Most nutrient absorption

occurs in small intestine

Structure of small intestine

Lacteal

Lymphvessel

Villi

Epithelialcells

Bloodcapillaries

MicrovilliMicrovilli(brush border)

Epithelial cells

• Aid in nutrient transport across epithelial cells of sm. intestine into bloodstream

Large intestine (colon)• Major function is to reabsorb water

Ascendingportion oflarge intestine

Ileumof small intestine

Rectum

AnusAppendix

Cecum

LargeIntestine

Here are a few review questions

What would happen if you had a defect in pepsin production?

What would happen if you had a defect in pepsin production?

• A. carbohydrate would not be digested well

• B. meat would not be digested at all

• C. perhaps decreased absorption of protein

What would happen if you had a defect in salivary amylase

production?

• A. You would die

• B. You would be unable to digest starch

• C. The pH of the stomach would be affected

• D. None of the above

What would happen if you had a defect in salivary amylase

production?

Which of the following would you least like to donate to science

while you are still alive?• A. Cecum

• B. Pancreas

• C. Reproductive organs

What would happen if you had a defect in small intestine

enteropeptidase?

What would happen if you had a defect in small intestine

enteropeptidase?• A. Pancreatic enzymes would not be

activated

• B. Liver enzymes would increased

• C. Your small intestine would become blocked

• D. None of the above

Variations of vertebrate digestive system

• Herbivorous mammals– Specialized fermentation chambers

Coyote vs. Koala

Smallintestine

Stomach

Cecum

Colon(largeintestine)

Carnivore Herbivore

Small intestine

Why does herbivory require specializations?

• Plant tissue– Harder to break up– Contains cellulose– Nutrients less concentrated than meat

Structure of cellulose

Only bacteria and protozoa can break down cellulose

Via the enzymecellulase

Cecum

• Pouch at junction between lg and sm intestine

• Large cecum in rabbits, some rodents, koala, horses

• Full of symbiotic bacteria

Stomach

Cecum

Colon(largeintestine)

Herbivore

Small intestine

Symbiosis

• “living together”

Cecum function

• Fermentation chamber

• Bacteria breakdown cellulose

• Feces must be reingested

Stomach

Cecum

Colon(largeintestine)

Herbivore

Small intestine