Chapter 41

Animal Nutrition

Overview: The Need to Feed

– Herbivores eat mainly autotrophs (plants and algae)

– Carnivores eat other animals

– Omnivores regularly consume animals as well as plants or algal matter

Essential Nutrients

• There are four classes of essential nutrients:

– Essential amino acids

– Essential fatty acids

– Vitamins

– Minerals

Essential Amino Acids

• Animals require 20 amino acids and can synthesize about half

• Essential amino acids- must be obtained from food in preassembled form

• “Complete” proteins- provides all the essential amino acids (meat, eggs, and cheese)

• Most plant proteins are incomplete in amino acid makeup

Beans and otherlegumes

Corn (maize)and other grains

Lysine

Essential amino acids for adults

Tryptophan

Isoleucine

Leucine

Phenylalanine

Threonine

Valine

Methionine

Essential Fatty Acids

• Animals can synthesize most of the fatty acids they need

• The essential fatty acids are certain unsaturated fatty acids

Vitamins

• Vitamins are organic molecules required in the diet in small amounts

• 13 essential vitamins

• Two categories: fat-soluble and water-soluble

Minerals

• Minerals are simple inorganic nutrients, usually required in small amounts

Dietary Deficiencies

• Undernourishment- diet with less chemical energy than the body requires

• Malnourishment- absence from the diet of one or more essential nutrients

Undernourishment

• An undernourished individual will

– Use up stored fat and carbohydrates

– Break down its own proteins

– Lose muscle mass

– Suffer protein deficiency of the brain

– Die or suffer irreversible damage

Malnourishment

• Malnourishment can cause deformities, disease, and death

The main stages of food processing are ingestion, digestion, absorption, and elimination

• Ingestion is the act of eating

Suspension Feeders• Many aquatic animals are suspension

feeders, which sift small food particles from the water

Substrate Feeders

Leaf miner caterpillar,a substrate feeder

Caterpillar Feces

Substrate feeders are animals that live in or on their food source

Fluid Feeders• Fluid feeders suck nutrient-rich fluid from a

living host

Mosquito, a fluid feeder

Bulk Feeders• Bulk feeders eat relatively large pieces of food

Rock python, a bulk feeder

• Digestion is the process of breaking food down into molecules small enough to absorb

– Enzymatic hydrolysis splits bonds in molecules with the addition of water

• Absorption is uptake of nutrients by body cells

• Elimination is the passage of undigested material out of the digestive compartment

Ingestion Digestion Absorption Elimination

Undigestedmaterial

Chemical digestion(enzymatic hydrolysis)

Nutrientmoleculesenter bodycells

Smallmolecules

Mechanicaldigestion

Food

Piecesof food

1 2 3 4

Digestive Compartments

• Intracellular Digestion- food is engulfed by endocytosis and digested within food vacuoles

• Extracellular Digestion- food particles are broken down outside of cells

Gastrovascularcavity

Food

Epidermis

Mouth

Tentacles

Gastrodermis

Esophagus

Mouth

Pharynx

Crop Gizzard

Typhlosole

Intestine

Lumen of intestine

Anus

(b) Grasshopper

Foregut

(c) Bird

(a) Earthworm

Midgut Hindgut

Esophagus RectumAnus

Mouth

Crop

Gastric cecae

Esophagus

Mouth

CropAnus

StomachGizzard

Intestine

Gastrovascular cavity- functions in both digestion and distribution of nutrients

Complete digestive tract (alimentary canal)- digestive tube with two openings, a mouth and an anus

Esophagus

Mouth

Pharynx

Crop Gizzard

Typhlosole

Intestine

Lumen of intestine

Anus

(a) Earthworm

(b) Grasshopper

Foregut

Mouth

Crop

Gastric cecae

Esophagus RectumAnus

Midgut Hindgut

(c) Bird

StomachGizzard

Intestine

Esophagus

AnusCrop

Mouth

Organs of the mammalian digestive system

• Peristalsis- rhythmic contractions of muscles to push along food

• Sphincters regulate the movement of material between compartments

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Cecum

Anus

Ascendingportion oflarge intestine

Gall-bladder

Smallintestine

Largeintestine

Smallintestine

Rectum

Pancreas

Liver

Salivary glands

TongueOral cavityPharynxEsophagus

Sphincter

Stomach

Sphincter

Duodenum ofsmall intestine

Appendix

The Oral Cavity, Pharynx, and Esophagus

• Oral cavity- mechanical digestion takes place

– Salivary glands deliver saliva to lubricate food

• Amylase- initiates breakdown of glucose polymers

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

The Oral Cavity, Pharynx, and Esophagus

• The tongue shapes food into a bolus and provides help with swallowing

• Pharynx (throat)- opens to both the esophagus and the trachea (windpipe)

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

The Oral Cavity, Pharynx, and Esophagus

• Esophagus conducts food from the pharynx down to the stomach by peristalsis

– Swallowing causes the epiglottis to block entry to the trachea

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

LarynxTrachea

Epiglottisup

Pharynx

Tongue

Glottis

Esophagus

Esophagealsphinctercontracted

Food

Tostomach

Tolungs

Epiglottisdown

Esophagealsphincterrelaxed

Glottis upand closed

Epiglottisup

Esophagealsphinctercontracted

Sphincterrelaxed

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Glottisdownand open

Digestion in the Stomach- Chemical Digestion in the Stomach

• Gastric juice is made up of hydrochloric acid and the enzyme pepsin

• Parietal cells secrete hydrogen and chloride ions separately

• Chief cells secrete inactive pepsinogen, it is activated to pepsin when mixed with HCl

• Mucus protects the stomach lining from gastric juice

Esophagus

Small intestine

Stomach

Sphincter

Folds ofepithelialtissue

Sphincter

5 µm

Interior surfaceof stomach

Interior surfaceof stomach

Chief cells

Epithelium

Parietal cell

Pepsinogen and HClare secreted.

HCl convertspepsinogen to pepsin.

Pepsin activatesmore pepsinogen.

Chief cell

PepsinPepsinogen

HCl

H+

Cl–

Parietal cells

Mucus cells

Gastric gland2

3

1

1

2

3

Stomach Dynamics• 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

Esophagus

Small intestine

Stomach

Sphincter

Folds ofepithelialtissue

Sphincter

5 µm

Interior surfaceof stomach

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)

Digestion in the Small Intestine

• Major organ of digestion and absorption

• Duodenum (first part of small intestine)- acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Secretinand CCK

Stomach

GallbladderLiver

+

Duodenum ofsmall intestine

Bile

Gastrin

Secretin

PancreasCCK

CCKKey

StimulationInhibition

+

–

+

++ –

Pancreatic Secretions

• The pancreas produces proteases trypsin and chymotrypsin, protein-digesting enzymes that are activated after entering the duodenum

• Its solution neutralizes the acidic chyme

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Bile Production by the Liver

• Aids in digestion and absorption of fats

• Bile is made in the liver and stored in the gallbladder

Anus

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Secretions of the Small Intestine

• The epithelial lining of the duodenum produces several digestive enzymes

• Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water

Absorption in the Small Intestine

• The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen

• The enormous microvillar surface greatly increases the rate of nutrient absorption

Muscle layers

Vein carrying bloodto hepatic portal vein

Villi

Intestinal wall

Key

Nutrientabsorption

Largecircularfolds

Microvilli (brushborder) at apical(lumenal) surface

Key

Nutrientabsorption

Bloodcapillaries

Epithelialcells

Villi

Lymphvessel

Basal surface

LactealEpithelial cells

Lumen

Absorption in the Large Intestine• Colon of the large intestine is connected to

the small intestine

• Cecum aids in the fermentation of plant material and connects where the small and large intestines meet

• Appendix- an extension off the cecum, which plays a very minor role in immunity

• The colon recover waters that has entered the alimentary canal and houses E. coli strains, some of which produce vitamins

Cecum

Anus

Ascendingportion oflarge intestine

Smallintestine

Largeintestine

Smallintestine

Rectum

Appendix

Dental Adaptations

• The teeth of poisonous snakes are modified as fangs for injecting venom

• All snakes can unhinge their jaws to swallow prey whole

Incisors

(c) Omnivore

Molars

(b) Herbivore

(a) Carnivore

Canines Premolars

Stomach and Intestinal Adaptations

• Herbivores have longer alimentary canals than carnivores, they need more time to digest vegetation

Cecum

Small intestine

HerbivoreCarnivore

Colon(largeintestine)

StomachSmall intestine

Mutualistic Adaptations

• Many herbivores have fermentation chambers, where symbiotic microorganisms digest cellulose (ruminants)

Esophagus

OmasumAbomasum

Intestine

Rumen Reticulum1 2

4 3

Energy Sources and Stores

• Animals store excess calories primarily as glycogen in the liver and muscles

• Energy is secondarily stored as adipose, or fat, cells

Overnourishment and Obesity

• Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat

• Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart attacks, and strokes

• The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival

LeptinPYY

Insulin

Ghrelin

Obese mouse with mutantob gene (left) next to wild-type mouse.