Lecture 13 Outline (Ch. 41)

I. Animal Nutrition Overview

II. Food Intake

III. Digestive Compartments

IV. Adaptations

V. Energy sources and stores

VI. Summary

What is/are the overall function(s) digestion?

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Overview: The Need to Feed

• Food is taken in, taken apart, and taken up in the process of animal nutrition

• In general, animals fall into three categories:– Herbivores eat mainly autotrophs

(plants, algae)– Carnivores eat other

animals– Omnivores regularly

consume animals as well as plants or algal matter

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• Meat, eggs, cheese - provide all nine essential amino acids ( “complete” proteins)

• Individuals eating only plant proteins need specific plant combinations for all essential amino acids

Essential Parts of Diet

Beans and other legumes

Corn (maize)and other grains

Lysine

Essential amino acids for adults

Tryptophan

Isoleucine

Leucine

Phenylalanine

Threonine

Valine

Methionine

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• Animals can synthesize most fatty acids they need• The essential fatty acids are certain unsaturated fatty acids that

must be obtained from the diet

Essential Parts of Diet

• Vitamins: organic molecules needed in small amounts

• 13 essential vitamins for humans• Fat-soluble & water-soluble

B-complex

Biotin/B7

Vitamin C (ascorbic acid)

Vitamin A

Vitamin D

Vitamin E

Vitamin K

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Minerals

• Minerals: inorganic nutrients, small amounts neededCalcium

Phosphorus

Potassium

Sulfur

Chlorine

Sodium

Magnesium

Iron

A diet missing a certain essential part or not enough calories overall leads to malnourishment or undernourishment

If a person is following a vegan diet, why is it recommended to eat a variety of plant sources?

Remember, these are the parts of diet:• Chemical energy (converted to ATP)• Organic carbon and nitrogen • Essential nutrients must be obtained

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Ingestion: the act of eating

• Suspension feeders - many aquatic animals, which sift small food particles from the water

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

• Fluid feeders suck nutrient-rich fluid from a living host• Bulk feeders eat relatively large pieces of food

Food Intake

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Humpback whale, a suspension feeder

Baleen

Leaf miner caterpillar, substrate feeder

Caterpillar Feces

Mosquito, a fluid feeder Rock python, a bulk feeder

Label each region of the digestive tract below:

What are the function(s) of each region?

Ingestion Digestion Absorption Elimination

Undigestedmaterial

Chemical digestion(enzymatic hydrolysis)

Nutrientmoleculesenter bodycells

Smallmolecules

Mechanicaldigestion

Food

Piecesof food

1 2 3 4

Food Intake

Digestion: process of breaking food down into molecules small enough to absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules

Absorption is uptake of nutrients by body cells

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

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Digestive Compartments

• Most animals process food (i.e. hydrolysis) in specialized compartments

• Reduces risk animal digesting its own cells/ tissues

Gastrovascularcavity

Food

Epidermis

Mouth

Tentacles

Gastrodermis

Gastrovascular Cavity:

For both digestion and distribution of nutrients

Cells secrete digestive enzymes

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• More complex animals: digestive tube with two openings (mouth, anus)

“Tube within a tube”

• Called alimentary canal

• Specialized regions, carry out digestion and absorption stepwise

Digestive Compartments 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

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Cecum

Anus Anus

Ascendingportion oflarge intestine

Gall-bladder

Smallintestine

Largeintestine

Smallintestine

Rectum

Pancreas

Liver

Salivary glands

TongueOral cavity

PharynxEsophagus

Sphincter

Stomach

Sphincter

Duodenum ofsmall intestine

Appendix

Liver

Pancreas

Smallintestine

Largeintestine

Rectum

StomachGall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth

Digestive Compartments

• Mammalian alimentary canal and accessory glands that secrete digestive juices through ducts

Food moves by peristalsis

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Larynx

Trachea

Pharynx

Tongue

Esophagus

Food

Tostomach

Tolungs

Epiglottisdown

Esophagealsphincterrelaxed

Epiglottisup

Sphincterrelaxed

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Oral Cavity, Pharynx, Esophagus

• Food bolus, saliva added, digestion begins with amylase and mucus

• Pharynx, junction opens to both the esophagus and the trachea (windpipe)

• Esophagus conducts food pharynx to stomach by peristalsis

• Epiglottis blocks entry to the trachea, and larynx.

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Digestion in the Stomach• The stomach stores food and secretes gastric juice,

which converts a meal to acid chyme

• Highly folded• Gastric juice -

hydrochloric acid (parietal cells) and the enzyme pepsin (chief cells)

• Pepsin initially secreted as pepsinogen

• Mucus protects the stomach lining from gastric juice

Esophagus

Small intestine

Epithelium

Stomach

Sphincter

Parietal cell

Chief cell

Folds ofepithelialtissue

Pepsin

Sphincter

Pepsinogen

HCl

H+

Cl–Mucus cells

Gastric gland

1

2

3

5 µ

m

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Digestion in the Small Intestine

• The small intestine: longest section of alimentary canal• Major organ of enzymatic

digestion and absorption

• 1st: duodenum - acid chyme from

stomach mixes with digestive juices from pancreas, liver, gallbladder, and the small intestine itself.

- 2nd: jejunum- 3rd: ileum

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Digestion in the Small Intestine

liver/gallbladder bile aids digestion

and absorption of fats

small intestinelining of duodenum

(brush border) produces several digestive enzymes

jejunum and ileum mainly absorb water & nutrients

pancreas proteases trypsin &

chymotrypsinamylase & lipasebicarbonate

neutralizes the acidic chyme

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Fat digestionNucleic acid digestion

Protein digestion

Fat (triglycerides)DNA, RNA

Nucleotides

Pancreaticnucleases

Pancreatic lipase

Glycerol, fatty acids,monoglycerides

Nucleotidases

Nucleosides

Nucleosidasesandphosphatases

Nitrogenous bases,sugars, phosphatesAmino acids

Dipeptidases, carboxy-peptidase, andaminopeptidase

Small peptides

Pancreatic carboxypeptidase

Smallerpolypeptides

Pancreatic trypsin andchymotrypsin

Small polypeptides

Proteins

Pepsin

Carbohydrate digestion

Polysaccharides Disaccharides

Salivary amylase

Smallerpolysaccharides

Maltose

Pancreatic amylases

Disaccharides

Disaccharidases

Monosaccharides

Smallintestine(enzymesfromepithelium)

Smallintestine(enzymesfrompancreas)

Stomach

Oral cavity,pharynx,esophagus

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Absorption in the Large Intestine

• The colon of the large intestine is connected to the small intestine

Feces stored in rectum until eliminated

• The cecum aids in fermentation of plant material,- connects where the small and large intestines meet

• Human cecum extension (appendix), -minor role in immunity

Here’s our generalized digestive tract again:

What are the secretions and purpose from each region listed below:

Mouth & teeth

EsophagusStomach

Small intestine

Large intestine

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• The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins

• Two sphincters between the rectum and anus control bowel movements

– Internal smooth muscle sphincter (involuntary)

– External striated muscle sphincter (voluntary)

Absorption in the Large Intestine

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Mutualistic Adaptations• Many herbivores have symbiotic microorganisms that

digest cellulose• The most elaborate adaptations in ruminants

Esophagus

OmasumAbomasum

Intestine

Rumen Reticulum1 2

4 3

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• Herbivores generally longer alimentary canals than carnivores; longer time needed to digest vegetation

• Coprophagy – method to recover more nutrients by ingesting feces

Cecum

Small intestine

HerbivoreCarnivore

Colon(largeintestine)

StomachSmall intestine

Adaptations

Enzymes for digesting plant matter

Homeostasis:90 mg glucose/100 mL blood

Stimulus:Blood glucose

level risesafter eating.

Stimulus:Blood glucose

level dropsbelow set point.

Energy Sources and Stores

Pancreas releases insulin – cells uptake sugars

Pancreas releases glucagon – liver releases sugars

If you eat a meal high in sugar, what happens?

Describe the steps including changes in blood sugar and changes in hormones.

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Energy Sources and Stores

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

• Energy secondarily stored as adipose, or fat, cells

• Fewer calories taken in than expended fuel is taken from storage and oxidized

100 µm

Fat cells

• Excessive intake of food energy, excess stored as fat

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

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LeptinPYY

Insulin

Ghrelin

Energy Sources and Stores

• The complexity of weight control in humans is well-studied

• Mice that inherit a defect in the gene for leptin become very obese

Ghrelin – secreted by stomach, stimulates appetite

Insulin – secreted by pancreas, suppresses appetite

Leptin – released by fat cells, suppresses appetite

PYY – secreted by Sm. Intestine, suppresses appetite

hypothalamus

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Obese mouse with mutant ob gene (left) – mutant for leptin production – next to wild-type sibling mouse.

The gene db codes for the leptin receptor. If mice are mutant for the db gene what happens?

1. They fail to make leptin – increased appetite

2. They fail to detect leptin – decreased appetite

3. They fail to detect leptin – increased appetite

4. They fail to make leptin – decreased appetite