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Animal Nutrition 1

Some of the best known and

fascinating adaptations of animals

involve their feeding and digestion

Examples:

• Reptile swallowing prey

• Baleen whales

http://www.youtube.com/watch?v=vJvfjiCTvq4

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Pythonhttp://www.youtube.com/watch?v=aDW5HpdFals

Starfishhttp://www.youtube.com/watch?v=i-EJuL0ix5Q

http://www.youtube.com/watch?v=rE8l-KFQlhY

Animal diversity of feeding strategies and digestive physiology

• Filter feeders,

predators

• Digestive systems:

no true tissues and

organs,

gastrovascular

cavity, true digestive

system (alimentary

canal)

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Simple intracellular digestion

• Example

paramecium

• Food taken up into

food vacuoles

where enzymatic

and chemical

digestion occurs

Figure 33.3 Anatomy of a sponge

Intracellular digestion by

phagocytosis in choanocyte

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Extracellular digestion

• A. outside organism

• B. gastrovascular cavities

• C. alimentary canal

Extracellular digestion

• Secrete digestive

enzymes onto

food source

• Absorb nutrients

• Best known in

fungi and

bacteria, some

higher animals

Gastrovascular

cavity: Hydra

-extracellular

digestion

-increased

surface area

-disadvantage?

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Extracellular digestion

• A. outside organism

• B. gastrovascular cavities

• C. alimentary canal

Gastrovascular cavity vs. Alimentary

Canal

Alimentary canal: a simple view

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mouth

Mechanical

digestion storage

absorption

anus

Basic parts of alimentary canal

Alimentary canal: mammalian

Mouth

• Mechanical

• Enzymatic

• Salivary amylase

– Digests starch

• Food formed into bolus

• Moistened and

dissolving with saliva

• Peristaltic contraction

to stomach

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Stomach

-muscular organ,

approx. 1 liter

capacity

-esophageal

sphincter, pyloric

sphincter

-rugae (ridges)

Digestive

mechanisms in

stomach

• Mechanical

• Chemical

• enzymatic

Mechanical

• Mixing and churning

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Digestive mechanisms

• Mechanical mixing and churning

• Chemical - pH around 2

– Also breaks food down

• Enzymatic – Pepsin (protease) breaks down

protein

• Absorption – low surface area, water, small

molecules such as ethanol, aspirin

Why doesn’t

pepsin digest

stomach?

Activation of

pepsin

-chief cells –

pepsinogen

(inactive)

-parietal cells -

HCl

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Small intestine

• Most of the

enzymatic

digestion occurs

here

• Acid neutralized

• Starch, protein,

lipids digested

Why doesn’t the small intestine digest

itself?

Fig. 37.13

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Most nutrient

absorption takes

place in small

intestine

• Structure: another

example of

increasing surface

area

Structure of

small intestine

Microvilli

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Large intestine

(colon)

• Major function is

to reabsorb water

• Rich in symbiotic

bacteria

• Bacteria digest

cellulose

• Some symbiotic

bacteria produce

vitamin K

Variations of vertebrate digestive

system

• Herbivorous mammals

– Specialized fermentation chambers