Animal Nutrition

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Fluid feeders suck nutrient-rich fluid from a living host.

Mosquito, a fluid feeder

Slide 21

Bulk feeders eat relatively large pieces of food.

Rock python, a bulk feeder

Slide 22

Digestion is the process of breaking food down into soluble molecules - small enough to absorb.

In chemical digestion, the process of 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.

Slide 23

The four stages of food processing

Ingestion

Digestion

Mechanical & Chemical

Digestion

Absorption

Elimination

Undigested material

Chemical

digestion (enzymatic

hydrolysis)

Nutrient molecules enter body cells

Small molecules

Mechanical digestion

Food

Pieces of food

1

2

3

4

Slide 24

Digestive Compartments

Most animals process food in specialized compartments. These compartments reduce the risk of an animal digesting its own cells and tissues.

Intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles.

Extracellular digestion is the breakdown of food particles outside of cells. It occurs in compartments that are continuous with the outside of the animal’s body.

Slide 25

Digestion in a hydra

Gastrovascular cavity

Food

Epidermis

Mouth

Tentacles

Gastrodermis

Slide 26

Animals with simple body plans have a gastrovascular cavity with only one opening that functions as mouth / anus. This gastrovascular cavity functions in both digestion and distribution of nutrients.

More complex animals have a digestive tube with two openings, a mouth and an anus.

This one way digestive tube is called a complete digestive tract or an alimentary canal. It can have specialized regions that carry out digestion and absorption in a stepwise, efficient fashion.

Slide 27

Variation in alimentary canals

Esophagus

Mouth

Pharynx

Crop

Gizzard

Typhlosole

Intestine

Lumen of intestine

Anus

(b) Grasshopper

Foregut

(c) Bird

(a) Earthworm

Midgut

Hindgut

Esophagus

Rectum

Anus

Mouth

Crop

Gastric cecae