1. Digestive Systems
Before food can be used for energy, it must be broken down (digested) and absorbed into the body.

2. 2 types of digestive systems:
Intracellular digestion – food is digested inside the cell.
intra
extra
Extracellular digestion – food is broken down outside the cell in a digestive tract or cavity, then absorbed into the body.

3. Intracellular digestion
Extracellular digestion
both
Mollusks, annelids,
Arthropods, echinoderms,
All chordates
Sponges
Cnidaria
Flatworms

4. Extracellular digestion:
Single opening –
cnidarians & flatworms (gastrovascular cavity)
Digestive tract – one way tube
from mouth  anus

5. Invertebrate digestive tracts
Roundworms, annelids, mollusks, echinoderms
Specialized regions (stomach, intestines)
Allows food to be processed more efficiently

6. Non-vertebrate chordates
Filter feeders –
feed by straining suspended matter and food particles from water

7. Vertebrate digestive tracts
Organs are adapted to different feeding habits:
carnivores – shorter digestive tracts
herbivores – longer digestive tracts to help with digesting the plant material

8. Parts of the digestive system:
Mouth – mechanical digestion and the beginning of chemical digestion
Esophagus – tube leading from mouth to stomach – helps move the food with peristalsis
Stomach – mechanical and chemical digestion
Small intestine – most of the chemical digestion
Large intestine (colon) – removes water from the undigested material
Rectum – holds the wastes until the body is ready get rid of it

9. In some animals: Crop – stores food
Gizzard – grinds the food (mechanical digestion)
gizzard
crop
Found in annelids, insects, mollusks, birds, reptiles, and some fish.

10. More parts: (accessory organs)
Liver – produces bile which helps to digest fats
Gall bladder – stores the bile and releases it to the small intestine
Pancreas – produces digestive enzymes that help to digest fats, proteins, and carbohydrates in the small intestine

11. Liver
Gall bladder

12. Small intestine:
Folded surface, forming finger-like projections called villi
Villi are covered by thousands of smaller projections called microvilli
Villi and microvilli increase surface area for absorption of nutrients.

13. Animation: Organs of Digestion
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14. Class work Label and color the human digestive system
(use different colors for each part).
Write a poem or letter about the digestive system