1. The Digestive System

2. The Digestive System
Breaks down food into smaller particles so cells can use it
Built around alimentary canal (one-way tube passing through body)
Digestive system includes: mouth, pharynx, esophagus, stomach, small intestine, and large intestine
Accessory structures include: salivary glands, pancreas, and liver

3. The Digestive System ACCESSORY ORGANS ALIMENTARY CANAL
Figure 22.5
The Digestive System
ACCESSORY ORGANS
ALIMENTARY CANAL
Oral cavity (mouth)
Tongue
Pharynx
Salivary glands
Esophagus
Liver
Gallbladder
Stomach
Pancreas
Small intestine
Colon of large intestine
Appendix
Rectum
Anus

4. The Mouth
Chewing (mastication) begins process of mechanical digestion = physical break down of large pieces of food into smaller pieces
Saliva, a digestive enzyme, begins breaking down food molecules (starches like crackers) into different molecules = chemical digestion
Saliva also moistens food and makes it easier to chew/swallow and helps fight infections by killing some bacteria on food
The muscular tongue
tastes,
shapes food into a ball, and
pushes the food to the back of the mouth for swallowing.

5. The Pharynx The pharynx During swallowing, a reflex
connects the mouth to the esophagus and
opens to the trachea, which leads to the lungs.
During swallowing, a reflex
moves the opening of the trachea upward and
tips the epiglottis to close the trachea entrance

6. The Pharynx BREATHING SWALLOWING Epiglottis Epiglottis down up Pharynx
Figure 22.7
The Pharynx
BREATHING
SWALLOWING
Epiglottis up
Epiglottis down
Pharynx
Adam’s apple
Trachea closed
Air flowing into open trachea (windpipe)
Esophagus
closed
Food flowing into open esophagus

7. The Esophagus
Clump of food (bolus) goes down throat and into esophagus
Bolus moves through esophagus by peristalsis – contractions of smooth muscle surround esophagus squeeze food down esophagus
“Heartburn” is caused by stomach acid entering the esophagus and irritating the lining of the esophagus

8. Swallowing

9. The Stomach Bolus empties into the stomach from the esophagus
Stomach continues mechanical and chemical digestion of food
Chemical digestion – some glands in the stomach produce mucus to protect the wall of stomach and other glands produce hydrochloric acid (HCl). The acid activates an enzyme called pepsin (made by another set of glands). Pepsin and HCl together chemically break down food molecules
Mechanical digestion – stomach muscles contract and churn to mix food with stomach juices (mixture now called chyme). After an hour or two, chyme moves into the small intestine

10. The Small Intestine, Pancreas, and Liver
Chyme enters first part of small intestine called duodenum
Location where most chemical digestion takes place (small intestine)
Small intestine is 6.5m long and 2.5cm wide
Enzyme from pancreas and liver enter duodenum
Pancreas releases two enzymes – one to help chemically digest food and the other to neutralize the stomach acid
Liver releases bile to help break down fats from food

11. The Liver and Pancreas Bile Liver Stomach Bile Gallbladder Chyme
Figure 22.11
The Liver and Pancreas
Bile
Liver
Stomach
Bile
Gallbladder
Chyme
Intestinal enzymes
Pancreatic juice
Duodenum of
small intestine
Pancreas

12. The Small Intestine, Pancreas, and Liver (continued)
After duodenum, most chemical digestion is completed and the rest of the small intestine absorbs nutrients
Projections called villi create and enormous surface area for absorption of nutrients
Contractions of smooth muscle move chyme along

13. Epithelial cells and blood capillary
Figure 22.13
The Small Intestine
Blood vessels
Muscle
layers
Interior of
intestine
Intestinal wall
Nutrient
absorption
Villi
Interior of
intestine
Nutrient
absorption
Nutrient
absorption
Microvilli
Epithelial
cells
Blood
capillaries
Lymphatic
vessel
Blood
Epithelial cells and blood capillary
Villi

14. The Large Intestine (Colon)
Large intestine is 2m long and 7cm wide
Removes water from undigested material left over from small intestine
Bacteria in large intestine helps digestion
Concentrated waste material remaining after water removal is eliminated from body
What is the condition called when too much water is reabsorbed in the large intestine?
Constipation
What is the condition called when not enough water is reabsorbed in the large intestine?
Diarrhea

15. The Large Intestine (Colon)
Figure 22.14
The Large Intestine (Colon)
Colon of
large
intestine
Small
intestine
Sphincter
End
of small
intestine
Rectum
Anus
Nutrient
flow
Appendix

16. Path of Digestion = mouth – esophagus, stomach, small intestine, large intestine, anus