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. Gallbladder (behind liver)
The Digestive System
Mouth
Salivary glands
Stomach
Pancreas (behind stomach)
Large intestine
Small intestine
Rectum
Gallbladder (behind liver)
Liver
Esophagus
Pharynx

4. The Mouth
Chewing 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

5. 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

6. Swallowing

7. 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

8. 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

9. 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

10. The Small Intestine Small Intestine Villus Circular folds
Villi
Epithelial cells
Capillaries
Lacteal
Vein
Artery

11. The Liver and Pancreas Liver Bile duct Pancreas Gallbladder
Duodenum
Bile duct
Pancreas
Pancreatic duct
To small intestine

12. 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

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