1. The Digestive System

2. Digestive System Overview
Known as gastrointestinal (GI) tract or alimentary canal.
Open at both ends to the outside world.
Consists of long convoluted tube with accessory organs.

3. Steps in Digestion
Ingestion
Digestion
Absorption
Elimination

4. Types of Digestion Mechanical Food mass is shredded, torn & churned.
Occurs in mouth & stomach.
Chemical
Chemicals & enzymes break down food.
Occurs in mouth, stomach & small intestine.

5. Organs of the Digestive System
Oral Cavity
Esophagus
Stomach
Small Intestine
Large Intestine

6. Oral Cavity Lips, tongue, teeth & jaw muscles.
Increases surface area of food.
Food mixes with saliva and amylase.
A bolus forms and is swallowed.
The bolus passes through the pharynx, past the epiglottis & through the esophagus.

7. Esophagus Muscular tube that connects pharynx & stomach.
The cardiac or lower esophageal sphincter connects the esophagus to the stomach (prevents b).
Peristalsis is a series of coordinated muscular contractions that propels food along the digestive tract.

8. Stomach J-shaped stretchable organ.
Acts as a reservoir for food (1.5 L).
Movement of food controlled by two sphincters:
Cardiac sphincter: Between the stomach & the esophagus.
Pyloric sphincter: Between the stomach & the small intestine.

9. Stomach Folds (rugae) allow for expansion.
Mechanical digestion: Walls churn & squeeze.
Chemical digestion: Gastric juices.
Hydrochloric acid secreted by gastric glands.
Pepsinogen released & converts to pepsin.
Bolus becomes a liquefied paste (chyme).

10. Stomach
Mucus cells secrete mucus to line & protect stomach from HCl (aq).
Ulcers: HCl (aq) burns a hole through the mucus, irritating the stomach cells below.

11. Small Intestine Major site of digestion & absorption (80%).
6 m long & has a SMALLER diameter than the large intestine.
Lined with tiny finger-like projections called villi, which project into the lumen.
Microvilli line the villi.
Villi & microvilli increase the surface area for absorption.

13. Small Intestine
Consists of three sections:
Duodenum
Jejunum
Ileum.

14. Small Intestine Mechanical digestion via muscular contractions.
Chemical digestion via intestinal and pancreatic secretions.
Villi and microvilli responsible for absorption.
Absorbed nutrients transported to the liver.

15. Large Intestine Reabsorbs water, salt & some vitamins.
Holds & compacts unabsorbed material.
1.5 m long & has a LARGER diameter than the small intestine.
Consists of four sections:
Caecum
Colon
Rectum
Anus.

16. Large Intestine Chyme enters caecum, through the ileocaecal valve.
Waste products compacted into feces (3/4 water, 1/4 solid matter).
Feces pass through the rectum & exit the body through the anus.
Appendix attached to caecum, exact function is unknown.

17. Large Intestine Defecation controlled by two sphincters:
Rectal sphincter: Between the large intestine & the rectum.
Anal sphincter: Between the rectum & the anus.

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