BIOLOGY: Digestive System

Digestive System
: breaks down food into molecules that can be absorbed and utilized by the cells of the body
: a long , hollow tube called the gastrointestinal tract or GI tract

ACTIVITIES INVOLVED IN THE DIGESTIVE PROCESS:
1. Digestion - breakdown of food into simpler molecules that can be absorbed by the body

• Mechanical digestion - breaks food into pieces w/o the changing of the chemical structure
• Chemical digestion - food is broken down into smaller, simpler molecules (chemical structure is altered)

2. Absorption - cells absorb H2O, minerals and other materials essential to life from their environment

3. Elimination - removal of waste


PARTS OF THE DIGESTIVE SYSTEM

1. MOUTH - the teeth and tongue begin mechanical digestion (mastication a.k.a chewing)
-Amylase in the saliva begins the chemical digestion of starch

TEETH - tear and crush the moistened food

3 Basic Shapes (teeth)
a. Incisors - the sharp, front teeth (biting and tearing pieces of food)
b. Canines - pointed teeth (tear and shred food)
c. Molars - teeth at the back mouth, have large top surfaces (crush and grind food)

TONGUE - push the food to the esophagus
Saliva gland- produces saliva
Saliva
: dissolves food molecules
: contains LYSOZYME that fights infection by digesting the cell wall of many bacteria


2. ESOPHAGUS - muscular tube which carries the bolus (chewed food, partially digested food) and liquids from the throat to the stomach

• Peristalsis - wave-like contractions of smooth muscles that move food into the digestive tract
• Epiglottis - small flap of tissue that directs the proper passageway of air and food

3. STOMACH - a muscular sac with thick, expandable walls
- when the stomach walls contract strongly...
mixing and churning the food (mechanical) begins the action of hydrochloric acid (HCI) and an enzyme called Pepsin (chemical)

• Gastrin - stimulates secretion of HCI (hydrochloric acid)
• HCI - converts pepsinogen to pepsin
  
• Pepsin - breaks down proteins
• Chyme - partially digested food + digestive secretions

4. SMALL INTESTINE (18 to 23 ft. long)
- site for the complete digestion and absorption of food
- provided with thousands of tiny finger-like projections called villi

3 parts of the Small Intestine:
1. Duodenum - the first 12 inches of the small intestine
2. Jejunum - where most of the nutrients are absorbed into the blood
3. Ileum - where the remaining nutrients are absorbed before moving into the large intestine

5. LARGE INTESTINE
- also known as colon
- absorbs left over H2O , salts, and vitamins
- remaining materials are compacted into feces
- final 6 inches (rectum)

PANCREAS
- produces hormones (insulin) that regulate sugar levels
- produces sodium bicarbonate that neutralizes the stomach acid

LIVER - produces bile

Bile - breakdowns lipids