Digestive System

Function

• Ingestion• Digestion• Absorption• Elimination

Types of Digestion

• Physical digestion: – Mechanically breaking down the food

• Chemical digestion:– Chemically breaking down the food with the

help of chemicals (Enzymes)

Principle Structures

• Mouth (Ingestion/Digestion)– Physical : teeth, water, mucus– Chemical: saliva – salivary amylase - starch– Bolus– Epiglottis– Esophagus– Peristalsis– Esophageal sphincter

• Stomach (Digestion/Absorption)– Physical: Churning –– Chemical: Gastric Juice

(gastrin)• Water• Mucus (protection)• HCl – parietal cells (pH 1-3)• Pepsinogen –chief cells →(HCl) Pepsin – Proteins

– Pyloric Sphincter

• Small Intestine (Digestion/Absorption)– Duodenum, Jejunum, Ileum– absorption of nutrients into

blood stream– villi/microvilli → capillaries (proteins/sugars) and lacteals (lipids) → liver via diffusion,

– Chemical (mostly duodenum)• pH 8 – bicarbonate ion –

pancreas (secretin)• Accessory organs

– Pancreas (enzymes -proteins, CHO’s, lipids)

– Liver (bile salts –emulsifies lipids; conversion into glucose/glycogen; deamination)

– Gallbladder (stores/releases bile -cholecystokinin )

• Large Intestine (Absorption/Elimination)– Concentrates/stores/

eliminates waste– Colon- absorbs water,

salts; produce Vit B-12 and K

– Rectum/Anal canal –stores feces

– Elimination via 2 sets of sphincters (peristalsis)