10.2 The Human Digestive System

digestive tract and accessory organs transform food into

energy

> 6m long, 2.5 cm wide

1.5m long, 5 cm wide

The Mouth Salivary glands secrete saliva

Parotid gland parotid duct

Submandibular gland submandibular duct

Sublingual glands many smaller ducts

Chemical digestion

Amylase: Starch simple sugars

Mechanical digestion

Teeth

Tongue: food soft bolus

The Esophagus

Epiglottis prevents bolus from entering the lungs

Esophagus transport bolus through peristalsis (wave-like

muscular contractions)

Mucus keeps passage moist

Video: peristalsis

The Stomach

Esophagus esophageal / cardiac sphincter stomach

Food triggers secretion of gastric juice (salts, enzymes, HCl,

water, mucus)

Mucus – protects stomach from acid

Pepsin – enzyme to digest protein

HCl – activates pepsinogen pepsin

Mechanical digestion:

3 layers of muscle fibres

Bolus chime (a thick liquid)

pyloric sphincter small intestine

The Small Intestine

3 parts: duodenum, jejunum, ileum

To absorb nutrients:

Many villi and microvilli

Long length

The Small Intestine

Duodenum

digestion and absorption

Pancreas: pancreatic enzymes for all macromolecules

Gall bladder: fat fat droplets

Jejunum

more folds,

continues breakdown and absorption of proteins and

carbohydrates

Ileum

fewer villi

continues absorption

push unabsorbed particles through

The Accessory Organs

Pancreas:

Secretes 1L of fluid into duodenum daily

Carbohydrases, proteases, lipases: chemical digestion

Bicarbonate: raise the pH to help enzymes

The Accessory Organs

Liver:

Secretes bile (bile pigments & salts)

Fat fat droplets

Bile is stored in gall bladder and released into duodenum

Chemical Digestion

Enzyme Action

Enzyme Action

Enzyme functions affected by

Temperature

pH

Different enzymes have

different optimal range

Nutrient Absorption - Monosaccharides

Absorbed and carried by blood to liver

Liver converts monosaccharides to glucose

Blood carried glucose to all cells (source of energy)

Liver: excess glucose glycogen

Glycogen stored in liver and muscles

Nutrient Absorption – Amino acids

Absorbed and carried by blood to liver

Liver converts amino acids to:

Sugars

energy-releasing chemicals

New proteins

waste

Nutrient Absorption – Glycerol + fatty

acids

Absorbed by cells in small intestine

Reassembled to form triglycerides

Coated with proteins bloodstream

broken down by lipase

absorbed by cells for energy

The Large Intestine

Shorter, wider

Aka colon

Re-absorb water

Anaerobic bacteria break down food and produce vitamins

Muscle contraction push undigested materials to rectum

feces

Digestion Timeline

Homework

P.419 #1-11, 13-15