10.2 The Human Digestive System - Ms. Ho-Lau's...
Transcript of 10.2 The Human Digestive System - Ms. Ho-Lau's...
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
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