Lecture 22
Digestive System II
24-1
Small Intestine
Duodenum
Jejunum
Ileocecal valve
Ileum
Fig. 26.14
• Site of greatest amount of digestion and absorption
• Divisions
– Duodenum (“twelve finger widths”)
– Jejunum (“empty”)
– Ileum (“twisted”)
24-2
Small Intestine Secretions
• Mucus
– Protects against digestive enzymes and stomach
acids
• Digestive enzymes
– Disaccharidases: Break down disaccharides to
monosaccharides
– Peptidases: Hydrolyze peptide bonds
– Nucleases: Break down nucleic acids
24-3
Duodenum and Pancreas
Duodenum
• 25cm in adult
• Accessory glands empty secretions into duodenum
Fig. 26.20
24-4
Histology of Small Intestine
Fig. 26.15
• Circular folds, villi and microvilli increase surface area
• Epithelial cells produced by intestinal glands
24-5
Liver
Inferior
vena cava
Posterior
Left lobe
Right lobe
Caudate lobe
Left lobe
Inferior
vena cava
Hepatic
portal vein
Gallbladder
(a) Anterior view
Right lobe
Common
hepatic duct
Quadrate lobe
Cystic duct
Gallbladder
Anterior
(b) Posteroinferior view
Fig. 26.18
• 4 Lobes
• Ducts
– Cystic duct joins with common hepatic duct to form common
bile duct
– Common bile duct joins pancreatic duct
24-6
Functions of the Liver
• Bile production
– Salts emulsify fats, neutralizes stomach acid
– Stored in gall bladder
– Gallstones can form as precipitate of cholesterol
• Storage
– Glycogen, fat, vitamins, copper and iron
• Nutrient interconversion
• Detoxification
– Removal of ammonia and conversion to urea (eliminated by kidneys in
urine)
• Phagocytosis
– Removal of worn-out and dying red and white blood cells, some
bacteria
• Synthesis
– Blood proteins
24-7
Pancreas
• Anatomy
– Endocrine
• Insulin
– Exocrine
• Pancreatic juice
–
–
–
–
Digestive enzymes
Released in inactive form
Become active in duodenum
Digest protein, fats, carbohydrates, and nucleic acids
24-8
Review Question
Digestion of proteins is started in the ______________
and completed in the ________________.
(a) Oral cavity, stomach
(b) Stomach, small intestine
(c) Esophagus, small intestine
(d) Oral cavity, small intestine
(e) Esophagus, stomach
24-9
Large Intestine
Transverse colon
• Extends from ileocecal
valve to anus
• Consists of cecum, colon,
rectum, anal canal
• Movements sluggish (1824 hours)
Descending
colon
Ascending
colon
Cecum
Vermiform
appendix
Sigmoid
colon
Ileocecal
valve
Cecum
Vermiform appendix
Ileum
Rectum
Anal canal
Fig. 26.16
24-10
Movement in Large Intestine
• Mass movements
Rectal valve
– Common after meals
• Defecation reflex
Rectum
Anal canal
– Distension of the rectal wall by
feces
• Defecation
– Usually accompanied by voluntary
movements to expel feces through
abdominal cavity pressure caused
by inspiration (breathing in) and
contraction of abdominal wall
muscles
Veins
Internal
anal sphincter
Anus
External
anal sphincter
Fig. 26.16
24-11
Points to Remember
• Stomach
– Mixes food
– Protein digestion
– Limited absorption (aspirin)
• Small intestine
– Receives secretions of liver and pancreas
– Chemical and mechanical digestion
– Transports undigested material
• Large intestine
– Absorb water
– Form, store and expel feces
24-12
Questions?
24-13