Download Figure 23.17b

Figure 23.17b
Histology of Small Intestine

MALT – mucosa-associated lymphoid tissue
Solitary lymphatic nodules
Aggregated lymphatic follicles (Peyer’s patches)

Submucosa






Duodenal (Brunner’s glands)
Alkaline secretion
Muscularis
Serosa
Adaptive Structures Small Intestine



Circular folds / plicae circulares
Villi
Lacteal



Microvilli
Brush border


Lymphatic capillary
Brush border enzymes
Intestinal juice


1-2 liters / day
pH 7.6
Figure 23.18a
Figure 23.18b
Figure 23.18c
Figure 23.18d
Mechanical Digestion in Small Intestine

Segmentation




Localized
Mix chyme with digestive juices
Important for process of absorption
Peristalsis

Movement along the length of small intestine
Chemical Digestion in Small Intestine


Completes digestion of food from the
stomach
Carbohydrates

Pancreatic amylase





Glycogen and starch only
-dextrinase
Sucrase
Lactase
Maltase
Chemical Digestion in Small Intestine

Proteins





Trypsin
Chymotrypsin
Elastase
Carboxypeptidase
Peptidases
Chemical Digestion in Small Intestine

Lipids


Pancreatic lipase
Emulsification


Amphipathic bile salts
Nucleic acids


Nucleosidases
Phosphatases
Table 23.4 pt 1
Table 23.4 pt 2
Absorption in Small Intestine






Passage of digested nutrients from gastointestinal tract into
blood or lymph
90% of nutrients absorbed through small intestine
Monosaccharides
Facilitated diffusion
 Fructose
Secondary active transport
 Glucose
 Galactose
Enter blood through hepatic portal system
Figure 23.19a
Figure 23.19b
Absorption in Small Intestine

Amino acids



Active transport
Na+-dependent secondary active transport
Dipeptides and tripeptides

Symporter with H+
Absorption in Small Intestine

Lipids by simple diffusion



Micelles formed due to amphipathic nature of bile
salts
Chylomicrons




Due to emulsification and digestion
Triglycerides coated with proteins
Leave cells via exocytosis
Enter blood vessels via lymphatic system
Enterohepatic circulation
Absorption in Small Intestine

Electrolytes



Diffusion
Active transport
Secondary active transport

Vitamins

Water

Osmosis
Figure 23.20
Table 23.5
Concept 23.7
Large Intestine
Anatomy of Large Intestine

Mesocolon attaches to posterior abdominal wall

4.
Regions
Cecum
Colon
Rectum
Anal canal

Ileocecal sphincter (valve)
1.
2.
3.

Allows passage into large intestine
Figure 23.21a
Figure 23.21b
Anatomy of Large Intestine
1.
2.
3.
4.
Cecum
•
Pouch
•
Attached appendix / veriform appendix
Colon
•
Ascending
•
Transverse
•
Descending
•
Sigmoid
•
Right and Left colic (splenic) flexures
Rectum
Anal canal
•
Anal columns
•
Anus
•
Internal and external sphincter
Histology of Large Intestine




Mucosa
 Absorptive cells absorb mainly water
 Goblet cells secrete mucus
 Lymphatic nodules
Submucosa
Muscularis
 Haustra
 External longitudinal smooth muscle
 Teniae coli
 Internal circular smooth muscle
Serosa
 Epiploic appendages
Figure 23.22a
Figure 23.22b
Figure 23.22c
Figure 23.22d
Mechanical digestion in Large Intestine

Gastroileal reflex



Haustral churning



Intensifies after a meal
Occurs 3 or 4 times a day
Distension and contraction of haustra
Peristalsis
Mass peristalsis
Chemical Digestion in Large Intestine


Bacteria:
Ferment carbohydrates




Gases produced are flatus or flatulence when
excessive
Break down proteins
Decompose bilirubin
Feces formed of dried chyme, inorganic salts,
mucus, bacteria, undigested foods and other
substances
Defecation Reflex



Empties the rectum
Response to distention of rectal wall
External anal sphincter voluntarily relaxed
defecation occurs
Table 23.6
Table 23.7
Concept 23.8
Phases of Digestion
Phases of Digestion

Cephalic
Gastric
Intestinal

Cephalic Phase




Stimulation of the senses activates CNS
Prepares mouth and stomach for food
Figure 23.23
Phases of Digestion



Gastric Phase
Begins with food in the stomach
Neural regulation




Negative feedback system
Stretch receptors
Chemoreceptors
Hormonal regulation



Gastrin
Released by G cells of gastric glands
Controlled by negative feedback mechanism (pH)
Phases of Digestion

Intestinal Phase



Begins with food in the small intestine
Inhibitory effects to slow exit of chyme
Neural regulation


Enterogastric reflex
Distension of duodenum
Phases of Digestion

Intestinal Phase continued

Hormonal regulation

Cholecystokinin (CCK)




Stimulates release of pancreatic juice
Contraction of gallbladder wall
Relaxes sphincter of hepatopancreatic ampulla
Secretin



Response to acidic chyme
Stimulates flow of pancreatic juice for buffering
Inhibits secretion of gastric juice
Table 23.8
Concept 23.9
Food Molecules
Six Main Types of Nutrients
1.
2.
3.
4.
5.
6.

Water
Carbohydrates
Lipids
Proteins
Minerals
Vitamins
Essential nutrients cannot be made in
sufficient amounts by the body
Guidelines for Healthy Eating

Variety
Maintain healthy weight
Choose low fat foods
Lots of vegetables, fruits, and grains
Sugar in moderation
Salt and sodium in moderation
Alcohol in moderation

Food Guide Pyramid






Figure 23.24
Nutrients


Minerals
 Inorganic elements constitute 4% of body mass
 Regulate enzymatic reactions
 Serve as coenzymes
Vitamins
 Organic molecules required in small amounts
 Most function as coenzymes
 Most cannot be synthesized by body
 Provitamins
 Fat-soluble vitamins
 A, D, E, and K
 Water soluble vitamins
 B and C
 Antioxidant vitamins
Concept 23.10
Metabolism
Metabolic Reactions

Metabolism


Enzymes



Catalyze chemical reactions
May require coenzymes
Anabolic reactions



All the chemical reactions of the body
Synthesis or building reactions
Endergonic – energy consuming
Catabolic reactions


Decomposition reactions
Exergonic – produce more energy than consumed
Metabolic Reactions


Coupling of catabolism and anabolism by
ATP
ATP is catabolized




Provides energy for synthesis of other bonds
Drives other anabolic reactions
Anabolic reaction of ADP and a phosphate to
produce ATP
Approximately 40% of energy released in
catabolism is used



60% converted to heat
Some for body heat
Most lost to environment
Figure 23.25
Carbohydrate Metabolism

Carbohydrates catabolized to monosaccharides




After absorption monosaccharides are:




Glucose
Fructose
Galactose
Used to synthesize ATP
Converted to glycogen
Build triglycerides
Glucose can be converted to several amino acids
Glucose Metabolism

Cellular respiration
C6H12O6 + 602 + 36 or 38 ADP’s + 36 or 38 P →
6CO2 + 6 H2O + 36 or 38 ATP’s

Glycolysis




Transition step


Acetyl coenzyme A production
Krebs cycle


Anaerobic cellular respiration
Energy transfer to coenzymes NAD+ and FAD
Electron transport chain


ATP produced
Aerobic cellular respiration
Figure 23.26
Glucose Anabolism

Glycogen




Storage form of carbohydrates
~ 500 g can be stored
Synthesis stimulated by insulin
Gluconeogenesis

Synthesis of new glucose molecules from protein
and lipid decomposition
Figure 23.27
Lipid Metabolism

Catabolism

Lipolysis
Hormones enhance lipolysis






Epinephrine
Norepinephrine
Cortisol
Different mechanisms for lipid catabolism
Ketone bodies
Figure 23.28
Lipid Metabolism




Anabolism
Insulin stimulates liver and adipose cells to
synthesize triglycerides
All excess food types can be converted to
triglycerides
Other lipids produced:




Phospholipids
Lipoproteins
Thromboplastin
Myelin sheaths
Lipid Transport in Blood





Lipoproteins
Lipids combined with proteins
More water soluble
Transportable in blood
Categorized by size and density
Lipoproteins

Largest and lightest to smallest and heaviest
1.
Chylomicrons
•
•
Carried by lymph to blood
Transport dietary lipids to adipose
Very low-density lipoproteins (VLDLs)
2.
•
•
Transport triglycerides to adipose
Converted to LDLs
Low-density lipoproteins (LDLs)
3.
•
•
Transport 75% of cholesterol to cells
Deposit cholesterol to smooth muscle and arteries
High-density lipoproteins (HDLs)
4.
•
Transport cholesterol from body cells to liver for elimination
Protein Metabolism


Amino acids not stored as proteins
Used to synthesize:







ATP
Structural proteins
Enzymes
Replace damaged proteins
Antibodies
Transporters
Converted to triglycerides when in excess
Protein Catabolism







Catabolism
Protein breakdown occurs regularly
Some amino acids used to generate ATP
Deamination
Anabolism
Formation of peptide bond to synthesize proteins
Carried out by ribosomes
Amino Acids

20 amino acids in body

10 essential



10 nonessential



Cannot be synthesized by body
Must be present in diet
Able to be synthesized by body
Complete protein
Incomplete protein
Table 23.9
End Chapter 23