Physiology Chapters 20: Digestive System

Front 1

Motility (5)

Back 1

-Is movement of food through GI tract by means of:
=Ingestion--taking food into mouth
=Mastication--chewing food & mixing it with saliva
=Deglutition--swallowing food
=Peristalsis--rhythmic wave-like contractions that move food through GI tract

Front 2

Secretion (3)

Back 2

-Release of exocrine & endocrine products into GI tract
-Exocrine secretions include: HCl, H20, HC03-, bile, lipase, pepsin, amylase, trypsin
-Endocrine secretions include hormones into stomach & small intestine
=Help regulate GI system
=E.g. gastrin, secretin, CCK, GIP, VIP

Front 3

Digestion and Absorption of Nutrients & Water (6)

Back 3

Carbohydrates
Proteins
Lipids
Absorption of vitamins
Absorption of minerals
Absorption of water

Front 4

Carbohydrates (2)

Back 4

-Typical diet: 250–800 grams carbohydrates
-Most consumed as disaccharides or polysaccharides
=Sucrose
=Lactose
=Maltose
=Starch
=Glycogen
=Cellulose (fiber, cannot be digested)

Front 5

Carbohydrate Digestion (2)

Back 5

-Only monosaccharides absorbed
-Disaccharides and polysaccharides must be digested to monosaccharides

Front 6

Digestion of Starch (2)

Back 6

-Enzyme of digestion
=Salivary amylase
=Pancreatic amylase
-End product
=Disaccharides (maltose)

Front 7

Further Digestion (7)

Back 7

-Enzymes of digestion
=(Gluco)amylase – polysaccharides  glucose
=Sucrase – sucrose  fructose + glucose
=Lactase – lactose  galactose + glucose
=Maltase – maltose  2 glucose
-Location of enzymes—brush border of small intestine
=“Brush border enzymes”

Front 8

Proteins (6)

Back 8

-Typical diet: 125 grams/day protein
=Only require 40–50 grams
-Proteins to be digested and absorbed include
=Consumed in diet
=Secreted into lumen of intestinal tract
=Sloughed off with cells lining intestinal tract

Front 9

Proteins
-Proteins digestion products

Back 9

-Proteins digestion products
=Amino acids
=Dipeptides
=Tripeptides

Front 10

Types of Proteases (6)

Back 10

-Endopeptidases
=Split polypeptides at interior peptide bonds
=Product = small peptide fragments
-Exopeptidases
=Cleave off amino acids from one end of polypeptide
=Product = amino acids

Front 11

Protein Digestion in Stomach (4)

Back 11

-Protein digestion begins in stomach
-Enzyme = pepsin
-Inactive (secreted form) = pepsinogen
-Activated by acid

Front 12

Pepsin: Activation and Activity (5)

Back 12

-Chief cells secrete pepsinogen
=Pepsinogen is the inactive form
=HCl cleaves pepsinogen to pepsin
=Pepsin = active form
-Parietal cells secrete HCl

Front 13

Protein Digestion in Small Intestine (2)

Back 13

-Pancreatic proteases
=Trypsin
=Chymotrypsin
=Carboxypeptidase
-Brush border proteases
=Aminopeptidase (peptidase)
=Enterokinase

Front 14

Absorption of Dipeptides and Tripeptides

Back 14

Broken down inside cell to amino acids

Front 15

Lipids (6)

Back 15

-Typical diet: 25–160 grams lipids
=90% triglycerides
-Lipids face special problem in digestion and absorption
=Not water soluble
=Do not mix with stomach, intestinal contents
=Form fat droplets

Front 16

Lipid Digestion (4)

Back 16

-Enzymes of digestion = lipases
-Secreted from pancreas
-Lipases can only act on molecules near edge of fat droplet
-Bile salts increase surface area of droplets by breaking large droplet into several small droplets = emulsification

Front 17

Bile Salts (4)

Back 17

-Synthesized in liver from cholesterol
-Secreted in bile to duodenum
-Amphipathic molecule
-Emulsify fat

Front 18

Absorption of Monoglycerides and Fatty Acids (3)

Back 18

-Lipids enter Golgi apparatus to be packaged into chylomicrons (lipoprotein)
-Chylomicrons secreted by exocytosis into interstitial fluid
-Chylomicrons enter lymphatic system via lacteal

Front 19

Absorption of Vitamins (7)

Back 19

-Fat-soluble vitamins (A, D, E, and K)
=Absorbed with lipids
=Dissolve in lipid droplets, micelles, chylomicrons
-Water-soluble vitamins
=Require special transport proteins
-Vitamin B12
=Absorbed only when bound to intrinsic factor

Front 20

Gastrointestinal Secretion and Its Regulation (4)

Back 20

-Saliva secretion
-Acid and pepsinogen secretion in the stomach
-Secretion of pancreatic juice and bile
-Rates of fluid movement in the digestive tract

Front 21

Regulation of Pepsinogen Secretion into Stomach (3)

Back 21

-Pepsinogen secretion regulated in sync with acid secretion
=Parasympathetic nervous system
=Gastrin

Front 22

Gastric-Phase Regulation of Secretion (4)

Back 22

-Stimuli of gastric secretion
=Proteins, peptides, and amino acids
=Distension of stomach
-Short and long reflex pathways trigger gastrin, acid, and pepsinogen release

Front 23

Protective Mechanisms of Stomach (3)

Back 23

-Include:
=Impermeability of parietal & chief cells to HCl
=A layer of alkaline mucus containing HC03-
=Rapid rate of cell division (entire epithelium replaced in 3 days)

Front 24

Inhibition of Secretion (3)

Back 24

-Gastric phase
=Exit of food removes stimuli for secretion
=Increased acidity inhibits gastrin release

Front 25

Inhibition of Secretion (6)

Back 25

-Intestinal phase
=Entry of food into duodenum causes
+Increased osmolarity
+Increased fat and acid
+Increased distension
=Long and short reflex pathways inhibit acid and pepsinogen secretion

Front 26

Intestinal PhaseEntry of Chyme into Duodenum (4)

Back 26

-Secretin is secreted in response to duodenal pH < 4.5
=Stimulates release of HC03- (buffer) into SI by pancreas
=Stimulates bile secretion by liver
-CCK is secreted in response to fat & protein content of chyme in duodenum
=Stimulates release of pancreatic enzymes
=Negative feedback on gastric juice?
=Stimulates bile release
-Glucose insulinotrophic peptide (Gastric inhibitory) (GIP)
=Inhibits gastric secretion
=targets pancreas for insulin release
-Vasoactive intestinal peptide (VIP)
=targets sm int. - increased absorption

Front 27

Digestion & Absorption of Carbohydrates (5)

Back 27

-Most carbohydrates are ingested as starch--a polymer of glucose
-Salivary amylase begins starch digestion
-Pancreatic amylase converts starch to oligosaccharides
=Oligosaccharides hydrolyzed by SI brush border enzymes (maltase, lactase, Sucrase)
=Goal Monosaccharide (glucose) in blood

Front 28

Digestion & Absorption of Protein (4)

Back 28

-Begins in stomach when pepsin digests proteins to form polypeptides
-In SI, from pancreas (trypsin, chymotrypsin)
-In SI from pancreas (carboxypeptidase)
-In SI from SI (peptidase)

Front 29

Digestion & Absorption of Lipids (4)

Back 29

-Occurs in SI
-Arrival of lipids in duodenum causes secretion of bile
-Fat is emulsified by bile
-Lipase from Pancreas breaks down further
=Into triglycerides & phospholipids