Module 15 - Digestive System Flashcards
Mouth Function
- Breakdown of food through chewing (mastication)
- Chemical breakdown through saliva
- Forms bolus
Saliva Composition
- Majority water
- Some ions & protein
- Under ANS control
Saliva Function
- Lubrication of food bolus
- Beings digestion carbs via salivary amylase enzyme
Salivary Glands
- Parotid
- Submandibular
- Sublingual
- Produce 2L/day each
Esophagus Function
- Connects mouth & pharynx to stomach
- Straight muscular tube
Stomach Function
- Stores, mixes & digests some food
- Delivers food to small intestine
Liver Function
- Produces & secretes bile
Gallbladder Function
- Stores & concentrates bile
Pancreas Function
- Secretes digestive enzymes, hormones, HCO3-
Small Intestine Function
- Digestion & absorption of majority of food particles
Large Intestine Function
- Stores & concentrates undigested material
- Absorbs salt & water
Rectum Function
- Triggering of defecation reflex
GI System Processes
- Secretion
- Digestion
- Absorption
- Motility
- Excretion
Secretion
- Release of digestive fluids into lumen of GI tract
Digestion
- Breakdown of food into small molecules
- By digestive enzymes
Absorption
- Small molecules taken up by circulatory system
- Distributed throughout body
Motility
- Movement of food through system
- Contraction of smooth muscle lining
Excretion
- Removal of unwanted waste products
- After wanted material is reabsorbed
Swallowing Process
- Food bolus pushed to back of tongue
- Triggers swallow reflex
- Uvula of soft palate closes over nasopharynx
- Larynx lifted by neck muscles
- Epiglottis bends over glottis, covering larynx
- Bolus moves down esophagus
- Through cardiac orifice
- Into stomach by peristalsis
Peristalsis
- Wave of smooth muscle contractions
Stomach Areas
- Fundus, upper
- Body, middle (largest)
- Antrum/pylorus, lower
Pyloric Sphincter
- Distal portion
- Regulates emptying of stomach into small intestine (duodenum)
Empty Stomach
- Folds (rugae)
- Increase surface area
- Allow for expansion when food comes
Stomach Digestion
- Proteins begin process by pepsin enzyme
Stomach Absorption
- Alcohol & aspirin
Peristaltic Contraction
- Activates mixing of chyme
- Move chyme through pyloric sphincter into small intestine
Motility
- Muscle activity moving substances through tract
Mucus
- Secreted by cells in body & antrum of stomach
- Protects smooth muscle lining from HCl
HCl Function
- Unfolds complex protein & connective tissue
- Kills bacteria
- Activates conversion of pepsinogen to pepsin
Pesinogen (Pepsin)
- Secreted by stomach body cells
- Active enzyme pepsin breaks down large proteins
Intrinsic Factor
- Vitamin B12 absorption
Pancreas Functions
- Exocrine, digestion
- Endocrine, glucose homeostasis
Excorine Process
- Secreted into pancreatic duct
- Merges with common bile duct
- Enters duodenum
Pancreas Products
- Amylase (carbohydrate-digesting enzyme)
- Trypsin, chymotrypsin, proteases (protein digesting enzymes)
- Lipase (fat-digesting enzyme)
Pancreas Secretion
- Sodium bicarbonate
Pancreatic Amylase
- Digest starch (polysaccharide) to maltose (disaccharide)
Small Intestine Segments
- Duodenum (1st, shortest)
- Jejunum (2nd)
- Ileum (3rd, longest)
Ileocecal Sphincter
- End of small intestine
- Empty into ascending colon of large intestine
Inner Wall
- Composed of folds
- Contain villi (projections)
- Large surface area for food contact
Villi
- Contain capillary network
- Lymphatic lacteal
Epithelial Cells
- Secrete digestive enzymes
- Cover villi
- Microvilli (lumen facing) forming bush border
Small Intestine Function
- Majority of digestion & reabsorption (duodenum & jejunum)
Small Intestine Absorption
- Digestive material to circulatory & lymphatic systems
Enhancement of Absorption
- Large surface area (villi lining)
- Large blood supply
- Motility
Small Intestine Digestion
- Digestive enzymes, pancreas & epithelial cells
- Bile
Large Intestine Structure
- Begins at ileocecal valve
- Connects to small intestine via ileum
- Ascending, longitudinal, descending limb
- Curved sigmoid section
- Rectum ending at anus
- Larger diameter than small intestine
- Lacks folds
- Smaller villi
Large Intestine Functions
- Water & electrolyte absorption
- Mucus secretion
- Digestion (small amount)
- Store & concentrate feces
Water & Electrolyte Absorption
- Na+ active transport
- Water osmosis
Mucus Secretion
- Protects lining from chemical & mechanical damage
- Lubricates forming feces
- K+ & HCO3- secreted into colon
Digestion (Large Intestine)
- Undigested polysaccharides metabolized into free fatty acids (bacteria)
- Bacteria produce gas (flatus)
- Vitamin K for blood coagulation
Carbohydrate Types
- Monosaccharides
- Disaccharides
- Polysaccharides
Monosaccharides
- Single building block
- Glucose, fructose, galactose
Disaccharides
- Two monosaccharides
- Maltose, lactose, sucrose
Polysaccharides
- 3+ building blocks
- Starch, glycogen
Carb Digestion Mouth
- Starting point
- Salivary amylase
- Break up large polysaccharides
Carb Digestion Stomach
- None
- Acidic environment
Carb Digestion Small Intestine
- Pancreatic amylase into duodenum, digest polysaccharide to disaccharide
- Pancreas secretes HCO3- to neutralize stomach acid
- Disaccharides require specific enzymes to break down
Small Intestine Enzyme Location
- Bush border of microvilli
- Intestinal epithelial cells
Lactose Intolerance
- Inability to digest lactose
- No/little lactase enzyme
Carb Absorption
- Na+/K+ pump on basal side of intestinal epithelial cells
- Establish Na+ gradient (high outside)
- Powering Na+/glucose co-transporter on luminal side
- Moves glucose into cell
- Glucose diffuse out basal side via facilitated diffusion
Protein Composition
- Long linked amino acid chains
- Different enzymes required for different amino acid groups
- Must be broken into building blocks before absorption
Protein Digestion Stomach
- Beginning
- HCl converts pepsinogen to active pepsin
- HCl aids to uncoil proteins to give pepsin access
- Pepsin digests protein chains into polypeptides
- Polypeptides pass through pyloric sphincter
Protein Digestion Small Intestine
- HCO3- neutralized acidic stomach chyme
- Pepsin becomes inactive
- Trypsin & chymotrypsin (pancreatic enzymes) continue digestion
- Proteases enzymes continue process
Proteases Enzymes
- Produced in pancreas
- Secreted into small intestine
- Brush border of intestinal epithelial cells
Proteases Enzyme Classes
- Endopeptidases, break bonds between amino acids (inner)
- Exopeptidases, break bonds at ends of amino acid (outer)
Protein Absorption
- After proteins broken into single amino acids
- Na+/K+ pump on basal side of intestinal epithelial cells
- Establish Na+ gradient (high outside)
- Powering Na+/amino acid co-transporter on luminal cell
- Moving amino acids into cell
- Remaining small peptides absorbed by endocytosis
Fat/Lipids Composition
- Phospholipids, cholesterol
- Not water soluble, don’t mix with water
Emulsification
- Churning action of stomach
- Breaks down large fat drops to aid enzymes with digestion
Bile
- Product of liver
- Transported to gallbladder (stored & concentrated)
- Not an enzyme
- Composed of water, bile salt, ions, fatty acids
Bile Function
- Released into duodenum
- Bile salts keep lipid drops emulsified
- Preventing formation of large droplets
Colipase
- Protein
- From pancreas
- Allows lipase to gain access to interior of fat droplet
Lipase Enzyme
- Digestion of lipids from interior
Fat Digestion
- Pancreatic lipase attacks phospholipids & removes 2 chains
- Monoglyceride remains
- Lipase works from interior to shrink droplets
- Droplets form micelles
Micelles
- Single layer of bile salts
- Surrounding small lipid droplet
- Ferry droplets to intestinal epithelial cells for absorption
Absorption Fatty Acids & Monoglycerides
- Lipid soluble
- Diffuse through cell membrane
- Smooth endoplasmic reticulum
- Combine with cholesterol & proteins to form chylomicrons
Chylomicrons
- Packaged into secretory vessels by Golgi apparatus
- Enter lacteals of lymphatic system
Absorption of Cholesterol
- Specific active transport system
Absorption of Bile Salts
- Left behind after lipid absorption
- Reabsorbed by transport system in ileum cells
- Returned to liver to be reused
Lipid Soluble Vitamins
- Diffuse through cell membrane
- Absorbed like fats
- Vitamins A, D, E, K
Water Soluble Vitamins
- Absorbed by carrier-mediated mechanisms
- Require Na+ concentration gradient & co-transporter
- Vitamins B, C, folic acid, niacin
Water Production
- 80% water in saliva & digestive enzymes
- 20% water & food
Water Absorption
- Small Intestine, high
- Large intestine, low
Water Absorption Process
- Osmotic gradient forms as other solutes are absorbed
- Epithelial cells develop higher solute concentration
- Water flows into cells via osmosis
- As solutes move out of cell, water follows
Absorption of Na+
- Na+/K+ pump on basal lateral surface
- Establish Na+ gradient (high outside)
- Na+ move into cell from lumen
- Na+ absorbed with carbs & amino acids
Absorption K+
- Passively absorbed
- Concentration gradient forms as solutes are absorbed
- High concentration in lumen
- Passive diffusion into cells
Unregulated Processes
- Digestion
- Absorption
Regulated Processes
- Motility
- Enzyme secretion
Hormonal Regulation
- Release of chemicals from intestinal cells
- Response mechanical stimulation/neural activation
Neural Regulation
- Enteric NS, division of ANS
Enteric NS
- Sympathetic & parasympathetic divisions can influence digestive activity
- Altering activity of enteric nerves
ENS Nerve Effects
- Smooth muscle walls
- Enzyme-secreting cells
- Endocrine cells
- Blood vessels
PSYN Alteration
- Increase gastric motility & secretions
- Production of watery saliva
SYN Alteration
- Decreases gastric motility
- Secretes thick saliva (dry mouth)
ENS Short Loop
- Begins with mechanical distension/chemical changes
- Changes detected by sensors of ENS creating reflex
- Activating effector organs
- Causing release of enzymes/altering motility
ENS Long Loop
- Stimulated by sight/smell of food
- Detected by sensors (eyes/nose)
- Send signals through PSYN to ENS
- Alter enzyme release/motility
Interstitial Cells
- Smooth muscle cells
- Surrounding tract
- Alter own membrane potentials
- Producing BERS
BER Membrane Potential
- Does not meet threshold
- Need additional stimulus
BER Frequencies
- Stomach 3/min
- Duodenum 12/min
Secretin Hormone
- Presence of acid
- Inhibits stomach emptying
- Causes release of HCO3- & bile
- Neutralizing acid for optimal enzyme function
Cholecystokinin (CCK)
- Presence of fats
- Slows emptying of stomach
- Releasing enzymes & bile
Glucose-Dependent Insulinotropic Peptide
- Response to glucose & amino acids
- Stimulates insulin release
- May inhibit stomach emptying
Gastrin Hormone
- Secreted by G cells in stomach antrum
- Response to proteins, mechanical distention & PSYN
- Secrete HCl to convert pepsinogen to pepsin
Gastric Acid Phases
- Cephalic, brain
- Gastric, stomach
- Intestinal, intestine
Cephalic Phase
- Increase gastric acid secretion
- Response to sight, smell, taste, chewing
- Anticipatory response
- Activating ENS, long loop
Cephalic Phase Effects
- Parietal cells release HCl
- G cells release gastrin
- Increased stomach motility
Gastric Phase
- Presence of food/amino acids in stomach
- Triggering ENS
- Short loop
Gastric Phase Effects
- Release of HCl
- Release of gastrin
- Release of pepsinogen
- Increased gastric motility
Intestinal Phase
- Presence of glucose, fat, acidic chyme
- Activating ENS
- CCK, secretin, glucose-dependent insulinotropic peptide
Intestinal Phase Effects
- Decreased motility
- Inhibit secretions in stomach