Digestive System
GI TRACT ORGANS
Oral cavity
Oropharynx
Esophagus
Stomach
Small intestine
Large Intestine
Anus
ACCESSORY ORGANS
Salivary glands
Pancreas
Liver
Gall bladder
GI TRACT LAYERS
Mucosa
Submucosa
Submucosal plexus
Muscularis externa
Smooth muscle
Myenteric plexus
DIGESTIVE PROCESSES
Ingestion
Motility
Peristalsis
Segmentation
Secretion
Mucus
HCl
Bicarbonate
Enzymes
Hormones
Digestion
Carbohydrates
Salivary amylase
Pancreatic amylase
Dextrinase
Sucrase
Maltase
Lactase
Lactose intolerance
Proteins
Peptidases
Pepsin
Trypsin
Chymotrypsin
Lipids
Bile and lipid emulsification
Breaking large fat gobules into smaller fat droplets
Function of bile salts
Salivary lipase
Gastric lipase
Pancreatic lipase
Nucleic acids
Nucleases
Absorption
Sublingual absorption of medicines
Nitroglycerin
Gastric absorption
Aspirin
Alcohol
Absorption in Small Intestine
Glucose, amino acids, vitamins and minerals are absorbed into capillaries
Fatty acids etc. absorbed into lacteals
Compaction
Defecation
DIGESTIVE REGULATION
GI Regulation – sensors
Mechanoreceptors are activated by distension of the digestive walls by food (bolus or
chyme)
Chemoreceptors activated by H+, proteins, and lipids in chyme
Osmoreceptors are activated by amino acids and glucose
GI Regulation sensory regulatory phases
Cephalic phase
Smell, taste or thought of food
Gastric phase
Stimuli arising in stomach
Intestinal phase
Stimuli arising in small intestine
GI Regulation integration and output
Autonomic nervous system
Enteric nervous system
Separate nervous system located within the GI wall
Submucosal and Myenteric plexuses
Influenced by autonomic system
Gastrointestinal hormones
Gastrin
Cholecystokinin (CCK)
Secretin
Glucose dependent insulinotropic peptide (GIP)
GI Regulation neural pathways
Short pathway
Receptor to intrinsic enteric plexuses out to effector
Long pathway
Receptor to CNS to effector
GI Regulation – effectors
Secretory cells within digestive organs
Smooth muscles within digestive organs
Muscle Activity or Motility
Self generating graded potentials or slow waves
Can produce action potentials
Strength not rate of contractions
Autonomic nerves and hormones
DIGESTIVE ORGANS AND THEIR FUNCTIONS
Oral Cavity and Salivary Glands
•
Mastication
•
Taste
•
Digestion of carbohydrates
Salivary amylase
Starch and glycogen
Cephalic phase and chemoreceptors (taste buds) activate salivary secretion through
parasympathetic stimulation
Esophagus
Muscular tube
Upper esophageal sphincter
Lower esophageal (cardiac) sphincter
Acid reflux (heartburn)
Swallowing Reflex
Mechanoreceptors in oropharynx start the reflex
Bolus presses on epiglottis closing off airways and preventing inspiration
Upper esophageal sphincter opens
Peristaltic contractions move bolus downward
Lower esophageal sphincter opens
Bolus enters stomach
Stomach
Anatomy
Stomach – Functions
•
Secretion
Mucus – lubrication
Pepsinogen - pepsin
Gastrin - hormone
Intrinsic factor - vitamin B12
•
Food separation – HCl
•
Digestion of proteins – pepsin
•
Mixes chyme – peristalsis
•
Storage of chyme
•
Delivers chyme to duodenum
Gastric Regulation of Secretions
Cephalic phase stimulates HCl, pepsinogen, and gastrin secretion
Gastric phase
Proteins and peptides in stomach activate chemoreceptors and mechanoreceptors and
stimulate secretion
Intestinal phase
Chyme, lipids and H+ in duodenum activate mechanoreceptors, chemoreceptors, and
osmoreceptors inhibit pepsinogen and acid secretion
Gastric Regulation of Motility
Cephalic phase stimulates motility
Gastric phase
Mechanoreceptors and chemoreceptors stimulate motility
Gastrin stimulates motility
Intestinal phase
Mechanoreceptors, and chemoreceptors in duodenum inhibit motility
CCK, secretin, and GIP inhibits motility
Small Intestine – Anatomy
Small Intestine – Functions
•
Digestion of food
Pancreatic enzymes
Intestinal mucosal enzymes
•
Absorption of nutrients
•
Secretion of hormones
CCK, GIP and secretin
•
Entrance area for pancreas, liver and gall bladder secretions
Pancreas
Production of bicarbonate
Buffer acids from stomach
Production of digestive enzymes
Peptidases
Lipase
Pancreatic amylase
Nucleases
Liver
Bile production and secretion
Gall bladder
Bile storage, concentration and release
Bile salts emulsify fats and lipids in small intestine
Motility of Small Intestine
Short periods of peristalsis
Long periods of segmentation
Distension of intestine triggers motility strength
Gastrin promotes motility in ileum
Large Intestine or Colon
Anatomy
Large Intestine – Functions
•
Absorption of minerals
•
Absorption of water and compaction of chyme into feces
•
Defecation
Motility in Large Intestine
Segmentation
2-3 times per hour
Mass movement
Strong peristaltic contractions
3-4 times per day
Swift movement of chyme
Gastrocolic reflex
Peptic Ulcer