UNIT Ⅻ
GSATROINTESTINAL PHYSIOLOGY
Metabolism
Nutrients
Water Electrolytes Vitamins carbohydrate protein fat
Food
Alimantary tract
Chapter 62 General principles of gastrointestinal function Chapter 63 Propulsion and mixing of food in the alimentary tract Chapter 64 Secretory functions of the alimentary tract Chapter 65 Digestion and absorption in the alimentary tract
Chapter 62 General principles of gastrointestinal function
the activity of gastrointestinal smooth muscle
Control of gastrointestinal functions by nervous and hormonal systems
Activity of gastrointestinal smooth muscle Resting potentials Slow waves Spike potentials Movements of the gastrointestinal tract
Resting potentials
Membrane potential (mv)
0 -10 -20 -30 -40 -50 -60
stretch acetylcholine parasympathetic depolarization hormones norepinephrine hyperpolarization sympathetic
Slow waves 0 Membrane potential(mv)
-10
stomach 3 duodenum 12 terminal ileum 8-9
-20 -30 -40 -50 -60
Slow wave
Basic electrical rhythm
Spike potentials
Membrane potential(mv)
0
Amplitude of slow wave
-10
The resting potentials
-20 -30 -40 -50 -60
Contraction of smooth muscle
Spike potentials Spike potentials
Action potentials of nerve fibers
Mechanism of depolarization 1
Ca
2+
Na+
inflow
Na+ inflow
Movements in the gastrointestinal tract
Propulsive movement
mixing movement
Promote the food move along the alimentary tract
Keep the gastrointestinal contents mixed
Propulsive movement
Oral cavity
Peristalsis
Distention of the gut Physical irritation of the gut Chemical irritation of the gut
anus
mixing movement
Oral cavity
Peristalsis sphincter
Local intermittent constractions anus
Summary of activity 0
Resting potentials
Membrane potential(mv)
-10 -20
Slow waves
-30 -40 -50 -60
Spike potentials Contraction of smooth muscle
Control of gastrointestinal functions by nervous and hormonal systems
Nervous regulation
hormonal regulation
Hormonal regulation
cholecystokinin secretin Gastric inhibitory peptide
Break down products of food
Increase the contractility of the gallbladder
“I” cells
cholecystokinin
Increase the secretion of pancreatic juice Inhibit stomach motility
acidic gastric juice
“S” cells
Increase the secretion of pancreatic juice
secretin Inhibit the activity of most gut
Fatty acids amino acids carbohydrate
Mucosa of the upper small intestine
Gastric inhibitory peptide
Inhibit the activity of stomach
Nervous regulation Enteric nervous system (ENS)
Extrinsic nervous system
Enteric nervous system (ENS)
myenteric plexus (Auerbach’s plexus)
submucosal plexus (Meissner’s plexus)
myenteric plexus (Auerbach’s plexus) Excitatory effects Increase the intensity of contraction Increase the rate of the rhythm of contraction Increase the velocity of conduction of contraction along the tract
Inhibitory effects
Sphincter Pyloric sphincter
Oral cavity
sphincter
anus
submucosal plexus (Meissner’s plexus)
secretion absorption contraction
Extrinsic nervous system
parasympathetic nervous sympathetic nervous
parasympathetic nervous
increase
Enteric nervous system
sympathetic nervous
norepinephrine Smooth ENS muscle Decrease Activity of gastrointestinal tract
Irritation of the gut mucosa Distension of the gut Chemical substances
Afferent sensory nerve fibers from the gut
ENS Sympathetic ganglia Spinal cord or brain stem
Gastrointestinal reflexes stimulation
ENS
Sympathetic ganglia
Spinal cord or brain stem
Activity of gastrointestinal tract
Summary of nervous regulation Irritation of the gut mucosa Distension of the gut Chemical substances
Afferent sensory nerve fibers from the gut
ENS Sympathetic ganglia Spinal cord or brain stem
Chapter 63 Propulsion and mixing of food in the alimentary tract Oral cavity and esophagus Stomach Small intestine Large intestine
Oral cavity and esophagus
Mastication
Swallowing
Mastication 1. Mastication is important for the digestions of fruits and raw vegetables.
Cellulose membrane
2. Mastication increases the Total surface area rate of digestion by grinding exposed to the the food into particles. digestive juices 3. Mastication prevents excoriation of GI and increase the emptying of food.
Swallowing The process of food coming into the stomach from oral cavity . 1.Voluntary stage
Oral cavity
2.Pharyngeal stage
Pharynx
3.Esophageal stage
Esophagus
Pharynx Esophagus Stomach
1.Voluntary stage
Oral cavity
The pressure of the tongue upward and backward against the palate.
Pharynx
2.Pharyngeal stage
Pharynx
Esophagus
Receptors (pharynx) Trigeminal nerves
Glossopharyngeal nerves
Brain stem 5th ,9th ,10th ,12th cranial nerves Series of automatic pharyngeal muscle contractions
2.Pharyngeal stage
Pharynx
1.the trachea is closed 2.the passage between the pharynx and nasal cavities is closed 3.the esophagus is opened 4.a fast peristaltic wave originates in the pharynx and forces the bolus of food into the upper esophagus.
Esophagus
3.Esophageal stage
Esophagus
Stomach
peristalsis primary The continuation of the peristaltic wave that begins in the pharynx and spread into the esophagus
secondary Distension of the esophagus Myenteric nervous system
Vagal afferent
medulla Vagal efferent Glossopharyngeal nervous
esophagus
Lower esophageal sphincter (gastroesophageal sphincter)
Oral cavity
Prevents reflux of stomach contents into the esophagus sphincter
stomach
Recpetive relaxation of the stomach Oral cavity
sphincter
stomach stomach
Stomach Orad portion First two thirds of the body body
Caudal portion The remainder of the body plus the antrum
antrum
Stomach 1.The storage of large quantities of food 2. Mixing this food with gastric secretions to from chyme 3. Slow emptying of chyme from the stomach into the small intestine
Chyme
The mixture of food and gastric secretions
The storage of large quantities of food Food enter the stomach
Brain stem
stomach
afferent efferent
Vagal nerve
Vago-vagal reflex
Mixing and propulsion of food into the stomach
Basic electrical rhythm
Constrictor waves Mixed waves
Mixing and propulsion of food into the stomach Constrictor waves
Propulsive movements mixing movements
pylorus
Pyloric pump
Mixing and propulsion of food into the stomach Constrictor waves
mixing movements
The opening of pylorus is small Pyloric muscle contracts
pylorus
Pyloric sphincter Water and fluids polyrus
Hunger contractions Constrictor waves occur when the food is present in the stomach Hunger contractions occur when the stomach has been empty for several hours or more Hunger contractions cause mild pain in the stomach which is called hunger pang after much longer starvation
Regulation of stomach emptying Pyloric pump Pyloric sohincter polyrus
Emptying of the stomach Nervous factor Gastric factors Hormonal factor Nervous factor Duodenal factors Hormonal factor
Gastric factors
Stretching of the stomach Local myenteric reflexes
Slightly inhibit the pylorus
Accentuate the activity of the pyloric pump
Gastric factors
foods (especially digestive products of meat) Antral mucosa releases gastrin
Increase the movement of the gastric body
Accentuate the activity of the pyloric pump
Nervous factor Duodenal factors Hormonal factor
Duodenal factors
Nervous factor
Chyme in the duodenum stimulate the duodenum in different ways
Nervous reflex Slightly increase the contraction of pyloric sphincter
Decrease the activity of the pyloric pump
The stimulation of chyme in the duodenum 1.The distention of the duodenum 2.The irritation of the duodenal mucosa 3.The acidity of chyme 4.The osmolality of chyme 5.The breakdown products in the chyme
Nervous reflex
Enterogastric reflexs
1. through enteric nervous system 2. Stimulation of duodenum Extrinsic nervous Sympathetic ganglia Sympathetic nervous fibers stomach 3. Through the vagus nerves to the brain stem, then inhibit the excitatory signals transmitted to the stomach through vagi
Hormonal factor foods Duodenal mucosa Release hormones increase the contraction of pyloric sphincter
Decrease the activity of the pyloric pump
Hormonal factor
cholecystokinin secretin
Decrease the stomach motility
Gastric inhibitory peptide
summary Pyloric pump
The force of emptying
Pyloric sphincter
Control the emptying
polyrus
summary excitatory Gastric factors
Duodenal factors inhibitory
Nervous factor Hormonal factor
Nervous factor Hormonal factor
Small intestine
Mixing contractions propulsive contractions
Mixing contractions
segmentation contractions
Propulsive movements segmentation contractions peristalsis Peristaltic rush
peristalsis 1.Occur in any part of the small intestine 2. Move analward at a slow velocity 3. Are weak and die out after traveling only 3 to 5 centimeters 4. The net movement of chyme in the small intestine is very slow
peristalsis
the entry of chyme into the duodenum
Distention of the stomach elicit peristalsis of small intestine through myenteric plexus, which is called gastroenteric reflex
Peristaltic rush Powerful and rapid peristalsis Is produced by intense irritation of the intestinal mucosa, infectious diarrhea Travel long distances to sweep the contents of the intestine into the colon and thereby relieve the small intestine irritative chyme and excessive distention
Ileocecal valve and ileocecal sphincter Sphincter remains constricted and slows the emptying of ideal contents into the cecum
cecum ileum
The lips of the ileocecal valve protrude into the lumen of the cecum to prevent the backflow of fecal contents from the colon into the small intestine
Large intestine 1. Absorption of water and electrolytes from the chyme to form solid feces Proximal half of the colon 2. Storage of fecal matter until it can be expelled distal half of the colon
Mixing movements
haustrations
Circular constrictions is longer Circular constrictions is larger so the constriction of the lumen could produce occlusion
propulsive movements
Mass movements
Defecation
Is initiated by defecation reflexes
Enteric nervous system reflex Parasympathetic reflex
Cerebral cortex
Pudendal nerve
Descending colon Sigmoid
contract
rectum Internal anal sphincter
relax
external anal sphincter
Enteric nervous system reflex When feces enter the rectum Distend the rectal wall
Myenteric plexus
external anal sphincter Internal anal sphincter Descending colon Sigmoid rectum
Parasympathetic reflex When feces enter the rectum Nerve endings in the rectum are stimulated
Pelvic nerves, spinal cord
external anal sphincter Internal anal sphincter Descending colon Sigmoid rectum
Chapter 64 Secretory functions of the alimentary tract Subserve two primary functions 1.digestive enzymes are secreted in most areas from the mouth to the distal end of the ileum 2. Mucous glands, from the mouth to the anus provide mucus for lubrication and protection of all parts of the alimentary tract
1. General principles of alimentary tract secretion 2. Secretion of saliva 3. Gastric secretion 4. Pancreatic secretion 5. Secretion of bile 6. Secretion of the small intestine and the large intestine
General principles of alimentary tract secretion
mucus
Act as a lubricant that protects the surfaces from excoriation and digestion
Organic substances
Digestive enzyme
Water and electrolyte
Chloride, sodium
General principles of alimentary tract secretion
Basic mechanisms of stimulation of the alimentary tract glands Basic mechanism of secretion by glandular cells
Basic mechanisms of stimulation of the alimentary tract glands The presence of food in the gastrointestinal tract Tactile stimulation chemical irritation distension directly
indirectly
Secretion of glands
Enteric nervous system
Basic mechanisms of stimulation of the alimentary tract glands Secretion of glands
Parasympathetic nerves
Increase the secretion
Sympathetic nerves Constriction of the blood vessels decrease the secretion
Basic mechanisms of stimulation of the alimentary tract glands Sympathetic stimulation can have s dual effect : 1. Sympathetic stimulation alone usually increase secretion 2. If other factors have caused copious secretion, superimposed sympathetic stimulation reduces the secretion because of vasoconstrictive reduction of the blood supply
Basic mechanisms of stimulation of the alimentary tract glands In the stomach and intestine, several different gastrointestinal hormones help regulate the secretion of glands. These hormones are liberated from the gastrointestinal mucosa in response to the presence of food in the lumen of food These hormones are absorbed into the blood and carried to the glands and stimulate the secretion
Basic mechanism of secretion by glandular cells Water and electrolyte Ductal cell Extracellular fluid
Glandular duct
Secretion of saliva parotid Salivary glands
submandibula r sublingual buccal
Serous secretion Serous secretion mucous secretion mucous secretion
Saliva contains two types of protein secretion: 1.Serous secretion: contains ptyalin, which is an enzyme for digesting starches 2.mucous secretion: contains mucin, which is for lubricating and surface protective purpose
Secretion of ions in the saliva Resting conditions Large quantities 7 times as great as of K+ that in plasam
saliva
Large quantities of HCO3A few of Na+ A few of Cl-
2 or 3 times One seventh or one tenth their concentrations inplasam
Secretion of ions in the saliva Submandibular salivary glands: acini and salivary ducts ducts
acini
Salivary secretion is a two-stage operation:
Acini secrete primary secretion
Ptyalin, mucin, ions
As the primary secretion flows through the ducts, two major active transport pocesses take place to modify the ionic
Secretion of ions in the saliva ducts ClNa+ K+ HCO3acini
1. Na+ are actively reabsorbed and K+ are actively secreted in exchange for the Na+ 2. There is excess of Na+ reabsorption over K+ secretion, so creates electrical negativity in the ducts, and in turn cause Clto be reabsorbed passively. 3. HCO3- are secreted into the lumen actively or by exchange of Cl-
Secretion of ions in the saliva 1. During maximal salivary, the salivary ionic concentrations change considerably ducts
acini
2. The rate of formation of primary secretion by the acini increase greatly 3. The acinar secretion then flows through the ducts so rapidly that the ductal reconditioning of the secretion is considerably reduced. 4. Compared with the saliva under resting conditions, the [Cl-] increase and the [K+] decrease.
Nervous regulation of salivary secretion Parasympethetic nervous salivary secretion
Taste and tactile stimuli from the oral cavity, sour taste, presence of smooth objects, rough objects Sympethetic nervous
Gastric secretion Oxyntic glands (gastric glands) Tubular glands
Hydrochloric acid, pepsinogen, intrinsic factor, mucus
Pyloric glands pepsinogen, gastrin, mucus
Gastric secretion Mucous neck cells: mucus and pepsinogen Oxyntic glands (gastric glands)
Peptic(chief) cells: pepsinogen Parietal(oxyntic) cells: Hydrochloric acid, intrinsic factor
Basic mechanism of hydrochloric acid secretion Parietal cells secrete an acid solution, pH is about 0.8, which is about 3 million times that of the arterial blood canaliculi
apical
canaliculi
Na+ K+ Cl-
basal
Extracellular fluid
K+ HCl
Cl-
H2O
OH-
H+
H+-K+ATPase
H+ K+
Cl-
Osmotic pressure H2O OH- + CO2
HCO3-
Cl-
K+ HCl H2O H+ OH- + CO2
HCO3-
Cl-
Secretion and activation of pepsinogen Peptic(chief) cells and Mucous neck cells secrete deferent types of pepsinogen which have the same functions pepsinogen
Has no digestive activity
HCl pepsin
Has digestive activity
Secretion and activation of pepsinogen Pepsin is an active proteolytic enzyme in a highly acid medium(optimum pH 1.8to 3.5). but above a pH of 5 pepsin become inactiveted in a short time. HCl functions: 11111111111 1. Activate the pepsinogen 2222 2. Provide the acid circumstances for the activity of pepsin
Secretion and activation of pepsinogen Pepsin is an active proteolytic enzyme in a highly acid medium(optimum pH 1.8to 3.5). but above a pH of 5, pepsin become inactiveted in a short time. HCl functions: 11111111111 1. Activate the pepsinogen 2222 2. Provide the acid circumstances for the activity of pepsin
Pyloric glands - secretion of mucus and gastrin Pyloric glands pepsinogen mucus gastrin
Lubricate food movement
Surface mucous cells Surface mucous cells lie on the surface of gastric mucosa between the glands. Surface mucous cells secrete large quantities of ciscid mucus Mucus is insoluble and coats the stomach mucosa with a gel layer, providing a mayor shell of protection for the stomach wall and contributing to lubrication of food transport Mucus is alkaline, therefore the normal underlying stomach wall is not directly exposed to the highly acidic
Regulation of gastric secretion The basic neurotransmitters and hormones that directly stimulate secretion by the gastric glands: Peptic cells acetylcholine mucus cells parietal cells gastrin parietal cells histamine
Regulation of gastric secretion Located in the pyloric glands Stimulate the release of histamine
gastrin G-34, G-17
Gastrin cells (G cells)
Meats reach the antral stomach
Regulation of gastric secretion
Stimulate the secretion of HCl
Located in the body of stomach and is adjacent to the gastric glands histamine
gastrin
enterochromaffin cells
acetylcholine
Regulation of gastric secretion acetylcholine Pepsinogen secretion HCl The rate of secretion of pepsinogen is strongly influenced by the amount of acid in the stomach
Feedback inhibition of gastric secretion of both acid and pepsinogen by excess acidity When the acidity of the gastric juices increases to de pH below 3.0, the gastric mechanism for stimulating gastric secretion becomes blocked. Block the secretion of gastrin excess acidity
Cause an inhibitory nervous reflex that inhibits gastric secretion
Feedback inhibition plays an important roles in protecting the stomach against excessive acidity and excessive pepsin concentration and also in maintaining optimal pH for function of the peptic enzymes
Regulation of gastric secretion gastrin acetylcholine histamine secretion of HCl inhibit excess acidity
Pepsinogen secretion inhibit
Pancreatic secretion acini duct
acinus
Pancreatic enzymes
+ ducts
H2O, Na+, HCO3-, other ions Pancreatic secrfetion
Pancreatic digestive enzymes Pancreatic secretion contains enzymes for digesting all three major types of food: protein,
carbohydrates,
fats
Pancreatic amylase
Pancreatic lipase
trypsin chymotrypsin Carboxypolypeptidase Elastases, nucleases
Cholesterol esterase phospholipase
inactive
enterokinase
trypsinogen chymotrypsinogen
trypsin chymotrypsin
procarboxypolypeptidase Carboxypolypeptidase
protein trypsin chymotrypsin peptides Carboxypolypeptidase Amino acids
starches
glycogen
Pancreatic amylase
Disaccharides and trisaccharides
Pancreatic lipase
Neutral fat
Fatty acids and monoglycerides
Cholesterol esterase
Cholesterol esters
phospholipase
phospholipid
Acini also secrete trypsin inhibitor trypsin inhibitor prevents the activation of trypsin, therefore inhibit the other proteolytic enzymes trypsin inhibitor prevents the digestion of pancreas by trypsin and other enzymes When the pancreas is severely damaged, large quantities of pancreatic secretion become pooled in the damaged areas of the pancreas. Under these conditions, the effect of trypsin inhibitor is sometimes overwhelmed, so pancreatic secretions become activated and literally digest the pancreas, which produce a kind of disease called acute pancreatitis
Secretion of bicarbonate ions
ducts
HCO3-
There are large numbers of HCO3- in the pancreatic juice, which could neutralize the HCl emptied into the duodenum from the stomach
Luminal border Osmotic pressure increase
Na+
HCO3-
H+ Carbonic anhydrase
H2O H2CO3 H2O+CO2 CO2
Na+ blood
Blood border
Regulation of pancreatic secretion three basic stimuli are important in causing pancreatic secretion
Nervous endings acetylcholine Intestinal mucosa cholystokinin Intestinal mucosa secretin
Stimulate the acinar cells of the pancreas much more than the ductal cells Cause production of large quantities of pancreatic enzymes but relatively small quantities of fluid and ions Cause production of large quantities of fluid and ions but relatively small quantities of pancreatic enzymes
Phases of pancreatic secretion
Cephalic phase
Account for 20% of the total secretion of pancreatic enzymes after a meal
gastric phase
5 to 10% Secretin
intestinal phase
cholecystokinin
Secretin Acid chyme “S” cells secretin Secretin is absorbed into the blood
Secrete large quantities of water and NaHCO3
pancreas
NaHCO3 Neutralize HCl coming from the stomach HCl+ NaHCO3 =NaCl+H2CO3
CO2
H2O
Protect the stomach mucosa
Provides an appropriate pH for action of the pancreatic enzymes, which function optimally in a slightly alkaline or neutral
cholecystokinin Break down products of food “I” cells
Secrete large quantities of pancreatic enzymes
cholecystokinin cholecystokinin is absorbed into the blood
pancreas
Secretion of bile Large quantities of bile salts Emulsifying function Detergent action on the fat particles in the food, so decrease the surface tension of the particles Break the fat globules into small size to increase the area of the fats exposed to lipase
Promote the digestion of fats
Promote the absorption of fats
Promote the absorption of fats Some breakdown products of fats are insoluble and can not be absorbed by intestine, Bile salts form minute complexes with these lipids, which are called micelles Micelles are soluble, so could ferry these lipids to the mucosa
Secretion of the small intestine and large intestine
mucus Small intestinal secretions
bicarbonate Water and other ions
Secretion of the small intestine and large intestine
Large intestinal secretions
mucus bicarbonate
link Spike potentials
Ca
Action potentials of nerve fibers
2+
Na+ inflow
Na+ inflow
ENS myenteric plexus
submucosal plexus
Inrease the intensity of contraction Increase the rate of the rhythm of contraction Increase the velocity of conduction of contraction Inhibit the Sphincter
secretion absorption contraction
Sympathetic ganglia Spinal cord or brain stem sympathetic nervous parasympathetic nervous
ENS ENS Smooth muscle
Movement of alimentary tract Secretion of digestive juices and digestion of the food Absorption of nutrients Circulation of blood through the gastrointestinal organs Control of these functions by nervous and hormonal systems
myenteric plexus (Auerbach’s plexus)
submucosal plexus (Meissner’s plexus)
neurotransmitters acetylcholine
Excitatory effects
norepinephine
Inhibitory effects