Gastrointestinal Physiology Flashcards
major organs of the digestive tract
-oral cavity
-pharynx
-esophagus
-stomaach
-small intestine
-large intestine
accessory organs of the digestive tract
-teeth
-tongue
-salivary glands
-liver
-gall bladder
-pancreas
secretion
-release of water acids, enzymes, buffers and salts
-by epithelium of digestive tract, glandular organs and gallbladder
absorption
movement of organic molecules, electrolytes, vitamins, minerals and water
-across digestive epithelium into interstitial fluid of digestive tract
motility of digestive tract
-rhytmic cycles of activity
-controlled by pacesetter cells that undergo spontaneous depolarization
-wave of contraction spreads throughout entire muscular sheet
peristalsis steps
-1. circular muscles behind bolus contract which ciruclar muscles ahead of bolus contract
-2. longituidnal muscles ahead of bolus contract shortening adjacent segments
3. wave of contraction in circulare muscle layer force bolus forwards
segmentation
-cycles of contraction that churn and fragment the bolus mixing contents with intestinal secretions
-does not follow set pattern
-does not push any materials in any one direction
3 mechanisms of regulation of digestive functions
-local factors
-nueral mechanisms
-hormonal mechanisms
local factors regulating digestive functions
-pH, volume or chemical composition of intestinal contents can have direct, localized effects on digestive activity
-stretching of intestinal wall can stimulate localized contractions
-local factors may stimulate release of chemicals such as prostaglandins, histamine and other chemicals
nueral factors regulating digestive functions
-visceral motor nuerons control smooth muscle contraction and glandular secretion (located in the myenteric plexus)
-short reflexes control small segments of digestive tract and operate entirely outside CNS
-long reflexes have internuerons for peristalsis, and PSNS motor fibers synapse in myeneteric plexus
hormonal factors regulating digestive functions
-enteroendocrine cells in digestive tract produce many peptide hormones that affect almost every aspect of digestion
-travel through bloodstream to reach target organs
functions of oral cavity
-sensory analysis
-mechanical digestion
-lubrication
-limited chemical digestion of carbs and lipids
tongue functions
-mechanical digestion
-manipulation to chew
-sensory analysis by touch temp and taste
-secretion of mucins and linguinal lipase
extrinsic and intrinsic tongue muscles
-extrinsic for gross movements
-intrinsic for precise movements
glands of oral cavity
-salivary glands
-parotid glands
-sublinguinal glands
salivary glands
-parotid, sublinguinal, submandibular
-rach pair has distinctive cell organization
parotid glands
inferior to zygomatic arch
-serous secretion that has amylase
-each is drained by parotdi duct that empties near upper molar
sublinguinal glands
covered by mucous membrane of lfoor of mouth
-produces mucus that acts as a buffer and lubricant
-numerous sublinguinal ducts that open along either side of linguinal frenulum
espohagus
-conveys food to stomach
-begins posterior to cricoid cartilage
-enters abdominopelvic cavity through espohageal hiatus
-innervated by PSNS and symathetic fibers through espohageal plexus
-restin muscle tone prevents air from enterin and prevents backflow of materials in stomach
functions of saliva
-cleaning oral surfaces
-moist and lubcricate food
-keep pH of food near 7.0
-control bacteria and limit acid they produce
-dissolve chemcials that stimulate taste buds
-initating digestion of complex carbs with salivary amylase
regulation of salivary secretion
-PSNS and SNS regulation of salivary glands
-PSNS stimulation accelerates secretion by all salivary glands
PSNS efferents
-originate in MO
-stimulated by any object in mouth through stimulating receptors monitored by the CN 5 (trigeminal) or taste buds innervated by 7, 9 and 10
degulitition
-can be initiated volunatrily but proceeds automatically
-swalloing reflex begins when tactile receptors on palatal arches and uvula are stimulated by bolus
-information is relayed to swalloing center of MO
-buccal, pharyngeal, and espohageal phases
buccal phase of deglutition
phayngeal phase of deglutition
espohageal phase of deglutition
major functions of the stomach
-temporary storage of ingested food
-mechanical digestion with muscular contractions
-chemical digestion of food with acid and enzymes
regions of stomach
-cardia, fundus, body, pyloric part
chyme
-partially digested food mixed with acidic secretions of stomach
rugae
-prominant folds in mucosa of empty stomache
-flattena s stomach fills
-allow for expansion of gastric lumen
muscalaris mucosae and muscular layer of stomach
-contain extra layers of smooth muscle cells
-oblique layer in addition to circular and longitudinal layers
gastric glands
-in fundus and body of stomach that extend deep into underlying lamina propria
-each gastric pit communcated with several gastic glands (parietal and chief cells)
-secrete about 1.5L of gastric juice each day
cells of gastric glands
-parietal cells and chief cells
parietal cells
-proximal portions of gastric glands
-secrete intrinsic factor that helps absorb B12
-also indirectly secrete HCl
chief cells
-base of gastric gland
-secrete pepsinogen
-pepsinogen converted to pepsin by HCl in gastric lumen
secretion of hydrochloric acid ions
pyloric glands
-located in pyloric part of stomach
-produce mucous secretions
enteroendocrine cells
-produce at least seven hormones
-G cells produce gastrin that stimulate secretion by parietal and chief cells, stimulate contraction of gastric wall
-D cells release somatostatin that inhibit release of gastrin
chemical digestion in stomach
-some digestion of carbs by salivary amylase, and lipids by linguinal lipase
-as stomach contents become more fluid pH approaches 2.0, preliminary digestion of proeteins by pepsin increases
-nutrients are not absorbed in stomach
why are nutrients not absorbed in stomach
-mucus coverin epithelial cells means not exposes to chyme
-epitheld one have right trasnport mechanism
-gastric lining is somewhat impermeable to water
-digestion has not been completes by the time chyme leaves the stomach
regulation of gastric activity
-production of acid and enzymes by gastric mucosa can be controlled by CNS, short reflexes, hormones of digestive tract
three overlapping phases of gastric control
-cephalic, gastric and intestinal phase
cephalic phase of regulation of gastric activity
gastric phase of regulation of gastric activity
intestinal phase of regulation of gastric activity
Pancreas anatomy
-posterior to stomacj
-extends from duodenum toward spleen
-retroperitoneal
-wrapped in thin conncective tissue capsule
endocrine cells of pancreatic islets
-secrete insulin and glucagon into bloodstream-
exocrine cells of pancreas
-acinar cells and epithelial cells of duct system
-secrete alkaline pancreatic juice into small intestine
-1000ml of pancreatic juice a dya that contain enzymes water and ions
-controlled by hormones from the durodeum
pancreatic enzymes
-pancreatic alpha amylase
-pancreatic lipase
-nucleases
-proteolytic enzymes
pancreatic alpha amylase
-carbohydrase
-breaks down certain starches
-almost identical to salivary amylase
pancreatic lipase
-breaks down certain complex lipids
-releases products that are easily absorbed
nucleases
-break down RNA or DNA
proteolytic enzymes
-break down proteins
-proteases break large proteins
-peptidases break small peptide chains into individual AA
-70 percent of all pancreatic enzyme production is proteolytic
-secretedas inactive proenzymes and are activated after reaching the small intestine
proenzymes secreted by pancreas
-trysinogen is converted to trypsin in duodenum
-chymotrypsinogen converted to active chymotrypsin by trypsin
-procarboxypeptidase converted to active carboxypeptidase by trypsin
-proelastase converted to active elastase by trypsin
liver functions
-metabolic regulation
-hematological regulation
-bile production
where does all blood leaving absorptive surfaces of digestive tract enter
-flows into liver by hepatic portal system
what is the function of liver cells
-extract nutrients or toxins from blood before blood reaches systemic circulation through hepatic veins
-liver removes and stores excess nutrients and corrects nitroent deficiencies by mobilizng stored reserves or performing synthetic activities
regulatory activities of liver afect
-carb metabolism
-lipid met.
-AA met
-waste removal
-vitamin storage
-drug inactivation
what is the largest blood reservoir in the body
-liver
hematological regulation by liver involves
-phagocytosis and antigen presentation
-synthesis of plasma proteins
-removal of circulatin hormones
-removal of antibodies
-removal or storage of toxins
bile duct system
-liver secretes buke into a network of channels called bile canaliculi that lie between adjacent liver cells
-right and left hepatic ducts collect bile from all bile ducts of liver lobes and unit to form common hepatic duct
from the common heptaic duct bile enters either
-the bile duct which empties into dueodenal ampulla
-cystic duct which leads to gall bladder
productions and functions of bile
-bile salts break ;ipid droplets apart (emulsify) in dueodeum that increase SA exposure
-stomach only creats large lipid droplets which is not small enough for pancreatic lipase to interact with
enterhepatic circulation
-cycling of bile salts between liver and SI
physiology of gallbladder
-stores and concentrates bile prior to secretion into small intestine
-full = 40-70mL of bile
cystic duct
-extends from the gall bladder
-unites with common heptatic duct to form bile ducts
-bile duct joins pancreatic duct before emptying into dueodenal ampulla
how does bile composition change in the gall bladder
-full gall bladder contains 40-70mL of bile
-water is absorbed
-bile salts and other components become increasingly concentrated
when does the gall bladder release bile into the duedeumim
-when stimulation by CCK
-without CCK the hepatopancreatic sphincter remals closed and the bile exiting the liver in common hepatic duct enters cystic duct and is stored in gallbladder
what happens when chyme enters the duedeom and CCK is release
-hepatopancreatic sphincter relaxes
-gallbladder contracts
sections of small intestine and main function
-duodenum - mixing bowl that recieves chyme from stomach and digestive secretions from pancreas and liver
-jejunum - site of most chemical digestion and nutrient absorption
-ileum - ends at ileocecal valve
intestinal juice
-1.8 liters enters intestinal lumen each day
-intestinal juice moistens chyme,
- assists in buffering acids
-keeps digestive enzymes and products of digestion in solution
brush border enzymes
-integral membrane proteins on intestinal microvilli
-break down materials in contact with brush border
enterpeptidase
-a brish border enzyme
-activates pancreatic trypsinogen
intestinal motility
-after chyme arrives in duodeum weak peristaltic contractions move it slowly towards jejumum
-contractions are myenteric reflexes not under CNS control
-parasympathetic stimulation accelerates local peristalsis and segmentation
reflexes of small intestine
-gastroenteric reflex
-gastroileal reflex
gastroenteric reflex
-stimulates motility and secretion along entire small intestine
gastroileal reflex
-triggers opening of ileocecal valve
-allows materials to pass from small intestine into large intestine
enterogastric reflex
-causes constriction of pyloric sphincter
nueral mechanisms involving the CNS
-prepare Gi for activity through PSNS innervation
-inhibit gastrointestinal activity through sympathetic activity
-coordinate movements of materials along digestive tract trhough reflexes
-motor neuron synapses in digestive tract release NT
major hormones of duodenum
-gastrin
-secretin
-gastric inhibitory peptide
-cholecytokinin
-vasoactive intestinal peptide
-enterocrinin
gastrin
-secretes by G cells when exposed to incompletely digested proteins
-promotes increased stomach motility
-stimulates production of acids and enzymes
secretin
-released when chyme arrives in duodeum
-increases secretion of buffers by pancreas and bile by liver
-reduced gastric motility and secretory rates
gastric inhbitory peptide
-secreted when fats and carbs enter small intestine
cholecystokinin
-secreted when chyme arrives in duodenum
-accelerates pacreatic production and secretion of digestive enzymes
-relaxes hepatopancreatic sphincter and contracts gall bladder ejecting bile and pancreatic juice into duodenum
vasoactive intestinal peptide
-stimulates secretion of intestinal glands
-dilates regional capillaries
-inhibits acid production in stomach
enterocrinin
-released when chyme enters duodenum
-stimulattes alkaline mucus production by submucosal glands
functions of large intestine
-absorbtion and reabsorption of water, nutrients, bile salts, organic wastes, vitamins and toxins produced by bacteria
-compaction of intestinal contents into feces
-storage of fecal material prior to defecation
vitamins of the large intestine
-normal bacterial in colon make vitamins that supplement the diet
-vitamin K - clotting (prothrombin)
-Biotin (glucose metabolsim)
-B5 (needed to make steroid hormones and NT)
bilirubin and the large intestine
-bacteria convert bilirubin to urobilinogens and stercobilinogens
-some urobilinogens are absorbed in the blood and excreted in urine
-urobilinogens and sterconilinogens remaining in colon are converted to urobilins and stercobilins by exposure to oxygen
batceria break down peptides in feces and generate
-ammonia as soluble ammonium ions
-indole and skatole (smelly)
-hydrogen sulfide that p roduced rotten egg odour
bacteria feed on
-indigestible carbs
-produce flatus (intestinal gas) in LI
motility of LI
-gastroileal an dgastoenteric reflexes move materials into cecum
-movement from cecum to transverse colon is very slow allowing hours for water resorption through peristaltic waves and segmentation
-movement from transverse colon through rest of large intestin results from powerful persiatlalic mass movements
what initials defectaion reflex
-distention of rectal wall
-involved two positive feedback loops
-both triggered by stretch receptors in rectum
positive feedback loops of LI
-intrinsic myeneteric defecation reflex (short, triggering peristaltic ocntractions in sigmoid colon and rectum)
-Parasympthateic defecation reflex (long, coordinated by sacral parasympthatic nuerons and sitmulates mass movements)
elimination of feces
-requires relaxation of internal and external anal sphincters (reflexes open internal sphincter)
-somatic nervous system must be activated to consciously open external sphincter
processing and absorbtion of nutrients
-digestive system breaks down physical structure of food then disassembles component molecules
-molecules reelased into bloodstream aare absorbed by cells and either used to make ATP, or used to synthesize carbs, lipids, proteins
digestive enzymes function
-break molecular bond in large organic molecules through hydrolysis
-divided into classes by their specific substrates (carbohydrases, proteases, lipases)
digestive enzymes are secreted by
-salivary glands
-tongue
-stomach
-pancreas
brush border enzymes function
-break down digestive fragments further
two steps to carb digestion
- salivary amylase and pacrratic alpha amylase
- brish border enzymes (maltase, sucrase, lactase)
absorption of monosaccharides
-via facilitated diffusion and contrasnport which differ in: number of transported substances, concentration gradients, ATP requirement
lipid digestion and absorption
-involves linguinal lipase and pacreatic lipase
-triglycerides –> monoglycerides + FA by pancreatic lipase
-monoglycerides interact with bile salts to form micells
-new triglucerides are assembled by intestinal cells by joining with steroids, PL, vtiamins and proteins to form chylomicrons
-most chylomicrons diffuse into intestinal lacteals
protein digestion and absorbtion
-complex and time consuming
-invlves mechanical digestion, HCl and proteases
-Dipeptidases in epithelial surfaces break short peptides into AA
nucleic acid digestion and abospriton
-broken down into nucleotides
-BBE digestive nucletodies into sugars, phosphates and N bases and absorbed by active transport
water absorbtion
-cells cannot actively absorb or secrete water
-movement of water across digestive tract involves passive water flow down osmotic gradients
ion absorbtion
-osmosis doesnt distinguish solutes
-to maintain homeostasis, concentrations of specific ions must be regulate
-rate of sodium ptake is proprtional to concenration of sodium in intestine, increased by aldosteron
-calcium ion absorbtion involved active transport at epithelial surface, rate is increased by calcitriol
-potassium ions increase in concentration as other solutes move out of lumen, diffuse into epithelial cells along centration gradient
absorbtion of mg, Fe, and other cations
-need carrier proteins
-needs ATP
anion absorbtion
-abosrbed by diffusion or carrier mediated transport
phosphate and sulfate ion absorbtion
-enter epithelial cells only by active transport
age related changes of digestive system
-dividison of epithelial stem cells drops
-smooth muscle tone decreases
-effects of cumuative changes become apparent
-cancer
-dehydration
-changes in other systems have direct or indirect effects on digestive system
is the digestive system an endocrine organ and does it produce NT
-produces a variety of hormones (yes to endocrine)
-produces NT
