Physiology Flashcards
What is the pharyngoesophageal sphincter comprised of and what is it’s function?
circular layer of striated muscle; keeps air from entering esophagus & stomach during breathing
What is the function of the gastroesophageal (cardiac) sphincter?
controls entrance AND reflux of food; normally tonically contracted when no food is waiting on entrance to stomach; receptive relaxation when food is swallowed & protects against reflux of digested stomach contents
What does the esophagus pass through?
The hiatus; weakness allows stomach fundus to protrude back into thoracic cavity’s mediastinum (hiatal hernia)
What is tonic contractile activity and what organ parts have it?
- usually found between two organs
- musculature is in a state of stable contraction to occlude lumen
- UES, LES, ileocecal sphincter, internal anal sphincter, proximal stomach, pyloric sphincter
What is phasic contractile activity & what organ parts have it?
- periodic contraction lasting a few seconds followed by relaxations often on a cyclical pattern
- esophagus, antrum, SI, colon
What are segmenting contractions and which organs/organ parts have it?
- mix chyme w/secretions (like bile or pancreatic enzymes) & bring contents in contact w/mucosa for digestion & absorption
- SI & LI
What are haustral contractions and what organs/organ parts have it?
- special kind of segmenting contraction of longer duration; brings contents into contact w/mucosa for water & electrolyte absorption
- occurs in LI
What is the primary type of muscle contraction through the GI tract?
What can cause increased motility (and increased bowel sounds)?
1) inflammation
2) effect of toxins in/around GI tract
3) unabsorbed materials
What can cause decreased motility (and decreased bowel sounds)?
1) ileus
2) obstruction
What effect does the SNS have on the GI tract?
- “fight or flight”
- thorocolumnar division
- stimulation will cause a decrease in activity including decreased motility & secretions
What effect does the PNS have on the GI tract?
- “rest & digest”
- craniosacral division
- stimulation will cause an increase in activity including increased motility & secretions
What are the plexuses of the enteric NS (intrinsic)?
- myenteric (auerbach)
- submucosal (meissner)
Where is the myenteric plexus located and what is it’s function?
- located b/t circular & longitudinal muscle layers (in GI tract wall)
- concerned w/ motility
What are the functions of the submucosal plexus?
- located in GI tract wall
- controlling the function of each segment of the intestinal tract
- integrates signals from the mucosal layer into local control of motility, intestinal secretions, & absorption of nutrients
What factors increase the excitability of smooth muscle contraction?
- stretching smooth muscle (cramping from gas or constipation d/t stretch)
- PNS stimulation (rest & digest)
What factors decrease the excitability of smooth muscle contraction?
- SNS stimulation (fight or flight)
What is the oral phase of swallowing?
voluntary; bolus collected at back of mouth & tongue can lift food to touch the posterior oropharynx
What is the pharyngeal phase of swallowing?
food in pharynx stimulates closure of all pharyngeal openings except esophagus & food is moved to top of the esophagus; UES relaxes then closes after bolus passage
What is the esophageal phase of swallowing?
begins once food bolus has passed the UES; vagus nerve stimulates peristaltic contractions & LES relaxation
What are the impulses carried for the swallowing reflex & esophageal motility?
- voluntary initiation
- sensory impulses in pharynx & esophagus integrate w/motor impulses from swallowing center in medulla & lower pons
- invol motor impulses for oral & pharyngeal phases carried in CN V, lX, X, & Xll
impulses for esophageal phase carried in CN X
What are the two functions of the secretory glands of the GI tract?
1) produce mucous (to lubricate & protect mucosal layer)
2) secrete fluids & enzymes (to aid in digestion & absorption of nutrients)
What are the 3 functions of saliva?
1) protection, moisten, & lubrication (mucous)
2) protective antimicrobial action (lysozyme)
3) initiate digestion of starches (ptyalin and amylase)
What is the function of mucous secreting cells?
barrier of protection
What is the function of parietal cells?
secrete hydrochloric acid (HCl) & intrinsic factor (necessary for B12 absorption)
What is the function of chief cells?
secretes pepsinogen which is converted to pepsin when exposed to low pH of stomach
What are the functions of gastrin?
stimulate gastric acid & pepsinogen
increases gastric blood flow
stimulates gastric smooth muscle contraction
stimulates growth of gastric and intestinal mucosal cells
What is the most common site for a gastric ulcer?
lesser curvature of the stomach
What is the function of cholecystokinin?
stimulates CTX of GB, secretion of pancreatic enzymes, slows gastric emptying, inhibits food intake
What is the function of secretin?
stimulates the secretion of bicarb-containing fluids by the pancreas & liver
What is the secretion of the LI?
mucous
What is secreted by the bowels during episodes of inflammation or irritation?
large amounts of water and electrolytes
What are the metabolic activities of gut flora?
1) fermentation of undigestible dietary residue & mucous to produce short chain FAs
2) vitamin synthesis & mineral absorption
What are the trophic effects of the gut flora?
“grooming” of intestinal epithelial cells
What are the protective effects of the gut flora?
protection of the colonized host against invasion by pathogenic organisms
What brush border enzymes aid in the digestion of carbs and proteins and where do they adhere?
1) aminopeptidases
2) maltase
3) sucrase
4) lactase
- Adhere to the border of the villus structure
What is the pathophysiology of carb digestion & absorption?
- begins in mouth w/salivary amylase
- pancreatic secretions also contain amylase (breaks starches down into disaccharides)
- brush border enzymes convert disaccharides into monosaccharides & then they are absorbed into the bloodstream
What is the pathophysiology of fat digestion and absorption?
- large fat gobules (mainly trigs) are broken down into smaller particles (emulsification) by agitation in the stomach & bile from the liver
- pancreatic lipase splits trigs into free fatty acids & monoglycerides
- bile salts form micelles that transport free FAs & monoglycerides to surface of villi
- ultimately transported through lymphatics as chylomicrons
- small quantities of short & medium chain FAs are absorbed into the portal blood & fat that is not absorbed is excreted into the stool (steatorrhea)
What is the pathophysiology of protein digestion & absorption?
- protein digestion begins in the stomach w/pepsin & proteins are broken down into AA by pancreatic enzymes called proteases in SI
- brush border enzymes then break down the proteins into peptides that are 1-3 AAs long
- Absorption occurs through mucosal membrane
What are the functions of the liver?
1) produces bile
2) metabolizes hormones and drugs
3) synthesizes plasma proteins & blood clotting factors
4) stores vitamins & minerals
5) maintains blood glucose levels
6) regulates VLDL levels
What are the metabolic functions in regard to carb metabolism?
1) stores excess glucose as glycogen
2) synthesizes glucose
3) converts excess carbs to trigs for storage in adipose tissue
What are the metabolic functions of the liver in regard to lipid metabolism?
1) to derive energy from neutral fat (trigs) it needs to be split into glycerol & FAs
What are the metabolic functions of the liver in regard to AA metabolism?
- Transaminaton/deamination of AA’s –> ammonia that must be removed quickly & is synthesized into urea and then one of the following occurs:
- excretion by kidneys
- excretion into intestines & converted back to ammonia by enteric bacteria &brought back to liver [for round 2]
What increases ammonia production?
- ingestion of high protein foods - GI bleeding (this process is impaired with advanced liver disease)
What is bilirubin a product of?
RBC breakdown
What is free biliruben?
unconjugated- insoluble in plasma
What is conjugated bilirubin?
soluble constituent of bile
What is unobilinogen?
highly soluble substance that is either excreted in feces or absorbed into portal circulation where it is reexcreted into bile or eliminated by kidney
What are the 4 major causes of jaundice?
1) excessive RBC destruction
2) impaired uptake of bilirubin
3) decreased conjugation of bilirubin
4) obstruction of bile flow in canaliculi of hepatic lobules, intrahepatic or extrahepatic bile ducts
What is prehepatic jaundice and what conditions cause it?
excessive RBC destruction
- hemolytic transfusion reaction, hereditary disorders of RBCs, acquired disorders, hemolytic dz of newborn & AI heme anemia
What is intrahepatic jaundice and what conditions cause it?
liver damage
- decreased bilirubin uptake, decreased bilirubin conjugation, hepatocellular liver damage, drug induced cholestasis
What is posthepatic jaundice?
obstruction of bile flow
- structural disorders of bile duct, cholelithiasis, congenital atresia of extrahepatic bile duct, bile duct tumors
What are the labs to eval hepatobiliary function?
ALT, AST, serum protein, prothrombin time, fibrinogen, coag factors (ll, Vll, lX & X), serum bilirubin, GGT, alkaline phosphates (to look for bile duct disorders)
What are the contents of bile?
bile salts
cholesterol
bilirubin
lecithin
FAs
water
electrolytes
What is the function of the gallbladder and how is the passage of bile regulated?
products of food digestion (particularly lipids) stimulate the release of GI hormone cholecystokinin (CCK) which stimulates GB contraction
passage is regulated by pressure in common bile duct which is regulated by gallbladder
What happens after a cholecystectomy?
dilation of the common duct occurs & regulation of flow is controlled by sphincters in the common bile duct
What tissue secretes pancreatic juice and what is it composed of?
exocrine tissue (tubuloacinar glands)
- pancreatic juice is composed of an alkaline secretion and an enzyme-rich secretion
What is included in the enzyme-rich component of pancreatic juice?
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major enzymes of food digestion
- enzyme precursors of proteolytic enzymes: trypsin, chymotripsin, carboxypeptidase, & elastase
- phospholipase A, lipase
- pancreatic amylase, ribonuclease, deoxyribonuclease
- tripsin inhibitor (prevents activation of other enzymes)
