IOS Block 3 GI Physiology

What type of muscle is present in the esophagus?

skeletal (upper), smooth (lower)

what does the orad stomach help with?

gastric emptying by creating the pressure gradient between stomach and duodenum

where is the orad stomach located?

upper portion (fundus, cardia); thin walled

where is the caudad stomach located?

lower portion (body/corpus); thick walled

what role does the caudad stomach play in gastric emptying?

Gastric distension induces peristaltic waves to propagate food toward pylorus grinder to accelerate liquefaction and gastric emptying

what does the pylorus do?

filter which holds about 30 mL of chyme and allows 3 mL of chyme into duodenum per slow wave cycle

where is the pylorus located?

antrum area of stomach

what is the rate of the gastric pacemaker?

3 slow waves per minute

what mediates gastric emptying?

ENS, ANS, digestive hormones (gastrin, CCK, GIP, enteroglucagon)

what is the gastro-colonic reflex?

mass movements in colon cause urge to defecate

what is the gastro-ileal reflex?

relaxation of ileocecal sphincter, small intestinal contents enter colon

what does MMC stand for?

Migrating motor complex

what is phase I of MMC?

resting phase to recover muscle strength; inter digestive phase

what type of contractions occur in phase I of MMC?

quiescent to infrequent low amplitude non propagative contractions

what is phase II of MMC?

similar to fed state, but lasts 30-60 minutes; increasing/irregular activity

what type of contractions occur in phase II?

random, variable amplitude, sometimes propagating

what is phase III of MMC?

propagating and propulsive house keep contractions that are inhibited by fed state; last 10-20 minutes

what type of contractions occur in phase III MMC?

highest amplitude of normal small bowel contraction 15-40 mm Hg; occur every 60-90 minutes

what is Starling’s law of the intestine?

distention of gut sends afferent sensory signal to activate sensory neurons to cause circular muscle behind bolus to contract and circular muscle ahead of bolus to relax; longitudinal muscle contracts

what cells initiate the basal electrical rhythm?

intersitial cells of Cajal (ICC)

what is the basal electrical rhythm (BER)?

constant rhythmic depolarization

what cells participate in SIP Syncytium?

smooth muscle cells, interstitial cells of Cajal, PDGFRα

where are ICC located?

myenteric plexus

what are the layers of the gut?

serosa (connective tissue/peritoneum), longitudinal muscle, myenteric plexus, circular muscle, submucosal plexus, submucosal, muscularis mucosae, lamina propria, epithelium

what is Hirschsprung ?

failure of craniocaudal enteric neural crest derived cell migration leading to functional obstruction due to inability to relax smooth muscle disrupting peristalsis

what is produced by salivary glands/

mucins, alkaline electrolyte rich solution, ptyalin (α-amylase), lactoferrin, kallikrein, lingual lipase

what do von Ebner’s glands produce?

lingual lipase

what do mucins do?

lubrication to facilitate chewing, swallowing

what makes up the alkaline electrolyte rich solution in mouth?

HCO3-, K+

what is another name for ptyalin?

Α amylase

what does ptyalin do?

enzyme that breaks down carbohydrates at pH > 7

what is lactoferrin?

IgA

what is kallikrein?

enzyme secreted into the blood that increases bradykinin (vasodilator) levels which increases salivary glands blood flow

what does lingual lipase do?

enzyme that breaks down short chain fatty acids

what regulates salivary secretion?

parasympathetic postganglionic fibers from CN VII (facial) & CN IX (glossopharyngeal) nerves; sympathetic postganglionic fibers act on acinar and ductal cells

what neurotransmitter and receptor is used in parasympathetic regulation of salivary secretion?

ACh onto muscarinic receptors

what blocks parasympathetic stimulation of salivary secretion?

atropine

what neurotransmitter and receptor are used in sympathetic control of salivary secretion?

NE on β-adrenergic receptors

what causes dry mouth?

medications, nerve injury, Sjögren’s syndrome, sialothiasis, sialadenitis

how does sjogrens syndrome cause dry mouth?

autoimmune induced destruction of salivary glands

how does sialolithiasis cause dry mouth?

stones/Ca deposits in salivary glands partially/completely stop flow of saliva

how does sialadenitis cause dry mouth?

an infection/inflammation of salivary glands partially impedes saliva secretion

what do mucous neck cells secrete?

mucins/mucous/HCO3

what do mucous cells secrete?

mucous/HCO3; (located in antrum)

what do parietal (oxyntic) cells secrete?

HCL, IF

what do chief (peptic) cells secrete?

pepsinogen

what are endocrine cells in stomach?

G cells, D cells

what do G cells secrete?

gastrin

what does gastrin stimulate?

parietal cells

what stimulates G cells?

vagus, gastrin releasing peptide (GRP), distention of stomach

what do D cells secrete?

somatostatin

what does somatostatin do?

inhibits gastric H+ secretions

what do enterchromaffin Like cells secrete?

histamine

what does histamine do in stomach?

stimultes HCl production by parietal cells

how do parietal cells produce acid?

H+/Na+ exchanger brings Na into the cell to create gradient to allow 3Na+ to leave and 2K+ to enter via Na/K ATPase; K+ leak channels are present on both sides of the cell; H2O enters the cell and dissociates into H+ and OH-; OH- binds with CO2 (carbonic anhydrase) to form HCO3- and leaves cell in exchange for Cl- due to Cl-/HCO3- exchanger; then importantly H+/K+ ATPase pumps H+ into stomach to create acidic environment

what regulates gastric acid secretion?

ACh from vagus nerve, histamine from ECL cells, gastrin from G cells

what protects the cells in the stomach and duodenum from acid?

mucosal mucous barrier; prostaglandin production

when do ulcers occur?

loss of protective mucous barrier; excessive H+ and excess pepsin secretion; interference with protective factors by H pylori, NSAIDs, smoking, alcohol, stress

how does H pylori cause gastric ulcers?

urease coverts urea to NH3 which shifts the equilibrium to create more NH4 leading to a more alkaline environment for bacteria to grow

what is Zollinger-Ellison syndrome?

tumor in pancreas secretes large amounts of gastrin causing excess parietal cellswhat stimulates G acid production and excess parietal cell mass

what do S cells secrete?

secretin

what stimulates S cells?

high levels of acid in duodenum

what do I cell secrete?

CCK

when do I cells secrete CCK?

in response to high levels of fatty acids/proteins

what do K cells secrete?

GIP

when do K cells secrete CCK?

in response to chyme (FA/proteins)

what does GIP do?

stimulates pancreatic insulin release and reduces gastric H+ secretion

what do L cells secrete?

GLIP

what does GLIP do?

stimulates pancreatic insulin release and reduces gastric acid secretion

where does pancreatic cancer start?

Exocrine pancreas cells

what is the most common pancreatic cancer?

ductal cell carcinoma

what do acinar cells in pancreas secretes?

Proenzumes/zymogens; lipase-colipase, cholesterol hydrolyze, phospholipase A2; Α-amylase, trypsin inhibitor

what do ductule cells in pancreas secrete?

HCO3- and K+

what do neuroendocrine cells in pancreas secrete?

VIP

what is a VIPoma?

non-β islet cell pancreatic tumor causing WDHA syndrome (water diarrhea, hypokalemia, achlorhydria)

what vitamins require bile for absorption?

ADEK

what does PDGFRα stand for?

platelet derived growth factor receptor α

What is a tonic contraction?

smooth muscle remains contracted for a relatively long period of time and must be stimulated to relax

what is SGLT?

Na dependent glucose/galactose transport protein

what does SGLT do?

brings glucose and galactose into enterocytes along with sodium

how does glucose leave enterocytes?

Glut2 transporter into interstitial fluid/blood

what does GLUT2 transport?

glucose, galactose, and fructose

how does fructose enter enterocytes?

GLUT5

what activates pepsinogen to pepsin?

low pH

what activates trypsinogen to trypsin?

enterokinase in brush border

how are water soluble vitamins except B12 enter enterocytes?

Na dependent co transport mechanisms

how do FAs enter enterocytes?

diffusion across membrane

what causes steatorrhea?

Pancreatic insufficiency (pancreatitis, CF), elevated acid levels in duodenumwhat, bile salt deficiency, decreased enterocytes # or impaired function, inappropriate Apo B synthesis

where are carbohydrates most absorbed?

duodenum

Where are proteins mostly absorbed?

duodenum

where are lipids mostly absorbed?

duodenum

where are calcium absorbed?

dudodenum

where is iron absorbed?

duodenum

where is folate absorbed?

duodenum/jejunum

where are bile acids absorbed?

ileum

where are vit B12 absorbed?

ileum

what is inflammatory diarrhea?

impaired absorption by small or large intestines secondary to cell damage (inflammation, viruses, bacteria)

what is osmotic diarrhea?

accumulation within intestine of non-absorbable solutes as well as bacterial catabolism of glucose-galactose and accumulation of lactic acid

what is secretory diarrhea?

excessive stimulation of secretory cells present in crypts of small intestine and colon