GI physiology Flashcards
main organs of GI system
esophagus
stomach
small intestine
large intestine
accessory organs of digestion
salivary glands
pancreas
liver
gallbladder
main regions of the stomach
fundus
body
antrum
cardia
pylorus
function of pyloric sphincter
Acts as a gatekeeper controlling the passage of chyme from the stomach to the small intestine
3 parts of small intestine
duodenum
jejunum
ileum
primary function of small intestines
Digestion and Nutrient Absorption
main function of large intestine (colon)
absorbs water and electrolytes
stores feces until excretion
how long is large intestine
1.5 meters
which sphincters are under voluntary control
upper esophageal sphincter (UES) and external anal sphincter
what is the function of the lower esophageal sphincter (LES)
prevent acid reflux from stomach into esophagus
layers of GI tract
mucosa
submucosa
muscularis
externa
serosa
function of myenteric plexus
controls GI motility
what are the 2 divisions of the enteric nervous system
myenteric plexus (motility)and submucosal plexus (secretion and blood flow)
what is the role of the parasympathetic nervous system in digestion
stimulates digestion
increases motility
increases secretions
what neurotransmitters do inhibitory neurons release in the ENS
Nitric oxide and ATP
what hormone is released in response to stomach distension and protein presence
gastrin
what hormone stimulates bile release and pancreatic enzyme secretion
cholecystokinin (CCK)
what hormone is released in response to acidic chyme in the duodenum
secretin
what hormones regulate blood glucose after eating
GIP and GLP-1
what hormone stimulates appetite
ghrelin
what hormone inhibits gastric acid secretion and has an overall inhibitory effect on the GI tract
somatostatin
gastrointestinal tract
continuous tube extending from the mouth to the anus, responsible for digestion and absorption of nutrients
accessory organs
organs that aid digestion by secreting enzymes and other substances into the GI tract
peristalsis
Rhythmic contractions of circular and longitudinal muscles that propel food along the GI tract
chyme
semi liquid mixture of partially digested food and digestive secretions found in the stomach and small intestine
sphincter
circular muscle that regulates the passage of substances between different parts of the GI tract
enteric nervous system (ENS)
network of neurons in the GI tract that controls motility, secretion and blood flow independently of the CNS
gastrin
hormone secreted by G-cells in the stomach that stimulates acid secretion and enhances gastric motility
ghrelin
hormone secreted by P/D1 cells in the stomach that stimulates hunger
secretin
hormone releases by S-cells in the duodenum that stimulates bicarbonate secretion to neutralize stomach acid
motilin
hormone secreted by M-cells in the duodenum that stimulates the migrating motor complex to regulate fast motility
cholecystokinin (CCK)
hormone released by I-cells in the small intestine that stimulates bile release and pancreatic enzyme secretion
GIP
hormone secreted by K-cells in the duodenum that stimulates insulin release in response to glucose
GLP-1
hormone secreted by L-cells in the small intestine that enhances insulin secretion and slows gastric emptying
somatostain
hormone secreted by D-cells that inhibits that release of gastrin reducing acid production in the stomach
enteroendocrine cells (EECs)
specialized cells scattered throughout the GI tract that secrete hormones to regulate digestion
vagus nerve (cranial nerve X)
main parasympathetic nerve controlling the GI function, including motility and secretion
pyloric sphincter
muscular valve that controls the flow of chyme from the stomach into the duodenum
ileocecal valve
Sphincter that regulates the passage of digested material from the small intestine to the large intestine
major sphincters of the GI tract
UES, LES, pyloric, sphincter of oddi, ileocecal valve, internal and external anal sphincters
hormones and their functions
gastrin- stimulates acid secretion
CCK- stimulates bile release
secretin- stimulates bicarbonate secretion
ghrelin- stimulates hunger
GLP-1- Enhances insulin secretion
what is segmentation
mixing contractions in the small intestine that move chyme back and forth, aiding digestion and absorption
what is the role of interstitial cells of cajal (ICC)
pacemaker cells of the GI tract that generate slow waves and regulate smooth muscle contractions
what is the migrating myoelectric complex
cyclic motor pattern during fasting that helps clear the stomach and small intestine of residual food and secretions
what is the gastroileal reflex
reflex triggered by food in the stomach that promotes ileal emptying into the colon
what is the gastrocolic reflex
reflex where stomach distention stimulates colonic contractions, promoting bowel movements
what are the three phases of swallowing
- oral phase (voluntary)- food is pushed to the pharynx
- pharyngeal phase (involuntary)- reflexes prevent food from entry into airway
- esophageal phase (involuntary)-peristalsis moves food to the stomach
what is dysphagia
Difficulty swallowing, which can result from neuromuscular disorders or structural abnormalities
what is GERD
condition where stomach acid flows back into the esophagus, causing heartburn and irritation
what are the functions of the stomachs orad and caudad regions
orad region: food reception and storage
caudad region: mixing and propulsion of food
what is receptive relaxation
vagovagal reflex, where the stomach relaxes to accommodate incoming food
what is retropulsion
the process where the pyloric sphincter closes, forcing chyme back into the stomach for further mixing
what is the roe of haustrations in the colon
slow segmental contractions that aid in water and electrolyte absorption
what are mass movements in the colon
strong peristaltic contractions that rapidly move fecal material toward the rectum, occurring 1-3 times a day
what is the function of the ileocecal valve
Prevent backflow of colonic contents into the small intestine
what are the two reflexes involved in defecation
enteric defecation reflex- local ENS control of rectal contractions and sphincter relaxation
parasympathetic defecation relaxation- reinforces contraction and relaxation signals via the spinal cord
what is gastroparesis
a disorder where gastric emptying is delayed without mechanical obstruction, often linked to diabetes
what is the vomiting center
a brainstem region in the medulla that controls the vomiting reflex in response to various stimuli
what is the chemoreceptor trigger zone
brain area outside the blood brain barrier that detects toxins and triggers vomiting
muscles involved in peristalsis
circular muscle contracts behind the food bolus, and the longitudinal muscle relaxes ahead of it
how does segmentation differ from peristalsis
segmentation involves contractions in both directions while peristalsis moves food in one direction
cranial nerves involved in swallowing
trigeminal (V)-chewing and sensory input
glossopharyngeal (IX)- swallowing reflex
vagus (X)- controls pharyngeal and esophageal phases
3 muscle layers of stomach
outer longitudinal
middle circular
inner oblique (unique to stomach)
how does the pyloric sphincter regulate gastric emptying
it opens intermittently to allow chye passage into the duodenum
taenia coil in the colon
3 longitudinal muscle bands running along the colon, aiding in mass movements
steps of defecation reflex
rectum fills and stretch receptors activate
internal anal sphincter relaxes (involuntary)
external anal sphincter remains contracted until voluntary release
what is secretion in the GI tract
the process of adding fluids, enzymes and mucus to the GI lumen to aid digestion
how much fluid is secreted daily in the GI tract
approx 6.5 liters per day
what are the main types of GI secretions
saliva, gastric,pancreatic juice, bile, small intestine, large intestine
three major salivary glands and their secretions
parotid glands- serous (watery) secretion
submandibular glands- mixed (serous + mucus) secretion
sublingual glands- mixed (mostly mucus) secretion
key components of saliva
99.5% water
electrolytes
enzymes
mucus
antibacterial agents
how does saliva secretion change with flow rate
slow flow- more hypotonic (lower Na+ and Cl-)
fast flow- more isotonic (less time for modification)
what cranial nerves control saliva secretions
trigeminal
facial
glossopharyngeal
what is xerostomia
dry mouth due to reduced salivary secretion, leading to dental decay and difficulty swallowing
major components of gastric juice
HCL
intrinsic factor
mucus
pepsin
gastric lipase
main types of gastric cells and their secretions
parietal-HCL, intrinsic factor
cheif- pepsinogen, gastric lipase
mucous- mucus
G-cells- gastrin
D-cells-somatostatin
ECL cells- histamine
what stimulates gastric acid secretion
gastrin
histamine
acetylcholine(ACh)
how does the proton pump regulate stomach acidity
H+/K+ ATPase pump in parietal cells pumps H+ into the stomach in exchange for K+, making the lumen highly acidic
what are proton pump inhibitors and H2 blockers used for
they reduce gastric acid secretion and are used to treat GERD and ulcers
what is the function of intrinsic factor
binds vitamin B12 to allow absorption in the ileum
what happens if intrinsic factor is absent
pernicious anemia (B12 deficiency)
symptoms of pernicious anemia
fatigue
weakness
neurological issues
how is pernicious anemia treated
vitamin B12 injections
what causes peptic ulcers
H. pylori
NSAIDs
Excess acid secretion
how are peptic ulcers treated
antibiotics + proton pump inhibitors + H2 blockers
what are the functions of the pancreas
endocrine- release insulin and glucagon
Exocrine- secretes digestive enzymes and bicarbonate into the small intestine
main components of pancreatic juice
bicarbonate- neutralize stomach acid
digestive enzymes- amylase, lipase, proteases
how is pancreatic secretion regulates
secretin- stimulates HCO3- secretion
CCK- stimulates enzyme secretion
what happens in pancreatic insufficiency
inability to digest food properly, leading to steatorrhea (fatty, loose stool)
main components of bile
water (95%)
bile acids
phospholipids
bile pigments
cholesterol
function of bile
digestion and absorption of fats
Excretion of waste products
what is enterohepatic circulation
recycling of bile salts from the ileum back to the liver
what are gallstones
hardened deposits of cholesterol in the gallbladder, which can block bile flow
symptoms of gallstones
abdominal pain
nausea
jaundice
how are gallstones treated
cholecystectomy if severe
what is crohns disease
chronic IBD that affects the digestive tract
symptoms of crohns disease
abdominal cramps
diarrhea
weight loss
ulcers
fever
anemia
how does crohns disease affect bile salt absorption
if >40% of the ileum is removed, bile salts are excreted in feces, leading to fat malabsorption and diarrhea
enterohepatic circulation of bile salts
bile is secreted
reabsorbed in ileum
recycled to liver
where does most digestion and absorption occur
the small intestine
what is the function of enterocytes
they absorb nutrients and transport them into blood circulation
how do nutrients cross the intestinal epithelium
transcellular route (through cells, requires transporters)
paracellular route (between cells, passive diffusion)
what are the major dietary carbohydrates
sucrose (glucose+fructose)
lactose (glucose+galactose)
starches (glucose polymers)
how are starches digested
amylases break down alpha 1.4 bonds in amylose and amylopectin
brush border enzymes (maltase, isomaltase) complete digestion
how are monosaccharides absorbed
SGLT1 (active transport) absorbs glucose and galactose
GLUT5 absorbs fructose (facilitated diffusion)
GLUT2 transports monosaccharides into the blood
what is lactose intolerance
deficiency in lactase enzyme leading to undigested lactose, bloating and diarrhea
what enzymes break down proteins
pepsins in the stomach (activated by HCL, inactivated at pH>5)
pancreatic proteases (trypsin, chymotrypsin, elastase, carboxypeptidases)
brush border peptidases in the small intestine
how are amino acids absorbed
PEPT1 (secondary active transport) absorbs small peptides with H+
Na+ dependent transporters absorb free amino acids
why is lipid digestion more complex
fats are water insoluble, requiring emulsification and micelle formation
what is the function of bile salts
they emulsify fats breaking them into smaller droplets for digestion
what enzymes break down fats
pancreatic lipase hydrolyzes triglycerides into monoglycerides and free fatty acids
cholesterol esterase breaks down cholesterol esters
phospholipase A2 digests phospholipids
how are lipids absorbed
micelles carry lipids across the unstirred water layer
lipids diffuse into enterocytes
short chain fatty acids enter the blood
long chain fatty acids are re-esterfied and packaged into chylomicrons for lymphatic transport
how are fat soluble vitamins absorbed (A,D,E,K)
incorporated into micelles and absorbed with lipids
how is vitamin B12 absorbed
binds to intrinsic factor and is absorbed in the ileum
how are most water soluble vitamins absorbed
by Na+ dependent cotransporters
where does most water absorption occur
in the small intestine via osmosis, driven by Na+ transport
how is Na+ absorbed in the small intestine
SGLT1 (co transport with glucose)
Na+/H+ exchangers
Na+/amino acid cotransporters
how is Na+ absorbed in the colon
through epithelial Na+ channels (ENaC), regulated by aldosterone
what happens if Cl- secretion is excessive
leads to secretory diarrhea caused by activation of CFTR channels
what happens in glucose-galactose malabsorption
defective SGLT1 transporter prevents absorption, leading to severe diarrhea
how does excessive fructose intake cause digestive issues
overwhelms GLUT5, leading to fermentation by colonic bacteria
what is secretory diarrhea and what causes it
excessive fluid loss due to overactive Cl- secretion
how is secretory diarrhea treated
oral rehydration therapy, which relies on Na+-glucose cotransport
