PSL Final Flashcards
how do the pancreas, small intestine, and liver work together in digestion?
Liver: bile salts + bilirubin
Pancreas: bicarbonate + enzymes
Secreted to SI
role of small intestine in digestion?
peristalsis, main site for nutrient absorption, digests many nitrients
role of large intestine (colon) in digestion?
mass mvmt, absorb water + electrolytes, store fecal matter
how is the wall of the GI tract structured?
Four layers:
1. mucosa
2. submucosa
3. muscularis
4. serosa
also has enteric nervous system
what are the specialized cells of the mucosa?
transport: secrete acid + bicarbonate, absorbs water + nutrients + vitamins
enteroendocrine: secrete hormones to blood
exocrine:
goblet - secrete mucous
paneth - secrete antimicrobial compounds
how does nervous regulation of the digestive system work?
a:
external stimuli (smell food) -> sensory receptor -> cephalic brain -> neurons of myenteric and submucosal plexus -> smooth muscle or secretory cells (effectors) -> digestive system responses
b:
local stimulus (pH, stretch, etc) -> sensory receptors and neurons -> interneoruouns + cephalic brain -> same as above
c:
local stimulus -> efffectors -> same as above
what are the structures of the enteric nervous system?
myenteric (A, motility) and submucosal plexus (M, secretion and absorption) -> neurons
describe the mechanism of parasympathetic control of the digestive system
“Rest and Digest”
Vagus nerve (X) synapses on enteric system neurons -> acetylcholine release from postganglionic fibers -> (») gut muscle activity + relax sphincters + increase secretion
describe the mechanism of sympathetic control of the digestive system
“Fight or Flight” -> no digestion
postganglionic neurons innervate GI tract _> noradrenaline release-> inhibit gut movement + constrict sphincters + reduce secretion
how does the GI regulate its own activity?
pH, physical and chemical stimulation -> hormone release + other effects (peristalsis, etc)
what is the splanchnic circulation?
blood goes from aorta -> hepatic artery -> capillaries throughout entire tract -> hepatic portal vein in liver -> inferior vena cava
which arteries supply the GI tract?
stomach: celiac artery
SI: superior mesenteric artery
LI: super and infer m arteries
what absorbs fats into the lymphatic system?
central lacteals
how does blood flow in the liver?
- hepatocytes clean blood
- blood from hepatic portal vein and hepatic artery pools in sinusoids
- blood goes to central veins, drains into hepatic vein, returns to heart
how do GI smooth muscle cells operate as a single unit?
gap junctions join cells + action potentials travel in all directions
how do GI smooth muscle cells exhibit electrical properties?
slow waves, when they reach threshold -> action potential (slow wave determines frequency) -> contraction (also force of contraction and duration)
(1) interstitial cells of Cajal = pacemaker cells-> random AP via pacemaker potential (Ca triggers) -> spread AP to other non-pacemaker cells
compare and contrast heart and Cajal pacemaker cells.
Heart: uniform, depolarize 80 times per minute
Cajal: slow waves, deploraize 3/min(stomach) or 12/min(duodenum) via Ca entry
how is GI smooth muscle potential modulated?
depolarization: relaxes sphincters, stim by
- acetylcholine, stretch, parasympathetics
hyperpolarization: constrict sphincters, stim by
- noradrenaline, sympathetics
describe how deglutition (swallowing) works
- tongue pushes bolus against soft palate and back of mouth -> swallow reflex
- upper esophageal sphincter relaxes, epiglottins closes
- food goes to esophagus via peristalsis and gravity
describe the cranial nerves involved in voluntary and involuntary swallowing
Voluntary: CN 5, 9, 10, 12 (V, IX, X, XII) -> tongue moves against hard palette, respiration inhibited
Involuntary: CN 5, 7, 9, 10, 12 (V, VII, IX, XII) -> upward movement of soft palette, epiglottis closes, bases of tongue pushes food.
swallowing center in medulla and pons
how does food from the esophagus to the stomach?
food stimulates vagus nerve + swallowing center -> myenteric plexus -> peristalsis and relaxation of lower esophageal sphincter -> food in stomach
how does peristalsis move food?
- contraction of circular muscles behind food
- contraction of longitudinal muscles ahead of food (see diagram)
- circular muscle layer contraction -> food moves forward via rhythmic pulsation
how does the stomach accommodate and move food?
the vagovagal reflex links stretch of stomach to brain-> brain adjusts stomach size
peristalsis waves mix chyme -> stomach empties into duodenum
what does segmentation in the SI do?
- contractions at intervals along SI
- circular muscle contract + longitudinal muscle relax -> food mixes
how does ileocecal valve ensure one way movement from the S-LI?
- prevents backflow
- distension of ileum + gastroilieal reflex
- closed by distention of colon
how does the large intestine control mass movement?
waves of contraction -> slow movement (5-20cm/hour)
controlled by enteric nervous system:
- PNS»_space; motility
- SNS «_space;motility
how does brain trigger vomiting (emesis)?
vagus:
increase salvation + relax esophagus + contract pylorus
spinal nerves:
inspiration and contraction of abdominal muscles
phrenic nerve:
diaphragm descends
stomach:
undergoes reverse peristalsis
