GI- Peritoneum and Stomach Flashcards
mucosa
innermost layer of the human digestive tract; epithelium lamina propria, muscularis mucosa
submucosa
layer of CT directly under the mucosa
muscularis
smooth muscle w/ 2 layers; inner circular and outer longitudinal responsible for peristalsis
serosa/adventitia
outermost layer incl. mesothelium and thin CT; when we reach the abdominal pelvic cavity, adventitia → serosa (thin layer of epithelium secreting serosal fluid to allow organs to move around in abdominal pelvic cavity; has some CT to glue epithelium down to muscularis)
enteric nervous system
helps coordinate peristalsis
peristalsis
alternating waves of muscle contraction and relaxation used to move food through the GI tract
what are the components of the ENS?
myenteric plexus, submucosal plexus, interstital cells of Cajal
myenteric plexus
nerve supply between the two layers of the muscularis externa; provides smooth, coordinated contraction for peristalsis
submucosal plexus
neuronal network in submucosa of esophageal, stomach, and intestinal walls that regulates enzyme secretion
interstitial cells of Cajal
pacemaker cells of the gut
ENS role
generate localized reflexes
what do sensory neurons from mucosal epithelium detect?
stretch, pH changes or chemical composition to regulate activities of either plexus (parasympathetic and sympathetic responses of the ANS)
what is sensory info. also shared with in the ENS?
shared with the spinal cord (stretch as a pain signal)
what does parasympathetic output do?
SLUDD, also fine tunes the end muscles or epithelium and glands (major innervation by CN X)
what does sympathetic output do?
decreases SLUDD, mainly by constricting blood vessels to gut
sympathetic innervation for the gut
ganglia are located at the collateral ganglia
what are the 3 collateral ganglia?
celiac, superior mesenteric, inferior mesenteric; they sit at the base of major arteries supplying blood to GI tract and follow blood supply to get to the wall
- communicate input all at once to “shut down” function in fight or flight response
parasympathetic innervation
cranial and sacral output innervating mostly proximal and some distal parts of the GI tract (CN X); ganglia sit in the walls of organs
what part of the gut does the vagus nerve innervate?
liver, stomach, small intestine, 2/3 of the large intestine
what nerve innervates the sigmoid colon?
pelvic splanchic nerves; sacral in origin (lower spinal cord) to initiate the defecation reflex
peritoneum
a multilayered membrane that protects and holds the organs in place within the abdominal cavity
parietal peritoneum
the outer layer of the peritoneum that lines the interior of the abdominal wall
visceral peritoneum
the inner layer of the peritoneum that surrounds the organs of the abdominal cavity
what are the 5 folds of the peritoneum?
falciform ligament, lesser omentum, greater omentum, mesentery, and mesocolon
falciform ligament
attaches liver to anterior abdominal wall and diaphragm and divides it into 2 major lobes
lesser omentum
structure attached to the lesser curvature of the stomach and attaches it to the inferior surface of the liver
greater omentum
hangs down from the greater curvature of stomach and folds back up to attach to large intestins; is first fold seen containing lots of adipose, blood vessels and lymphatic tissue
mesentery
Suspends the small intestine; huge double layer of the parietal peritoneum that attaches parts of the intestine to the posterior abdominal wall
mesocolon
suspends the transverse colon from the posterior abdominal wall; allows it to freely move when feces are moving through the large intestine
which structures in the abdominal cavity are retroperitoneal?
pancreas, duodenum, ascending and descending colon, kidneys
in addition to the 4 layers, what are the alterations in the stomach?
rugae, the innermost oblique muscle layer and serosa
rugae
specialized foldings of the mucosa allowing the stomach to expand for larger capacity
innermost oblique muscle layer
third layer aiding mechanical digestion (churning to mix gastric secretions to pulverize food)
what are the regions of the stomach?
cardia, fundus, body, pylorus
cardia
area around the opening of the esophagus and closest to the heart
fundus
Very top of the stomach; holding area for semi-digested food
body of the stomach
greatest region where 3 muscular laters are most developed w/ intense rugae
pyloric region
3 subregions:
Antrum
Canal
Pyloric
curvatures of the stomach
greater and lesser
what are the main functions of the stomach?
having an extremely acidic environment to digest proteins and break down + mix chyme to be put into the duodenum, produce intrinsic factor for vitamin B12 absorption in the small intestine
what is the significance of vitamin B12?
DNA synthesis; since it is an animal source the protein must first be natured to release the vitamin which the intrinsic factor will then bind, absorb drugs
venous drainage of the stomach
superior mesenteric v. drains R gastro-omental, splenic vein drains L gastro-omental and short gastric v., L and R gastric veins; all of which drain into the hepatic portal vein
hepatic portal system
all capillary beds within the wall of the GI tract converge and form veins that enter the liver, which then disperse into another set of capillary beds; the ultimate goal os to detoxify and process nutrients
what layer of the GI wall contains gastric pits?
the mucosa
gastric pit histology
apical region (mucus cells), parietal cells, chief cells, G-cells
mucous cells of gastric pit
substances contain mucin and some water + lots of HCO3- (protect stomach and epithelial damage from stomach acid)
parietal cells of gastric pit
secrete HCl and produce intrinsic factor
chief cells of gastric pit
secrete pepsinogen, gastric lipase
G-cells of gastric pit
secrete gastrin (released locally in stomach and acts on nearby cells, endocrine to act on distal cells on other parts of stomach/intestine)
what is the role of gastrin?
stimulates gastric acid secretion by increasing parietal and chief cell activity, tighten the LES, increase gastric motility and relax the pyloric sphincter
HCl production in stomach
carbonic acid dissociates into bicarb and H+; H+ is pumped out of gut in exchange for K+, meanwhile bicarb. travels down [ ] gradient using an antiporter which simultaneously pulls in Cl- from the blood, HCl combines in the lumen while bicarb. is used for protective mucus
how is HCl secretion regulated?
promoted by gastrin from eneteroendocrine cells, ACh from parasympathetic nerve fibres, and histamine from mast cells (lamina propria = proton pump (H+/K+ ATPase)
what are the 3 digestion phases?
cephalic phase, gastric phase, intestinal phase
cephalic phase
the earliest phase of digestion, in which sensations and thoughts of food prepare the stomach to secrete enzymes and contract (vagus n. output)
gastric phase
phase of gastric secretion that begins when food enters the stomach; stretch receptors detect distention, dumping of food intensifies activity locally through ENS (food presence also causes pH to become alkaline as detected by chemoreceptors- alkaline tide)
intestinal phase
intestines communicate neural and hormonal responses to talk back to stomach
secretin
enteroendocrine cells stimulates the pancreas to release bicarbonate to neutralize acid in duodenum (inhibit actions of submucosal plexus)
CCK
stimulates gall bladder to secrete bile to emulsify fats in the small intestine and act on myenteric plexus to slow contraction
enterogastric reflex
causes parasympathetic output to the stomach to decrease and less chyme leaves the stomach; long acting and neural involving the brainstem (via medulla)
why do we vomit (emesis)?
extreme distention and irritants (bacterial toxins, ethanol, certain foods/drugs)
what does vomiting involve?
afferent signals to the medulla (vomit center)
and efferent signals to the diaphragm, abdominal muscles, relaxation of esophageal sphincters, closing off of nasopharynx (soft palate)
What cranial nerve innervates the ANS AND ENS?
Cn 10- vagus
Where do the collateral ganglia sit?
Sit on major blood vessels going out to GI tract
Does sympathetic stimulation increase or decrease the activity of submucosal plexus and superior mesenteric?
Decrease
Where does the vagus nerve end?
Sigmoid colon
What serves as a highway for blood vessels nerves and lymphatics in and out of GI?
Folds
Is there fat within the folds (mesentery)?
Yes
What is in the potential space of abdominal cavity?
No air just lubricating fluid
Where do immune responses occur?
Greater omentum
What is sometimes considered its own organ?
Mesentery
What food is the only food that suspends an organ from the inferior surface of the diaphragm and the anterior abdominal wall?
Falciform; sickle shaped
What substance does the innermost oblique layer make?
Milky white substance called chyme which gets sent to the intestines
Does the rugae act to increase surface area for absorption?
No; we do not absorb nutrients in the stomach as it’s not broken down yet
Function of pyloric antrum
Opening to pyloric canal
Function of pyloric canal
Directs stuff towards pylorus
Function of pylorus
Delivers chyme to small intestines
Function of pyloric sphincter
End of stomach; separates contents of stomach from contents of intestine; smooth muscle
Layer of pyloric and function
Longitudinal, circular, and oblique
- help produce churning action of stomach
pH of the stomach
1.5-3.5
Functions of stomach
- absorbs some drugs and alcohol
- very little absorption
- breaks down and mixes and out chyme into duodenum
- hydrochloric acids denature and digest proteins
- produces intrinsic factor for B12 absorption
How do cells get in and out and access energy into adipocytes
Gastro-mental surfaces provides blood vessels that run through the greater omentum
Where does all the blood go from the GI?
One big portal system.. hepatic portal vein
What does the left and right gastric drain?
Lesser curvature of the stomach
What does the superior mesenteric vein drain?
left and right gastro omentals
Superior mesenteric vein drains..
A lot of small intestine because it’s an early vein and some of the large intestine but not all
What does the splenic vein drain?
Draining left gastro omental and short gastric artery… area of stuff that needs addition vein for drainage
Whole goal of blood drainage
All ingested and absorbed nutrients from gi will enter the Venice blood and it’s the livers job to do things like detoxify things that are bad and also process nutrients and proteins
How much chyme is release during each peristaltic wave?
3ml
What promotes increased gastric emptying?
Increase secretion of gastric
What inhibits gastric emptying?
Increased secretion of CCK
