GI 2 Flashcards
1
Q
What are the 4 layers of the GI tract?
A
- mucosa: epithelium, lamina propria, muscularis mucosa (smooth muscle which puts overlying epithelium into folds)
- submucosa: blood vessels, nerves, lymphatics, and glands residing here
- muscularis: inner circular and outer longitudinal layer
- serosa/adventitia: single layer of epithelial cells secreting lubricating fluid (mesothelium) and thin layer of connective tissue gluing it to musclar layer
2
Q
What is the function of the enteric nervous system? What does it consist of?
A
- generate peristalsis
- peristalsis: alternating waves of muscle contraction and relaxation used to move food through the GI tract
- 100 + million neurons from esophagus to anus
- myenteric plexus: controls musclar activities of the tube
- submucosal plexus: controlling activity of the glands
- sends neurons out to touch the epithelium and tell them to make mucus/enzymes
- interstitial cells of Cajal (spread out along length of tube) are pacemaker cells more important in the myenteric plexus setting up waves of peristalsis
- tube can generate its own reflex by detecting it chemically and sensing stretch which creates local reflex
3
Q
How does the ANS interact with the ENS?
A
- fine tunes its functions
- parasympathetic: SLUDD gets turned up by para fibres that come into myenteric and submucosal plexus
- sympathetic will quiet SLUDD activities
- parasympathetic is good at fine tuning functions of GI tract because it also goes out directly to the smooth muscle (not just through the 2 plexi)
- most of the GI tract is regulated by CNX
- very distal portion of GI tract is controlled by splanchnic nerves or nerves at sacral level of spine
- mucosal epithelium contains receptors for stretch and pH and shares this information with the plexi and spinal cord to generate reflexes
4
Q
What are the collateral ganglia for the GI tract and where are they located?
A
- celiac, super and inferior mesenteric
- located on major blood vessels supplying GI tract
- sympathetic nerves ride along blood vessels
- sympathetic stimulation can quiet GI tract through the plexi but it mainly does this by constricting the BVs supplying the gut
5
Q
What is the parasympathetic innervation to the GI tract?
A
- CN X does most of GI organs
- at sigmoid colon, splanchnic nerves from sacral spinal cord take over
6
Q
What is the peritoneum?
A
- serosa covering abdominal organs
- visceral peritoneum on organ
- most of the organs are being suspended from the posterior abdominal wall by folds or a double layer of peritoneum
- folds serve to get nerves and BVs to and from various parts of GI tract and all originate from posterior abdominal wall
7
Q
What is the falciform ligament?
A
- divides the left and right lobes of the liver
- fold of peritoneum
- only one that suspends an organ from the inferior surface of the diaphragm and from the anterior abdominal wall
8
Q
What is the greater omentum?
A
- large flap of peritoneum
- first thing you see when you open abdominal cavity
- hangs off of greater curvature of stomach and attaches to transverse colon
9
Q
What is the lesser omentum?
A
-exists on inferior surface of liver and stomach
10
Q
What is the mesentery?
A
- if you protract away the greater omentum, can see the mesentery
- fold of peritoneum that is suspending the small intestines from the posterior abdominal wall
- biggest peritoneal fold
11
Q
What are the 5 peritoneal folds?
A
*liver also moves with diaphragm
12
Q
What are retroperitoneal structures?
A
- structures that are glued to the posterior abdominal wall by the peritoneum (but not suspended by it)
- pancreas, duodenum, ascending and descending colon, kidneys, etc.
13
Q
What are rugae?
A
- in mucosa of stomach
- specialized folds
- stomach can expand because of these
- they will flatten out as the stomach expands (like a shower curtain)
14
Q
What are the alterations in the stomach?
A
- rugae
- innermost oblique muscle layer
15
Q
What is the innermost oblique muscle layer?
A
- 3rd layer of muscle in the stomach
- to get contractions happening in 3D
- pulverizes food and mixes it with gastric secretions and forms chyme
16
Q
What are the regions of the stomach?
A
- cardia (closest portion to the heart)
- fundus (top most portion of stomach- bolus of food waits here to be pulverized down in the body of the stomach)
- body (largest region, has intense folds of mucosa (rugae) which disappear when stomach expands)
- pyloric antrum, pyloric canal, and pylorus (small opening at the end towards small intestine)
- pyloric region is where most intense churning and muscular action occurs
- pyloric sphincter: separates contents of stomach from contents of intestine
20
Q
Describe the blood supply to the stomach
A
- most blood supply comes from the celiac trunk (first major branch off of abdominal aorta)
- anastomosis on smaller curvature of the stomach (left and right gastric arteries)
- anastomosis on greater curvature of the stomach (left and right gastro-omental arteries)
21
Q
Describe the venous drainage to the stomach
A
- all of the blood from the alimentary canal will be funneled to the liver through the hepatic portal vein
- liver processes nutrients that come across the GI tract and any toxins that you may have ingested will be broken down
- anastomosis on smaller and greater curvatures of the stomach (left and right gastric and gastro-omental veins)
22
Q
What are the gastric pits?
A
- form cup shaped arrangements
- where HCl and enzymes are produced (eg. pepsin, gastric lipase)
- secretions moved through gastric pits to the lumen of the stomach where it mixes with food bolus
23
Q
Describe the histology of the gastric pit and the roles of each cell type
A
- near the top is largely lined by mucous cells which secrete tenacious mucous that gets stuck to epithelium, has a lot of bicarb in it (base) to neutralize acid right beside epithelial cells- protects the stomach from its own acid
- parietal cell located in the crypts secretes HCl and produces intrinsic factor
- chief cells secrete pepsinogen (large proteins) and gastric lipase (fats)
- endocrine cells (release endocrine hormones); G cells because they release gastrin- gastrin tells parietal and chief cells when food is present to increase their activities, increases tightness of lower esophageal sphincter (so you don’t get acid in esophagus), increase gut motility, start to relax the pyloric sphincter
- gastrin goes through blood stream and circulates to find its target cells
24
Q
How is HCl produced?
A
- Water and CO2 combine to form carbonic acid accelerated by carbonic anhydrase in parietal cell, carbonic acid dissociates into a proton and bicarb. H+ released from parietal cell by proton pump that uses ATP (antiporter moving K+ in and H+ out). Potassium leak channels on surface to let K+ out to allow pump to keep working.
- Use built up concentration of bicarb in the parietal cell to power the entry of chloride through another antiporter (HCO3- out and Cl- in). Leak channel allows Cl- to move out into gastric lumen.
27
Q
What is the cephalic phase of digestion?
A
- occurs when there is no food in the stomach
- can be looking at/thinking about/smelling food which creates neural signals that go through the cortex to hypothalamus and result in parasympathetic output
- conveyed by vagus nerve to the stomach
- interacts with submucosal and myenteric plexi to increase gastric juice secretion, G cells secrete gastrin, and cause increased gastric peristalsis
28
Q
What is the gastric phase of digestion?
A
- food is present in the stomach (detects this from sensory receptors which detect distention as well as chemoreceptors which detect increase in pH of gastric juice from food and saliva entering and partially neutralizing the acid)
- start making more acid
- sensory receptors talk with submucosal plexus and myenteric plexus to start secretions and gastric motility
- G cells can sense presence of food which amplifies secretions and motility
29
Q
What is the intestinal phase of digestion?
A
- intestines talking back to stomach
- stretch receptors detect stretch in duodenum and chemoreceptors that detect fatty acids and glucose in duodenum
- enteroendocrine cells secrete CCK and secretin
- enterogastric reflex via medulla oblongata: long acting, sensory neurons that go to spinal cord, brain stem, and signal to autonomic areas to slow the stomach, brain stem will create output to stop stimulating myenteric and submucosal plexi
- secretin goes to stomach and talks to submucosal plexus and says to decrease gastric juices (intestine needs more time), tells myenteric plexus to slow contractions
- CCK only talks to muscular layers to quiet muscular contractions to give intestines more time
30
Q
What promotes gastric emptying?
A
31
Q
What inhibits gastric emptying?
A
