GI Tract Organization & Stomach (Exam 1) Flashcards
The muscularis layer of the GI tract has skeletal muscle (voluntary control) on the upper 1/3 of the esophagus, but where else is it located?
test q
-mouth
-pharynx
-anus
The muscularis layer of the GI tract has skeletal muscle (voluntary control) on the mouth, upper 1/3 of the esophagus, pharynx, and the anus. What does it control?
test q
swallowing and defecation
The muscularis layer of the GI tract has smooth muscle with involuntary control. What fibers does it have and what is its function?
test q
-has both inner circular fibers and outer longitudinal fibers
-it mixes, crushes, and propels food along by peristalsis
Which plexus has both parasympathetic and sympathetic innervation of circular and longitudinal smooth muscle layers?
test q
myenteric plexus / auerbach plexus
What plexi comprise the enteric NS?
test q
myenteric plexus and submucosal plexus
Which layer of the GI tract is the meissner/submucosal nerve plexus in?
test q
submucosal layer
Which layer of the GI tract is the auerbach/myenteric nerve plexus in?
test q
muscularis layer
What are the 4 layers of the GI tract from deep to superficial?
test q
deepest= mucosa
submucosa
muscularis
serosa (superficial)
The mucosal layer of the GI tract has stratified squamous in the mouth, esophagus, and anus. It resists __________. The rest of the GI is simple columnar and secretes enzymes and/or absorbs nutrients. Enterocytes line the simple columnar epithelium. What other cells are here and what do they secrete?
test q
abrasion
goblet cells secrete mucus
enteroendocrine cells secrete hormones controlling organ function
The mucosal layer of the GI tract contains lamina propria that is a thin layer of loose connective tissue and contains….
blood vessels and lymphatic tissue
The mucosal layer of the GI tract has muscularis mucosae with thin layer of smooth muscle that causes folds to form and increase _____ to allow _____________. This also increases local movements and absorption with exposure to new nutrients. The villus here is finger-like projections that expose enzymes to allow absorption of these new nutrients
SA, stretching
The submucosa of the GI tract is ___________________ tissue that contains blood vessels, glands, and lymphatic tissue
loose connective
The submucosal layer of the GI tract has submucosal/meissner plexuses that mainly have parasympathetic input. What does parasympathetic innervation regulate here?
regulates vasoconstriction and local movement by muscularis mucosa
The serosa of the GI tract covers all organs and walls of cavities not open to the outside of the body. It secretes serous fluid for _______________. The serosa consists of connective tissue covered with simple squamous epithelium
lubrication
The myenteric/auerbach plexus is found between longitudinal and circular muscle layers of the muscularis externa and allows for….
test q
GI movement
What is the function of the submucosal/meissner plexus?
test q
-GI secretion
-local blood flow
-muscularis mucosa
-villi movement
T/F: the enteric NS (ENS) extends from the esophagus to the gut and directly controls the GI system, receives ANS input, but can operate independently of ANS/CNS
true
The enteric NS is located in the myenetric/auerbach plexus and submucosal/meissner plexus. What does each one control?
test q
myenteric/auerbach plexus controls gastric motility
submucosal/meissner plexus controls secretory cells, blood flow, muscularis mucosa, and vili movement
The enteric NS has GI reflex pathways that regulate secretion and motility in response to stimuli present in the lumen, usually distention and pH shifts of chyme. What do the chemoreceptors look for here?
looking for lipids and carbs
Which plexus is closest to epithelium?
submucosal plexus
mechanosensors are found in….
epithelium
The ANS inputs to the ENS. Parasympathetically, it controls activity in general of the ENS, myenteric and submucosal plexus. The parasympathetic division controls motility, glandular secretion, gastric, and colonic blood flow. The ________ nerve supplies the upper GI tract to the transverse colon. The _________ nerves form the hypogastric plexus and increases most ENS actions via cholinergic fibers that terminates on ganglion cells of intramural plexuses
test q
vagus, pelvic
The ANS inputs to the ENS. Sympathetically, it mildly inhibits activity. The _________ neurotransmitters have an inhibitory effect on synaptic transmission in the enteric plexuses. The sympathetic division causes _________________ of GI blood vessels and is easily overcome by auto-regulatory escape when needed. The sympathetic division also inhibits glandular function, motor activity, and certain digestive sphincters
NE/epi, vasoconstriction
What is the parasympathetic neurotransmitter?
ACh
What are the 3 smooth muscle layers of the muscularis externa in the stomach?
longitudinal (outermost layer)
circular layer
oblique layer (innermost layer, allows the stomach to churn chyme)
T/F: there is both peristalsis and churning in the stomach
true
What is the function of the oblique layer a part of the muscularis externa layer of the stomach?
permits greater churning and mixing of food with gastric juices
What are the 4 regions of the stomach?
cardiac, fundus, body, pylorus
The cardiac region of the stomach surrounds the….
cardiac orifice
Which region of the stomach is dome shaped beneath the diaphragm?
fundus region
What is the mid-portion of the stomach called?
body of the stomach
rugae in the stomach allow for….
stretching
The pyloric region of the stomach consists of the….
antrum, pyloric canal, and pylorus
The pylorus of the stomach is continuous with the ______________ through the pyloric valve/sphincter
duodenum
The greater curvature of the stomach is a _______________ surface
convex lateral
The lesser curvature of the stomach is a __________________ surface
concave medial
The stomach has ANS nerve supply. The sympathetic division is connected via the ________________________. The parasympathetic division is connected via the ______________
test q
splanchnic nerves and celiac plexus, vagus n.
The stomach is lined with what type of epithelium?
simple columnar epithelium
The stomach is lined with simple columnar epithelium. The epithelial cells extend down into the lamina propria forming…..
gastric pits and gastric glands
The gastric glands have 2 types of glands. What are they?
endocrine and exocrine glands
The exocrine glands within the stomach have 3 cells. What are they?
1) mucus neck cells
2) chief cells
3) parietal cells
What are mucus neck cells?
test q
-secrete mucus
-helps with low pH in stomach (protection)
What are chief cells?
test q
-zymogenic (precursor)
-secretes pepsinogen (zymogen) and gastric lipase
What are parietal cells?
test q
-oxyntic = secretes HCI
-also secretes intrinsic factor
What are the endocrine cells found in the gastric glands? What are their function?
test q
G cells
-secrete the hormone gastrin into the bloodstream
define endocrine
hormones are secreted from the interstitial fluid into the bloodstream and act on target cells
define exocrine
secretions enter tubes or ducts that lead to body surfaces
define paracrine
hormones enter the interstitial fluid but affect only neighboring cells
-ogen=
zymogen (precursor)
ex: pepsinOGEN
What converts pepsinogen to pepsin?
HCl (hydrochloric acid)
pepsinogen is a proteolytic enzyme, whereas pepsin is a digestive protease
What cell makes pepsinogen?
chief cells
What is the function of intrinsic factor?
test q
helps absorption of vit B12 for RBC production
What is gastrin and G cell? What is its function?
-G cells secrete gastrin into the bloodstream
-gastrin is the “get out of here” hormone that releases most gastric juices
-gastrin increases gastric motility/churning
-gastrin relaxes pyloric sphincter to allow food out of stomach
-gastrin constricts esophageal sphincter preventing entry
Gastrin is secreted into the blood and carried to the gastric _________ and __________ regions, where the majority of HCl secreting parietal cells are found
fundus, cardiac
What is the difference between a surface mucus cell and mucus neck cell?
both secrete mucus, but location is different
surface mucus cells are near the gastric pit, whereas mucus neck cells are deeper in the gastric glands
surface mucus cells secrete alkaline fluid containing mucin
mucous neck cells secrete acidic fluid containing mucin
Which cell secretes gastric lipase?
chief cells
Which cell secretes gastrin?
G cells
What are the 3 layers of the muscularis of the stomach?
-longitudinal layer
-circular layer
-oblique layer (innermost layer), promotes churning
The serosa of the stomach is a part of the __________ peritoneum
visceral
Technically, the muscularis mucosae is the….
muscularis interna
The submucosa of the stomach has lymphatic nodules called….
mucosa associated lymphoid tissue (MALT)
What is mechanical digestion?
peristaltic movements called mixing waves that churn the food
Are carbs digested in the stomach?
no
What is chemical digestion?
-conversion of proteins into peptides by pepsin, an enzyme that is most effective in the very acidic environment (pH 2) of the stomach
-gastric lipase splits certain molecules in butterfat of milk and other lipids into fatty acids and monoglycerides (this has a limited role in the adult stomach though)
The stomach wall is impermeable to most substances, however, some water, electrolytes, certain drugs especially like _________, and alcohol can be absorbed through the stomach lining
aspirin
What is a peptic ulcer?
-breach of the acidic GI tract
-most commonly caused by H. pylori which is a spiral shaped gram neg acidophilic bacterium
-can also be caused by abuse of NSAIDS on an empty stomach
How is gastric acid prevented from damaging the epithelial cells of the stomach?
mucus protects the epithelial cells of the stomach
When does protein digestion begin?
-when HCl denatures proteins molecules and transforms pepsinogen to pepsin and that breaks peptide bonds between the AAs
Protein digestion begins when HCl denatures protein molecules and transforms pepsinogen to pepsin and that breaks peptide bonds between the AAs. What digestion occurs after this?
fat digestion
-gastric lipase splits triglycerides in milk fat and other lipids (this enzyme is most effective in pH of 5-6, which is most commonly seen in infant stomachs)
HCl helps kill what?
microbes in food
What cells protect the stomach walls from being digested?
mucus cells
What are 2 gastric factors related to chemical and mechanical digestion?
volume of chyme and fluidity
Increased volume/distention stimulates….
gastric motility
Increased fluidity in stomach allows more rapid….
gastric emptying
In mechanical digestion there is gentle mixing waves every 15-25 seconds that mixes boluses with gastric juice to turn it into chyme- partially digested food, water, HCl, and digestive enzymes. Then there are more vigorous waves that travel from the body of the stomach to the _________ region. The waves will intensify near the pylorus and squirt out 1-2 tsps of chyme with each wave through the ____________
pyloric, pyloric valve
What food do we ingest and digest in the stomach? Which one stays in the stomach the longest?
test q
carbs, proteins, fats (nucleic acids will be later)
protein stays in the stomach longer than fat
What are the 3 gastric secretion phases?
1) cephalic phase
2) gastric phase
3) intestinal phase
Which gastric secretion phase is the longest? Shortest?
longest= gastric phase
shortest= intestinal phase
What is the cephalic phase of gastric secretion initiated by?
the CNS (it prepares the mouth and stomach for food that is ABOUT to be eaten)
During the cephalic phase of gastric secretion, the cerebral cortex stimulates the parasympathetic NS. 3 cranial nerves are involved here. What are the 3 cranial nerves and what do they do here?
CN VII and IX stimulate the salivary glands
CN X increases stomach muscular and glandular activity
Which CNs stimulate the salivary glands?
CN VII and IX
Which CN increases stomach muscular and glandular activity?
CN X
How do you know stomach muscular activity is increased?
stomach growls, feels like stomach is empty (this is cephalic phase of gastric secretion)
What are vagovagal reflexes?
-reflexes that go from stomach to brain and then back to stomach
-its enteric reflexes (ENS)
gastric phase is the stomach….
working
During the gastric phase of secretion, the nervous control keeps the stomach active. Stretch receptors and chemoreceptors provide info to the CNS and ENS. Vigorous peristalsis and glandular secretions continue. When digested, chyme is released gradually into the duodenum. What is this dependent on?
test q
calories, it depends on what you eat
During the gastric phase of secretion, there are endocrine influences over stomach activity. Distention and presence of protein causes G cells to secrete gastrin into the bloodstream, which increases 3 things. What 3 thing increase?
test q
1) stomach glandular secretion (especially HCl by the parietal cells)
2) stomach churning
3) pyloric sphincter relaxation
When does the intestinal phase of gastric secretion begin?
when chyme begins entering the SI (duodenum)
During the intestinal phase of gastric secretion, stretch receptors, fatty acids, and/or sugar signals to the medulla. What nerves are involved here and what to they do? What reflex is also here?
sympathetic nerves slows stomach activity and increases intestinal activity
enterogastric reflex inhibits gastric motility and increases the contraction of the pyloric sphincter to decrease gastric emptying
What 3 hormones are secreted during the intestinal phase of gastric secretion?
test q
1) secretin
2) cholecystokinin (CCK)
3) gastric inhibitory polypeptide (GIP)
What is the function of secretin during the intestinal phase of gastric secretion?
test q
stimulates the flow of pancreatic juice, inhibits the secretion of gastric juice
What is the function of CCK during the intestinal phase of gastric secretion?
test q
decreases stomach emptying and stimulates the secretion of pancreatic juice and bile
What is the function of gastric inhibitory polypeptide (GIP) during the intestinal phase of gastric secretion?
test q
decreases stomach secretions, motility, and emptying
During the cephalic phase of gastric secretion, receptors for sight, smell, and taste of food are activated from the thoughts of food in the cerebral cortex, hypothalamus, and medulla. This will send parasympathetic impulses along the vagus nerve and activate the submucosal plexus. What function does the submucosal plexus have here?
it increases gastric juices and peristalsis
During the gastric phase of gastric secretion, stretch receptors detect distention of the stomach and chemoreceptors detect increased pH of gastric juices. This is because the presence of food in the stomach increases the pH of stomach. What is activated during this phase?
increase gastric juice and peristalsis
enteroendocrine G cells secrete gastrin into the blood which activates/increases gastric juices and peristalsis even more
Once theres enough gastric peristalsis and leads to increased gastric emptying, it leads to the intestinal phase of gastric secretion. Stretch receptors detect distention of duodenum and the chemoreceptors detect fatty acids and glucose in the duodenum. This causes the enteroendocrine G cells to secrete 2 hormones and cause a reflux. What are these hormones and reflux called and what happens as a result?
G cells secrete:
-CCK and secretin
enterogastric reflux via the medulla occurs
this causes inhibitory effects on gastric peristalsis and gastric juice secretion, forcing the pathway to slowdown before the body gets anymore food
What is the fancy word for vomiting?
emesis
Vomiting is the forceful propulsion of gastric contents, stomach and sometimes upper __________ and ______________, out of the mouth
jejunum, duodenum
What is vomiting often triggered by?
select all that apply test q!!!!!!!
-pain, repulsive sights, smells, and emotional factors
-motion sickness and vestibular disorders
-pharyngeal stimulation, gastric/duodenal distention or irritation
-endogenous toxins, onset of pregnancy, numerous drugs, radiation, contaminated food
What body responses occur right after vomit?
test q
-profuse salivation and sweating
-increased heart rate
-nausea
Vomit is coordinated by area postrema and the vomiting center in the medulla through CN ____
X (10)
Strong nausea initiates sweating and relaxation of the stomach and lower esophagus, but causes tension in the gastric and esophageal muscles by the triggered afferent nerve impulses. After the impulses, there is contraction of the upper SI, followed by contraction of the pyloric sphincter and pyloric region of the stomach. The movement of contents of upper _______________________________ region go to the body and fundus of the stomach. It continues to go upward when the lower and upper esophageal sphincters are relaxed and set the stage for vomiting
jejunum, duodenum, and pyloric
What are the 5 steps of the vomiting cycle?
test q
1) deep inhalation
2) closure of glottis and raising of soft palate
3) suspension of breathing
4) contraction of diaphragm and abdominal muscles to compress stomach
5) ejection of gastric contents
note: step 3 here is the same as pharyngeal stage of swallowing
Prolonged vomiting, especially in infants and the elderly, can be serious bc the loss of gastric juices and fluids can lead to disturbances in both fluid and acid base balance. Most of the gastric juices are reabsorbed along the SI but it can still lead to….
dehydration, loss of gastric protons, and chloride (needs of digestion will replace protons in gut from bloodstream)
If vomiting is prolonged/uncontrolled it can lead to what 2 health problems?
hypokalemia and metabolic alkalosis
What is hypokalemia?
-mediated by the kidney
-its proton loss that is accompanied by matched potassium exertion
What is metabolic alkalosis?
pH of body tissues is elevated beyond normal range
What is a very rare complication of prolonged vomiting?
metabolic acidosis
-due to loss of duodenal bicarbonate
-will have opposite effects of metabolic alkalosis, which is more likely to occur
How does propulsion differ amongst body regions?
-mouth= voluntary/buccal phase of deglutition initiated by tongue, propels food into pharynx
-pharynx and esophagus= peristaltic waves move food bolus to stomach and accomplishing involuntary/ pharyngeal/esophageal phase of deglutition
-stomach= peristaltic waves mix food with gastric juice and propel it into duodenum
What chemical digestion occurs in the stomach?
digestion of proteins begun by pepsin
What does salivary amylase digest?
starches and oligosaccharides
What does lingual lipase digest and where?
triglycerides on the tongue
