Digestive tract (aka GI tract) Covering an internal lumen (which is actually "outside" the body) The disassembly line of our body
Accessory digestive organs Teeth, pancreas, assisting in mechanical and chemical digestion
Which of the following best describes the role of the esophagus in digestion...
FINAL BIO 252 QUESTIONS AND
COMPLETE SOLUTIONS
Digestive tract (aka GI tract) ✅Covering an internal lumen (which is actually "outside"
the body)
The disassembly line of our body
Accessory digestive organs ✅Teeth, pancreas, assisting in mechanical and chemical
digestion
Which of the following best describes the role of the esophagus in digestion?
✅Connects the mouth to the stomach and has no role in chemical digestion
It's role is just propulsion
3 roles of the stomach ✅1. Storage facility. Most digestion happens in the small
intestine so we just don't have enough room so we need to store in in stomach
2. Disassembly. First step in digestion of proteins. It's not essential, but it's difficult
without it.
3. Defense. Acidic environment gets rid of pathogens.
Rugae ✅These are the foldings inside the stomach that allow the stomach to expand
and then it makes it so it doesn't tear apart when it stretches
Fundus ✅store room in the stomach where some of the food waits until we can deal
with it.
3 smooth muscle layers in the stomach ✅Longitudinal muscle most external
Circular muscle within that
And then most deep, oblique muscle
The cells lining the stomach secrete mucin (mucous)
The lining is dotted with millions of gastric pits
What structural modification underlies the stomach's ability to mechanically digest food?
✅The stomach has an extra group of muscles called the oblique muscles that are
responsible for the churning and mechanical digestion of food
Chyme ✅Gastric juice + digestive food
Either delivered in small amounts to the duodenum or forced backward into the stomach
for further mixing
The curious case of Alexis St Martin ✅Dr. William Beaumont
In michigan, wanted to study the stomach and body
,Alexis St Martin was shot and it went through left part of body. Went through stomach
and out
Took different types of food and tied it to a string and put it in his stomach and waited
and took it out to see if it was digested or not.
Mucous neck cells ✅in the gastric glands.
Secrete a thin mucous layer
Parietal cells ✅in the gastric glands. Secrete intrinsic factor and hydrochloric acid
Intrinsic factor has nothing to do with stomach. Really is just important protein that has
receptors on walls of small intestine that binds to essential vitamin (B12) because it
can't be digested by itself
There is a sublingual supplement (put it under your tongue)
This lets you absorb B12 directly into the capillaries in the bottom of your mouth
Chief cells ✅in the gastric glands. Secrete pepsinogen. This gets modified and
becomes an active enzyme. Becomes an enzyme in an acidic environment called
pepsin. Pepsin can do digestion of proteins. Acidic environment comes from HCL from
parietal cells
HCL assists in pepsin synthesis and activity
Breaking down cell walls of plant foods
Defense against pathogens
Gastric juice ✅Mucus, HCL, pepsinogen
Secreted to the lumen
Enteroendocrine cells ✅G cells: Gastrin
Gastrin will go back and promote secretion of gastric juice
How does gastrin from the bottom make it to parietal cells and chief cells? ✅Gastrin is
a protein that serves as a hormone so it goes through the blood vessels.
Dave Barnes had agonizing pain in his abdomen, followed by heartburn and vomiting.
The doctor told him he has a gastric ulcer in his stomach, caused by the Helicobacter
bacteria. It is most likely that the bacteria: ✅Penetrated the mucus layer of the
stomach
Enteric system ✅Part of autonomic nervous system
From the gut
Acts as an independent system. More neurons here than in whole spinal cord
All local reflexes
The nervous system of the stomach
Long reflexes (interacts with the brain)
Parasympathetic. Medulla oblongata controls gastric secretion and vagus nerve goes all
the way down to the stomach
, Three phases of regulation ✅Cephalic (head)
Gastric (stomach)
Intestinal (duodenum)
What does NOT stimulate the secretion of hcl in the stomach? ✅Secretin
Secreted by the small intestine and it inhibits gastric activity
Peristaltic waves move toward the pylorus at the rate of 3 per min. How? ✅We have
cells that determine the pace
Regulation of gastric emptying ✅In general, the same mechanisms regulating gastric
secretion will also regulate gastric emptying (mainly: intestinal phase)
Carb-rich chyme quickly moves through the duodenum (4 hours)
Fat-laden chyme is digested more slowly causing food to remain in the stomach longer
(~6 hours)
Vomiting ✅Stimulation of the vomiting center in the medulla
Increase in the intraabdominal pressure, relaxation of the esophageal sphincter, and
elevation of the soft palate, closing the connection between the oropharynx and
nasopharynx
From where is bile secreted? ✅liver
Which system will send signals to the hepatopancreatic sphincter NOT to contract, and
when? ✅When it is contracted nothing passes through
Sympathetic says no digestion when you are stressed
Intestinal phase tells it not to contract because chyme is already in it
Mucosa layer lines the wall of the duodenum to do what? ✅Adaptation to digestion and
absorption: fold within a fold
Stomach has 3 layers of muscle, the rest of digestive only has 2
First level of folding: circular folds
The chyme runs slowly through the duodenum, assuring complete digestion and
absorption
What structural modifications of the small intestine wall increase surface area? ✅Deep
circular folds of the mucosa and submucosa
Villi: fingerlike extensions of the mucosa. Have enterocytes on them
Microvilli: tiny projections of membranes of the absorptive mucosal cells on the
enterocytes. Tiny projections of plasma membranes forming a "brush border". Contain
the brush border enzymes. Assist in digestion of carbs and proteins in the small
intestine
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