Week 9: Digestive pt2 Flashcards
chief cells make precursors for?
digestive enzymes in the stomach that are going help in protein digestion
parietal cells make what?
HCI acid that’s gonna be important in:
1. HCI acid converts those inactive precursors released in lumen of stomach by chief cells into their active forms
2. HCI converts pepsinoge to pepsin
pepsin starts working on breaking down what?
chemical bonds
why is low pH in stomach gonna denature proteins important?
denaturing them is gonna unfold them which makes it easier for the pepsin and other protein digesting enzymes in stomach and SI to actually break covalent bonds and make smaller pieces
parietal cells have?
carbonic anhydrase
CO2 and H2O in the parietal cells…
- carbonic anhydrase puts them together to make carbonic acid
- carbonic acid breaks down into bicarbonate and H+
what will we do with the bicarbonate and H+?
different than RBC
- H+ will get pumped into the gastric lumen against its concentration gradient
- bicarbonate is gonna go out towards blood in exchange for chloride ion (chloride shift)
- chloride channel at luminal end of parietal cell and chloride will move into parietal cell and move down its concentration gradient into lumen of stomach
- HCI i just secreted HCI acid
bicarb is gonna wind up in the blood and bicarb is a ___ base
buffer
if you put bicarb in the blood, what happens?
it can take up some H+ in the blood
what we see when we’re actively digesting, because the stomach is secreting HCI acid and you’re putting more bicarb in the blood, depending on how much HCI you’re making, what happens to the arterial pH?
right after you eat a meal, the arterial pH becomes a little higher
- not a huge change but measurable and that increase, bc we put bicarb in the blood, is called the alkaline tide?
is this going to completely disrupt your acid-base balance in your blood?
absolutely not
- not a huge change
what is the carrier that is inhibited by prilosec
H+ transporter also called a proton pump
that whole class of drug is called?
proton pump inhibitors
When reading a label on a proton pump inhibitor, it will tell you 2 things, the first thing is?
it is not gonna give you immediate relief if you have a heart burn or acid reflux
what is the second thing?
you shouldn’t take it past the certain period of time without talking to doctor
what is the reason for that?
our cells generally respond well to completely blocking something . (turning it down or up, we can adjust to) but completely shutting off a carrier thats supposed to move something out of that cell, if you do it over a long period of time, it is gonna mess things up in that cell and cause problems
when thinking about parietal cells, what is our focus generally on?
hydrochloric acid secretion
what else is coming from parietal cells?
intrinsic factor secretions
what does intrinsic factor bind?
vitamin B12
-keeps it from being digested and helps it get absorbed
what is a problem we see in people who had to have a large part of body removed?
they don’t have enough parietal cells left to make enough intrinsic factor to get them enough vitamin B12 to their bone marrow.
what condition do they end up having?
pernicious anemia
person who has pernicious anemia is not going to be able to absorb enough vitamin B12 to keep their?
bone marrow up
what else causes pernicious anemia?
lack of intrinsic factor, stomach cancer, stomach ulcers, autoimmune disease
how are you gonna control secretion?
nervous system and hormones
what is the parasympathetic system involved in?
stimulating the secretory activity of chief cells and parietal cells
what other hormone is involved in stimulating secretory activity of chief cells and parietal cells
gastrin
what is the diameter of the small intestine?
about 1 inch, 20 ft
small intestine is divided into three sections that include?
Duodenum, Jejunum, and Ileum
What does the duodenum connect to?
“connects here to the stomach with the pyloric sphincter in between”
- uppermost section of small intestine, attached to pylorus
- C-shaped
how long is the duodenum?
10 inch
where is the jejunum starts?
where the C of the duodenum ends
- begins where digestive tube turns abruptly downward and forward
how long is the jejenum?
8ft long
how long is the ileum?
about 12 inch
is there a clear indication where ileum starts?
no
small intestine is all about?
surface area
why is it surface area for secretion?
we’re gonna have to contribute things that are gonna help with final stage of digestion
why is it surface area for absorption?
most of what we absorb is going to be absorbed in small intestine
if 20ft of small intestine is not enough, there are also _____ ____________ in small intestine that will increase surface area in inner part of small intestine
three modifications
what are the three modifications?
- plicae (plica singular)
- Villi
- Microvilli (Brush border)
what are plicae?
circular folds in lining of small intestine
- you have them in jejunum, ileum, and duodenum
what are villi?
- stick up like fingers off of plicae
spaces in between villi called?
intestinal crypts
what is inside of each villus?
arteriole, venule, and lactyl
what is a lactyl?
lymphatic capillary in digestive system
what are one of the functions of the lymphatic system?
to carry lipids that the digestive system absorbed and so we get them into the lymphatic system through these lactyl’s
the villus is covered by?
an epithelial layer: simple columnar epithelium
what are enterocytes?
intestine cells
- epithelial cells that line small intestine
the enterocytes have what?
microvilli
all three modifications together do what?
increase surface area in the small intestine 100x
Plicae, villi, and microvilli are modifications of the ?
mucosa that we see in the small intestine
we dont have any of those things in?
esophagus and stomach
what are the characteristics of an epithelial tissue?
they reproduce
there are stuff moving past these villi all the time which leads to?
some possibility of friction damage and we need to be able to replace any cells that come off this layer bc the epithelia are supposed to be barriers
what happens here?
we have stem cells to replace epithelia down in the crypt and as these stem cells divide, they get moved up the crypt and eventually they get all the way to the top. the reward to getting up to the top is by getting knocked off the villus and become part of what’s getting digested or leaving body’s waste
what is the potential problem here?
it is dark in small intestine and moist and there are a lot of nutrients
- make bacteria heaven
- down in crypts, there is not much moving past and so bacteria can hang out in the crypts and kill stem cells and we could lose our epithelial barrier
down in the bottom of the crypt, we have another set of cells called?
paneth cells
what do paneth cells do?
secrete antibacterial enzymes
- they’re down in the bottom of the crypt as protection for the stem cells
- they also secrete other things that help to inhibit bacterial growth
- helps maintain a balance
what will you mainly see the small intestine produce?
water with some bicarb in it
most digestive enzymes we will use in the small intestine are either?
anchored membrane proteins that are attached to lumen end of the enterocytes or they’re things made by pancreas and put in small intestine
goblet cells contribute a little bit to the juice because?
they will make mucus to make material easier to move through the small intestine
what do we not understand?
the step by step regulation of producing intestinal juice
what do we know?
- having food in the small intestine especially in duodenum is going to stimulate some juice production and change chemical composition a little bit.
- acid in small intestine stimulate intestinal juice
why would you want more intestinal juice if you have acid or acidic contents in small intestine?
dilutes the acid
what is the hormone vasoactive intestinal peptide going to do?
- stimulate production of intestinal juice
- makes capillaries in the villi more permeable (easier for stuff to get absorbed and moved into the blood)
- gonna act on stomach to decrease gastric motility and gastric secretion
why would you want VIP to turn down gastric activity?
slow down digestion in stomach so you can continue to work what is in the duodenum
how to control intestinal motility?
intrinsic stretch reflex
what does that say?
if you stretch the duodenum/other parts of small intestine, it will increase motility from that point forward
what happens if we stretch duodenum and stuff keeps coming in from the stomach?
that stretch will cause the stuff in the small intestine to move forward faster ending up in diarrhea
what is another thing that controls intestinal motility?
CCK
with respect to intestinal motility, CCK is the only hormone that?
increase intestinal motility
endocrine cells in duodenum is going to release?
CCK into the blood when chyme arrives in small intestine that is high in fat or high in partially digested protein
how long is the pancreas?
6-9 inches long