Glossary of The Digestive System 2 (Physio T III)

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The fundus and body are sometimes collectively known as what?
oxyntic mucosa
The intrinsic factor secreted by the fundus and body of the stomach is necessary for what?
for absorption of vitamin B-12 which is required to properly shape RBC
The antrum is sometimes referred to as what area?
the pyloric gland area
What do the chief cells lining the glands secrete?
pepsinogen (enzyme that digests proteins)
What do the parietal cells lining the glands secrete?
HCl and intrinsic factor
What do the g cells in the pyloric gland area secrete?
What do the d cells in the pyloric gland area produce?
What do the enterochromaffinlike (ECL) cells in the oxyntic mucosa produce?
Name 5 kinds of cells found in the oxyntic mucosa?
1. surface epithelial cells

2. mucous cells

3. chief cells

4. parietal cells

5. ECL cells
Where are the glands that secrete digestive juices and how much do they secrete daily?
1. secreted by glands at base of gastric pit

2. 2 L secreted daily
What type of secretions are the secretion of digestive juices?
3 Gastric exocrine cells in the oxyntic mucosa?
1. mucous cells

2. chief cells

3. parietal cells
Describe mucous cells of the oxyntic mucosa?
line pits and entrance of glands, secrete thin, watery mucous
Describe chief cells of the oxyntic mucosa?
line gastric glands, numerous, secrete pepsinogen
Describe parietal cells of the oxyntic mucosa?
line gastric glands, fewer then chief cells; secrete HCl and intrinsic factor
Where are exocrine secretions released?
into the gastric lumen
Paracrine vs. endocrine secretions?
Paracrine is secreted and acts locally (from endocrine cells), Endocrine is secreted into blood
Endocrine and paracrine secretions are what kind of factors?
Name the 3 cells involved with endocrine and paracrine secretion?
1. ECL cells

2. G cells

3. D cells
Describe the ECL cells?
1. in oxyntic mucosa

2. secrete paracrine (histamine)
histamine is a what?
Describe G cells?
1. in pyloric gland area

2. secrete hormone (gastrin)
Describe D cells?
1. in pyloric gland area (but even more in duodenum)

2. secrete paracrine (somatostatin)
HCl is secreted by what cells?
By the parietal cells of the oxyntic mucosa
How low is the pH in the stomach?
as low as 2
4 functions of the low pH of the stomach?
1. converts inactive pepsinogen into active pepsin, initiating protein digestion

2. Denatures proteins (uncoiling from tertiary structures)

3. Breakdown of connective tissue and muscle fibers

4. Kills most microorganisms
Describe the mucus lining on the gastric mucosa surface? (3)

1. mechanical injury

2. self-digestion (pepsinogen)

3. alkaline, neutralizing HCl near gastric lining
What do parietal cells make?
Bicarbonate and Cl are what kind of transport?
secondary active transport
How do hydrogen ions (H+) go into the stomach?
primary transport
Describe Carbonic anhydrase?
An enzyme found in the parietal cells and RBC
, converts CO2 and H2O to produce carbonic acid which dissociates into H+ ion and bicarbonate ion
When H+ is transported into the stomach via primary transport what is being pumped into the cells?
Why does the bicarbonate ion go into the stomach?
it's a great buffer
How does Cl- get into stomach and for what reason?
via Cl channel, to produce HCl in stomach
What do the chief cells secrete?
Pepsinogen is inactive, so what doesn't it do?
does not digest cells and proteins
What can pepsinogen do?
autocatalyze itself to active pepsin which aids in protein digestion.
Pepsinogen can autocatalyze but what is needed initially to start the process?
For Mucous Cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. Alkaline mucus

2. Mechanical stimulation

3. protection
For Chief cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. Pepsinogen

2. ACh, gastrin

3. Active, begins protein digestion
For Parietal Cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. HCl, intrinsic factor

2. ACh, gastrin, histamine

3. Activates pepsinogen, etc. vit. B-12
For ECL cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. Histamine

2. ACh, gastrin

3. Stimulates parietal cells
For G cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. gastrin

2. protein products, ACh

3. Stimulates parietal, chief, and ECL cells
For D cells:
1. Product secreted
2. Stimuli for secretion
3. Function of Product
1. Somatostatin

2. Acid

3. Inhibits parietal, G, and ECL cells
The threes cells with exocrine products?
(digestive juices)
1. mucous cells
2. chief cells
3. parietal cells
The 3 cells with endocrine/paracrine products?
1. ECL cells
2. G cells
3. D cells
The 4 chemical messengers (stimuli) that influences secretion of gastric juice?
1. ACh
2. Gastrin
3. Histamine
4. Somatostatin
ACh is released from what kind of nerve plexuses general?
intrinsic nerve plexuses
What does ACh stimulate?
parietal and chief cells
What is ACh released in response to?
short reflexes and vagal stimulation (vagal is external stimulation, so both intrinsic and external)
Where is Gastrin released from?
G cells
What does gastrin stimulate?
parietal and chief cells
What is gastrin released in response to?
What cells release histamine?
ECL cells
What does histamine stimulate?
acts locally on parietal cells to increase HCl release
What is histamine released in response to?
Gastrin and ACh
What cells release somatostatin?
D cells
What does somatostatin inhibit?
locally inhibits secretions from parietal, G, and ECL cells
Where are D cells located?
some in antrum but even more in duodenum
3 phases involved in the control of gastric secretion?
1. Cephalic phase

2. Gastric phase

3. Intestinal phase
Describe the Cephalic phase of gastric secretion control?
stimuli from head (seeing, smelling, etc) increases secretion of HCl and pepsinogen via vagal (extrinsic) nerve activity
Describe the Gastric phase of gastric secretion control?
Stimuli in stomach (eg, proteins) initiate gastric secretions via intrinsic nerve plexuses and extrinsic vagal pathway
Describe the Intestinal phase of the control of gastric secretion?
INHIBITORY, shuts off flow of gastric juices via factors in duodenum (eg, fat, acid, etc)
Where does Carbohydrate digestion begin and continue? why?
Begins in mouth and continues in the stomach, there is actually not a lot of digestion in the stomach
-food is not mixed with gastric secretions in the stomach
-the salivary amylase continues to work in the internal mass of food
Where does salivary amylase come from?
the mouth
Where does protein digestion begin? Why?
in the antrum, this is where food is mixed with HCl and pepsin
What 2 things does the stomach absorb? What does it not absorb?
1. absorbs alcohol (lipid soluble)

2. absorbs Aspirin (weak acid, lipid soluble here)

3. not food
How is the stomach lining protected from gastric secretions?
by gastric mucosal barrier
-mucosal membrane is almost impermeable to hydrogen ions
What does drinking coffee do to the gastric juices?
increases them
What does drinking alcohol do to the gastric juices?
increases them
The mucus coating in the stomach lining is impermeable to what?
Where is the pancreas located relative to the stomach?
behind it
The pancreas contains what types of cells?
exocrine and endocrine
Hormones, insulin, glucagon and islets of langerhans are associated with what?
Endocrine pancreas
Acinar and duct cells are associated with what?
Exocrine pancreas
Acinar cells produce what?
digestive enzymes
Duct cells are responsible for what?
aqueous alkaline fluid (NaHCO3, sodium bicarbonate)
3 enzymes released by the Acinar cells of the exocrine pancreas?
1. Proteolytic enzymes

2. Pancreatic enzymes

3. Pancreatic lipase
Name 3 proteolytic enzymes?
1. trypsin (from trypsinogen)

2. chymotrypsin

3. carboxypeptidase
What does pancreatic amylase do?
converts starch to disaccharides
What does pancreatic lipase do?
hydrolyzes dietary lipids
The enzymes trypsin and chymotrypsin act on what substrate to produce what action?
substrate = proteins
action = proteins to peptides
What substrate does carboxypeptidase act on? What is the action?
substrate = proteins
Action = removes last AA from carboxy end of peptide
What substrate does the enzyme lipase act on? What is the action produced?
substrate = fat

action = converts triglycerides into fatty acids and monoglycerides
What substrate does the enzyme pancreatic amylase act on? What action is produced?
Substrate = polysaccharide

Action = converts polysaccharides into glucose and maltose
What substrate does the enzyme RNAse and DNAse act on? What action is produced?
substrate = nucleic acid

action = converts nucleic acids into nucleotides
Digestive enzymes secreted by which cells in pancreas?
acinar cells
What cells secrete aqueous NaHCO3 solution?
Duct cells
The endocrine portion of the pancreas is AKA?
islets of langerhahn
Exocrine portion of pancreas?
acinar and duct cells
Hormones seen in pancreas?
insulin, glucagon
4 part process triggered by Acid in the duodenal lumen?
1. increases secretin release from duodenal mucosa

2. Secretin (hormone) is carried by blood and stimulates the pancreatic duct

3. this increases the secretion of aqueous NaHCO3 into the duodenal lumen

4. This increase in NaHCO3 feedsback to the acid in the duodenal system and neutralizes it
4 part process triggered by Fat and protein products in duodenal lumen?
1. Increases CCK release from duodenal mucosa

2. CCK is carried in the blood and stimulates the pancreatic acinar cells

3. the increases the secretion of pancreatic digestive enzymes into duodenal lumen

4. These digetive enzymes then feedback and digests the fat and protein products that began the process
2 components that are not actually part of the GI tract? What is their importance?
1. Liver and Gallbladder

2. integral to processing food
Liver does more than just what?
What secretion from the liver is involved in digestion?
bile secretion
Liver is involved in the metabolic processing of what?
Liver does what to body wastes?
detoxifies or degrades it
Liver synthesizes what?
plasma proteins
What does the liver store? (5)
1. glycogen

2. fats

3. iron

4. copper

5. vitamins
What does the liver activate?
vitamin D
What does the liver remove? (what cells involved in process)
removes bacteria and worn-out RBCs (Kupffer cells: resident macrophages)
What does the liver secrete?
cholesterol and bilirubin
What kind of system is the liver?
portal (2 capillary beds connected by a vessel)
The liver is what kind of portal system? explain.
hepatic portal system. blood enters liver from the digestive tract via hepatic portal system. Portal vein breaks into capillary network, the liver sinusoids.
The functional units of the liver are known as?
the liver lobules
Describe the liver lobules (3).
1. hexagonal arrangements of tissue surrounding central vein

2. lobules delineated by vascular and bile channels (hepatocytes continuously secrete bile into these channels)

3. Bile ducts from lobules converge to form common bile duct (duct transports bile from liver to duodenum)
What is stored in the gallbladder between meals?
After a meal what happens to bile?
liver and gallbladder secrete bile into small intestine for fat digestion
Liver has it's own supply of what?
has it's own blood supply
(hepatic portal vein)
What 2 structures bring blood into the liver?
1. hepatic artery

2. hepatic portal vein
Thru what structure does the blood exit the liver?
central vein (which leaves via the hepatic vein)
Hepatocytes are what?
liver cells
Each hepatocyte is in contact with what 2 things?
sinusoid on one side and bile duct on the other
Bile could be described as what kind of fluid?
aqeous alkaline fluid
The components of bile: such as bile salts, cholesterol, and lecithin do what?
Stabilize fat, aid in fat digestion and absorption
The component of bile, bicarbonate ion, does what?
neutralizes acid in the duodenum
Give an example of a bile waste product? How is it excreted?
ex. bilirubin
-excreted via GI tract
Bile salts are derivatives of what?
Bile salts (cholesterol derivatives) are recycled through what?
thru enterohepatic circulation
What is the common bile duct?
a connection from the liver to the small intestine (gall bladder is also attached)
Where is bile stored?
gall bladder till needed by small intestine
What does bile do to fats?
emulsifies them
Describe 3 aspects of bile's emulsification of fats?
1. fat globules broken into smaller droplets

2. increases surface area, facilitates enzymatic attack

3. pancreatic lipase anchored to fat droplets by polypeptide colipase
Bile salts are adsorbed to the surface of what? Why?
small fat droplets, to prevent the droplets from recoalescing
Most potent stimulus for increased bile secretion?
bile itself
When bile is adsorbed to the surface of small fat droplets to prevent the droplets from recoalescing what are they forming?
The core of the micelle vs the outer shell?
the core is hydrophobic (fats)
the outer shell is hydrophilic (water soluble head of bile salts)
What else is involved in the micelles of bile and fats?
lecithin (has water soluble TAIL and hydrophobic HEAD)
What is bilirubin?
waste product excreted in the bile
What kinds of mechanisms cause bile secretion?
1. chemical

2. hormonal

3. neural
What is a choleretic?
any mechanism that increases bile secretion
Give a chemical mechanism that increases bile secretion?
bile salts
Give a hormonal mechanism that increases bile secretion?
secretin (from duodenum)
Give a neural mechanism that increases bile secretion?
vagus nerve (shows there is external and intrinsic stim. throughout entire tract)
If there is nothing in the GI tract what happens to bile?
it is stored in the gall bladder
What is the gall bladders main function?
stores and secretes bile
When is bile stored?
between meals
When is bile emptied?
during meals
What is possible in the gall bladder?
Can the gall bladder be removed?
yes, but not very common
What does the secretion of CCK do to the gall bladder?
stimulates contraction, relaxes sphincter of Oddi, releases bile into duodenum
What is CCK release triggered by? What is an especially potent trigger?
Chyme reaching small intestine
-fat is esp. potent
Where does most digestion and absorption occur?
the small intestine
Three segments of the small intestine?
1. Duodenum

2. Jejunum

3. Ileum
Motility in the small intestine occurs via what?
Describe the motility (segmentation) of the small intestine?
1. it mixes and slowly propels chime

2. segmentation contraction is intitiated by BER cells

3. Circular smooth muscle responsiveness is influenced by the distension of the intestine, gastrin, and extrinsic nerve activity
The motility (via segmentation) of the small intestine is under what control?
What would the an SNS response do to motility?
stop it because you would be in fight or flight mode
What is a BER cell?
involved in segmentation contractions
-basic electric rhythm (pacesetter cells that increase to threshold to have APs)
Travel time during motility of small intestine?
3-4 hours
What pushes the food down through the small intestine?
the way that the frequency of segmentation decreases as you move out of the duodenum to the jejumen to the Ileum.
What causes stomach growling?
the migrating motility complex
Describe 3 aspects of the migrating motility complex?
1. Weak, repetitive, peristaltic waves (moves a short distance then dies out, occurs between meals when segmentation ceases)

2. "internal housekeeper": sweeps intestine clean between meals

3. motilin : hormone secreted by endocrine cells of small intestine regulates migrating motility complex
Describe the iliocecal juncture of the small intestine?
1. sphincter

2. between the small and the large intestine

3. prevents contamination of small intestine by colonic bacteria
What 2 things enhances the relaxation of the iliocecal sphincter?
1. hormones (gastrin)

2. local intrinsic neural plexuses that register distension and relax to open sphincter
The small intestine does not secrete what into the lumen?
digestive enzymes
What does secrete enzymes into the small intestine lumen?
What is completely digested in the small intestine due to enzymes from the pancreas?
What are fats digested to in the small intestine?
free fatty acids and monoglycerides
What two things need further digestion even after the pancreas has released enzymes into the lumen of the small intestine?
proteins and carbohydrates
What do exocrine cells in the small intestine secrete?
Aqueous salt and mucus solution (aka succus entericus)
What does the succus entericus from the exocrine cells provide?
1. protection and lubrication

2. lots of H2O for hydrolysis, a key part of digestion
Although the small intestine does not secrete digestive enzymes what does it produce?
it produces enzymes
Where do the enzymes produced by the small intestine act?
they act intracellularly at the brush border to complete digestion
What does the lumen take care of?
What does the brush border take care of?
proteins and carbs
Describe the structure of the brush border?
special, hairlike projections on epithelial cells of small intestine
The plasma membrane of the brush border of the small intestine contains what 3 categories of membrane bound enzymes?
1. Enterokinase

2. Dissacharidases (maltase, sucrase, lactase)

3. Aminopeptidases
Describe enterokinase (membrane-bound enzyme of brush border of small intestine)?
activates pancreatic enzyme, trypsinogen
Describe the dissacharidases (maltase, sucrase, lactase) found in the brush border of the small intestine?
complete carbohydrate digestion
(membrane bound enzyme)
Describe aminopeptidases of the brush border of the small intestine?
(membrane bound enzyme)
hydrolyzes small peptide fragments into AA components
Of all the electrolytes which one's are the only ones with controlled absorption?
Calcium and Fe
What is lacking or nonfunctional in lactose intolerant people?
What does the villi increase?
surface area on the brush border
The central lacteal is what kind of vessel?
lymph vessel
What in the brush border is a source of new epithelial cells (contains stem cells)?
The crypt of Lieberkuhn
Where are the transport mechanisms of the small intestine observed?
In the epithelial cells in the inner lining of the small intestine (there are a variety of transport mechanisms)
2 types of transport mechanisms seen in epithelial cells in small intestine?
1. Energy dependent Na+ transport absorption drives passive water absorption

2. Carbohydrate and protein: both absorbed by 2ndary active transport (except fructose) and enter blood
What in the small intestine drives passive water absorption?
energy dependent Na+ transport absorption
How does energy dependent Na+ transport absorption drive passive water absorption?
1. Na+ is pumped from the lumen into the interstitial fluid, then it enters the capillaries by diffusion

2. Na+ transport creates osmotic pressure, water follows the sodium
How are proteins and carbodhydrates absorbed? What do they enter?
absorbed by 2ndary active transport and enter blood
What is the exception to the fact that carbs are absorbed by 2ndary active transport? Explain.
Fructose is the exception. it has passive facilitated diffusion
Describe transport of the carbohdrates glucose and galactose?
2ndary active transport, co-transported by Na+
Amino acids and peptides transport is what type?
2ndary active
What enzymes involved in carbohydrate digestion?
lactase, maltase, and sucrase, salivary amylase, pancreatic enzymes
What does carbohydrate digestion leave us with?
Energy is needed for what transport during carbohydrate digestion? What goes along for the ride?
energy needed from Na+ transport, glucose and galactose go along for the ride
Proteins can get in our body how?
exogenous or endogenous
What enzymes are involved in the digestion of protein?
pepsin, pancreatic proteolytic enzymes
Carbohydrate digestion and protein digestion ultimately end up being released into the what?
Digestion of fat ultimately ends up being released where?
into lymph system thru central lacteal
There are no enzymes where?
in brush border of small intestine
Why don't lipids need transport molecules?
passive diffusion because lipophilic
The absorption of vitamins is mainly what?
Water-soluble vitamins are absorbed with what?
Fat-soluble vitamins are absorbed in what?
Iron and Ca+ absorption is what?
Only part of ingested iron can be what?
Some absorbed iron is immediately transported where?
to the blood
What carries some iron to the bone marrow? For what reason?
Transferrin, for RBCs
Where is excess iron stored?
in ferritin pool
Where is unused iron lost?
in the feces
Fe is used in the production of what?
Most calcium is absorbed by what?
active transport
Approx. how much of ingested calcium is absorbed and how much is eliminated?
about 2/3 absorbed and 1/3 is eliminated
What needs to be present for the active transport of calcium?
vitamin D (parathyroid is also involved)
Most absorbed nutrients immediately pass through what?
immediately pass thru the liver for processing (except fats)
Why don't fats pass thru the liver for processing?
because they are in the lymph
Venules leave the small intestine via what? Where do they empty?
leave via villi and empty into the hepatic portal vein
What does the hepatic portal vein carry?
blood and all absorbed contents to the liver
Products of digestion are subject to what?
metabolic processing in the liver
Once in the liver any absorbed toxic substances are what?
3 major categories of nutrients?
1. carbohydrates

2. proteins

3. fats
Enzymes for digesting carbohydrates.
1. amylase

2. Disaccharidases (maltase, sucrase, lactase)
What are the 2 different sources for amylase?
1. salivary glands

2. exocrine pancreas
What is the site of action for amylase secreted by the salivary glands?
mouth and body of stomach
What is the site of action for amylase secreted by the exocrine pancreas?
small intestine lumen
What is the action of amylase secreted by the salivary glands?
hydrolyzes polysaccharides to disaccharides
What is the action of amylase secreted by the exocrine pancreas?
Hydrolyzes disaccharides to monosaccharides
The end product, absorbable units of nutrients, produced by amylase?
monosaccharides, especially glucose
Enzymes responsible for digesting proteins? (3)
1. Pepsin

2. Trypsin, chymotrypsin carboxypeptidase

3. aminopeptidases
Source of pepsin?
stomach chief cells
Site of action of pepsin?
stomach antrum
Action of pepsin?
hydrolyzes proteins to peptide fragments
Source of trypsin etc?
exocrine pancreas
Site of action for trypsin etc.
small intestine lumen
Action of trypsin etc.
attack different peptide fragments
Source of aminopeptidases?
small intestine epithelial cells
Site of action for aminopeptidases?
small intestine brush border
Action of aminopeptidases?
hydrolyzes peptide fragments to AAs
Absorbable units of nutrients derived from proteins?
AAs and a few small peptides
2 enzymes responsible for digesting fat?
1. lipase

2. bile salts (NOT AN ENZYME)
Source of lipase?
exocrine pancreas
Source of bile salts?
Site of action for both lipase and bile salts?
small intestine lumen
Action of lipase?
hydrolyzes triglycerides to fatty acids and monoglycerides
Absorbable nutrients that are the end result of fat?
fatty acids and monoglycerides
Action of bile salts?
emulsify large fat globules for attack by pancreas lipase
The large intestine is mainly what?
a drying and storage organ
Where is most digestion and absorption accomplished?
small intestine
What does the colon receive?
indigestible food, unabsorbed biliary components, and any remaining fluid
What does the colon extract and what does it eliminate?
extracts water and salt...eliminates feces
What does the colon have that helps fight diseases?
Describe the smooth muscle of the anal sphincter?
internal...relaxes under ANS do not have voluntary control over it
Describe the skeletal muscle of the anal sphincter?
external...voluntary control
What kind of contractions slowly shuffle colonic contents back and forth?
Haustral contractions
Are haustral contractions propulsive?
no, they are simply for mixing purposes
How are haustral contractions initiated?
By autonomous rhythmic contractions of smooth muscle in wall of large intestine

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