2 - Gastrointestinal 02 Flashcards
What causes acute pancreatitis?
Pancreatic secretions build up in the pancreas and overwhelm the effects of trypsin inhibitor
Where is pancreatic bicarb secreted?
Mainly in the epithelial cells in the ductules and ducts leading from the acini
What are the basic stimuli for pancreatic secretion?
- Acetylcholine
- Cholecystokinin (CCK)
- Secretin
Describe the cephalic phase of pancreatic secretion
acetylcholine released by the vagus causes moderate amounts of secretion (20%) into the acini
Describe the gastric phase of pancreatic secretion
nervous stimuli accounts for 5-10% of secretion
During what phase does pancreatic secretion become copious?
Intestinal Phase
________ stimulates copious secretion of bicarb ions, which neutralizes acidic stomach chyme in the intestines
secretin
Describe the intestinal phase of pancreatic secretion
Acid from the stomach releases secretin from the wall o fthe duodenum
Fats and amino acids from the duodenum release CCK
Secretin and CCK are absorbed in the blood
secretion causes copious secretion of pancreatic fluid and bicarb
CCK causes secretion of enzymes
How much bile does the liver secrete each day?
600-1000 ml/day
Bile serves two functions:
- Fat digestion*: Bile acids emulsify large fat particles and aid in absorption of digested fat through the mucosal membrane
- Excretion*: Bile serves as a means of excretion of bilirubin and excess cholesterol (among many other things)
What is the purpose of the gallbladder?
stores and concentrates bile
By far the most abundant substances secreted in the bile are:
bile salts
What substance stimulates gallbladder emptying?
CCK
gallbladder emptying requires relaxation of the _______
sphincter of oddi
The precursor of the bile salt is:
cholesterol
Without the presence of bile salts, what would happen?
40% of ingested fats would be lost into the feces
often leads to a metabolic deficit
What percentage of bile salts used in the intestines are reabsorbed into the blood?
95%!
Why does chronic inflammation of the gallbladder lead to gallstones?
Changes the absorptive characteristics of the GB mucosa
Allows excessive absorption of water and bile salts, but leaves behind cholesterol
Cholesterol gets more and more concentrated
Begins to precipitate and form crystal, which progress to gallstones
Secretion of mucus into the small intestine is acheived by _______ glands
Brunner’s Glands
located in the wall of the first few cm of the duodenum
Makes sense, because this is the area right before bicarb rich secretions from the pancreas and GB enter via the sphincter of oddi
Why do peptic ulcers often occur in the duodenum, as well as the stomach?
Brunner’s glands are inhibited by sympathetic stimulation, leaving the duodenal bulb unprotected
What are the crypts of liberkuhn?
small pits over the entire surface of the SI
Comprised of goblet cells and enterocytes
What are enterocytes?
Cells that secrete large quantities of water and electrolytes
reabsorb the water and electrolytes along with the end products of digestion
They crypts of Lieberkuhn produce marked secretion of watery fluid into the intestines. How do they do this?
- actively secrete Cl
- Actively secrete bicarb
Secretion of these causes an electrical drag of positively charged Na ions through the membrane into the secreted fluid
This mass movement causes osmotic movement of water into the gut
What is the life cycle of an intestinal epithelial cell?
5 days
The most important regulator of SI secretion is:
local enteric nervous reflexes
How dose the mucosa of the LI differ from the SI?
Both have crypts of lieberkuhn
but the LI contains no villi
The epithelial cells only secrete mucus
What does elevated Parasympathetic stimulation of the LI cause?
Excess mucus secretion
Ropy, mucoid diarrhea
What are polyscaccharides?
How are they formed?
monosaccharides bound to one another by condensation:
A H+ is removed from one monosaccharide and the OH- is removed from another to form water
What is hydrolysis?
The opposite of condensation
returning the H and OH from H2O, thereby separating polysaccharides into monosaccharides
Almost the entire fat portion of the diet consiste of ______
triglycerides
What is the composition of a triglyceride?
Three fatty acid molecules condensed with a single glycerol
How is the digestion of carbs, fats, and proteins similar?
How is it dissimilar?
All three are broken down by hydrolysis
The only difference is the types of enzymes required to promote hydrolysis for each type
All of the digestive enzymes are _______
proteins
Where does carbohydrate digestion begin?
The mouth
Starches and maltose are broken down into _______
Lactose is broken down into _______
Sucrose is broken down into _____
Glucose
Galactose and Glucose
Fructose and Glucose
Proteins are amino acids bound by
peptide linkages
Why is cholesterol considered to be a fat if it contains no fatty acids?
Sterol compound, but it exhibits similar physical and chemical characteristics
derived from fats and metabolized similarly
Most protein digestion results from:
pancreatic proteolytic enzymes:
trypsin, chymotripsin, carboxypolypeptidase, elastase
Where are peptides finally broken down into amino acids?
inside the cytosol of the enterocyte
What is the first step in fat digestion?
Emulsification of fat by bile acids and lecithin
Why is it so critical that fats be emulsified?
Lipases are water soluble. They can only attach fat globules on their surface, so the surface area has to be high
What is the role of bile salts in fat digestion?
They aid in reabsorption by forming micelles
They “ferry” nonsoluble fatty acids from to the brush border epithelial cells
They are absorbed into the blood via the epithelium
No cholesterol is absorbed from the gut without the help of:
bile salt micelles
Why is the stomach such a poorly absorptive area?
lacks villus
tight cell junctions
Only highly _____ soluble substances can be absorbed in small quantities from the stomach
lipid
aspirin and alcohol
What are valvulae conniventes
Folds of Kerckring
increase the surface area of the absportive mucosa by about three-fold
Describe how the intestinal mucosa surface area is increased
Folds of Kerckring (3x)
Villi (10x)
Brush border (microvilli) (20x)
Combined, increase absoprtive area by 1000x
How is sodium reabsorbed from the gut
Actively pumped out of epithelial cells into the blood via ATPase pump, which reduces the sodium concentration inside the cell
sodium moves down this steep gradient from the chyme into the epithelial cell
Aldosterone triggers intestinal sodium reabsorption primarily in the:
Large intestines
How is bicarb reabsorbed in the small intestines?
Sodium-hydrogen countertransport
These H+ ions combine with HCO3 to form H2CO3
Converted into H2O and CO2
CO2 is blown off through the lungs
What role does the Large Intestine play in bicarb regulation?
Can secrete HCO3- in exchange for absorption of Cl-
Provides the LI with bicarb to neutralize the acid products formed by bacteria
How does cholera cause life-threatening diarrhea?
Cholera toxin enters epithelial cells and stimualtes cAMP formation
Opens tremendous numbers of Cl channels, allowing Cl to flow rapidly from inside the cell tot he intestines
activates a sodium pump that pumps sodium ions into the crypts to keep a net charge
Water pours into the gut
Besides sodium, what electrolytes are actively reabsorbed in the intestines?
calcium, iron, potassium, magnesium
phosphate
How is glucose reabsorbed?
Transported by a sodium co-transport (SGLT1) into the epithelial cell
diffues through GLUT2 into the blood
How much sodium and chloride are lost in the feces each day?
Almost none
What are alternative names for the proximal and distal colon
Correspond with their roles:
absorbing colon
storage colon
How does sodium transport in the LI differ from the SI?
LI has much tighter junctions, so there is less backleak
the LI can absorb sodium ions more completely and against a stronger gradient,
especially when aldosterone is present
This means the LI is also ideal for reabsorbing water
How much fluid can the intestines absorb each day?
5-8 L
the rest is excreted as feces
What is the composition of feces?
75% water
25% solid matter which is composed of:
dead bacteria, fat, inorganic matter, protein, and roughage
What causes the brown color of feces?
stercobilin and urobilin, both derivatives of bilirubin
What causes the odor of feces?
bacterial actions produce:
indole
skatole
mercaptans
and hydrogen sulfide
_______, _______, and ________ increase the rate of gastric motility.
How?
Gastrin
Motilin
Vagus PNS
Lower the threshold potential
______ and _____ decrease gastric motility. How?
SNS
Secretin
raise the threshold potential
What stimulates secretion of CCK?
What does it do?
products of fat digestion in the duodenum
inhibits food intake
reduces gastric motility
decreases gastric emptying
What is the effect of hyperglycemia on gastric emptying?
Hypoglycemia?
Decreases
Increases
Parietal cells secrete what? (3)
HCl
intrinsic factor
gastroferrin
Chief cells secrete what?
pepsinogen
acidic lipase
In the pyloric glands, G cells secrete ______
Enterochromaffin-like cells secrete ______
and
D cells secrete ______
gastrin
histamine
somatostatin
What are the three main actions of gastric HCl?
- dissolve food
- act as a bactericide
- convert pepsinogen to pepsin
A high rate of gastric secretion results in _______ in the venous blood
“alkaline tide”
may result in alkaline urine as well
What hormones inhibit gastric acid secretion?
Somatostatin
secretin
CCK
GLP1
ANP
Prostaglandins
What stimulates acid secretion?
vagus nerve –> Ach–>Gastrin –>Histamine–> Parietal cells make acid
ALSO:
caffeine
calcium
ghrelin
What is special about gastric lipase?
Unlike pancreatic and intestinal lipases, it can be active in an acidic environment
_________ and ________ protect the mucosal barrier by stimulating secretion of mucus and bicarb and inhibiting acid secretion
prostaglandins
nitric oxide
The cephalic phase of gastric secretion is mediated by the ______ nerve via the _____ plexus
vagus
myenteric
Hyperglycemia inhibits _______ and increases _______ in the stomach
motility
secertion
What are the two main stimuli of the gastric phase?
- distention of the stomach (vagus and enteric local reflex)
- prescen of digested protein (stimulates gastrin)
Trace the small intestines
duodenum
treitz ligament
jejunum
ileum
ileocecal valve
The digestion and absorption of fat occurs in four phases:
- emulsification and lipolysis
- micelle formation
- fat absorption
- resynthesis of triglycerides and phospholipids
Calcium is primarily reabsorbed in the:
ileum
Why are bile salts important in the regulation of calcium uptake
Bile salts enhance calcium absorption by facilitating the absorption of Vitamin D, which is fat soluble
Anything that decreases fat absorption will decreases Ca levels
Following a massive hemorrhage, the intestinal cells will start reabsorbing more iron after about three days.
Why?
Intestinal stem cells in the crypts of Lieberkuhn sense the need
they take three days to develop and migrate to the tips of the villi, where they absorb iron
Ileogastric reflex inhibits _____ when ______
gastric motility
ileum is distended
Intestinointestinal Reflex inhibits _______ when ______
intestinal motility
one part of the intestines is overdistended or irritated
Gastroileal reflex stimulates ______ when _____
ileal motility and relaxation of ileocecal sphincter
gastric motility and secretion is increased
Trace the large intestines
cecum
ascending
transverse
descending
sigmoid
rectosigmoid sphincter
internal anal sphincter
external anal sphincter
What are paneth cells?
small intestinal cells near the crypts
produces defensins and other antimicrobial peptides and lysosomes
What are peyer patches?
lymph nodules in the SI containing collections of lymphocytes, plasma cells, and macrophages
Play a major role in antigen processing and immune defense
What is special about intestinal macrophages?
When they phagocytize pathogenic bacteria, they don’t produce any harmful cytokines
What is the largest solid organ in the body?
Liver
What are kupffer cells?
liver macrophages
largest population of tissue macrophages in the body
central to innate immunity and healing after liver injury
Also produce bilirubin
List the cells in the liver involved in immunity
Kupffer (macrophages)
Stellate
Natural Killer Cells
What is a choleretic agent?
Substance that stimulates the liver to secrete bile
List 4 choleretics
- high concentration of bile salts
- secretin
- CCK
- Vagal Stimulation
What happens to heme and globin once they are separated?
Globin is further broken down in AAs which are recycled to make proteins
Heme is converted biliverdin and iron
Iron attaches to transferrin and is stored in the liver or used by the bone marrow to make new RBCs
Biliverdin is converted to bilirubin and released into the plasma, where it binds to albumin
Bound to albumin it is called “unconjugated bilirubin”
What happens to unconjugated bilirubin?
In the plasma, serves as an antioxidant and provides cytoprotection
Once it gets to the liver, converted to water-soluble conjugated bilirubin
Excreted in the bile
What happens to conjugated bilirubin after it’s been secreted in bile?
Once it makes its way from the duodenum to the distal ileum, it is deconjugated by bacteria and converted to urobilinogen
Urobilinogen is reabsorbed in the intestines and transported to the kidney
Excreted as urobilin
Gives urine its yellow color
How are amino acids converted to carbohydrates?
Deamination
Removal of Ammonia
Why is elevated LDH indicative of hemolysis?
LDH is largely found inside RBCs
Why are elevated ALT and AST indications of liver damage?
Both are enzymes in hepatocytes that are critical in deamination
If they are present in the blood stream, it means liver cells are breaking down and these enzymes are escaping
How long does the liver store Vitamin A?
Several years!
Why is the exocrine pancreas called “exocrine”
it’s secreting substances into the inner lumen of the intestines, which is actually the outside of the body
