What are the effective stimuli for the Gastric Phase of secretion? 

distension of the stomach (mechanoreceptors)

and

bathing of gastric mucosa w/ amino acids and peptides, which stimulates G cells

Long reflexes are also called ________? 

vagovagal reflexes

-meaning that both afferent and efferent impulses are carried by neurons in the vagus nerve 

True or False?

Gastrin is released when the pH is below 2 

False 

Gastrin release is inhibited when the antral pH drops below 3. Acid in the stomach is believed to stimulate somatostatin secretion, thereby preventing gastrin release.

In the fingerprint of Parotid Saliva, what are the relationships of K+ and Cl- to plasma, respectively? 

K+ is always higher than plasma

(highest at low flow rates)

Cl- is always less than in plasma

(highest at high flow rates) 

What are the antibacterial compounds present in saliva? 

Lactoferrin

(chelates iron needed for bacterial growth)

lysozyme

(attacks bacterial cell walls)

binding glycoprotein for IgA

(ingredient in secretory IgA - immune response against viruses and bacteria) 

What enzymes are present in saliva and what do they do? 

 a-amylase, lingual lipase, & kallikrein

a-amylase (aka ptyalin) cleaves internal a 1,4 glycosidic bonds

lingual lipase hydrolyzes lipid. can remain active through stomach and intestine 

kallikrein converts plasma protein to bradykinin (potent vasodilator) 

Saliva in the intercalated duct is ____ to plasma.

A. Hypertonic

B. Hypotonic

C. Similar in ionic composition 

C. Similar in ionic composition 

Saliva in the striated duct is ______ to plasma.

A. Hypertonic

B. Hypotonic

C. Similar in ionic composition 

B. Hypotonic

-striated duct epithelium relatively impermeable to water, net absorption of Na+ and Cl- exceeds net secretion of K+ and HCO3- 

Saliva has the highest ___ concentration of any digestive juice.

A. Na+

B. K+

C. Cl-

D. HCO3- 

B. K+ 

Does saliva become more or less isotonic with plasma at high rates of secretion? 

Saliva approaches being isotonic with plasma at high rates of secretion. 

What compound can inhibit Na+/K+ pumps? 

Ouabain 

-Na+/K+ ATPase is located on the basolateral membranes of gall bladder cells and is responsible for the high concentration of bile salts.

-Aspirin can also inhibit Na+/K+ ATPase in the stomach, thereby decreasing membrane potential and damaging buffer capacity of the mucus membrane 

What gastic juice ingredient is required for the absorption of B12 by the ileal mucosa? 

Intrinsic Factor (IF) 

-secreted by parietal cells in humans 

What do Chief Cells secrete?

Chief cells secrete pepsinogen, the precursor to pepsin.

They also secrete gastric lipase, which, like lingual lipase, is an acidic lipase; both are particularly important for babies, but play a less important role in adults due to activity of pancreatic lipase.

What is Zollinger-Ellison Syndrome (ZES)? 

Disorder where excess gastrin production causes increased HCl secretion. Gastrin secreting tumors often the cause, with ulcers in stomach and duodenum from increased acid. 

Omezaprole might be prescribed to treat ulcers. 

What is Steatorrhea? What can cause it? 

Steatorrhea is excess lipids in the stool. Can be due to lack of bile acids and defects in pancreatic enzymes (lipase) or mucosal cells (such as in CF patients).  

What do parietal cells secrete?

Where are they located? 

Parietal cells secrete HCl and IF (in humans).

They are located in the oxyntic gland area of the proximal stomach. 

What is the largest ion gradient "known to man"?

What drug inhibits it? 

The -70 to -80 mv potential across the resting oxyntic gland mucosa is caused by the entry of Cl− into the parietal cell and its uphill movement from the blood into the lumen. The movement of Cl− from blood to lumen against both electrical and chemical gradients is the result of excess OH− (and hence HCO3) in the cell after the H+ has been pumped out via the K+/H+ pump.
 

Omeprazole (aka Prilosec) is a proton pump inhibitor that binds irreversibly. It binds selectively in acidic environments (not to proton pumps in kidney or colon), thus making it a "brilliant drug". 

Gastric juice is isotonic with plasma:

A. at high rates of secretion

B. at low rates of secretion 

C. at all rates of secretion

D. at no point 

C. at all rates of secretion 

What are the 3 major stimulantsof acid secretion by the gastric parietal cells? 

Gastrin (endocrine)

-"little" gastrin most active (17aa), 4 terminal peptides active part and same as CCK 

ACh (neurocrine)

histamine (paracrine - released from ECL cells in response to gastrin and ACh) 

Somatostatin and prostaglandins regulate parietal cell secretion through what G-protein receptor? 

Gi (inhibitory) 

How do gastric juice concentrations of H+, Na+, Cl- and K+ compare to those found in plasma?

At all rates of secretion the concentrations of H+, K+, and Cl− are higher than those in plasma, and the concentration of Na+ is lower than that in plasma. Gastric juice and plasma—regardless of the secretory rate—are approximately isotonic.

True or False:

Somatostatin inhibits Parietal Cell, G Cell, and ECL secretions. 

True

(HCl, Gastrin, and Histamine) 

Which is the path less taken?:

G cell } ECL } Parietal cell 

or

G cell } Parietal cell 

The direct pathway is the one less taken:

(G cell sectretes gastrin which directly stimulates the Parietal cell secretion of HCl) 

The indirect pathway is the more significant pathway: (G cell secretes Gastrin, which stimulates ECL cell to release histamine, which stimulates Parietal cell) 

Which pancreatic enzymes are secreted by the acinar cells in their active form? In their inactive form? 

Pancreatic lipase and amylase are secreted in their active form.

Pancreatic proteases are stored and secreted in their inactive form (zymogen) and converted in the lumen, so as to avoid self-digestion.

In humans, secretin is potentiated by what substance(s)? 

ACh and Insulin

True or False?

Undigested proteins do not stimulate CCK.

True. 

What stimulates CCK ?

What inhibits it? 

Protein products stimulate CCK release and fatty acids longer than 8 carbon atoms release CCK.

Trypsin inhibits CCK 

What substance potentiates the effects of ACh on the parietal cell?

What drug(s) can effectively block acid release by interrupting this potentiation?

histamine potentiates ACh

Tagement (Cimetidine) blocks H2 receptors

atropine blocks M3 receptors

Which second messenger pathway does secretin activate? 

cAMP 

What are the 2 most important primary bile acids?

What are they made from? 

-Cholic acid (3 OH) and chenodeoxycholic acid (2 OH)

-synthesized from cholesterol by cholesterol 7a hydroxylase 

Bile acids form _____ as a result of their amphopathic properties. 

micelles 

In vivo, most bile acids exist as conjugates of which amino acid(s)? 

Taurine or glycine 

True or False:

Bile acids are secreted as needed for digestion, and then excreted with the feces. 

False

Bile acids are secreted continuosly by the liver and recycled via the enterohepatic pathway. 

How and where are secondary bile acids made?

Primary bile acids are converted into secondary bile acids by bacteria in the intestine. The bacteria either deconjugate or dehydroxylate the bile acids, which makes them more lipid-soluble.

cholic acid } deoxycholic acid

chenodeoxycholic acid } lithocholic acid

What is the choloretic effect? 

The suppression of bile acid synthesis during recycling (probably by inhibiting 7-a hydrolase) 

During the cephalic phase stimulation of the lower digestive organs is mediated entirely by _________ . 

The vagal nerve 

What postganglionc transmitter stimulates the gastric parietal cell during the cephalic phase? 

What blocks this stimulation? 

ACh

Low doses of Atropine (M3 receptor) 

What are the 2 phases of the intestinal phase?

What marks each? 

Stimulatory and Inhibitory

Food enters duodenum during stimulatory phase and acid secretion has to be maintained until stomach is emptied.

During inhibitory phase CCK inhibits acid secretion by activation of the D cell. GIP is released from K cells and also inhibits parietal acid secretion. Both CCK and GIP are released by fatty acids.

Secretin inhibits G cells and decreases parietal response to secretagogues. 

80% of pancreatic juice is secreted during what phase? 

Intestinal 

Monitor peptide and CCK releasing peptide 

What is the "law of the intestine"? 

the coordinated peristaltic response by the intestine to a stimulus of say, food.

Contraction above, relaxation below, point of stimulation. Repeat. 

- invoked to explain how food is normally moved through small bowel.

What is the Migrating Motor Complex (MMC)? 

The transient locus of wave-like contractions that take place in fasting humans. It takes approximately 1.5 hours for it to sweep from the duodenum through the ileum.

Feeding abolished MMCs and starts more or less continuous contractions of varying amplitude. 

What are Insterstitial Cells of Cajal (ICCs)? 

They are pacemaker-like cells in the smooth muscle of the GI tract that govern contractions. Determine maximum contractile frequency. Branched processes form gap juntions with smooth muscle, couple electric activity of longitudinal and smooth layers.

True or False?

Slow wave activity (BER) always takes place whether or not contractions are taking place. 

True 

What effect does Epinephrine have on intestinal contractions?

Serotonin?

Prostaglandins? 

Epinephrine inhibits contraction.

Serotonin and certain prostaglandins stimulate contractions. 

What effect does CCK have on gastric motility?

Gastrin?

Motilin?

Insulin?

Secretin?

Glucagon? 

CCK, gastrin, motilin, and insulin stimulate motility.

Secretin and glucagon inhibit contractions. 

True or False:

During digestion of a meal, most contractions are of the segmenting type. 

True

-short peristaltic contractions occur randomly during this time, too. 

What are two external features of the large intestine not found on the small intestine? 

taeniae coli and haustra

-note that rectum does not have either 

What is Hirschsprung's Disease? 

congenital mega-colon

leads to severe constipation

treated with surgical removal of diseased segment 

What is Hartnup's disease? 

A rare hereditary disorder in which one of the major neutral amino acid transport proteins is deficient in the brush border of the small intestine and the proximal renal tubule. Individuals with Hartnup disease have elevated urinary levels of certain neutral amino acids. However, such patients are not malnourished because the affected neutral amino acids are well absorbed as components of dipeptides and tripeptides in the upper small intestine.

 

Direct neurocrine stimulation of the parietal cell by ACh is through release by

A. Sympathetic nerve terminals

B. Parasympathetic nerve terminals 

What signaling pathway and second messenger are used? 

B. Parasympathetic nerve terminals 

-ACh binds to M3 receptor and initiates Gq } IP3 } Ca

pathway to stimulate H+/K+ pump 

What stimulates the D cell?

What inhibits it? 

Gastrin stimuates the D cell to release Somatostatin

ACh inhibits the D cell 

What blocks the M3 receptor in the parietal cell? 

Atropine

-was once given to people for ulcers 

What do Ca++ and cAMP do in the parietal cell? 

They open Cl- and K+ channels 

True or False:

CO2 diffuses across the parietal cell membrane 

False. The CO2 needed for HCO3- production comes from parietal cell metabolism. HCO3- is transported into the blood using its own electrochemical gradient, and provides energy needed for Cl- entry. 

CCK type B receptors:

Where are they found?

What binds to them?

What signaling mechanism do they use?

What inhibits them? 

Found on the basolateral membrane of parietal cells

Gastrin Binds

Use same signaling pathway as M3 (Gq } IP3 } Ca)

*No specific inhibitors* 

What parietal cell regulators utilize the Adenyl Cyclase/cAMP pathway? 

Histamine  (H2 receptors)

Somatostatin (Somatostatin receptors - inhibitory)

Prostaglandins (Prostaglandin receptors - inhibitory) 

True or False:

ECL cells are found in the gastric epithelium 

False. They are found in the mucosa at base of the glands in fundus. Aids in histamine's paracrine function. 

Is the mucous secreted by the mucous neck cells soluble or insoluble mucous? 

Insoluble.

Helps to protect stomach from pepsins and acid, along with bicarbonate secretion,

prostaglandin E2, tight junctions, and pressure in gastric pits (tornados) 

What is the difference in transporter expression between parietal cells near the surface of gastric pits and those deep in the pits? 

Surface parietal cells express HCO3/Cl transporters on their basolateral membrane

Deep pit parietal cells express Na/K/2 Cl transporters on their basolateral membrane, which may help create an environment less prone to ulcers. 

What do Aspirin, Acetaminophen, and Celebrex all have in common?

What does Aspirin do that the others do not? 

All are anti-inflammatory drugs

Only Aspirin is a COX-1 inhibitor (decreses prostaglandin and prostacyclins - damages gastric mucosal lining) 

How do stress ulcers form? 

a-adrenergic agonists are present in high amounts and decrease gastric HCO3- secretion. 

ACh, released from the _________ is the most important neurocrine regulator of the pancreas.

How do sympathetic nerves affect the pancreas? 

Vagus nerve

They mainly affect blood flow 

What will a vagotomy do? 

-Reduce pancreatic secretions

-eliminate primary peristaltic wave during swallowing

-abolish receptive relaxation of proximal stomach

-disorganize the slow wave responsible for duodenal emptying

Where are CCK type A receptors expressed? 

In rats, on the basolateral membrane of the pancreatic acinar and duct cells, and in the "vicinity of the pancreas" in humans.

CCK only a direct regulator in rodents. Activates vagovagal pathway in human pancreatic acinar cells. 

True or False:

The type of enzyme released by your pancreas is partially diet-dependent. 

True.

- there are over 20 kinds of pancreatic enzymes. 

-in addition to proteases, lipases, and amylases, there are:

-deoxyribonuclease and ribonuclease (nucleic acids)

-pancreatitis associated protein (bacteriostatic action, helps maintain pancreatic integrity when injured)

What secretions can reach a pH of 8 at maximal secretory rate? 

saliva and pancreatic juice 

How does secretin affect CFTR channels? 

- Secretin binds to basolateral membrane in pancreatic duct cells.

- Activates cAMP

- cAMP opens CFTR Cl- channels at the apical membrane

(Negative lumen established by Cl- transport encourages Na+ and H2O to follow through paracellular channels. How CF results in thick mucous) 

achalasia and dysphagia are disorders of what part of the body? 

Esophagus

achalasia, a failure of the lower esophageal sphincter to relax, can lead to dysphagia, difficulty swallowing. 

What is stercobilin?

Urobilin? 

Bile pigments (made from bilirubin)  that give feces and urine their color, respectively.

What is cholecystectomy?

Cholelithiasis? 

Removal of the gall bladder

Gall stones 

What are the 3 stages of deglutition? 

(swallowing)

1. oral stage - voluntary

2. pharyngeal phase - involuntary 

(trachea closed off)

3. esophageal phase - involuntary

(peristaltic waves move bolus through relaxed esophageal sphincter)

True or False:

Gastrin increases the tone of the lower esophageal sphincter. 

True