GI Secretory Functions, Digestion, Absorption Flashcards
What are the gland types of the digestive tract?
Unicellular mucous glands Crypts of Lieberkuhn Tubular glands Complex glands: -Salivary glands -Pancreas -Liver
What are the mechanisms of stimulation?
Food contact and local epithelial stimulation
Autonomic stimulation (parasympathetic mostly)
Higher brain centers
Hormonal stimulation
What are the functions of mucous (secretion of water and electrolytes?
Adheres to food and other particles
Spreads thin film over surfaces
Coats wall of gut, preventing actual contact of food.
What causes fecal particles to adhere to one another?
Mucous
What is resistant to digestion by GI enzymes and has amphoteric properties making it useful for buffering small amounts of acids and bases?
Mucous
What are the salivary glands?
Parotid, submandibular and sublingual
Parotid gland secretions are what?
Almost entirely serous
Submandibular and sublingual secretions are waht?
Mixed
Where does the first stage of salivary secretion of ions occur?
In acini
First stage of salivary secretion of ions contains what?
ptyalin (alpha-amylase)
First stage of salivary secretion of ions is typical of what?
Extracellular fluid
Where does the second stage of salivary secretion of ions occur?
In salivary ducts
In the salivary ducts there is active and passive secretion and reabsorption of what ions?
Active reabsorption of sodium ions
Active secretion of potassium ions
Active/passive secretion of bicarbonate ions
Passive reabsorption of chloride ions due to -70 mv in ducts
What is the final ionic concentration of saliva normally?
?
What is the concentration of ions during maximal secretion?
?
Nervous regulation of salivary secretion is via what?
parasympathetic system
List factors that stimulate or inhibit salivary secretions
?
What are the secretory cell types in gastric glands?
Mucous neck cells
Chief (peptic) cells
Parietal (oxyntic) cells
What cell secretes pepsinogen?
Chief cells
What is pepsinogen?
The inactive form of pepsin
What is pepsin?
A proteolytic enzyme that functions at a pH range of 1.8 to 3.5
What is the release of pepsinogen stimulated by?
Ach from vagus nerves or gastric enteric nervous plexus
Response to acid in stomach
Chief cells also release what in addition to pepsinogen?
Intrinsic factor
What cell secretes HCl?
Parietal cells
Describe how HCL is made by parietal cells?
H2O in the cell breaks down into H and OH
Hydrogen is pumped out in exchange of K
K leaks out
OH combines with CO2 in the cell to form HCO3
HCO3 is pumped into the extracellular fluid in exchange for Cl
Cl is secreted through chloride channels into the canaliculi
*Na+ is reabsorbed into the cell due to Na+-K+ basolateral pump
Stimulation of gastric secretions is via what nervous system?
parasympathetic
What is gastrin secreted by?
By gastrin (G) cells in pyloric glands
What are the two forms of gastrin?
G-34 and G-17 (more abundant)
The release of gastrin is in response to what?
To the presence of protein in pylorus
Gastrin in the pylorus causes what?
enterochromaffin-like cells to release histamine
What does the presence of histamine cause?
The secretion of HCl
What are the phases of gastric secretions?
Cephalic phase
Gastric phase
Intestinal phase
Describe the cephalic phase
Via the vagus nerve and is stimulated when food is seen or smelled. Parasympathetics excite pepsin and acid production
Describe the gastric phase
It is the phase when food is in the stomach
Local nervous secretory reflexes
Vagal reflexes
Gastrin-histamine stimulation
Describe the intestinal phase
Feedback to the stomach in result of the material being feed to it
HCl + NaHCO3 ->
NaCl + H2CO3
What are the digestive enzymes for proteins?
Trypsin, chymotrypsin, and carboxypolypeptidase (pancreatic secretions and by glandular cells)
What inhibitor is secreted by the pancreas?
Trypsin inhibitor
What is the purpose of trypsin inhibitor?
Necessary to prevent the action of trypsin on the pancreatic tissues themselves
What are the digestive enzymes for carbohydrates?
Pancreatic amylase
What are the digestive enzymes for fat?
Pancreatic lipase, cholesterol esterase, phospholipase
pancreatic secretions
How are bicarbonate ions produced for pancreatic secretion?
H20 + CO2 (from the blood) (involves carbonic anhydrase) ->
H2CO3 -> HCO3 + H
HCO3 + Na are actively transported into duct lumen
Hydrogen ions are exchanged for sodium ions
What regulates pancreatic secretions?
Acetylcholine, cholecystokinin, secretin
Acetylcholine for pancreatic secretion regulation comes via what?
Parasympathetic nerves and enteric nervous system
Cholecystokinin release is stimulated by what?
Presence of food in upper intestine
What is cholecystokinin secreted by?
Duodenal and upper jejunal mucosal cells
What does the release of cholecystokinin result in?
Dramatic increase in secretion of pancreatic enzymes
The release of secretin is stimulated by what?
Presence of acidic food in upper intestine
What is secretin secreted by?
Duodenal and upper jejunal mucosal cells
What does secretin stimulate?
Release of large amounts of sodium bicarbonate
Bile is secreted continuously by what?
Hepatocytes in the liver
Where is bile stored?
In the gallbladder until needed
In the gallbladder, how is bile concentrated?
By active transport of sodium followed by secondary absorption of chloride ions, water, and other diffusible constituients
What factors stimulate the release of bile from the gall bladder?
Presence of fatty food in duodenum
How is bile salts synthesized in liver?
Cholesterol is converted to cholic acid or chenodeoxycholic acid, which are then conjugated with glycine or taurine
What are the functions of bile salts?
Emulsification
Complex with lipids to form micelles for absorption across intestinal mucosa
What are the causes of gallstones?
Too much absorption of water from bile
Too much absorption of bile acids from bile
Too much cholesterol in bile
Inflammation of eptihelium
What are the main cell types that make up crypt of Lieberkuhn?
Goblet cells
enterocytes
List the secretions of Paneth cells
?
Describe condensation reactions
Used to remove hydrogen ions and hydroxyl ions from building block in order to allow the bonding of monomer into polymers
Describe hydrolysis
Incorporating water molecules in such as a way that polymers are broken down into monomers
