Digestion of nutrients, fluids, electrolytes physio , Liver & pancreas physio Flashcards
How much water is absorbed daily?
8.8 L/day
Which organ absorbs the most water?
Small Intestine
Where is the major source of water and electrolytes in a diarrheic stool from?
The small intestines
True or False? The volume of fluid moving from blood to lumen (secretion) is LESS than that moving from the lumen to the blood (absorption), thus resulting in net absorption.
TRUE!!!
True or False? Luminal fluid remains Isotonic with plasma while Stool water is Hypotonic.
FALSE!! Luminal fluid remains Isotonic with plasma while Stool water is HYPERTONIC
Fill in the blanks. “ In the luminal fluid , Water is absorbed from _______ solutions and enters _________solutions.”
Water is absorbed from HYPOTONIC solutions and enters HYPERTONIC solutions
True or False? the Na+ and Cl− concentrations in the lumen progressively become LOWER than the plasma concentrations.
TRUE!!
What is the major anion found in the duodenum?
Chloride (Cl-)
What are the major anions found in the Ileum?
Chloride (Cl- )and Bicarbonate (HCO3-)
What are the major anions in the Colon?
Chloride (Cl- )and Bicarbonate (HCO3-)
By what pathways do ions move between the gut lumen and the blood ?
Transcellular and paracellular pathways
Fill in the blanks. “ Passive movement of Na+ into or out the lumen is regulated by ________.”
Tight junctions OR zonnulae occludens
The rate of the passive movement of Na+ into or out the lumen is affected by?
Electrochemical gradients and Starling forces .
True or False? The tight junctions ( zonulae occludens) are more permeable to Na+ and Cl- than K+.
FALSE!! The tight junction is about twice as permeable to Na+ and K+ as it is to Cl−
Na + & K+ »_space;» Cl-
What is the Potential difference in the colon ?
20 mV
What is the Transmural Potential difference in the small intestine?
2 to 5 millivolts due to the relatively leaky epithelium.
True or False? The driving force for Cl− absorption is greater in the colon.
TRUE!!
What is the primary mechanism for colonic Na+ absorption?
Restricted diffusion
Which hormone increases the number of Na+ channels and enhances Na+ absorption?
Aldosterone
Restricted diffusion in the colon (electrogenic process) is dependent on channels that are under regulation by ?
Mineralocorticoids
True or False? All areas of the colon absorb Na+ & Cl-.
TRUE!!
What are the transport mechanisms for the absorption of Sodium and chloride in the small intestines?
- Movement of Na+ by restricted diffusion through water-filled channels.
- The co-transport of Na+ with organic solutes (e.g., glucose and amino acids)
- The co-transport of Na+ with Cl.
- The counter- transport of Na+ in exchange for H+
What is the main mechanism for absorption of Potassium(K+) in the small intestines ?
Diffusion through paracellular pathways
What is the main mechanism for absorption of Potassium(K+) in the colon?
The presence of K+ channels on the apical & basolateral membrane.
With regards to Water absorption, what is the function of the duodenum?
The duodenum functions to bring chyme into osmotic equilibrium with plasma (converts hypertonic chyme into isotonic chyme)
note: very little water absorption occurs in the duodenum
True or False? If a hypertonic solution is placed in the duodenum, isotonicity is reached by a rapid flow of water from blood to lumen, thereby increasing the volume of the original solution.
TRUE!!
What happens if a Hypotonic solution enters the intestines?
If a hypotonic solution enters the intestine, the flux of water from lumen to blood is greater than from blood to lumen and leads to net absorption of fluid. This in turn is followed by the isotonic uptake of fluid.
Which drugs can increase gut absorption of water?
Opiates - morphine and codeine
True or False? Adrenergic (α-receptor) or anticholinergic stimuli tend to increase absorption of water, but cholinergic or antiadrenergic stimuli tend to decrease absorption or water.
TRUE!!
The influence of aldosterone on Na+ transport is exerted at two points. What are those two points?
- There is an increase in Na+ permeability of the brush border membrane caused by the activation of new Na+ channels.
- In addition, aldosterone apparently increases the number of Na+ pump molecules in the basolateral membrane.
Fill in the blanks. “ In the Jejunum/ Ileum, osmotically active particles produced by digestion are removed by _____.”
Absorption
Where does the small and the large intestines secrete water and electrolytes?
In the crypt cells
note: secretion of water & electrolytes is responsible for maintaining a liquid chyme.
The trans-cellular secretion of what anion accounts for most of the secretory activity of the intestines?
Cl-
The apical membrane of the crypt cells contain at least two different Cl− channels. What stimulates the activation of these channels?
- One is activated by increases in intracellular Ca2+ and is stimulated by acetylcholine released by the enteric nervous system.
- The other type is stimulated by agents that increase cyclic adenosine mono- phosphate (cAMP) and is identical to the cystic fibrosis transmembrane conductance regulator (CFTR) that also is found in pancreatic and airway epithelial cells.
What are the agents that stimulate the Chloride channel on the intestinal crypt cells that activate adenylate cyclase to increase cAMP?
VIP
Secretin
Prostaglandin
Fill in the blanks. “ Active transport for calcium absorption is facilitated by?
Vitamin D & Parathyroid hormone
Where is calcium absorbed in the small intestines?
In the proximal small intestines
What is the name of the protein found in enterocytes that Calcium interacts with to minimize the rise in intracellular free Ca2+?
Calbindin
What is the name of the transporter that allows for the Exit of Ca2+ at the basolateral membrane against an electrochemical gradient ?
Ca2+-ATPase
A rise in the plasma Calcium levels causes what?
Inhibition of the secretion of parathyroid hormone.
Where is the formation of cholecalciferol?
In the skin
What regulates Calcium absorption?
Ca2+ absorption is regulated over the long term by plasma Ca2+ levels.
What substance is important in solubilizing iron?
Gastric acid
What represents a largest fraction of dietary iron?
Nonheme iron
What substances reduce the Ferric state (Fe 3+ to the Ferrous state Fe 2+)?
Organic acids such as ascorbic or citric acid
Fe 2+ is transported into the enterocytes by ?
divalent metal transporter 1 (DMT1)
True or False? In Iron deficiency , Ferritin is DECREASED and more Fe 2+ is passed into the blood.
TRUE!!
Fill in the blanks.”In Iron Overload, _______ decreases while _______ increases.”
Transferrin decreases
Ferritin stores Increases
Fill in the blanks. “ Bile drains into bile canaliculi via ________ & _____________ to hepatic ducts.
Intralobular & Interlobular
What is bile produced from?
Hepatocytes
Fill in the blanks. “ The secretion of bile acids carries _______ &____________into the bile by osmotic filtration.”
Water and Electrolytes
What is the main function of bile in the lumen of the intestines?
Within the lumen of the intestine bile participates in the emulsification, hydrolysis, and absorption of lipids
Fill in the blanks. “ Canicullar bile is secreted by __________ in response to the osmotic effects of anion transport.”
Ductule cells
Fill in the blanks. “ The portion of bile stimulated by secretin and contributed by the ducts is termed________________.”
Bile acid independent or ductular secretion
What is the major constituent of bile?
Bile acids
What is the rate limiting step for the conversion of cholesterol to bile acids?
7α-hydroxylation of cholesterol by the hepatic enzyme 7α-hydroxylase
How many bile acids are present in bile?
4 bile acids
What bile acids are formed by the liver and are known as the primary bile acids?
Cholic acid and chenodeoxycholic acid.
What are the names of the bile acids that are formed after a fraction of the primary bile acids are dehydroxylated by bacteria in the gut?
Deoxycholic acid and lithocholic acid ( secondary bile acids)
How many bile acids are formed from the colon?
20
What is the ratio of the four bile acids present in bile?
4:2:1: ( very small amounts)
(4)Cholic acid : (2) chenodeoxycholic acid: (1) deoxycholic : lithocholic acid (small amounts).
Fill in the blanks.”The solubility of bile acids depends on the ___________ present and the state of the terminal ___________.”
The solubility of bile acids depends on the number of HYRDROXYL GROUPS present and the state of the terminal CARBOXYL GROUP
Which bile acid is the most soluble?
Cholic acid
Fill in the blanks.” The The liver conjugates the bile acids to the amino acids , ____________ OR ________.”
Glycine or Taurine
What process forms bile salts?
Conjugation of Bile acids
What is the name of the nucleus found in bile acids?
Cyclopentanoperhydrophenanthrene nucleus
Which components of the bile acid structure are hydrophilic?
- Hydroxyl groups
- The peptide bond of the side chain
- Either the carbonyl or sulfonyl group of glycine or taurine.
Which components of the bile acid structure are hydrophobic?
Cholesterol nucleus and methyl groupings.
True or False? The behaviour of bile acids are dependent on their concentration.
TRUE!!
What is the major phospholipid found in bile acids?
Lecithins
In what form are bile pigments soluble ?
When they are conjugated with glucuronic acid.
What are the inorganic ions found in bile?
Sodium (Na +)
Potassium (K+)
Calcium ( Ca 2+)
Chloride (Cl-)
Bicarbonate (HCO 3-)
How many bile salts are present in the enterohepatic circulation?
2.5 grams
Where are Primary acids synthesised (cholic acid and chenodeoxycholic acid ) ?
By hepatocytes ( in the liver)
Where are secondary bile acids produced?
They are produced in the intestine through the action of microorganisms on primary bile acids.
Fill in the blanks. “ In regards to the removal of bile acids from the portal blood, Uptake across the basolateral or sinusoidal membrane of the enterocytes is mediated primarily by two types of system: __________ &____________.”
- Na+ taurocholate cotransporting polypeptide (NTCP)
- The organic anion transport proteins (OATPs)
What is the function of Na+ taurocholate cotransporting polypeptide (NTCP)?
It can take up both conjugated and unconjugated bile acids.
What is the function of The organic anion transport proteins (OATPs)?
They can take up both bile acids and other organic anions.
What is the primary bile pigment in humans?
Bilirubin
True or False? Bile acids are anions
TRUE!!
In the pancreas, the acinar cells produce what substance?
Digestive enzymes
In the pancreas, the ductule ( centroacinar) cells produce what substance?
A large volume of watery secretion containing sodium (Na+) and HCO3− as its major constituents.
What is the efferent nerve supply of the pancreas?
- Sympathetic post-ganglionic fibers emanate from the celiac and superior mesenteric plexuses and accompany the arteries to the organ.
*Parasympathetic preganglionic fibers are distributed by branches of the vagi coursing down the antral-duodenal region.
True or False? At all rates of secretion, pancreatic juice is essentially isotonic with extracellular fluid.
TRUE!!
What are the main ions present at a LOW flow rates of Pancreatic secretions?
Na+ & Cl-
What are the main ions present at a HIGH flow rates of Pancreatic secretions?
Na+ & HCO3
Fill in the blanks. “ The opening of the cystic fibrosis transmembrane conductance regulator (CFTR), is activated by _________.”
Cyclic AMP in response to stimulation by secretin.
True or False? In the pancreas, Cystic fibrosis transmembrane conductance regulator (CFTR) is present in acinar cells not duct cells.
FALSE!! It is present in Duct cells not Acinar cells.
Which pancreatic enzymes are secreted in the active form?
Pancreatic amylase & lipase
Which pancreatic enzymes are secreted in the inactive form?
Pancreatic protease
Where are newly synthesised pancreatic enzymes collected?
In the Rough Endoplasmic reticulum cisternae.
Fill in the blanks. “ Within the condensing vacuoles, the Pancratic enzymes are concentrated to form _________.”
Zymogen granules
How does CCK stimulate pancreatic enzyme rich secretions?
CCK activates cholinergic reflexes via CCK1 receptors on vagus nerve afferents , and acetylcholine (Ach) activates muscarinic receptors on the acinar cell. The results are a release of calcium (Ca2+) from the endoplasmic reticulum and the subsequent activation of protein kinases, which stimulate exocytosis.
What regulates the control pancreatic secretion?
Secretin, CCK, and vagovagal reflexes.
Fill in thee blanks. “ ______________ account for most pancreatic secretion, but secretion is also stimulated during the cephalic and gastric phases.”
Intestinal stimuli
What is the Stimulus for the the Cephailc phase of Pancreatic secretion?
Conditioned reflexes, smell, taste, chewing, and swallowing.
True or False? ACh has a greater effect on the enzymatic release form acini cells.
TRUE!!
What is the stimulus for the Intestinal phase for Pancreatic stimulation?
Proteins, Fats and H+ entering the duodenum
What is the duodenal threshold?
pH 4.5
True or False? CCK increases the expression of the genes for proteases and decreases the expression for amylase.
TRUE!!
What hormones inceases the gene expression for lipase?
Secretin and gastric inhibitory peptide (GIP) increase the expression of the gene for lipase
What is the Chief Dietary form of Fats?
Triglycerides
Phopholipids
Cholesterol
Cholesterol esters
What are the chief forms of fat in Plasma?
Cholesterol
Triglycerides
Phopholipids
Non-esterified fatty acids
The enzyme lingual lipase is secreted by ?
Von Ebner glands on the dorsal surface of the tongue
What enzyme is secreted by the fundic cells?
Gastric lipase
Where does most fat digestion take place?
In the duodenum
What enzyme is responsible for fat digestion in the duodenum?
Pancreatic lipase
Fill in the blanks. “ The activation of pancreatic lipase requires ________.”
Colipase
Where is collapse activated and what is required for colipase?
It is activated in the intestinal lumen and requires trypsin.
What is the function of colipase?
It helps to anchor lipase to the fat droplets
Fill in the blanks.” Bile salts lipase catalyses the hydrolysis of _____.”
Cholesterol esters
Esters of fat-soluble vitamins
Phospholipids
How does lipid enter cells?
By carrier mediated transport & passive diffusion
Where is Fat absorption greatest?
In duodenum & jejunum
How is Fat transferred in blood?
Free unesterified fatty acids
Where does the Monoacylgycerol pathway takes place?
In the Smooth Endoplasmic reticulum
What is the Monoacylgycerol pathway?
This is the pathway by which monoglycerids are acylated to diglycerides then triglycerides.
Where does in the Chylomicron formation occur?
In the Rough endoplasmic reticulum.
Emulsification of fats is mainly achieved by?
Bile salts & Lecithin
What are the rate- limiting steps of Digestion of Fats?
- Assembly & exocytosis of chylomicrons
- Lack of Beta-lipoproteins will result in the mucosal cells becoming engorged with fatty products.
True or False? Free fatty acids greater than 12 carbon atoms are re-esterified to triglycerides in the mucosal cells.
TRUE!!
Where is the vomitting centre located?
It is near the nucleus tractus solitaires at the level of the dorsal motor nucleus of the vagus.
What are the voluntary & involuntary acts that affect the extrinsic defection reflex?
Deep inspiration
Closure of the glottis
Lowering of the diaphragm
Contractions of the abdominal muscle.
What regulates the Migrating Myoelectric complex?
Motilin
