Flashcards in Gastrointestinal Physiology - Theoretical Questions Deck (127)
What is the hormone responsible for the contraction of the Gallbladder? What is the trigger for its release?
What is another important target for it? in this regard?
CCK - I cells in Duodenum detect Chyme
relaxation of the sphincter of Oddi
What are the special cells of the bile duct? what do they release?
Cholangiocytes - Release Bicarbonate
What is the chemical nature of Bile salts? what does this allow them to do?
They have an Amphipathic structure allowing them to self assemble into Micelles that have an Hydrophobic (Lipophilic) interior that can store Fats- Emulsification.
What is the importance of emulsification?
Increasing the surface area (Large to small particles of fat) thus allowing pancreatic lipase to effectively form Glycerol and FAs from it
What happens when the gallbladder is impaired?
Steatorrhea - oily feces. Bile will be secreted more quickly then they are emulsifying
How much of the bile salts are circulated back? how?
Through enterohepatic circulation 95% of Bile salts are being circulated back. Na cotransport carries them back to blood.
What is the point from which bile secretion is sufficient for bile activity to be useful?
CMC - Critical micelle concentration
What is the neural regulation of Bile secretion?
Vagus - Ach - GB contraction and Bile secretion
Vagus - VIP and No Sphincter relaxation
Sympathetic - GB relaxation
What are 4 locations of Natrium reabsorption in the GI? How?
Duodenum - Na/H exchanger
Jejunum - SGLT, AA/Na cotransporter and Na/H excha.
Ileum - SGLT, AA/Na cotransporter and Na/H excha.
Colon - ENaC (Aldosterone) and Na/H exchanger
How is Calcium reabsorption in the GI regulated?
PTH - allows for 1,25 HydroxyVitD formation in the Kidney and thus allowing for the Calbindin protein, NIS and Ca channels to form in the enterocytes.
What are the water Absorption fragments? What are the divisions in the GI? How are they absorbed?
9L in total = 1L from Intake and 8L from Digestion.
8.5L in the small intestine and 0.5L in colon (Liquid state).
Paracellularly or with Aquaporins.
What are the transporters allowing for Monosaccharide absorption in enterocytes?
SGLT1 for Cotransport of Glucose/Galactose with Na
GLUT5 for Fructose
GLUT2 (basal surface)
What are the proteins allowing absorption of Iron in enterocytes?
DMT-1 is the Apical membrane transporter, Apoferritin is the intracellular binding protein and Transferrin is the Basal membrane transporter. Storage in Liver.
(Also Heme transporter and Heme oxygenase if bound)
What is the process of Vit B12 (Cobalamin) protection from degredation until it reaches the Enterocytes?
1)Cobalamin is bound to Proteins
2)Cobalamin is released from digested proteins and bind Haptocorrin from Gastric Glands
3)Cobalamin is released from digested Haptocorrin and binds Intrinsic factor in the duodenum (From Parietal)
4)Intrinsic factor receptor on enterocytes binds the IF-CBL complex.
How is VitB12(Cobalamin) absorbed once it is in contact with enterocytes?
Intrinsic factor receptor on enterocytes binds the IF-CBL complex. The endosome formed releases IF and the receptor for degredation or recycling. Transcobalamin II will form a complex with CBL and through the circulation go for storage in Liver.
How are vitamins A, D, E and K absorbed?
Lipid soluble: by passive with lipids
How are vitamins Bs, C, Niacin, Biotin absorbed?
Water soluble: By cotransport with Na
How are Tri- and Dipeptides differ in absorption from Amino acids?
Tri- and Dipeptides - Proton cotransporter from Na/H exchanger formed gradient.
Amino acids simply cotranslocate with Na concentration gradient.
What will happen for lactose intolerant people eating lactose? why?
Osmotic diarrhea: Impaired Lactase function on brush border causes accumulation of Lactose that osmotically attracts water from Enterocytes. Loss of water and Gut bacteria overdigestion.
Where do Nicotine and Ethanol are able to be absorbed?
Oral cavity (and ethanol in stomach as well)
After fatty acids and MAGs are formed in the micelles what are the 3 steps of Absorption of Lipids in the Intestine?
1)Diffusion of fatty acids,
monoglycerides, and cholesterol
2)Re-esterification in cell to
triglycerides and phospholipids
3) Chylomicrons form in cell (requires
apoprotein) and are transferred
What is the Respiratory Quotient? How is it calculated?
It is a unitless value signifying the food consumption properties - Higher RQ means well fed. for Carbohydrates it is 1, Proteins 0.8 and Fats 0.7 . It is calculated as Vco2/Vo2.
How much does one calorie worth in KJ?
1 Calorie = 4.23 KJ/g
What is the rule of Isodynamics?
Different kinds of foods can replace each other function through biochemical processes in the body.
What are the specific food quality requirement that are crucial for ones well being?
Essential FAs and AAs
What does our food content equal to in means of metabolism?
TEE - Total Energy Expenditure
Resting state and no External work is done:
What will the TEE be equal to?
How can we calculate it?
TEE will be equal to Heat production
Direct calorimetry - Ice melting is proportional to Heat produced.
Indirect calorimetry - Oxygen consumption: 1 O2L = 21KJ.
Active state and External Work is done:
What will the TEE be equal to?
TEE=BMR + DIT + EE
DIT - Diet Induced Thermogenesis
BMR - Basal metabolic Rate
EE - Energy Expenditure for Physical Activity
Requirements for measurement (Heat production)?
-12 hr after a meal
-no physical activity
-At rest no drugs
-20 degree thermoneutral environment