3.6 Gastrointestinal Physiology Flashcards
What are the products or RBC destruction?
hemoglobin
1) globin= metabolized
2) heme= bilirubin + iron
where does bilirubin come from?
normally the spleen or liver from RBC destruction
is bilirubin glucuronide or free bilirubin more water soluble?
bilirubin glucuronide is more H2O soluble
what makes bilirubin glucuronide?
bilirubin + glucuronic acid
**oxidized glucose!!!
what is jeundice?
high concentration of bilirubin (when oxidized) causing the skin and eyes to look yellow
1) what is normal plasma bilirubin?
2) abnormal?
3) If abnormal, causes?
1) 0.5mg/ml= almost entirely free/unconjugated
2) up to 40mg/day= much can become the conjugated type
3) skin usually appears jaundiced (yellow) around 1.5 mg/dl
what are the two primary types of jaundice in adults?
1) hemolytic jaundice
2) obstruction jaundice
describe hemolytic jaundice
caused by increae in RBC destruction
describe obstruction jaundice
caused by damaged liver cells or obstructed bile ducts
measurement of plasma bilirubin level provides info regarding cause of jaundice… meaning?
- high levels of UNconjugated bilirubin= hemolytic jaundice
* high levels of CONjugated bilirubin= obstructive jaundice
1) colon main secretion?
2) ions secreted?
1) mucus
2) K+ secreted with absorption of Na+
HCO3- secreted with absorption of Cl-
what are the major dietary nutrients?
carbohydrates
fats
proteins
carbohydrate digestion?
1/2 daily calory intake
- 2/3 starch
- 1/3 sucrose and lactose
carb digestion begins? continues? ends?
- begins in mouth with salivary amylase (ptyalin)
- continues in stomach INSIDE bolus (ptyalin)
- ends in SI with pancreatic amylase and brush border enzymes
most of carb breakdown happens?
with pancreatic amylase (70%)
–30% with salivary
fats dietary intake?
1/3 daily caloric intake
*mostly triglycerides
fat or carb store more calories?
fat
*you can store twice as many calories per gram of fat than any other type of nutrient
where is fat digestion?
*begins in SI with pancreatic lipase
=triglyceride + lipase = monoglyceride + 2 fatty acids
protein dietary intake?
1/6 of daily caloric intake
*numerous kinds ingested and some secreted into GI tract
protein digestion happens where? with what enzyme?
BEGINS IN STOMACH and ends in SI via pepsin
*none in mouth
what is the only enzyme that adequately digests collagen?
pepsin
what three enzymes break down proteins?
trypsin, chymotrypsin and polypeptidases break down small proteins and polypeptides
what protein performs the final breakdown to AA?
how many?
BRUSH BORDER aminopeptidases
*20 different types
where is the bulk of water absorption?
not much water absorption where?
8 1/2 in SI!
- more proximal= more absorption (duodenum best)
- not much happens in stomach
breakdown of water absorption and the location
- 4 SI
- 4 prox colon
- 2 = feces
how much surface area available to absorption? WHY so much?
250 meters squared
BECAUSE MICROVILLI has VILLI on it
monosaccharides absorbed where?
SI
fructose absorption through?
facilitated diffusion
glucose and galactose abortion through?
how do they LEAVE?
secondary active transport coupled to Na+ in first 20% of SI
- 2 Na+ binding sites; 1 sugar binding site
- glu and galac are COMPETING
- LEAVE epithelial cells via facilitated diffusion transporters in basolateral membranes
fat absorption?
micelles deliver lipids to surfaces in SI and release them
*DO NOT need special transport bc lipids DIFFUSE freely into intesinal epithelium (fat dissolves fat)
after diffusion into epithelium, what happens to fatty acids and monosaccharides?
re-synthesized into triglycerides in ER to maintain diffusion gradient for FA and MG to enter cell
What is unique about newly re-synthesized into triglycerides in ER?
they are given a lipoprotein coat and called CHYLOMICRON
what is a chylomicron?
a newly re-synthesized triglycerides in the ER that was given a protein coat
what happens to chylomicrons once made? what is there path to blood?
1) diffuse out of the epithelial cell into the interstitium
2) then into lymphatic lecteals
3) lymphatics capillaries in intestinal villi
4) eventually into thoracic duct
5) into blood
some of the short chain fatty acids diffuse out of the epithelial cells and directly into?
portal blood (not into chylomicrons in ER)
proteins are absorbed in what form? How?
what mechanisms?
absorbed as AA via secondary active transport coupled to Na+ (but there are some Na_ independent processes)
**separate mechanisms for diff types of AA such as neutral, basic, acidic, proline, OH-proline
AA are transported OUT of intestinal epithelial cells and into the blood via?
facilitated diffusion carrier protein in the basolateral membrane
are intact proteins commonly absorbed?
- very few absorbed in adults across intestinal epithelium
- INFANTS have a greater absorptive capacity for intact proteins for getting antibodies from moms milk via passive immunity
what mechanisms does water use to get absorbed?
osmosis. .. 80-90% in SI
* 0.5 to 1 L passed on to LI
Requires energy to get Na in or out of the cell?
OUT =active transport
what is the most abundant solute in chyme?
Na+
What is the mechanism of transport to get Na+ in and out of cell?
considered active transport
- passive diffusion INto mucosal cell thru lumenal membrane
- active transport OUT basolateral membrane via Na+/K+ ATPase pump
How is chloride like a “little brother”?
Cl- and HCO3- follow Na+ around
How does Cl- and HCO3- cross membranes?
they follow electrochemical gradient estalished by the pumping of cations (aka Na+)
How do we absorb K+?
1) we wait for Na+ to enter (and thenCl- and CHO3-) which is then followed by H2O. water dilutes conc and makes it more favorable for K+ to enter
2) Na+/K+ ATPase pump
What vitamins are NOT absorbed in upper SI?
B12 and some Vit K
What are the fat soluble vitamins?
How are they absorbed?
A D E K
- solubilized in micelles
- absorbed via same pathway as fat
- interference with fat absorption = decrease in fat soluble vitamin absortion (ex: decrease panc enzymes or bile action)
what vitamins are important for blood clotting?
calcium and K
what vitamin is important for calcium absorption?
D
what are water soluble vitamins?
thiamin, riboflavin, niacin, pyridoxine, pantothenate, biotin, ascorbic acid, folate, and vitamin B12
what water soluble vitamins are absorbed via Na+ dependent contransporters?
thiamin, riboflavin, niacin, pyridoxine, pantothenate, biotin, ascorbic acid
what water soluble vitamins are absorbed via Na+ INdependent contransporters?
folate
what water soluble vitamins are absorbed via intrinsic factor?
vitamin B12
what is Vit B12?
a large and charged molecule that binds to intrinsic factor (secreted by parietal cells in gastric glands)
B12 is required for?
RBC formation
what happens if you are deficient in B12 or intrinsic factor?
PERNICIOUS ANEMIA
*if no intrinsic factor then you must have injections of B12
what determiens Ca absorption?
1) 30-80% of ingested Ca is absorbed depending on deficieny (increase) or excess (decrease) Ca++ found in body
2) Calcium is dependent on Vit D which makes Ca binding proteins in mucosal cells
3) Calcium active transport via Vit D dependent Ca++H+ ATPase pump
What is an inhibitor of Ca absorption?
phosphate and phytates which form insoluble Ca++ compounds
What are promoters of Ca++ absorption?
slight acidity and Ca+ binding proteins
Ca++ facilitated diffusion from lumen mostly requires?
carrier protein such as IMCal (intestinal membrane calcium binding protein)
Ca++ active absorption through basolateral membrane via a?
vitamin D-dependent pump (Ca++ ATPase)
Fe++ absorption utilizes what carrier protein?
DMT1
how much of absorbed Fe++ goes into blood?
10%
Fe++ facilitated diffusion into mucosal cells, where most of it binds to?
apoferritin protein
apoferritin VS ferritin?
- apoferritin= ONLY protein
* Ferritin= protein AND iron complex for STORAGE
what does ferritin do?
intracellular iron storage complex
where is most Fe++ stores?
liver and intestine
what happens to the small amount of Fe++ that does not bind to apoferritin?
it is actively transported out of the mucosal cells and into the blood, where it binds to the carrier protein called apotransferin and becomes transferin
apotransferin vs transferin
- apotransferin = ONLY protein
* transferin= protein AND iron complex that TRAVELS in the blood
where is apotransferin found in significant amounts?
hepatocytes, where Fe++ binds with it and is stored as the compound ferritin (like in the intestinal epithelial cells)
Fe++ is largely DEpendent on the saturation of?
protein
*when storage proteins and tranport proteins are saturated, absorption stops
What does Vit D do?
1) promoate making of binding proteins in mucosal cells
2) making and activity of pumps that pump Ca+ outside the membrane into blood
what is PTH?
a parathyroid hormone which activates vit D in kidney when Ca is LOW in the blood
*VERY IMPORTANT FOR REGULATING Ca+
colon has active absorption of?
Na+ and Cl-
- more proximal = more absorption
- requires ATP because against conc gradient
colon has passive absorption of?
water via osmosis
- Vit K produced by intestinal bacteria (passive diffusion)
- vit B12 (endocytosis, facilitated by intrinsic factor)78
