GIT - Lecture 8 Flashcards
What do pancreatic lipases break down?
fats
Pancreatis lipases break down fats into what kind of molecules?
fatty acids, di/monoglycerides
Pancreatic lipase can only function under the presence of what enzyme?
colipase
What does pancreatic pro-colipase react with trypsin to form?
colipase
In addition to pancreatic lipase, what else breaks down fats into fatty acids and mono/diglycerides?
bile salts
What organ produces bile salts?
liver
Which organ is the largest gland of the body?
the liver
What are the 4 functions of the liver?
- storage
- synthesis
- detox
- metabolism
What does the liver secrete? From where?
bile from hepatic ducts
Where does bile travel?
in the common bile duct
Where is bile released?
into the SI at the same location as the pancreatic juice
What is the volume of bile produced by the liver every day?
0.5-1.0L/day
What kind of fluid is bile?
isotonic
What are the 4 main components of bile and which is the most present?
Na+, K+, Cl-, HCO3 (most present)
What is the pH of liver bile?
7.8-8.2
What is the function of the pH of liver bile?
it helps neutralize acidic chyme
What are the 4 components of liver bile?
- bile acids
- bile pigments
- cholesterol
- phospholipids
What is the % of solids in liver bile?
3%
Are there digestive enzymes present in bile?
no
Bile secretion by the liver is ___.
continuous
Entrance of bile into duodenum is ___.
intermittent
What is the volume of bile entering the small intestine?
<500-700 mL/day
Why is only <500-700 mL of liver bile enter the small intestine rather than the total quantity?
because as the spincter of Oddi is closed, the bile salts produced by the liver have nowhere to go so they get stored in the gallbladder
How much fluid can the gallbladder hold?
50-100 mL
What is the % of solids in the gallbladder?
10-20%
What kind of pH is found in the gallbladder?
7.0-7.5
What is there less of in the gallbladder?
bicarbonate
What does the gallbladder do to bile salts?
stores and concentrates them
If there aren’t enough bile salts, what happens to cholesterol and phospholipids?
they precipitate and cause gallstones
Bile salts are synthesized in the liver from ___.
cholesterol
What do bile salts facilitate?
digestion, transport, and absorption of FAT by forming water-soluble complexes with the fats
What do bile salts facilitate the transport and absorption of?
fat-soluble vitamins (A, D, E, K)
What kind of cells are bile salts?
amphipathic
Where do the phospholipids of cholesterol burry their hydrophobic portions?
in the non-polar side of the micelle
Bile salts help form…
stable emulsions
Most bile salt is reabsorbed into which kind of blood?
portal blood
How is most bile salt returned to the liver?
via enterohepatic circulation
The entire bile salt pool is recirculated several times a day between:
liver -> GIT -> liver
What is the positive feedback of bile salts?
they regulate hepatic bile flow
The more bile salt returned via portal blood, the ___ the volume of bile secreted
larger
What will happen to bile secretion if we removed the ileum?
it will decrease
What is the negative feedback of bile salts?
they regulate the synthesis of new bile salts
The most bile salt is returned in portal blood, the ___ the amount of new bile salt being synthesized
smaller
What will happen to bile salt synthesis if we remove the ileum?
the liver will produce more bile salts
Why is cholesterol kept in solution?
because it is insoluble in water
If cholesterol precipitates, it may give rise to ___.
gallstones
In bile, the solubility of cholesterol increases by how much?
2 x 10^6
What are the 2 intra-intestinal functions of bile salts?
- act as detergents and help form stable emulsions
- assist in the transport of fat and fat-soluble vitamins from SI -> intestinal cells
What is the intracolonic function of bile salts?
they inhibit Na+ transport and H2O absorption
Excess of what in the colon causes diarrhea?
bile salt
What 2 kinds of cells are found in the pancreas?
- release a large volume of juice rich in HCO3
- release a small volume of juice rich in enzymes
The pancreas contains cells that release a large volume of juice rich in ___
HCO3
The pancreas contains cells that release a small volume of juice rich in ___
enzymes
What are choleretics?
agents which cause the liver to secrete a large volume of bile
What are cholagogues?
agents which cause an increase gallbladder emptying
What is the Law of Reciprocal Activity?
if the gallbladder is contracted, the Sphincter of Oddi will be relaxed and vice versa
Polysaccharides get broken down into disaccharides via what enzymes?
salivary and pancreatic amylase
What level polysaccharides need to be broken down in order to be absorbed?
into monosaccharides
Proteins get broken down into small peptides via what enzymes?
pepsin, trypsin, chymotrypsin
What do proteins need to be broken down into in order to be absorbed?
amino acids, di and tripeptides
Fats are broken down into mono, diglycerides and fatty acids via which enzymes?
lipase, co-lipase and bile salts
Final steps in digestion are mediated by which kind of enzymes?
intestinal enzymes
Where are intestinal enzymes produced?
at the site where absorption will take place
What produces intestinal enzymes?
mucosa
The small intestine secretes what kind of juice?
intestinal juice
What are the 3 components of intestinal juice?
water, mucus, ions
What does the small intestine receive to aid digestion?
pancreatic juice enzymes
What kind of enzymes does the small intestine contain?
brush border enzymes
What are brush border enzymes attached to?
the microvilli of small intestine epithelial cells
What does the small intestine do for mechanical digestion?
segmentation
What does the small intestine do for chemical digestion?
chyme mixes with pancreatic juice, intestinal juice and bile
Where does the absorption of digestion nutrients occur?
in the small intestine
What allows for secretion, digestion and absorption in the small intestine?
increased surface area
What is the region where the invaginations are in the small intestine?
crypt region
What is the region where digestion is completed in the small intestine?
villus region (in the villi)
What are the names of the cells found in the villus region that absorb all the nutrients?
enterocytes
What do enterocytes have on their surface? Why?
microvilli where they produce the enzymes
Crypt cells lack what kind of enzymes?
digestive enzymes
What do crypt cells secrete a large volume of?
alkaline fluid (succus entericus)
What is the name of the alkaline fluid produced by the crypt cells?
Succus Entericus
What kind of fluid is succus entericus?
isotonic
What is the pH of the succus entericus?
7.5-9
Do villi secrete fluid?
no but they complete digestion and absorb nutrients and fluid
Enterocytes in the villi synthesize digestive enzymes which remain where?
in the brush border
What is the major enzyme produced by the small intestine?
enterokinase
Where are disaccharases produced?
in the brush border
What is also happening in the crypt region in addition to the production of Succus Entericous
rapid cell division
Where do the cells undergoing rapid cell division in the crypt region do and go?
divide into the cell types that will populate the lumen
Why is it important that there is rapid cell division in the crypt region and that it moves to the lumen?
because the cells in the lumen are constantly being damaged by the enzymes and wearing out because of their constant use
In the villus, fats are absorbed via the ___.
lacteals
What are chylomicrons?
fat and protein complexes absorbed at the level of the lacteal
Fats are processed by which system?
the lymphatic system
Carbohydrates and sugars return to the liver via the ___ ___ ___.
hepatic portal vein
How are carbohydrates and sugars absorbed?
via the capillary
What kind of fluid are colonic secretions?
alkaline
What ions are both present in the same concentration (100-150 mEq/L) in the colonic secretions?
HCO3 and K+
What is there a lot of in colonic secretions?
mucin
Are there any digestive enzymes of absorption of nutrients in the colon?
no
What kind of activity is there a lot of in the colon?
bacterial activity
What reflexes and factors regulate intestinal secretions?
- local enteric reflexes
- vago-vagal reflexes
- hormonal factors
How many litres are actually entering the GIT every day?
9 liters
What contributes to the 9 L of fluid entering the GIT every day?
2 litres ingested + 7 litres secretes
In addition to water, what is also reabsorbed from the lumen of the GIT?
very large quantities of ions
How many grams of protein is released into the GIT via secretions?
80 g
Most of absorption is ___.
reabsorption
What are the sites of exchange characterized by?
- very large surface area of small intestine
- intimate contact with blood vessels
Which GI organ is essential to life?
small intestine
Why is the SI the only GI organ essential to life?
because the colon cannot take over nutrient absorption
What kind of blood flow goes to the intestine?
postprandial
What is the rate of flow in to intestine?
1-2L/min
What does each villus have?
a capillary loop and lacteal
What is the lymph flow rate?
1-2 mL/min
Where is the major area of absorption of nutrients?
the duodenum
What is absorbed mostly at the ileum but it produced in absorbed in small quantities throughout the small intestine?
ileum
Where does vitamin B12 only have absorptive sites?
ileum
How does absorption take place? (5)
- simple diffusion
- facilitated diffusion
- active transport
- pinocytosis
- osmosis
Water always follows the osmotic gradient generated by the movement of ___ and ___.
ions and nutrients
What are the requirements for absorption?
- Adequate Digestion
- Adequate Sites for Absorption
- Adequate Transit Time for Absorption
- Adequate Co-factors, Transporters
How many litres of water is absorbed by the SI?
7 L
How many litres of water is absorbed by the colon?
2 L
What is the maximum capacity of absorption of water from the SI?
15 L/day
What is the maximum capacity of absorption of water from the colon?
4-5L
Is the efficiency of the GIT high or low? Why?
high due to effective coordination of activities within an organ and between organs
What is GIT transit time related to?
the functional activities of each organ
