GI 5 Flashcards
3 categories of pancreatic secretions
Endocrine
Digestive enzymes
Bicarbonate
Where do pancreatic and liver secretions enter
At beginning of small intestine through sphincter of oddi
What is 2 epithelium that pancreas contains
- Endocrine secretory epithelium (islets)
- Exocrine secretory epithelium
What do endocrine secretory epithelium secrete
Insulin and glucagon
What do exocrine secretly epithelium secrete
Digestive enzymes and NaHCO3
What is the stimuli for exocrine secretory epithelium
Distension of small intestine, neural signals, CCK
What is exocrine portion of pancreas form
Grape like clusters: acini
What do acinar cells secrete
Digestive enzymes
What do duct cells secrete
NaHCO3 that enters digestive tract
what are many pancreatic digestive enzymes released as
Zymogens (inactive form of enzyme)
- some secreted in active form
What is trypsinogen converted to and by
Trypsin by enteropeptidase (brush border enzyme)
Once trypsin converted what does it do
Activates all other zymogens
What does bicarbonate produced in duct cells do
Neutralizes acid entering from stomach
- this why pancreas start at beginning of sm. Int.
What do duct cells have high levels of
Carbonic anhydrase
What transporters does apical membrane of pancreas have
HCO3-/Cl- exchanger and CFTR channel
What transporters does basolateral membrane of pancreas have
NKCC2, N/K ATPase, K+, Na/H exchanger
Bicarbonate secretion process
- Cl enters cells and leaves apical side through CFTR
- Cl then renter cell in exchange for HCO3
- Leaky junction allow movement of ions and water
- Negative ions in lumen attract Na, water follows
What is largest internal organ
Liver
Where is liver
Lies under diaphragm toward right side of body
6 roles of liver
- glucose and fat metabolism
- protein synthesis
- hormone synthesis
- urea production
- detoxification
- storage
Inputs into liver
Hepatic portal vein and hepatic artery
Outputs of liver
Bile duct and hepatic vein
Where does bile duct secrete into
Duodenum
Common hepatic duct
Takes bile to gallbladder for storage
Gallbladder
Storage reservoir for liver secretions related to digestion (bile)
Common bile duct
Takes bile from gallbladder to lumen of sm int
Hepatic artery
Brings oxygenated blood containing metabolites from peripheral tissues to liver
Hepatic portal vein
Blood rich in absorbed nutrients from digestive tract brought to liver
sphincter of oddi
Controls release of bile and pancreatic secretions into duodenum
What dos liver secrete
Bile
Bile
Non-enzymatic solution secreted from hepatocytes
3 main components of bile
- bile salts (bile acid/amino acid)
- bile pigments (bilirubin)
- cholesterol
What is excreted in bile
Xenobiotics and drugs
How are hepatocytes organized
Into hexagons
Fats and related molecules
Triglycerides (90%), cholesterol, phospholipids, long chain fatty acids, fat soluble vitamins
Why is fat digestion complicated
Fats are not water soluble
How does bile assist with fat digestion
Coarse emulsion of large fat droplets in chyme broken to smaller, stable particles by bile salts to let enzymes digest
How are emulsions made
Bile salts coat lipid droplet
What enzymes from pancreas digest triglycerides
Lipase and colipase
What is triglyceride broken down into
2 free fatty acids and a monoglyceride
What are micelles
Small disks with bile salts, phospholipids, fatty acids, cholesterol, mono- and diglycerides
- proceed to wall for absorption
What is absorbed from micelles when comes in contact with brush border
- monoglycerides and fatty acids move out enter cells by diffusion
- cholesterol is transported in
Once part of Micelles absorbed what happens within cell of small intestine
- absorbed fats reformed in ER and combine with chol and proteins
- form chylomicrons
What happens to chylomicron
Removed by lymphatic system (lacteal)
How much bile salts are excrete
5%
What secretes and stores bile
Hepatocytes in gallbladder
What happens to bile during a meal
Recycled multiple times
Where is bile taken back up
At ileum taken up by capillary bed and brought back to liver by hepatic portal vein
What are gallstones
Hardened deposits within gallbladder likely due to excess chol or bilirubin
- block sphincter or hepatic duct
What does gallstones cause
Upper right abdominal pain, jaundice
Gallbladder removal
Carbs ingested
Starch and sucrose
- glucose polymers, disaccharides, monosaccharides
Glucose polymers
Glycogen, cellulose
Disaccharides
Lactose, maltose
Monosaccharides
Glucose and fructose
What does salivary and pancreatic amylase break down
Glucose polymers to disaccharides (maltose)
What are disaccharides then broken down by
Intestinal brush border enzymes, disaccharidases
Glucose or galactose absorption
Enters with Na on SGLT on apical
Exits on GLUT2 on basolateral
Fructose absorption
Enters on GLUT5 on apical
Exits on GLUT2 on basolateral
Normally glucose phosphorylated when entering cell what do enterocytes do differently
Use glutamine so glucose-6-phosphate is not formed and free glucose stays high facilitating basolateral transport (absorption)
How much digested proteins are not from ingested foods
30-60%
- dead cells, enzymes and mucus
2 categories of enzymes for protein digestion
Endopeptidase (proteases)
Exopeptidase
Endopeptidases include
Pepsin in stomach, trypsin and chymotrypsin in small int
What do endopeptidases do
Attack peptide bonds in amino acid chain forming fragments
How is endopeptidase released
Zymogens
What do exopeptidases do
Release amino acids from peptides one at a time
What is name of certain exopeptidase based on
Side they full from
Where are aminopeptidases
Sit on amino terminal end
Brush border enzyme
To kinds of exopeptidases
Aminopeptidase
Carboxypeptidase
Where are carboxypeptidases
Carbohydrate-terminal end
3 types of pancreatic caarboxypeptidases
A1, A2, and B
What does protein digestion primarily result in
Free AAs, dipeptides and tripeptides
What protein is absorbed after digestion
Mostly as free amino acids, some di and tripeptides
- if larger then tri absorbed by transcytosis
What are single AAs transported with on apical and basolateral
Apical: Na cotrasnporters
Basolateral: Na exchangers
What are di- and tripeptides transported on apical membrane
Oligopeptide transporter (H+ cotransporter)
What happens to di and tripeptides once in cell
Digested to single AAs in cell (peptidases) and exit via Na-AA exchanger
How are peptides larger than 3 AAs transported
Via transcytosis after binding to receptor on luminal surface
Transcytosis
Combination of endocytosis, vesicular transport then exocytosis
Why are most small peptides carried intact across cell by transcytosis
Could potentially act as antigens stimulating antibody production causing allergic reaction
What could play role in intolerances or allergies in infants
Peptide absorption high (villi are small)
Feeding too much solid
Fat soluble vitamins that are absorbed with fats
A, D, E, K
Water soluble vitamins absorbed by mediated transport
C and most B
How is B12 absorbed
In ileum after forming complex with intrinsic factor released from parietal cells
- on own will not absorb
How is mineral absorbed
Active transport
What minerals have regulated absorption
Iron (hormone: hepcidin, when high cause transporter to internalize)
Calcium (regulated by vit D3)
