1.4.3 Nutrient Assimilation Flashcards
Na+ dependent absorption of glucose is considered what?
Secondary active transport due to the energy of the sodium electrochemical gradient is established by the Na/K ATPase
What are the requirements for optimal activity of pancreatic lipase?
Colipase
Neutral pH
Bile salts
Where are the different breakdown products absorbed?
How does flow rate alter the ionic composition of the pancreas secretions?
As flow increases the concentration of bicarbonate increases and the concentration of Cl- decreases
Absorption of carbohydrates is dependent on what?
Na+ dependent through the specific transporter SGLT1
What are the two types of passive transport?
Passive diffusion - permeable to the membrane
Facilitate diffusion - protein in membrane that forms channel
Bile salts and vitamin B12 are have specific transport mechanisms where?
Ther terminal ileum
What are some important characteristics of colipase?
What is the membrane protein associated with facilitated diffusion of Glucose, galactose and fructose in the gut?
GLUT 5
What is a main protein digestors in the intestinal lumen?
Pancretic proteases
What is this an image of?
Microvillus Membrane
Protein digestion begins in the stomach with what enzyme?
Pepsin
What is the importance of bile salts in lipid digestion?
Bile salts emulsify lipids into micelles and assist binding of colipase to the lipase at the droplet interface
What is the major lipolytic enzyme?
Pancreatic lipase
Small peptides are absorbed by what membrane channel?
PEPT1 - an H+ dependent transporter
What is this an image of?
How do the villus and crypts differ?
What is this an image of?
Enterocyte - formation of the chylomicrons
What is the difference between these two images of the gall bladder?
Left - resting
Right - active
Electron micrographs of gallbladder. Note the microvilli (MV) on the apical surface of the cells. These epithelial cells transport sodium chloride from the lumen to the subjacent connective tissue. Water follows passively, causing the bile to become concentrated. Notice large numbers of mictochondria (dark ovals) consistent with active electrolyte/fluid transport. When the epithelium is actively transporting electrolytes/fluid, the intercellular spaces become distended (Active).
Knockout of what two genes can cause problems in sodium recycling?
Cldn2 and Cldn15
Where does amylase cleave starches at?
alpha-1,4-bonds
Enterokinase activates what?
Converts trypsinogen to trypsin
Trypsin will activate all others!
What are these images?
Left bile canalicus
Sinusoid
What is the process of Na recycling in the gut?
Na+ is able to be recycled paracellularly and transverse tight junction proteins.
Claudin proteins control paracellular Na+ permeability
What is this an image of?
Tight junctional complexes
Fill in this chart
Describe the unstirred layer in the intestine lipid digestion and absorption
What is the difference between an endopeptidase and exopeptidase?
Endopeptidase - cleave internally yielding products that are 2-6 AA long
Exopeptidase - cleaves at the terminal segment yielding free AA
During times between meals how does trypsin affect CCK release?
Where there is no protein to break down, Trypsin will continually break down CCK-RP and Monitor peptide and keep them from binding to the CCK cell (I cell)
Monosaccharides exit through what in the basolateral membrane of the intestine?
The GLUT2 transporter
Single AA absorption is dependent on what?
Na-AA transport
Where are chylomicrons synthesized?
Smooth endoplasmic reticulum
In the proximal duct what is the main mechanism of bicarbonate secretion?
There is little of it and it works with the CFTR channel that is secreting Cl- into the lumen and exchanges HCO3- for luminal Cl- through the antiporter.
Bicarbonate is always secreted with?
Mucous
How does bicarbonate secretion change in the distal channel of the pancreas?
The CFTR channel acts as a direct secretor of HCO3-
What is the importance of oligosaccharidases present in the brush border?
These convert oligosaccharides and disaccharides to monosaccharides for absorption
Only monosaccharides can be absorbed
CCK-RP release by enterocytes will have what effect?
It is activated by FAs and AAs which will bind to receptor on CCK cell and CCK will be released into the bloodstream
Explain the process of lipid digestion and absorption?
The process of dietary lipid digestion and absorption. a | Dietary lipid digestion begins in the stomach, where lipids are subjected to partial digestion by gastric lipase and form large fat globules with hydrophobic triacylglycerol (TAG) cores surrounded by polar molecules, including phospholipids (PLs), cholesterol (CL), fatty acids (FAs) and ionized proteins. The digestive processes are completed in the intestinal lumen, where large emulsions of fat globules are mixed with bile salts (BS) and pancreatic juice containing lipid digestive enzymes to form an aqueous suspension of small fatty droplets to maximize exposure to the pancreatic lipases for lipid hydrolysis. Monoacylglycerol (MAG), diacylglycerol (DAG) and free FAs that are released by lipid hydrolysis join BS, CL, lysophosphatidic acid (LPA) and fat-soluble vitamins to form mixed micelles that provide a continuous source of digested dietary products for absorption at the brush-border membranes of the enterocytes. b | FAs and MAG enter the enterocytes by passive diffusion and are facilitated by transporters, such as intestinal FA-binding protein (IFABP), CD36 and FA-transport protein-4 (FATP4). They are then re-esterified sequentially inside the endoplasmic reticulum by MAG acyltransferase (MGAT) and diacylglycerol acyltransferase (DGAT) to form TAG. Phospholipids from the diet as well as bile — mainly LPA — are acylated by 1-acyl-glycerol-3-phosphate acyltransferase (AGPAT) to form phosphatidic acid (PA), which is also converted into TAG. Dietary CL is acylated by acyl-CoA:cholesterol acyltransferase (ACAT) to cholesterol esters (CE). Facilitated by microsomal triglyceride transfer protein (MTP), TAG joins CE and apolipoprotein B (ApoB) to form chylomicrons (CM) that enter circulation through the lymph.
What are the three types of active transport?
Symport - two substances brought in together
Antiporter- “exchange” of molecules
Primary active transport - ATP creates energy to drive the molecule against its gradient
AGAINST THE GRADIENT
Describe the protein cleavage of some of the peptidases?
How does digestion of long chain triglycerides differ from short and medium chain triglycerides?
What is the main carbohydrate digestive enzyme?
Pancreatic-alpha-amylase
