Digestion and absorption

duodenum.

About 50% of the ingested protein is digested and absorbed in the _______

brush border

Absorption occurs in the small intestine. The _____in the luminal membrane of the intestine amplifies the surface area t

sodium.

Amino acids are transported across the apical membrane via specific amino acid transporters: one for acidic, basic, neutral, and imino amino acids. Much of this occurs as cotransport with _____

facilitated diffusion

Amino acids move across the basolateral membrane via different transporters by ______.

lecithin

An emulsification is a suspension of fat droplets held apart by ______, bile salts, fatty acids, and other agents. The surface area available for digestion is increased dramatically by emulsification.

emulsification

An important function of the bile salts released into the duodenum is to perpetuate the _______of fat droplets by decreasing the surface tension at the oil-water interface.

terminal ileum.

Bile acids are absorbed in the ______

transcobalamin II.

In the ileum, IF-B12 binds to a brush border protein and B12 is absorbed through the intestinal cell by an unknown mechanism. B12 appears in the portal blood bound to a protein called _______

Cystinuria

Intestinal malabsorption of amino acids occurs in various hereditary diseases. ______is a disease characterized partly by defective transport of cystine in the proximal renal tubule and the small bowel.

chylomicrons

Lipid droplets called ______ are formed in the cell. " " are coated with apoprotein, phospholipid and free cholesterol. " " leave the basolateral side by exocytosis and enter gaps between endothelial cells comprising lacteals and leave the intestine via the lymph.

small intestine

Most starch breakdown occurs in the ________by luminal and membrane digestion

jejunum.

Most sugar assimilation is complete in proximal _______

Glycerol ester

Pancreatic Lipase or________lipase: This enzyme is secreted in active form and cleaves the 1 and 3 ester linkages of triglyceride, yielding two free fatty acids and one 2-monoglyceride.

intrinsic factor (IF)

Parietal cells secreted ______that binds vitamin B12. B12 can also bind to " " in the stomach although most of it is R-B12 complex. In the intestine, pancreatic proteases break up the R-B12 complex and B12 binds to" " which is resistant to pancreatic proteases.

diffusion of micelles

Since the lipids move through the luminal membrane quite rapidly, the rate-limiting step of lipid uptake is the ______ through the unstirred layer.

facilitated transport.

The luminal membrane of the brush border also contains cholesterol esterase that hydrolyzes cholesterol esters. Cholesterol moves across the apical membrane via _______

pepsin pancreatic proteases

The primary enzymes associated with protein digestion include: 1 2

absorption

There is a very large disaccharidase reserve in the small intestine. Thus the rate limiting step in carbohydrate assimilation is ________not digestion.

chymotrypsin

This enzyme attacks peptide bonds involving aromatic amino acids, leucine, glutamine, and methionine and yields peptide products with these amino acids at C-terminal end.

Pinocytosis

Transport processes across the intestinal cells include:______, Passive diffusion, Facilitated diffusion, Active transport

Trehalose

________ - glucose dimer with 1,1 linkage

secondary active

in small intestine: Glucose moves from the lumen into the cell via _____ transport by a sodium-cotransport mechanism.

amylopectins and glycogen

Salivary & Pancreatic α-Amylase: 1) Attacks internal 1,4 bonds of amylose and yields maltose & maltotriose. 2) Attacks _______and_______ to yield similar products as well as the α- limit dextrins, which are branched oligosaccharides.

Lactose

_______ intolerance refers to a condition of low levels of brush border lactase. Undigested " " passes on to the colon where it is metabolized by colonic bacteria. This produces gas and metabolic products that enhance colonic motility and cause diarrhea.

Starch

_______ is a high molecular weight compound of two polysaccharides - amylose & amylopectin.

sodium cotransport

_______ protein facilitates the movement of long-chain fatty acids by a membrane protein called microvillous membrane fatty acid-binding protein (MVM-FABP).

Amylopectin

_______- plant starch; in addition to 1,4 linkages there are 1,6 linkages every 20 to 30 glucose units.

Lactose

________ - 1 molecule of galactose bound to glucose by a β1,4 glycosidic linkage

Glycogen

________ - high molecular weight polysaccharide with more 1,6 linkages than amylopectin

Colipase:

________ Enzyme is secreted with pancreatic lipase and is essential for the function of pancreatic lipase. " "prevents bile salts from inactivating pancreatic lipase.

Maltose

________- glucose dimer with 1,4 linkages

Phospholipase A2

________: Activated by trypsin. Bile salts and phospholipids form mixed micelles that become substrates for " " The enzyme requires bile salts in hydrolyzing dietary phospholipids at the 2 position and producing lysophospholipid and free fatty acids.

Cholesterol Esterase

________: Hydrolyzes cholesterol esters yielding one fatty acid and free cholesterol. It also hydrolyzes all three linkages of triglycerides as well as the esters of vitamins A, D. and E.

Glucose-galactose malabsorption

_________ syndrome is a rare disease caused by a mutation in the apical-membrane glucose transporter. Ingestion of glucose, galactose, or starch causes severe diarrhea. Fructose is well tolerated and can be fed to infants with this disease.

Enterokinase or enteropeptidase

________converts trypsinogen to trypsin. " "is located on the brush border of the duodenal and jejunal enterocytes. Trypsin then activates pancreatic precursors including trypsinogen. Trypsin attacks bonds involving basic amino acids at the C-terminal end.

Congenital lactose

________intolerance is a rare condition in newborns who lack sufficient lactase and have diarrhea when fed breast milk or formula containing lactose. These infants are fed formula with sucrose or fructose as the major carbohydrate.

Luminal

_______digestion refers to chemical breakdown by enzymes secreted by salivary glands, stomach and pancreas.

Cobalamin (vitamin B12)

_______plays a major role in the production of red blood cells.

absorption

_______refers to the epithelial transport mechanisms that move digested products into the blood or lymph

Adaptation

______refers to functional adjustments that maintain homeostasis or allow one to cope better with the environment.

gastric lipase

enzymes involved in digestions of lipids: Cells of the gastric fundus secrete _____that acts on outer ester linkages to produce fatty acids and diglycerides. In the absence of pancreatic lipase, " " may play an essential role in lipid digestion.

Lingual

enzymes involved in digestions of lipids: _____Lipase: Produced by serous glands in the tongue

facilitated diffusion.

in small intestine: Glucose moves out of the cell across the basolateral membrane via _________ Galactose is transported by the same mechanism.

diffuse

micelles ____through apical membrane

trypsin chymotrypsin elastase carboxypeptidase

pancreatic proteases include: 1 2 3 4

(A, D, E, & K)

the fat soluble vitamins______,______,______,_____ are absorbed via the micelle action noted above. These vitamins diffuse into the cell, enter the chylomicrons, leave the intestine in the lymph and are transported to the blood via the thoracic duct.

four

Brush Border Peptidases: The brush border of the duodenum and small intestine contains numerous peptidases. These peptidases are integral membrane proteins with their active sites facing the lumen. They include aminopeptidases, dipeptidases, and dipeptidyl aminopeptidases. These enzymes are active against peptides of ______or more amino acids and reduce the peptides produced by pancreatic proteases to oligopeptides and amino acids.

50

Carbohydrate intake is approximately 300 g/day or roughly ____% of the daily calories.

pepsin

Chief cells secrete the precursor pepsinogen. Stomach acid converts pepsinogen to _______, which digests 10-15% of the dietary protein. " "activity terminates when acid gastric contents mix with alkaline pancreatic juice in the small intestine.

secondary active transport

Conjugated bile acids are transported across the apical membrane via ______that is sodium dependent. Unconjugated bile acids are less polar and thus diffuse through the apical membrane. The absorbed bile acids leave the intestine via the portal blood.

secondary active

Di- and tripeptides are transported across the apical membrane more rapidly than amino acids. A single membrane transport system with broad specificity is responsible for absorption of these small peptides. This is a ________transport system powered by H+ gradients.

solubility

A vitamin is an organic compound that cannot be manufactured by the body. Vitamins are needed in small quantities for normal metabolic function and growth and maintenance of the body. The major consideration with intestinal absorption of vitamins is _____

25

An increase in blood glucose of at least ______mg/dl over fasted levels indicates normal hydrolysis of lactose and normal absorption of glucose.

pernicious anemia.

Any disease condition that interferes with the production or secretion of IF or with the binding of the IF-B12 complex to its receptor in the ileum leads to malabsorption of B12 and _______

micelles.

Bile salts perform an important function in the absorption of lipolytic products. When their concentration in the intestine is raised to a critical level, bile salt monomers form water- soluble aggregates called ________

Trehalase

Brush Border Carbohydrases: _______- breaks 1,1 bond of trehalose to glucose

Sucrase

Brush Border Carbohydrases: _______ & Isomaltase - hydrolyze α-limit dextrins, maltotriose and maltose

Isomaltase

Brush Border Carbohydrases: ________ (also called α-dextrinase) hydrolyses the 1,6 bond of α-limit dextrins

Sucrase

Brush Border Carbohydrases: ________ cleaves 100% of sucrose to yield glucose and fructose

Lactase

Brush Border Carbohydrases: ________- splits lactose into glucose and galactose

Glycoamylase

Brush Border Carbohydrases: _______hydrolyses the oligosaccharides

passive diffusion.

Controversy exists regarding absorption of the water-soluble vitamins (B1, B2, B6, B12, C, biotin, folic acid, nicotinic acid, and pantothenic acid). When taken in high doses, these might be absorbed via _______ However, specific sodium-coupled cotransporters have been reported for these vitamins.

jejunum

Di- and tripeptides are transported across the apical membrane more rapidly than amino acids. A single membrane transport system with broad specificity is responsible for absorption of these small peptides. This is a secondary active transport system powered by H+ gradients.The _______ is more active than the ileum in uptake of di- and tripeptides.

luminal & membrane.

Digestion can be divided into two types: 1 2

GLUT 5 GLUT 2.

Fructose moves across the apical membrane via facilitated diffusion by ______ and crosses the basolateral membrane also via facilitated diffusion by ______

passive diffusion

Lipids enter epithelial cells by a sequence of chemical and physical events that render water- insoluble molecules capable of being absorbed by_______

small intestine.

While some food assimilation occurs in the mouth and stomach, almost all of it occurs in the _____

Amylose

_____ - straight chain polymer of glucose linked by α-1,4 glycosidic bonds

Cytoplasmic

_____ Peptidases: Many proteins move into intestinal cells as di- and tripeptides. Cellular peptidases convert these into single amino acids.

Membrane

_____ digestion refers to enzymes synthesized by epithelial cells and inserted into the apical membrane.

Hartnup

_____ disease is a rare hereditary disorder where one of the major neutral amino acid transport proteins is deficient in the brush border of the small intestine. It is also absent in the proximal tubule of the nephron. Individuals with " "disease have elevated urine levels of neutral amino acids. These people still absorb neutral amino acids in the gut quite well because of efficient absorption in the form of di- and tripeptides.

Sucrose

______ - glucose disaccharide consisting of 1 mol of glucose bound at the number 1 carbon to the number 2 carbon of fructose

Micelles

______ have a hydrophilic outer surface and hydrophobic center where the water-insoluble monoglycerides are solubilized. Lysophospholipids, cholesterol, and fat-soluble vitamins may be solubilized.

Digestion

______ is the enzymatic breakdown of food

Pancreatic

_______ Lipases are the major enzymes responsible for the majority of lipid digestion.

Elastase

_______ attacks peptide bonds involving neutral aliphatic amino acids and yields products with neutral amino acids at C-terminal end.

carboxypeptidase

_______ attacks peptides with aromatic and neutral aliphatic amino acids at C-terminal end and attacks peptides with basic amino acids at C-terminal end. Two isoforms (A & B)

Luminal

_______ digestion begins in the mouth with salivary amylase and ends in the small intestine with pancreatic amylase.