Biochemistry 22 And 23 - Digestion And Absorption I And Ii

Front 1

Discuss the medical importance of digestion and absorption of the major food groups (carbohydrates, lipids, proteins)

Back 1

Carbohydrates - Carbohydrates are a major component for energy metabolism. They provide also sugars that can be eventually stored as glycogen mainly in liver and muscle. A high carbohydrate diet, however, can lead to increased fatty acid de-novo synthesis in the liver and eventually can lead to an increase of fat depots of the human body
Proteins - Dietary protein digestion is important, as it does not only provide amino acids in general, but it also delivers the dietary essential amino acids which cannot be synthesized in humans. Milk, eggs, soybeans have a perfect score regarding dietary essential amino acids, followed by meats. The mixture of different plant food improves the score when eaten at the same time. (e.g. beans and wheat)
Lipids - Dietary important for energy metabolism and storage in human fat cells. Dietary essential fatty acids are required for membrane fluidity and synthesis of eicosanoids. Oleic acid and the dietary essential fatty acids are protective against CHD. Cold water fish are rich in ω-3 fatty acids.
Vitamins and minerals - Most vitamins are found in plants, exception is vitamin B12. The intrinsic factor formed in the parietal cells of the stomach is needed for eventual uptake of B12 into the intestinal mucosal cell (ileum). Lipid-soluble vitamins reach the liver inside of chylomicron remnants.

Front 2

Describe the digestion in the mouth and in the stomach (role of salivary amylase and gastric lipase)

Back 2

Salivary α-amylase - A digestive enzyme released by salivary glands into the mouth. Salivary a-amylase cleaves α(1 ,4) glycosidic bonds of starch and glycogen to branched oligosaccharides. (It cannot cleave the α(1, 6) glycosidic bonds at branch points. Cellulose is not digested as it contains β(1, 4) glycosidic bonds. Lingual lipase - A digestive acidic enzyme that originates in the mouth. It is mostly swallowed and will be active in the stomach. This is important for milk digestion in newborns.
Digestion in the Stomach - When stimulated by the ingestion of food, G-cells in the antrum of the stomach release gastrin which stimulates the parietal cells to release of gastric acid (HCl) and intrinsic factors. Mucus will be released by mucus cells. Chief cells will release pepsinogen and gastric lipase.
Gastric Acid - The functional component of gastric acid is the hydrochloric acid. It functions to denature proteins and nucleotides, including the salivary α-amylase. It also destroys most bacteria, viruses, and parasites.
Gastric Lipase - An acidic digestive enzyme which, along with the swallowed lingual lipase, begins digestion of lipids by cleaving TAGs with medium-chain fatty acids found in milk without the presence of bile acids. These medium-chain fatty acids are later taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver.
Pepsinogen and Pepsin - Pepsinogen is the non-enzymatic precursor to pepsin and released by chief cells. It is auto-catalytically activated to pepsin at high proton concentration in the lumen of the stomach. The generated pepsin can then cleave pepsinogen and generates by enzymatic proteolysis more pepsin. Pepsin is an endopeptidase that is stable at low pH.

Front 3

Salivary α-amylase

Back 3

A digestive enzyme released by salivary glands into the mouth. Salivary a-amylase cleaves α(1 ,4) glycosidic bonds of starch and glycogen to branched oligosaccharides. (It cannot cleave the α(1, 6) glycosidic bonds at branch points. Cellulose is not digested as it contains β(1, 4) glycosidic bonds.

Front 4

Lingual lipase

Back 4

A digestive acidic enzyme that originates in the mouth. It is mostly swallowed and will be active in the stomach. This is important for milk digestion in newborns.

Front 5

Gastric Acid

Back 5

The functional component of gastric acid is the hydrochloric acid. It functions to denature proteins and nucleotides, including the salivary α-amylase. It also destroys most bacteria, viruses, and parasites.

Front 6

Gastric Lipase

Back 6

n acidic digestive enzyme which, along with the swallowed lingual lipase, begins digestion of lipids by cleaving TAGs with medium-chain fatty acids found in milk without the presence of bile acids. These medium-chain fatty acids are later taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver.

Front 7

Pepsinogen and Pepsin

Back 7

Pepsinogen is the non-enzymatic precursor to pepsin and released by chief cells. It is auto-catalytically activated to pepsin at high proton concentration in the lumen of the stomach. The generated pepsin can then cleave pepsinogen and generates by enzymatic proteolysis more pepsin. Pepsin is an endopeptidase that is stable at low pH.

Front 8

Discuss the biochemical and clinical consequences of insufficient acid production in the stomach and the effect of antacids

Back 8

Gastric acid (HCL) is a strong acid needed for optimal food digestion. The acid denatures proteins and nucleic acids for better digestion and it also destroys bacteria and fungi found in food. It also provides the acidic environment necessary for functional pepsin, gastric lipase, and lingual lipase. With insufficient acid production (such as in the elderly) or excessive neutralization with antacids, pH will be increased resulting in lower ability to denature proteins and nucleic acids, weaken the ability to destroy bacteria and other pathogens, and cause your digestive enzymes to not function in their optimal environment.

Front 9

Discuss the digestion of lipids found in breast milk

Back 9

Breast milk is especially high in medium chain fatty acids (8-12). These are fatty acids along with TAGs are targeted by lingual and gastric lipase and are digested in the stomach. Afterwards, they are taken up into intestinal mucosal cell and released into the portal vein. These are the only types of digest lipids that reach directly to the liver. This is especially important in infants such that they have an immediate energy source available to them at an early age.

Front 10

Describe the role of gastrin and the activation of pepsinogen in the stomach.

Back 10

Gastrin - A peptide hormone released by G-cells in the antrum of the stomach and stimulates parietal cells to secrete gastric acid.
Chief Cells - Secretory cells that release pepsinogen and gastric lipase. It is stimulated by a variety of factors including the vagus nerve and the acidic environment generated by released gastric acid.
Pepsinogen is auto-catalytically activated by the low pH environment of the stomach generated by gastric acid. The pepsin it converts to also activates other pepsinogen via enzymatic proteolysis, causing an exponential activation of functional pepsin.

Front 11

Gastrin

Back 11

A peptide hormone released by G-cells in the antrum of the stomach and stimulates parietal cells to secrete gastric acid.

Front 12

Explain the mechanisms involved with the release and the functions of cholecystokinin and secretin

Back 12

Secretin - A peptide hormone. It is produced and released by S-cells of the duodenum, located in the crypts of Lieberkühn. It is released in response to pH change, such as from the acid chyme of the stomach. Secretin also helps regulate the pH of the duodenum by: inhibiting the secretion of gastric acid from the parietal cells of the stomach; and stimulating the production of bicarbonate from the centroacinar cells and intercalated ducts of the pancreas.
Cholecystokinin (CCK) - "bile sac move". It is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein in the small intestine. It is synthesized and secreted by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum. Activates secretion of bile from the gallbladder. inhibits gastric motility which allows neutralization of acidic chyme. Activates enteropeptidase, an enzyme that is normally membrane-bound in the brush border of the duodenum. Activates secretion of pancreatic enzymes and proteins.
Enteropeptidase - An enyzme that is normally membrane bound in the brush border of the duodenum. It becomes motile in the intestinal lumen by stimulation from Cholecystokinin (CCK).

Front 13

Secretin

Back 13

A peptide hormone. It is produced and released by S-cells of the duodenum, located in the crypts of Lieberkühn. It is released in response to pH change, such as from the acid chyme of the stomach. Secretin also helps regulate the pH of the duodenum by: inhibiting the secretion of gastric acid from the parietal cells of the stomach; and stimulating the production of bicarbonate from the centroacinar cells and intercalated ducts of the pancreas.

Front 14

Cholecystokinin (CCK)

Back 14

"bile sac move". It is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein in the small intestine. It is synthesized and secreted by I-cells in the mucosal epithelium of the small intestine and secreted in the duodenum. Activates secretion of bile from the gallbladder. inhibits gastric motility which allows neutralization of acidic chyme. Activates enteropeptidase, an enzyme that is normally membrane-bound in the brush border of the duodenum. Activates secretion of pancreatic enzymes and proteins.

Front 15

Enteropeptidase

Back 15

An enyzme that is normally membrane bound in the brush border of the duodenum. It becomes motile in the intestinal lumen by stimulation from Cholecystokinin (CCK). It converts the zymogen Trypsinogen into active Trypsin.

Front 16

Indicate the role of HCO3- in pancreatic secretion and bile

Back 16

Bicarbonate is released in the duodenum via secretin stimulation. It helps stabilize the pH of the acid chyme from about 2 to 7-8. This change in pH is essential for the deactivation of pepsin from the stomach and for optimal enzymatic activity of pancreatic enzymes and bile.

Front 17

Describe the proteolytic activation of zymogens using trypsinogen, other pancreatic proteases and prophospholipase A2 as examples

Back 17

Trypsinogen is released from the pancreas with an trypsin inhibitor to prevent premature activation. In the duodenum, trypsinogen is converted to trypsin via the enzyme enteropeptidase. Trypsin converts trypsinogen into trypsin via enzymatic proteolysis, exponentially increasing the number of active trypsin. Trypsin will than go about converting several zymogens into their active enzyme forms. This includes the proteases: chymotrypsinogen to chymotrypsin, proelastase to elastase, and procarboxypeptidases to carboxypeptidases; and the lipases: procolipase to colipase and prophospholipase A2 to phospholipase A2. They digest each other once dietary protein is absent, essentially deactivating and recycling themselves.

Front 18

Describe the specific cleavage sites in proteins of digestive proteases like trypsin, chymotrypsin and elastase

Back 18

Trypsinogen and Trypsin - Trypsinogen is the zymogen of trypsin. Trypsinogen is converted to trypsin via enteropeptidase or trypsin. Trypsin is an endopeptidase that cleave peptide bonds after Arg or Lys residues, unless followed by Pro. It has a long, narrow pocket for a binding site. Trypsin also activates various other peptidases and lipases.
Chymotrypsinogen and Chymotrypsin - Chymotrypsinogen is the zymogen of chymotrypsin. It is converted to its active form via trypsin. Chymotrypsin is an endopeptidase that cleave peptide bonds after bulky and aromatic residues Phe, Trp, or Tyr, unless followed by Pro. Cuts more slowly after His, Met or Leu. It has a large, wide pocket for its binding site.
Proelastase and Elastase - Proelastase is the zymogen of elastase. It is converted into its active form by trypsin. Elastase is an endopeptidase that cleave peptide after Ala, Gly, Ser, or Val, unless followed by Pro. It has a small pocket for its binding site.
Procarboxypeptidases A or B and Carboxypeptidases A or B - Procarboxypeptidases are the zymogen of carboxypeptidases which are converted to their active form by trypsin. Carboxypeptidases A or B are exopeptidases and cleave from the carboxyl-end.

Front 19

Trypsinogen and Trypsin

Back 19

Trypsinogen is the zymogen of trypsin. Trypsinogen is converted to trypsin via enteropeptidase or trypsin. Trypsin is an endopeptidase that cleave peptide bonds after Arg or Lys residues, unless followed by Pro. It has a long, narrow pocket for a binding site. Trypsin also activates various other peptidases and lipases.

Front 20

Chymotrypsinogen and Chymotrypsin

Back 20

Chymotrypsinogen is the zymogen of chymotrypsin. It is converted to its active form via trypsin. Chymotrypsin is an endopeptidase that cleave peptide bonds after bulky and aromatic residues Phe, Trp, or Tyr, unless followed by Pro. Cuts more slowly after His, Met or Leu. It has a large, wide pocket for its binding site.

Front 21

Proelastase and Elastase

Back 21

Proelastase is the zymogen of elastase. It is converted into its active form by trypsin. Elastase is an endopeptidase that cleave peptide after Ala, Gly, Ser, or Val, unless followed by Pro. It has a small pocket for its binding site.

Front 22

Procarboxypeptidases A or B and Carboxypeptidases A or B

Back 22

Procarboxypeptidases are the zymogen of carboxypeptidases which are converted to their active form by trypsin. Carboxypeptidases A or B are exopeptidases and cleave from the carboxyl-end.

Front 23

Discuss the intestinal digestion of proteins (endo- and exopeptidases),lipids (pancreatic lipase, cholesterol esterase and phospholipase A2), carbohydrates (amylase and disaccharidases) and nucleic acids (nucleases).

Back 23

Endopeptidase - Proteolytic peptidases that break peptide bonds of non-terminal amino acids
Exopeptidase - Proteolytic peptidase that catalyzes the cleavage of the terminal (or the penultimate) peptide bond; the process releases a single amino acid or dipeptide from the peptide chain.
Colipase - A coenzyme of pancreatic lipase which is activated from its zymogen form, procolipase, via trypsin.
Pancreatic Lipase - It is secreted from the pancreas, and is the primary lipase that hydrolyzes dietary fat molecules in the human digestive system, converting triglyceride substrates found in ingested oils to monoglycerides and free fatty acids. The generated monoglycerides and free fatty acids are readily absorbed into the intestinal mucosa calls. Pancreatic lipase requires colipase as a cofactor and the emulsification activity of bile salts and other detergents (like lysophosphotidylcholine) to localize the TAG substrate.
Cholesterol Esterase - Converts cholesterol esters into free cholesterol.
Phospholipase A2 - Phospholipase which cleaves the acyl bond at the second glycerol position. Important for converting phosphotidylcholine, which is both a component of bile and a dietary lipid, into lysophosphotidylcholine, which have detergent character. Assist bile salts in emulsification.
Pancreatic α-Amylase - Acts on oligosaccharides and eventually forms the disaccharides sucrose, lactose, maltose and isomaltose.
Disaccharidase - Intestinal disaccharidases include: Sucrase-isomaltase (Converts sucrose to glucose and fructose), Lactase (Converts lactose to glucose and galactose), and Maltase-glucoamylase (Converts Maltase into 2 glucoses)
Pancreatic Nucleases/Phosphodiesterases - Converts nucleic molecules into mononucleotides. Nucleotides are further broken down into ribose/dioxyribose and primidine/purine bases. Ribose, deoxyribose, and primidines are absorbed into the intestinal mucosal cells and then transferred to the liver via portal vein. Purines on the other hand are converted to uric acid in the intestinal mucosa cell and are then transferred to the kidney for excretion.

Front 24

Endopeptidase

Back 24

Proteolytic peptidases that break peptide bonds of non-terminal amino acids

Front 25

Exopeptidase

Back 25

Proteolytic peptidase that catalyzes the cleavage of the terminal (or the penultimate) peptide bond; the process releases a single amino acid or dipeptide from the peptide chain.

Front 26

Colipase

Back 26

A coenzyme of pancreatic lipase which is activated from its zymogen form, procolipase, via trypsin.

Front 27

Pancreatic Lipase

Back 27

It is secreted from the pancreas, and is the primary lipase that hydrolyzes dietary fat molecules in the human digestive system, converting triglyceride substrates found in ingested oils to monoglycerides and free fatty acids. The generated monoglycerides and free fatty acids are readily absorbed into the intestinal mucosa calls. Pancreatic lipase requires colipase as a cofactor and the emulsification activity of bile salts and other detergents (like lysophosphotidylcholine) to localize the TAG substrate.
Cholesterol Esterase - Converts cholesterol esters into free cholesterol.

Front 28

Phospholipase A2

Back 28

Phospholipase which cleaves the acyl bond at the second glycerol position. Important for converting phosphotidylcholine, which is both a component of bile and a dietary lipid, into lysophosphotidylcholine, which have detergent character. Assist bile salts in emulsification.

Front 29

Pancreatic α-Amylase

Back 29

Acts on oligosaccharides and eventually forms the disaccharides sucrose, lactose, maltose and isomaltose.

Front 30

Disaccharidase

Back 30

Intestinal disaccharidases include: Sucrase-isomaltase (Converts sucrose to glucose and fructose), Lactase (Converts lactose to glucose and galactose), and Maltase-glucoamylase (Converts Maltase into 2 glucoses)

Front 31

Pancreatic Nucleases/Phosphodiesterases

Back 31

Converts nucleic molecules into mononucleotides. Nucleotides are further broken down into ribose/dioxyribose and primidine/purine bases. Ribose, deoxyribose, and primidines are absorbed into the intestinal mucosal cells and then transferred to the liver via portal vein. Purines on the other hand are converted to uric acid in the intestinal mucosa cell and are then transferred to the kidney for excretion.

Front 32

Describe the function of bile salts within digestion. Predict the consequences of decreased bile salts on digestion of dietary lipids

Back 32

Bile - A fluid produced by the liver and stored in the gall-bladder. It is released into the duodenum via CCK stimulation of surrounding smooth muscle. The main functional component of bile are bile salts, which acts as a emulsification agent. They also contain Cholesterol and bilirubin for excretion from the body. Cholesterol is well dissolved in bile due to the presence of phosphatidylcholine (PC) which improves the solubility of free cholesterol.
Bile Salts - Bile salts are the main functional component of bile. They act as emulsifiers, isolating and grouping groups of TAGs. They facilitate transport of free cholesteroland conjugated bilirubin in bile from the liver to the duodenum, emulsification of dietary lipids for digestion by pancreatic enzymes, and uptake of products of lipid digestion into intestinal mucosal cells.
Cholelithiasis - (cholesterol gallstone disease) can result from reduced secretion of bile salts, or also from enhanced biliary cholesterol secretion which can lead to oversaturation of bile with cholesterol and lead to less solubility of cholesterol. Gallstones are mostly cholesterol gallstones (90%) and are commonly found in the gallbladder, in the cystic duct or in the Ampulla of Vater. The blockage of bile ducts lead to reduced digestion of lipids. It also impairs the release of conjugated bilirubin and leads to obstructive jaundice. Characteristic serum marker is alkaline phosphatase from the irritated and blocked bile ducts.

Front 33

Bile

Back 33

A fluid produced by the liver and stored in the gall-bladder. It is released into the duodenum via CCK stimulation of surrounding smooth muscle. The main functional component of bile are bile salts, which acts as a emulsification agent. They also contain Cholesterol and bilirubin for excretion from the body. Cholesterol is well dissolved in bile due to the presence of phosphatidylcholine (PC) which improves the solubility of free cholesterol.

Front 34

Bile Salts

Back 34

Bile salts are the main functional component of bile. They act as emulsifiers, isolating and grouping groups of TAGs. They facilitate transport of free cholesteroland conjugated bilirubin in bile from the liver to the duodenum, emulsification of dietary lipids for digestion by pancreatic enzymes, and uptake of products of lipid digestion into intestinal mucosal cells.

Front 35

Cholelithiasis

Back 35

Cholelithiasis - (cholesterol gallstone disease) can result from reduced secretion of bile salts, or also from enhanced biliary cholesterol secretion which can lead to oversaturation of bile with cholesterol and lead to less solubility of cholesterol. Gallstones are mostly cholesterol gallstones (90%) and are commonly found in the gallbladder, in the cystic duct or in the Ampulla of Vater. The blockage of bile ducts lead to reduced digestion of lipids. It also impairs the release of conjugated bilirubin and leads to obstructive jaundice.

Front 36

Discuss the uptake of primary and secondary bile acids into the liver via the enterohepatic circulation

Back 36

Primary bile acids are only formed in the liver. Primary bile acids are cholic acid and
chenodeoxycholic acid. The hepatocytes uses free cholesterol for the synthesis of cholic acid and chenodeoxycholic acid. Secondary bile acids are formed from primary bile acids by intestinal bacteria mainly in the ileum. Secondary bile acids are deoxycholic acid and lithocholic acid. Deoxycholic acid is formed from cholic acid and lithocholic acid is formed from chenodeoxycholic acid. Both, primary and secondary bile acids are conjugated only in the liver. Conjugation involves adding a glycine to cholic/deoxycholic acid to form glycocholic/glycodeoxycholic acid AND adding taurine to lithocholic acid /lithocholic acid to form taurolithocholic/taurolithocholic acid. The conjugation affectively reduces the pKa of the bile acids which will cause them to be charged molecules in the intestinal lumen. These conjugated bile acids are hence called bile salts. They are stored in the bile and then released into the intestines for their function in lipid digestion. The bile salts are then reabsorbed into the intestinal mucosal cells as bile acids and free glycine and taurine. 95% reach the liver via the enterohepatic circulation (portal vein). Bile acids are essentially recycled so the liver doesn't have to invest cholesterol into making additional bile acids/salts.

Front 37

Predict the effect of bile duct obstruction on lipid digestion and absorption

Back 37

The blockage of bile ducts lead to reduced digestion of lipids. It also impairs the release of conjugated bilirubin and leads to obstructive jaundice. Characteristic serum marker is alkaline phosphatase from the irritated and blocked bile ducts.

Front 38

Predict the consequences of pancreatic disease (cystic fibrosis and pancreatitis) on digestion

Back 38

Pancreatitis - Pancreatitis is a condition caused by prematurely active trypsin in the pancreas or pancreatic ducts. When trypsin is abnormally active in the pancreas or in the pancreatic duct, then it activates there the other pancreatic zymogens. In this abnormality, the highly active proteases and phospholipase A2 will destroy the proteins and the phospholipid membranes of the pancreas and the pancreatic duct.
Pancreatic Cystic Fibrosis - Patients with cystic fibrosis have dried mucus that blocks the pancreatic duct and leads to less pancreatic enzymes mostly for digestion of dietary proteins and lipids. The pancreas is damaged by fibrosis (cystic fibrosis of the pancreas) which can also lead to insulin deficiency. Patients should eat frequently a calorie-rich diet containing carbohydrates to compensate for the reduced secretion of pancreatic enzymes. Diet should also be rich in medium-chain fatty acids as those lipids are readily digested in the stomach. Additionally, modified pancreatic enzymes can be ingested.

Front 39

Pancreatitis

Back 39

Pancreatitis is a condition caused by prematurely active trypsin in the pancreas or pancreatic ducts. When trypsin is abnormally active in the pancreas or in the pancreatic duct, then it activates there the other pancreatic zymogens. In this abnormality, the highly active proteases and phospholipase A2 will destroy the proteins and the phospholipid membranes of the pancreas and the pancreatic duct.

Front 40

Pancreatic Cystic Fibrosis

Back 40

Patients with cystic fibrosis have dried mucus that blocks the pancreatic duct and leads to less pancreatic enzymes mostly for digestion of dietary proteins and lipids. The pancreas is damaged by fibrosis (cystic fibrosis of the pancreas) which can also lead to insulin deficiency. Patients should eat frequently a calorie-rich diet containing carbohydrates to compensate for the reduced secretion of pancreatic enzymes. Diet should also be rich in medium-chain fatty acids as those lipids are readily digested in the stomach. Additionally, modified pancreatic enzymes can be ingested.

Front 41

Describe the absorption of amino acids, monosaccharides and fats into intestinal mucosal cells

Back 41

Absorption of Amino Acids - Amino acids are taken up by intestinal mucosal cells via secondary active transport with group specific transporters. Most of the amino acid transporters are sodium-dependent co-transporters. Amino acids enter the blood system via facilitated transport and travel to the liver.
Absorption of Fats - Lipids, being non-polar, readily diffuse into the cell. However, their hydrophobic nature make them difficult to transport in free form. They are packaged into chylomicrons and sent into the lymph where they travel freely before moving into the blood system.
Absorption of monosaccharides - Glucose and galactose are taken up via secondary active transport with SGLT-1 with sodium ions against a gradient. Fructose is taken up by facilitated transport with GLUT-5. GLUT-5 also facilitates glucose transport at high concentrations at low affinity. GLUT-2 facilitates the transport of all the monosaccharides into the blood stream which is destined for the liver.

Front 42

Differentiate primary, secondary and congenital lactose intolerance based on age of onset and the primary biochemical defect.

Back 42

Lactose Intolerance - the condition where an individual is unable to digest the disaccharide lactose in the small intestine. This allows lactose to reach the large intestine, where colonic bacteria degrade lactose to lactic acid and short chain fatty acids. This fermentation leads to hydrogen gas, carbon dioxide and methane. H2 can be measured in the breath. Incomplete digestion leads via the osmotic effect to uptake of water into the intestine, bloating and diarrhea. This leads to dehydration of the whole body due to water loss in feces.
Primary Lactose Intolerance - Lactase is normally high in infants and young age due to the primary diet being milk. In primary lactose intolerance, the quantity of functional lactase decreases significantly as the individual gets older.
Secondary Lactose Intolerance - This is lactose intolerance that isn't caused by decrease lactase quantity/quality. Lactose can still enter the large intestine due to damage or loss
of intestinal mucosal cells (food poisoning). Severe diarrhea or gastroenteritis due to
rotavirus can also lead to intestinal injury. Additionally, celiac disease is immune-mediated damage in response to gluten (protein in grains).
Congenital Lactase Deficiency -This is the most severe case of lactose intolerance. It is a rare autosomal recessive disorder which was life threatening in the past. Ingestion of milk would lead to severe diarrhea and dangerous dehydration or even death! The affected baby needs early-on a special formula without lactose that can substitute human milk.

Front 43

Describe the absorption of glucose into intestinal cells

Back 43

Glucose and galactose are taken up via secondary active transport with SGLT-1 with sodium ions against a gradient. Fructose is taken up by facilitated transport with GLUT-5. GLUT-5 also facilitates glucose transport at high concentrations at low affinity. GLUT-2 facilitates the transport of all the monosaccharides into the blood stream which is destined for the liver.

Front 44

Describe the fate of purine bases after uptake into intestinal mucosal cells

Back 44

The purine bases do not reach the liver and are degraded to uric acid inside of the intestinal mucosal cell and are released eventually by the kidney.

Front 45

Describe the formation of chylomicrons in the intestinal mucosal cells.

Back 45

Lipids (Triglycerides, phospholipids, and cholesterol) are packaged into chylomicrons within the intestinal mucosal cells. They transport dietary lipids from the intestines to other locations in the body first via the lymphatic system then the blood stream.

Front 46

Indicate the biochemical mechanisms in the various causes of steatorrhea (pancreatic disease, biliary tract obstruction, intestinal mucosal disease)

Back 46

Steatorrhea - is the presence of excess fat in feces. It have various causes which mostly result in the decreased ability to digest fat. Causes include:
Lack of conjugated bile salts due to liver damage including liver cirrhosisor due to bile duct obstruction by gallstones or pancreatic tumor.
Defects related to pancreatic juice such as deficiency of enzymes, lack of transport of enzymes into the intestines like seen in CF, or lack of bicarbonate secretion which would impair the adjustment of the pH in the duodenum.
Defective mucosal cells related to uptake of nutrients. A shortened bowel could also lead to steatorrhea.