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Macronutrient Digestion
Digestion - the process of breaking down food for it to become usable in the body.
The digestive (gastrointestinal) tract is within the body but also considered outside of the body because the system is open at both ends (mouth and anus). Therefore, it is in contact with the outside environment of the human/animal and in order to enter the body the food or compound must be absorbed from the small intestine into the cells and circulated through the body (like how something would need to be absorbed by the skin outside the body). Everything that is not absorbed into the body, leaves through the anus as feces.
Gastrointestinal or Digestive Tract
Really good YouTube video that explains Digestion:
Overview of Digestion
Mastication (chewing food)
Salivary amylase begins carb digestion and lingual lipase begins lipid digestion, both playing a minor role in overall digestion.
Peristalsis is the wave-like muscular contractions that move contents through entire digestive tract.
Swallowing moves the chewed food (bolus) to esophagus then it enters the stomach through the lower esophageal sphincter (regulates entry into the stomach).
Stomach
G-cells secrete gastrin, which in turn stimulates the parietal and chiefcells.
The digestive (gastrointestinal) tract is within the body but also considered outside of the body because the system is open at both ends (mouth and anus). Therefore, it is in contact with the outside environment of the human/animal and in order to enter the body the food or compound must be absorbed from the small intestine into the cells and circulated through the body (like how something would need to be absorbed by the skin outside the body). Everything that is not absorbed into the body, leaves through the anus as feces.
http://commons.wikimedia.org/wiki/Image:Digestivetract.gif
Digestive Accessory Organs
Accesory organs are organs that are not part of the digestive tract, but that serve a role in digestion.
They include salivary glands, liver, gall-bladder and pancreas.
Digestive Accessory Organs
They include salivary glands, liver, gall-bladder and pancreas.
Really good YouTube video that explains Digestion:
Overview of Digestion
Mastication (chewing food)
Salivary amylase begins carb digestion and lingual lipase begins lipid digestion, both playing a minor role in overall digestion.
Peristalsis is the wave-like muscular contractions that move contents through entire digestive tract.
Swallowing moves the chewed food (bolus) to esophagus then it enters the stomach through the lower esophageal sphincter (regulates entry into the stomach).
Stomach
G-cells secrete gastrin, which in turn stimulates the parietal and chiefcells.
The stomach produces HCl (through parietal cells), so it is really acidic
This acidity causes the enzymes from the mouth (salivary amylase and lingual lipase) to denature.
Stomach cells (chief cells) secrete pepsinogen which is activated by HCl to produce pepsin (begins protein breakdown)
Mucus is produced as well by neck cells to prevent the stomach from digesting itself.
Gastric lipase continues breakdown of lipids here
Chyme (partially digested food up to this point) leaves stomach through a different sphincter (pyloric sphincter).
Small intestineis where is bulk of digestion is performed
Chyme (very acidic) enters into duodenum (first part of small intestine).
The arrival of chyme stimulates the secretion of the hormones Secretin and Cholocystokinin (CCK) which do 3 things:
-stimulates pancreas to secrete bicarbonate and pancreatic enzymes (together = pancreatic juice).
- stimulates liver (where bile is made) to secrete bile to gall bladder (where bile is stored & concentrated)
-causes gall bladder to contract and release bile into duodenum
So…. Bile, bicarbonate, and enzymes are now in the small intestine.
Bicarbonate neutralizes acid so it doesn't denature proteins (enzymes and small intestine itself)
Enteropeptidase (enzyme in small intestine) begins cascading effect (process of activating pancreatic enzymes: proteases and colipase by cleaving off ends)
Once activated these work in digestion of proteins, and lipids:
-Proteins: Proteases breaks down proteins to amino acids and small peptides
-Carbs: Pancreatic amylase (enzyme from pancreatic juice) breaks them down to disaccharides and monosaccharides
-Lipids: Colipase helps pancreatic lipase cleave off SN-1 and SN-3 so there is 2-Monoglycerides and free fatty acids left
Brush Border is where they prepare for absorption
-Proteins: Peptidases cleaves peptides to make individual amino acids or small peptides
-Carbs: Disaccharidases cleave disaccharides into monosaccharides (glucose, galactose, and fructose)
-Lipids: Mixed micelles are formed. Contain 2-monoglyceride, free fatty acids (cleaved off previously), bile acids, cleaved phospholipids, and cholesterol.
Absorption
Transporters take monosaccharides, amino acids, and small peptides into the Enterocyte (absorptive cell of small intestine).
Mixed micelles diffuse into the cells.
Carbs: Glucose and Galactose absorbed by SGLT1 into enterocyte (active absorption)
This acidity causes the enzymes from the mouth (salivary amylase and lingual lipase) to denature.
Stomach cells (chief cells) secrete pepsinogen which is activated by HCl to produce pepsin (begins protein breakdown)
Mucus is produced as well by neck cells to prevent the stomach from digesting itself.
Gastric lipase continues breakdown of lipids here
Chyme (partially digested food up to this point) leaves stomach through a different sphincter (pyloric sphincter).
Small intestineis where is bulk of digestion is performed
Chyme (very acidic) enters into duodenum (first part of small intestine).
The arrival of chyme stimulates the secretion of the hormones Secretin and Cholocystokinin (CCK) which do 3 things:
-stimulates pancreas to secrete bicarbonate and pancreatic enzymes (together = pancreatic juice).
- stimulates liver (where bile is made) to secrete bile to gall bladder (where bile is stored & concentrated)
-causes gall bladder to contract and release bile into duodenum
So…. Bile, bicarbonate, and enzymes are now in the small intestine.
Bicarbonate neutralizes acid so it doesn't denature proteins (enzymes and small intestine itself)
Enteropeptidase (enzyme in small intestine) begins cascading effect (process of activating pancreatic enzymes: proteases and colipase by cleaving off ends)
Once activated these work in digestion of proteins, and lipids:
-Proteins: Proteases breaks down proteins to amino acids and small peptides
-Carbs: Pancreatic amylase (enzyme from pancreatic juice) breaks them down to disaccharides and monosaccharides
-Lipids: Colipase helps pancreatic lipase cleave off SN-1 and SN-3 so there is 2-Monoglycerides and free fatty acids left
Brush Border is where they prepare for absorption
-Proteins: Peptidases cleaves peptides to make individual amino acids or small peptides
-Carbs: Disaccharidases cleave disaccharides into monosaccharides (glucose, galactose, and fructose)
-Lipids: Mixed micelles are formed. Contain 2-monoglyceride, free fatty acids (cleaved off previously), bile acids, cleaved phospholipids, and cholesterol.
Absorption
Transporters take monosaccharides, amino acids, and small peptides into the Enterocyte (absorptive cell of small intestine).
Mixed micelles diffuse into the cells.
Carbs: Glucose and Galactose absorbed by SGLT1 into enterocyte (active absorption)
Fructose absorbed by GLUT5 into enterocyte (passive absorption)
Proteins: amino acids absorbed by amino acid transporter and small peptide chains absorbed by PEPT1.
Proteins: amino acids absorbed by amino acid transporter and small peptide chains absorbed by PEPT1.
From entrocyte:
-Carbs – GLUT2 transporter transports monosaccharides to capillaries (passive)
-Proteins – a number of transporters transports amino acids to capillaries (peptides get broken down to amino acids)
-Lipids- Get reformed to triglycerides and phospholipids (reesterfied) which are packed into chylomicrons ( lipoprotein). Chylomicrons are then secreted into lacteal, which is part of the lymph system and which eventually connects to cardiovascular system through the thoracic duct emptying into the subclavian vein.Short chain fatty acids bind with albumin in the capillary.
Transported to liver:
Lipoprotein lipase cleaves off triglycerides (fat) from chylomicrons for tissues around the body, which leads to formation of chylomicron remnants (whats left, contain lower triglyceride levels), which is taken up by the liver.
Capillaries (containing monosaccharides and amino acids) go through the portal vein to liver.
Liver takes up galactose and fructose. Most glucose is left in the blood stream (stimulates the glycemic response).
We haven't talked about amino acids yet
Glycemic Response
Glucose enters the pancreas through a GLUT transporter, and if it is high secretes insulin ( a hormone).
Muscle and Adipose contain a GLUT4 transporter that responds to insulin binding to the receptor
In that it causes the GLUT4 transporters inside the cell to move to the cell surface and begin taking up glucose
Insulin moves glucose to edge cell so muscles and adipose can start taking it up.
This uptake lowers blood glucose levels so that we can continue or intake of glucose.
-Proteins – a number of transporters transports amino acids to capillaries (peptides get broken down to amino acids)
-Lipids- Get reformed to triglycerides and phospholipids (reesterfied) which are packed into chylomicrons ( lipoprotein). Chylomicrons are then secreted into lacteal, which is part of the lymph system and which eventually connects to cardiovascular system through the thoracic duct emptying into the subclavian vein.Short chain fatty acids bind with albumin in the capillary.
Transported to liver:
Lipoprotein lipase cleaves off triglycerides (fat) from chylomicrons for tissues around the body, which leads to formation of chylomicron remnants (whats left, contain lower triglyceride levels), which is taken up by the liver.
Capillaries (containing monosaccharides and amino acids) go through the portal vein to liver.
Liver takes up galactose and fructose. Most glucose is left in the blood stream (stimulates the glycemic response).
We haven't talked about amino acids yet
Glycemic Response
Glucose enters the pancreas through a GLUT transporter, and if it is high secretes insulin ( a hormone).
Muscle and Adipose contain a GLUT4 transporter that responds to insulin binding to the receptor
In that it causes the GLUT4 transporters inside the cell to move to the cell surface and begin taking up glucose
Insulin moves glucose to edge cell so muscles and adipose can start taking it up.
This uptake lowers blood glucose levels so that we can continue or intake of glucose.
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Latest page update: made by crystal0
, Feb 26 2009, 11:28 PM EST
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