Podcast
Questions and Answers
How does butyrate, produced from bacterial fermentation of resistant starch and nonstarch polysaccharides in the large intestine, potentially protect against colorectal cancer?
How does butyrate, produced from bacterial fermentation of resistant starch and nonstarch polysaccharides in the large intestine, potentially protect against colorectal cancer?
- By serving as a primary energy source for cancer cells, inhibiting their growth.
- By exerting antiproliferative effects on intestinal cells, reducing tumor development. (correct)
- By directly inhibiting bacterial growth, reducing overall inflammation.
- By promoting rapid cell division in the intestinal lining, preventing tumor formation.
Why does lactase activity typically decrease after weaning in most mammals and humans?
Why does lactase activity typically decrease after weaning in most mammals and humans?
- To prepare the digestive system for the introduction of more complex carbohydrates.
- As a result of genetic mutations that accumulate over a lifetime.
- Due to the reduced exposure to lactose, leading to decreased enzyme production. (correct)
- To prevent the digestion of maternal antibodies present in breast milk.
How does SGLT 1 facilitate the absorption of glucose and galactose in the small intestine, and what implications does this have for individuals with malabsorption issues?
How does SGLT 1 facilitate the absorption of glucose and galactose in the small intestine, and what implications does this have for individuals with malabsorption issues?
- By converting glucose and galactose into fructose, which is then absorbed via a separate transport protein.
- By using a sodium gradient created by the Na+-K+ pump to actively transport glucose and galactose, allowing absorption against their concentration gradients. (correct)
- By utilizing ATP to directly transport monosaccharides across the cell membrane, ensuring complete absorption regardless of concentration gradients.
- By depending on the concentration gradient of monosaccharides to passively diffuse them across the intestinal epithelium.
How does the secretion of bile salts into the intestinal lumen aid in the digestion and absorption of lipids, particularly in relation to cholesterol management?
How does the secretion of bile salts into the intestinal lumen aid in the digestion and absorption of lipids, particularly in relation to cholesterol management?
How do plant sterols and stanols reduce plasma cholesterol concentrations, considering their mechanism of action in the intestinal mucosa?
How do plant sterols and stanols reduce plasma cholesterol concentrations, considering their mechanism of action in the intestinal mucosa?
How is trypsinogen activated in the small intestine, and what is the cascade effect of this activation on other proteases?
How is trypsinogen activated in the small intestine, and what is the cascade effect of this activation on other proteases?
How do the different specificities of endopeptidases like pepsin, trypsin, chymotrypsin, and elastase contribute to the efficient digestion of proteins?
How do the different specificities of endopeptidases like pepsin, trypsin, chymotrypsin, and elastase contribute to the efficient digestion of proteins?
What is the role of intrinsic factor in vitamin B12 absorption, and what condition results from its deficiency?
What is the role of intrinsic factor in vitamin B12 absorption, and what condition results from its deficiency?
How does vitamin D upregulate calcium absorption in the intestine, and what are the implications for individuals with vitamin D deficiency?
How does vitamin D upregulate calcium absorption in the intestine, and what are the implications for individuals with vitamin D deficiency?
How does hepcidin regulate iron absorption, and what conditions can lead to reduced hepcidin synthesis and increased iron absorption?
How does hepcidin regulate iron absorption, and what conditions can lead to reduced hepcidin synthesis and increased iron absorption?
Given that inorganic iron is better absorbed in the Fe2+ state, why does the presence of vitamin C in the diet enhance iron absorption, particularly when iron salts are used to treat anemia?
Given that inorganic iron is better absorbed in the Fe2+ state, why does the presence of vitamin C in the diet enhance iron absorption, particularly when iron salts are used to treat anemia?
How does the dual isotopically labeled water method (2H₂18O) allow for the estimation of total energy expenditure, and what is the principle behind this technique?
How does the dual isotopically labeled water method (2H₂18O) allow for the estimation of total energy expenditure, and what is the principle behind this technique?
How is the basal metabolic rate (BMR) affected by age and gender, and what physiological factors account for these differences?
How is the basal metabolic rate (BMR) affected by age and gender, and what physiological factors account for these differences?
How does increased secretion of cytokines in conditions like cancer and AIDS contribute to hypermetabolism and cachexia?
How does increased secretion of cytokines in conditions like cancer and AIDS contribute to hypermetabolism and cachexia?
How does respiratory burst in response to infection lead to the development of kwashiorkor, particularly in the context of antioxidant nutrient deficiencies?
How does respiratory burst in response to infection lead to the development of kwashiorkor, particularly in the context of antioxidant nutrient deficiencies?
In measuring nitrogen balance, why does the analysis of total nitrogen intake provide a reasonable estimate of protein intake, despite nucleic acids also containing nitrogen?
In measuring nitrogen balance, why does the analysis of total nitrogen intake provide a reasonable estimate of protein intake, despite nucleic acids also containing nitrogen?
Why does a high protein intake not result in positive nitrogen balance, even though it increases the rate of protein synthesis?
Why does a high protein intake not result in positive nitrogen balance, even though it increases the rate of protein synthesis?
In cases of significant trauma or infection, why does the body exhibit a net catabolism of tissue proteins, and how does this relate to the synthesis of acute-phase proteins?
In cases of significant trauma or infection, why does the body exhibit a net catabolism of tissue proteins, and how does this relate to the synthesis of acute-phase proteins?
If one of the essential amino acids is lacking in the diet, what is the limiting consequence for the body's ability to synthesize proteins, regardless of total protein intake?
If one of the essential amino acids is lacking in the diet, what is the limiting consequence for the body's ability to synthesize proteins, regardless of total protein intake?
How do the dietary intakes of cysteine and tyrosine affect the requirements for methionine and phenylalanine, respectively, considering their roles as precursors?
How do the dietary intakes of cysteine and tyrosine affect the requirements for methionine and phenylalanine, respectively, considering their roles as precursors?
What is the primary reason marine mammals produce high-fat milk lacking carbohydrates, and why do their pups lack lactase?
What is the primary reason marine mammals produce high-fat milk lacking carbohydrates, and why do their pups lack lactase?
How does the glycemic index affect blood sugar fluctuations, and why are foods with a low glycemic index generally considered more beneficial?
How does the glycemic index affect blood sugar fluctuations, and why are foods with a low glycemic index generally considered more beneficial?
How does pancreatic lipase facilitate digestion, explain the use of pancreatic inhibitors, and explain the treatment of obesity?
How does pancreatic lipase facilitate digestion, explain the use of pancreatic inhibitors, and explain the treatment of obesity?
Why must water be supplemented with metabolic fuels for fats, carbs, amino acids, and proteins?
Why must water be supplemented with metabolic fuels for fats, carbs, amino acids, and proteins?
Why does overnutrition lead to noncommunicable diseases such as diabetes?
Why does overnutrition lead to noncommunicable diseases such as diabetes?
Why are minerals more dependent on being chelated?
Why are minerals more dependent on being chelated?
Why does protein provide a net of 0.66 g per kg body weight?
Why does protein provide a net of 0.66 g per kg body weight?
Is the body more susceptible to retaining fluids if one is diagnosed with marasmus?
Is the body more susceptible to retaining fluids if one is diagnosed with marasmus?
How does bile interact with the intestinal lumen to increase fatty acids?
How does bile interact with the intestinal lumen to increase fatty acids?
What happens to lipids after being digested?
What happens to lipids after being digested?
When protein is needed, how much is needed for a daily intake?
When protein is needed, how much is needed for a daily intake?
If one has trauma, what will happen to the protein during the recovery?
If one has trauma, what will happen to the protein during the recovery?
How does the digestion of carbohydrates, lipids, proteins, vitamins, and minerals work?
How does the digestion of carbohydrates, lipids, proteins, vitamins, and minerals work?
How will measuring the respiratory quotient estimate energy requirements?
How will measuring the respiratory quotient estimate energy requirements?
How can protein requirements be determined and why are some proteins not more equal than others?
How can protein requirements be determined and why are some proteins not more equal than others?
What is required of fiber, minerals, protein and carbs:
What is required of fiber, minerals, protein and carbs:
Why does deficiency occur, especially when adequate efforts are introduced?
Why does deficiency occur, especially when adequate efforts are introduced?
Heliobacter secretion can do:
Heliobacter secretion can do:
Why is the glycemic index of certain foods, particularly those high in nonstarch polysaccharides, considered to be nearly zero?
Why is the glycemic index of certain foods, particularly those high in nonstarch polysaccharides, considered to be nearly zero?
What is the critical role of colipase in the digestion of triacylglycerols by pancreatic lipase?
What is the critical role of colipase in the digestion of triacylglycerols by pancreatic lipase?
How do plant sterols and stanols lower body cholesterol levels, and what is the underlying mechanism in the intestinal mucosa?
How do plant sterols and stanols lower body cholesterol levels, and what is the underlying mechanism in the intestinal mucosa?
How does the activation of trypsinogen by enteropeptidase initiate a cascade effect that is crucial for protein digestion in the small intestine?
How does the activation of trypsinogen by enteropeptidase initiate a cascade effect that is crucial for protein digestion in the small intestine?
How does the transport of free amino acids across the intestinal mucosa differ from the transport of dipeptides and tripeptides, and why?
How does the transport of free amino acids across the intestinal mucosa differ from the transport of dipeptides and tripeptides, and why?
How does vitamin D facilitate an independent process involving new protein synthesis while upregulating calcium absorption in the intestine?
How does vitamin D facilitate an independent process involving new protein synthesis while upregulating calcium absorption in the intestine?
What is the role of hepcidin in iron homeostasis, and how do conditions like hypoxia or anemia influence its expression?
What is the role of hepcidin in iron homeostasis, and how do conditions like hypoxia or anemia influence its expression?
Why is the dual isotopically labeled water method (²H₂¹⁸O) considered a reliable technique for estimating total energy expenditure over a period of weeks?
Why is the dual isotopically labeled water method (²H₂¹⁸O) considered a reliable technique for estimating total energy expenditure over a period of weeks?
How does the replacement of metabolically active muscle tissue with adipose tissue affect basal metabolic rate (BMR) with age, even when body weight remains stable?
How does the replacement of metabolically active muscle tissue with adipose tissue affect basal metabolic rate (BMR) with age, even when body weight remains stable?
What mechanisms contribute to hypermetabolism and increased energy expenditure in cancer and AIDS patients?
What mechanisms contribute to hypermetabolism and increased energy expenditure in cancer and AIDS patients?
How does severe impairment of cell proliferation in the intestinal mucosa impact nutrient absorption in individuals suffering from marasmus?
How does severe impairment of cell proliferation in the intestinal mucosa impact nutrient absorption in individuals suffering from marasmus?
What is the role of the respiratory burst in infection-induced kwashiorkor, and how do deficiencies in antioxidant nutrients exacerbate this condition?
What is the role of the respiratory burst in infection-induced kwashiorkor, and how do deficiencies in antioxidant nutrients exacerbate this condition?
What is the key purpose of measuring total nitrogen intake to estimate protein intake, considering that nucleic acids also contain nitrogen?
What is the key purpose of measuring total nitrogen intake to estimate protein intake, considering that nucleic acids also contain nitrogen?
Why does a high protein intake not necessarily lead to a positive nitrogen balance in healthy adults?
Why does a high protein intake not necessarily lead to a positive nitrogen balance in healthy adults?
How does the synthesis of acute-phase proteins contribute to a negative nitrogen balance following trauma or infection?
How does the synthesis of acute-phase proteins contribute to a negative nitrogen balance following trauma or infection?
What are the metabolic and regulatory consequences when an essential amino acid is severely limited or absent in the diet?
What are the metabolic and regulatory consequences when an essential amino acid is severely limited or absent in the diet?
How do the dietary intakes of cysteine and tyrosine influence the nutritional requirements for methionine and phenylalanine, respectively?
How do the dietary intakes of cysteine and tyrosine influence the nutritional requirements for methionine and phenylalanine, respectively?
What is the primary reason for the variance observed in the glycemic index of starch-rich foods?
What is the primary reason for the variance observed in the glycemic index of starch-rich foods?
How does the consumption of resistant starch and nonstarch polysaccharides contribute to the prevention of colorectal cancer?
How does the consumption of resistant starch and nonstarch polysaccharides contribute to the prevention of colorectal cancer?
What is the metabolic consequence of ingesting high amounts of fructose and sugar alcohols?
What is the metabolic consequence of ingesting high amounts of fructose and sugar alcohols?
What is the underlying mechanism for the development of lactose intolerance in most adults?
What is the underlying mechanism for the development of lactose intolerance in most adults?
Besides pancreatic lipase, what other factors are critical for efficient triacylglycerol digestion in the small intestine?
Besides pancreatic lipase, what other factors are critical for efficient triacylglycerol digestion in the small intestine?
How do inhibitors of pancreatic lipase function in the treatment of obesity?
How do inhibitors of pancreatic lipase function in the treatment of obesity?
What is the mechanism by which plant sterols and stanols reduce cholesterol absorption in the intestine?
What is the mechanism by which plant sterols and stanols reduce cholesterol absorption in the intestine?
What triggers the activation of trypsinogen, and how does this process contribute to overall protein digestion?
What triggers the activation of trypsinogen, and how does this process contribute to overall protein digestion?
How does the absorption of amino acids and small peptides differ in the small intestine, and what is the nutritional implication of these differences?
How does the absorption of amino acids and small peptides differ in the small intestine, and what is the nutritional implication of these differences?
How does vitamin D influence calcium absorption in the intestine?
How does vitamin D influence calcium absorption in the intestine?
Why is the regulation of iron absorption so tightly controlled in the human body?
Why is the regulation of iron absorption so tightly controlled in the human body?
How does hepcidin regulate iron homeostasis, and what is the effect of reduced hepcidin levels on iron absorption?
How does hepcidin regulate iron homeostasis, and what is the effect of reduced hepcidin levels on iron absorption?
How does severe impairment of cell proliferation in the intestinal mucosa impact nutrient absorption?
How does severe impairment of cell proliferation in the intestinal mucosa impact nutrient absorption?
What role does the respiratory burst play in the development of infection-induced kwashiorkor?
What role does the respiratory burst play in the development of infection-induced kwashiorkor?
How does the amount of metabolically active muscle tissue affect basal metabolic rate (BMR) with age?
How does the amount of metabolically active muscle tissue affect basal metabolic rate (BMR) with age?
How does the dual isotopically labeled water method (²H₂¹⁸O) allow for an accurate estimation of total energy expenditure?
How does the dual isotopically labeled water method (²H₂¹⁸O) allow for an accurate estimation of total energy expenditure?
What metabolic adaptations contribute to hypermetabolism and increased energy expenditure in cancer and AIDS patients?
What metabolic adaptations contribute to hypermetabolism and increased energy expenditure in cancer and AIDS patients?
Why does measuring total nitrogen intake provide a useful estimate of protein intake, even though nucleic acids also contain nitrogen?
Why does measuring total nitrogen intake provide a useful estimate of protein intake, even though nucleic acids also contain nitrogen?
Under what physiological conditions does a high protein intake fail to result in a positive nitrogen balance?
Under what physiological conditions does a high protein intake fail to result in a positive nitrogen balance?
In cases of trauma or severe infection, how does the synthesis of acute-phase proteins affect nitrogen balance?
In cases of trauma or severe infection, how does the synthesis of acute-phase proteins affect nitrogen balance?
What are the primary consequences for the body when an essential amino acid is severely limited or absent in the diet?
What are the primary consequences for the body when an essential amino acid is severely limited or absent in the diet?
Why is the dietary intake of cysteine considered when determining the nutritional requirement for methionine?
Why is the dietary intake of cysteine considered when determining the nutritional requirement for methionine?
Why is the glycemic index of foods high in nonstarch polysaccharides considered to be close to zero?
Why is the glycemic index of foods high in nonstarch polysaccharides considered to be close to zero?
What is the key role of colipase in the digestion of triacylglycerols by pancreatic lipase?
What is the key role of colipase in the digestion of triacylglycerols by pancreatic lipase?
How will measuring the respiratory quotient provide an accurate estimation of energy requirements?
How will measuring the respiratory quotient provide an accurate estimation of energy requirements?
Why may some protein be more equal than others?
Why may some protein be more equal than others?
What can Heliobacter secretion do?
What can Heliobacter secretion do?
During trauma recovery, what will happen to the protein during?
During trauma recovery, what will happen to the protein during?
The glycemic index is determined by comparing the blood glucose response after consuming a carbohydrate relative to the response after consuming an equivalent amount of fructose.
The glycemic index is determined by comparing the blood glucose response after consuming a carbohydrate relative to the response after consuming an equivalent amount of fructose.
Individuals with congenital deficiency of sucrase-isomaltase typically experience sucrose intolerance, leading to diarrhea, but thrive normally on a diet containing no sucrose.
Individuals with congenital deficiency of sucrase-isomaltase typically experience sucrose intolerance, leading to diarrhea, but thrive normally on a diet containing no sucrose.
In individuals with lactose intolerance, lactase activity increases after weaning, fully preventing any lactose-related digestive issues later in life.
In individuals with lactose intolerance, lactase activity increases after weaning, fully preventing any lactose-related digestive issues later in life.
Glucose and galactose are absorbed in the small intestine via separate transport proteins, facilitating independent regulation of their absorption rates.
Glucose and galactose are absorbed in the small intestine via separate transport proteins, facilitating independent regulation of their absorption rates.
Hydrolysis of triacylglycerols is primarily a function of pancreatic lipase, which acts on the sn-2 ester bond to produce 1,2-diacylglycerols and free fatty acids.
Hydrolysis of triacylglycerols is primarily a function of pancreatic lipase, which acts on the sn-2 ester bond to produce 1,2-diacylglycerols and free fatty acids.
In intestinal epithelial cells, 2-monoacylglycerols are reacylated to triacylglycerols via the monoacylglycerol pathway, while glycerol is released in the lymphatics.
In intestinal epithelial cells, 2-monoacylglycerols are reacylated to triacylglycerols via the monoacylglycerol pathway, while glycerol is released in the lymphatics.
Plant sterols and stanols enhance cholesterol absorption in the intestines by improving cholesterol esterification, thereby increasing its incorporation into chylomicrons.
Plant sterols and stanols enhance cholesterol absorption in the intestines by improving cholesterol esterification, thereby increasing its incorporation into chylomicrons.
The activity of digestive proteases, such as trypsin and chymotrypsin, is initiated by the presence of high concentrations of dietary protein.
The activity of digestive proteases, such as trypsin and chymotrypsin, is initiated by the presence of high concentrations of dietary protein.
Free amino acids are absorbed across the intestinal mucosa via passive diffusion, requiring no specific transport proteins or sodium-dependent mechanisms.
Free amino acids are absorbed across the intestinal mucosa via passive diffusion, requiring no specific transport proteins or sodium-dependent mechanisms.
Vitamin B12 absorption is directly dependent on vitamin D, and both are facilitated by zinc-binding ligands secreted by the exocrine pancreas.
Vitamin B12 absorption is directly dependent on vitamin D, and both are facilitated by zinc-binding ligands secreted by the exocrine pancreas.
High concentrations of fatty acids in the intestinal lumen enhance calcium absorption by forming soluble calcium salts, which are easily absorbed.
High concentrations of fatty acids in the intestinal lumen enhance calcium absorption by forming soluble calcium salts, which are easily absorbed.
Iron absorption is strictly controlled and down regulated by hepcidin. People who regularly consume alcohol are at a lower risk of iron deficiency.
Iron absorption is strictly controlled and down regulated by hepcidin. People who regularly consume alcohol are at a lower risk of iron deficiency.
A diet high in calcium during meals significantly improves iron absorption by facilitating the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+).
A diet high in calcium during meals significantly improves iron absorption by facilitating the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+).
Increasing age has a smaller effect on BMR (basal metabolic rate) than body weight does, regardless of a person's gender.
Increasing age has a smaller effect on BMR (basal metabolic rate) than body weight does, regardless of a person's gender.
The dual isotopically labeled water method estimates energy expenditure by measuring differences in the elimination rates of deuterium (²H) from water and oxygen-18 (¹⁸O) from both water and carbon dioxide.
The dual isotopically labeled water method estimates energy expenditure by measuring differences in the elimination rates of deuterium (²H) from water and oxygen-18 (¹⁸O) from both water and carbon dioxide.
In cachexia, patients exhibit more loss of body fat compared to muscle protein, distinguishing it from marasmus, where protein loss is more prominent.
In cachexia, patients exhibit more loss of body fat compared to muscle protein, distinguishing it from marasmus, where protein loss is more prominent.
Kwashiorkor is primarily caused by a severe deficiency in dietary fat intake, leading to edema and fatty infiltration of the liver.
Kwashiorkor is primarily caused by a severe deficiency in dietary fat intake, leading to edema and fatty infiltration of the liver.
During trauma and infection the body increases protein catabolism over protein synthesis and in turn excessive amounts of threonine and cysteine are lost.
During trauma and infection the body increases protein catabolism over protein synthesis and in turn excessive amounts of threonine and cysteine are lost.
The dietary intakes of cysteine and tyrosine do not affect the dietary requirements for methionine and phenylalanine. There is no relation between these amino acids.
The dietary intakes of cysteine and tyrosine do not affect the dietary requirements for methionine and phenylalanine. There is no relation between these amino acids.
Humans require at least three truly dispensable amino acids in their diet; alanine, aspartate, and glutamate.
Humans require at least three truly dispensable amino acids in their diet; alanine, aspartate, and glutamate.
Match each enzyme with its primary substrate:
Match each enzyme with its primary substrate:
Match the following terms with their definitions related to energy balance:
Match the following terms with their definitions related to energy balance:
Match the following terms related to lipid digestion with their correct description:
Match the following terms related to lipid digestion with their correct description:
Match each vitamin with its role in mineral absorption:
Match each vitamin with its role in mineral absorption:
Match the following conditions with their primary characteristics:
Match the following conditions with their primary characteristics:
Match the following enzymes with their functions in protein digestion:
Match the following enzymes with their functions in protein digestion:
Match the following terms related to protein requirements with their definitions:
Match the following terms related to protein requirements with their definitions:
Match each monosaccharide with its primary absorption mechanism in the small intestine:
Match each monosaccharide with its primary absorption mechanism in the small intestine:
Match the following substances with their effects on iron absorption:
Match the following substances with their effects on iron absorption:
Match each condition with its metabolic adaptation:
Match each condition with its metabolic adaptation:
Flashcards
Essential components of the diet
Essential components of the diet
Metabolic fuels (mainly carbohydrates and lipids), protein, fiber, minerals, vitamins, and essential fatty acids.
Macromolecule Breakdown
Macromolecule Breakdown
Polysaccharides, triacylglycerols, and proteins must be broken down into monosaccharides, fatty acids, and amino acids for absorption and utilization.
Undernutrition
Undernutrition
A condition of impaired growth, defective immune system and reduced work capacity due to lack of nutrition.
Overnutrition
Overnutrition
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Excessive gastric acid secretion
Excessive gastric acid secretion
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Cystic fibrosis
Cystic fibrosis
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Lactose intolerance
Lactose intolerance
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Glycemic index
Glycemic index
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Amylases
Amylases
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Disaccharidases
Disaccharidases
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Monosaccharide Absorption
Monosaccharide Absorption
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Triacylglycerols
Triacylglycerols
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Pancreatic lipase
Pancreatic lipase
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Micelles
Micelles
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Intestinal Epithelium Actions
Intestinal Epithelium Actions
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Unesterified cholesterol and plant sterols
Unesterified cholesterol and plant sterols
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Endopeptidases
Endopeptidases
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Exopeptidases
Exopeptidases
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Zymogens
Zymogens
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Calcium Absorption
Calcium Absorption
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Phytic acid
Phytic acid
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Inorganic iron
Inorganic iron
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Hepcidin
Hepcidin
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Obesity
Obesity
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Undernutrition
Undernutrition
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Basal Metabolic Rate (BMR)
Basal Metabolic Rate (BMR)
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Overall Physical Activity Level (PAL)
Overall Physical Activity Level (PAL)
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Marasmus
Marasmus
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Kwashiorkor
Kwashiorkor
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Cachexia
Cachexia
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Nitrogen Equilibrium
Nitrogen Equilibrium
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Essential Amino Acids
Essential Amino Acids
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Dietary fiber
Dietary fiber
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Respiratory quotient
Respiratory quotient
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Iron
Iron
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Iron Absorption
Iron Absorption
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Energy
Energy
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Physical Activity Ratio (PAR)
Physical Activity Ratio (PAR)
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Vitamin D
Vitamin D
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Measuring protein and amount needed
Measuring protein and amount needed
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Reduction/impairment
Reduction/impairment
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Positive Nitrogen Balance
Positive Nitrogen Balance
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Negative Nitrogen Balance
Negative Nitrogen Balance
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Proteases
Proteases
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Hypermetabolic State
Hypermetabolic State
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Protein loss in Trauma
Protein loss in Trauma
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Carbohydrate Digestion
Carbohydrate Digestion
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Steatorrhea
Steatorrhea
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Pepsin Activation
Pepsin Activation
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Respiratory Quotient (RQ)
Respiratory Quotient (RQ)
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Lactose intolerance effects
Lactose intolerance effects
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Lingual and gastric lipases
Lingual and gastric lipases
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Protein resistance
Protein resistance
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Peptide absorption
Peptide absorption
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Estimating total energy expenditure
Estimating total energy expenditure
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Pepsin Function
Pepsin Function
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Sucrase-Isomaltase Deficiency
Sucrase-Isomaltase Deficiency
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Resistant Starch Benefits
Resistant Starch Benefits
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Protease Activation
Protease Activation
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Impaired fat absorption
Impaired fat absorption
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Hepcidin Function
Hepcidin Function
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Study Notes
Digestion and Absorption of Nutrients:
- Carbohydrates, lipids, proteins, vitamins, and minerals are described.
- Consequences of undernutrition include marasmus, cachexia, and kwashiorkor.
- Protein requirements are determined by protein quality for maintaining nitrogen balance.
Biomedical Importance:
- A balanced diet requires metabolic fuels (carbohydrates and lipids), protein, fiber, minerals, essential fatty acids, and vitamins.
- Complex dietary molecules like polysaccharides, triacylglycerols, and proteins must be broken down into simpler forms like monosaccharides, fatty acids, and amino acids for absorption.
- Undernutrition can lead to impaired growth, a weakened immune system, and reduced work capacity; overconsumption leads to obesity, diabetes, cardiovascular disease, and cancer.
- Vitamin A, iron, and iodine deficiencies are major global health concerns, with deficiencies in other vitamins and minerals also contributing to ill health.
- Gastric ulcers can result from excessive gastric acid secretion, often linked to Helicobacter pylori infections.
- Gallstones can form due to changes in bile composition.
- Cystic fibrosis can cause undernutrition and steatorrhea due to exocrine pancreatic secretion failure.
- Lactose intolerance results from lactase deficiency, leading to gastrointestinal issues upon lactose consumption.
- Celiac disease is an allergic reaction to wheat gluten, triggered by the absorption of intact peptides.
- Globally, overweight and obesity are more prevalent than undernutrition, with deficiencies in vitamins A, iron, and iodine posing significant health risks.
- Although nutrient deficiency is rare in developed countries, vulnerable populations remain at risk, and adequate intakes to prevent deficiency may still be insufficient for optimal health and longevity.
Carbohydrate Digestion and Absorption:
- Digestion releases oligosaccharides, further broken down into monosaccharides.
- The glycemic index measures blood glucose increase after carbohydrate consumption compared to glucose.
- Glucose and galactose have a glycemic index of 1 (or 100%), as do lactose, maltose, isomaltose, and trehalose, which give rise to these monosaccharides on hydrolysis.
- Fructose and sugar alcohols have lower indexes.
- Starch's glycemic index varies based on hydrolysis rates.
- Low glycemic index foods are more beneficial due to reduced insulin fluctuation.
- Resistant starch and nonstarch polysaccharides support bacterial fermentation, producing butyrate, which nourishes intestinal cells and may protect against colorectal cancer.
- Amylases from saliva and the pancreas break down starch into dextrins, glucose, maltose, and branched dextrins by catalyzing random hydrolysis of α(1 → 4) glycoside bonds.
- Disaccharidases on intestinal cells' brush borders hydrolyze disaccharides into monosaccharides for absorption.
- Lactase deficiency leads to lactose intolerance, while sucrase-isomaltase deficiency causes sucrose intolerance.
- Lactose intolerance is common after weaning due to reduced lactase activity, leading to discomfort from bacterial fermentation of lactose.
- Lactase persistence into adulthood occurs in people of North European origin and nomadic tribes of sub-Saharan Africa and Arabia; marine mammals lack lactase because their milk has no carbohydrates.
- Glucose and galactose absorption uses a sodium-dependent process via the SGLT1 protein, and they compete for absorption.
- Fructose and sugar alcohols are absorbed by carrier-mediated diffusion, and excessive intake can cause osmotic diarrhea due to bacterial fermentation.
Lipid Digestion and Absorption:
- The major dietary lipids are triacylglycerols and, to a lesser extent, phospholipids.
- Lipids being hydrophobic molecules must be hydrolyzed and emulsified into small droplets.
- Lingual and gastric lipases begin triacylglycerol hydrolysis.
- Production of 1,2-diacylglycerols and free fatty acids aids emulsification.
- Pancreatic lipase requires colipase.
- Primary ester links at positions 1 and 3 in triacylglycerols, leading to 2-monoacylglycerols and free fatty acids.
- Pancreatic esterase hydrolyzes monoacylglycerols.
- Only approximately 25% of ingested triacylglycerol is completely hydrolyzed to glycerol and fatty acids before absorption.
- Bile salts emulsify lipid digestion products into micelles, facilitating absorption along with fat-soluble vitamins.
- Intestinal epithelium cells hydrolyze 1-monoacyglycerols into fatty acids and glycerol, while 2-monoacylglycerols are re-esterified.
- Glycerol is transported into the hepatic portal vein, while long-chain fatty acids are esterified into triacylglycerols and secreted as chylomicrons into the lymphatics.
- Short- and medium-chain fatty acids are absorbed directly into the hepatic portal vein.
- Cholesterol is absorbed into lipid micelles, esterified, and incorporated into chylomicrons, while plant sterols compete with cholesterol for esterification, reducing cholesterol absorption.
Protein Digestion and Absorption:
- Native proteins are resistant to digestion, requiring denaturation by heat and gastric acid.
- Endopeptidases (like pepsin, trypsin, chymotrypsin, and elastase) hydrolyze internal peptide bonds.
- Pepsin works on amino acids with bulky side chains.
- Trypsin, chymotrypsin, and elastase target lysine, arginine, aromatic amino acids, and small neutral aliphatic amino acids, respectively.
- Exopeptidases (carboxypeptidases and aminopeptidases) hydrolyze peptide bonds from the ends of peptides.
- Dipeptidases and tripeptidases break down di- and tripeptides in the intestinal brush border.
- Proteases are secreted as inactive zymogens activated by hydrolysis.
- Pepsinogen is activated to pepsin by gastric acid and pepsin.
- In the small intestine, enteropeptidase activates trypsinogen to trypsin, which then activates other zymogens.
- Free amino acids are absorbed via sodium-dependent active transport, with multiple transporters for different amino acid types.
- Dipeptides and tripeptides are hydrolyzed in the intestinal cells.
- Relatively large peptides may be absorbed intact and can stimulate antibody formation, leading to allergic reactions.
Vitamin and Mineral Digestion and Absorption:
- Vitamins and minerals are released from food during digestion
- Fat-soluble vitamins are absorbed in lipid micelles, while water-soluble vitamins and mineral salts use active transport or carrier-mediated diffusion.
- Vitamin B12 requires intrinsic factor for absorption.
- Calcium absorption depends on vitamin D, which induces calbindin synthesis and recruits calcium transporters.
- Phytic acid in cereals binds calcium and other minerals, reducing absorption and Phytase founded in yeast, can deactivate phytate.
- Fatty acids can reduce calcium absorption by creating insoluble calcium salts and oxalate may also cause calcium deficiency.
- Iron absorption is limited and regulated to prevent toxicity.
- Inorganic iron is transported into mucosal cells via a proton-linked divalent metal ion transporter and bound to ferritin.
- Iron is transported out of mucosal cells by ferroportin if transferrin is available in plasma
- Hepcidin downregulates ferroportin synthesis when iron reserves are adequate.
- Vitamin C, alcohol, and fructose enhance iron absorption.
- Heme iron is more readily absorbed than inorganic iron.
- Calcium impairs iron absorption.
Energy Balance and Requirements:
- Energy Balance is achieved through water, metabolic fuels, like fats, amino acids, and carbohydrates from proteins.
- Food intake should directly relate to BMR
- Excess: Obesity, while Deficit: Emaciation and related diseases
- Body Mass Index of 20-25kg is the recommended range
- Energy expenditure can be measured via heat output measuring oxygen consumption
- Energy Expenditure = 20kJ/L
- Total Energy Expenditure is estimated using isotopically labelled water
- Body Mass Index defines an estimated individual energy requirements depending on weight, age, gender and body weight
- Decrease in BMR related to age is linked to reduced muscle tissues
- Physical Activity levels affect the average BMR depending on multiple or lack of activity
- 10% of a meal is spent on expenditure in reserves for activity i.e. Glycogen production
- The two forms of Undernutrition are defined as Marasmus and Kwashiorkor. Undernourished patients show the same symptoms as Marasmus
- The hyper metabolic disorder is linked to cancer causing significant loss of protein
Protein and Amino Acid Requirements:
- Protein nutrition can be determined by measuring protein intake and body output.
- Protein output = 6.25 = Protein MG
- Intake = Output defines Nitrogen Balance as a state. Three states are achieved
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- Equilibrium: intake equals output with not body change
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- Positive Balance: Seen in children
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- Net loss negative protein resulting from a lack of consumption
- The daily requirement is 0.66g intake
- Trauma can cause a loss of protein
- There are essential and non-essential amino acids that can be synthesized or from non-essential sources
- There are limited sources of non-essential amino acids coming from Methionine creating a requirement for protein intake
- The body requires amino acids in correct proportions to replace tissue proteins, dividing them into essential (indispensable) and nonessential groups.
- Nine amino acids are essential: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
- Cysteine and tyrosine are synthesized from methionine and phenylalanine, affecting their dietary requirements.
- Three amino acids (alanine, aspartate, and glutamate) are truly dispensable, synthesized by transamination of common metabolic intermediates.
- Other nonessential amino acids may have requirements that can outstrip the capacity for synthesis under certain circumstances.
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