Learning Objectives Flashcards
1
Q
What is the role of macronutrients in human nutrition?
A
Macronutrients serve as a source of energy, act as building blocks for various bodily structures, and have hormone-like functions in human nutrition.
2
Q
How do macronutrients compare to micronutrients in daily nutrient intake?
A
Compared to micronutrients, macronutrients make up the greatest portion of daily nutrient intake. Specifically, carbohydrates should constitute 45-65% of daily energy intake, lipids should be 20-35% of energy intake, and protein should account for 10-35% of energy intake.
3
Q
What are the potential health effects of an excess caloric intake?
A
Excess caloric intake can lead to obesity due to increased fat retention, and this can have detrimental health effects, including an increased risk of various diseases.
4
Q
Explain the role of macronutrients in human metabolism and its significance for understanding nutrient-disease relationships.
A
Macronutrients play a crucial role in human metabolism, affecting energy production, growth, development, and metabolic regulation. Imbalances in macronutrient distribution can impact metabolism and contribute to diseases such as cardiovascular disease, cancer, obesity, diabetes, and mental health disorders.
5
Q
What is metabolism, and why is it a key concept in understanding nutrient-disease relationships?
A
Metabolism refers to the set of integrated biochemical reactions needed to maintain life, with the outcome of producing energy. It is a key concept in understanding nutrient-disease relationships because imbalances in metabolism, often influenced by macronutrient distribution, can lead to or exacerbate various diseases.
6
Q
What organs make up the gastrointestinal (GI) tract, and what are their functions?
A
The GI tract comprises the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine. These organs come into contact with food and play various roles in digestion and absorption.
7
Q
What are the accessory organs in the digestive system, and how do they facilitate digestion?
A
Accessory organs in the digestive system, including the salivary glands, tongue, liver, gallbladder, and pancreas, facilitate digestion by producing enzymes, bile, and other secretions that aid in the breakdown of food.
8
Q
Describe the role of oral activity and salivary glands in the carbohydrate digestive process.
A
Oral activity, involving teeth and jaw muscles, mechanically breaks down food for digestion. Salivary glands produce saliva, which contains enzymes like salivary amylase for the chemical breakdown of food, particularly carbohydrates. Saliva also contains lingual lipase, which aids in lipid digestion.
9
Q
What is the function of the esophagus in digestion, and how does it move food to the stomach?
A
The esophagus moves the bolus (food mixed with saliva) from the oral cavity to the stomach. It accomplishes this through a combination of voluntary swallowing and involuntary peristalsis, a wavelike motion that pushes the food toward the stomach. The gastroesophageal sphincter prevents stomach contents from entering the esophagus.
10
Q
Explain the structure and functions of the stomach.
A
The stomach is flexible in size, allowing it to expand from a resting volume of 50mL to 1.0-1.5L when fed. It consists of various parts, including the cardia, fundus, body, and antrum. The fundus initiates digestion, while the body produces gastric juices and mechanically mixes the bolus with smooth muscle contractions. The antrum grinds food and mixes it with gastric juices to form chyme, which is then propelled into the small intestine through strong peristalsis.
11
Q
What are the key components of gastric juice, and what is the role of hydrochloric acid in digestion?
A
Gastric juice contains mucous for stomach lining protection, chief cells that produce enzymes like pepsinogen and lipase, parietal cells that secrete intrinsic factor and hydrochloric acid (HCl), and G-cells that release the hormone gastrin. Hydrochloric acid is crucial for denaturing proteins, activating pepsinogen to pepsin (a protein-digesting enzyme), and releasing nutrients from organic complexes. It also has antibacterial properties.
12
Q
How does chyme leave the stomach and enter the duodenum, and what role does somatostatin play in this process?
A
Chyme exits the stomach through the pyloric sphincter into the duodenum. Somatostatin is released to slow down stomach processes, ensuring that chyme is not constantly entering the small intestine. When chyme enters the duodenum, somatostatin signals the presence of chyme in the small intestine.
13
Q
What is the main site for nutrient digestion and absorption in the digestive system?
A
The small intestine, including the duodenum, jejunum, and ileum, is the main site for nutrient digestion and absorption in the digestive system.
14
Q
Describe the structural adaptations of the small intestine that contribute to its large surface area for absorption
A
The small intestine has a specialized inner membrane with large folds, finger-like projections called villi, and even smaller hair-like folds called microvilli. These structures increase the surface area significantly, allowing for efficient absorption. The lining is covered with absorptive cells known as enterocytes, which further enhance nutrient absorption.
15
Q
How and where is nutrient digestion typically completed in the small intestine (final step)?
A
Nutrient digestion in the small intestine is usually completed in the brush border, where enzymes in the glycocalyx on the surface of enterocytes break down nutrients. The glycocalyx helps digest nutrients further before they enter the enterocytes for absorption.
16
Q
What are the different mechanisms of nutrient absorption in the small intestine?
A
Nutrient absorption in the small intestine can occur through diffusion, facilitated diffusion, active transport, and pinocytosis, depending on the nutrient type and concentration.
17
Q
Explain the functions of the pancreas in digestion.
A
The pancreas plays a vital role in digestion by producing digestive enzymes that enter the duodenum. These enzymes digest carbohydrates, proteins, and lipids. Additionally, the pancreas secretes bicarbonate to neutralize the acidic chyme from the stomach, making the small intestine alkaline and conducive to enzyme activity.
18
Q
How does the liver regulate metabolism and nutrients in the body?
A
The liver is a central organ that regulates metabolism and nutrients in the body. It produces bile, which helps emulsify lipids in the small intestine, and is connected to the central circulation through a central vein. The liver decides what nutrients are stored, brought into circulation, or eliminated from the body.
19
Q
What is the function of the gallbladder, and what is the composition and function of bile? Where is it released and what hormone regulates it?
A
The gallbladder concentrates and stores bile, which is a greenish-yellow fluid. Bile primarily contains bile acids and salts that emulsify lipids, along with cholesterol, phospholipids, and bile pigments. The gallbladder releases bile into the duodenum, and this process is controlled by the hormone cholecystokinin.
20
Q
What role does the large intestine play in digestion, and how does it absorb nutrients?
A
The large intestine, comprising the ascending, transverse, and descending colons, absorbs water, sodium, and other remaining nutrients from the chyme. It utilizes mechanisms such as diffusion, facilitated diffusion, active transport, and pinocytosis to absorb these substances.
21
Q
A
22
Q
What is the primary role of carbohydrates in the human diet?
A
: Carbohydrates serve as a major energy source, supplying around half or more of the total caloric intake.
23
Q
How are carbohydrates classified?
A
Carbohydrates are classified into two major classes: simple carbohydrates and complex carbohydrates.
24
Q
Define simple carbohydrates.
A
Simple carbohydrates are structurally the simplest, consisting of one sugar unit, known as a monosaccharide unit. They are the most important in human nutrition and include glucose, fructose, and galactose.
25
Explain the classification of monosaccharides.
Monosaccharides are classified based on the number of carbons and functional group (aldehyde or ketone group). They can occur from triose through heptose.
26
What is the significance of optical activity in carbohydrates?
Optical activity in carbohydrates is due to the presence of one or more chiral carbon atoms in the molecule. It is denoted as D or L orientation and affects enzymatic breakdown. Most sugars are in D orientation.
27
How do monosaccharides exist in solution, and what is the significance of alpha and beta forms?
Monosaccharides can exist in a cyclic/ring form in solution. The alpha form has the -OH group pointing up, while the beta form has the -OH group pointing down.
28
What are pentoses, and why are they of limited dietary importance?
Pentoses have 5 carbons in the ring and are of limited dietary importance. They can be synthesized in the body and are transformed into metabolically important compounds, such as ribose and deoxyribose.
29
Describe disaccharides and their orientation.
Disaccharides consist of two sugar units connected with a glycosidic bond. The orientation (alpha vs. beta) depends on the second unit, except for sucrose, where anomeric carbons are blocked by the glycosidic bond.
30
What are oligosaccharides, and how are they digested?
Oligosaccharides are long chains of glucose that must be digested by gut microbiota since they are non-digestible by stomach enzymes. They act as dietary fiber.
31
Explain the role of dextrins in nutrition.
Dextrins can be oligo- or polysaccharides depending on the chain length. They are composed of chains of glucose and are used as additives in foods, pharmaceuticals, and nutritional supplements.
32
What are some examples of polysaccharides, and where are they found?
Polysaccharides include starch, glycogen, and cellulose. Starch is found in vegetables and legumes, glycogen in organ meats and animal products, and cellulose in the cell walls of plants.
33
How is sugar consumption classified in Canada?
Sugar consumption in Canada is classified into total sugars (including natural and added sugars) and added sugars (sugars added during food processing).
34
Where does carbohydrate digestion begin in the human body, and what enzymes are involved?
Carbohydrate digestion begins in the oral cavity with the help of salivary glands containing α 1-4 amylase, which hydrolyzes α 1-4 glycosidic bonds.
35
What is the role of pancreatic α 1-4 amylase in carbohydrate digestion?
Pancreatic α 1-4 amylase specifically hydrolyzes α 1-4 glycosidic bonds in the duodenum and is responsive to diet composition.
36
Describe the intraluminal phase of carbohydrate digestion.
In the intraluminal phase, digestion of starch and dextrins occurs in the duodenum, where dextrins are broken down into maltose and/or limit dextrins.
37
What enzymes are found in the brush border of the small intestine, and what is their role in carbohydrate digestion?
: The brush border contains oligosaccharidases, which digest disaccharides into monosaccharides, such as maltase breaking down maltose into glucose.
38
What are some sources of carbohydrates in the diet?
Sources of carbohydrates include monosaccharides found in sweet foods, disaccharides like sucrose in refined table sugar and maltose in bread, oligosaccharides present in vegetables, and polysaccharides like starch in vegetables and legumes.
39
What is the significance of glycogen, and where is it found?
Glycogen is the storage form of glucose in animal tissues, particularly in the liver and skeletal muscle. It has many branch points for efficient cleavage when glucose is needed.
40
What is cellulose, and how is it different from other polysaccharides?
Cellulose is present in plant cell walls, is non-digestible, and is considered a dietary fiber. It is not considered an energy source.
41
What is absorption of carbohydrates?
Absorption of carbohydrates is the process by which digestive products pass out of the digestive tract, enter the cells lining the digestive tract, and enter the bloodstream or lymphatics.
42
How are glucose and galactose absorbed into the mucosal cell?
Glucose and galactose are absorbed into the mucosal cell (enterocyte) against a concentration gradient through active transport, facilitated by the SGLT1 transporter on the brush border.
43
How does glucose leave the mucosal cell after absorption?
Glucose leaves the mucosal cell through either diffusion (25%) or facilitated diffusion using the GLUT2 transporter (60%).
44
How is fructose absorbed and transported?
Fructose is absorbed through facilitated diffusion via GLUT5 on the brush border and leaves the enterocyte through facilitated diffusion using GLUT2. It is quickly transported via the portal vein into the liver.
45
What are the glucose transporters and their functions?
GLUT1 transports glucose to the central nervous system and erythrocytes. GLUT2 transports glucose to the liver, kidneys, and small intestine. GLUT4 is insulin-dependent for muscle uptake. GLUT5 is specific for fructose uptake.
46
What is the primary transporter responsible for the absorption of glucose and galactose on the brush border of the mucosal cell?
SGLT1 is the primary transporter responsible for the absorption of glucose and galactose against a concentration gradient on the brush border of the mucosal cell.
47
How is sodium involved in the absorption of glucose and galactose in the enterocyte?
Sodium is required to be bound to the transporter (SGLT1) for the binding site of glucose/galactose to open, enabling their absorption against the concentration gradient.
48
How is glucose/galactose moved out of the enterocyte, and what is required for this process?
Glucose/galactose is moved out of the enterocyte through facilitated diffusion using GLUT2. To maintain low sodium levels in the enterocyte, sodium is pumped out using ATPase, which requires ATP.
49
What happens to glucose and galactose after leaving the mucosal cell, and how are they transported to the liver?
Glucose and galactose quickly enter the portal vein after leaving the mucosal cell. About 25% of glucose/galactose is moved into the portal vein through diffusion, and about 10% through facilitated diffusion using GLUT2.
50
How is fructose absorbed and transported differently from glucose and galactose?
Fructose is absorbed through facilitated diffusion via GLUT5 on the brush border, and it leaves the enterocyte through facilitated diffusion using GLUT2. It is quickly transported to the liver via the portal vein.
51
How is excess fructose absorption affected, and what can mitigate this?
Excess fructose absorption can be inefficient, leading to intestinal distress. Combining fructose intake with high glucose intake can improve absorption due to the disaccharidase-related transport system.
52
What is the role of insulin in glucose transport?
Insulin facilitates glucose uptake into tissues via GLUT4 transporters, especially in muscle and adipose tissue, through insulin-dependent pathways.
53
What is GLUT1 deficiency syndrome, and how does it affect individuals?
GLUT1 deficiency syndrome is a rare genetic disorder where the lack of GLUT1 transport protein leads to "glucose deficiency in the brain," resulting in symptoms related to cognition, behavior, and movement.
54
What are the acute and chronic symptoms of hyperglycemia (elevated blood glucose)?
Acute symptoms include dehydration, while chronic symptoms involve glycosylation of proteins, organ damage, and excess glycosylation disrupting normal membrane integrity.
55
How is blood glucose regulated through glucose production and disposal?
Elevated blood glucose is managed through increased glucose uptake, glycogenesis, and insulin-dependent pathways. Low blood glucose is managed through glycogenolysis, gluconeogenesis, and adrenal gland stimulation.
56
How is galactose metabolized in the liver?
Galactose is phosphorylated in the hepatocytes, converted into glucose derivatives, and can enter glucose metabolism and be stored as liver glycogen.
57
What percentage of glucose is used in the liver?
40-70% of glucose is used in the liver, extensively metabolized to meet the energy needs of the liver.
58
What happens when blood glucose levels are below the normal range?
Hypoglycemia can occur, leading to symptoms like fatigue, dizziness, unconsciousness, seizures, and potential brain damage.
59
What are the metabolic effects of insulin on glucose uptake and synthesis?
Insulin increases glucose uptake in muscles (GLUT4), liver (GLUT2), and enhances glycogen synthesis (glycogen synthase), while inhibiting glycogen breakdown (glycogen phosphorylase).
60
What is the glycemic index (GI)?
The glycemic index measures how a food item impacts blood glucose levels compared to a reference food (usually glucose) during a 2-hour period following consumption.
61
How is glycemic load (GL) calculated?
Glycemic load (GL) is calculated as GI (Glycemic Index) multiplied by the grams of carbohydrates in a serving of food. It considers both the quality and quantity of carbohydrates in a meal.
62
What are the main metabolic pathways for glucose utilization in the absence of oxygen?
In the absence of oxygen, glucose can be converted to pyruvate, which is then reduced to lactate, providing energy. This process occurs in erythrocytes due to their lack of mitochondria.
63
Name the primary metabolic pathways of carbohydrate metabolism.
The primary metabolic pathways of carbohydrate metabolism are glycogenesis, glyconeolysis, glycolysis, gluconeogenesis, and the tricarboxylic acid cycle (TCA cycle).
64
In which cellular organelle does glycolysis occur?
Glycolysis occurs in the mitochondria of cells.
65
What is the primary role of glycolysis?
The primary role of glycolysis is to produce pyruvate, which can then enter the glucose oxidation process and the tricarboxylic acid (TCA) cycle to generate energy.
66
What is the first regulatory step in glycolysis?
The first regulatory step in glycolysis is glucose phosphorylation, where glucose is converted to glucose D6-phosphate. In the liver, this is catalyzed by glucokinase, which is induced by insulin and not inhibited by its product (G-6-P). In other tissues, hexokinase is responsible and is insulin-independent, reaching maximum speed at normal blood glucose concentrations and being allosterically inhibited by G-6-P.
67
What is the second regulatory step in glycolysis?
The second regulatory step in glycolysis is catalyzed by phosphofructokinase, which converts glucose 6-phosphate to fructose 1,6-bisphosphate. This enzyme is allosterically regulated, with ATP and ADP positively regulating it.
68
How is glycolysis stimulated and inhibited?
Glycolysis is stimulated by phosphofructokinase 2, which converts fructose 6-phosphate to fructose 2,6-bisphosphate, further stimulating glycolysis. It is inhibited by fructose bisphosphatase 2 during low blood glucose levels, leading to reduced metabolic rate.
69
What is the net gain of ATP through glycolysis in aerobic conditions?
In aerobic conditions, glycolysis results in a net gain of 7 ATP molecules per glucose molecule.
70
What are the fates of pyruvate?
Pyruvate can be metabolized in various ways, including entering the tricarboxylic acid (TCA) cycle, forming lactate, being involved in amino acid metabolism, or being converted back into glucose through gluconeogenesis.
71
How does fructose enter glycolysis?
Fructose enters glycolysis through the action of phosphofructokinase and fructokinase. In the liver, fructose can also be phosphorylated to ensure it does not circulate freely.
72
What is the net gain of ATP through glycolysis in anaerobic conditions?
In anaerobic conditions, glycolysis results in a net gain of 2 ATP molecules per glucose molecule, with lactate formation.
73
In which cellular organelle does the tricarboxylic acid (TCA) cycle occur?
The tricarboxylic acid (TCA) cycle, also known as the citric acid cycle or Krebs cycle, occurs in the mitochondria.
74
What is the net gain of ATP through the tricarboxylic acid (TCA) cycle?
The net gain of ATP through the TCA cycle is 25 ATP molecules per glucose molecule.
75
What is the primary function of the HMP (hexosemonophosphate) shunt, also known as the pentose phosphate pathway?
The primary function of the HMP shunt is to produce pentose phosphates, which are essential for the synthesis of nucleic acids (DNA and RNA) and other nucleotides (ATP, ADP, AMP)
76
What is the significance of the reduced co-substrate NADPH produced by the HMP shunt?
NADPH produced by the HMP shunt is used for various purposes, including biosynthesis of fatty acids, maintaining reducing substrates in erythrocytes, and drug metabolism in the liver.
77
In which tissues is the HMP shunt highly active, and why?
The HMP shunt is highly active in tissues such as the liver, adipose tissue, adrenal cortex, and lactating mammary gland because these tissues have a high demand for NADPH, which is essential for fatty acid synthesis and other cellular processes.
78
What are the sources of glucose production for gluconeogenesis?
Gluconeogenesis can use various non-carbohydrate intermediates as sources of glucose production, including pyruvate, lactate, glycerol, and amino acids.
79
Where does gluconeogenesis primarily occur in the body, and why is it important?
Gluconeogenesis primarily occurs in the liver and, to a lesser extent, in the kidneys. It is important for maintaining blood glucose levels and supplying glucose to tissues, particularly those highly dependent on glucose, such as the brain and erythrocytes.
80
How does the gluconeogenesis pathway differ from glycolysis?
The gluconeogenesis pathway is essentially the reverse of glycolysis, and key enzymes in glycolysis are bypassed or regulated differently. For example, pyruvate cannot be directly converted to phosphoenolpyruvate (PEP) in gluconeogenesis and must go through oxaloacetate in the cytoplasm. Additionally, glucose-6-phosphate cannot be converted directly back to glucose and requires glucose-6-phosphatase.
81
What is the Cori cycle, and how does it relate to lactate as a glucogenic precursor?
The Cori cycle is a metabolic pathway where lactate, produced during exercise or in tissues like erythrocytes, is taken up by the liver and converted into glucose-6-phosphate via gluconeogenesis. This glucose can then be released into the bloodstream when needed.
82
Where is glycogen primarily stored in the body, and what is its significance?
Glycogen is primarily stored in the liver and muscles. It plays a crucial role in maintaining blood glucose homeostasis and serves as a reserve of instant energy for muscles.
83
What is the role of glycogenin in glycogen molecules?
Glycogenin serves as the core of glycogen molecules, where glucose units are attached. It helps initiate the branching of glycogen and ensures that glucose can be released one molecule at a time.
84
How is glycogen regulated, and what hormones are involved in its regulation?
Glycogen storage is stimulated by insulin, while the release of glucose from glycogen is stimulated by glucagon and epinephrine.
85
What are the gluconeogenic precursors, and where do they come from?
Gluconeogenic precursors include lactate (from anaerobic glycolysis), glucose (from aerobic glycolysis), glycerol (from fatty acid formation), and certain amino acids (which can be converted to pyruvate).
86
What is glycogenolysis, and how is it regulated?
Glycogenolysis is the cleavage of glycogen to release glucose molecules. It is regulated by hormones like glucagon and epinephrine, which stimulate the activation oWhat are the four stages of the fed-fast cycle, and what regulates each stage?f enzymes responsible for breaking down glycogen into glucose.
87
What are the four stages of the fed-fast cycle, and what regulates each stage?
The four stages of the fed-fast cycle are:
Fed state (regulated by insulin)
Postabsorptive or early fasting state (regulated by glucagon)
Fasting state
Starvation state (or long-term fast)
88
What is the primary hormone that regulates the fed state, and what happens during this stage?
The fed state is primarily regulated by insulin. During this stage, blood glucose levels increase, and insulin is activated.
89
Which hormone is responsible for regulating the postabsorptive or early fasting state, and what characterizes this stage?
The postabsorptive or early fasting state is regulated by glucagon. This stage occurs from about 3 hours to 12-18 hours following a meal.
90
Describe the fasting state and its duration within the fed-fast cycle.
The fasting state occurs from 18 hours to 2 days without food intake. During this stage, the body undergoes various metabolic changes.
91
What is the starvation state, and how does it differ from the fasting state?
The starvation state is a fully adapted state of food deprivation that can last several weeks. It differs significantly from the fasting state and has a profound impact on metabolism.
92
What are the metabolic effects of insulin, and which enzymes are targeted by insulin?
Insulin increases glucose uptake in muscle and liver, promotes glycogen synthesis, decreases glycogen breakdown, and increases glycolysis and acetyl-CoA production. It targets enzymes such as glucose transporter, glucokinase, glycogen synthase, and phosphofructokinase-1.
93
What are the metabolic effects of glucagon, and which enzymes are targeted by glucagon?
Glucagon decreases glycolysis, increases glucose formation (gluconeogenesis), decreases glycolysis in the liver by inactivating pyruvate kinase, increases glycogen breakdown by activating glycogen phosphorylase, and decreases glycogen formation by inhibiting glycogen synthase. It also increases fructose-bisphosphate 2.
94
What are dietary and functional fibers, and how do they differ?
Dietary fiber consists of non-digestible carbohydrates and lignin present in plants, while functional fiber is composed of isolated, non-digestible carbohydrates with beneficial effects. They have different roles in the body.
95
Describe the composition of dietary fiber and its factors of influence.
Dietary fiber consists of non-digestible carbohydrates and lignin, with variations based on plant species, plant parts, and maturity. For example, cereals are rich in hemicellulose, lignin, and cellulose, while fruits and vegetables are high in cellulose and pectin.
96
What is cellulose, and how does it behave in the body?
: Cellulose is a dietary and functional fiber, the primary component of plant cell walls, water-insoluble, and poorly fermented. It's found in bran, legumes, nuts, root vegetables, and more
97
Explain hemicellulose, its characteristics, and dietary sources.
Hemicellulose is a dietary fiber found in plant cell walls with varying solubility and fermentability. It's present in bran, whole grains, nuts, legumes, and certain fruits and vegetables.
98
: Describe the features and dietary sources of pectins.
Pectins are dietary and functional fibers found in plant cell walls, water-soluble, gelforming, and highly fermentable. They are mainly found in jams and jellies made from fruits.
99
: What are lignin's characteristics and dietary sources?
Lignin is a dietary and functional fiber, a structural component of plants, insoluble in water, and poorly fermented. It's found in foods like strawberries.
100
Explain gums, their properties, and their uses in food processing.
Gums are dietary and functional fibers secreted at the site of plant injury, water-soluble, and highly fermented by bacteria. They are used as gelling and thickening agents in food processing
101
What are beta-glucans, and how do they impact the body?
Beta-glucans are dietary and functional fibers, water-soluble, highly fermentable, and form viscous gels in the GI tract. They regulate cholesterol and blood glucose levels and are found in oats and barley.
102
What are resistant starches (RS) and their different types?
Resistant starch is starch that resists enzymatic digestion. RS1 and RS2 are dietary fibers found in whole grains and some legumes, while RS3 and RS4 are functional and partially fermentable starches found in cooked starchy foods.
103
Describe fructans and their properties.
Fructans are dietary fibers made of fructose units, promote the growth of beneficial bacteria, and are found in foods like artichokes, onions, wheat, barley, and rye.
104
Explain chitin and chitosan, their role in the body, and dietary sources.
Chitin and chitosan are insoluble fibers that bind dietary lipids in the stomach. They're found in the shells of shrimp and lobster.
105
hat are psyllium (mucilages) and their effect on the body?
: Psyllium is a functional fiber known for its high water binding capacity. It acts as a laxative and reduces serum lipids.
106
What are the major roles of fiber in the body, and how do different fiber types affect digestion?
Fiber has four major roles: solubility in water, water-holding capacity, adsorption or binding ability, and degradation or fermentability, affecting nutrient absorption and digestion.
107
How does solubility in water impact fiber's effect on digestion? What are the soluble fiber?
Soluble fibers like fructans, psyllium, beta-glucans, pectins, and gums form gels in the GI tract, delaying gastric emptying, increasing transit time, and decreasing nutrient absorption.
108
How does water-holding capacity and viscosity impact fiber's role in digestion?
Fiber's water-holding capacity affects satiety, the mixing of chyme with digestive enzymes, enzyme function, nutrient diffusion, and transit time in the GI tract.
109
What is the adsorption/binding capacity of certain fibers, and what does it affect?
Some fibers have adsorption/binding capacity that diminishes lipid absorption, increases fecal bile excretion, lowers serum cholesterol, and alters the absorption of minerals, carotenoids, and phytochemicals.
110
Explain the fermentability of different fiber types and its physiological effects.
: Fibers vary in fermentability, affecting the generation of short-chain fatty acids, prebiotic capacity, and the absorption of minerals, carotenoids, and phytochemicals.
High fermentability = enhanced mineral uptake, production of SCFA, creating acidic environment
Low fermentability = inhibited mineral absorption,increased fecal volume, scavengers for ROS
111
What are probiotics, and how do they differ from prebiotics?
Probiotics are live bacteria with the ability to reach the intestine intact, while prebiotics are non-digestible fibers promoting the growth of beneficial bacteria. Probiotics are available in supplements or foods like yogurt.
112
How does fiber relate to the prevention and management of diabetes mellitus?
Fiber, by trapping glucose in GI gels, has a hypoglycemic effect, aiding in diabetes mellitus management.
113
How can fiber help prevent heart disease and obesity?
Fiber has hypolipidemic effects, lowers cholesterol, and increases satiety, which can prevent heart disease and obesity.
114
What role does fiber play in managing gastrointestinal disorders and colon cancer?
Fiber, through its effects on beneficial bacterial species and formation of short-chain fatty acids, is protective against colon cancer and beneficial in managing gastrointestinal disorders.
115
: Explain the food matrix issue in the context of fiber.
: In some cases, whole foods rich in a mixture of fibers are more beneficial than isolated fiber supplements.
116
What are the recommended intakes for fiber, and how are they determined?
Adequate Intakes are based on the amount of fiber needed to protect against heart disease, with suggested intakes of 14 grams of fiber per 1,000 kcal, translating to 38g/day for men and 25g/day for women.
117
How is fiber content typically labeled on food products?
On food labels, total fiber is indicated, which is the sum of dietary fiber and functional fiber.
118
What are the primary functions of lipids in the human body?
Lipids serve as an energy storage source, play structural roles in cell membranes, act as signaling molecules, assist in the absorption of fat-soluble vitamins, and have dietary and nutritional roles.
119
How do fatty acids' chain length impact their properties, and give examples of short, medium, and long-chain fatty acids?
Chain length influences the properties of fatty acids. Examples include short-chain fatty acids (2-4 carbons), medium-chain fatty acids (6-12 carbons), and long-chain fatty acids (>12 carbons).
120
: Explain the relationship between the number of double bonds in fatty acids and their properties.
Saturated fatty acids have no double bonds (0), monounsaturated fatty acids have one double bond (1), and polyunsaturated fatty acids have two or more double bonds (2-6). More double bonds lead to lower melting points and increased susceptibility to oxidation.
121
What is the significance of cis and trans double bonds in fatty acids?
Cis double bonds introduce kinks, increasing fatty acid fluidity. Trans double bonds are less common and have been associated with health issues like coronary heart disease.
122
Explain the nomenclature for fatty acids and how it represents their structure.
Fatty acids are named by specifying the number of carbons, double bonds, and their position in the carbon chain. The omega (ω) designation indicates the position of the first double bond relative to the methyl end of the chain.
123
What are neutral fats, and how are they structured?
Neutral fats are composed of one, two, or three fatty acids esterified to glycerol, usually with different fatty acids in each position. They form the storage form of lipids in the body.
124
What are the biological roles of phospholipids in the body?
Phospholipids serve as structural components in cell membranes, act as physiologically active compounds, participate in immune function, and function as second messengers in cell signaling.
125
What are the primary physiological roles of sphingolipids, especially in nervous tissue and blood group determinants?
Sphingolipids play a role in myelin sheaths of nervous tissues and medullary sheaths in the brain. They also provide determinants for blood groups A, B, and O.
126
Explain the significance of cholesterol in the body and its dietary sources.
Cholesterol, found in animal-derived food sources, is essential in the body, serving as a precursor for sex hormones, bile acids, and vitamin D. It can be ingested through the diet or synthesized endogenously.
127
Describe the process of fat digestion in the mouth and stomach.
In the mouth, mechanical separation of lipids occurs. Lingual lipase is secreted under the tongue for hydrolyzing dietary fat. In the stomach, gastric lipase further contributes to fat digestion, and emulsification increases surface area.
128
What role does the liver play in fat digestion, and how are bile acids synthesized?
The liver synthesizes bile acids, which are amphipathic molecules derived from cholesterol. They aid in emulsifying lipids, making them more water-soluble.
129
Explain the release of pancreatic enzymes and their role in lipid digestion in the small intestine.
In the small intestine, pancreatic enzymes are released, including pancreatic lipase, cholesterol esterase, and phospholipase A2, to further hydrolyze lipids in micelles. Bile salts stabilize micelles.
130
What is the significance of emulsification in fat digestion, and how is it achieved?
Emulsification is crucial for fat digestion, as it increases the surface area for enzymatic action. Bile salts, along with other factors, aid in the emulsification of fats.
131
What are the components of a micelle?
The components of a micelle in lipid absorption include 1-monoacylglycerol, 2-monoacylglycerol, free fatty acids, lysophosphatidylcholine, other lysophospholipids, cholesterol, and cholesterol ester.
132
Where is the re-absorption of bile acids primarily occurring during lipid absorption?
The re-absorption of bile acids primarily occurs in the ileum.
133
How are fatty acids with more than 12 carbons reactivated in the enterocytes during lipid absorption?
Fatty acids with more than 12 carbons are reactivated in the enterocytes by coupling with CoA using the enzyme acyl-CoA synthetase. This reaction converts the fatty acids to triacylglycerols or other long-chain fatty acids.
134
What is the primary function of VLDL (Very Low-Density Lipoproteins) in lipid transport? How is it released and what is it regulated by?
The primary function of VLDL is to transport and deliver endogenous lipids to peripheral tissues. It releases triacylglycerol via lipoprotein lipase, and its regulation is influenced by insulin and glucagon.
135
How does LDL (Low-Density Lipoprotein) contribute to cholesterol transport in the body?
LDL carries the majority of cholesterol in plasma (about 70%) and delivers it to peripheral and liver cells. This is achieved through a receptor-mediated process involving apoB-100, which recognizes LDL receptors on cells.
136
What is the role of HDL (High-Density Lipoprotein) in lipid transport, and which apolipoprotein plays a crucial role in this process?
HDL plays a role in "reverse cholesterol transport," removing excess cholesterol from cells and extrahepatic tissues and returning it to the liver. ApoA1 is a major apolipoprotein involved in this process.
137
What are some functions of apolipoproteins in lipid transport?
Apolipoproteins stabilize lipoproteins in the aqueous environment, are recognized by specific receptors, and can stimulate enzymatic reactions. For example, apoB-100 serves as a ligand for the LDL receptor, while apoC-2 is an activator of extrahepatic lipoprotein lipase.
138
What is the role of HDL (High-Density Lipoprotein) in cholesterol metabolism, and why is it often referred to as "good" cholesterol?
HDL plays a role in cleaning up cholesterol in the bloodstream, hence its reference as "good" cholesterol. It helps transport excess cholesterol from cells and tissues back to the liver for excretion.
139
Describe the potential negative consequences of high levels of circulating LDL (Low-Density Lipoprotein) cholesterol in the blood.
High levels of circulating LDL cholesterol can lead to atherosclerosis, which involves the buildup of fatty plaques in blood vessels. This condition can cause arterial injury, narrowing of blood vessels, inflammation, and increased risk of cardiovascular diseases like heart attacks and strokes.
140
What factors can lead to abnormal lipid profiles (dyslipidemia) and an increased risk of atherosclerosis?
Factors contributing to dyslipidemia and an increased risk of atherosclerosis include genetic predisposition (e.g., familial hypercholesterolemia), lifestyle factors (e.g., excessive caloric intake, little physical activity, overweight/obesity, stress), and chronic diseases like diabetes.
141
How is the lipid profile assessed, and what parameters are typically measured in a lipid profile blood test?
The lipid profile is assessed through a blood test conducted in a fasting state. It includes measurements of total cholesterol, LDL cholesterol, HDL cholesterol, and triacylglycerols. These parameters help assess cardiovascular risk and guide dietary and lifestyle recommendations
142
How does the quality and composition of dietary fat, particularly the types of fatty acids, influence blood lipid profiles?
Dietary fats high in saturated fatty acids (SFA) can increase blood LDL cholesterol, contributing to a higher risk of atherosclerosis. In contrast, unsaturated fatty acids, such as polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA), have a more favorable impact, with PUFA decreasing total cholesterol and LDL cholesterol.
143
What role does dietary cholesterol play in influencing plasma cholesterol levels, and how do plant sterols help regulate cholesterol absorption?
Dietary cholesterol can increase plasma cholesterol levels, especially in individuals with low dietary cholesterol intake or hyperresponsive characteristics. Plant sterols displace cholesterol in mixed micelles, reducing cholesterol absorption and helping regulate blood cholesterol levels.
144
How does fiber intake influence plasma cholesterol levels, and what mechanisms are involved?
Fiber intake can reduce plasma cholesterol by increasing bile and cholesterol excretion, altering bile composition, inhibiting the enzyme HMG CoA reductase, and promoting the production of short-chain fatty acids through colonic fermentation.
145
hat is the impact of the source of protein (animal versus plant) on blood cholesterol levels?
Animal-derived protein intake is associated with elevated cholesterol levels, while plant-derived protein has a hypocholesterolemic effect. This difference is due to the higher saturated fat content and cholesterol in animal sources and the presence of plant sterols and fiber in plant sources.
146
How does coffee consumption affect blood cholesterol levels, and what component of coffee is responsible for this impact?
Coffee consumption, particularly brewed coffee, can increase blood cholesterol levels due to the presence of cafestol, a potent stimulator of LDL. The levels of cafestol can vary depending on the brewing time.
147
What are the roles of omega-3 fatty acids in the body, and what sources provide these essential fatty acids?
Omega-3 fatty acids play roles in cognitive development, brain function, cardiovascular health, and more. They are primarily sourced from fish, flaxseed, and other seed oils.
148
What are the four stages of the fed-fast cycle, and which hormone regulates the fed state?
The four stages are the fed state, postabsorptive state, fasting state, and starvation state. The fed state is regulated by insulin.
149
Name the key organs involved in lipid metabolism and briefly describe their roles.
The liver is responsible for lipoprotein formation (VLDL and HDL), as well as bile salt formation. Adipose tissue is the site of fat storage.
150
In the liver during the fed state, describe the process of triacylglycerol (TAG) formation and VLDL release.
TAG is formed using dietary free fatty acids through coupling with CoA. VLDL is formed with TAG, apolipoproteins, cholesterol, and cholesterol esters. TAG is then taken up by peripheral tissues through a process of intravascular hydrolysis.
151
How does the liver handle energy when there is excess carbohydrate intake after a high-carbohydrate meal?
Excess carbohydrates lead to the formation of glucose-6-P, which can have various fates, including replenishing glycogen stores, α-glycerol-3-phosphate formation for TAG synthesis, and contributing to the hexose monophosphate shunt for NADPH production for fatty acid synthesis.
152
Explain the distribution of cholesterol and cholesterol esters from chylomicron remnants in the liver during the fed state.
Cholesterol from chylomicron remnants can be converted into bile salts, secreted into the bile, or incorporated into VLDL or HDL for release into the bloodstream.
153
In adipose tissue during the fed state, how is energy stored, and what role does insulin play in this process?
Insulin stimulates the storage of energy by promoting the formation of lipoprotein lipase, which hydrolyzes triacylglycerols in chylomicrons and VLDL. These hydrolyzed products are re-esterified to form triacylglycerols for energy storage.
154
How does adipose tissue respond during the postabsorptive or fasting state, and what hormones regulate this process?
In the fasting state, adipose tissue releases energy. Hormones like glucagon and epinephrine activate hormone-sensitive lipase to hydrolyze stored triacylglycerols, releasing fatty acids and glycerol into the bloodstream.
155
What is the primary role of the liver in lipid metabolism during the postabsorptive or fasting state?
In the fasting state, the liver forms triacylglycerols and re-releases them into the bloodstream, but at a lower rate compared to the fed state. The liver also oxidizes fatty acids to provide energy.
156
Explain the concept of ketogenesis, when it occurs, and its significance.
Ketogenesis is the formation of ketone bodies in the liver, which happens during prolonged fasting, low-carb diets, uncontrolled diabetes, or energy deficits. Ketone bodies serve as an alternative energy source when glucose is scarce.
