Learning Objectives Flashcards
What is the role of macronutrients in human nutrition?
Macronutrients serve as a source of energy, act as building blocks for various bodily structures, and have hormone-like functions in human nutrition.
How do macronutrients compare to micronutrients in daily nutrient intake?
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.
What are the potential health effects of an excess caloric intake?
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.
Explain the role of macronutrients in human metabolism and its significance for understanding nutrient-disease relationships.
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.
What is metabolism, and why is it a key concept in understanding nutrient-disease relationships?
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.
What organs make up the gastrointestinal (GI) tract, and what are their functions?
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.
What are the accessory organs in the digestive system, and how do they facilitate digestion?
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.
Describe the role of oral activity and salivary glands in the carbohydrate digestive process.
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.
What is the function of the esophagus in digestion, and how does it move food to the stomach?
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.
Explain the structure and functions of the stomach.
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.
What are the key components of gastric juice, and what is the role of hydrochloric acid in digestion?
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.
How does chyme leave the stomach and enter the duodenum, and what role does somatostatin play in this process?
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.
What is the main site for nutrient digestion and absorption in the digestive system?
The small intestine, including the duodenum, jejunum, and ileum, is the main site for nutrient digestion and absorption in the digestive system.
Describe the structural adaptations of the small intestine that contribute to its large surface area for absorption
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.
How and where is nutrient digestion typically completed in the small intestine (final step)?
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.
What are the different mechanisms of nutrient absorption in the small intestine?
Nutrient absorption in the small intestine can occur through diffusion, facilitated diffusion, active transport, and pinocytosis, depending on the nutrient type and concentration.
Explain the functions of the pancreas in digestion.
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.
How does the liver regulate metabolism and nutrients in the body?
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.
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?
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.
What role does the large intestine play in digestion, and how does it absorb nutrients?
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.
What is the primary role of carbohydrates in the human diet?
: Carbohydrates serve as a major energy source, supplying around half or more of the total caloric intake.
How are carbohydrates classified?
Carbohydrates are classified into two major classes: simple carbohydrates and complex carbohydrates.
Define simple carbohydrates.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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%).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
