Study Notes: - Glycolysis is the process that occurs in the cytosol and breaks down glucose into two pyruvic acid molecules. - Glycolysis produces a small amount of ATP through substrate-level phosphorylation. - The Krebs cycle, which takes place in the mitochondria, generates most of the carbon dioxide produced during cellular respiration. - The Krebs cycle also produces a small amount of ATP through substrate-level phosphorylation. - The electron transport chain, located in the mitochondrial cristae membranes, is the main site for ATP production. - Hydrogen atoms, carrying energy, are removed during glycolysis and the Krebs cycle and temporarily passed to vitamin-containing coenzymes. - The coenzymes deliver the hydrogen atoms and their associated electrons to protein carriers in the electron transport chain. - In the electron transport chain, the hydrogen atoms are split into hydrogen ions (H+) and electrons (e−). - The electrons move from carrier to carrier, releasing their energy gradually. - This energy release allows for the attachment of phosphate to ADP, producing ATP. - Free oxygen acts as the final electron acceptor, combining with electrons and hydrogen ions to form water. - Oxidative phosphorylation, the process occurring in the electron transport chain, is responsible for the majority of ATP synthesis. - Unlike fuel burning, oxidative phosphorylation minimizes energy loss as heat and light. - Maintaining stable blood glucose levels is important because glucose is the primary fuel for ATP production. - Excess glucose in the blood is stored as glycogen in liver and muscle cells during hyperglycemia. - If glucose levels remain high, the excess is converted into fat. - Consuming large amounts of sugary foods can lead to rapid fat deposition in adipose tissues. - During hypoglycemia, when blood glucose levels are low, the liver breaks down stored glycogen and releases glucose into the blood for cellular use. Study Notes: - The liver is primarily responsible for lipid metabolism in the body. - Liver cells use some fats to produce ATP for their own energy needs. - The liver also synthesizes lipoproteins, thromboplastin (a clotting protein), and cholesterol using fats. - The liver releases the remaining fat breakdown products into the blood. - Body cells take up these fat products and cholesterol from the blood and use them to build cell membranes, steroid hormones, myelin sheaths of neurons, and fatty cushions around organs. - Stored fats serve as the body’s most concentrated source of energy. 1 gram of fat yields twice as much energy as 1 gram of carbohydrate or protein. - To be used for ATP synthesis, fat products need to be broken down to acetic acid. - Acetic acid is completely oxidized within the mitochondria, resulting in the production of carbon dioxide, water, and ATP. - When there is insufficient glucose for cellular energy needs, larger amounts of fats are used to produce ATP. - In such conditions, fat oxidation is fast but incomplete, leading to the accumulation of intermediate products like acetoacetic acid and acetone in the blood. - This accumulation causes the blood to become acidic (acidosis or ketoacidosis), and acetone can be detected in the breath, giving it a fruity odor. - Ketoacidosis is commonly observed in situations like “no-carbohydrate” diets, uncontrolled diabetes mellitus, and starvation when the body heavily relies on fats for energy. - Cholesterol is never used as a cellular fuel but plays a role in functional molecules and structural formation. - Excess fats are stored in fat depots such as the hips, abdomen, breasts, and subcutaneous tissues. - While subcutaneous fat provides insulation for organs, excessive amounts can restrict movement and place additional demands on the circulatory system. Study Notes: - Proteins are essential components of cellular structures and are conserved by body cells. - Ingested proteins are broken down into amino acids. - The liver processes the blood from the digestive tract and takes up amino acids it needs. - The remaining amino acids circulate in the blood and are taken up by body cells. - Cells use amino acids to build proteins for their own use (enzymes, membranes, muscle proteins) and for export (mucus, hormones, etc.). - Cells actively transport amino acids into their interior using ATP, even if they already contain more amino acids than what is in the blood. - This active uptake ensures that all the needed amino acids (around 20 types) are available for protein synthesis. - Essential amino acids must be obtained through the diet since cells cannot produce them. - Amino acids are primarily used for protein synthesis, but they can be used to produce ATP when proteins are abundant and carbohydrates and fats are unavailable. - When amino acids are oxidized for energy, their amine groups are removed as ammonia. - The remaining molecule enters the Krebs cycle pathway in the mitochondria. - Ammonia is toxic to body cells, especially nerve cells. - The liver combines ammonia with carbon dioxide to form urea. - Urea is a non-toxic waste product that is excreted from the body in urine. - The liver plays a crucial role in detoxifying ammonia and producing urea to protect body cells. Study Notes: - The liver is a versatile and complex organ with multiple functions crucial for survival. - In addition to its role in digestion (manufacturing bile), the liver performs various functions. - Liver cells detoxify drugs and alcohol, degrade hormones, and produce substances vital to the body (cholesterol, blood proteins, lipoproteins). - The liver plays a central role in metabolism, processing nearly every class of nutrient. - The liver has a surplus of tissue, and even if damaged or removed, it can regenerate rapidly and easily. - The hepatic portal circulation brings nutrient-rich blood from the digestive viscera directly to the liver, ensuring the liver’s needs are met first. - Liver cells remove amino acids, fatty acids, and glucose from the blood during its slow circulation through the liver. - These nutrients can be stored for later use or processed in various ways by the liver. - Liver phagocytic cells remove and destroy bacteria that enter the blood from the digestive tract. - The liver helps maintain blood glucose levels by storing excess glucose as glycogen through glycogenesis and releasing glucose through glycogenolysis when needed. - Gluconeogenesis allows the liver to produce glucose from noncarbohydrate substances like fats and proteins. - Hormones such as thyroxine, insulin, and glucagon play a vital role in controlling blood sugar levels and glucose handling in the body. - The liver oxidizes some fats for its own energy production (ATP) and breaks down the rest into simpler substances or stores them as fat reserves. - The liver synthesizes all blood proteins from the amino acids it picks up from the blood. - Albumin, the most abundant blood protein, helps maintain fluid balance in the bloodstream. - Clotting proteins produced by the liver are important for blood clot formation. - The liver also synthesizes nonessential amino acids and detoxifies ammonia by converting it to urea. - Nutrients and liver metabolism by-products are released into the blood and drained from the liver through the hepatic vein, entering the systemic circulation for use by other body cells. Study Notes: - Cholesterol is an important lipid in the diet but is not used as an energy fuel. - Instead, cholesterol serves as the structural basis for steroid hormones, vitamin D, and is a major building block of plasma membranes. - Only about 15% of blood cholesterol comes from the diet, while the liver produces the remaining 85%. - Cholesterol is eliminated from the body when it is broken down and secreted in bile salts, which are eventually excreted in feces. - Lipoproteins are small lipid-protein complexes that transport fatty acids, fats, and cholesterol in the bloodstream since they are insoluble in water. - Low-density lipoproteins (LDLs) transport cholesterol and other lipids to body cells, where they are used in various ways. - High levels of circulating LDLs increase the risk of fatty substance deposition on arterial walls, leading to atherosclerosis. - LDLs are commonly referred to as “bad lipoproteins” due to their association with atherosclerosis. - High-density lipoproteins (HDLs) transport cholesterol from tissue cells or arteries to the liver for disposal in bile. - High levels of HDLs are considered “good” because the cholesterol is destined to be broken down and eliminated from the body. - The relative ratio of LDLs and HDLs in the blood determines the likelihood of cholesterol deposits in artery walls. - Favorable HDL/LDL ratios can be achieved through aerobic exercise, a diet low in saturated fats and cholesterol, and avoiding smoking and excessive coffee consumption. - Both LDLs and HDLs are necessary, and their balance is important for maintaining cardiovascular health. Study Notes: 1. Energy Balance Importance: - Energy balance refers to the equilibrium between energy intake and energy output in the body. - It is essential for maintaining body weight and overall health. - Energy balance ensures that the energy obtained from food is balanced with the energy expended by the body. - When energy intake matches energy output, body weight remains stable. - Imbalances in energy intake and output can lead to weight gain or weight loss. 2. Consequences of Energy Imbalance: - Positive Energy Balance: When energy intake exceeds energy output, it leads to weight gain and can result in obesity. Excess energy is stored as fat. - Negative Energy Balance: When energy intake is less than energy output, it leads to weight loss. The body utilizes stored energy (fat) for fuel. - Prolonged positive energy balance can lead to chronic weight gain and obesity-related health issues such as diabetes, cardiovascular disease, and joint problems. - Prolonged negative energy balance can lead to malnutrition, muscle wasting, decreased immune function, and other health complications. 3. Regulation of Food Intake: - Mechanisms exist to regulate food intake and prevent excessive weight gain or loss. - The hypothalamus, a region in the brain, plays a crucial role in regulating feeding behavior. - The hypothalamus releases peptides that influence hunger and satiety. - Neural signals from the digestive tract, bloodborne signals related to body energy stores, hormones, body temperature, and psychological factors contribute to the regulation of food intake. - Feedback signals from these factors are sent to the feeding centers of the brain, influencing appetite and food consumption. 4. Factors Influencing Metabolic Rate: - Metabolic rate refers to the rate at which the body utilizes energy (measured in kilocalories or kcal). - Several factors influence metabolic rate: - Basal Metabolic Rate (BMR): It is the amount of heat produced by the body at rest, reflecting the energy needed for essential life activities (breathing, heartbeat, kidney function). - Surface area: Individuals with larger surface areas tend to have higher metabolic rates. - Gender: Generally, men have higher metabolic rates than women due to differences in body composition and muscle mass. - Age: Children and adolescents have higher metabolic rates due to energy requirements for growth. Metabolic rate decreases with age as muscle mass declines. - Thyroxine production: Thyroxine, a hormone produced by the thyroid gland, plays a crucial role in determining metabolic rate. Higher levels of thyroxine lead to increased metabolic rate. - Body composition: Lean muscle mass contributes to a higher metabolic rate, as muscle tissue requires more energy than fat tissue. 5. Assessment of Thyroid Activity: - Thyroxine is often referred to as the “metabolic hormone” as it influences metabolic rate. - In the past, basal metabolic rate (BMR) tests were conducted to assess thyroid activity indirectly. - Nowadays, thyroid activity is more easily assessed through blood tests that measure thyroid hormone levels. - Blood tests can determine if there are any abnormalities in thyroid hormone production, helping diagnose conditions like hypothyroidism or hyperthyroidism. Note: It’s important to consult healthcare professionals for accurate information and personalized advice regarding energy balance, weight management, and thyroid function. Study Notes: 1. Hyperthyroidism Effects: - Hyperthyroidism refers to an overactive thyroid gland, resulting in excessive production of thyroid hormones. - Excess thyroid hormones increase the metabolic rate of the body. - Effects of hyperthyroidism include: - Increased catabolism of stored fats and tissue proteins, leading to weight loss despite increased hunger and food intake. - Weakening of bones due to increased breakdown of bone tissue. - Atrophy of body muscles, including the heart, due to increased breakdown of muscle proteins. 2. Hypothyroidism Effects: - Hypothyroidism refers to an underactive thyroid gland, resulting in insufficient production of thyroid hormones. - Reduced thyroid hormone levels lead to a slowed metabolic rate. - Effects of hypothyroidism include: - Slowed metabolism, resulting in weight gain and difficulty losing weight. - Obesity due to reduced energy expenditure. - Diminished thought processes and cognitive function. 3. Total Metabolic Rate (TMR): - Total metabolic rate refers to the total amount of kilocalories (energy) the body needs to support all ongoing activities. - TMR includes the energy required for basal metabolic rate (BMR) as well as additional energy needed for physical activity and digestion. - Muscular work, such as exercise, is a major contributor to increased TMR. - Even slight increases in skeletal muscle activity can significantly raise the metabolic rate. - Intense exercise can cause the TMR to increase up to 15 to 20 times the normal rate, and it remains elevated for several hours afterward. 4. Energy Balance and Weight Maintenance: - Homeostasis is maintained when the total number of kilocalories consumed is equal to the TMR. - When food intake matches the energy requirements of the body, weight remains constant. - Excess kilocalories consumed beyond the TMR lead to the formation of fat deposits and weight gain. - Insufficient kilocalories consumed to meet the TMR lead to the breakdown of fat reserves and tissue proteins to satisfy energy needs. - Weight-loss diets often aim to create an energy deficit by reducing kilocalorie intake below the TMR, leading to the utilization of stored energy (fat and tissue proteins) for fuel. - Regular exercise can further increase the TMR, aiding in weight loss by increasing energy expenditure. 5. Calculation of Daily Caloric Requirements: - The total kilocalories needed by an individual are calculated based on factors such as body size and age. - In weight-loss diets, a reduction of 20 percent or more from the calculated daily caloric requirements is often recommended. Study Notes: Body temperature regulation is crucial for maintaining homeostasis in the body. The hypothalamus, located in the brain, acts as the body’s thermostat and continuously monitors and regulates body temperature around a set point of 35.6°C to 37.8°C (96°F to 100°F). Heat-Promoting Mechanisms: 1. Vasoconstriction: When the environmental temperature is low or the core body temperature drops, the blood vessels in the skin constrict, redirecting blood flow to deeper organs. This conserves heat and prevents heat loss from the skin. 2. Shivering: When the core body temperature drops beyond what vasoconstriction can handle, shivering occurs. Shivering is an involuntary contraction of voluntary muscles, particularly skeletal muscles, which generates heat. Homeostatic Imbalance 14.13: Prolonged exposure to cold can lead to hypothermia, where the body’s vital signs decrease. The individual may become drowsy and comfortable, even though they were previously feeling extremely cold. If left untreated, hypothermia can progress to coma and death as metabolic processes slow down. Heat-Loss Mechanisms: 1. Radiation: Most heat loss occurs through the skin via radiation. When the body temperature rises above the desired level, blood vessels serving the skin dilate, and heat radiates from the skin surface. 2. Evaporation: Excess heat can be lost through the evaporation of perspiration from the skin surface. Evaporation is an efficient cooling mechanism, especially in dry air. However, in humid conditions, evaporation occurs at a slower rate, reducing the effectiveness of heat loss. Homeostatic Imbalance 14.14: When normal heat loss processes become ineffective, hyperthermia can occur. Hyperthermia is an elevated body temperature that depresses the hypothalamus. The body enters a positive feedback cycle, where the rising temperature increases the metabolic rate, leading to more heat production. Without intervention, heat stroke can occur, potentially causing permanent brain damage. Immediate measures such as immersion in cool water and fluid administration are necessary. Heat Exhaustion: Heat exhaustion occurs during or after vigorous physical activity and is characterized by excessive loss of body fluids (dehydration). Symptoms include low blood pressure, a rapid heartbeat, and cool, clammy skin. Heat-loss mechanisms still operate in heat exhaustion. Fever: Fever is a controlled hyperthermia that often results from infection but can also be caused by other conditions. Pyrogens released by macrophages, white blood cells, and injured tissue cells act on the hypothalamus, raising the body’s thermostat setting. Heatpromoting mechanisms such as vasoconstriction and shivering are initiated. Once the disease process is reversed, the thermostat is reset, causing heat-loss mechanisms to swing into action. Fever helps speed healing processes and inhibits bacterial growth. It's important to maintain body temperature within a narrow range to support efficient metabolism and overall homeostasis.
