Biochemistry of Nutrition BIOC1305 PDF

Biochemistry of Nutrition BIOC1305  Topic 8 Water as an important nutrient Composition of body fluid compartments Source and Fluid and electrolyte balance Function and thirst mechanism Excess water effect and severe dehydration By: Dr Mohammad Rehan Ajmal K...

Biochemistry of Nutrition BIOC1305  Topic 8 Water as an important nutrient Composition of body fluid compartments Source and Fluid and electrolyte balance Function and thirst mechanism Excess water effect and severe dehydration By: Dr Mohammad Rehan Ajmal Khan Introduction There are more than 50 known nutrients (including amino acids and fatty acids) and many more chemicals in food thought to influence human function and health (Box 1.1). Nutrients do not exist in isolation, except for water  Why body composition is important? Many diseases and disorders are related to abnormal body composition or to changes in body composition. The most common of these conditions is obesity, in which the amount of body fat is excessively high, leading to abnormalities in lipid and carbohydrate metabolism, high blood pressure, and adult-onset diabetes. At the other end of the nutritional spectrum, energy and protein malnutrition results in a decrease in the amount of fat and protein stores in the body, and many diseases are related to abnormalities in total body water or to the distribution of body water across the intracellular and extracellular spaces. 6 There is variation in water content of the body The water content in the body varies with age. In a fetus, the water content slowly decreases from more than 90% after conception to about 80% before delivery at about 7 months of gestation. A new born has about 70% body water, which is about 82% of the fat-free mass. This value slowly decreases further to 72% of the fat-free mass until the body is chemically mature at age 15–18 years. In general, males have more body water (related to body weight) than females, as their body fat content is lower. The total amount of water in the body is high and, depending on the body fat content, can be as high as 60–70% of total body weight. Total body water can be divided into intracellular water and extracellular water, and the ratio of the two is an important health parameter that is disturbed in many diseases 7 Water is important component of human body Human beings are creatures that are primarily composed of water. It is the essence of life and the aqueous base solution in which all essential biochemical processes occur that produce life. Humans are approximately 75% water by mass as infants and 50% to 60% water by mass as adults. Furthermore, fluid is always in flux through various regulatory mechanisms to maintain appropriate concentrations throughout the various compartments of the body. Fluid is regulated mainly through passive diffusion following the concentration gradients of osmotically active solutes; however, hydrostatic pressures can influence fluid movement between spaces 8 Cellular Level The distribution of fluid throughout the body can be broken down into 2 general categories: intracellular fluid and extracellular fluid. Intracellular fluid is approximately 40% of the total body weight. It is the total space within cells primarily defined as the cytoplasm of cells. In general, intracellular fluids are stable and do not readily adjust to rapid changes. This space is where many chemical reactions occur, it is important to maintain an appropriate osmolality. The extracellular fluid comprises approximately 20% of total body weight and is further subcategorized as plasma at approximately 5% of body weight and interstitial space, which is approximately 12% of body weight. Additional fluid spaces are possible in pathological scenarios and are categorized as transudate or exudate based on location and etiology.  The exact chemical composition of body fluid is highly variable. This is dependent on which portion of the body, as well as which organ of the body, contains the fluid. Extracellular fluid and interstitial fluid are similar in composition. Extracellular spaces contain high concentrations of sodium, chloride, bicarbonate, and proteins but are relatively lower in potassium, magnesium, and phosphate. Interstitial fluids physiologically tend to have a low concentration of proteins. Intracellular fluids tend to be inversed with high levels of phosphate, magnesium, potassium, and proteins but lower sodium, chloride, and bicarbonate. 10 Water has important contribution in the body cell mass Cell mass includes the cells with all their contents, such as water, proteins, and minerals. Extracellular fluid contains about 95% water, which is plasma in the intravascular space and interstitial fluid in the extravascular space. Extracellular solids are mainly proteins (e.g., collagen) and minerals (bone minerals and soluble minerals in the extracellular fluid). Body composition at the cellular level is not easy to measure, owing to its complex nature 11 Intracellular fluids (ICF) are found inside cells and are made up of protein, water, electrolytes, and solutes. The most abundant electrolyte in intracellular fluid is potassium. Intracellular fluids are crucial to the body’s functioning. In fact, intracellular fluid accounts for 60% of the volume of body fluids and 40% of a person’s total body weight Extracellular fluids (ECF) are fluids found outside of cells. The most abundant electrolyte in extracellular fluid is sodium. The body regulates sodium levels to control the movement of water into and out of the extracellular space due to osmosis. Extracellular fluids can be further broken down into various types. The first type is known as intravascular fluid that is found in the vascular system that consists of arteries, veins, and capillary networks. Intravascular fluid is whole blood volume and also includes red blood cells, white blood cells, plasma, and platelets. Intravascular fluid is the most important component of the body’s overall fluid balance. Loss of intravascular fluids causes the nursing diagnosis Deficient Fluid Volume, also referred to as hypovolemia. Intravascular fluid loss can be caused by several factors, such as excessive diuretic use, severe bleeding, vomiting, diarrhea, and inadequate oral fluid intake. If intravascular fluid loss is severe, the body cannot maintain adequate blood pressure and perfusion of vital organs. This can result in hypovolemic shock and cellular death when critical organs do not receive an oxygen-rich blood supply needed to perform cellular function. A second type of extracellular fluid is interstitial fluid that refers to fluid outside of blood vessels and between the cells. For example, if you have ever cared for a patient with heart failure and noticed increased swelling in the feet and ankles, you have seen an example of excess interstitial fluid referred to as edema. The remaining extracellular fluid, also called transcellular fluid, refers to fluid in areas such as cerebrospinal, synovial, 12 Metabolic reactions generate of water molecules ▪ Glycolysis, a sequence of reactions in which glucose is converted to pyruvate, with concomitant production of ATP, is the prelude to the citric acid cycle and electron transport chain, which together release the energy contained in glucose. ▪ Under aerobic conditions pyruvate enters mitochondria, where it is completely oxidized to carbon dioxide and water 13 https://www.ncbi.nlm.nih.gov/books/NBK482447/ Electrolyte balance is important Sodium is the major extracellular electrolyte and exists as the fully water-soluble cation. Chloride is also mainly found in ECF and is fully water soluble as the chloride anion. Both ions are readily absorbed from the digestive tract. Glucose and anions such as citrate, propionates, and bicarbonate enhance the uptake of sodium. The “average” 70 kg male has about 90 g of sodium with up to 75% contained in the mineral apatite of bone. Plasma sodium is tightly regulated through a hormone system, which also regulates water balance, pH, and osmotic pressure. Potassium is the major intracellular electrolyte and exists as the fully water-soluble cation. More than 90% of dietary potassium is absorbed from the digestive tract. 14 A variety of pathological conditions induce abnormalities in fluid balance. Fluid balance abnormalities are either an overload of fluid or a decrease in effective fluid. Fluid overload is clinically known as edema. Edema occurs most commonly in soft tissues of the extremities but can occur in any tissue. Decreases in fluid load are commonly referred to as dehydration. Edema manifests as swelling in the soft tissues of the limbs and face, followed by an increase in size and tightness of the skin. Peripheral edema is reducible by increasing the pressure in the interstitial space and is measured by pressing a finger into the tissue, temporarily creating a dimple in the edematous skin. Likewise, wearing compression stockings can reduce peripheral edema by increasing interstitial hydrostatic pressure, forcing fluid back into the capillaries.  Pulmonary edema is when excess fluid swells into the interstitial tissues of the lung. Symptoms include shortness of breath and chest pain. Orthopnea, or impaired respiration while lying flat, may also be present as the excess fluid is distributed across the entire lung. Pulmonary edema is life-threatening as it compromises gas exchange in the lungs, and conditions can quickly decompensate. Pulmonary edema is associated with cardiac failure and renal failure. Classically, cardiac failure causes pulmonary edema through decreased pumping efficiency and capacity of the left atrium and ventricle. This creates back pressure in the pulmonary veins, increasing pressure in the vessels. Subsequently, hydrostatic pressures in the pulmonary capillaries are increased, “pushing” fluid into the interstitial lung space following the Starling equation. Renal failure causes edema through a failure to remove fluids and osmotic components from the body. The net result is increased osmotic pull into tissues and increased hydrostatic push out of capillaries. 16 Liver disease is also capable of inducing edema. This is due to a failure to produce osmotically active proteins—specifically, a failure to produce albumin. Albumin is found physiologically primarily in the plasma of the extracellular blood. It is typically not found in the interstitial space. As such, a decrease in body albumen directly decreases the “pull” of osmotic pressure into the capillaries. Edema is treated for symptomatic relief using a variety of medications, including diuretics, to remove fluid from the body via the renal system. Diuretics are closely associated with inducing contraction metabolic alkalosis. Albumin may be supplemented in cases of low plasma albumin. Lifestyle changes can include reducing sodium intake, restricting fluid intake, and wearing compression stockings. However, targeting the underlying pathology to improve cardiac, hepatic, or renal function offers better results than symptomatic treatment by removing fluid, replacing osmotic components, or other lifestyle changes. 17 Dehydration It is largely due to inadequate water intake to meet the body’s metabolic needs. The average adult has an obligatory intake requirement of 1600 mL per day. This value increases depending on activity and metabolism. Primary sources of normal fluid loss include urine, sweat, respiration, and stool. Pathological causes include diarrhea, vomiting, infection, and increased urination secondary to diabetes mellitus or diabetes insipidus. Dehydration manifests clinically as decreased urine output, dizziness, fatigue, tachycardia, increased skin turgidity, and fatigue or confusion in severe cases. Whenever possible, oral fluid replacement should be attempted. In more urgent situations, intravenous fluid replenishment should be based on bolus supplementation of the deficit of fluids and a maintenance replenishment of obligatory intake requirements. 18 Dehydration is treatable- if managed properly Intravenous fluid replacement options include normal saline (0.9% NaCl), one-half normal saline (0.45% NaCl), Dextrose 5% in either normal saline or one-half normal saline, and lactated Ringer solution. The choice of replacement fluids is patient scenario-specific and dependent on the electrolyte status of laboratory evaluation. Burn patients require specialized increases in fluid replacement secondary to the immense loss of free water through their wounds. 19 Importance of electrolytes. Electrolytes help to produce energy, support hydration, and stimulate muscle contractions like those keeping the heart beating. Certain prepared foods, as well as whole foods like spinach, turkey, and oranges contain them https://www.healthline.com/health/fitness-nutrition/electrolytes-food 20 Foods with electrolytes include: spinach kale avocados broccoli potatoes beans almonds peanuts soybeans tofu strawberries watermelon oranges bananas tomatoes milk buttermilk yogurt fish, such as flounder turkey Chicke veal raisins olives 21 Thirst may be defined as the subjective sensation of a desire or need for water. It is sometimes associated with feelings of dry mouth, headache, or irritability but these symptoms are not specific to thirst since they also have other causes. It must also be distinguished from cultural, social, psychological, medical, and other motivations to drink. The opposite of thirst is the feeling of satiation. It is not simply the absence of thirst but a conscious aversion to drinking that can make unflavored fluids taste unpleasant. It may be associated with other less specific symptoms such as fullness or even nausea, particularly if a large amount of water is drunk within a short space of time. 22 The homeostatic regulation of fluid intake by the brain is multifactorial. Osmotic, ionic, hormonal, and nervous signals converge on, and are integrated within, the central nervous system. Consequentially, neural circuitry (yet to be identified) that subserves the conscious perception of thirst may become activated. The satiation or extinction of thirst following the intake of water involves the participation of other sensory and integrative neural pathways that also interact with this circuitry but that are beyond the scope of this article. So too are the pathophysiological influences that alter the thirst mechanism so that it becomes either overactive or insensitive to fluid loss. For example, a significant proportion of the elderly have a reduced thirst responsiveness that may result in them becoming severely dehydrated. Conversely, psychogenic polydipsia that is observed in some psychological disorders may cause life-threatening water intoxication. 23 doi: 10.3390/nu11122864 Water comprises over 80% of human brain, cardiac, skeletal muscle, kidney and gastrointestinal tissues ; it also is the medium in which metabolism, excretion, absorption, secretion and diffusion occur. Because water is essential for the survival of humans, selective pressures have forged mechanisms that regulate total body water (TBW) volume during periods of abundance, perturbation and insufficiency. 24 The thirst drive and motivation to seek/consume water are vital aspects of the homeostatic regulation of total body water volume and tonicity, in response to intracellular dehydration, increased plasma osmolality, decreased plasma volume, decreased blood pressure, and extracellular hypovolemia 25 26 Homeostatic normalization of intracellular hydration, plasma osmolality, blood pressure, and extracellular volume (i.e., due to water and food intake), which result from a persistent, strong motivation to drink. These responses result in reduced thirst and decreased motivation to seek/consume water. 27 28 Thirst has a key role in the maintenance of body fluid homeostasis by driving water intake to compensate for losses incurred as a result of breathing, sweating and the production of urine Thirst is associated with the activation of neurons in the anterior cingulate cortex and insular cortex; activation of these neurons might be induced via relay midline thalamic neurons Two distinct types of thirst emerge under different circumstances: homeostatic thirst is evoked in response to an existing water deficit, whereas anticipatory thirst occurs before an impending deficit Homeostatic thirst is induced in response to hypernatraemia, hyperosmolality and hypovolaemia, whereas anticipatory thirst occurs in response to food intake or hyperthermia or before sleep Thirst is rapidly inhibited by oropharyngeal afferents in response to water intake; inputs from gastric distension sensors can also provide feedback signals that suppress thirst https://doi.org/10.1038/nrneph.2017.149 29 Factors that influence thirst are categorized as either homeostatic (i.e., volume, pressure, concentration) or relatively rapid non-homeostatic (anticipatory) inputs. Solid and dashed arrows represent, respectively, factors that increase and decrease thirst. Abbreviations: NaCl, sodium chloride; Posm, plasma osmolality; Ang II, angiotensin II. https://doi.org/10.1038/nrneph.2017.149 30 31 The fluid–electrolyte balance of all vertebrates is subject to stringent homeostatic controls which maintain intracellular and extracellular ionic and osmotic conditions that are critical for normal cell functions. Mammals, fish, amphibians, reptiles, birds, rodents, and humans share the common needs of maintaining osmolality, total body water, extracellular volume, and blood pressure. However, vertebrates obtain and conserve water and essential electrolytes via a wide range of taxonomic-specific evolutionary adaptations, including sodium appetite, restricted water loss from the body surface, regulation of urine contents, and water storage. These vertebrate mechanisms of fluid–electrolyte balance are necessarily diverse, due to differences of environmental conditions (e.g., land, water, air, temperature, solar radiation, water availability) and life activities (e.g., avoiding predators, seeking food and water, migration). As a result, large species-specific differences of water consumption exist (i.e., expressed as % of body weight/24 h): man, 3%; dog, 5%; cattle, 6%, rabbit, 11%, and rat, 16%. 32 Dehydration Dehydration is the absence of enough water in your body. The best way to beat it is to drink before you get thirsty. If you’re thirsty, you’re already mildly dehydrated, and that can cause signs of dehydration like headache, fatigue, dizziness and more. Dehydration can contribute to life-threatening illnesses like heatstroke. Dehydration is a condition in which you lose so much body fluid that your body can’t function normally. It occurs when you lose more fluids than you take in. Dehydration may happen on a particularly hot day if you sweat a lot, or if you’re sick with fever, diarrhea or vomiting. It can also occur if don’t drink enough water, or if you’re taking a medication that increases your pee (urine) output. 33 What does water do for your body? Up to 78% of your body is made of water. Your brain is made up of 73% water, and so is your heart. Your bones are 31% water, your muscles and kidneys are 79%, and your skin is 64%. A whopping 83% of water makes up your lungs. Some of the functions of water: Aid digestion and get rid of waste. Your joints work. Water lubricates them. Make saliva (which you need to eat). Balance your body’s chemicals. Your brain needs it to create hormones and neurotransmitters. Deliver oxygen all over your body. Cushion your bones. Regulate your body temperature. Act as a shock absorber for your brain, your spinal cord and, if you’re pregnant, the fetus. Water is important to your body, especially in warm weather. It keeps your body from overheating. When you exercise, your muscles generate heat. To keep from burning up, your body needs to get rid of that heat. The main way your body discards heat in warm weather is through sweat. As sweat evaporates, it cools the tissues beneath. Lots of sweating reduces your body’s water level, and this loss of fluid affects normal bodily functions. 34 What are the symptoms of dehydration? Dry tongue and dry lips. No tears when crying. Fewer than six wet diapers per day (for infants), and no wet diapers or urination for eight hours (in toddlers). Sunken soft spot on your infant’s head. Sunken eyes. Dry, wrinkled skin. Deep, rapid breathing. Cool, blotchy hands and feet. Dehydration symptoms in adults may include: Headache, delirium and confusion. Tiredness (fatigue). Dizziness, weakness and lightheadedness. Dry mouth and/or a dry cough. High heart rate but low blood pressure. Loss of appetite but maybe craving sugar. Flushed (red) skin. Swollen feet. Muscle cramps. Heat intolerance or chills. Constipation. Dark-colored pee (urine). Your pee should be a pale, clear color. 35 What are the risk factors for dehydration? Anyone can become dehydrated if they don’t drink enough water. But infants and children are at a higher risk because they may be unable to communicate that they’re thirsty. This is especially important when they’re sick. So, make sure to monitor the amount of fluids your child takes in. Adults ages 65 and older are also at a higher risk. They don’t carry as much water in their bodies and they can’t tell as easily when they’re thirsty. If you’re a caregiver, especially for someone with memory problems, offer them drinks frequently. Even if they’re enduring an uncomfortable infection like a UTI (urinary tract infection), they still need to consume liquids. 36 What are the complications of dehydration? If you or your child has symptoms of severe dehydration, get medical care right away. Severe dehydration can lead to serious complications, including: Electrolyte imbalances. Heat-related illnesses like heatstroke. Kidney issues including kidney stones and kidney failure. Shock, coma and even death. https://health/diseases/9013-dehydration