BMS 531 Properties of Water 2025 PDF

Properties of Water Emily Masser, PhD BMS 531.05 2025 1 Objectives 1. Recall and describe the different fluid compartments of the body. 2. Outline how water plays an important role in the solubility of biomolecules. 3. Explain why nonpolar gases require water soluble “carrier...

Properties of Water Emily Masser, PhD BMS 531.05 2025 1 Objectives 1. Recall and describe the different fluid compartments of the body. 2. Outline how water plays an important role in the solubility of biomolecules. 3. Explain why nonpolar gases require water soluble “carrier proteins.” 4. Define an amphipathic compound and describe why they form micelles. 5. Describe the hydrophobic effect and how this contributes to the structure of biomolecules. 6. Explain osmosis, osmotic pressure, osmolarity, osmolality, isosmotic, hyposmotic, and hyperosmotic. 7. Describe tonicity and explain how it’s different from osmolarity/osmolality. 8. Define isotonic, hypotonic, and hypertonic. 2 Objectives 9. Show the direction of water flow in a solute gradient and explain the effect on the cell. 10.Explain why macromolecules are not stored in their monomeric form. 11.Describe aquaporins (AQPs) and explain the need for them in the kidneys. 12.Describe the effect of antidiuretic hormone (ADH)/arginine vasopressin (AVP)/vasopressin on cell volume. 13.Describe the mechanisms that control the release of ADH/AVP. 14.Explain the role of water, salt, and aquaporins in diabetes insipidus. 15.Recall the underlying cause(s) of central and nephrogenic diabetes insipidus. 3  Fluid Compartments Cells live in a carefully regulated fluid environment Fluid inside cells, intracellular fluid (ICF), occupies the intracellular compartment Fluid outside of cells, extracellular fluid (ECF), occupies the extracellular compartment Cell membranes separate these compartments 4 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Fluid Compartments Total-body water (TBW) is the sum of the ICF and ECF volumes ~60% of total-body weight in a young adult human man ~50% of total-body weight in a young adult woman Women typically have a higher ratio of adipose to muscle ~65-75% of total-body weight in an infant 5 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Fluid Compartments Of the ~17 L of ECF, ~20% (~3 L) is contained within the intravascular compartment Total volume of this intravascular compartment is the blood volume, ~6 L Extracellular 3 L of blood volume is the plasma volume ~3 L consists of erythrocytes, leukocytes, and platelets Hematocrit 6 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Fluid Compartments About 75% (~13 L) of the ECF is outside the intravascular compartment, it bathes the non- blood cells of the body Within this interstitial fluid are two smaller compartments: Connective tissue, such as cartilage and tendons Bone matrix Capillaries separate the intravascular and interstitial 7 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Fluid Compartments ~5% (~1 L) of ECF is trapped within spaces that are completely surrounded by epithelial cells This transcellular fluid includes: Synovial fluid within joints Cerebrospinal fluid surrounding the brain and spinal cord Does not include fluids, strictly speaking, outside of the body: GI tract or urinary bladder 8 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Fluid Compartments Electrolytes are distributed throughout the fluid compartments Both anions and cations are distributed to maintain electrical neutrality Cationic electrolytes include Na ,+ + 2+ K , Ca , and Mg 2+ - - Anions include Cl , HCO3 , and negatively charged proteins 9 Boron and Boulpaep Concise Medical Physiology: Figure 5.1 Water Functions Chemical reactions Solvent and transport medium Nutrient catabolism Water in body fluids contains Body temperature regulation numerous dissolved Water has a high specific heat, substances (solutes) does not readily change Maintenance of blood volume temperature Water helps to maintain blood Sweat facilitate heat removal pressure and sustain Lubrication and protection cardiovascular system function Secretions facilitate body Acid-base (pH) balance processes as well as cushion Water is needed for reactions and protect tissues involving buffers 10  Hydrogen Bond and H2O Properties Hydrogen atom shares an electron pair with oxygen Oxygen attracts electrons more strongly Hydrogen partial positive Oxygen partial negative Attraction between oxygen of one water molecule and hydrogen of another Hydrogen bond Cohesive forces 11 Lehninger Principles of Biochemistry, 8e: Figure 2-1  Hydrogen Bond and H2O Properties Water molecules can H-bond with four other water molecules In liquid, water molecules in continuous motion In ice, each molecule is fixed H-bond with four other molecules H-bond accounts for high melting point Much energy required to break sufficient hydrogen bonds 12 Lehninger Principles of Biochemistry, 8e: Figure 2-2  H2O Forms H-Bonds with Polar Solutes Hydrogen bonds are not unique Butane (CH3(CH2)2CH3) has a to water boiling point of only -0.5°C Readily form between an Butanol (CH3(CH2)2CH2OH) has electronegative atom and a a boiling point of 117°C hydrogen atom covalently bonded to another electronegative atom H—C do not participate in hydrogen bonding 13 Lehninger Principles of Biochemistry, 8e: Figure 2-3  H2O Forms H-Bonds with Polar Solutes Uncharged but polar biomolecules dissolve readily in water Hydrogen bond between hydroxyl (OH) group or carbonyl oxygen and H2O Alcohols, aldehydes, ketones and compounds containing N—H form hydrogen bonds with H2O 14 Lehninger Principles of Biochemistry, 8e: Figure 2-4  H2O Interacts with Charged Solutes Water plays an important role in the solubility of biomolecules Water is a polar solvent Hydrophilic dissolves in water “Water loving” Greek, hydros means “water” and philia means “friendship” Nonpolar solvents easily dissolve hydrophobic biomolecules ”Water fearing” Greek, phobos means “fear” 15 Lehninger Principles of Biochemistry, 8e: Table 2-1  H2O as a Solvent Water dissolves salts such as NaCl by hydrating and stabilizing + - the Na and Cl ions Readily dissolves charged biomolecules Compounds with functional groups such as ionized - carboxylic acids (-COO ), protonated amines (-NH3 )+ Water replaces solute-solute H- bonds with solute-water H-bonds 16 Lehninger Principles of Biochemistry, 8e: Figure 2-6  Nonpolar Gases Poorly Soluble in H2O Biologically important gases are nonpolar O2 and N2, electrons are shared equally by both atoms CO2, C=O bond is polar, but the two dipoles cancel each other out Water soluble “carrier proteins” Hemoglobin and myoglobin CO2 + H2O → H2CO3 17 Lehninger Principles of Biochemistry, 8e: Table 2-2  Nonpolar Force Unfavorable Changes Biomolecules with polar groups readily dissolve in water Glucose can form hydrogen bonds with multiple water molecules Uncharged nonpolar molecules disrupt hydrogen bonds between water molecules without forming new H-bonds Water molecules form a water shell — motion is restricted 18 Biochemistry, 2e: Figure 2.25  Amphipathic Amphipathic compounds contains both polar and nonpolar regions Nonpolar regions cluster together, polar regions maximize interactions with each other and the solvent Hydrophobic effect Micelles – stable structures of amphipathic compounds Biological membranes 19 Lehninger Principles of Biochemistry, 8e: Figure 2-7  Hydrophobic Effect Contribute to the structure and function of biomolecules Hydrophobic portions cluster together away from water Leucine and isoleucine often found in the interior of folded protein Hydrophobic amino acids minimize exposure to water 20 Biochemistry, 2e: Figure 2.26  Hydrophobic Effect Hydrophobic effects between nonpolar amino acids in proteins play a major role in protein folding Nonpolar collapse into the core of the protein Polar amino acids located on the surface to increase solubility Stabilize the overall three- dimensional structure 21 Biochemistry, 2e: Figure 2.27  Water and Sodium Balance Water movement among the various compartments is strongly affected by sodium in the ECF Osmotic pressure regulates the water movement between interstitial and intracellular space Hydrostatic pressure contributes to movement across capillary walls 22 Boron and Boulpaep Concise Medical Physiology: Figure 5.1  Osmosis Water spontaneously moves across a semipermeable membrane from low solute to higher solute concentration Osmosis or osmotic flow Water molecules will diffuse by osmosis from higher water concentration to lower water concentration Net effect is solute concentration becomes equal in two solutions 23 Biochemistry, 2e: Figure 2.30  Osmotic Pressure Consequence of osmosis Pressure required to stop the net flow of water molecules Depends on the number of solute molecules Solutions with the same osmotic pressure are isosmotic Hyperosmotic if a solution has a higher osmotic pressure Hyposmotic if a solution has a lower osmotic pressure 24 Biochemistry, 2e: Figure 2.31 Osmolarity/Osmolality Regulate Volume The unit of measurement of osmotic pressure is osmole (Osm) Number of moles that a solute contributes to the osmotic pressure Osmolarity is a measure of a solute’s ability to generate osmotic pressure Number of osmoles of solute per liter of solution (Osm/L) Osmolality uses water mass in place of volume Number of osmoles per kilogram of solvent (Osmol/kg H2O) How many particles a solute dissociates when dissolved in H2O Glucose does not dissociate in solution → 180 mg = 1 mmol can potentially generate 1 mOsm of osmotic pressure NaCl → Na+ and Cl- → 1 mmol NaCl will generate ~2 mOsm of osmotic pressure 25  Tonicity Osmolarity/osmolality is determined by total concentration of all solutes present In contrast, tonicity is determined by the concentration of only those solutes that do not enter the cell Extracellular osmolarity = cytosol are isotonic relative to that cell Hypertonic: ↑ osmolarity Hypotonic: ↓ osmolarity 26 Lehninger Principles of Biochemistry, 8e: Figure 2-12  Tonicity Solution containing NaCl (0.3 Osm/kg water) and urea (0.1 Osm/kg water) — hyperosmotic compared with cytosol (0.3 Osm/kg water) Solution is isotonic because it does not produce a permanent change in cell volume Normal plasma is an isotonic solution because Na+ is the predominant plasma solute 27 Lehninger Principles of Biochemistry, 8e: Figure 2-12  Glucose Storage Effect of solutes on osmolarity depends on the number of dissolved particles, not their mass Macromolecules have less effect on osmolarity than equal mass of their monomeric components Storing fuel as a polysaccharide (glycogen) rather than glucose avoids an increase in osmotic pressure 28 Lehninger Principles of Biochemistry, 8e: Figure 15-2  Nature and Distribution of Solutes Osmolarity of the ECF is regulated to reduce deleterious osmotic movement of water Cell membranes allow passage of water in and out of cells Osmotic pressure associated with solute concentrations influences water movement, which occurs by osmosis Solutes maintain osmolarity and water distribution 29 Advanced Nutrition and Human Metabolism, 8e: Figure 12.1  Nature and Distribution of Solutes Within cells (intracellular), potassium represents the major cation and phosphate as the major anion In contrast to the intracellular fluid, the ECF contains sodium as the major cation and chloride as the major anion Sodium-potassium ATPase pumps maintain the intracellular + K and extracellular Na + 30 Advanced Nutrition and Human Metabolism, 8e: Figure 12.1  Nature and Distribution of Solutes Often changes in ECF osmolarity result in water movement between compartments Gain of water without solutes in the ECF compartment ↓ ECF osmolarity associated with overhydration Excessive overconsumption of water dilutes the plasma, resulting in hyponatremia (low plasma sodium) 31 Advanced Nutrition and Human Metabolism, 8e: Figure 12.1  Nature and Distribution of Solutes Loss of water without solutes from the ECF compartment ↑ ECF osmolarity making it hypertonic ↑ Plasma Na+ (hypernatremia) Dehydration Hypervolemia results from gain of salt and water into the plasma Hypovolemia (volume depletion) occurs with losses of both Excessive vomiting or diarrhea 32 Advanced Nutrition and Human Metabolism, 8e: Figure 12.1  ECF Volume and Osmolarity Both ECF volume and osmolarity are critical in the control of fluid balance To maintain plasma volume, water must move into the plasma if the ECF osmolarity increases or if hypovolemia occurs In contrast, water must move out if the ECF osmolarity decreases or hypervolemia occurs Thirst also contributes to water balance when deficits occur 33 Advanced Nutrition and Human Metabolism, 8e: Figure 12.1  Aquaporins Increase H2O Permeability Water molecules can move across cell membranes by simple diffusion Plasma membranes of many cell types contain aquaporins (AQPs) Family of membrane channel proteins Allow water and a few other small uncharged molecules Greatly increase water permeability 34 Molecular Cell Biology, 9e: Figure 11-8  Aquaporins Increase H2O Permeability Transport water in either direction depending on osmotic gradient Tetramer of identical 28-kDa subunits Each subunit contains six membrane-spanning α-helices that form a central pore Several water molecules can move simultaneously — hydrophilic amino acids extend into the middle of the channel 35 Molecular Cell Biology, 9e: Figure 11-8  Water Reabsorption Aquaporin 2 is found in the kidney epithelial cells Absorb water from the urine When water intake exceeds homeostatic needs, dilute urine passes through the collecting ducts to the bladder If there is a need to conserve water, fluid can be recovered Recovery of water and final urine concentration is governed by the presence of AQPs and regulated by antidiuretic hormone (ADH; also known as arginine vasopressin or vasopressin) 36 Lippincott Illustrated Reviews, 2e: Figure 27.16  Water Reabsorption When cells are in their resting state and water is being excreted to form urine, aquaporin 2 is sequestered inside of the cell When ADH/vasopressin binds to the cell-surface receptor → aquaporin 2-containing vesicles fuse with the plasma membrane Increasing the rate of water uptake and return to circulation When water intake increases and circulating ADH/vasopressin levels fall, AQPs are removed from the membrane 37 Lippincott Illustrated Reviews, 2e: Figure 27.16  Effects of Antidiuretic Hormone (ADH) In humans, water input is controlled through thirst, water output is adjusted by the kidneys Water deficiency, kidneys diminish excretion Water excess, kidneys ↑ water excretion and urine flow Renal excretion of water is controlled by ADH Urine volume is linked to solute amount and ADH levels 38 Renal Pathophysiology: The Essentials, 5e: Figure 3.7  Control of ADH Secretion ADH decreases urine output → more concentrated urine Increase in plasma osmolality → release of ADH Osmoreceptor cells shrink ↑ Plasma ADH ↑ Water reabsorption Osmotically concentrated urine ADH and thirst protect against hypernatremia 39 Medical Physiology: Principles for Clinical Medicine, 6e: Figure 23.3  Control of ADH Secretion Decrease in plasma osmolality Osmoreceptor cells swell ↓ ADH release ↓ Water reabsorption Dilute urine is excreted Plasma osmolality restored by elimination of excess water Urine osmolality is a linear function of plasma ADH 40 Medical Physiology: Principles for Clinical Medicine, 6e: Figure 23.4  Control of ADH Secretion Blood volume controls ADH release ↑ Blood volume inhibits ADH release ↓ Blood volume (hypovolemia) stimulates ADH release Excess volume, ↓ plasma ADH would promote excretion With hypovolemia, ↑ plasma ADH would promote reabsorption or conservation of water 41 Medical Physiology: Principles for Clinical Medicine, 6e: Figure 23.5  Control of ADH Secretion Receptors for blood volume include stretch receptors in the right atrium of the heart and in the pulmonary veins More stretch results in more impulses to the brain, which inhibit ADH release Producing large volume of dilute urine when lying down in bed at night, exposed to cold weather, or when immersed in water Blood into more central vessels Increase central blood volume 42 Medical Physiology: Principles for Clinical Medicine, 6e: Figure 23.5  Control of ADH Secretion Plasma osmolality and blood volume most often work in concert to ↑ or ↓ ADH release ↑ Water intake will ↓ ADH ↓ Plasma osmolality ↑ Blood volume Excess water loss will ↑ ADH ↑ Plasma osmolality ↓ Blood volume 43 Medical Physiology: Principles for Clinical Medicine, 6e: Figures 23.4 and 23.5  Diabetes Insipidus (DI) Inactivating mutations in either vasopressin receptor or aquaporin 2 gene Central (CDI): lack of ADH release Nephrogenic (NDI): resistant to ADH Fail to significantly decrease urine volume or increase urine osmolality as plasma osmolality increases 44 Renal Pathophysiology: The Essentials, 5e: Figure 3.8  Diabetes Insipidus (DI) CDI can result from damage to hypothalamus or pituitary gland Surgery is the most common Head injury is also common Hereditary NDI Most result from mutations in the AVPR2 gene — encodes the vasopressin V2 receptor Smaller percentage caused by mutations in AQP2 gene — encodes aquaporin 2 protein 45 Renal Pathophysiology: The Essentials, 5e: Figure 3.8 Diabetes Mellitus vs. Diabetes Insipidus Diabetes (German for “siphon” or “to pass through”) mellitus Elevated blood glucose due to relative (Type II) or absolute (Type I) deficiency in insulin Type 1 – formerly called insulin-dependent diabetes mellitus Absolute deficiency of insulin – autoimmune attack on β cells of pancreas Type 2 – formerly called non-insulin-dependent diabetes mellitus Combination of insulin resistance and dysfunctional β cells Diabetes insipidus Diminished water reabsorption due to lack of or resistance to ADH Urinate large volumes of dilute urine Do NOT have elevated blood glucose 46