Body Composition
Water is the most abundant single constituent of the body and is the medium in which all metabolic reactions occur. Water accounts for about 60% of the weight in an adult man and about 50% of the body weight in an adult woman (Fig. 1-1)1; the difference is due to increased body fat in women. In a neonate, total body water may represent 70% of body weight. Total body water is less in obese individuals, reflecting the decreased water content of adipose tissue. Advanced age is also associated with increased fat content and decreased total body water (Table 1-1).
Body fluids can be divided into intracellular and extracellular fluid, depending on their location relative to the cell membrane (see Fig. 1-1).1 Approximately two-thirds of the total body fluid in an adult are contained inside the estimated 100 trillion cells of the body. The fluid in these cells, despite individual differences in constituents, is collectively designated intracellular fluid. The one-third of fluid outside the cells is referred to as extracellular fluid. Extracellular fluid is divided into interstitial fluid and plasma (intravascular fluid) by the capillary membrane (see Fig. 1-1).1
Interstitial fluid is present in the spaces between cells. An estimated 99% of this fluid is held in the gel structure of the interstitial space. Plasma is the noncellular portion of blood. The average plasma volume is 3 L, a little over half of the blood volume of 5 L. Plasma is in dynamic equilibrium with the interstitial fluid through pores in the capillaries; the interstitial fluid serving as a reservoir from which water and electrolytes can be mobilized into the circulation. Loss of plasma volume from the intravascular space is minimized by colloid osmotic pressure exerted by the plasma proteins.
Other extracellular fluid that may be considered as part of the interstitial fluid includes cerebrospinal fluid, gastrointestinal fluid (because it is mostly resorbed), and fluid in potential spaces (pleural space, pericardial space, peritoneal cavity, synovial cavities). Excess amounts of fluid in the interstitial space manifest as peripheral edema.
The normal daily intake of water (drink and internal product of food metabolism) by an adult averages 2.5 L, of which about 1.5 L is excreted as urine, 100 mL is lost in sweat, and 100 mL is present in feces. All gases that are inhaled become saturated with water vapor (47 mm Hg at 37°C). This water vapor is subsequently exhaled, accounting for an average daily water loss through the lungs of 300 to 400 mL. The water content of inhaled gases decreases with decreases in ambient air temperature such that more endogenous water is required to achieve a saturated water vapor pressure at body temperature. As a result, insensible water loss from the lungs is greatest in cold environments and least in warm temperatures. The remaining 400 mL is lost by diffusion through the skin. This is insensible water loss, not perceived as sweat. Insensible water loss is limited by the mostly impermeable layer of the skin (cornified squamous epithelium). When the cornified layer is removed or interrupted, as after burn injury, the loss of water through the skin is greatly increased.
Blood Volume
Blood contains extracellular fluid, the plasma, and intracellular fluid, mostly held in erythrocytes. The body has multiple systems to maintain intravascular fluid volume, including renin-angiotensin system, and arginine vasopressin (antidiuretic hormone) that increase fluid reabsorption in the kidney and evoke changes in the renal tubules that lead to restoration of intravascular fluid volume (see Chapter 17).
The average blood volume of an adult is 5 L, comprising about 3 L of plasma and 2 L of erythrocytes. These volumes vary with age, weight, and gender. For example, in nonobese individuals, the blood volume varies in direct proportion to the body weight, averaging 70 mL/kg for lean men and women. The greater the ratio of fat to body weight, however, the less is the blood volume in milliliter per kilogram because adipose tissue has a decreased vascular supply. The hematocrit or packed cell volume is approximately the erythrocyte fraction of blood volume. The normal hematocrit is about 45% for men and postmenopausal women and about 38% for menstruating women, with a range of approximately ± 5%.
Constituents of Body Fluid Compartments
The constituents of plasma, interstitial fluid, and intracellular fluid are identical, but the quantity of each substance varies among the compartments (Fig. 1-2).2 The most striking differences are the low protein content in interstitial fluid compared with intracellular fluid and plasma and the fact that sodium and chloride ions are largely extracellular, whereas most of the potassium ions (approximately 90%) are intracellular. This unequal distribution of ions results in establishment of a potential (voltage) difference across cell membranes.
The constituents of extracellular fluid are carefully regulated by the kidneys so that cells are bathed in a fluid containing the proper concentrations of electrolytes and nutrients. The normal amount of sodium and potassium in the body is about 58 mEq/kg and 45mEq/kg, respectively (note that normal serum level of sodium is 137 to 142 mEq/L and potassium is 3.5 to 5.5 mEq/L, reflecting the intracellular and extracellular predominance of each electrolyte). Trauma is associated with progressive loss of potassium through the kidneys due in large part to the increased secretion of vasopressin and in variable part (depending on the type of surgery) to the role of nasogastric suctioning and direct potassium loss. For example, a patient undergoing surgery excretes about 100 mEq of potassium in the first 48 hours postoperatively and, after this period, about 25 mEq daily. Plasma potassium concentrations are not good indicators of total body potassium content because most potassium is intracellular. There is a correlation, however, between the potassium and hydrogen ion content of plasma; the two are increasing and decreasing together.
Osmosis
Osmosis is the movement of water (solvent molecules) across a semipermeable membrane from a compartment in which the nondiffusible solute (ion) concentration is lower to a compartment in which the solute concentration is higher (Fig. 1-3).3 The lipid bilayer that surrounds all cells is freely permeable to water but is impermeable to ions. As a result, water rapidly moves across the cell membrane to establish osmotic equilibration, which happens almost instantly.
Cells control their size by controlling intracellular osmotic pressure. The maintenance of a normal cell volume and pressure depends on sodium–potassium adenosine triphosphatase (ATPase) (sodium–potassium exchange pump), which maintains the intracellular–extracellular ionic balance by removing three sodium ions from the cell for every two potassium ions brought into the cell. The sodium–potassium pump also maintains the transmembrane electrical potential and the sodium and potassium concentration gradients that power many cellular processes, including neural conduction.
The osmotic pressure exerted by nondiffusible particles in a solution is determined by the number of particles in the solution (degree of ionization) and not the type of particles (molecular weight) (see Fig. 1-3).3 Thus a 1-mol solution of glucose or albumin and 0.5-mol solution of sodium chloride exert the same osmotic pressure, because the sodium chloride exists as independent sodium and chloride ions, each having a concentration of 0.5 mol. Osmole is the unit used to express osmotic pressure in solutes, but the denominator for osmolality is kilogram of water. Osmolarity is the correct terminology when osmole concentrations are expressed in liters of body fluid (e.g., plasma) rather than kilogram of water (osmolality). Because it is much easier to express body fluids in liters of fluid rather than kilograms of free water, almost all physiology calculations are based on osmolarity. Plasma osmolarity is important in evaluating dehydration, overhydration, and electrolyte abnormalities.
Normal plasma has an osmolarity of about 290 mOsm/L. All but about 20 mOsm of the 290 mOsm in each liter of plasma are contributed by sodium ions and their accompanying anions, principally chloride and bicarbonate. Proteins normally contribute <1 mOsm/L. The major nonelectrolytes of plasma are glucose and urea, and these substances can contribute significantly to plasma osmolarity when hyperglycemia or uremia is present, as suggested by the standard calculation of plasma osmolarity:
Plasma osmolarity = 2 (Na+) + 0.055 (glucose) + 0.36 (blood urea nitrogen).
Tonicity of Fluids
Packed erythrocytes must be suspended in isotonic solutions to avoid damaging the cells (e.g., Fig. 1-4).4 A 0.9% solution of sodium chloride is isotonic and remains so because there is no net movement of the osmotically active particles in the solution into cells, and the particles are not metabolized. A solution of 5% glucose in water is initially isotonic when infused, but glucose is metabolized, so the net effect is that of infusing a hypotonic solution. Lactated Ringer solution plus 5% glucose is initially hypertonic (about 560 mOsm/L), but as glucose is metabolized, the solution becomes less hypertonic.
Fluid Management
The goal of fluid management is to maintain normovolemia and thus hemodynamic stability. Crystalloids consist of water; electrolytes; and, occasionally, glucose that freely distribute along a concentration gradient between the two extracellular spaces. After 20 to 30 minutes, an estimated 75% to 80% of an isotonic saline or a lactate-containing solution will have distributed outside the confines of the circulation, thus limiting the efficacy of these solutions in treating hypovolemia. Indeed, the ability of crystalloids to restore perfusion in the microcirculation is doubtful.5
Hypotonic intravenous fluids equilibrate with extracellular fluid, causing it to become hypotonic with respect to intracellular fluid. When this occurs, osmosis rapidly increases intracellular water, causing cellular swelling. Increased intracellular fluid volume is particularly undesirable in patients with intracranial mass lesions or increased intracranial pressure. Protection from excessive fluid accumulation in the interstitium (extravascular lung water) is mediated by lymphatic flow, which can increase as much as 10-fold.
Hypertonic saline solutions (7.5% sodium chloride) have been useful for rapid intravascular fluid repletion during resuscitation as during hemorrhagic and septic shock. Hypertonic saline solutions compare favorably with mannitol for lowering intracranial pressure.6 The primary effect of hypertonic saline solutions (increase systemic blood pressure and decrease intracranial pressure) most likely reflects increased intravascular fluid volume because of fluid shifts and movement of water away from uninjured regions of the brain. The use of hypertonic saline solutions is viewed as short-term treatment as hypertonicity and hypernatremia are likely with sustained administration. Furthermore, patients with hypotension due to traumatic brain injury who received prehospital resuscitation with hypertonic saline solutions have similar neurologic outcomes to those treated with conventional fluids when assessed 6 months after the initial injury.7
Dehydration
Loss of water by gastrointestinal or renal routes or by diaphoresis (excessive sweating) is associated with an initial deficit in extracellular fluid volume. At the same instant, intracellular water passes to the extracellular fluid compartment by osmosis, thus keeping the osmolarity in both compartments equal despite decreased absolute volume (dehydration) of both compartments. The ratio of extracellular fluid to intracellular fluid is greater in infants than adults, but the absolute volume of extracellular fluid is obviously less, explaining why dehydration develops more rapidly and is often more severe in the very young. Clinical signs of dehydration are likely when about 5% to 10% (severe dehydration) of total body fluids have been lost in a brief period of time. Physiologic mechanisms can usually compensate for acute loss of 15% to 25% of the intravascular fluid volume, whereas a greater loss places the patient at risk for hemodynamic decompensation.
Cell Structure and Function
The basic living unit of the body is the cell. It is estimated that the entire body consists of 100 trillion or more cells, of which (amazingly) about 25 trillion are red blood cells.4 Each organ is a mass of cells held together by intracellular supporting structures. A common characteristic of all cells is dependence on oxygen to combine with nutrients (carbohydrates, lipids, proteins) to release energy necessary for cellular function. Almost every cell is within 25 to 50 µm of a capillary, assuring prompt diffusion of oxygen to cells. All cells exist in nearly the same composition of extracellular fluid (milieu interieur or interior milieu, the extracellular fluid environment), and the organs of the body (lungs, kidneys, gastrointestinal tract) function to maintain a constant composition (homeostasis) of extracellular fluid.
Cell Anatomy
The principal components of cells include the nucleus (except for mature red blood cells), and the cytoplasm, which contains structures known as organelles (Fig. 1-5).8 The nucleus is separated from the cytoplasm by a nuclear membrane, and the cytoplasm is separated from surrounding fluids by a cell (plasma) membrane. The membranes around the cell, the nucleus, and organelles are lipid bilayers.
Cell Membrane
Each cell is surrounded by a lipid bilayer that acts as a permeability barrier, allowing the cell to maintain a cytoplasmic composition different from the extracellular fluid. Proteins and phospholipids are the most abundant constituents of cell membranes (Table 1-2). The lipid bilayer is interspersed with large globular proteins (Fig. 1-6).9 The lipid bilayer of cell membranes is readily permeable to water, both through passive diffusion and through aquaporins, specialized proteins in the membrane that function as water channels (described in the following text). Lipid bilayers are nearly impermeable to water-soluble substances, such as ions and glucose. Conversely, fat-soluble substances (e.g., steroids) and gases readily cross cell membranes.
There are several types of proteins in the cell membrane (see Table 1-2). In addition to structural proteins (microtubules), there are transport proteins (sodium–potassium adenosine ATPase) that function as pumps, actively transporting ions across cell membranes. Other proteins function as passive channels for ions that can be opened or closed by changes in the conformation of the protein. There are proteins that function as receptors to bind ligands (hormones or neurotransmitters), thus initiating physiologic changes inside cells. Another group of proteins functions as enzymes (adenylate cyclase) catalyzing reactions at the surface of cell membranes. The protein structure of cell membranes, especially the enzyme content, varies from cell to cell.
Transfer of Molecules through Cell Membranes
Diffusion
Oxygen, carbon dioxide, and nitrogen move through cell membranes by simple diffusion through the lipid bilayer. Because of the slowness of diffusion over macroscopic distances, organisms have developed circulatory systems to deliver nutrients within reasonable diffusion ranges of cells (Table 1-3). Water is also able to diffuse through cells, although not as freely as gases. Lipids generally diffuse readily through the lipid bilayer. However, cell membranes are virtually impermeable to ions and charged water-soluble molecules, especially those with molecular weights of greater than 200 daltons.
Poorly lipid-soluble substances, such as glucose and amino acids, may pass through lipid bilayers by facilitated diffusion. For example, glucose combines with a carrier to form a complex that is lipid soluble. This lipid-soluble complex can diffuse to the interior of the cell membrane where glucose is released into the cytoplasm, and the carrier moves back to the exterior of the cell membrane, where it becomes available to transport more glucose from the extracellular fluid (Fig. 1-7).4 As such, the carrier renders glucose soluble in cell membranes that otherwise would prevent its passage. Insulin greatly speeds facilitated diffusion of glucose and some amino acids across cell membranes.
Endocytosis and Exocytosis
Endocytosis and exocytosis transfer molecules such as nutrients across cell membranes without the molecule actually passing through the cell membrane. The uptake of particulate matter (bacteria, damaged cells) by cells is termed phagocytosis, whereas uptake of materials in solution in the extracellular fluid is termed pinocytosis (Fig. 1-8).10 The process of phagocytosis is initiated when antibodies attach to damaged tissue and foreign substances (opsonization), facilitating binding to specialized proteins on the cell surface and endocytosis. Fusion of phagocytic or pinocytic vesicles with lysosomes allows intracellular digestion of materials to proceed. Neurotransmitters are ejected from cells by exocytosis, a process that requires calcium ions and resembles endocytosis in reverse.
Sodium–Potassium Adenosine Triphosphatase
As mentioned previously, sodium–potassium ATPase, also known as the sodium–potassium pump, is an ATP-dependent sodium and potassium transporter on the cell membrane that ejects three sodium ions from the cell in exchange for the import of two potassium ions (Fig. 1-9).4 This action maintains oncotic equilibration across the cell membrane, reducing the number of intracellular ions to balance the large number of protein and other intracellular constituents. It also is responsible for the transmembrane electrical potential, creating a net positive charge on the outside of the cell from the excess of positive sodium ions outside compared to number of positive potassium ions inside of the cell. Lastly, it creates the sodium gradients responsible for propagation of the action potential and the potassium gradient that rapidly restores the resting membrane potential after conduction of an action potential. In the brain, the sodium–potassium pump accounts for nearly 50% of energy consumption.11
Other ion transporters include hydrogen–potassium ATPases in the gastric mucosa and renal tubules, the transporter that exchanges protons for potassium ions. Calcium ATPases are responsible for maintaining very low cytoplasmic concentrations of calcium either by ejecting calcium from the cell (plasma membrane calcium ATPase) or sequestering calcium in the endoplasmic reticulum via the sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA ATPase).12
Ion Channels
Ion channels are transmembrane proteins that generate electrical signals in the brain, nerves, heart, and skeletal muscles (Fig. 1-10).13 Ion channels use the energy stored in the chemical and electrical gradients created by sodium–potassium ATPase to rapidly initiate changes in transmembrane potential, causing conduction of an action potential.
Because of their charge, most ions are relatively insoluble in cell membranes such that their passage across these membranes is thought to occur through protein channels. These channels are likely to be intermolecular spaces in proteins that extend through the entire cell membrane. Some channels are highly specific with respect to ions allowed to pass (sodium, potassium), whereas other channels allow all ions below a certain size to pass (Table 1-4). Tetrodotoxin is a specific blocker of sodium ion channels as a result of binding to the extracellular side of the channel, whereas tetraethylammonium blocks potassium ion channels by attaching to the inside surface of the membrane.
Genes encoding the protein ion channels may be defective, leading to diseases such as cystic fibrosis (chloride channel defects), long Q-T interval syndrome (mutant potassium or, less commonly, sodium channels), hereditary nephrolithiasis (chloride channel), hereditary myopathies including myotonia congenital (chloride channel), and malignant hyperthermia (calcium channel defects).13 Many drugs target ion channels, including common intravenous anesthetics and, perhaps, inhalational anesthetics. Ion channels are discussed in detail in Chapter 3.
Protein-Mediated Transport
Protein-mediated transport is responsible for movement of specific substrates across cell membranes. P glycoprotein is responsible for the movement of many drugs across the cell membrane, notably including the transport of morphine out of the central nervous system (CNS), slowing the rate of rise of morphine in the CNS. Virtually all transport of molecules against concentration gradients requires proteins, which use energy provided by ATP to pump the molecule against the concentration gradient.
Active transport via proteins requires energy that is most often provided by hydrolysis of ATP. Indeed, carrier molecules are enzymes known as ATPases that catalyze the hydrolysis of ATP. The most important of the ATPases is sodium–potassium ATPase, which is also known as the sodium–potassium pump. Substances that are actively transported through cell membranes against a concentration gradient include sodium, potassium, calcium, hydrogen, chloride, and magnesium ions; iodide (thyroid gland); carbohydrates; and amino acids.
Sodium Ion Cotransport
Despite the widespread presence of sodium–potassium ATPase, the active transport of sodium ions in some tissues is coupled to the transport of other substances. For example, a carrier system present in the gastrointestinal tract and renal tubules will transport sodium ions only in combination with a glucose molecule. As such, glucose is returned to the circulation, thus preventing its excretion. Sodium ion cotransport of amino acids is an active transport mechanism that supplements facilitated diffusion of amino acids into cells. Epithelial cells lining the gastrointestinal tract and renal tubules are able to reabsorb amino acids into the circulation by this mechanism, thus preventing their excretion.
Other substances, including insulin, steroids, and growth hormone, influence amino acid transport by the sodium ion cotransport mechanism. For example, estradiol facilitates transport of amino acids into the musculature of the uterus, which promotes development of this organ.
Aquaporins
Aquaporins are protein channels that permit the free flux of water across cell membranes.14 In the absence of aquaporins, diffusion of water might not be sufficiently rapid for some physiologic processes. Genetic defects in aquaporins are responsible for several clinical diseases, including some cases of congenital cataracts15 and nephrogenic diabetes insipidus.16
Nucleus
The nucleus is primarily made up of the 46 chromosomes, except the nucleus of the egg cell, which contains 23. Each chromosome consists of a molecule of DNA covered with proteins. The nucleus is surrounded by a membrane that separates its contents from the cytoplasm, through which substances, including RNA, pass from the nucleus to the cytoplasm.
The nucleolus is a non–membrane-bound structure within the nucleus responsible for the synthesis of ribosomes. Centrioles are present in the cytoplasm near the nucleus and are concerned with the movement of chromosomes during cell division.
Structure and Function of DNA and RNA
DNA consists of two complementary nucleotide chains composed of adenine, guanine, thymine, and cytosine (Fig. 1-11).17 The genetic message is determined by the sequence of nucleotides. DNA is transcribed to RNA, which transfers the genetic message to the site of protein synthesis (ribosomes) in cytoplasm. Cell reproduction (mitosis) is determined by the DNA genetic system. The human genome has now been 99% sequenced and is composed of just 20,000 to 25,000 genes.18 The protein encoding genes account for only 1% to 2% of our DNA, the rest being regulatory sequences, non–protein-encoding RNA sequences, introns, and a considerable amount of DNA termed “junk” because it has no known function. Our genome differs from that of chimpanzees by just 1%.19
Genes are regulated by specific regulatory proteins and RNA molecules. Regulatory proteins are the target of many hormones, such as steroids, and drugs (antineoplastic drugs).
Cytoplasm
The cytoplasm consists of water; electrolytes; and proteins including enzymes, lipids, and carbohydrates. About 70% to 80% of the cell volume is water. Cellular chemicals are dissolved in the water, and these substances can diffuse to all parts of the cell in this fluid medium. Proteins are, next to water, the most abundant substance in most cells, accounting for 10% to 20% of the cell mass.
The cytoplasm contains numerous organelles with specific roles in cellular function.
Mitochondria
Mitochondria are the power-generating units of cells containing both the enzymes and substrates of the tricarboxylic acid cycle (Krebs cycle) and the electron transport chain. As a result, oxidative phosphorylation and synthesis of adenosine triphosphate (ATP) are localized to mitochondria. ATP leaves the mitochondria and diffuses throughout the cell, providing energy for cellular functions. Mitochondria consist of two lipid bilayers, the outer bilayer in contact with the cytoplasm, and the inner layer that houses most of the biochemical machinery and the mitochondrial DNA. The space between these two membranes functions as a reservoir for protons created during electron transport. It is the movement of these protons back to the matrix, through the inner membrane, that drives most of the conversion of ADP to ATP, the primary form of intercellular energy, by ATP synthase.20
Increased need for ATP in the cell leads to an increase in the number of mitochondria. A number of diseases are known to be based on aberrant mitochondrial function.21 The common element of mitochondrial diseases is aberrant cellular energetics. There are approximately 1,500 proteins responsible for mitochondrial function. Of these, only 13 are encoded by mitochondrial DNA, the balance being encoded by nuclear DNA. Thus, the vast majority of mitochondrial diseases follow standard models of genetic inheritance.
Endoplasmic Reticulum
The endoplasmic reticulum is a complex lipid bilayer that wraps and folds, creating tubules and vesicles in the cytoplasm. Ribosomes, composed mainly of RNA, attach to the outer portions of many parts of the endoplasmic reticulum membranes, serving as the sites for protein synthesis (hormones, hemoglobin). The portion of the membrane containing these ribosomes is known as the rough endoplasmic reticulum. The part of the membrane that lacks ribosomes is the smooth endoplasmic reticulum. This smooth portion of the endoplasmic reticulum membrane functions in the synthesis of lipids, metabolism of carbohydrates, and other enzymatic processes. The sarcoplasmic reticulum is found in muscle cells, where it serves as a reservoir for calcium.
Lysosomes
Lysosomes are lipid membrane–enclosed globules scattered throughout the cytoplasm, providing an intracellular digestive system. Lysosomes are filled with digestive (hydrolytic) enzymes. When cells are damaged or die, these digestive enzymes cause autolysis of the remnants. Bactericidal substances in the lysosome kill phagocytized bacteria before they can cause cellular damage. These bactericidal substances include (a) lysozyme, which dissolves the cell membranes of bacteria; (b) lysoferrin, which binds iron and other metals that are essential for bacterial growth; (c) acid that has a pH of <4; and (d) hydrogen peroxide, which can disrupt some bacterial metabolic systems.
Lysosomal storage diseases are genetic disorders caused by inherited genetic defect in lysosomal function, resulting in accumulation of incompletely degraded macromolecules. There are about 50 known lysosomal storage diseases, including Tay-Sachs, Gaucher, Fabry, and Niemann-Pick disease.22
Golgi Apparatus
The Golgi apparatus is a collection of membrane-enclosed sacs that are responsible for storing proteins and lipids as well as performing postsynthetic modifications including glycosylation and phosphorylation. Proteins synthesized in the rough endoplasmic reticulum are transported to the Golgi apparatus, where they are stored in highly concentrated packets (secretory vesicles) for subsequent release into the cell’s cytoplasm, or transport to the surface for extracellular release via exocytosis. Exocytotic vesicles continuously release their contents, whereas secretory vesicles store the packaged material until a triggering signal is received. Neurotransmitter release is a highly relevant (to anesthesia) example of regulated secretion. The Golgi apparatus is also responsible for creating lysosomes.
References
1. Gamble JL. Chemical Anatomy, Physiology, and Pathology of Extracellular Fluid. 6th ed. Boston, MA: Harvard University Press; 1954.
2. Leaf A, Newburgh LH. Significance of the Body Fluids in Chemical Medicine. 2nd ed. Springfield, IL: Charles C Thomas; 1955.
3. Ganong WF. Review of Medical Physiology. 21st ed. New York, NY: Lange Medical Books/McGraw-Hill; 2003.
4. Guyton AC, Hall JE. Textbook of Medical Physiology. 10th ed. Philadelphia, PA: W.B. Saunders; 2000.
5. Funk W, Baldinger V. Microcirculatory perfusion during volume therapy. A comparative study using crystalloid or colloid in awake animals. Anesthesiology. 1995;82:975–982.
6. Qureshi AI, Suarez JI. Use of hypertonic saline solutions in treatment of cerebral edema and intracranial hypertension. Crit Care Med. 2000;28:3301–3313.
7. Cooper DJ, Myles PS, McDermott FT, et al. Prehospital hypertonic saline resuscitation of patients with hypotension and severe traumatic brain injury. A randomized controlled trial. JAMA. 2004;291:1350–1357.
8. Junqueira LC, Carneiro J, Kelley RO. Basic Histology. 7th ed. Norwalk, CT: Appleton & Lange; 1992.
9. Lodish HF, Rothman JE. The assembly of cell membranes. Sci Am. 1979;240:48–63.
10. Berne RM, Levy MN, Koeppen BM, et al. Physiology. 5th ed. St. Louis, MO: Mosby; 2004.
11. Kety SS. The general metabolism of the brain in vivo. In: Richter D, ed. Metabolism of the Nervous System. London, United Kingdom: Pergamon; 1957:221–237.
12. Uhlén P, Fritz N. Biochemistry of calcium oscillations. Biochem Biophys Res Commun. 2010;396:28–32.
13. Ackerman MJ, Clapham DE. Ion channels—basic science and clinical disease. N Engl J Med. 1997;336:1575–1586.
14. Agre P, King LS, Yasui M, et al. Aquaporin water channels—from atomic structure to clinical medicine. J Physiol. 2002;542:3–16.
15. Kozono D, Yasui M, King LS, et al. Aquaporin water channels: atomic structure and molecular dynamics meet clinical medicine. J Clin Invest. 2002;109:1395–1399.
16. Bichet DG. Nephrogenic diabetes insipidus. Adv Chronic Kidney Dis. 2006;13:96–104.
17. Murray RK, Granner DK, Mayes PA, et al. Harper’s Biochemistry. 21st ed. Norwalk, CT: Appleton & Lange; 1988.
18. International Human Genome Sequencing Consortium. Finishing the euchromatic sequence of the human genome. Nature. 2004;431:931–945.
19. Chimpanzee Sequencing and Analysis Consortium. Initial sequence of the chimpanzee genome and comparison with the human genome. Nature. 2005;437:69–87.
20. Walker JE, Cozens AL, Dyer MR, et al. Structure and genes of ATP synthase. Biochem Soc Trans. 1987;15:104–106.
21. Scharfe C, Lu HH, Neuenburg JK, et al. Mapping gene associations in human mitochondria using clinical disease phenotypes. PLoS Comput Biol. 2009;5:e1000374.
22. Parkinson-Lawrence EJ, Shandala T, Prodoehl M, et al. Lysosomal storage disease: revealing lysosomal function and physiology. Physiology. 2010;25:102–115.