72 Questions
What is the approximate proportion of total body water (TBW) in obese individuals?
45%
Which fluid compartment includes plasma volume?
Extracellular fluid (ECF)
In which age group are differences in total body water (TBW) between males and females reduced?
Elderly
What contributes to marked variability in total body water proportion between lean and obese individuals?
Adipose tissue composition
Which compartment includes fluid regulated by active cellular transport?
Transcellular fluid
What is the major division of total body water (TBW) between different fluid compartments?
Extracellular fluid and intravascular fluid
Which fluid compartment includes cerebrospinal fluid and urine?
Transcellular fluid
What contributes to the differences in total body water (TBW) between lean and obese individuals, according to the text?
Adipose tissue composition
Which compartment contains lymphatic fluid and protein-poor fluid occupying cell spaces?
Interstitial fluid
what is the ratio between ICF and functional ECF
2:1
What is the approximate water of total body weight (TBW) ?
60%
What is the percentage of total body water (TBW) in neonate?
80%
What is the percentage of total body water (TBW) in 6 month old infant?
70%
What is the process by which solute particles fill the available solvent volume by motion from areas of high to low concentration?
Diffusion
What is the process by which water molecules diffuse across a semipermeable membrane into a region of higher solute concentration?
Osmosis
What is the hydrostatic pressure required to resist the movement of solvent molecules in osmosis?
Osmotic pressure
What does the osmotic pressure of a solution depend on?
The number of osmotically active particles
Which law governs the diffusion of solutes across permeable membranes?
Fick's law of diffusion
What is the primary factor that reduces the number of particles free to exert an osmotic effect in body fluids compared to ideal solutions?
Interionic interactions
What is the approximate total osmotic pressure of plasma in mm Hg?
5545 mm Hg
Which of the following best describes molality?
The number of moles of a substance present in 1 kg of solvent
What is the normal range for body osmolality in mOsm/kg?
285 - 290 mOsm/kg
Which of the following substances makes the largest contribution to plasma osmolality?
Sodium and its related anions
What is the primary factor that determines tonicity, the effective osmolality across a cell membrane?
The presence of solutes that cannot freely diffuse across the membrane
What is the primary contributor to oncotic pressure in plasma?
Proteins
What is the approximate contribution of oncotic pressure to the total plasma osmotic pressure of 5545 mm Hg?
25 - 28 mm Hg
Which of the following factors contributes to increasing the effective oncotic pressure of plasma proteins?
The negative charge on proteins (Gibbs-Donnan effect)
What is the primary function of the endothelial glycocalyx layer (EGL) in the capillary structure?
To prevent platelet and leukocyte adhesion and is an important semipermeable layer contributing to endothelial barrier function.
Where does the exclusion of larger molecules like proteins from the interstitial fluid occur?
At the level of the glycocalyx
What is the primary channel for transcapillary fluid flow according to the text?
The intercellular clefts between the endothelial cells
What is the approximate thickness of the endothelial glycocalyx layer (EGL) according to the text?
1 μm
what us the mechanism of protein transport into the ISF across the endothelial cells ?
endocytosis and exocytosis
What is the approximate volume of the subglycocalyceal layer (SGL) according to the text?
700 to 1000 mL
What is the primary factor that determines the net filtration of water into the interstitial fluid at the arteriolar end of the capillary?
The hydrostatic pressure gradient
What is the primary process by which water not reabsorbed by the capillary is removed from the interstitial fluid?
Lymphatic drainage
Which of the following is a characteristic of the nonfenestrated capillary, the most common capillary type?
It has a continuous basement membrane and a single layer of endothelial cells
Which statement about the cell membrane is correct?
It separates the intracellular and extracellular compartments
What is the fundamental mechanism that maintains ionic concentration gradients across cell membranes?
Primary active transport via ATP hydrolysis
Which of the following transport mechanisms does NOT require energy from ATP hydrolysis?
Facilitated diffusion through solute channels
What is the term used when a solute is transported in the same direction as an ion moving down its concentration gradient during secondary active transport?
Cotransport
Which transport mechanism allows the fastest movement of solutes across cell membranes?
Solute channels
What is the clinical relevance of the "no-absorption" rule for continuous capillaries?
Raising capillary oncotic pressure by albumin infusion will reduce fluid filtration but not cause fluid reabsorption.
In the setting of acutely subnormal capillary pressures, what is the limitation on the transient period of autotransfusion?
It is limited to approximately 500 mL of fluid.
In the setting of supranormal capillary pressures, how does the infusion of colloids and crystalloids affect fluid filtration?
Crystalloid infusion increases fluid filtration more than colloid infusion.
According to the revised endothelial glycocalyx layer (EGL) model, what factor influences the intravascular volume effects of crystalloids and colloids?
The preexisting capillary pressures (context sensitivity).
In the process of secondary active transport, what drives the movement of solutes against their concentration gradient?
An ion moving down its concentration gradient
According to the revised endothelial glycocalyx layer (EGL) model, what factor influences the intravascular volume effects of crystalloids and colloids?
The exclusion of larger molecules like colloids from the subglycocalyceal layer (SGL)
What is the primary contributor to oncotic pressure in plasma?
Plasma proteins
What contributes to marked variability in total body water proportion between lean and obese individuals?
Differences in body fat percentage
What is the primary process by which water not reabsorbed by the capillary is removed from the interstitial fluid?
Lymphatic drainage
what is the amount of crystalloid required to get intravascular volume effects similar to colloid
1.5:1
What is the role of ADH in the kidneys?
Stimulates water reabsorption
What triggers the release of ADH?
Increased plasma tonicity
Which mechanism prevents decreased urine production during acute blood loss?
Activation of the RAA axis
What is the primary role of the renin-angiotensin-aldosterone (RAA) axis?
Promote salt and water retention
In response to rapid blood loss, what is the initial effect of increased sympathetic outflow?
Increased heart rate
Which organ releases renin in response to low blood volume?
Kidneys
What is the purpose of AVP (arginine vasopressin) in fluid balance?
Stimulate kidney tubules for water reabsorption
How does ADH contribute to concentrated urine formation?
"Increasing aquaporin 2 water channel insertion"
According to the passage, why does increasing capillary colloid oncotic pressure by administering exogenous albumin fail to reduce edema?
The no-absorption rule prevents reabsorption of fluid from edematous tissues.
What is the primary reason for the appearance of free heparin, chondroitin, and hyaluronic acid in the plasma, according to the passage?
Hyperglycemia and inflammatory mediators causing glycocalyx injury and shedding.
Based on the information in the passage, which of the following statements is true regarding hypoalbuminemia in critical illness?
Hypoalbuminemia is a marker of disease severity but has no direct impact on edema formation.
According to the passage, which of the following factors can lead to glycocalyx injury and shedding?
Tumor necrosis factor (TNF) and bradykinin
Based on the information in the passage, which of the following statements is true regarding the role of the endothelial glycocalyx layer (EGL)?
The EGL plays a role in determining the intravascular volume effects of crystalloids and colloids.
What is the primary mechanism that acts rapidly to bring cardiovascular parameters toward normal after rapid infusion of fluid to a normovolemic healthy adult?
Pressure receptor-mediated venodilation and venous blood pooling
What is the primary organ that regulates the equilibrium between input and output of circulating volume in the chronic setting or acute alterations in blood volume?
The kidneys
What is the primary mechanism that allows the excretion of excess sodium and water after acute hypervolemia, rather than natriuretic peptide activity?
A combination of passive processes and suppression of the RAA axis
What is the key mechanism for the long-term maintenance of normal blood volume according to the text?
Pressure-volume control mechanism
What is the main reason why the circulation acts as an open system in the chronic setting or in acute alterations in blood volume, rather than a closed system?
To allow the kidneys to regulate the equilibrium between input and output
What is the primary mechanism that leads to a rapid increase in glomerular filtration rate (GFR) and reduced proximal tubule reabsorption of water and sodium after acute hypervolemia?
Glomerulotubular imbalance resulting from the marginal reduction in plasma colloid osmotic pressure
What is the primary factor that determines the long-term maintenance of normal blood pressure, rather than simply being a product of cardiac output, vascular compliance, and resistance?
Pressure natriuresis and diuresis
delayed responses to major blood loss restore plasma volume within
12 to 72 hours
Study Notes
Fluid Compartments
- Water makes up approximately 60% of total body weight, varying with age, gender, and body composition
- Adipose tissue contains little water compared to other tissues, leading to marked variability in total body water (TBW) proportion between lean and obese individuals
- TBW is divided between anatomic and functional fluid compartments within the body, with the major division between intracellular fluid (ICF) and extracellular fluid (ECF)
Physiochemical Laws Governing Fluid and Electrolyte Movement
- Diffusion is the process by which solute particles fill the available solvent volume by motion from areas of high to low concentration
- Osmosis is the movement of water molecules across a semipermeable membrane into a region of higher solute concentration
- Osmotic pressure is the hydrostatic pressure required to resist the movement of solvent molecules
- Osmolality is the number of osmoles present in 1 kg of solvent, and normal body osmolality is 285 to 290 mOsm/kg
Oncotic Pressure and Tonicity
- Oncotic pressure is the component of total osmotic pressure that is due to colloids, such as proteins
- Tonicity is the effective osmolality of a solution with respect to a particular semipermeable membrane
- Tonicity is important in determining in vivo distribution of fluids across a cell membrane and is sensed by the hypothalamic osmoreceptors
Vascular Endothelium and Capillary Function
- The barrier function of the vascular endothelium is particularly relevant perioperatively because of its key role in maintaining intravascular fluid volume
- The structure of capillaries varies depending on the underlying organ function
- Water and electrolytes can move freely across the vascular endothelial barrier through the endothelial glycocalyx layer (EGL)
- The EGL is a semipermeable layer that covers fenestrations and intercellular clefts and has a thickness of up to 1 μm
Fluid Compartment Barriers and Distribution
- The cell membrane separates the intracellular and extracellular compartments and is impermeable to large hydrophilic molecules and charged particles
- Solute transport across cell membranes can occur by passive diffusion, carrier proteins, and solute channels
- The volume and composition of each fluid compartment depend on the barriers separating it from neighboring compartments### Edema and Capillary Colloid Oncotic Pressure
- Hypoalbuminemia is a marker of disease severity in critical illness, but administering exogenous albumin or other colloids to increase capillary COP does not reduce peripheral or pulmonary edema, nor improve overall outcomes in sepsis.
- The no-absorption rule explains why increasing COP gradient across the capillary wall by administering albumin does not lead to reabsorption of fluid from edematous tissues.
- Degradation of the endothelial glycocalyx layer impairs endothelial barrier function, leading to increased permeability and edema.
- Physiologic insults such as natriuretic peptides, hyperglycemia, and inflammatory mediators can lead to glycocalyx injury and shedding.
Physiologic Control of Overall Fluid Balance
- In health, 60% of daily water loss is through urinary excretion, with the remaining 40% lost through insensible losses and sweating.
- Integrated cardiovascular and renal neuroendocrine mechanisms maintain fluid volume homeostasis in response to perioperative challenges.
- Sensors that monitor fluid volume include hypothalamic osmoreceptors, low-pressure baroreceptors, and high-pressure baroreceptors.
- The hypothalamus integrates sensory inputs to trigger either increased water intake or increased water output via antidiuretic hormone (ADH) secretion.
Regulation of Circulating Volume
- Acute changes in intravascular volume lead to compensatory mechanisms to correct the abnormality, including vasoconstriction, mobilization of venous reservoirs, and reduced urine production.
- The sensor organs for acute changes in circulating volume are the low-pressure and high-pressure baroreceptors.
- Renal vasoconstriction leads to a reduced volume of filtrate and activates the renin-angiotensin-aldosterone (RAA) axis.
- Rapid infusion of fluid to a normovolemic healthy adult leads to an initial rise in venous and arterial pressure, followed by mechanisms to return circulating volume toward normal, including pressure receptor-mediated venodilation and reduction in systemic vascular resistance.
Long-Term Control of Circulating Intravascular Volume
- In health, short-term variations in blood volume are very small, and the cardiovascular system behaves as a closed system with arterial pressure a product of peripheral resistance, vascular compliance, and the Starling curve.
- In the chronic setting, the circulating volume will vary, and equality of input and output must be restored to avoid chronic fluid retention or dehydration.
- The kidneys are the primary organ regulating this equilibrium, largely through pressure natriuresis and diuresis.
- The pressure-natriuresis curve is relatively flat in health, allowing excess intake of salt and water to be excreted without long-term rises in circulating volume or blood pressure.
Learn about the distribution of water in the human body and how it varies depending on factors like age, gender, and body composition. Understand the differences in total body water proportion between lean and obese individuals, as well as between adult males and females.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
