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What determines the net fluid movement (bulk flow) across capillaries?
What is responsible for returning excess fluid to circulation?
What is the primary factor determining fluid filtration across capillaries?
Valves are found in which of the following?
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The Starling force with the highest outwardly directed filtration pressure is:
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Most lymph of the body returns to circulation via the:
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What is the normal capillary hydrostatic pressure?
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What are the three main types of capillaries based on their structure?
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What causes capillaries to dilate when tissues are active due to metabolites?
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What primarily influences the formation of edema in the interstitium?
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Which of the following is a consequence of hyponatremia?
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What is the primary regulator of fluid volume intake?
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What is the main source of fluid intake?
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What primarily governs electrolyte intake?
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What is the main regulator of fluid output?
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What is the primary factor influencing the movement of fluid between the intravascular and interstitial compartments?
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Which of the following is a cause of hyponatremia?
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What is the main mechanism for returning excess fluid from the interstitial space to the circulation?
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What is the consequence of hypernatremia?
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Which of the following factors contributes to edema formation?
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What is the main function of the kidneys that maintains ECF composition and volume?
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As glomerular filtrate flows through the nephron, what is the correct sequence of structures it encounters?
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Which of the following occurs during micturition?
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The kidneys reside in the 1 space between 2. Nociceptive afferents that mediate pain in kidney disease parallel the sympathetic efferents of approximately these same segments.
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Mesangial cells regulate:
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What causes capillaries to dilate when tissues are active due to metabolites?
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What primarily controls afferent arteriolar resistance in the autoregulation of renal blood flow?
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What is the paracrine signaling molecule that passes from the macula densa to the afferent arteriole?
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Which enzyme is secreted from the granular cells of the juxtaglomerular apparatus?
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What is the primary vasoconstrictor that increases total peripheral resistance and decreases glomerular filtration rate?
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What primarily ensures a constant delivery of NaCl to the distal tubule for final processing of urine?
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What is the possible role of macula densa feedback in increasing glomerular filtration rate after a high protein meal?
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Which of the following factors increases glomerular filtration rate?
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What primarily influences the formation of edema in the interstitium?
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Which of the following decreases glomerular filtration rate?
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What causes an increase in glomerular filtration rate similar to hyperglycemia?
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Which of the following hormones controls Na+ and H2O reabsorption in the kidneys?
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What is the primary factor used to estimate Glomerular Filtration Rate (GFR) for a substance that is freely filtered but not reabsorbed or secreted?
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Which physical forces affect reabsorption in the kidneys?
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What is the main function of antidiuretic hormone (ADH) in the kidneys?
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What is the primary hormone synthesized by the hypothalamus that controls ECF osmolarity?
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Which substance can be used to estimate Glomerular Filtration Rate (GFR), but overestimates it by 10%?
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What is the primary hormone affected by substances like nicotine and ethanol, and is stimulated by reduced plasma volume?
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What is the primary factor used to express solute excretion as a percentage of filtered load, and is useful in determining altered tubular transport?
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What is the primary hormone that controls Na+ and H2O reabsorption in the kidneys, and is stimulated by the angiotensin II?
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What is the primary function of the countercurrent multiplier mechanism in the kidneys?
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What is the significance of the thirst mechanism in controlling extracellular fluid osmolarity and sodium concentration?
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What is the role of the osmoreceptor-ADH feedback system in the regulation of extracellular fluid osmolarity?
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In normal kidneys, which of the following is true of the osmolarity of the renal tubular fluid that flows through the early distal tubule in the region of the macula densa?
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A female runner has high circulating ADH and normal renal function. Where is water most reabsorbed in her renal tubules?
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Under conditions of normal renal function, what is true of the concentration of urea in tubular fluid at the end of the proximal tubule?
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Where is ADH synthesized?
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What is the primary osmotically active solute in the extracellular fluid (ECF) that determines ECF osmolarity?
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What is the maximum range for urine concentration in terms of osmolarity?
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What is the primary mechanism for excreting excess water by forming dilute urine?
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Which of the following is the primary function of aldosterone?
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What is the primary effect of vasopressin (ADH) on the kidneys?
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What is the main stimulus for aldosterone secretion?
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What is the main function of angiotensin II in the renal system?
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What is the primary effect of vasopressin V1 receptors activation?
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Which of the following is the primary function of the macula densa in the JG apparatus?
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What is the primary role of renin in the Renin-Angiotensin System (RAS)?
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What is the primary effect of aldosterone on Na+ and K+ levels in the body?
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What is the primary effect of angiotensin II on the efferent arteriole?
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What is the primary function of vasopressin V2 receptors activation?
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Which of the following is a correct indication for dialysis?
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What is the primary mechanism of action of most diuretics?
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What is the main difference between prerenal, intrarenal, and postrenal causes of Acute Kidney Injury (AKI)?
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Which of the following hormones is produced by the kidney and explains pathophysiology related to CKD?
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Which diuretic is used for glaucoma and prophylaxis for altitude sickness?
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What is the most common cause of acute kidney injury (AKI) or acute renal failure (ARF) perioperatively?
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What is the primary symptom of chronic kidney disease (CKD) or chronic renal failure (CRF)?
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Study Notes
Formation of Edema in the Interstitium
- The three tunics and two main cell types present in arteries and veins are the tunica adventitia, tunica media, and tunica intima, with arteries acting as high-pressure reservoirs and veins as low-pressure reservoirs.
- Capillaries, composed of a single layer of endothelial cells, make up only about 5% of circulating blood at any given time but play a crucial role in the exchange of oxygen, carbon dioxide, and nutrients.
- The microcirculation, consisting of over 10 billion capillaries with a surface area of 500–700 square meters, facilitates solute and fluid exchange, nutrient transportation to tissues, waste removal, and vasomotion.
- Vasomotion, the intermittent contraction of metarterioles and precapillary sphincters, causes capillaries to dilate when tissues are active due to metabolites, with the lack of oxygen being the most important factor in increasing periods of capillary flow in most tissues.
- The structure of capillary walls comprises a unicellular layer of endothelial cells surrounded by a basement membrane, with various modes of exchange across capillaries, including lipid-soluble molecules passing across cells, membrane carriers facilitating ion movement, and transcytosis for large molecules.
- Capillaries come in three main types: continuous, fenestrated, and sinusoid, each allowing different levels of permeability for substances to pass through the endothelium via diffusion and filtration.
- Diffusion and filtration are the primary means of substance transfer between plasma and interstitial fluid, with concentration differences across capillaries enhancing diffusion and pressure gradients determining the direction of bulk flow.
- The interstitium, the space between cells, contains primarily gel-like interstitial fluid, with collagen fibers and proteoglycan filaments as the major solid structures, and only very little free fluid under normal conditions.
- Edema, the accumulation of excess fluid in the interstitial space, occurs when the balance between filtration and reabsorption from capillaries into the interstitium is disrupted, leading to an increase in interstitial fluid volume.
- The permeability of capillary pores for different substances varies according to their molecular diameters, with extreme differences in permeabilities among capillaries in different tissues.
- The tight junctions of the brain allow only water and small molecules to pass, highlighting the selective permeability of capillaries in different tissues.
- The formation of edema in the interstitium is influenced by the disruption of the balance between filtration and reabsorption from capillaries, leading to an increase in interstitial fluid volume and the accumulation of excess fluid.
Formation of Edema in the Interstitium
- The three tunics and two main cell types present in arteries and veins are the tunica adventitia, tunica media, and tunica intima, with arteries acting as high-pressure reservoirs and veins as low-pressure reservoirs.
- Capillaries, composed of a single layer of endothelial cells, make up only about 5% of circulating blood at any given time but play a crucial role in the exchange of oxygen, carbon dioxide, and nutrients.
- The microcirculation, consisting of over 10 billion capillaries with a surface area of 500–700 square meters, facilitates solute and fluid exchange, nutrient transportation to tissues, waste removal, and vasomotion.
- Vasomotion, the intermittent contraction of metarterioles and precapillary sphincters, causes capillaries to dilate when tissues are active due to metabolites, with the lack of oxygen being the most important factor in increasing periods of capillary flow in most tissues.
- The structure of capillary walls comprises a unicellular layer of endothelial cells surrounded by a basement membrane, with various modes of exchange across capillaries, including lipid-soluble molecules passing across cells, membrane carriers facilitating ion movement, and transcytosis for large molecules.
- Capillaries come in three main types: continuous, fenestrated, and sinusoid, each allowing different levels of permeability for substances to pass through the endothelium via diffusion and filtration.
- Diffusion and filtration are the primary means of substance transfer between plasma and interstitial fluid, with concentration differences across capillaries enhancing diffusion and pressure gradients determining the direction of bulk flow.
- The interstitium, the space between cells, contains primarily gel-like interstitial fluid, with collagen fibers and proteoglycan filaments as the major solid structures, and only very little free fluid under normal conditions.
- Edema, the accumulation of excess fluid in the interstitial space, occurs when the balance between filtration and reabsorption from capillaries into the interstitium is disrupted, leading to an increase in interstitial fluid volume.
- The permeability of capillary pores for different substances varies according to their molecular diameters, with extreme differences in permeabilities among capillaries in different tissues.
- The tight junctions of the brain allow only water and small molecules to pass, highlighting the selective permeability of capillaries in different tissues.
- The formation of edema in the interstitium is influenced by the disruption of the balance between filtration and reabsorption from capillaries, leading to an increase in interstitial fluid volume and the accumulation of excess fluid.
Regulation of Tubular Reabsorption in the Kidneys
- Tubules can increase reabsorption rates to maintain Na+ and volume homeostasis in response to increased tubular load
- Glomerulotubular balance is compared to tubuloglomerular feedback which maintains GFR
- Peritubular physical forces including increased arterial pressure and colloid osmotic pressure affect reabsorption
- Hormones such as aldosterone, angiotensin II, and antidiuretic hormone control Na+ and H2O reabsorption
- Sympathetic nervous system activation decreases Na+ and H2O excretion, increases tubular reabsorption
- Antidiuretic hormone (ADH) is synthesized by the hypothalamus and controls ECF osmolarity
- ADH secretion is stimulated by reduced plasma volume and is affected by substances like nicotine and ethanol
- The rate of urinary excretion of a substance is affected by glomerular filtration, tubular reabsorption, and tubular secretion
- Fractional excretion (FE) expresses solute excretion as a percentage of filtered load and is useful in determining altered tubular transport
- Calculating FENA is useful in determining prerenal versus renal pathology in acute renal failure
- Clearance can be used to estimate GFR for a substance that is freely filtered but not reabsorbed or secreted
- Inulin can be used to estimate GFR, while plasma creatinine is also used clinically, but overestimates GFR by 10% and is used to determine stages of renal failure
The Role of Thirst in Fluid Balance
- The main osmotically active solute in the extracellular fluid (ECF) is Na+, which determines ECF osmolarity by its volume and the amount of ECF water.
- Total body water is regulated by fluid intake influenced by factors that determine thirst and renal water excretion.
- The relationship between urine osmolarity and specific gravity is crucial, with normal urine concentration ranging from 1200-1400 mOsm/L and 50-70 mOsm/L.
- Kidneys excrete excess water by forming dilute urine through decreased antidiuretic hormone (ADH) release and reduced water permeability in distal and collecting tubules.
- Renal response to water ingestion increases urine volume and causes urine dilution in the ascending loop of Henle, with or without ADH.
- Excreting concentrated urine requires increased ADH, high osmolarity of renal medulla, and increased water reabsorption.
- The minimum urine volume required to excrete solute, known as obligatory urine volume, is not autoregulated and is a useful monitor in surgical cases.
- Humans have a limited urine concentrating ability (~ 600 mOsm/day), explaining why drinking seawater results in dehydration.
- In renal disease, impaired urine concentrating ability may increase the obligatory urine volume to 2.0 L/day.
- Factors contributing to the buildup of solute in the renal medulla include countercurrent multiplier, recirculation of urea, and vasa recta preserving hyperosmolarity.
- The net effects of the countercurrent multiplier include trapping solutes in the renal medulla and establishing a horizontal gradient of solute concentration.
- The vasa recta, a countercurrent exchanger, helps preserve the hyperosmolarity of the renal medulla and plays a crucial role in changes in the osmolarity of the tubular fluid.
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