Block 6 Renal Physiology Part 5

Hemoglobin is a large protein molecule that is not freely filtered by the kidneys. The glomerular filtration barrier in the kidneys allows small molecules like urea, leucine, and inulin to pass through, but larger molecules like hemoglobin are unable to pass through the filtration barrier. Therefore, hemoglobin is not freely filtered and is not excreted in the urine under normal circumstances.

The concentration of Na+ in the plasma is 141 mEq/L, which means that there are 141 milliequivalents of Na+ ions in every liter of plasma. Bowman's space is a part of the renal corpuscle where the initial filtration of blood occurs in the kidneys. During this filtration process, substances such as Na+ are filtered from the blood into Bowman's space. Since Bowman's space is the initial site of filtration, the concentration of Na+ in Bowman's space would be the same as in the plasma, which is 141 mEq/L. Therefore, the correct answer is c. 141 mEq/L.

In a patient with mercury poisoning, the clearance of glucose is least changed. This is because aquaporins, which are inhibited by mercury, primarily facilitate the movement of water molecules across cell membranes. Glucose, on the other hand, is transported across membranes by glucose transporters, which are not directly affected by mercury. Therefore, the clearance of glucose is less likely to be significantly altered in a patient with mercury poisoning compared to other substances such as water, sodium, bicarbonate, and potassium.

When there is a blockage of the ureter by a kidney stone, it will increase the hydrostatic pressure of the tubular fluid. The blockage prevents the normal flow of urine, leading to a buildup of pressure in the tubular fluid. This increased pressure can cause backflow of urine into the kidneys, leading to renal damage and further complications.

The release of ANP is stimulated by increased blood volume. ANP, or atrial natriuretic peptide, is a hormone released by the heart in response to stretching of the atria due to increased blood volume. It acts to increase the excretion of sodium and water by the kidneys, thereby reducing blood volume and blood pressure. Therefore, when blood volume is increased, ANP is released to help regulate fluid balance in the body.

In congestive heart failure, the heart is unable to pump blood effectively, leading to increased pressure in the systemic capillaries. This increased pressure causes fluid to leak out of the capillaries and into the surrounding tissues, resulting in edema. Renal failure, decreased ADH, increased plasma oncotic pressure, and increased urine output are not direct causes of edema in congestive heart failure.

The inner medullary collecting duct is the portion of the nephron where both urea and water reabsorption are controlled by ADH. ADH, or antidiuretic hormone, regulates the reabsorption of water in the kidneys. In the inner medullary collecting duct, ADH increases the permeability of the duct to water, allowing for its reabsorption back into the bloodstream. This mechanism helps to concentrate urine and conserve water in the body.

Patient c is severely dehydrated because the solid line representing the normal condition is significantly higher than the dotted line, indicating a significant decrease in hydration levels.

The correct answer is the proximal tubule. The proximal tubule is the portion of the nephron where the secretion of para-aminohippuric acid (PAH) occurs. PAH is a substance commonly used to measure renal plasma flow and tubular secretion. It is actively secreted into the proximal tubule and then excreted in the urine. This process helps in the clearance of PAH from the body and plays a crucial role in the regulation of renal function.

The late distal tubule is the portion of the nephron located in the cortex and contains both principal and intercalated cells. It is responsible for the reabsorption of sodium and the secretion of potassium and hydrogen ions. This segment plays a crucial role in the regulation of electrolyte balance and acid-base homeostasis in the kidneys.

When Patient Y drinks 2 L of pure water within 5 minutes, it causes a rapid increase in water intake. This leads to a decrease in the osmolality of the blood, as the water dilutes the solute concentration. As a compensatory mechanism, the body increases the excretion of water through urine to maintain homeostasis. This results in an increase in CH20 (free water clearance), which is the rate at which the kidneys can excrete free water. Therefore, the variable that will be increased as compared to normal is e. CH20.

The vasa rectae are long, straight capillaries that run parallel to the loops of Henle in the kidney. They are responsible for maintaining the concentration gradient in the medulla of the kidney. Due to their narrow diameter and limited blood flow, the vasa rectae have the lowest blood flow among the options listed. The renal artery, afferent arterioles, peritubular capillaries, and renal vein all have higher blood flow compared to the vasa rectae.

Increases in tubular fluid flow result in contraction of the afferent arteriole. This is because tubuloglomerular feedback is a mechanism that regulates glomerular filtration rate (GFR) by sensing changes in tubular fluid flow. When there is an increase in tubular fluid flow, it indicates that there is a high volume of fluid entering the tubules. To prevent excessive filtration, the afferent arteriole constricts, reducing the blood flow into the glomerulus and consequently decreasing the GFR. This helps to maintain a balance in fluid and electrolyte levels in the body.

The proximal tubule is the portion of the nephron where urea reabsorption is independent of ADH levels. ADH, or antidiuretic hormone, regulates the reabsorption of water in the kidneys. However, urea reabsorption in the proximal tubule occurs through passive diffusion, meaning it does not require the presence of ADH. This is because the proximal tubule is highly permeable to urea, allowing it to be reabsorbed back into the bloodstream regardless of ADH levels.

Radioactive Cl- is a marker for extracellular water (ECW). This means that when radioactive Cl- is introduced into the body, it will primarily stay in the extracellular fluid compartments, such as the blood plasma and interstitial fluid, rather than entering the intracellular compartments. Therefore, it can be used to measure the volume of ECW in the body.

When ADH levels in the plasma are maximal, it means that the body is trying to conserve water. ADH acts on the kidney to increase water reabsorption, which leads to the concentration of urine. The medullary interstitial osmotic gradient refers to the concentration gradient in the kidney's medulla, which allows for the reabsorption of water. When ADH levels are maximal, this gradient is at its highest, ranging from 300 mOsm/L to 1200 mOsm/L. This allows for the maximum reabsorption of water and the production of concentrated urine.

Patient d has ascites. Ascites is the accumulation of fluid in the abdominal cavity, causing abdominal distension. In the diagram, the solid line represents the normal condition, while the dotted line represents the condition after a change. In this case, patient d has an enlarged abdomen indicated by the dotted line, suggesting the presence of ascites.

Inhibition of the Na+/K+ ATPase will lead to an increase in the clearance of Na+. The Na+/K+ ATPase is responsible for actively pumping Na+ out of the cell and K+ into the cell, against their concentration gradients. By inhibiting this transporter, less Na+ will be pumped out of the cell, resulting in an increased concentration of Na+ in the extracellular fluid. This increased concentration will then drive Na+ clearance through other mechanisms, such as passive diffusion or other transporters.

The patient's symptoms of excessive urine output and constant thirst, along with high levels of ADH in the plasma, suggest a dysfunction in the kidneys' response to ADH. This is characteristic of nephrogenic diabetes insipidus, where the kidneys are unable to respond to ADH and reabsorb water properly. The normal levels of plasma glucose and insulin, as well as the absence of urinary glucose, rule out uncontrolled diabetes mellitus. SIADH is characterized by low levels of ADH, which is not the case here. A defect in the Na+/glucose symporter and compulsive drinking do not explain the symptoms. Therefore, the most likely diagnosis is nephrogenic diabetes insipidus.

The hydrostatic pressure in the interstitium favors reabsorption of water into peritubular capillaries. Hydrostatic pressure is the force exerted by fluid against the walls of blood vessels. In this case, the hydrostatic pressure in the interstitium creates a pressure gradient that helps to push water from the interstitium into the peritubular capillaries. This process is important for reabsorbing water and maintaining fluid balance in the body. The other options (a, c, and d) do not favor reabsorption of water into peritubular capillaries.

Based on the given information, the solid lines represent the normal condition and the dotted lines represent the condition after a change. Since there is a change in the dotted line for patient e, it suggests that this patient has adrenal insufficiency.

Based on the information given, the solid lines represent the normal condition and the dotted lines represent the condition after a change. Since there is no change indicated in any of the lines, it can be inferred that none of the patients have had a hypoosmotic contraction. Therefore, the correct answer is e.

Plasma volume refers to the amount of fluid present in the blood plasma. On average, plasma volume is approximately 4% of a person's body weight. In this case, the man weighs 80 kg, so his plasma volume would be closest to 4% of 80 kg, which is 3.2 kg. Since 1 liter of water weighs approximately 1 kg, the man's plasma volume would be closest to 3.2 liters, which is closest to option a. 4 L.