Chapter 14 - The Kidneys and Regulation of Water and Inorganic Ions

Which of the following hormones would act on the kidney collecting ducts to increase water reabsorption as would occur during dehydration (increased plasma osmolarity)? A) Aldosterone B) Angiotensin C) Renin D) ADH (vasopressin) E) ANP (atrial natriuretic peptide)

ADH or anti-diuretic hormone, also called vasopressin, acts on the collecting ducts, increasing their permeability to water, leading to increased reabsorption of water and thus decreasing its loss in the urine. This is a significant and effective process, which retains body water during times of dehydration. The renin-angiotensin system stimulates the release of aldosterone from the adrenal cortex. Aldosterone can also help increase water reabsorption but only by increasing reabsorption of sodium (and thus water) in the proximal and distal tubules. ANP or trial natriuretic peptide would lead to a decrease in reabsorption of sodium and water.

Which of the following is NOT a function of the renal system? A) Regulating the concentration of water and ions in the body B) Excreting waste products C) Secreting hormones D) Producing glycogen

The kidney doesn't produce glycogen. However, it can perform gluconeogenesis to produce glucose. All of the other functions are typical renal functions.

The hormone that most directly influences Na+ reabsorption in the collecting duct is A) Aldosterone B) Angiotensin C) Renin D) Vasopressin

Aldosterone directly binds receptors within distal tubule and cortical collecting duct cells leading to an increase in the synthesis of proteins involved in Na+ transport. Renin is released in response to low sodium concentrations and functions as the enzyme that converts angiotensinogen to angiotensin I. Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II stimulates adrenal cells to secrete aldosterone. Vasopressin plays no role in Na+ reabsorption.

Which of the following drugs would be most effective in treating hypertension? A) An alpha-adrenergic agonist B) An ADH agonist C) An angiotensin-converting enzyme inhibitor D) A stimulator of aldosterone synthesis

An angiotensin-converting enzyme (ACE) inhibitor would be the most effective drug combating hypertension. ACE inhibitors inhibit the production of Angiotensin II from Angiotensin I, a process which occurs as the blood passes through the capillaries. Angiotensin II has several actions in the body that promote an increase in blood pressure, so blocking its production would decrease the elevated blood pressure in hypertension. The actions of Angiotensin II include vasoconstriction action on peripheral arterioles and stimulation of release of aldosterone from the adrenal cortex. Aldosterone directly and indirectly increases renal reabsorption of sodium and water respectively. This will result in an increase in plasma volume, thus increasing blood pressure. Alpha-adrenergic agonists would cause vasoconstriction, and thereby further increase blood pressure. An ADH agonist would cause fluid retention and possibly vasoconstriction, which would most likely also increase hypertension.

Which of the following is a hormone formed in the blood as a result of converting a non-functional precursor protein into a functional protein which causes vasoconstriction, resulting in increased arterial pressure? A) Renin B) Aldosterone C) Angiotensin D) Vasopressin

Angiotensin has a vasoconstricting effect. Angiotensin I is formed in the blood by the action of the kidney hormone renin which enzymatically converts angiotensinogen to angiotensin I. The latter is then further converted to a more potent peptide, angiotensin II by angiotensin-converting enzyme produced by endothelial cells of capillaries. Angiotensin II causes vasoconstriction in the peripheral blood vessels, including the kidney, thus increasing blood pressure. Aldosterone is a steroid hormone formed by the adrenal cortex, and ADH is a peptide hormone made in the hypothalamic neurons and released at the site of the posterior pituitary.

Which of the following is NOT a basic renal process? A) Glomerular filtration B) Tubular reabsorption C) Tubular secretion D) Erythropoietin production

Erythropoietin production is an endocrine function of the kidney. Glomerular filtration, tubular reabsorption and secretion are all basic renal processes that are carried out by various parts of kidney nephrons and collecting ducts. Urine formation begins with glomerular filtration at the Bowman's capsule. As the filtrate flows through the proximal and distal tubules, some substances are reabsorbed and some are secreted into the tubules. The collecting ducts are also involved in reabsorption.

Which of the following is NOT associated with the increase in hypoosmotic urine production in persons with diabetes insipidus? A) Failure of the posterior pituitary to secrete vasopressin B) A blood glucose concentration that exceeds transport maximum in the nephron resulting in glucose, and thus water, remaining in the urine C) The inability of the kidneys to respond to vasopressin D) The inability of the kidneys to respond to ADH

Excessive glucose in the blood results in an osmotic dieresis. When blood glucose concentrations exceed the transport maximum of glucose, the glucose remaining in the filtrate causes water to remain in the filtrate as well. This condition is usually the result of diabetes mellitus. Central diabetes insipidus results from a lack of production of vasopressin by the hypothalamus or its release from the posterior pituitary. Nephrogenic diabetes insipidus results from the failure of the collecting ducts to respond to vasopressin. Vasopressin is also known as antidiuretic hormone (ADH).

Which of the following components of the filtration membrane form the filtration slits? A) The capillary endothelial cells B) The basement membrane C) The podocyte cells D) The capillary endothelial cells and the podocyte cells

Filtration slits are the gaps that exist between the foot processes of the podocyte cells as they make contact with the basement membrane.

Which of the following will cause an increase in the glomerular filtration rate? A) Increasing the hydrostatic pressure of the blood B) Increasing the colloid osmotic pressure of the blood C) Increasing sympathetic nerve discharge to glomerular afferent arterioles D) Efferent arteriole vasodilation

Glomerular filtration rate is largely dependent on the hydrostatic pressure of blood (pumping force of the heart) which helps force plasma through the glomerular pores into the interior of the Bowman's capsule. Osmotic pressure of the blood tends to exerts its force in the opposite direction since plasma albumins do not get filtered and stay in the plasma. This is one reason that if blood pressure falls below a critical limit, glomerular filtration ceases due to osmotic pressure equaling or being larger that the hydrostatic pressure. Increasing sympathetic discharge to the afferent arterioles causes vasoconstriction and decreases the blood flow and the hydrostatic blood pressure in the glomerular capillaries, which decreases the filtration rate. Vasodilation of the efferent arterioles decreases the hydrostatic pressure in the glomerular capillary and reduces glomerular filtration rate.

Reabsorption of glucose in the kidney proximal tubules occurs by A) Diffusion, depending on plasma glucose concentration B) An active transport process that is linked to sodium reabsorption C) An active transport process that is linked to amino acid transport D) Active transport with no link to the transport of any other substance

Glucose is filtered at Bowman's capsule. It is reabsorbed in the proximal convoluted tubules through a secondary active transport process, which is co-dependent on the active transport (reabsorption) of sodium. Glucose reabsorption is very effective and essentially complete up to a certain level (transport maximum for glucose) which is about 180 mg of glucose per 100 ml of plasma. Over this limit, all transporter mechanisms are fully saturated and the additional glucose will not be reabsorbed but will remain in the glomerular filtrate. This is why the urine of people with untreated diabetes mellitus will contain glucose; their plasma glucose concentration can be over 180 mg/dl (normal levels are about 100 mg/dl).

Which of the following statements regarding renal handling of water by the kidneys is correct? A) In the absence of vasopressin, urine is isoosmotic with plasma. B) In the absence of vasopressin, water cannot be reabsorbed in the proximal tubules. C) In the absence of vasopressin, the cortical collecting ducts have very low permeability to water. D) In the absence of vasopressin, the distal tubules secrete water.

In the absence of vasopressin, the cortical collecting ducts have very low permeability to water and very little water is reabsorbed at these sites. Vasopressin does not influence water absorption in the tubule segments prior to the collecting ducts. In the presence of vasopressin, the water permeability of the collecting ducts markedly increases due to increased number of aquaporins incorporated in the collecting duct membranes. Water then moves down its osmotic gradient from the collecting ducts into the interstitial space through the aquaporins and is eventually returned back into the plasma. In the absence of vasopressin, urine is hypo-osmotic because water is not reabsorbed in the collecting ducts. Water is not secreted by any region of the nephrons or collecting ducts.

Which of the following substances is NOT involved in the buffering functions of the kidney? A) Oxalate B) Phosphate C) Ammonia D) Bicarbonate

Oxalate is not a known kidney buffer. Bicarbonate is the most effective buffering agent in the plasma and in the kidney. Phosphate also acts as a buffer in the urine and accepts hydrogen ions. Ammonia production is also important when acidity in the filtrate is increased for a long period.

The juxtaglomerular apparatus is composed of the A) Juxtaglomerular cells B) Macula densa C) Mesangial cells D) Juxtaglomerular cells and mesangial cells E) Juxtaglomerular cells and macula densa

The juxtaglomerular apparatus consists of the juxtaglomerular cells and the macula densa. This structure is located at the point where the ascending limb of the loop of Henle passes between the afferent and efferent arteriole. Although the mesangial cells are also in this location, they are not a part of the juxtaglomerular apparatus.

The presence of this substance in the urine is considered a sign of kidney disease or kidney disorder. A) Urea B) Electrolytes (e.g. sodium and potassium) C) Plasma proteins (e.g., albumins) D) Glucose

Plasma proteins such as albumins are not filtered through the filtration barrier into Bowman's space, mainly due to their large size. Therefore the appearance of proteins in the urine is a sign of a pathological condition, such as a kidney disease, in which the glomerular capillary wall loses its structural and functional integrity, allowing proteins to pass through. Urea is a waste product of the metabolism of nitrogen containing compounds such as proteins. It is formed mainly by the liver, excreted by the kidney, and is a normal constituent of urine. Electrolytes are also excreted in the urine as a way of regulating their concentrations in the plasma. The presence of glucose in urine does not usually indicate renal damage but rather inability to adequately control blood glucose levels.

Which of the following is true about the reabsorption process of substances such as sodium, glucose and amino acids in the nephron? A) It involves the Bowman's capsule B) It is restricted to the loop of Henle C) It occurs mainly in the proximal convoluted tubules D) It occurs mainly by osmosis

Reabsorption of substances such as sodium, glucose and amino acids takes place largely in the proximal convoluted tubules. Bowman's capsule is the site of filtration of plasma, and no reabsorption takes place there. The loop of Henle is the site of counter current exchange mechanisms which help set up an osmotic gradient from the cortex to medulla for the purpose of increasing water reabsorption in the collecting ducts in the presence of ADH (vasopressin).

Which of the following does NOT contribute to the hypertonic medullary interstitium? A) Solute reabsorption in the ascending limb of the loop of Henle B) Sodium reabsorption in the distal tubule C) Urea reabsorption from the proximal tubule D) Urea recycling between the loop of Henle and the collecting duct

Reabsorption of urea in the proximal tubule does not add to the hypertonicity of the renal medulla interstitium. The medullary interstitium is hypertonic due to the action of the countercurrent multiplier and the recycling of urea between the loop of Henle and the collecting duct. The countercurrent multiplier is characterized by solute reabsorption in the ascending limb and water reabsorption in the descending limb of the loop of Henle.

In the process of reabsorption via transporters, when the binding sites on a renal transport protein become saturated A) The transport maximum for that transporter has been reached B) The substance being transported will begin to decrease in concentration in the urine C) The rate of transport will increase in order to reabsorb even more of the substance being transported D) The transporters will stop functioning

Saturation of binding sites on a transport protein occurs when the transport maximum has been reached. At that point the rate of transport cannot increase further, and the substance being transported will begin to increase, not decrease, in concentration in the urine as it is no longer reabsorbed. Transporter saturation does not prevent a transporter from functioning; it only means that all binding sites are currently occupied by the ligand.

Which of the following substances is NOT commonly secreted by the renal tubules? A) Sodium ions B) Potassium ions C) Drugs such as penicillin D) Hydrogen ions

Sodium is reabsorbed from the filtrate, but never secreted. Each of the others is commonly secreted into the filtrate.

Despite the presence of the Na+/K+ ATPase pumps in the basolateral membrane of most nephron tubules, the secretion of K+ into the lumen is limited to the cortical collecting duct cells because only these cells have luminal K+ leak channels. A) True B) False

The Na+/K+ ATPase pumps in the basolateral membrane of most tubular cells transport K+ into those cells, but this K+ diffuses back across the basolateral membrane through K+ leak channels located there. Only in collecting duct cells are the K+ leak channels found in the luminal membrane allowing K+ to diffuse into the lumen.

Which of the following is NOT a component of the filtration barrier within the renal corpuscle? A) The endothelial cells that form the glomerular capillary B) A thin layer of smooth muscle that surrounds the glomerular capillary C) The epithelial cells that compose the visceral layer of Bowman's capsule (podocyte cells) D) The thin basement membrane that lies between the endothelial cells of the capillary and the epithelial cells of Bowman's capsule

The filtration membrane consists of the endothelial cells that form the glomerular capillary, the podocyte cells, and the thin basement membrane that lies between these cell layers. Although a modified type of smooth muscle cells (mesangial cells) surrounds the capillary loops, they are not part of the filtration pathway.

Which of the following statements regarding renal regulation of hydrogen-ion concentration by the kidneys is true? A) Renal regulation of extracellular H+ concentration is dependent upon regulating the amount of hydrogen ion filtered by the kidneys. B) Renal regulation of extracellular H+ concentration is dependent upon regulating the amount of hydroxides secreted by the kidneys C) Renal regulation of extracellular H+ concentration is accomplished in part by regulating the amount of bicarbonate ion excreted by the kidneys D) Most of the H+ excreted in the urine is bound to bicarbonate

The kidneys are largely responsible for hydrogen ion balance in the body by regulating the excretion and reabsorption of H+ and bicarbonate. Hydrogen is excreted in multiple forms.

Which of the following structures composes the renal corpuscle? A) Glomerular capillaries B) Bowman's capsule C) Afferent arteriole D) Glomerular capillaries and Bowman's capsule E) Afferent arteriole and Bowman's capsule

The renal corpuscle is composed of the glomerular capillaries which are surrounded by Bowman's capsule. The afferent arteriole supplies blood to the glomerular capillaries, but it is not contained within the corpuscle.

Movement of water out of the collecting ducts takes place by bulk flow. A) True B) False

This statement is false. Movement of water out of the collecting ducts occurs by osmosis. Water moves through aquaporins under the force provided by an osmotic gradient. Bulk flow of water is flow due to hydrostatic pressure gradients, as occurs with glomerular filtration.

Much like small organic nutrients, calcium reabsorption by the kidney occurs in the proximal tubule and is not subject to regulation. A) True B) False

This statement is false. While the kidney readily reabsorbs about 60% of the filtered calcium, the remainder of calcium reabsorption is under the control of parathyroid hormone (PTH).

The entire volume of plasma in the average person is filtered by the kidney approximately every 30 minutes. A) True B) False

This statement is true. Considering that the filtration rate is 125ml/min, it would take 24 minutes to filter the 3L of plasma in the average person. Reabsorption of substances such as sodium, glucose and amino acids takes place largely in the proximal convoluted tubules. Bowman's capsule is the site of filtration of plasma, and no reabsorption takes place there. The loop of Henle is the site of counter current exchange mechanisms which help set up an osmotic gradient from the cortex to medulla for the purpose of increasing water reabsorption in the collecting ducts in the presence of ADH (vasopressin).

Stretch receptors located in the bladder wall are important for micturition. A) True B) False

This statement is true. Micturition or urination describes the process by which urine is ejected from the bladder. As the bladder fills with urine, stretch receptors located in the muscular wall of the bladder become stimulated. Afferent fibers from these stretch receptors send signals to the spinal cord and stimulate efferent parasympathetic neurons which cause the detrusor muscles to contract, expelling urine from the bladder through the urethra.

The loss of 0.5 liter of sweat will provoke a greater sense of thirst than the loss of the same volume of blood plasma. A) True B) False

This statement is true. Sweat is a hypo-osmotic solution containing mainly water, sodium and chloride. Sweating causes a decrease in extracellular volume and an increase in body fluid osmolarity (a decrease in plasma water concentration and increase in plasma sodium concentration). Thirst is stimulated by higher plasma osmolarity, i.e., increased plasma sodium concentration. Therefore sweating would induce a greater sense of thirst than a loss of blood volume, which does not change plasma osmolarity.

In all nephron segments, the active transport of sodium by tubular cells is accomplished by the action of the Na+/K+ ATPase pump in the basolateral membrane. A) True B) False

This statement is true. The Na+/K+ ATPase pump is found in the basolateral membrane of tubular cells in all portions of the nephron where sodium is reabsorbed. However, different types of transport proteins are responsible for transporting sodium across the luminal membrane in different nephron segments.

In a healthy kidney, the rate of reabsorption of most organic nutrients (such as glucose) by the kidney is not actively regulated and is very efficient. A) True B) False

This statement is true. The kidneys reabsorb filtered organic nutrients such as monosaccharides and amino acids with great efficiency, and they are normally completely reabsorbed. This process occurs without active regulation.

When the clearance of a molecule is less than the glomerular filtration rate (GFR) of that molecule, which of the following statements regarding that molecule is true? A) It is filtered and is not subject to reabsorption or secretion B) It is filtered and is partially reabsorbed C) It is filtered and is partially secreted D) It is totally filtered

Whenever the clearance of a substance is less than GFR, that substance must undergo reabsorption. If its clearance matched GFR, then it was neither reabsorbed nor secreted. If its clearance was greater than GFR, then it must have been secreted. There is no information to determine if it is totally filtered.