Week 13: Renal Physiology

Match these vocabulary terms to their meanings.

Renin is released by cells of the juxtaglomerular apparatus in response to afferent arteriole pressure and the degree of stretch of the arteriole wall. The structural and functional unit of the kidney is a nephron. The specialized capillary bed responsible for the pressure that drives filtration is the glomerulus. An elevated level of urea in the blood is uremia.

Reabsorption of which of the following drives the reabsorption of water and many other solutes in the proximal tubule?

Sodium Sodium ions are reabsorbed down their concentration gradient into the tubular cells. Na+/K+ pumps in the tubular cell membranes are responsible for maintaining the concentration gradient. The energy provided by the Na+ gradient is used to fuel secondary active transport of many other substances.

Aldosterone causes the reabsorption of ________ in the kidney tubule.

Sodium The secretion of aldosterone stimulates the synthesis and retention of more sodium channels and sodium-potassium pumps in the kidney tubule, therefore enhancing sodium reabsorption.

ADH causes the reabsorption of ________ in the kidney tubule.

Water ADH (antidiuretic hormone) causes aquaporins to be inserted into the cell membranes of the collecting duct cells, facilitating the reabsorption of water from the filtrate, back into the blood.

The secretion of ADH is directly stimulated by _______.

a change in body fluid osmolarity

During reabsorption of water in the proximal convoluted tubule, what causes water to diffuse from the lumen into the interstitial space?

an increase in the osmolarity of the interstitium

The secretion of aldosterone is directly stimulated by _______.

angiotensin II

When blood pressure increases, what changes can occur to maintain glomerular filtration rate?

constriction of the afferent arteriole and dilation of the efferent arteriole

Secretion of ADH would _______.

decrease in urine output

The addition of aldosterone _______.

decreased the urine volume

Which of the following resulted in an increase in glomerular filtration rate?

decreasing the efferent arteriole diameter and increasing the afferent arteriole diameter

As the number of glucose carriers increased, the concentration of glucose in the _______.

distal tubule decreased and bladder decreased

Which of the following is NOT a function of the kidneys? -maintenance of electrolyte balance in the body -maintenance of plasma osmolarity -maintenance of acid-base balance of the blood -exchange of oxygen and carbon dioxide with the tissues

exchange of oxygen and carbon dioxide with the tissues

Altering the radii of the afferent and efferent arterioles provides for _______.

glomerular filtration rate homeostasis and glomerular hydrostatic pressure homeostasis

GFR regulation mechanisms primarily affect which of the following?

glomerular hydrostatic pressure (HPg) Much like other capillaries in the body, hydrostatic pressure within the glomerular capillaries produces net outward movement of fluid. Unique to glomerular capillaries, HPg is consistently higher than other capillaries (~55 mm Hg), which ensures the one-way movement of fluid and solutes out of the glomerulus under normal conditions.

When the beaker pressure was lowered, which of the following decreased?

glomerular pressure, glomerular filtration rate and urine volume

The functions of the nephron include all of the following EXCEPT _______. -tubular secretion -tubular reabsorption -glomerular filtration

glomerular secretion

What is the name for the "ball" of capillaries found in the renal corpuscle?

glomerulus

Which structures form the filtration membrane in the nephron?

glomerulus and the glomerular capsule

Which of the following materials is NOT reabsorbed in the nephron loop? -glucose -chloride ions -water -sodium ions

glucose Virtually all of the glucose in the filtrate is reabsorbed in the proximal convoluted tubule before reaching the nephron loop.

When the glucose transport maximum is reached, _______.

glucose is excreted in the urine and not all of the glucose is reabsorbed

What is(are) the driving force(s) for filtration in the nephron?

hydrostatic pressure gradients and osmotic pressure gradients

What is the primary driving force (pressure) that produces glomerular filtration?

hydrostatic pressure of blood (blood pressure)

ADH is produced in the _______.

hypothalamus

Which of the following resulted in a decrease in glomerular capillary pressure?

increasing the efferent arteriole diameter and decreasing the afferent arteriole diameter

Which of the following would decrease glomerular filtration rate?

increasing the efferent arteriole radius and/or decreasing the afferent arteriole radius

What does a high concentration of NaCl in the renal tubule at the juxtaglomerular apparatus (JGA) most likely indicate?

insufficient NaCl reabsorption due to high GFR

Because the alteration of the afferent or efferent arteriole occurs within the nephron, we refer to this mechanism as _______.

intrinsic

The reabsorption of water and solutes _______.

is passive, depends on concentration gradients and is into the peritubular capillaries

What is the osmolarity of the filtrate at the end of the proximal tubule?

isotonic - 300 mOsm The osmolarity of the filtrate would be about 300 mOsm because both solutes and water are reabsorbed in the proximal tubule. As particles are reabsorbed, water follows osmotically.

Which of the following are mechanisms of intrinsic control of glomerular filtration (renal autoregulation)?

myogenic mechanism and tubuloglomerular feedback Both of these mechanisms occur strictly within kidney (i.e., intrinsic controls). The myogenic mechanism is mediated by smooth muscle within the afferent arteriole. In contrast, tubuloglomerular feedback is mediated by macula densa cells of the juxtaglomerular apparatus (JGA).

If the osmotic pressure in the glomerular capillaries increased from 28 mm Hg to 35 mm Hg, would net filtration increase or decrease?

net filtration would decrease Yes, because osmotic pressure opposes filtration, increasing osmotic pressure would decrease net filtration.

What is the limiting factor for the reabsorption of most actively transported solutes in the proximal tubule?

number of transport carriers in the luminal membrane The number of carriers is the rate-limiting factor. For example, in Diabetes Mellitus, plasma glucose levels are very high, and the sodium-glucose transporter cannot transport (reabsorb) all the glucose passing through the proximal tubule. Glucose is therefore found in the urine.

Which substance would be found in higher concentration if the membrane were damaged?

protein

Glucose reabsorption occurs in the _______.

proximal convoluted tubule

In this activity, the drain beaker (second beaker in the flow) simulates the _______.

renal vein

Granular cells of the juxtaglomerular apparatus (JGA) regulate GFR indirectly through which mechanism?

renin-angiotensin mechanism When systemic blood pressure decreases, granular cells release renin which ultimately causes the formation of angiotensin II. Angiotensin II causes widespread vasoconstriction of systemic arterioles and the increase of blood volume due to aldosterone release.

The active transport of which ion out of proximal convoluted tubule cells causes the reabsorption of both water and solutes?

sodium

Interstitial fluid is located in the _______.

spaces surrounding the kidney tubule

Focus your attention on the "key players" outlined in the first part of Focus Figure 25.1. Drag and drop the terms to the appropriate blanks in the sentences. Terms may be used once, more than once, or not at all.

1. The long nephron loops of the juxtamedullary nephrons are located in the renal medulla. 2. The long nephron loops create the medullary osmotic gradient and act as countercurrent multipliers. 3. The vasa recta preserve the medullary osmotic gradient and act as countercurrent exchangers. 4. The collecting ducts use the medullary osmotic gradient to concentrate urine. collecting ducts returned

Calculate the net filtration pressure if capillary hydrostatic pressure is 60 mm Hg, capillary osmotic pressure is 25 mm Hg, and capsular hydrostatic pressure is 10 mm Hg.

25 mm Hg Yes, 60 - (25 + 10) = 25 mm Hg. The two pressures that oppose filtration must be subtracted from the force favoring filtration.

At which concentration of glucose carriers was the glucose concentration reduced to zero?

400

What is the normal range for glomerular filtration rate?

80 - 140 ml/min

Which hormone had the greater effect on urine volume?

ADH

In severe dehydration or blood loss, what would be the levels of ADH and what would be the urine flow rate?

ADH - high; low urine flow rate (0.25 ml/min) Yes, ADH would be high, causing a large percentage of the water to be reabsorbed. Therefore, the urine flow rate would be low.

In severe dehydration or blood loss, would ADH levels be high or low, and would urine production be high or low?

ADH - high; urine production - low

In overhydration, what would be the levels of ADH (high, normal, or low) and what would be the osmolarity of the urine?

ADH - low; 100 mOsm (urine)

Which of the following statements about ADH (antidiuretic hormone) is correct? -ADH would increase urine volume. -ADH is released by the posterior pituitary gland. -ADH inserts water channels into the luminal membrane of the proximal tubules. -ADH is synthesized by the adrenal gland and works in the kidney. Submit

ADH is released by the posterior pituitary gland. This is correct. ADH is synthesized in the hypothalamus and stored and released by the posterior pituitary gland.

Through the tubuloglomerular feedback mechanism, how would an increase in filtrate NaCl concentration affect afferent arteriole diameter?

Afferent arteriole diameter would decrease.

Lisa suffers from kidney stones. One small stone manages to get lodged in the ascending limb of the nephron loop of one of her nephrons. Predict what would happen to the amount of filtrate produced over time by this particular nephron.

Decrease in filtrate production due to an increase in hydrostatic pressure in the capsular space

Which of the following transporters in the luminal membrane results in secretion? -Na+-H+ countertransport -Na+-glucose cotransporter -potassium ion channel -glucose carrier transporter

Na+-H+ countertransport

If the osmotic pressure in the glomerular capillaries increased from 28 mmHg to 35 mmHg due to dehydration, would net filtration increase or decrease?

Net filtration would decrease.

Glucose is transported _______.

through the basolateral membrane by facilitated diffusion (and through the apical membrane by secondary active transport)

Most solutes that are reabsorbed in the proximal convoluted tubule use which of the following pathways?

transcellular Yes, most substances are reabsorbed first through the luminal and then through the basolateral membranes of the proximal convoluted tubule.

Macula densa cells of the juxtaglomerular apparatus (JGA) regulate GFR through which intrinsic mechanism?

tubuloglomerular feedback The JGA is a region of the nephron where the afferent arteriole and its associated tubule are closely apposed. This anatomical arrangement allows macula densa cells to adjust GFR according to the NaCl concentration in filtrate. This is called tubuloglomerular feedback because it allows the contents of the tubules (tubulo-) to affect the glomerular filtration rate.

When ADH is present in the filtrate, _______.

urine concentration increases

With the valve between the collecting duct and the urinary bladder closed, _______.

urine volume was zero

Which of the following should NOT be found in the filtrate in the Bowman's capsule? -glucose -white blood cells -potassium -sodium

white blood cells

The urine was the most concentrated _______.

with both ADH and aldosterone

Which of the following statements about aldosterone is NOT correct? -Aldosterone increases sodium reabsorption by increasing the number of Na+-K+ ATPase pumps in the luminal membrane of the proximal tubule. -Aldosterone is produced in the adrenal cortex. -Aldosterone is stimulated by decreased plasma sodium levels and increased plasma potassium levels. -Aldosterone increases the number of passive sodium channels in the luminal membrane of the distal tubule and collecting duct, thus aiding sodium reabsorption.

Aldosterone increases sodium reabsorption by increasing the number of Na+-K+ ATPase pumps in the luminal membrane of the proximal tubule. This is the incorrect statement. Aldosterone increases the number of Na+-K+ ATPase pumps in the basolateral membrane of the distal tubules and collecting ducts.

The flow of filtrate through the tubules is elevated. Complete the following statements to indicate the effects of this high rate of flow. The descriptive terms may be used once, more than once, or not at all. Drag and drop the terms on the left to complete the sentences on the right. Words may be used once, more than once, or not at all.

Filtrate flow through the renal tubule increases when glomerular filtration rate increases. When filtrate flow through the renal tubule increases, reabsorption of sodium chloride by the tubule decreases. When filtrate flow through the renal tubule increases, the concentration of sodium chloride remaining in the filtrate increases. When filtrate flow through the renal tubule increases, the macula densa responds by releasing vasoconstrictors. When filtrate flow through the renal tubule increases, the afferent arteriole responds by vasoconstricting.

Drag and drop each of the terms at the left to the correct definition at the right.

Filtration is the process by which water and solutes flow from the blood into the capsular space in the renal corpuscle. Reabsorption is the movement of water and solutes from the filtrate in the renal tubule into the blood. Secretion is the movement of selected solutes from the blood of the peritubular capillaries into the renal tubule for excretion.

When the macula densa detects an increase in NaCl concentration in the renal filtrate, what happens to the glomerular filtration rate (GFR)?

GFR decreases.

As the pressure in the beaker was increased, which of the following occurred?

Glomerular filtration rate increased, and urine volume increased.

Match these prefixes to their meanings.

The prefix nephr- means kidney. The prefix ur- means urine, urinary tract, or urea. The prefix glomerul(o)- means glomerulus of the kidney. The prefix juxta- means situated near.

What happened to the urine concentration when the solute gradient in the interstitial space was increased?

The urine concentration increased.

What happened to the urine volume when the solute gradient in the interstitial space was increased?

The urine volume decreased.

What will happen to the urine volume if ADH is NOT added to the collecting duct?

The urine volume will increase.

Through which pathway are most water and solutes reabsorbed in the kidney tubule?

Transcellular Most water and solutes are reabsorbed by the transcellular pathway across the cell. This means that transport must take place across the apical membrane and across the basolateral membrane for the substance to move from the lumen of the kidney tubule into the blood.

Patients with uncontrolled diabetes mellitus often have glucose in their urine. This is because the concentration of glucose in the filtrate exceeds the ____________ of the carrier proteins in the proximal tubule.

Transport maximum

Which of the following describes the order in which blood flows through the nephron?

afferent arteriole, glomerulus, efferent arteriole

The myogenic mechanism of renal autoregulation primarily involves smooth muscle in which blood vessels?

afferent arterioles

The reabsorption of sodium in the DCT is regulated primarily by __________.

aldosterone and ANP Aldosterone increases Na+ reabsorption, and atrial natriuretic peptide (ANP) inhibits Na+ reabsorption.

Which of the following substances is not normally found in filtrate? -water and small solutes -nitrogenous waste particles, such as urea -blood cells and large particles -ions, such as sodium and potassium

blood cells and large particles

Filtrate in a typical healthy nephron will NEVER include __________.

blood cells and proteins

The pressure in the left source beaker simulates _______.

blood pressure

In this activity, we will explore the effect of _______.

blood pressure on glomerular filtration rate

How are nutrient molecules such as glucose and amino acids reabsorbed through the apical surfaces of the tubule epithelia?

by secondary active transport

When the efferent arteriole constricts, _______.

the back pressure in the Bowman's capsule increases

Focus your attention on Focus Figure 25.1. Which of the following is NOT a property used to establish the medullary osmotic gradient? -the filtrate flow through the ascending and descending limbs of the long nephron loops of juxtamedullary nephrons -the ascending limb's impermeability to water and permeability to salt -the descending limb's permeability to water and impermeability to salt -the blood flow through the ascending and descending portions of the vasa recta

the blood flow through the ascending and descending portions of the vasa recta The flow of blood through the ascending and descending portions of the vasa recta does not establish the osmotic gradient. The vasa recta act as countercurrent exchangers to preserve the osmotic gradient.

With the valve between the collecting duct and the urinary bladder closed and with the pressure increased, _______.

the glomerular filtration rate increased and the glomerular pressure increased

With ADH added but in the absence of aldosterone, _______.

the potassium concentration increased and urine volume decreased

What are the two main parts of the nephron?

the renal corpuscle and the renal tubule

The decreased intracellular concentration of sodium in tubular cells during active transport is caused by which of the following mechanisms?

the sodium-potassium ATPase pump in the basolateral membrane Yes, this pump moves sodium out of the cell into the interstitium, thus decreasing intracellular sodium.

Which of the following best describes glomerular filtration rate (GFR)?

the volume of filtrate created by the kidneys per minute Fluid and small solutes that leave the glomerulus are collectively termed filtrate. Glomerular filtration is driven by glomerular hydrostatic pressure (HPg) and produces ~125 ml of filtrate per minute.