Topic 5 - Renal Physiology

Question 1

The urine concentration of potassium is greater than that of plasma.

Answer 1

True

Question 2

The plasma concentration of calcium is greater than that of urine.

Answer 2

True

Question 3

Urine normally contains about 2 mmol l-1 of bicarbonate.

Answer 3

False

Urine pH contains no bicarbonate. If plasma pH is elevated (alkalemia), the kidneys will excrete bicarbonate so that urine pH rises.

Question 4

Urine pH is normally greater than that of plasma.

Answer 4

False

Question 5

Urine normally contains no measurable quantity of protein.

Answer 5

True

Question 6

Renal plasma flow can be measured by the clearance of PAH.

Answer 6

True

Question 7

The kidneys receive about a fifth of the resting cardiac output.

Answer 7

True

Question 8

As cardiac output increases during exercise renal blood flow rises.

Answer 8

False

Question 9

Renal blood flow is maintained within narrow limits by autoregulation.

Answer 9

True

Question 10

Increased activity in the renal sympathetic nerves results in increased blood flow to the kidneys.

Answer 10

False

As cardiac output rises in exercise, renal blood flow does not increase. It usually falls due to vasoconstrictor activity in the sympathetic nerves supplying the smooth muscle of the afferent arterioles.

Question 11

The glomerular filtrate is identical in composition to plasma.

Answer 11

False

The concentration of small molecules in the glomerular filtrate is the same as in plasma but the filtrate contains very little protein (unlike plasma).

Question 12

The glomerular filtration rate can be determined by measuring the clearance of inulin.

Answer 12

True

Question 13

A substance that has a clearance less than that of inulin must have been reabsorbed by the renal tubules.

Answer 13

False

A clearance less than that for inulin can be due to either a barrier to filtration (e.g. plasma proteins) or reabsorption by the renal tubules (e.g. glucose).

Question 14

The glomerular filtration rate is about 125 ml min-1 in an adult male.

Answer 14

True

Question 15

The glomerular filtration rate depends on the pressure in the afferent arterioles.

Answer 15

True

Question 16

The absorption of small molecules by the renal tubules always occurs via specific transport proteins.

Answer 16

False

Although most small molecules and ions are absorbed via the transcellular route (and therefore utilize carrier proteins or ion channels), some are absorbed via the paracellular route by solvent drag or as a result of charge differences between the lumen and the interstitial space.

Question 17

The appearance of glucose in the urine reflects a saturation of the glucose carriers of the proximal tubule.

Answer 17

True

Question 18

Glucose transport and amino acid transport across the epithelia of the renal tubules is linked to sodium transport.

Answer 18

True

Question 19

The transport maximum for glucose is about 360 mg min-1.

Answer 19

True

Question 20

If the renal clearance of a substance exceeds that of inulin then it must be secreted into the tubules.

Answer 20

True

Question 21

The GFR is closely matched to the transport capacity of the tubules.

Answer 21

True

The GFR is closely matched to the transport capacity of the tubules by glomerulotubular feedback.

Question 22

In a healthy person the proximal tubules reabsorb all of the filtered glucose.

Answer 22

True

Question 23

The filtered bicarbonate is absorbed by anion transport.

Answer 23

False

Tubular bicarbonate is converted to carbon dioxide and water by the secretion of hydrogen ions by an Na+-H+ antiporter in the proximal tubule and an H+ ion ATPase in the distal tubule. It then enters the tubular cells as CO2 and water where it is reconverted to bicarbonate. It passes from the cells to the blood in exchange for chloride ions.

Question 24

All the filtered bicarbonate is normally reabsorbed in the first half of the proximal tubule.

Answer 24

False

While most of the filtered bicarbonate is reabsorbed in the proximal tubule, the fluid reaching the distal tubule contains about 2 mmol l-1.

Question 25

The proximal tubules secrete bile salts into the tubular fluid.

Answer 25

True

Question 26

All nephrons have loops of Henle that penetrate deep into the medulla.

Answer 26

False Superficial cortical nephrons do not have long loops of Henle. Only about 15 per cent of all nephrons extend deep into the medulla. These are the juxtamedullary nephrons.

Question 27

The descending thin limb of the loop of Henle is permeable to water.

Answer 27

True

Question 28

The osmolality of the fluid at the hairpin bend of the loop of Henle may exceed 1200 mOsm kg-1.

Answer 28

True

Question 29

The thick ascending limb of the loop of Henle transports sodium ions in the same way as the proximal tubule.

Answer 29

False The thick ascending limb of the loop of Henle transports sodium, potassium, and chloride from the tubular fluid by a specific electroneutral carrier. In the proximal tubule, most sodium is reabsorbed with small organic molecules or bicarbonate.

Question 30

The thin ascending limb of the loop of Henle is impermeable to water.

Answer 30

True

Question 31

The uptake of sodium ions is regulated by the proximal tubule.

Answer 31

False Sodium balance is regulated by the activity of the cells of the distal tubules. The sodium uptake by the proximal tubules is obligatory and linked to the absorption of small organic molecules, chloride and bicarbonate.

Question 32

Macula densa cells secrete renin when plasma sodium is low.

Answer 32

False Renin is an enzyme that is secreted by the granulosa cells of the juxtaglomerular apparatus in response to low sodium in the fluid reaching the distal tubule. It cleaves angiotensin I from a precursor molecule called angiotensinogen which is always present in the plasma.

Question 33

Angiotensin II is formed from renin by the action of an enzyme found on the endothelium of the pulmonary blood vessels.

Answer 33

False

Question 34

Angiotensin II acts on the adrenal medulla.

Answer 34

False Angiotensin II acts on the zona glomerulosa of the adrenal cortex, which responds by secreting aldosterone.

Question 35

The adrenal glands secrete aldosterone in response to stimulation by angiotensin II.

Answer 35

True

Question 36

Plasma potassium is regulated by the sodium pump activity of the proximal tubules.

Answer 36

False Plasma potassium is regulated by the activity of the cells of the distal tubule.

Question 37

Calcium absorption by the distal tubules is decreased by parathyroid hormone.

Answer 37

False Calcium absorption by the cells of the distal tubule is INCREASED by parathyroid hormone.

Question 38

Phosphate absorption by the proximal tubule is regulated by parathyroid hormone.

Answer 38

True

Question 39

The intercalated cells of the distal tubule secrete hydrogen ions to reabsorb bicarbonate from the tubular fluid.

Answer 39

True

Question 40

Without the buffering action of phosphate, the kidneys would be able to excrete less than 1 mmol of hydrogen ions each day.

Answer 40

True

Question 41

Following the intake of a large volume of water, a normal person can produce urine with an osmolality of less than 100 mOsm kg-1.

Answer 41

True

Question 42

The renal medulla has an osmotic gradient that increases from the border with the cortex to the renal papilla.

Answer 42

True

Question 43

The osmotic gradient in the renal medulla results from the transport of sodium and chloride ions from the thick ascending limb of the loop of Henle to the interstitial fluid.

Answer 43

True

Question 44

ADH is secreted by the anterior pituitary in response to a decrease in the osmolality of the blood.

Answer 44

False ADH is secreted by the POSTERIOR pituitary in response to an INCREASE in plasma osmolality.

Question 45

ADH acts on the collecting ducts to increase their permeability to water.

Answer 45

True

Question 46

What does ADH stand for? What does it do?

Answer 46

Antidiuretic hormone - The hypothalamus sends a message to the pituitary gland which releases ADH. This travels in the blood to your kidneys and affects the tubules so more water is reabsorbed into your blood. As a result you make a smaller volume of more concentrated urine. AKA vasopressin.