Renal Physiology VIII

Question 1

The function of Calcitriol is to maintain plasma levels of

Answer 1

Ca2+ and PO4

Question 2

To accomplish this, calcitriol targets the renal tubules

and does which two things?

Answer 2

1. ) Stimulates Ca2+ reabsorption

2. ) Blocks PO4 excretion

Question 3

Calcitriol augments PTH-dependent Ca2+ reabsorption in the

Answer 3

Distal nephron

Question 4

A powerful stimulant of Ca2+ and PO4 absorption from the small intestine (CaHPO4)

Answer 4

Calcitriol

Question 5

In addition, Calcitriol induces Ca2+ and PO4 reabsorption from

Answer 5

Bone

Question 6

During renal failure, the lack of calcitriol may play into the condition of

Answer 6

Secondary hyperparathyroidism

Question 7

The overwhelming majority (approximately 99%) of body Ca2+ stores are housed within

Answer 7

Bone

Question 8

There is a modicum of Ca2+ existing predominantly in bound form within the

Answer 8

ICF and ECF

Question 9

Upon filtration from the glomeruli, Ca2+ reabsorption from the renal tubules follows the same general pattern as that of

Answer 9

Na+

Question 10

The vast majority of the filtered load of Ca2+ is reabsorbed from the

Answer 10

Proximal tubule

Question 11

Within the proximal tubule, this process is coupled to

Answer 11

Na+ and H2O reabsorption

Question 12

However, Ca2+ moves mainly via the

Answer 12

Paracellular route

Question 13

Within the TAL, Ca2+ reabsortion is again coupled to Na+ through the membrane potential gradients that are generated by

Answer 13

NKCC

Question 14

Thus loop diuretics that block Na+ reabsorption also impair Ca2+ reabsorption from the

Answer 14

TAL

Question 15

Within the distal tubule, Ca2+ reabsorption is stimulated by PTH and augmented by

Answer 15

Calcitriol

Question 16

Hence, elevated PTH will induce

Answer 16

Hypocalciuria

Question 17

Promote Ca2+ reabsorption from the distal tubule

Answer 17

Thiazide diuretics

Question 18

To summarize, in response to depressed blood [Ca2+], PTH is secreted by the parathyroid glands in order to do what two things?

Answer 18

1. ) Mobilize Ca2+ stores form bone

2. ) Thwart Ca2+ excretion by promoting reabsorption

Question 19

Targets the proximal tubule to impair PO4 reabsorption and facilitates Ca2+ reabsorption from the distal tubules

Answer 19

PTH

Question 20

In response to a PTH challenge, what would happen to the urinary concentrations of PO4 and Ca2+

Answer 20

Urine [PO4] would increase and urine [Ca2+] would decrease

Question 21

Secondary hyperparathyroidism is known as

Answer 21

High bone turnover renal osteodystrophy

Question 22

During chronic renal disease, Ca2+ reabsorption from the tubules is impaired; this results in

Answer 22

Hypocalcemia

Question 23

Recall that hypocalcemia is the predominant stimulus for

Answer 23

PTH secretion

Question 24

Since calcitriol is also produced within the kidney, chronic renal disease results in

Answer 24

Impaired calcitriol synthesis

Question 25

Without calcitriol, Ca2+ reabsorption from the kidney and GI tract is

Answer 25

Blunted (exacerbates hypocalcemia)

Question 26

Recall that calcitriol can block PTH secretion; therefore, diminished calcitriol production can exacerbate

Answer 26

Hyperparathyroidism

Question 27

Finally, as renal function is lost, we see the retention of

Answer 27

PO4

Question 28

Can directly induce hypocalcemia and has been shown to cause parathyroid hyperplasia

Answer 28

Hyperphosphatemia

Question 29

Note that extra-skeletal calcifications (metastatic calcification) may occur within the

Answer 29

Heart, skeletal muscle, lungs, and large blood vessels

Question 30

Myopathy and severe muscle weakness often occur with

Answer 30

Advanced renal failure

Question 31

A condition of inadequate production of, or resistance to PTH

Answer 31

Hypoparathyroidism

Question 32

As has been discussed, within the kidney PTH stimulates the production of calcitriol as well as the reabsorption of Ca2+ from the

Answer 32

Distal nephron (more specifically the distal convoluted tubule)

Question 33

Clinical signs of hypoparathyroidism are

Answer 33

Hypocalcemia, hyperphosphatemia, and low urinary Ca2+

Question 34

In hypoparathyroidism, we see a disruption in calcitriol production, this leads to which 2 tings?

Answer 34

1. ) Reduction in the ability to absorb dietary Ca2+ in small intestines 2. ) Reabsorption of Ca2+ in DCT is prevented

Question 35

Maintenance treatment of hypoparathyroidism involves the use of a form of -goal is to restore serum Ca2+ to just below normal

Answer 35

Vitamin D

Question 36

Why do we want to restore serum Ca2+ to just below normal levels when treating hypoparathyroidism?

Answer 36

Prevents symptoms of hypocalcemia while avoiding potential complications of elevated serum Ca2+

Question 37

Since PTH enables the reabsorption of Ca2+ from the distal nephron, low-normal serum Ca2+ must be maintained in order to prevent

Answer 37

Hypercalciuria and the resultant nephrolithiasis

Question 38

The kidney can 1. ) Concentrate urine approximately 2. ) Dilute urine approximately

Answer 38

1. ) 4-fold | 2. ) 10-fold

Question 39

The kindeys concentrating urine maintains body free H2O and is called

Answer 39

NEgtive free clearance

Question 40

The dilution of urine eliminates body free H2O and is called

Answer 40

Positive free H2O

Question 41

This process relies upon the

Answer 41

Countercurrent multiplier mechanism

Question 42

A key structure because of its ability to balance the concentrations of lumenal versus medullary interstitial NaCl and urea: the osmotic gradient

Answer 42

The loop of Henle

Question 43

Can the loop of Henle maintain the necessary osmotic gradients without help?

Answer 43

No

Question 44

A microvascular network that is intertwined among the loop of Henle

Answer 44

Vasa recta

Question 45

Establishes the so called counter-current exchange mechanism that maintains the hypertonicity of the medullary interstitium

Answer 45

Vasa Recta

Question 46

The vasa recta recycles NaCl, H2O, and a modicum of urea from the medullary interstitium back into

Answer 46

Systemic Circulation

Question 47

What are the three key properties of the vasa recta?

Answer 47

1. ) It's looped structure 2. ) Its relatively low blood flow 3. ) Its inability to perform active transport

Question 48

As blood descends the vasa, H2O loss from the plasma is initially

Answer 48

Robust

Question 49

H2O loss then declines precipitously toward the

Answer 49

Deep Medullary Zone

Question 50

Gradually increases from the more superficial to deep medullary zones

Answer 50

The influx of both NaCl and urea

Question 51

The diffusion of H2O and solutes occurs because of the medullary interstitial osmotic gradient that is supported by the

Answer 51

Nephron (counter-current multiplier)

Question 52

As blood ascends the vasa, solute loss (filtration) from the blood decreases because of the

Answer 52

Interstitial osmotic gradient

Question 53

However, as blood ascends the vasa, we see the promotion of

Answer 53

H2O reabsorption from the interstitium

Question 54

Does the blood leaving the vasa have more or less H2O and solutes than the blood that entered?

Answer 54

More (especially NaCl)

Question 55

Through this mechanism with the vasa recta, NaCl is translocated from the interstitium, back into

Answer 55

Systemic circulation

Question 56

The functional nephron operates as two looped tubes flowing in

Answer 56

Parallel

Question 57

The delivery system is the selectively permeable

Answer 57

Nephron proper (proximal tubule)

Question 58

Receives H2O, NaCl, K+, urea, etc. (as filtrate from glomerular blood); most of which is reabsorbed into the interstitium BECAUSE the interstitium contains osmotic gradients

Answer 58

Proximal Tubule

Question 59

Assists in maintaining the interstitial osmotic gradients by recycling H2O, NaCl, etc. back into systemic circulation

Answer 59

Vasa Recta

Question 60

Recall that changes in renal perfusion (i.e. renal BP) represent an immediate and profound signal to trigger alterations in renal

Answer 60

H2O and Na+ Handling