TOPIC 11 Control of K, Ca, Phosphate and Mg

Question 1

Total calcium in plasma: mEq/liter

Answer 1

Total calcium in plasma: 5 mEq/liter

Question 2

Total calcium in plasma: % distribution ionized, non-ionized and bound ?

Answer 2

50% in ionized form
40% bound to plasma protein
Amount bound to protein decreases with an increase in [H+]. Patients with alkalosis more susceptible to hypocalcemic tetany
10% bound in non-ionized form to other ions (phosphate, citrate)

Question 3

Amount of Ca bound to protein decreases with an increase in what ion?
what patients are more susceptible to this?

Answer 3

[H+]. Patients with alkalosis more susceptible to hypocalcemic tetany

Question 4

Ca Normal ion concentration: mEq/liter

Answer 4

2.4 mEq/liter (1.2 mmol/liter)

Question 5

Hypocalcemia:

Answer 5

increases muscle and nerve excitability (hypocalcemic tetany)

Question 6

Hypercalcemia

Answer 6

depressed neuromuscular excitability which

can lead to cardiac arrhythmias

Question 7

99% of calcium stored where?

Answer 7

bone
HUGE reservoir–if plasma concentration drops, body will move calcium from the bone
–if plasma concentration rises, body will move calcium back into the bone

Question 8

% Ca present in intracellular space and cell organelles

Answer 8

1%

Question 9

% Ca present in extracellular fluid

Answer 9

0.01%

Question 10

Parathyroid Hormone As with all ions, intake and output must be matched over time, with output changing to match match what?

Answer 10

to match the input

Question 11

PTH most important control agent for what?

Answer 11

calcium

Question 12

How is Parathyroid Hormone excreted?

Answer 12

90% excreted via gastrointestinal tract (feces) (≈900 mg/day)
10% excreted via kidneys (urine) (≈100 mg/day)

Question 13

PTH regulation accomplished through 3 actions: (stimulations)

Answer 13

Stimulation of bone resporption of calcium
Stimulation of vitamin D which stimulates calcium reabsorption by intestines
Direct stimulation of renal tubule reabsorption of calcium

Question 14

As extracellular calcium concentration falls: what is the parathyroid gland stimulated to do?
which does what?

(this is in regard to the bones)

Answer 14

Parathyroid gland directly stimulated to increase secretion of PTH
Increased PTH concentration stimulates bone to increase release of bone salts (resporption) which includes the release of large amounts of calcium

Question 15

As extracellular calcium concentration increases: what does the parathyroid gland do? which does what?

(this is in regard to the bones)

Answer 15

Parathyroid gland decreases PTH secretion
Decreased PTH concentration decreases salt
resporption to point where calcium will be added to the bone

Question 16

Difference between resp acidosis

Answer 16

increasing Volume of H+ with an end production of CO2

Question 17

When will we see phosphate in our urine?

Answer 17

if we have a higher than normal concentration and it exceeds our ability to reabsorb (Tmax

Question 18

Ca excretion rate ?

how much of body’s Ca are we actually filtering ?

Answer 18

Freely filtered, reabsorbed BUT NOT secreted
Excretion rate = Filtration–Reabsorption
Only filtering a very small percentage of the calcium that is actually present in the body!!!!!

Question 19

% Ca filtered load reabsorbed in the proximal tubule:

Answer 19

65% filtered load reabsorbed

Question 20

% Ca filtered load reabsorbed in the LOH?

Answer 20

25 to 30% filtered load reabsorbed

Question 21

% Ca filtered load reabsorbed in Distal tubule / Collecting tubule

Answer 21

4 to 9% filtered load reabsorbed

Question 22

% of Ca filtered load normally excreted?

Answer 22

Normally only 1% is excreted

Changes as plasma concentration changes (i.e. intake changes)

Question 23

Ca reabsorbed in the proximal tubule % carried via paracellular pathway and transcellular pathway ?

Answer 23

80% of amount reabsorbed carried by water via paracellular pathway
20% of amount reabsorbed via a transcellular pathway

Question 24

Ca reabsorbed via transcellular pathway works how? diffusion driven by what? and pumped out via what?

In Proximal Tubule

Answer 24

Diffusion through luminal membrane into cell driven by chemical gradient (higher [Ca++] in lumen than inside cell) AND by electrical gradient (interior of cell negative with respect to lumen
Pumped out of cell across basolateral membrane via Ca ATPase pump and Na-Ca counter-transport mechanism

Question 25

Ca % of reabsorption by paracellular pathway ? | In Thick Ascending Loop of Henle

Answer 25

Paracellular pathway accounts for 50% of reabsorption in loop Transcellular pathway accounts for 50% of reabsorption in loop

Question 26

Ca reabsorbed by paracellular pathway --- via how? | In Thick Ascending Loop of Henle

Answer 26

Passive diffusion down electrical gradient–lumen has slight positive charge compared to interstitial fluid

Question 27

Ca reabsorbed by Transcellular pathway -- what process? | In Thick Ascending Loop of Henle

Answer 27

Active process stimulated by PTH, Vitamin D (Calcitrol), and calcitonin (PTH concentration most important)

Question 28

In the Distal Tubulal - Ca Reabsorption is transported almost all via what pathway? and what type of transport is it?

Answer 28

Almost all transport via Transcellular pathway Active transport across basolateral membrane –diffusion into cell Increased [PTH] increases Ca ++ reabsorption Reabsorption also increased by Vitamin D and calcitonin

Question 29

In the Distal Tubulal - increased PTH does what to Ca++?

Answer 29

Increased [PTH] increases Ca++reabsorption | Reabsorption also increased by Vitamin D and calcitonin

Question 30

PTH is a Primary controller of what?

Answer 30

Regulation of Ca++Reabsorption / Excretion

Question 31

INCREASED Ca reabsorption means there is an increase in what 2 other things too?

Answer 31

From an ⬆️ PTH and there is an increase with that Plasma Phosphate Vit D3

Question 32

INCREASED Ca reabsorption caused by a decrease in what?

Answer 32

Caused by a ⬇️ BP and ECFV

Question 33

INCREASED Ca reabsorption caused by what kind of acid base status ?

Answer 33

Metabolic Acidosis

Question 34

Decreased Ca reabsorption caused by increase in what 2 things ?

Answer 34

⬆️ BP and ECFV

Question 35

Decreased Ca reabsorption caused by a decrease in what?

Answer 35

⬇️ PTH and goes along decrease Plasma Phosphate

Question 36

Decreased Ca reabsorption caused what kind of acid base status ?

Answer 36

Metabolic Alkalosis

Question 37

PTH has no effect in what Tubule (Following sodium and water reabsorption)

Answer 37

in Proximal Tubule | Following sodium and water reabsorption

Question 38

[Phosphate] affects [PTH]–As [Phosphate] increases, [PTH] does what?

Answer 38

increases

Question 39

[H+] major affect is on the transport | mechanisms in what Tubule?

Answer 39

Distal Tubule

Question 40

If filtered load under Tmax, all phosphate is what?

Answer 40

all phosphate reabsorbed

Question 41

If filtered load over Tmax, phosphate is what?

Answer 41

phosphate is excreted

Question 42

Phosphate Plasma threshold level is approx? mMol/L | Phosphate Normal plasma concentration around mMol/liter?

Answer 42

-0.8 mMol/liter -1 mMol/liter –Large intake of phosphate each day (milk & meat)

Question 43

Proximal Tubule: % of of filtered phosphate reabsorbed

Answer 43

75 to 80% Enters cells from lumen via Na -Phosphate co-transport mechanism Leaves cell via counter-transport mechanism across basolateral membrane

Question 44

Phosphate reabsorbed into Proximal Tubule by what transport mechanism?

Answer 44

Phosphate co-transport mechanism | Leaves cell via counter-transport mechanism across basolateral membrane

Question 45

Phosphate reabsorbed amount in LOH?

Answer 45

Loop of Henle: Very small amounts

Question 46

Phosphate reabsorbed amount in Distal Tubule?

Answer 46

10% of filtered phosphate reabsorbed

Question 47

Phosphate reabsorbed amount in Collecting Tubule?

Answer 47

Very small amounts

Question 48

Approximately what % of filtered phosphate is excreted?

Answer 48

10%

Question 49

Phosphate Tmax can change based on what?

Answer 49

intake | -Low intake, Tmax will increase over time

Question 50

As PTH increases bone resorption of what two other substances are also reSORBED?

Answer 50

calcium & phosphate are also resorbed

Question 51

Magnesium - where is it stored/located?

Answer 51

>50% stored in bone Most of what is left is located in the intracellular volume <1% located in extracellular volume

Question 52

Renal excretion of magnesium is ≈ what % of filtered load?

Answer 52

10 to 15% of filtered load

Question 53

TOTAL plasma magnesium = 1.8 mEq/liter BUT what % is bound? making what new amount free?

Answer 53

>50% is bound to plasma proteins so free ionized is 0.8 mEq/liter

Question 54

What % of Mg is absorbed in the GI tract?

Answer 54

only 50% is actually absorbed by the gastrointestinal tract

Question 55

What % of filtered load of Mg is reabsorbed in the Proximal Tubule?

Answer 55

Proximal Tubule: 25% of filtered load

Question 56

What % of filtered load of Mg is reabsorbed in the Loop of Henle?

Answer 56

Primary site of reabsorption–65% of filtered load

Question 57

What % of filtered load of Mg is reabsorbed in the Distal Tubule / Collecting Tubule?

Answer 57

<5% of filtered load

Question 58

⬆️ [Magnesium] results in what to reabsorption and excretion?

Answer 58

⬇️ reabsorption and ⬆️ excretion

Question 59

⬆️ EC fluid volume results in what to reabsorption and excretion?

Answer 59

⬇️ reabsorption and ⬆️ excretion

Question 60

⬆️ [Ca++] results in what to reabsorption and excretion?

Answer 60

⬇️ reabsorption and ⬆️ excretion

Question 61

K levels fluctuations?

Answer 61

Tightly controlled | –Usually changes less than ± 0.3 mEq/liter

Question 62

K amount %'s in intracellular & extracellular spaces?

Answer 62

98% located intracellular volume | –only 2% extracellular

Question 63

K first line of defense against changes in | extracellular concentration?

Answer 63

Movement between intra and | extracellular compartments possible

Question 64

K elimination how?

Answer 64

Only 5 to 10% of intake removed by feces | –rest must be removed by kidneys

Question 65

Insulin moves what 2 things into the cells following a meal?

Answer 65

potassium AND glucose

Question 66

Factors that shifts K+ into cells (Potential hypo) (4)

Answer 66

Insulin Aldosterone (also increase K secretion) Alkalosis Β-adrenergic stimulation

Question 67

Factors that shifts K+ out of cells (Potential hyper) (7)

Answer 67

``` Insulin deficiency Aldosterone deficiency Acidosis B-adrenergic blockade Cell lysis Strenuous exercise Increased extracellular fluid osmolarity ```

Question 68

Epinephrine stimulates β2-adrenergic receptors increasing movement of K+ where?

Answer 68

into the cell.

Question 69

β2-adrenergic blocking agents treats what? and can lead to what?

Answer 69

hypertension) can lead to hyperkalemia

Question 70

Increased [H+] will reduce action of Na-K ATPase with less transfer of what into the cells?

Answer 70

K+ into the cells

Question 71

With an increase in extracellular K osmolarity, water moves out of the cell increasing _____ [K+] which increases the rate of K+ diffusion ______

Answer 71

intracellular out of the cell

Question 72

Consistent Reabsorption of K % in proximal tubule?

Answer 72

65%

Question 73

Consistent Reabsorption of K % loop (mainly thick ascending segment)?

Answer 73

25 to 30%

Question 74

With normal K+ intake of 100 mEq/day what would feces and kidneys remove?

Answer 74

Feces removes 8 mEq | Kidneys must remove 92 mEq

Question 75

High potassium intake Distal tubule & cortical collecting tubule increase potassium what?

Answer 75

increase potassium secretion Very strong mechanism–rate of potassium excretion can exceed amount of potassium being filtered

Question 76

Low potassium intake -- Secretion rate does what?

Answer 76

decreases Can decrease secretion to point where there is net reabsorption Excretion can fall to 1% of filtered potassium (756 mEq/day x 0.01 = 8mEq/day)

Question 77

Principal Cells | Make up what % of cells in late distal and cortical collecting tubule?

Answer 77

90%

Question 78

Intercalated Cells Reabsorb what? In distal tubule and cortical collecting duct

Answer 78

Reabsorb potassium especially during potassium depletion

Question 79

H-K ATPase located where? and pumps what which ways? All taking place in distal and cortical collecting duct

Answer 79

Located tubular membrane Pumps H+ from tubular cell into lumen (secretion) Pumps K+ from tubular lumen into cell (reabsorption) K+ diffuses from cell into interstitial space via basolateral membrane

Question 80

H-K ATPase major effect only during what depletion? In distal and cortical collecting duct

Answer 80

Major effect only during potassium depletion

Question 81

Increased [H+] will do what to potassium secretion? In distal and cortical collecting ducts

Answer 81

DECREASE

Question 82

Stimulation of Potassium Secretion by what 3 things? In distal tubules and cortical collecting ducts

Answer 82

Increased extracellular [K+] Increased [aldosterone] Increased tubular flow rate

Question 83

Increased aldosterone increases rate of sodium reabsorption by what parts of the nephron?

Answer 83

late distal tubule and collecting duct

Question 84

[K+] of renal interstitial fluid increases (increased plasma concentration) which decreases amount of K+ diffusing from cell interior _____

Answer 84

into interstitial space

Question 85

Plasma Potassium & Aldosterone | Great example of _____ control system

Answer 85

negative feedback Factor being controlled (potassium) as feedback effect on controller (aldosterone)

Question 86

Small change in plasma [K+] produced __ change in aldosterone concentration

Answer 86

huge Normal aldosterone level is approximately 6 nag/dL

Question 87

Anything that affects our ability to produce aldosterone will have a big effect on ____ excretion!!

Answer 87

potassium

Question 88

High aldosterone (primary aldosteronism) --- ___kalemia

Answer 88

Hypokalemia

Question 89

Low aldosterone (Addison’s disease)- ___kalemia

Answer 89

Hyperkalemia

Question 90

Acidosis (___ H+) _____ potassium secretion

Answer 90

(INCREASED H+) reduces potassium secretion Reduces the activity of Na-K ATPase–decreases driving force for moving potassium from cell interior to tubular lumen Prolonged acidosis produces increased potassium excretion –Result of decreased reabsorption of sodium chloride and water in proximal tubule and increased distal tubular flow

Question 91

Alkalosis (___ H+) _____ potassium secretion

Answer 91

( Decreases H+) increases potassium secretion

Question 92

Increased distal tubular flow rate will ____ potassium secretion?

Answer 92

increase | Increased tubular flow rate can be caused by volume expansion; high sodium intake; specific diuretics