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FHB Exam 2 > Renal > Flashcards

Renal Flashcards

1
Q

What are the 8 functions of the kidneys?

A

1) Excrete metabolic waste
2) Regulate water and electrolyte balance
3) Regulate ECF volume
4) Regulate plasma osmolality
5) Regulate RBC production
6) Regulate vascular resistance
7) Regulate acid/base balance
8) Regulate vitamin D production

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2
Q

True or false: The kidneys synthesize electrolytes to respond to low plasma osmolarity

A

False. The kidneys cannot synthesize electrolytes (or water). They regulate water/electrolyte balance by manipulating the excretion to match the input

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3
Q

How does plasma osmolality change?

A

When inputs/outputs of water and dissolved solids are changed disproportionally (drinking pure water or eating a salty meal)

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4
Q

How do the kidneys regulate RBC production?

A

The kidneys produce a peptide hormone called eythropoietin in response to decreased partial pressure of O2 sensed in the cortical interstitium

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5
Q

How can anemia develop from renal failure?

A

The kidneys have lower metabolisms when failing, which results in a lower O2 consumption and thus a higher tissue pO2 in the cortex. This “tricks” they interstitial cells into decreasing production of erythropoietin which leads to anemia

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6
Q

What pathway leads to the renal regulation of vascular resistance?

A

The renin-angiotensin-aldosterone system has a major effect on vascular smooth muscle, thus regulating vascular resistance and blood pressure

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7
Q

What are the components of the urinary system?

A

Kidney, ureter, bladder, urethra

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8
Q

Describe the location of the pyramids within the kidney.

A

The bases of the pyramids are found at the corticomedullary border (closer to outside of kidney) and the apexes are located at the papilla within the minor calyxes

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9
Q

What structures are found “downstream” from minor calyxes?

A

Minor calyces empty into major calyces which feed into the renal pelvis (most expanded region of the ureter)

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10
Q

What are the major components of the nephron?

A

In order of flow: Renal corpuscle, proximal tubule, loop of Henle, distal tubule, and collecting duct system

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11
Q

What are the parts of the renal corpuscle?

A

The glomerular capillaries (vascular system) and the Bowman’s capsule (beginning of tubular system)

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12
Q

Describe the orientation of the thick ascending limb with respect to the afferent and efferent arterioles

A

The end of the thick ascending limb passes between the afferent and efferent arterioles of the same nephron. This region is called the macula densa.

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13
Q

What is the juxtaglomerular apparatus?

A

The JGA is made up of the macula densa of the thick ascending limb, extraglomerular mesangial cells and the renin-angiotensin II producing granular cells of the afferent arterioles.

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14
Q

What are podocytes?

A

Epithelial cells that cover the glomerular capillaries. They form the visceral layer of Bowman’s capsule and make up the filtration barrier along with the capillary endothelium and basement membrane.

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15
Q

Which component of the filtration barrier is a charge-selective filter?

A

The basement membrane contains many negatively charged proteins that form a charge-selective barrier

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16
Q

Which component of the filtration barrier is a size-selective filter?

A

The podocytes encircling the capillary endothelium are separated by gaps called filtration slits which form the size-selective filter that keeps large molecules out of Bowman’s space

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17
Q

What are the three layers of the filtration barrier?

A

The endothelium, the basement membrane and the foot processes of the podocytes

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18
Q

Which segments of the nephron contain many mitochondria?

A

The proximal tubule, thick ascending limb, and distal tubule

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19
Q

What cell types are found in the collecting duct?

A

Principal cells and intercalated cells

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20
Q

What is the difference in function between principal cells and the intercalated cells in the collecting duct?

A

Principal cells have few mitochondria and play important roles in reabsorption of NaCl and secretion of K+
Intercalated cells have many mitochondria and are involved with regulation of acid-base balance

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21
Q

What is the only cell type in the nephron that does not contain apically targeted cilia?

A

Intercalated cells are the only ones with out cilia in the tubule for mechanosensation

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22
Q

Where does blood not filtered in the glomerulus continue on to?

A

The efferent arteriole carries away unfilitered blood to the peritubular capillaries and the vasa recta

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23
Q

Do peritubular and vasa recta capillaries mix at all?

A

There is very little mixing. These two routes are parallel circuits.

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24
Q

What is clearance?

A

The volume of plasma completely cleared of a substance in one minute. If a substance is found in the urine, then the clearance > 0.
EXCRETORY function of the kidneys
C = Ux * V / Px

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25
Q

How are flow, concentration and load related?

A

Load (mg/min) = Concentration (mg/mL) * flow (mL/mn)

All three are basic units of renal function

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26
Q

What is the formula for conservation of mass in the kidney?

A 
IN = OUT
Pax*RPFa = (Pvx*RPFv) + (Ux*V)
Pax, Pvx = concentration of substance x in arteries/veins
RPFa, RPFv = renal plasma flow
Ux = urine concentration
V = urine blood flow rate
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27
Q

What are the four basic renal loads, and how are they related?

A

Filtration (F), Secretion (S), Reabsorption (R) and Excretion (E)
F + S = R + E (IN = OUT)

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28
Q

If Clearance < GFR, what happens to the substance?

A

The substance is filtered and reabsorbed

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29
Q

If C = GFR, what happens to the substance?

A

The substance is filtered

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30
Q

Can clearance be greater than GFR?

A

Yes. If the substance is secreted, than more of it can be cleared than the GFR

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31
Q

How can clearance be used to estimate GFR?

A

A substance that is not reabsorbed nor secreted but freely filtered will have a clearance equal to the GFR
F + S = R + E –> F = E because S = R = 0

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32
Q

If 120 mL/min of inulin is cleared in the urine, what is the GFR?

A

Inulin clearance equals GFR, so GFR = 120 mL/min

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33
Q

Although creatinine clearance is an estimate of GFR, why does it differ slightly?

A

Some creatinine is secreted, so the clearance is higher than GFR

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34
Q

What is the relationship between GFR and plasma creatinine levels?

A

Decreased GFR leads to increased plasma creatinine, although a large decrease is required to have detectably elevated creatinine

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35
Q

What quantity does PAH allow us to estimate?

A

Renal plasma flow

All PAH is removed from the plasma and excreted (via filtration and secretion)

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36
Q

How do you convert from renal plasma flow to renal blood flow?

A

RBF = RPF / (1-Hematocrit)

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37
Q

How is the filtration fraction calculated?

A

FF = GFR/ RPF = Cinulin/C_PAH

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38
Q

Rank these in order of magnitude: urine flow rate, renal blood flow, renal plasma flow, glomerular filtration rate

A

RBF > RPF > GFR > V

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39
Q

How do the components of ultrafiltrate and blood differ?

A

The ultrafiltrate has no proteins (RBCs, WBCs … etc)

The salt and organic compounds are similar between the two

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40
Q

What forces drive ultrafiltration across the capillaries?

A

Starling forces: hydrostatic and oncotic pressures

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41
Q

Describe the properties (size and charge) of molecules that are freely filtered

A

Neutral molecules smaller than 20 Angstroms (molecules between 20 and 42 are filter progressively less with increasing size)

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42
Q

At a given size, describe the difference in filtration between a cation, anion and neutral molecule

A

At any given size, cationic molecules are more readily filtered than neutral molecules, which are more readily filtered than anionic molecules

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43
Q

What is the formula for net ultrafiltration pressure? (starling equation)

A 
P = Pgc - Pbs - πgc + πbs
gc= glomerular capillaries
bs = bowman's space
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44
Q

What is the only force that favors filtration?

A

hydrostatic pressure within the glomerular capillaries

there is no oncotic pressure in Bowman’s capsule because no proteins are filtered

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45
Q

How does capillary oncotic pressure change along the length of the glomerular capillaries?

A

Capillary oncotic pressure increases along the length because fluid leaves but proteins stay

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46
Q

What is the main way that GFR is regulated?

A

By changing hydrostatic capillary pressure by changing the resistance of afferent and efferent arterioles

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47
Q

How do rates of filtration in the glomerulus differ from the rates in the systemic capillaries?

A

Much more filtration in the glomeruli

Kf is 100x greater in the glomerular and Pgc is twice as high

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48
Q

Describe the changes in GFR caused by changing the radius of the afferent and efferent arterioles.

A

GFR is increased by dilating the afferent arteriole or constricting the efferent arteriole.
GFR is decreased by constricting the afferent arteriole or dilating the efferent arteriole

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49
Q

How doe glomerulonephritis change GFR?

A

In the early stages, GFR is increased due to decreased πgc. In late stages the Pbs increases which decreases GFR

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50
Q

Describe the relative values of regional blood flow to the kidney

A

The renal cortex is highly vascularized (90% of RBF)
The outer medulla is lowly vascularized (8% of RBF)
The inner medulla is even less vascularized (2% RBF)

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51
Q

What are the only capillaries that go deep into the renal medulla?

A

Vasa recta

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52
Q

What is the major mechanism that keeps GFR constant?

A

Autoregulation via the myogenic mechanism

Smooth muscle cells constrict in response to stretching

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53
Q

What is tubuloglomerular feedback?

A

A negative feedback loop that helps maintain GFR
Increased GFR leads to increased [NaCl] in the tubular fluid. Increased [NaCl] is sensed by the macula densa, which releases a signal to increase the resistance of the afferent arteriole, thus decreasing GFR.

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54
Q

Why is tubular [NaCl] increased if GFR is high?

A

There is not enough time for normal levels of NaCl to be reabsorbed

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55
Q

What is the autoregulatory range for arterial pressures?

A

Autoregulation holds GFR and RBF constant between 100 mmHg and 180 mmHg

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56
Q

What percent of filtered water and NaCl end up being excreted in the urine?

A

Less than 1%

Nearly all the filtered water and NaCl is reabsorbed

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57
Q

What is the transcellular pathway?

A

Solutes crossing through cells via pumps and channels. This is a two step process.

Example: Na+ moves across cells by Na+/K+ ATPase pump

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58
Q

What is the paracellular pathway?

A

Solutes move between cells through tight junctions.
This is a one step process

Example: Ca, Mg, and K move between cells by solvent drag

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59
Q

What is the Fick principle in the kidneys?

A

If the blood flow to the kidneys decreases, then the kidneys require less oxygen
The difference between arterial and venous O2 stays the same unlike in skeletal muscle

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60
Q

How is glucose normally handled by nephrons?

A

Glucose s freely filtered. Normally, 100% of glucose is reabsorbed so none is excreted in the urine.

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61
Q

Describe the mechanism of glucose reabsorption in the early proximal tubule

A

The Na/K pump maintains a low intracellular Na. The Na gradient moves Glucose into the cell from the lumen via a Na/Glucose symporter. Glucose moves into blood from cells due to the glucose gradient (GLUT transporters)

62
Q

Describe the renal plasma threshold and what happens if glucose is greater than this value.

A

The RPT = 220 mg/dL
Above this value, some glucose will spill into the urine. The excreted amount increases until it parallels the filtered amount, signifying the transport maximum for glucose.

63
Q

What is splay?

A

RPT is reached before the Tm, so there is an increasing amount of splay as the excreted glucose increases to parallel the filtered load

64
Q

What is the formula for transport maximum?

A

Tm = (Pa * GFR) - (U * V)

65
Q

What is diuresis?

A

Urine flow > 1 mL/min
Low concentrations of ADH are in the plasma and water, urea are not reabsorbed as much.
Urine is high volume, low concentration

66
Q

What is an osmotic diuretic?

A

A molecule that holds excess water in the tubules via osmotic forces
Example: mannitol, glucose

67
Q

Describe what s reabsorbed in the proximal tubule

A

2/3 of filtered water, Na+, Cl- and K+

All of glucose and amino acids that are filtered

68
Q

What is the primary mechanism allowing for reabsorption of substances in the proximal tubule?

A

The Na/K ATPase pump provides the gradients and energy for movement of every substance including water

69
Q

Describe how sodium moves from the tubular lumen to the blood in the early proximal tubule

A

Na+ uptake via a Na+-H+ antiporter on the apical membrane
Na+ leaves the cell via Na/K ATPase pumps on the basolateral membrane
** There are also symporters that bring Na+ in from the tubular fluid coupling Na with glucose, Pi, amino acids, and lactate **

70
Q

In the proximal tubule, what does H+ secretion result in?

A

H+ secretion results in reabsorption of sodium bicarbonate into the bloodstream. This NaHCO3 provides the osmotic gradient responsible for the passive reabsorption of water

71
Q

How does Na reabsorption differ in the second half of the proximal from the first half of the tubule?

A

In the second half, Na reabsorption is coupled to Cl- rather than HCO3- or organic compounds

72
Q

Describe the transport mechanism of Na into the cells in the second half of the proximal tubule

A

Na enters the cell through the luminal membrane via parallel operation of a Na/H antiporter and one/more Cl-/anion antiporters. This results in a net uptake of NaCl into the cell. The H+-Anion complexes are recycled back out into the tubular fluid.

73
Q

What is isosmotic reabsorption?

A

When water reabsorption occurs in equal proportion with reabsorbed solutes, the concentration in the tubule remains the same

74
Q

What is the driving force for osmotic reabsorption of water across the proximal tubule?

A

Solutes accumulate in the lateral intracellular spaces which increases the osmolality of these compartments. This provides the osmotic gradient that causes water to move across the tubule.

75
Q

What is solvent drag?

A

When water moves across the transcellular and paracellular pathways, it “pulls” some solutes (mainly K+ and Ca2+) across the cells along with it.

76
Q

What percentage of protein is normally reabsorbed in the proximal tubule?

A

100%

77
Q

How do organic compounds move into the tubule?

A

Via Filtration and Secretion

78
Q

What does a urine/plasma osmolality ratio < 1.0 signify?

A

Diluted, pale urine, low [ADH]

79
Q

What is the different between permeabilities in the descending versus ascending loop of Henle?

A

In the descending limb, the tubule is permeable to H2O, but not NaCl, so the tubular fluid is concentrated by passive reabsorption of H2O
In the ascending limb, the tubule is impermeable to H2O, but permeable to NaCl, so NaCl moves out passively due to the gradient created by the descending limb.

80
Q

What are the channels and transporters involved with reabsorption of NaCl in the thick ascending limb?

A

1) NKCC2 symporter: moves Na+, 2Cl-, and K+ into the cell from the tubular fluid
2) K+ channel: on apical membrane, recycles K+ back out
3) Na-H+ antiporter on apical membrane
4) Basolateral Cl- channel
5) Na/K ATPase pump

81
Q

What is the electric charge of the tubular fluid in the loop of Henle?

A

It is positive. This causes passive paracellular reabsorption of cations due to electric repulsion.

82
Q

Is the early distal tubule permeable to water?

A

No. Water stays in the tubule while Na and Cl diffuse out, thus diluting the water in the tubular fluid

83
Q

What are the functional differences between principal cells and intercalated cells in the collecting duct?

A

Principal cells reabsorb NaCl and H2O and secrete K+

Intercalated cells secrete H+ or HCO3- and reabsorb K+

84
Q

Which of the following does not increase reabsorption of Na+ and Cl-: Angiotensin II, Aldosterone, Atrial Natriuretic Peptde, Sympathetic Nerves

A

ANP decreases reabsorption of Na+ and Cl- in response to increased ECF volume or increased blood pressure

85
Q

What are the routes that water is eliminated from the body?

A

The kidneys (urine)
Evaporation from skin and sweat
Respration
Fecal

86
Q

What are the compartments that make up total body water?

A

TBW (42L) is made up of ECF (14L) and ICF (28L)

ECF is further divided into interstitial fluid (10.5L) and plasma (3.5L)

87
Q

What is the normal osmolarity in every fluid compartment?

A

Around 300 mOsm/L

88
Q

What is positive water balance?

A

When intake of water is higher than loss of water

The kidneys respond to positive water balance by producing large volumes of hypoosmotic urine

89
Q

True or false: the kidneys control water excretion independently of excretion of Na+, K+ and urea

A

True. This allows water balance to be achieved without disrupting other homeostatic functions of the kidney

90
Q

What is ADH?

A

A peptide hormone produced in the hypothalamus and secreted from the posterior pituitary. Its main function is to retain body water in the distal convoluted tubule and collecting ducts of the kidneys

91
Q

What sensors are involved with the regulation of ADH?

A

Osmoreceptors in the hypothalamus sense the osmolality of body fluids and stimulate release of ADH to uptake more water.
Baroreceptors in the aortic arch and carotid bifurcation sense volume and pressure and inhibit the release of ADH leading to diuresis (large output of water).

92
Q

What regulatory molecules affect ADH levels?

A

Nicotine and Angiotensin II stimulate ADH release

ANP and ethanol inhibit ADH release

93
Q

How does plasma osmolality affect levels of ADH in the plasma?

A

Plasma [ADH] increases with increases in osmolality above 280 mOsm/kg H2O. Below 280, ADH levels are zero.
This is called “Osmotic Control” of ADH

94
Q

How does blood pressure affect levels of ADH in the plasma?

A

If blood pressure is decreased by about 10%, ADH levels increase in the plasma. ADH is not found in the bloodstream in response to increases in blood pressure.

95
Q

Describe the interaction between osmolality and blood volume/pressure stimuli on plasma ADH levels

A

There is a much sharper response to decreased plasma osmolality if volume or pressure is also decreased.

96
Q

Describe the mechanism of ADH increasing water permeability of the collecting duct

A

ADH interacts with V2 receptors on the basolateral surface of the collecting duct principal cells, stimulating Gs proteins leading to increased cAMP, increased PKA and the insertion of aquaporin 2 channels into the tubule. These channels increase permeability to water

97
Q

How does ADH affect urea permeability?

A

ADH increases urea permeability of the lower collecting duct. This permits the passive movement of urea into the deep renal medulla. The urea concentration builds up throughout the upper collecting duct, providing the gradient for passive transport.

98
Q

What are the axes on a Darrow-Yannet diagram?

A

The x-axis is compartment volume and the y-axis is compartment osmolarity
A vertical line represents the division between ICF and ECF

99
Q

What does a Darrow-Yannet diagram show us?

A

The equilibration states of fluid within the ECF and ICF in response to different disturbances.

100
Q

What are the three steps to using Darrow-Yannet diagrams to solve fluid shift problems?

A

1) Construct a normal DY diagram
2) Disturb the ECF compartment in terms of volume and osmolarity changes
3) If osmotic gradient exists, shift the water accordingly

101
Q

What is the major site in the nephron where solute and water are separated?

A

Henle’s loop

102
Q

What is antidiuresis?

A

A state of dehydration n which there are high concentrations of ADH in the plasma. Water and urea are reabsorbed and urine is low volume and high concentration

103
Q

Describe the osmolality changes as you move deeper into the kidney (from cortex to medulla)

A

The renal cortex is isotonic with plasma (300 mOsm/kg H2O)
Outer medulla is mildly hyperosmolar (300-480)
Inner medulla is strongly hyperosmolar (480-1200)

104
Q

What gradient allows for the concentration of urine in the distal tubule and collecting ducts?

A

The osmotic gradient that is produced in the loop of henle allows for concentration of urine in the presence of ADH

105
Q

What are the major species contributing to the inner medullary hyperosmolality?

A

Na (25%), Cl (25%), and urea (50%)

Total: 1200 mOsm/L

106
Q

What are the three mechanisms that cause the medullary hyperosmolality?

A

Countercurrent multiplier
Urea cycle
Countercurrent exchanger

107
Q

What is the countercurrent multiplier?

A

Vertical osmotic gradients are produced due tot he differential fluid and solute movement down and up the loop.
Descending loop: water permeable, solute impermeable
Ascending loop: water impermeable, solute permeable

108
Q

What portion of the nephron has the most active salt pumping in the kidney?

A

The thick ascending loop

Salt is pumped out and water stays in, making the fluid hyposmotic

109
Q

Describe the urea cycle

A

Urea is an end product of metabolism that is waste to be excreted

  • The upper collecting duct is impermeable to urea, so concentration goes up as fluid leaves
  • Urea can leave the lower collecting duct in the presence of ADH
  • Urea is picked up by ascending vasa recta and recycled into the descending loop of henle to repeat the process
110
Q

Does high medullary urea concentration set up an osmotic gradient for water reabsorption?

A

No. The gradient allows urea to be excreted in low volume urine. Because the lower collecting duct s permeable to urea, the urine urea concentration equilibrates with the medullary urea concentration

111
Q

What is the countercurrent exchanger?

A

The passive movement of water, salt and urea across the vasa recta capillary walls in the renal medulla to maintain the hyperosmotic gradient

  • Water moves out of the descending vasa recta down the osmotic gradient and into the ascending vasa recta
  • Salt moves out of the ascending vasa recta down the concentration gradient and into the descending vasa recta
112
Q

What are the net effects of countercurrent exchange?

A
  • The vasa recta concentration is higher exiting than entering
  • Water shunt keeps water out of the deep medulla
  • Salt trap keeps solutes in the deep medulla
113
Q

What happens if vasa recta flow is increased?

A

The medullary gradient is washed out and urine flow increases. There is less time for movement of Na, Cl and urea if flow increases.

114
Q

What is osmolar clearance?

A

An assessment of renal diluting/concentrating abilty
Equation: Cosm= (Uosm/Posm)*V
If U/P > 1, urine is concentrated (ADH antidiuresis)
If U/P < 1, urine is diluted (water diuresis)

115
Q

What is free water clearance?

A

CH2O: the amount of pure water the kidney adds to the urine to dilute it below the osmolality of blood
-CH2O: the opposite, amount of water kidney removes to concentrate urine

116
Q

What are the two components of urine flow?

A

V = Cosm + CH2O

Urine flow is made up of osmolar clearance and free water clearance

117
Q

Under normal physiologic conditions, how do alterations in Na+ balance change the volume and [Na+] of the ECF?

A

Volume changes, but [Na+] is maintained constant by the ADH and thirst systems

118
Q

What is effective circulating volume?

A

The portion of extracellular fluid volume within the vascular system that is effectively perfusing tissues.
ECV varies directly with volume of ECF, volume of vascular system, blood pressure and cardiac output

119
Q

How would a decrease in arterial pressure affect ECV?

A

Decreased AP will be sensed as decreased ECV by the volume sensors of the vascular system

120
Q

Describe low-pressure sensors and their effect on ECV

A

1) Natriuresis: atrial myocytes are stretched, they will produce ANP and release it. ANP decreases blood pressure by increasing NaCl excretion thus decreasing ECV.
2) Diuresis: engorgement of pulmonary vasculature decreases sympathetics and decreases ADH thus decreasing ECV

121
Q

Describe high-pressure sensors and their effect on ECV

A

Aortic and carotid baroreceptors sense high pressure and decrease sympathetics which decreases ADH and decreases ECV
Low tubular flow stimulates the JGA to release renin, which increases ECV via the RAA system

122
Q

What do increases in renal sympathetic nerve activity do to GFR, Renin and Na reabsorption?

A

Sympathetic stimulation decreases GFR, increases renin and increases Na reabsorption (via RAA system)

123
Q

What three factors stimulate renin secretion?

A

Perfusion pressure
Sympathetic nerve activity
Delivery of NaCl to the macula densa

124
Q

What is tubuloglomerular feedback?

A

Reduced delivery of NaCl to the macula densa regulates the GFR by increasing renin secretion which increases ECV and thus GFR

125
Q

What are the downstream events from increased circulating renin?

A

Renin converts angiotensinogen to angiotensin I.
Angiotensin converting enzyme in lungs converts AT-I to AT-II
AT-II stimulates ADH release from the posterior pituitary and causes thirst
AT-II also stimulates aldosterone release from the adrenal cortex, which increases water reabsorption

126
Q

What effect does aldosterone have on the kidney?

A

In the distal tubule and collecting duct, aldosterone stimulates the production of new Na/K ATPase pumps
More pumps increases Na reabsorption and K+ secretion, which leads to greater K+ excretion

127
Q

How does the affect of ANP compare to that of the RAA system?

A

ANP antagonizes the RAA system
ANP is produced in response to increased ECF volume, arterial pressure and venous pressure
ANP causes water diuresis, natriuresis, and decreases the concentrations of aldosterone and renin

128
Q

How much of filtered Na+ is reabsorbed in euvolemia?

A

99% of Na+ is normally reabsorbed

129
Q

What are the 3 responses of the nephron to increased ECV?

A

Increased GFR
Decreased Na+ reabsorption in proximal tubule
Decreased Na+ reabsorption in collecting duct

130
Q

What are the two most common causes for generalized edema?

A

Increased capillary hydrostatic pressure

Decreased capillary osmotic pressure

131
Q

What are the two sets of regulatory mechanisms that safeguard K+ homeostasis?

A

1) [K+] is regulated in the ECF

2) [K+] is regulated in the kidneys to match excretion with intake

132
Q

How much of K+ in the body is found within cells?

A

98% of K+ is intracellular

Normal concentration: 150 mEq/L

133
Q

What are the ranges of [K+] that define hyperkalemia and hypokalemia?

A

[K+]ecf > 5.0 mEq/L = hyperkalemia

[K+]ecf < 3.5 mEq/L = hypokalemia

134
Q

Why doesn’t plasma [K+] rapidly rise after a meal?

A

Ingested K+ is rapidly uptaken into cells in the GI tract. This absorbed K+ is eventually excreted by the kidneys

135
Q

What compounds trigger movement of K+ into cells?

A

Insulin, Epinephrine (beta receptors) and aldosterone

136
Q

What are the possible destinations of K+ in the extracellular fluid?

A

Either stored in tissue or excreted in the urine

137
Q

What can cause K+ release from cells?

A

Epinephrine (alpha receptors)
Cell lysis
Hyperosmolality of the ECF –> cells shrink –> concentrate K+ inside cell –> gradient pushes K+ out

138
Q

What is the most important hormone that shifts K+ into cells?

A

Insulin

139
Q

What 3 factors regulate the rate of K+ secretion by the distal tubule and collecting duct?

A

1) Na/K ATPase pump
2) Tubular cell to tubular lumen electrochemical gradient
3) K+ permeability of apical membrane

140
Q

How does K+ transport in the distal tubule differ between potassium depletion and normal/increased K+ intake?

A

In depletion, K+ is reabsorbed in the DT to preserve K+

If K+ is normal or in excess, K+ is secreted and eventually excreted by the nephron to lower [K+]

141
Q

What hormones alter K+ secretion?

A

Aldosterone increase K+ secretion
Glucocorticoids increase K+ secretion
(ADH has no net effect on K+ secretion)

142
Q

How does tubular fluid flow affect K+ secretion?

A

Increased flow rate (diuresis) increases K+ secretion and decreases ADH. Decreases in ADH decrease K+ secretion, thus maintaining K+ balance

143
Q

Describe the affect of metabolic acidosis on K+ secretion over time (acute and chronic)

A

In the short term, metabolic acidosis decreases K+ secretion and excretion, but as the acidosis becomes chronic, K+ secretion and excretion increase

144
Q

What are the two main factors contributing to Ca2+ homeostasis?

A

Amount of Ca2+ in the body

The balance between Ca2+ in the bone and the ECF

145
Q

Describe the route of the Ca2+ ingested from diet?

A

About 1500 mg/day are ingested, 1300 mg of which are excreted in feces. The other 200 mg are absorbed in the GI tract and then excreted in urine

146
Q

What effect does calcitriol have on renal handling of Ca2+?

A

Increased calcitriol leads to increased renal absorption and decreased excretion

147
Q

What hormone(s) cause(s) increased plasma Ca2+?

A

PTH and calcitriol

PTH increases bone reabsorption, kidney reabsorption and calcitriol (which facilitates the actions of PTH)

148
Q

What hormone(s) cause(s) decreased plasma Ca2+?

A

Calcitonin increases bone deposition, thus decreasing plasma Ca2+ levels

149
Q

What controls Ca2+ excretion?

A

hormonal regulation
PTH and calcitriol decrease Ca2+ excretion
Calcitonin increases Ca2+ excretion

150
Q

What effects do PTH, calcitriol and Calcitonin have on phosphate plasma concentrations?

A

PTH and calcitriol increase plasma phosphate

Calcitonin decreases plasma phosphate

151
Q

If plasma phosphate is elevated, what happens to urine phosphate levels?

A

Urine phosphate levels will be greater than zero if plasma phosphate is elevated because kidneys are normally reabsorbing phosphate at maximum levels.

FHB Exam 2 (3 decks)

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