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Module 12 - Renal and Urologic Disorders > Renal Function > Flashcards

Renal Function Flashcards

1
Q

What are the functions of the kidney?

A
  1. Filtering of blood and excretion of waste products
  2. Regulation of acid-base balance
  3. Regulation of blood volume and osmolality
  4. Regulation of blood electrolyte levels
  5. Release of ertyhropoietin
  6. Synthesis of calcitriol (active form of Vit D)
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2
Q

What is Urea?

A
  • a nitrogenous waste product of amino acid metabolism in the liver
  • urea is transported in the blood (BUN) to the kidney to be excreted
  • ongoing process - usually a small, but stable level of urea in the blood
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3
Q

What is creatinine?

A
  • A nitrogenous waste product of creatine phosphate breakdown in muscle
  • blood levels are higher in those with greater muscle mass and decrease with muscle loss
  • levels fluctuate with dietary meat intake
  • levels are not impacted by liver function, like urea
  • all creatinine is excreted by kidneys
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4
Q

How do the kidneys excrete Urea and creatinine?

A
  • both freely filtered by glomerulus
  • urea (50%) is reabsorbed, and creatinine is not
  • blood urea levels are normally higher than creatinine
  • BUN: Cr ratio is normally 10-20:1
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5
Q

How are the kidneys involved in acid-base regulation?

A

Regulate pH by altering:
- amount of HCO3 reabsorbed
- amount of H+ secreted

Renal compensation for acid-base imbalances takes hours or days

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6
Q

What is the effect of respiratory acidosis on urine pH?

A
  • respiratory acidosis = retention of CO2
  • H+ secreted and HCO3- is reabsorbed
  • pH of urine decreases (more acidic)
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7
Q

What are the effects of metabolic alkalosis on urine pH?

A
  • metabolic alkalosis = loss of H+
  • lungs respond first (slow, shallow breaths) - CO2 increases - converted to carbonic acid which dissociates into H+ and HCO3-
  • kidneys excrete more HCO3-
  • pH increases (more alkaline)
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8
Q

In osmoregulation, water intake and loss are adjusted to maintain plasma osmolality (Posm) at?

A

aprox 300 mOsm/L

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9
Q

How is blood K+ regulated?

A
  • K+ is filtered, reabsorbed and secreted
  • typical diet contains excess of K+
  • secretion occurs in the late DCT and CD under the influence of aldoseterone
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10
Q

How is blood Ca2+ regulated?

A
  • Cells of the early DCT have receptors for parathyroid hormone.
  • PTH binding stimulates Ca2+ reabsorption
    • kidneys also function in the activation of Vit D
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11
Q

What are the 3 key functions performed by the nephrons?

A
  1. glomerular filtration
  2. tubular reabsorption
  3. tubular secretion
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12
Q

How does glomerular filtration occur?

A
  • filtration pressures force water and solutes (ions, glucose, urea, etc.) through the filtration membrane
  • produces a cell-free and protein-free filtrate in the capsular space
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13
Q

What are the 3 pressures that glomerular filtration depends on?

A
  1. Glomerular Blood Hydrostatic Pressure (GBHP)
  2. Capsular Hydrostatic Pressure (CHP)
  3. Blood Colloid Osmotic Pressure (BCOP)
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14
Q

What is Glomerular Blood Hydrostatic Pressure (GBHP)?

A

Pressure that pushes water and solutes out of the blood thorugh the filtration membrane.

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15
Q

What is capsular hydrostatic pressure

A

Pressure of filtrate in teh capsular space pushing against the filtration membrane.

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16
Q

What is Blood Colloid Osmotic Pressure (BCOP)

A

Pressure exerted by plasma proteins that tend to pull water out of the filtrate and into the blood.

17
Q

What is the glomerular filtration rate (GFR)?

A

The volume of filtrate produced per minute by both kidneys (105-125 mL/min)

18
Q

GFR is proportional to what 3 things?

A
  1. net filtration pressure (mainly GBHP)
  2. surface area available for filtration
  3. permeability of the filtration membrane
19
Q

GFR is measured in order to?

A
  1. assess kidney function
  2. determine renal clearance to guide drug dosages
  3. monitor drug therapies that can damage kidneys
  4. monitor effectiveness of treatment for kidney disease
  5. assess kidney function in a potential donor for transplantation
20
Q

What happens with elevated GFR?

A

Needed substances cannot be reabsorbed quickly enough and are lost in the urine

21
Q

What happens if GFR is too low?

A

Everything is reabsorbed, including wastes that are normally disposed of.

22
Q

What do all mechanisms to regulate GFR have in common?

A

Adjust glomerular blood flow (and thus GBHP) to keep GFR within normal limits

23
Q

What is the effect of afferent arteriole dilation or efferent arteriole constriction on GFR?

A

Increased GBHP = Increased GFR

24
Q

What is the effect of afferent arteriole constriction and efferent arteriole dilation on GFR?

A

Decreased GBHP thus decreased GFR

25
Q

What is autoregulation of GFR (intrinsic control)?

A

Intrinsic mechanisms that maintain GFR despite normal fluctuations in BP.

MAP in range of 80-180mmHG = no change to GFR

Mechanisms include:
1. Myogenic mechanism
2. Tubuloglomerular feedback

26
Q

What is the myogenic mechanism of autoregulation control of GFR?

A

Increase in BP = initial increase in GFR

Afferent arteriole smooth muscle cells stretch

Muscle cells contract in response = constriction

Decreases glomerular blood flow (GFR maintained within the autoregulatory range)

This normalizes GFR within seconds of a change in BP.

27
Q

What is the tubuloglomerular feedback control of GFR?

A

Involves the juxtaglomerular apparatus (JGA).

Macula densa cells = detect NaCl concentration in the flitrate entering the DCT

Juxtaglomerular cells = detect stretch and release renin (activates RAAS)

28
Q

In the tubuloglomerular feedback control of GFR, juxtaglomerular cells release renin in response to?

A
  1. Decreased renal perfusion (decrease stretch of afferent arteriole walls)
  2. Direct sympathetic activation (juxtaglomerular cells contain beta-1 adrenergic receptors)
  3. Decrease tubular NaCl (detected by macula densa cells)
29
Q

What is the juxtaglomerular apparatus?

A

A collection of cells responsible for the hormonal regulation of the body’s blood pressure, the kidney’s blood flow and the glomerular filtration rate.

30
Q

What are juxtaglomerular cells?

A

Cells of the juxtaglomerlular apparatus that secrete renin, an enzyme that helps to increase your body’s blood pressure

31
Q

Where in the juxtaglomerular apparatus are juxtaglomerular cells located.

A

At the afferent arteriole.

32
Q

What are the goals of extrinsic controls (neural and hormonal) vs intrinsic goals of GFR?

A

Extrinsic = regulate GFR to maintain systemic BP

Intrinsic = maintain GFR despite fluctuations in BP

Extrinsic controls will override autoregulation (intrinsic) if blood volume needs to be increased

33
Q

What is involved in the neural (extrinsic) regulation of GFR?

A

Normal conditions at rest (PNS dominates):
- afferent and efferent arterioles are dilated
- autoregulatory mechanisms prevail in maintaining GFR

34
Q

What happens (neural/extrinsic regulation of GFR) when the sympathetic nervous system is activated?

A

NE and epinephrine act on a1 receptors of afferent arterioles= constriction and decreased GFR (overrides autoregulatory - intrinsic- mechanisms).

Also stimulates renin release by juxtaglomerular cells

35
Q

What is involved in the hormonal (extrinsic) regulation of GFR?

A

Angiotensin II:
- primarily causes the constriction of efferent arterioles to increase GFR (by increasing GHBP)
- at high levels can also constrict afferent arterioles

Atrial natriuretic peptide:
- released from cells of the atria when stretched (e.g. increased BV d/t volume overload)
- ANP dilates afferent arterioles = increased GFR (diuresis)
- inhibits Na+ reabsorption (natriuresis)

36
Q
A

Module 12 - Renal and Urologic Disorders (5 decks)

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