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Renal > Lecture 1: Intro kidney fxn > Flashcards

Lecture 1: Intro kidney fxn Flashcards

1
Q

What are the functions of the kidney?

A

Regulation of water + electrolyte balance
Regulation of acid-base balance

Excretion of metabolic waste
Excretion of hormones, drugs, and their metabolites

Regulation of BP
Regulation of RBC production

Synthesis of vitamin D
Gluconeogenesis

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2
Q

Define balance, explaining why long-term balance at steady state must equal zero for water and electrolytes

A

Balance = input - output

Must maintain constant ratio of solutes to water = constant plasma osmolality

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3
Q

How does kidney regulate water and electrolyte balance?

A

Kidney adjusts excretion of water and electrolytes to achieve balance in spite of wide variations in dietary intakes and non-renal losses => maintain constant plasma osmolality, Posm

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4
Q

How do kidneys regulate acid-base balance?

A

Regulate bicarbonate excretion

Synthesize new bicarbonate

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5
Q

What are metabolic wastes the kidneys excrete?

A

Urea

Uric acid

Creatinine

Miscellaneous pigments (from heme)

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6
Q

How do kidneys regulate arterial BP?

A

Maintains BP and effective circulating volume (by regulating extracellular fluid volume) @ level needed to stay in sodium balance

Role in regulation of vascular resistance

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7
Q

What is regulation of RBC production controlled by?

A

Erythropoietin (stimulates bone marrow to make more)

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8
Q

When is erythropoietin secreted?

A

Secreted by kidney in response to hypoxic conditions

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9
Q

What is the kidney’s role in vitamin D synthesis?

A

Converts vitamin D3 into active form = calcitriol

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10
Q

Define homeostasis

A

Tendency of an organism to maintain a stable internal environment

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11
Q

Distinguish between superficial cortical, midcortical, and juxtamedullary nephrons based on location of glomerulus and length of loop of Henle

A

Superficial cortical
Surface of cortex
Short-looped

Midcortical
Mid cortex

Juxtamedullary
Bottom of cortex, before medulla
Long-looped

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12
Q

Describe in sequence the vessels through which blood flows when passing from the renal artery to the renal vein

A

Renal artery
Segmental artery
Interlobular/Arcuate/Interlobular artery

Afferent arterial
(blood to individual nephrons!)

Glomerulus
Efferent arterial
Peritubular capillaries or Vasa Recta
(If cortical / juxtamedullary nephron)

Interlobular, arcuate, interlobular vv.
renal vein

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13
Q

Identify an unique feature of the kidney’s vascular bed

A

Unique:

Renal vasculature includes TWO capillary beds in series

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14
Q

Describe the 3 layers comprising the glomerular filtration barrier

A

Capillary endothelium

Basement membrane

Epithelial cells of Bowman’s capsule

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15
Q

Describe in sequence the tubular segments of the nephron

A

Proximal tubule
(Consulted + straight portions)

Loop of Henle
(Ends with tightly packed macula densa)

Distal nephron
(Distal convoluted, connecting tubule, collecting duct)

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16
Q

How do structures differ of epithelial cells in proximal convoluted tubule vs. collecting duct?

A

Brush border and more Leakey because not as much ‘tight’ tight junctions

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17
Q

What are the segments of the Loop of Henle?

A

Thin descending limb
Thin ascending limb **
Thick ascending limb
Ends @ macula densa

**only for long-looped nephrons

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18
Q

What is the function of the macula densa?

A

Monitor solute delivery and flow to distal nephron

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19
Q

What is the juxtaglomerular apparatus comprised of?

A

Macula densa

Extraglomerular mesangial cells

Granular cells (secrete renin)

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20
Q

What are two forms of feedback provided by having tubule loop back and return to corpuscle?

A

(1) tubuloglomerular feedback
- macula densa cells send signals to afferent arteriole to regulate glomerular filtration and renal blood flow (RBF)

(2) regulation of renin secretion
- macula densa cells send signals to granular cells

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21
Q

What are segments of collecting duct?

A

Cortical collecting duct

Outer medulla

Inner medulla

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22
Q

Where is the “end” of a nephron unit?

A

Connecting tubule

Collecting ducts are part of urinary tract

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23
Q

What is the function of the renal corpuscle?

A

Glomerular filtration

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24
Q

What is the function of the tubule?

A

Modifies composition of tubular fluid (TF) in order to make urine

These modifications involve processes of tubular reabsorption and secretion

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25
Q

Describe in sequence the structures of the urinary tract

A

From collecting duct, urine drains into

Minor calyx
Major calyx
Renal pelvis

Ureter
Bladder

Internal sphincter (SM)
External sphincter (SKM)

Urinary excretion

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26
Q

Compare the filtration of fluid in systemic vs. glomerular capillaries

A

Glomerular capillaries have higher filtration fraction (FF)

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27
Q

Define and list normal values for renal blood flow (RBF), renal plasma flow (RPF), glomerular filtration rate (GFR), and filtration fraction (FF)

A

RBF = 1.1 L/min

RPF = 600 mL/min

GFR = 120-125 ml/min
= 180 L/day

FF = 20% = GFR/RPF

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28
Q

Given the CO and hematocrit in a normal individual, predict:

RBF
RPF
GFR

A

RBF = CO * 0.2

RPF = (1 - hematocrit) * RBF

GFR = 0.2 * RPF

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29
Q

What is the ultrafiltrate?

What does it include and exclude?

A

Ultrafiltrate = fluid that filters out of glomerular capillaries

Excludes: cellular elements of blood (RBCs) + plasma proteins

Includes: small solutes

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30
Q

How are solutes transported in glomerular capillaries?

A

Convective transport!

Solutes dragged across capillary wall by fluid filtering out of capillaries

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31
Q

Define glomerular filtration

A

Fluid filtered by glomerular capillaries = 20% of RPF

Goes into tubule

Includes:
20% of water
20% of small solutes

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32
Q

Define tubular reabsorption and tubular secretion

A

Remaining 80% travels to efferent arteriole and 2nd capillary bed

Tubular reabsorption:
From tubule to blood
(From 20% that got filtered)

Tubular secretion:
Blood to tubular fluid

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33
Q

Define urinary excretion

A

Elimination of solutes and water in urine

Anything that exits inner medullary CD

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34
Q

Write a general equation that summarizes the kidney’s handling of a substance (“fundamental law of the kidney”)

A

Excretion =

Filtration + Secretion - Reabsorption

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35
Q

Identify the abbreviations and describe the units that are most commonly used in kidney physiology for

plasma concentration of solute X
Urine concentration of Solute X
Urine flow rate
Rate of tubular reabsorption of solute X
Rate of tubular secretion of solute X
A

[Plasma] = Px
Units: moles, mass, electrical equivalents, osmoles

Urine concentration = Ux
Units: same as Px

Urine flow rate = V dot or V
Units: ml/min; L/day

Tubular reabsorption = Rx
Tubular secretion = Sx
Units: mmol/min, mg/min, mEq/day

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36
Q

List typical normal plasma concentrations of sodium, potassium, chloride and bicarbonate

A

PNa = 140 mM

PK = 4 mM

PCl = 105 mM

PHCO3 = 24 mM

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37
Q

Define the rate of filtration of solute X and describe its units

A

Amount of solute filtered per unit time

Units: mmol/min, mg/min, mEq/day

38
Q

Write an equation for calculating rate of filtration of

(A) freely filtered solute
(B) solute that binds to plasma proteins

A

Freely filtered:
Rate of filtration = Px * GFR

Bound to plasma proteins:
Rate of filtration = fu * Px * GFR

Where fu = fraction of solute unbound

39
Q

Define the rate of excretion of solute X, describe its units and write an equation for its calculation

A

Amount of solute excreted per unit time

Units: mmol/min; mg/min; mEq/day

Rate of excretion = Ux * Vdot

40
Q

Write the fundamental law of the kidney for solute X (assume X is freely filtered)

A

Ux Vdot =

Px * GFR + Sx - Rx

41
Q

Write a modified form of fundamental law of the kidney for

(A) solute that’s filtered but not reabsorbed or secreted
(B) solute that’s filtered and reabsorbed but not secreted
(C) solute that’s filtered and secreted but not reabsorbed
(D) solute that’s filtered, reabsorbed and secreted with net reabsorption
(E) solute that’s filtered, reabsorbed with net secretion

A

Filtered:
Ux Vdot = Px * GFR

Filtered + reabsorbed:
Ux Vdot = Px * GFR - Rx

Filtered + secreted:
Ux Vdot = Px * GFR + Sx

Net reabsorption:
Ux Vdot = Px * GFR - net Rx

Net secretion:
Ux Vdot = Px * GFR + net Sx

42
Q

What are examples of substances that are filtered but not reabsorbed or secreted?

A

Inulin

Creatinine (some secretion)

43
Q

What are examples of substances that are filtered and reabsorbed (but not secreted)?

A

Na+

Cl-

glucose

Amino acids

44
Q

What are examples of substances that are filtered and secreted (but not reabsorbed)?

A

Organic anions

Organic cations

45
Q

What are examples of substances that are filtered, reabsorbed and secreted with net Rx or Sx?

A

K+

Urea

Uric acid

46
Q

What is a modified fundamental law of the kidney for water?

A

Vdot = GFR - R(H20)

47
Q

List the major electrolytes, nutrients, and waste products that represent the “cast of characters” for Renal System I

A

Electrolytes:
Na, K, Cl, HCO3
Phosphate, Ca, Mg (bone minerals)

Nutrients:
Glucose, amino acids

Wastes:
Creatinine, urea, uric acid

48
Q

Describe the reabsorption of sodium plus anions and water

A

Proximal tubule:
2/3 Na + anions, water reabsorbed

Thick ascending limb:
Reabsorbed 1/4 Na + anions, but NO water

Distal convoluted tubule:
Reabsorbs 4-8% Na + anions, but NO water

CNT, CD:
Reabsorbs 1-3% Na + anions, water permeability regulated by ADH

49
Q

State the approximate minimum and maximum values of urine osmolality (U osm) - how concentrated - in the normal kidney

Briefly explain how it can vary over such a wide range

A

Varying water reabsorption/ADH = varied U osm

U osm (min) = 50 mOsm/kg H2O
U osm (max) = 1200 mOsm/kg H2O
50
Q

Identify the concentrating and diluting segments

A

Diluting:
Thick ascending limb
Distal convoluted tubule
CNT, CD in absence of ADH

Concentrating:
Collecting duct in presence of ADH

51
Q

Define the medullary gradient

A

In region of medulla, there’s a gradient of increasing osmolality

Inner part of medulla (tip of papilla) = max concentrated

Because of medullary gradient, there is reabsorption of water in thin DL and reabsorption of NaCl in thin AL

52
Q

What is maximum osmolality in medulla determined by?

A

Length of loop of Henle

% of nephrons with long loops

53
Q

For ADH, identify its site of synthesis and secretion

A

Synthesized in hypothalamus

Secreted by posterior pituitary

54
Q

What is another name for ADH?

A

Vasopressin

55
Q

For ADH, list its major effects on tubular transport

A

Increases water permeability of CNT and CD
(Allows medullary gradient to pull water out of tubular fluid, resulting in increased osmolality of TF or more concentrated urine)

Increases urea permeability of inner medullary CD

56
Q

For ADH, briefly describe two mechanisms for regulating its secretion

Identify the mechanisms most important in regulation of kidney function

A

Dec. stretch of arterial BRs or veno-atrial mechanoreceptors = inc. ADH

*** Inc. plasma osmolality as sensed by osmo receptors in hypothalamus = inc. ADH

Inc. AngII in severe volume depletion can also stimulate inc. ADH secretion

57
Q

For Ang II, briefly describe the direct and indirect mechanisms for its slow pressor effects

A

Direct
Ang II = inc. sodium reabsorption in proximal tubule = inc. water reabsorption
Also inc. sodium reabsorption in DCT and CNT/CD

Indirect
Ang II = inc. aldosterone = inc. Na reabsorption in CNT/CD

58
Q

Review renin secretion regulators

A

Sympathetic division:
Inc. symp. Tone to kidneys = stimulate beta1 R’s on granular cells = inc. renin secretion

Renal baroreceptors
Dec. stretch of afferent arterioles = inc. renin secretion

Macula densa:
Dec. NaCl delivery = signal to increase renin secretion via adenosine and PG signaling molecules

Hormones:
Inc. AngII or ANP = dec. renin secretion

59
Q

For aldosterone, list its site of synthesis and secretion

A

Secreted by adrenal cortex

60
Q

For aldosterone, list its major effects on tubular transport

A

Na+ reabsorption in CNT/CD

Inc. K+ secretion in CNT/CD

61
Q

Describe two mechanisms for aldosterone regulation

A

Ang II = inc. aldosterone

Inc. plasma concentration of potassium = inc. aldosterone

62
Q

For ANP, review the regulation of its secretion

A

ANP is released from atria by stretch due to increased pressure or volume

63
Q

Describe effects of ANP on tubular transport of sodium

A

dec. Na+ reabsorption in CD (inc. Na+ excretion)

Effects on excretion of sodium are OPPOSITE to Ang II and aldosterone

64
Q

For sympathetic division, briefly describe its general effects on kidney function

A

Na+ retention, plasma volume expansion

Direct mechanism:
Inc. Na+ reabs. In PT = inc. water reabsorption
Inc. Na+ reabs. In DCT

Indirect mechanism:
Inc. symp tone to kidneys = inc. renin secretion = inc. Ang II

65
Q

What does PTH do?

A

Parathyroid hormone regulates excretion of bone minerals

66
Q

What are regulators of RBF and GFR?

A

ADH
Ang II
ANP
Sympathetic division

Other mediators = adenosine, PGs, NO

67
Q

What does 1 mEq equal?

A

1 mEq = 1 mmol of electrical charge

Electrolyte with valence v = v mEq of solute
Example: 1 mM CaCl2 = 4 mEq/liter

68
Q

What is 1 mOsm equivalent to?

A

1 mOsm = 1 mmol of particles

1 mmol of solute that dissociates into n discrete particles in solution = n mOsm of solute
Example: 1 mM CaCl2 = 3 mOsm/kg H2O

69
Q

What does 1 liter of water equivalent to?

A

1 liter of water = 1 kg of water

70
Q

What is a typical normal value for Vdot, or V?

A

1 ml/min or 1.5 L/day

71
Q

What is the percentage of nephrons with short loops of Henle?

A

80-90%

72
Q

What are short-looped and long-looped nephrons called?

A

All superficial cortical nephrons = short loop

All juxtamedullary nephrons = long-loop

73
Q

What is the plasma flow filtered into the interstitium in typical capillaries?

A

< 0.1%

74
Q

What is the percentage of filtered sodium + anions reabsorbed in the proximal tubule?

A

60-70%

75
Q

What is the percentage of filtered sodium + anions reabsorbed in the thick AL of the loop of Henle?

A

25%

76
Q

What is the percentage of filtered sodium + anions reabsorbed in the distal convoluted tubule?

A

4-8%

77
Q

What is the percentage of filtered sodium + anions reabsorbed in the connecting tubule and collecting duct?

A

1-3%

For “fine tuning” to maintain sodium balance

78
Q

In which segment of the tubule is the main epithelial cell type called the principle cell?

A

Connecting tubule (CNT) and the collecting duct (CD)

79
Q

What regions of the tubule are always permeable to water?

A

PT and thin DL

80
Q

Which is the most important diluting segment of the tubule?

A

Thick AL - reabsorbs 25% of filtered sodium + anions and is always impermeable to water

81
Q

Where is there negligible sodium reabsorption in the tubule?

A

Thin DL

82
Q

What is secreted in response to increased atrial stretch?

A

Atrial natriuretic peptides

83
Q

What is secreted in response to decreased atrial stretch?

A

ADH

84
Q

What increases sodium reabsorption in the PT?

A

Ang II

Also increases sodium reabsorption in the DCT and CNT/CD

85
Q

What does increased sodium reabsorption in the proximal tubule lead to ?

A

Since PT is always permeable to water, increased sodium reabsorption = increased water reabsorption

86
Q

What decreases sodium reabsorption in the collection duct?

A

ANP

87
Q

What inhibits renin secretion?

A

Ang II and ANP = hormonal renin secretion regulations

88
Q

How do rates of excretion and filtration relate if substance X is filtered and reabsorbed?

A

If filtered and reabsorbed (or filtered, reabsorbed and secreted with NET reabsorption!)

Rate of excretion < rate of filtration

Examples: Na, Cl, glucose, amino acids

89
Q

How do rates of excretion and filtration relate if a substance is filtered and secreted?

A

If substance X is filtered and secreted (or filtered, reabsorbed and secreted with NET secretion),

Rate of excretion > rate of filtration

Examples: PAH, Cr

90
Q

How do rates of excretion and filtration relate if substance is filtered and neither reabsorbed nor secreted?

A

Rate of excretion = rate of filtration

Example: inulin

Renal (17 decks)

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