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Physiology: Exam 3 > Lecture 2: Filtration and Clearance > Flashcards

Lecture 2: Filtration and Clearance Flashcards

1
Q

List the functions of the Kidneys (7)

A
  • Remove wastes
  • Regulate the volume and composition of ECF
  • Acid-base balance
  • Blood Pressure Regulation
  • Removal of Foreign Substances
  • RBC production
  • Vitamin D activity
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2
Q

Which vessels provide the vasculature for the kidneys?

A
  • Blood goes to the kidneys through the renal artery
  • Blood leaves the kidneys through the renal vein
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3
Q

What is the functional unit of the kidneys?

A

Nephrons (2 types)

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4
Q

What are the 2 types of nephrons in the kidneys and what are their locations?

A
  1. Cortical nephron: close to the kidney surface (cortex)
  2. Juxtamedullary nephron: Interphase between the cortex and medulla

Juxtamedullary nephron has longer loops up the tubule than cortical nephron

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5
Q

List the three types of capillary beds

A
  • Glomerular capillaries
  • Peritubular capillaries
  • Vasa recta

Capillary beds are located between the renal artery and vein

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6
Q

Where can you find glomerular capillaries in the kidneys?

A

Can be found in BOTH cortical nephron and juxtamedullary nephron

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7
Q

How do glomerular capillaries enter and exit the glomerulus and explain their function?

A
  • Enters through afferent arterioles, Exits through efferent arterioles
  • Function: Plays a major role in the filtration process d/t the different diameters of the afferent (bigger) and efferent (smaller) arteriole.

Different in diameter sizes drive the filtration process

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8
Q

Where can you find peritubular capillaries in the kidneys?

A

Can be found in BOTH cortical nephron and juxtamedullary nephron

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9
Q

How are the peritubular capillaries formed and explain their function?

A
  • Derived from the efferent arterioles which bifrucate and wrap around the tubules
  • Function: Absorption- able to do 2 way transport between the tubules and capillaries because of very close proximity between the two
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10
Q

Where can you find the vasa recta in the kidneys?

A

Can ONLY be found in the juxtamedullary nephron

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11
Q

How is the vasa recta formed?

A
  • Derived from efferent arterioles and have 2 components
  1. Descending vasa recta
  2. Ascending vasa recta
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12
Q

What is the major difference between the peritubular capillaries and the vasa recta?

A
  • Vasa recta are far away from the tubules compared to peritubular capillaries which are very close
  • So exchange of substances between tubules CANNOT happen in vasa recta
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13
Q

Exchange of substances CANNOT occur from the vasa recta and kidney tubules. Where in the vasa recta CAN exchange occur?

A

Exchange of substances between the descending vasa recta and ascending vasa recta

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14
Q

How much of the blood flow to the kidneys goes the the vasa recta?

A

10%

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15
Q

Which nervous system innervates the Kidneys?

A

Sympathetic Nervous System

Part of the ANS

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16
Q

What parts of the kidney receive sympathetic innvervation?

A
  • Afferent and Efferent Arterioles
  • Juxtaglomerular cells
  • Tubule
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17
Q

What sympathetic actions occur from the parts of the kidneys that recieve SNS inneravation?

  • Afferent and Efferent Arterioles
  • Juxtaglomerular cells
  • Tubule
A
  • Afferent and Efferent Arterioles: Control Vascular resistance
  • Juxtaglomerular cells: (modified SMC around afferent arterioles) ↑ secretion of the enzyme Renin
  • Tubule: ↑ Reabsorption

Renin is located in granules in the juxtaglomerular cells

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18
Q

What are the important cellular components (2) of the proximal tubule of the nephron?

A
  • Has brush borders (microvilli) for large surface area to help w/ absorption
  • Has many mitochondria to generate ATP to provide energy for absorption
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19
Q

Explain the cellular components of the thin descending and ascending limb of the nephron

A

Has few mitochondria, little active transport (mainly passive)

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20
Q

Other segments of the nephron have many _______ and other organelles

A

mitochondria

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21
Q

List the 3 processes of Urine Formation

A
  1. Filtration
  2. Reabsorption/Secretion
  3. Excretion
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22
Q

What is the main function of the glomerular filtration process?

A

Production of a protein-free filtrate of plasma

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23
Q

What are the 3 layers of the glomerulus?

A

Layers from inner to outer

  1. Capillary Endothelium
  2. Basement Membrane
  3. Bowman’s Capsule Epithelium (podocytes)

Also know as “Three Sieves in Series”

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24
Q

What layer of the glomerulus is the Capillary Endothelium? Explain its physical properties and function.

A
  • Layer: innermost layer
  • Physical property: Many fenestration holes
  • Function: 1st layer of the filtration process, highly permeable
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25
Q

What layer of the glomerulus is the Basement Membrane? And explain it’s physical properties and function.

A
  • Layer: Middle (2nd) layer
  • Physical property: Excerted by endothelial cells. Major component: Lamina
  • Function: 2nd layer of filtration process
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26
Q

What layer of the glomeruls is the Bowman’s Capsule Epithelium (podocytes)? And explain it’s physical properties and function.

A
  • Layer: Outermost layer
  • Physical properties: Podocytes are very specialized cells that contain foot processes with tiny slits
  • Function: 3rd layer of filtration process; tiny slits allows substances to pass through
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27
Q

The property of the filtration process depends on what two things?

A
  • The charge of the protein
  • The size of the protein

Filtration process wants to expel proteins

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28
Q

What occurs when the podocytes of the Bowman’s Capsule epithelium are damaged?

A
  • First sign of kidney failure or chronic kidney disease
  • Proteinuria-high levels of protein in the urine. The seal of the podocytes will become more permeable and more protein will get through

Podocytes are highly specialized so they do not regenerate after damage

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29
Q

Why is there NO filtration occurring between the capillaries and the interstitum?

A

Because the osmolality of these 2 compartments are also identical so no flow occurs

Osm. of capillary: 286.5 mOsm/L
Osm. of interstitum: 285 mOsm/L

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30
Q

What determines the filtration process in the kidneys?

A

Starling Law

FYI: Modified from Starling Law for Skeletal muscle capillary

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31
Q

Explain the Starling Forces for Skeletal Muscle Capillary and the changes that occurs across the Glomerular Capillary

A

Starling Forces for Skeletal Muscle Capillary- Low Flow, High Resistance

  • The Hydrostatic Pressure @ the beginning of the skeletal muscle capillary is high and eventually drops at the end of the capillary.
  • Oncotic Pressure stays the same from beginning to end

Starling Forces Across the Glomerular Capillary-High Flow,Low Resistance

  • The Hydrostaic Pressure @ the beginning of the glomerular capillary is high and stays high at the end. (drops very slighty, eg. PGC @ beginning=60, PGC @ end=58)
  • The Oncotic Pressure grows gradullly from beginning to end b/c the 3 layers of the glomerular capillary stops protein from going through
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32
Q

All the pressure in the glomerular capillary favors __________ movement

A

Outward

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33
Q

What is Glomerular Filtration Rate (GFR)?

A

The daily amount of what should be filtered out of our kidneys

34
Q

What is the ideal Glomerular Filtration Rate (GRF) of an adult?

A

125 ml/min=180 L/day

35
Q

What is the equation to determine the Glomerular Filtration Rate (GFR)?

A

GFR= Kf[(PGC-PBC)- πGC]

  • Kf=Filtration coefficient
  • PGC=Hydrostatic pressure of Glomerular capillary
  • PBC=Hydrostatic pressure of Bowman’s capsule
  • πGC=Oncotic pressure of Glomerular capillary

Another name for Kf is Hydraulic conductance

36
Q

The filtration coefficient, Kf helps determine GFR. What changes can happen to Kf that affects the GFR?

A

1.Changes in Permeability
2.Changes in Surface area

37
Q

What causes changes in the permeabiliy factor of Kf?

Kf: filtration coefficent

Kf (part of the GFR equation)

A
  • Toxicity can cause change
  • Permeability mainly stays CONSTANT
38
Q

What causes changes in the surface area factor of Kf?

Kf: filtration coefficent

Kf (part of the GFR equation)

A
  • Mesangial cell contraction or relaxtion can cause change
39
Q

What are mesangial cells and how do they affect the surface area of the filtration coefficient, Kf?

A
  • Modified SMCs in between the glomerular capillaries
  • Mesangial cell Contraction can reduce surface area (Angiotensin II, Endothelin II, Norepi, Epi, ADH)
  • Mesangial cell Relaxation increases surface area (Atrial natriuretic peptide, Nitric oxide)

Substances in () cause either contraction or relaxation of mesangial cells

40
Q

Which of the following would promote an increase in GFR?
a. Decrease BP
b. Decrease Renal Sympathetic
c. Increase plasma albumin
d. Increase Norepi

A

b. Decrease Renal Sympathetic

Renal sympathetic cause vasoconstriction, when decreased GFR will increase

41
Q

Define Clearance

A

A volume of plasma from which a substance is completely removed by the kidneys per unit time

42
Q

What is the Clearance equation?

A

Cx=UF·Ux/Px=volume/time (ml/min or L/day)

  • Cx: clearance of x(substance)
  • UF: urine flow
  • Ux: urine concentration of x
  • Px: plasma concentration of x
43
Q

Why do we need to know the clearance of substances?

A

Clearance of a substance can be used to measure GFR

44
Q

What substance can be used to measure GFR by measuring clearance?

A

Inulin (M.W.=5,000)

45
Q

List the properties of Inulin that makes it unique (6)

A
  • Freely Filtered (by the kidney)
  • Not Reabsorbed (by the kidney)
  • Not Secreted (by the kidney)
  • Not Metabolized (by the kidney)
  • Does Not Change GFR
  • Not Produced (by the kidney)
46
Q

What makes Inulin the perfect substance?

A
  • Amount Filtered=Amount Excerted (Filtered Inuln=Excreted Inulin)
  • GFR·P(IN)= UF·U(IN)
  • GFR: Glomerulus filtration rate
  • P(IN): conc. of inulin
  • UF: urine flow’
  • U(IN): Excreted inulin
47
Q

What is the equation to Measure GFR using Inuin?

Clearance of Inulin

A

GFR=C(IN)= UF·U(IN)/P(IN)

GFR: Glomerulus filtration rate

  • C(IN)=clerance of inulin
  • UF: urine flow
  • U(IN): Excreted inulin
  • P(IN): conc. of inulin

Review Slide 18

48
Q

Inulin is a marker that is used in laborartory settings. What marker is used in the Clinical setting to measure GFR?

A
  • Creatinine (endogenous marker)
  • The daily creatinine excretion must be collected over 24 hours

Creatinine is a metabolite from muscle activity

49
Q

List the important factors the help determine the Daily Creatinine Excretion (3)

A
  • Varies based on weight & gender
  • Equals creatinine production
  • May be normal even in chronic renal failure
50
Q

What is the equation of measuring GFR using daily creatinine excretion?

A
  • GFR=UF·U(creatinine)/P(creatinine)
  • GFR: Glomerular Filtration Rate
  • UF: urine flow
  • U(creatinine): creatinine excretion
  • P(creatinine): concentration of creatinine
51
Q

List the typical clerance values of substances that filter through the glomerulus (8)

A
  • PAH (p-amino-hyppurate)=650 ml/min
  • Creatinine: 130 ml/min
  • Inulin: 125 ml/min
  • Urea: 55 ml/min
  • Na+: 2 ml/min
  • H2O: 1 ml/min
  • Glucose: 0 ml/min
  • Albumin: 0 ml/min
52
Q

Why is the typical clearance value of glucose and albumin 0 ml/min?

A
  • Glucose=0 ml/min b/c its reabsorbed 100%
  • Albumin=0 ml/min b/c proteins does NOT go through filtration process to produce a “protein-free serum”
53
Q

What is the normal Renal BLOOD Flow (RBF) in both kidneys?

A

1200-1300 ml/min=20-25% of C.O.

C.O.=cardiac output

54
Q

What is the normal Renal PLASMA Flow (RPF) in both kidneys?

A

600-700 ml/min=RBF (1-hematocrit)

55
Q

What is the Filtration Fraction (FF)?

A
  • A ratio that tells how much plasma is being filtered out
  • GFR/RPF=125/650 ml/min=20%
56
Q

Explain the distribution of blood flow in the kidneys

A
  • MOST Blood=Cortex-1000 ml/min(75%)
  • Outer Medulla-240 ml/min (20%)
  • LEAST Blood=Inner Medulla-60 ml/min (5%)
57
Q

How do measure the Renal Plasma Flow (RPF)?

A

(Fick Method) Infuse a substance in a patient to acheive a steady plasma concentration

58
Q

What substance is used to measure general Renal Plasma Flow (RPF)?

A

PAH= Para-aminohippurate

59
Q

What is the equation used to measure Renal Plasma Flow (RPF)?

A
  • RPF= ERPH=(CPAH)/0.9
  • ERPH (Effective renal plasma flow)= CPAH (Clerance of PAH)

Review Slide 25

ERPH and CPAH are considered the same

60
Q

What is the typical clearance value for PAH?

A

650 ml/min

61
Q

GFR and RBF are _________ in parallel.

A

autoregulated

62
Q

What is the arterial blood pressure range that GFR and blood flow (RBF) autoregulate?

A

Steady regulation between 100-200 mmHg

63
Q

When does autoregulation of renal blood flow fail?

A

When arterial blood pressure falls below 80 mmHg

64
Q

BP higher than 200 mmHg causes GFR and RBF to _________, BP lower than 80-90 mmHg causes GFR and RBF _________.

A

Increases, Decreases

65
Q

Changes in ________ determines both renal blood flow and GRF

A

Vascular resistance

66
Q

What is the site of regulation for renal blood flow and GRF?

A

Afferent arterioles

67
Q

What determines the GFR in the arterioles?

A

Individual resistance in each arterioles

68
Q

What determine the RBF in the arterioles?

A

Overall vascular resistance of both arterioles (afferent & efferent)

69
Q

What changes occur in the P(GC), GFR, RBF, and FF when the resistance in the afferent arteriole increases?

A
  • ↓ P(GC)
  • ↓GFR
  • ↓RBF
  • ~FF (GFR/RBF)

Review Slide 28

70
Q

What changes occur in the P(GC), GFR, RBF and FF when the resistance in the efferent arteriole increases?

A
  • ↑ P(GC)
  • ↑ GFR
  • ↓ RBF
  • ↑ FF (GFR/RBF)

Review Slide 28

71
Q

What changes occur in the P(GC), GFR,RBF, and FF when the dilation in the efferent arteriole increases?

A
  • ↓ P(GC)
  • ↓GFR
  • ↑ RBF
  • ↓ FF

Review Slide 28

Decreases overall resistance

72
Q

What changes occur in the P(GC), GFR, RBF, and FF when the dilation in the afferent arteriole increases?

A
  • ↑ P(GC)
  • ↑ GFR
  • ↑ RBF
  • ~FF (GFR/RBF)

Review Slide 28

Decreases overall resistance

73
Q

Which arteriole (afferent or efferent) causes GFR and RBF to change in parellel?

A

Changes in afferent arteriole

74
Q

What are the two mechanisms of RBF Autoregulation?

A
  1. Tubuloglomerular feedback (TGF)-which is a flow-sensitive mechanism
  2. Myogenic response- which is a pressure-sensitive mechanism intrinsic to vascular smooth muscle
75
Q

Explain the Tubuloglomerular Feedback (TGF) mechanism for Autoregulation

A
  1. ↑ GFR
  2. ↑ NaCl delivery to the loop of Henle
  3. Signal generated by macula densa of JCA
  4. ↑ R(A)
  • Macula densa (MD) is a specialized cell that sends signals to reduce or increase BP

TGF= flow sensitive mechanism

76
Q

Explain the Myogenic Mechanism for Autoregulation

A
  • Myogenic response is a pressure sensitive mechanism intrinsic to vascular smooth muscle cells
  • Intrinsic ability of the arteries to constrict when BP rises and to vasodilate when it decreases
77
Q

What three factors determine the control of Renal Blood Flow?

A
  • Blood Pressure (↑BP=↑RBF; ↓BP=↓RBP)
  • Intrisic: Autoregulation
    1. Myogenic
    2. Tubuloglomerular feedback
  • Prostaglandins (↑ pressure, ↑prostaglandins→↑vasodilation to ↑ blood flow to kidney)
  • Extrinsic
    1. Nerves: Sympathetic
    2. Hormones: Angiotensin II (strongest-causes vasoconstriction)
78
Q

True or False. Glomerular capillary hydrostatic pressure is lower than that of muscle capillaries.

A

FALSE

79
Q

True or False. GFR can be measured by the clearance of creatine.

A

TRUE

80
Q

True or False. Afferent arteriole dilation will decrease GFR.

A

FALSE

81
Q

True or False. Sympathetic stimulation will decrease RBF and GFR.

A

TRUE

82
Q

True or False. A decrease in mean arterial blood pressure from 100 to 80 mmHg will result in a proportional decrease in RBF.

A

FALSE

Physiology: Exam 3 (10 decks)

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