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Physiology > Renal Hemodynamics > Flashcards

Renal Hemodynamics Flashcards

1
Q

Osmolarity =?

A

Osm = concentration * # of dissociable particles

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2
Q

mOsm/L =?

A

mOsm/L = mmol/L * (#of particles/mol)

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3
Q

Oncotic pressure

A

osmotic pressure generated by large molecules such as proteins (π)

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4
Q

What happens to the intracellular and extracellular fluid volume as well as osmolarity when you drink water?

A

Decreased osmolarity

Increased ECF and ICF

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5
Q

What happens to the intracellular and extracellular fluid volumes as well as osmolarity if you drink a hyperosmotic solution?

A

*pulls water from cells*

Increased osmolarity

Increased ECF

Decreased ICF

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6
Q

What happens to the intracellular and extracellular fluid volumes as well as osmolarity during sweating or dehydration (hypoosmotic)?

A

Increased osmolarity

Decreased ICF

Decreased ECF

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7
Q

What is an isoosmotic solution?

A

No change in osmotic pressure, so no water flows into the cell when ECF increases

Ex: Gatorade

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8
Q

Describe the flow of fluid through a nephron

A

Cortex

  1. Glomerulus
  2. Bowman’s capsule
  3. Proximal convoluted tubule
  • *Medulla**
    4. Thin descending loop of Henle
  1. Thin ascending loop of Henle
  2. Thick ascending loop of Henle

Cortex

  1. Distal convoluted tubule
  2. Cortical collecting tubule

Medulla

  1. Medullary collecting tubule
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9
Q

What is the juxtaglomerular (JG) apparatus and what are its two main cell types?

A

Portion of the tubule where the late thick ascending limb of Henle’s loop courses between the arterioles.

Granular cells

Macula densa cells

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10
Q

What is the function of granular cells (juxtaglomerular cells) in the JG apparatus?

A

Differentiated smooth muscle cells in the walls of arterioles; responsible for the secretion of renin (increases BP)

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11
Q

What is the function of macula densa cells in the juxtaglomerular apparatus?

A

Contributes to the control of glomerular filtration rate and to the secretion of renin

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12
Q

What is filtered load?

A

Mass of material filtered through glomeruli

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13
Q

What is reabsorption?

A

Process by which material is transported from the tubules to the peritubular capillaries

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14
Q

What is secretion?

A

Process by which material is transported from peritubular capillaries to the tubules

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15
Q

What is excretion?

A

Filtered load + reabsorption + secretion

Process by which material moves through the length of the nephron

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16
Q

What is the glomerular filtration rate (GFR)?

A

Rate at which material/substances are filtered through the glomerular capillaries

Main index of kidney function

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17
Q

What is glomerular filtration?

A

Bulk flow of fluid from glomerular capillaries into Bowman’s capsule

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18
Q

What is glomerular filtrate?

A

Fluid within Bowman’s capsule; normally doesn’t contain cells; essentially protein-free; contains most inorganic ions and low molecular weight organic solutes

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19
Q

Describe the flow of filtered substances into Bowman’s capsule

A
  1. Fenestrae in the glomerular capillary endothelial layer
  2. Basement membrane
  3. Slit in diaphragms between podocyte foot processes
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20
Q

What is the primary function of slit diaphragms of podocyte processes?

A

Size-selective filter

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21
Q

What are the physical aspects of filtrate that regulate filtration of substances? (2)

A
  1. Substance size: > 70 kDa mwt not filtered
  2. Electrical charge: negatively charged molecules are less filtered (surfaces of filtration barrier coated with polyanions)
22
Q

Does glucose get completely reabsorbed or secreted in the kidney?

A

Reabsorbed; no glucose should be present in the urine

23
Q

What are the physical aspects of the glomerulus-endothelial cell barrier that regulate the filtration of substances?

A

Permeability: size of spaces/fenestra between endothelial cells; size of spaces between epithelial podocytes of Bowman’s capsule

Volume of filtrate formed per unit time (GFR)

24
Q

What is a normal GFR for an adult human? (total for two kidneys)

A

~180 L/day

60 - 125 mL/min

25
Q

What GFR would indicate renal failure?

A

< 40 mL/min

26
Q

What is Kf?

A

Ultrafiltration coefficient (permeability * surface area of glomerular capillaries)

27
Q

GFR =?

A

GFR = Kf * net filtration pressure (NFP)

28
Q

How is permeability determined in regard to Kf? (2)

A
  1. size of space/fenestra between capillary endothelial cells
  2. Size of pores between epithelial podocytes of Bowman’s capsule
29
Q

How is surface area determined in regard to Kf?

A

mesangial (in glomerulus) cell status and number of viable nephrons

30
Q

What are the components of the Net Filtration Pressure equation?

NFP = (PGC + πBC) - (PBC + πGC)

A

NFP = (PGC + πBC) - (PBC + πGC)

PGC: glomerular-capillary hydrostatic pressure

πBC: oncotic pressure of fluid in Bowman’s capsule (typically 0 bc no protein in Bowman’s capsule)

PBC: hydrostatic pressure in Bowman’s capsule

πGC: oncotic pressure in glomerular-capillary plasma

31
Q

What is a normal NFP in humans?

A

+16 mm Hg

32
Q

What would be the result of an increased glomerular surface area due to relaxation of glomerular mesangial cells? (Kf)

Hint: GFR = Kf (PGC - PBC - πGC)

A

Increased GFR

33
Q

What would be the result of an increase in renal arterial pressure, decrease in afferent-arteriolar resistance, and increase in efferent-arteriolar constriction? (PGC)

Hint: GFR = Kf (PGC - PBC - πGC)

A

Increased GFR

34
Q

What would be the result of an increase in intratubular pressure due to an obstruction of tubule or extrarenal urinary system? (PBC)

Hint: GFR = Kf (PGC - PBC - πGC)

A

Decreased GFR; does not happen often

35
Q

What would be the result of an increase in systemic-plasma oncotic pressure and decrease in renal plasma flow? (πGC)

Hint: GFR = Kf (PGC - PBC - πGC)

A

Decreased GFR; increased protein in the blood

36
Q

What is a normal renal blood flow?

A

~1.1 L/min

37
Q

What factors determine RBF? (2)

A
  1. mean arterial pressure
  2. contractile state of renal arterioles
38
Q

Flow =?

A

F = (Paorta - Pvenous) / Resistance

F = ∆P/R

39
Q

What are the functions of renal blood flow? (5)

A
  1. Indirectly determines GFR
  2. Modifies rate of solute and water reabsorption by the proximal tubule
  3. Participates in the concentration (and dilution) of urine
  4. Delivers oxygen, nutrients, and hormones to nephron cells; returns CO2 and reabsorbed fluid and solutes to circulation
  5. Delivers substrates for excretion in urine
40
Q

What factors influence afferent and arteriolar caliber? (4)

A
  1. Renal sympathetic nerves (secrete norepinephrine); renal vasoconstriction
  2. Renin-angiotensin system
  3. Autoregulation
  4. Prostaglandins
41
Q

How are RBF and PGC affected during renal vasoconstriction? What does this ultimately lead to?

A

Decreased RBF and Small initial increase in PGC

Ultimately leads to a net decrease in NFP and a small decrease in GFR

42
Q

What is Angiotensin II and how is it made in the body?

A

A powerful vasoconstrictor that decreases RBF; part of the renin-angiotensin system

Angiotensinogen is converted to Angiotensin I by action of renin, which is then converted to Angiotensin II by action of angiotensin-converting enzyme (ACE)

43
Q

What effect does AngII have on the kidneys? PGC? RBF? Kf? GFR?

A

Constricts both afferent and efferent arterioles (more so efferent)

increasing PGC

decreases RBF

decreases Kf by acting on mesangial cells

decreases GFR

44
Q

What are the four major inputs that control the production of renin by granular cells of the JG apparatus?

A
  1. Intrarenal baroreceptors
  2. Macula densa
  3. Renal sympathetic nerves
  4. Angiotension II (negative feedback inhibition)
45
Q

How does autoregulation of RBF and GFR occur? (2)

A
  1. Myogenic response
  2. Tubuloglomerular feedback
46
Q

What is a myogenic response?

A

Intrinsic property of vascular smooth muscle; tendency to contract when stretched

47
Q

What is the function of tubuloglomerular feedback (TGF)?

A

Maintain relatively constant GFR during changes in MAP

48
Q

How does TGF function? (5 steps)

A

*Must be within “autoregulatory range”*

  1. Increased MAP causes increased GFR
  2. Increased GFR raises flow through tubules
  3. Increased flow increases delivery to macula densa
  4. Macula densa triggers release of adenosine by the JGA
  5. Adenosine constricts afferent arteriole, which increases resistance and decreases PGC which decreases GFR back to normal
49
Q

What is the autoregulatory range for MAP that allows for TGF to occur?

A

60-180 mm Hg

50
Q

What are prostaglandins and what effect do they have on blood vessels?

A

Metabolites of arachidonic acid produced by renal sympathetic stimulation and angiotensin II; vasodilators

Ex: PGI2 (prostacyclin) and PGE2

51
Q

How does nitric oxide (NO) affect renal blood flow?

A

Vasodilator; counteracts angiotensin II and catecholamines; produced by increased shear force on endothelial cells when blood flow increases

52
Q

How does dopamine affect renal blood flow?

A

Vasodilator produced by the proximal tubule; increases RBF and inhibits secretion of renin

Physiology (11 decks)

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