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CRP- Renal > Physiology of Glomerular Filtration and Hemodynamics > Flashcards

Physiology of Glomerular Filtration and Hemodynamics Flashcards

1
Q

What portion of the blood does the kidney filter?

A

the plasma

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2
Q

What is the difference between molaRITY and molaLITY?

A

just the denominator:
molarity= moles/LITER solvent (volume)
molality= moles/ Kg solvent (weight)

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3
Q

What is a 1 molar solution of NaCl?

A

molecular weight= 58.44 g/mole
so to make a 1 molar solution, you take:
58.44g/ 58.544g/mole/ 1L = 1 molar sultion.
This contains: 1 osmole/L Na+ and 1 osmole/L Cl- = 2 osmoles/liter

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4
Q

What does normal saline solution contain?

A

0.9% NaCl = 9 g NaCl in 1 L of H2O.
9g/ 58.44 g/mole/ 1 L= 0.154 molar NaCl
Remember the solution contains 0.154 osm/L Na+ and 0.154 osm/L Cl- = 308 mOsmol/L
This is isoosmotic (same number of particles dissolved as in the intercellular fluid).

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5
Q

What is important to remember about isotonicity?

A

only holds true if the solute particles are not permeable. Aka: only the solvent can be permeable.

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6
Q

What important functions of the body does the kidney maintain?

A
  • H2O balance
  • osmolarity
  • electrolytes (Na+, K+, Cl-, Ca++, H+, HCO3-, PO4, SO4, Mg++).
  • plasma volume
  • acid-base balance
  • excreting wastes (bilirubin, urea, uric acid, creatinine, and hormones).
  • excreting foreign compounds (drugs, food additives…)
  • producing erythropoetin
  • producing renin
  • converting vitamin D to its active form
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7
Q

How much blood flow do the kidneys receive?

A

20% of the cardiac output, however this is much more than the kidneys need in terms of O2 demand.

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8
Q

What are the branches of the kidney vasculature as the renal artery enters the renal pelvis off of the aorta?

A

segmental > interlobar > arcuate (between the medulla and cortex) > radial/cortical/interlobular arteries > afferent arteriole > glomerular capillaries > efferent arteriole > peritubular capillaries (cortical nephrons) or vasa recta (juxtaglomerular nephrons)

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9
Q

What is the functional unit of the kidney?

A

nephron (1.25 million in each kidney)

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10
Q

What is the path of the filtrate?

A
  • Filtering unit= glomerulus ( Malpighi’s corpuscles)
  • Tubular units= PCT > loop of henle > DCT > cortical connecting tubule > collecting tubule > collecting ducts (shared between multiple nephrons).
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11
Q

What volume does each glomerulus filter per day?

A

75 uL/day (and there are 2.5 million) so 187 liters a day!

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12
Q

What is the average GFR?

A

125 ml/min

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13
Q

What provides the driving force for fluid flow from Bowman’s capsule through the nephron?

A

hydrostatic pressure

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14
Q

Where is 2/3rds (120 L) of the filtrate reabsorbed?

A

in the PCT (due to brush border like luminal surface cells) that increase surface area and have many mitochondria on the basal membrane side to aid in transport of Na+ into the interstitium.
This occurs ISOOSMOTICALLY!!!!
Also nonselectively bc it is not under any extrinsic control.

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15
Q

What do we call the loop of henle?

A

countercurrent exchange mechanism

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16
Q

Are the thin and thick ascending limbs impermeable to water?

A

YES but Na, K, and 2 Cl- will be reabsorbed (forming the

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17
Q

Is the DCT under extrinsic control?

A

NO, but they have many transport mechanisms for various solutes.

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18
Q

Is the DCT impermeable to water?

A

mostly

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19
Q

Is the collecting tubule under extrinsic control?

A

YES hormonally (ADH or vasopressin released from the posterior pituitary under direct control from the hypothalamus) allows water reabsorption.

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20
Q

Is the collecting duct under extrinsic control?

A

YES highly for both solute and water reabsorption. Remember it traverses both the cortex and the medulla, down to the renal pelvis.

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21
Q

What happens to the filtrate as it descends down the loop of henle?

A

it becomes hyperosmotic (more concentrated as water exits, but solutes cannot).

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22
Q

What happens to the filtrate as it ascends up the loop of henle?

A

it becomes hypoosmotic as it enters the DCT (less concentrated as solutes exit, but water remains).

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23
Q

What does excretion equal?

A

filtration - reabsorption + secretion

K+ occurs with all of these, whereas glucose for ex. just gets filtered and reabsorbed

24
Q

How do the juxtaglomerular nephrons concentrate the urine?

A

the varying surrounding tissue osmolarity (cortex is 300 mOsm/L whereas deep in the medulla it is 1200 mOsm/L).

25
Q

How many lobes make up the kidney?

A

9-12 and function nearly independently. So you can lose most of the kidney and still have adequate functional ability.

26
Q

What is unique about the arrangement of afferent arterioles in terms of pressure as you go up in the renal cortex?

A

they angle in such a way off of the interlobular artery as to ensure equal pressures throughout them all (aka the pressure of the afferent arteriole in the uppermost area of the cortex will be the same as that of an afferent arteriole near the cortical-medullary border).

27
Q

How does blood flow change from the cortex to the medulla?

A

more blood flow overall in the cortex. As you go down into the medulla it decreases.

28
Q

What is extrinsic control?

A
  • sympathetic nervous system activity is the most important extrinsic regulator of renal blood flow.
  • RAAS
  • ADH
  • ANP, BNP
  • other vasoactive agents: constrictors= EPI/NE, endothelins, leukotrienes.
    dilators= prostaglandins, NO
29
Q

What is intrinsic control (autoregulation)?

A

renal ability to maintain renal blood flow and GFR within narrow limits, although MAP may vary between 80 to 160 mmHg.

  • myogenic (smooth muscle response)
  • juxtaglomerular apparatus
30
Q

What 3 systems control renin production?

A
  1. sympathetics nerves (catecholamines)
  2. intrarenal baroreceptors (juxtaglomerular cells of the afferent arteriole; produce and secrete renin).
  3. macula densa (tubular cells of the DCT= sense Na+ change and signal this to the adjacent JG cells).
31
Q

** How will the afferent arteriole respond to an INCREASE in MAP, via its intrinsic myogenic response, in order to keep GFR relatively constant?

A

it will CONSTRICT, to decrease blood flow to the glomerulus.

32
Q

** How will the afferent arteriole respond to a DECREASE in MAP, via its intrinsic myogenic response, in order to keep GFR relatively constant?

A

it will DILATE, to increase blood flow to the glomerulus.

33
Q

** How will the juxtaglomerular apparatus respond to a DECREASE in MAP, in order to keep GFR relatively constant?

A

less filtrate will be reaching the macula densa cells of the DCT, and they will sense a decrease in Na+ or Cl- (due to the ascending loop of henle absorbing more Na+ and Cl-). Because the macula densa cells abut the JG cells of the afferent and efferent arterioles they till signal the afferent arteriole to release renin, increase in vasodilating agents, and a decrease in vasoconstricting agents, and the opposite for the efferent arteriole (thus increasing GFR).

34
Q

What stays behind in the blood, from the glomerular filtrate?

A

proteins, RBCs, and WBCs

35
Q

** What is the filtration fraction (FF) equation?

A

FF= GFR/ RPF

*RPF (renal plasma flow)= RBF * (1- Hct), aobut 660 ml/min

36
Q

What 3 things determine GFR?

A
  1. hydraulic permeabililty
  2. surface area
  3. net filtration pressure (NFP)
    * Thus, GFR= permeability x SA x NFP
37
Q

What 4 forces govern fluid movement through the capillary?

A

Capillaries in the glomerulus are leaky:

  1. capillary pressure (Pc)
  2. interstitial fluid pressure (Pif)
  3. plasma osmotic pressure ((pi)p)
  4. interstitial osmotic pressure ((pi)if)
38
Q

What is the equation for NFP?

A

NFP= Pc- Pif- (pi)p+ (pi)if

* This will be + (about 10 mmHg) for the glomerular capillaries.

39
Q

Will the NFP of the peritubular capillaries (not the glomerular capillaries) be + or -?

A

negative (-) because these capillaries absorb fluid, not secrete/filter it like the glomerular capillaries.

40
Q

** What is the overall equation for GFR?

A 
GFR= Kf [(PGc - PBc) - Kp((pi)GC- (pi)BC)]
Kf= coefficient for permeability and SA.
Kp= reflection coefficient for molecules (proteins); should always be 1 (thus negligible) because proteins should not leak through.
41
Q

What 3 layers must the blood pass through as it is filtered in the glomerulus?

A
  1. capillary endothelial cells (fenestrated; leaky)
  2. basement membrane (lamina rara interna, lamina densa, and lamina rara externa).
  3. podocytes (contract and relax to adjust the permeability, since the filtrate must squeeze between them).
42
Q

What 2 factors affect the glomerular filtration barrier?

A
  1. size
  2. electrostatic forces
    * fiterability of 1 = freely filterable
    * filterability of 0.75= 75% filterable
43
Q

Why can’t albumin actually pass through the membrane if it is actually slightly smaller in size compared to the glomerular membrane?

A

because it is a negatively charged molecule, as is the membrane of the glomerular pores. Because, like charges repel, it will not be filtered.

44
Q

** What happens to GFR if you DECREASE Kf?

A

DECREASE GFR because you are decreasing SA.

45
Q

** What happens to GFR if you INCREASE PGc (glomerular capillary hydrostatic pressure)?

A

INCREASE GFR

46
Q

** What happens to GFR if you INCREASE PBc (bowman’s capsule hydrostatic pressure)?

A

DECREASE GFR

47
Q

** What happens to GFR if you INCREASE (pi)Gc (increase glomerular capillary oncotic pressure)?

A

DECREASE GFR

48
Q

What is important to remember about facilitated diffusion?

A

The carrier proteins (channels) can become SATURATED and this affects the rate at which molecules can diffuse. Aka: the rate can reach a maximum (i.e. glucose with Na+ through its co-transporter/symporter (SGCT2= early PCT, 1 glucose for 1 Na+; SGCT1= late PCT, and requires 2 Na+ for every 1 glucose) into the tubular cells and then glucose out into the interstitium via its own uniporter (GLUT2)).

49
Q

Will the PCT reabsorb nearly all of the filtered glucose?

A

YES

50
Q

What is the equation for filtered load?

A

Filtered load= GFR x [P]x

  • [P]x= plasma concentration
  • Thus the filtered load is directly proportional to to the plasma concentration (i.e. of glucose).
51
Q

** What happens when plasma glucose concentration increases to a level at which the filtered load of glucose exceeds the transport maximum (Tm) for reabsorption?

A

glucose will remain in the filtrate/urine (aka: it is EXcreted)

52
Q

What is the threshold value of glucose?

A

200 mg/100 ml

53
Q

What is the transport maximum (Tm) for reabsorption of glucose?

A

375 mg/100 ml

54
Q

** Why does threshold occur before the Tm for glucose?

MONEY QUESTION

A
  • This occurs due to anatomical differences between nephrons (i.e. some glomerular capillary beds are huge compared to their tubular transport processes, and some have small capillary beds with plenty of tubular transporters in comparison). So not all nephrons have the same Tm for glucose, and some begin to excrete glucose before others have reached their Tm.
  • The nephrons that set the threshold for glucose are those with LARGE glomerular capillary beds and FEW transport processes.
  • The nephrons that set the Tm for glucose are those with SMALL glomerular capillary beds and PLENTY of transport processes.
55
Q

What does splay (curved areas) represent on the titration curve?

A
  • the subpopulation of nephrons, which have different reabsorption capacities of glucose (i.e. some saturate before others). Basically the same as before, due to anatomical differences.

CRP- Renal (19 decks)

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