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Renal phys > GFR and RBF > Flashcards

GFR and RBF Flashcards

1
Q

Typical daily fluid intake

A
  • 2300 ml/day

- from ingestion of food and fluid (most) and carbohydrate oxidation (less)

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2
Q

Loss of body water

A
  • Insensible water loss (breathing; through the skin - 600-800)
  • Sweating (100)
  • Feces (100)
  • Excreted via kidneys (1400)
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3
Q

Extracellular fluid

A

-interstitial fluid
-blood plasma
^^^both separated by highly permeable capillary membrane (except to proteins)
-Transcellular fluid

  • 20% of body weight
  • low in K, P and proteins
  • high in Na, Cl, HCO3
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4
Q

Intracellular fluid

A
  • all of the fluid inside cells
  • 40% of body weight
  • low in Na, Ca, and Cl
  • high in K and P
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5
Q

Osmosis

A

the net diffusion of water across a selectively permeable membrane from a region of high water concentration to one that has a lower water concentration

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6
Q

Osmotic pressure

A

the equilibrium pressure between:

1) hydrostatic pressure
2) osmotic forces generated by addition of a SOLUTE

-proportional to the number of active or dissociable solutes/particles in the solution

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7
Q

Hydrostatic pressure

A

due to the increase in water in a compartment - pushing water into the solute free compartment

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8
Q

Osmoles

A
  • the total number of particles in a solution
  • 1 osmole = 1 mole of a solute particle

-if a molecule can dissociate into ions the osmoles EQUAL the number of ions

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9
Q

Osmolality

A

osmoles per KILOGRAM of water

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10
Q

Osmolarity

A

osmoles per LITER of water

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11
Q

Isotonic solution (tonicity)

A
  • intercellular and extracellular fluids are in osmotic equilibrium
  • the cell will not shrink nor swell (i.e. 0.9% NaCl solution)
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12
Q

Hypotonic solution (tonicity)

A

-a solution that has a LOWER concentration of impermeant solutes than the cell
-water will MOVE INTO CELLS
-cell SWELLING
(less than 0.9% NaCl solution)

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13
Q

Hypertonic solution (tonicity)

A

-a solution with a HIGHER concentration of impermeant solutes than the cell
-water will MOVE OUT OF cell
-cell SHRINKING
(more than a 0.9% NaCl solution)

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14
Q

Isosmotic solution

A

Osmolarity = cell

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15
Q

Hyperosmotic solution

A

osmolarity > normal extracellular fluid

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16
Q

Hypo-osmotic solution

A

osmolarity < normal extracellular fluid

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17
Q

Cellular volume changes due to

A
  • ingestion of fluid
  • intravenous infusion

-dehydration

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18
Q

Dehydration

A
  • not ingesting adequate fluids
  • loss of fluids in GI tract
  • sweating
  • fluid loss from kidneys
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19
Q

Step ONE in forming urine

A
  • body has to remove waste products from blood stream
  • blood arrives in the kidney via the RENAL ARTERY
  • INTERLOBULAR ARTERIES are the last major branches before filtration
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20
Q

Step TWO in forming urine

A
  • blood is delivered to the renal corpuscle via an AFFERENT ARTERIOLE
  • RENAL CORPUSCLE = glomerulus + Bowman’s capsule
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21
Q

Step THREE in forming urine

A
  • electrolytes, nutrients, waste products, and water filter out
  • RBCs and plasma proteins should not filter out under normal conditions
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22
Q

Glomerular Capillary Membrane

A
  • 3 layers (instead of 2)
    1) Endothelium
    2) Basement membrane
    3) Epithelial cell layer (podocytes)

-filter several hundreds of times more water and solutes than an average capillary

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23
Q

Selective filtration

A

-PORE SIZE

  • Fenestrae = big pores
  • Slit pores = small pores (formed from PEDICLES of podocytes)
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24
Q

Endothelium of glomerular capillary membrane

A
  • contains thousands of FENESTRAE
  • relatively large
  • negatively charged (prevents passage of plasma proteins)
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25
Q

Basement membrane of glomerular capillary membrane

A
  • meshwork of:
    1) Proteoglycan fibrillae
    2) Collagen
  • allows for flow of a lot of water and SMALL solutes to pass
  • proteoglycans have a strong NEGATIVE charge (inhibits passage of proteins)
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26
Q

Epithelium of glomerular capillary membrane

A
  • NOT a continuous later
  • PODOCYTES line the outer surface of the glomerulus
  • long foot-like projection that encircle capillaries (SLIT PORES)
  • negatively charged
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27
Q

Nutrients reabsorbed later by the Nephron

A
  • glucose
  • water
  • ions
  • AAs
  • bicarbonate
  • phosphate
28
Q

How does the filtration work?

A

Pressure differentials between the fluid in the GLOMERULUS and the fluid in the BOWMAN’S CAPSULE

29
Q

How does the body manage the pressures for filtration?

A
  • control of the smooth muscle of the:
    1) afferent arteriole
    2) efferent arteriole

-**changes in BP can have a significant and direct impact on GFR!!!

30
Q

Renal Plasma Flow (RPF)

A

the volume of blood plasma delivered to the kidneys per unit time, usually expressed in ml/min

RPF = GFR/FF

Typically ~550 ml/min resting

31
Q

Filtration Fraction (FF)

A

the proportion of the fluid reaching the kidneys which passes into the renal tubules

FF = GFR/RPF

Typically ~20%

32
Q

Glomerular Filtration Rate (GFR)

A

GFR = RPF X FF

Typical GFR = 110 ml/min

  • you filter ~160 L of plasma fluid a day
  • determined by balance of hydrostatic and colloid osmotic pressure across the capillary membrane
33
Q

How can the body INCREASE GFR?

A
  • altering RPF
    1) increase overall CO
    2) DILATE AFFERENT arterioles in kidney
  • altering FF
    1) CONTRACT EFFERENT arteriole, increased glomerular pressure
34
Q

Determinants of GFR

A
  • the sum of the HYDROSTATIC and COLLOID osmotic forces across the glomerular membrane
  • GFR = Kf X net filtration pressure
35
Q

Kf

A
  • capillary filtration coefficient
    1) permeability of the capillary
    2) surface area of the capillary

-typically 12.5 ml/min/mmHg

36
Q

Net Filtration Pressure

A

1) hydrostatic pressure inside GLOMERULAR CAPILLARIES
2) hydrostatic pressure inside BOWMAN’S CAPSULE
3) colloid osmotic pressure of glomerular capillary plasma proteins
4) colloid osmotic pressure of the proteins in Bowman’s capsule

=glomerular hydrostatic pressure - BCP - plasma proteins (glomerular oncotic p) + proteins in BC (capsule oncotic p)

37
Q

Forces that favor filtration

A
  • Glomerular hydrostatic pressure (60)

- Bowman’s capsule colloid osmotic pressure (0)

38
Q

Forces that inhibit filtration

A
  • Bowman’s capsule hydrostatic pressure (18)

- Glomerular capillary colloid osmotic pressure (32)

39
Q

Typical Net Filtration Pressure

A

60-18-32+0 = 10mmHg

40
Q

Colloid osmotic pressure in the glomerulus is proportional to the concentration of…

A

proteins in the blood stream

41
Q

A decrease in the amount of functional glomerular capillaries (i.e., age and disease) would do what to GFR?

A

Decrease GFR due to a decrease in Kf

42
Q

A decrease in the thickness of the capillary membrane (i.e., hypertension or diabetes mellitus) would do what to GFR?

A

Derease GFR due to a decrease in Kf

43
Q

An increase in Bowman’s capsule pressure (i.e. kidney stones) would do what to GFR?

A

Decrease GFR

44
Q

An increase in Glomerular capillary colloid osmotic pressure would do what to GFR?

A

Decrease GFR due to an increase in renal blood flow; a lower fraction of the plasma is initially filtered out

45
Q

A decrease in Glomerular capillary hydrostatic pressure would do what to GFR?

A

Decrease GFR

i.e., constricting afferent arterioles

46
Q

An increase in Glomerular capillary hydrostatic pressure would do what to GFR?

A

Increase GFR

i.e., an increase in arterial pressure, dilation of afferent arterioles, or constriction of efferent arterioles (slight)

47
Q

What is the most common physiological regulation of GFR?

A

Glomerular capillary hydrostatic pressure

48
Q

Renal Blood Flow (RBF)

A

RBF = (renal artery pressure - renal vein pressure) / total renal vascular resistance

49
Q

Renal artery pressure

A

= system arterial pressure

-kidneys maintain a fairly constant blood flow and GFR over a range of 80-170 mmHg

50
Q

Renal vein pressure

A

3-4 mmHg

51
Q

Renal vascular resistance

A
  • occurs in 3 places
    1) interlobular arteries
    2) afferent arterioles
    3) efferent arterioles
  • controlled by
    1) SNS
    2) hormones
    3) internal renal control mechanisms

-increase in resistance REDUCES blood flow

52
Q

Renal medulla and blood flow

A
  • ~1-2% of renal blood flow

- supplied by VASA RECTA that descend into the medulla with the loops of Henle of the juxtamedullary nephrons

53
Q

Renal cortex and blood flow

A

receives MOST of the renal blood flow

54
Q

Sympathetic regulation of GFR and renal blood flow

A

-mild-moderate sympathetic activation has LITTLE EFFECT

  • strong symp activation DECREASES GFR
    i. e., during severe acute situations (defense reaction, brain ischemia, sever hemorrhage)
55
Q

Epinephrine/norepi influence on GFR and renal blood flow

A
  • CONSTRICT afferent and efferent arterioles (decrease GFR)

- parallel symp activity - only DECREASE GFR in extreme circumstances (i.e., hemorrhage)

56
Q

Endothelin (autacoid) influence on GFR and renal blood flow

A

-released by damaged vascular endothelial cells of the kidney and other tissue; causes VASOCONSTRICTION to decrease blood loss

-seen in disease states such as:
1) Toxemia of pregnancy
2) Acute renal failure
3) Uremia
causes renal constriction and DECREASED GFR

57
Q

Angiotensin II (autacoid) influence on GFR and renal blood flow

A
  • powerful renal VASOCONSTRICTOR
  • usually released due to:
    1) decreased arterial pressure
    2) volume depletion
  • afferent arterioles = not reactive
  • efferent arterioles = highly sensitive (constrict)
  • maintain GFR (prevents a decrease)
  • decrease flow through the peritubular capillaries = increase reabsorption of Na and H2O water in renal tubules
58
Q

Endothelial-derived nitric oxide (autacoid) influence on GFR and renal blood flow

A
  • maintains VASODILATION of kidneys
  • allows normal excretion of Na and H2O
  • INCREASES GFR

-atherosclerosis and damage to endothelium DECREASES nitric oxide production; increased renal VASOCONST. and BP

59
Q

Prostaglandins and Bradykinin (autacoids) influence on GFR and renal blood flow

A
  • VASODILATORS, INCREASE renal blood flow and GFR
  • counteract the vasoconstriction of afferent arterioles

*Aspirin after surgery can cause big reductions in GFR

60
Q

Autoregulation of GFR and renal blood flow

A
  • an INTRINSIC mechanism that keeps blood flow and GFR relatively constant
  • arterial pressure can range from 70-160 mmHg with only about 10% change in GFR
  • without autoregulation and increase in BP would quickly deplete the blood volume
61
Q

Tubuloglomerular Feedback

A
  • AUTOREGULATION
  • feedback mechanism linking Na concentration with renal artery resistance
  • ensures a constant delivery of NaCl to the DISTAL TUBULES
62
Q

Renal cells sense a decrease in Na concentration

A
  • AUTOREGULATION
  • DECREASES resistance to blood flow in the afferent arterioles (increases GFR)
  • RENIN is released
    1) increases formation of Angiotensin I -> Angiotensin II
    2) CONSTRICTION of efferent arterioles
    3) INCREASES GFR
63
Q

Myogenic Mechanism

A
  • the ability of the individual blood vessels in the body to resist stretching during increased arterial pressure
  • likely has a DIRECT effect on GFR and renal blood flow regulation
  • thought to protect the kidneys from damage during an increase in BP
64
Q

if excretion rate = filtration rate-reabsorption rate (but NOT 0)

A
  • excretion rate is less than filtration rate of a substance

- i.e., electrolytes (Na, HCO3, Cl)

65
Q

if excretion rate = 0

A
  • no excretion in the urine, all of the substance is reabsorbed from the tubules into the blood
  • i.e., AAs and glucose
66
Q

if excretion rate = filtration rate + secretion rate

A
  • allows for rapid clearing of the substance from the system
  • excretion in large amounts in the urine

-i.e., organic acids and cases, foreign substances, and drugs

67
Q

What happens when the negative charge of the glomerular capillary membrane is compromised?

A
  • basement membrane LOSES it’s electrical charge

- ALBUMIN is filtered and will appear in the urine (proteinuria) (frothy appearance)

Renal phys (8 decks)

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