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Renal phys > GFR and RBF > Flashcards

GFR and RBF Flashcards

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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
Basement membrane of glomerular capillary membrane
- 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)
26
Epithelium of glomerular capillary membrane
- NOT a continuous later - PODOCYTES line the outer surface of the glomerulus - long foot-like projection that encircle capillaries (SLIT PORES) - negatively charged
27
Nutrients reabsorbed later by the Nephron
- glucose - water - ions - AAs - bicarbonate - phosphate
28
How does the filtration work?
Pressure differentials between the fluid in the GLOMERULUS and the fluid in the BOWMAN'S CAPSULE
29
How does the body manage the pressures for filtration?
- 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
Renal Plasma Flow (RPF)
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
Filtration Fraction (FF)
the proportion of the fluid reaching the kidneys which passes into the renal tubules FF = GFR/RPF Typically ~20%
32
Glomerular Filtration Rate (GFR)
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
How can the body INCREASE GFR?
- altering RPF 1) increase overall CO 2) DILATE AFFERENT arterioles in kidney - altering FF 1) CONTRACT EFFERENT arteriole, increased glomerular pressure
34
Determinants of GFR
- the sum of the HYDROSTATIC and COLLOID osmotic forces across the glomerular membrane - GFR = Kf X net filtration pressure
35
Kf
- capillary filtration coefficient 1) permeability of the capillary 2) surface area of the capillary -typically 12.5 ml/min/mmHg
36
Net Filtration Pressure
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
Forces that favor filtration
- Glomerular hydrostatic pressure (60) | - Bowman's capsule colloid osmotic pressure (0)
38
Forces that inhibit filtration
- Bowman's capsule hydrostatic pressure (18) | - Glomerular capillary colloid osmotic pressure (32)
39
Typical Net Filtration Pressure
60-18-32+0 = 10mmHg
40
Colloid osmotic pressure in the glomerulus is proportional to the concentration of...
proteins in the blood stream
41
A decrease in the amount of functional glomerular capillaries (i.e., age and disease) would do what to GFR?
Decrease GFR due to a decrease in Kf
42
A decrease in the thickness of the capillary membrane (i.e., hypertension or diabetes mellitus) would do what to GFR?
Derease GFR due to a decrease in Kf
43
An increase in Bowman's capsule pressure (i.e. kidney stones) would do what to GFR?
Decrease GFR
44
An increase in Glomerular capillary colloid osmotic pressure would do what to GFR?
Decrease GFR due to an increase in renal blood flow; a lower fraction of the plasma is initially filtered out
45
A decrease in Glomerular capillary hydrostatic pressure would do what to GFR?
Decrease GFR i.e., constricting afferent arterioles
46
An increase in Glomerular capillary hydrostatic pressure would do what to GFR?
Increase GFR i.e., an increase in arterial pressure, dilation of afferent arterioles, or constriction of efferent arterioles (slight)
47
What is the most common physiological regulation of GFR?
Glomerular capillary hydrostatic pressure
48
Renal Blood Flow (RBF)
RBF = (renal artery pressure - renal vein pressure) / total renal vascular resistance
49
Renal artery pressure
= system arterial pressure -kidneys maintain a fairly constant blood flow and GFR over a range of 80-170 mmHg
50
Renal vein pressure
3-4 mmHg
51
Renal vascular resistance
- 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
Renal medulla and blood flow
- ~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
Renal cortex and blood flow
receives MOST of the renal blood flow
54
Sympathetic regulation of GFR and renal blood flow
-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
Epinephrine/norepi influence on GFR and renal blood flow
- CONSTRICT afferent and efferent arterioles (decrease GFR) | - parallel symp activity - only DECREASE GFR in extreme circumstances (i.e., hemorrhage)
56
Endothelin (autacoid) influence on GFR and renal blood flow
-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
Angiotensin II (autacoid) influence on GFR and renal blood flow
- 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
Endothelial-derived nitric oxide (autacoid) influence on GFR and renal blood flow
- 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
Prostaglandins and Bradykinin (autacoids) influence on GFR and renal blood flow
- VASODILATORS, INCREASE renal blood flow and GFR - counteract the vasoconstriction of afferent arterioles *Aspirin after surgery can cause big reductions in GFR
60
Autoregulation of GFR and renal blood flow
- 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
Tubuloglomerular Feedback
- AUTOREGULATION - feedback mechanism linking Na concentration with renal artery resistance - ensures a constant delivery of NaCl to the DISTAL TUBULES
62
Renal cells sense a decrease in Na concentration
- 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
Myogenic Mechanism
- 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
if excretion rate = filtration rate-reabsorption rate (but NOT 0)
- excretion rate is less than filtration rate of a substance | - i.e., electrolytes (Na, HCO3, Cl)
65
if excretion rate = 0
- no excretion in the urine, all of the substance is reabsorbed from the tubules into the blood - i.e., AAs and glucose
66
if excretion rate = filtration rate + secretion rate
- 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
What happens when the negative charge of the glomerular capillary membrane is compromised?
- 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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