renal hemodynamics 2

Question 1

what is the relation between renal blood flow ( RBF ) and renal plasma flow ( RPF ) ?

Answer 1

go hand in hand and affect filtration

Question 2

what is the difference between renal blood flow RBF and renal plasma flow RPF?

Answer 2

theres not much difference

but in filtration :

renal plasma flow is the portion of blood that is actually filtered so its important to distinguish while doing the calculation

Question 3

what is the effect sympathetic nervous system on glomerular filtration ?

Answer 3

^^^Increase afferent resistance

increase efferent resistance

MAINLY AFFERENT CONSTRICTIONS

Lead to :

Decreased Glomerular filtration rate
+
^^^Decreased renal blood flow

Strong sympathetic nervous system activation —-> vasoconstriction of afferent and efferent arterioles —-> DECREASE GFR and RBF

Under normal condition —> Mild or moderate sympathetic stimulation of renal arterioles has LITTLE OR NO EFFECT ON GFR or RBF

In acute severe conditions —-> like SEVERE HEMORRHAGE —–> SEVERE INCREASE IN RESISTANCE DUE TO INCREASED SYMPATHETIC STIMULATIONS OF RENAL VESSELS —-> REDUCE GFR and RBF

Question 4

what is the effect of catecholamines / norepinephrine on glomerular filtration rate?

Answer 4

similar to sympathetic

^^Increased resistance of AFFERENT arterioles

Increased resistance of EFFERENT arterioles

MAINLY AFFERENT CONSTRICTION

Lead to :

Decreased glomerular filtration

^^ DECREASED RENAL BLOOD FLOW

Norepinephrine and epinephrine released from adrenal medulla —> CONSTERTION OF AFFERENT AND EFFERENT ARTERIOLES —> decrease GFR and RBF decrease

They are like sympathetic , they only do a significant effect under crisis like hemorrhage but not under normal conditions

Question 5

what is the angiotensin 2?

Answer 5

hormone activated in response to low blood pressure

hypovolemia via renin angiotensin system

Question 6

what is the effect of angiotensin 2 on glomerular filtration rate?

Answer 6

selectively constrict efferent arterioles

Increase resistance of efferent arterioles

lead to :

initially increasing GFR , after prolonged activation lead to decrease GFR

Decrease renal blood flow ( cuz less blood is continued into the efferent arterioles )

NO EFFECT ON AFFERENT ARTERIOELS

preferably constricts the efferent arterioles in physiological conditions , POWERFULT RENAL VASOCONSTRICTION OF EFFERENT ARTEIOLES

Question 7

why doesnt ang 2 work on afferent arterioles?

Answer 7

due to the release of nitric oxide and prostaglandins which will counteract the vasoconstrictions of ang 2

will escape by prostaglandin in paracrine fashion

Question 8

what is the effect of prostaglandins on glomerular filtration rate?

Answer 8

Lead to vasodilation of efferent and afferent arterioles

MAINLY AFFERENT DILATION

^^^Decrease resistance of afferent arterioles ( blood flows faster )

Decreased resistance of efferent arterioles

lead to :

Increased GFR

^^ Increased RBF ( SIGNIFICANT )

Tend to increase GFR BUT IT IS NOT VERY IMPORTANT REGULATORS in normal conditions

IN stressful conditions such as after surgery or volume depletions, if the person is ON NSAIDS —> then prostaglandin synthesis may be decreased LEADING TO REDUCTION IN GFR —-> SO IT WONT LEAD TO VASODILATION AND AND INCREASE GFR and when lost it decreases GFR

IT IS IMPORTANT IN CRISIS BUT NOT UNDER NORMAL CONDITIONS

Question 9

What is the effect of endothelin derived vasodilators ( NITRIC OXIDE ) on GFR?

Answer 9

Vasodilator of both :

^^^Decreased resistance of afferent arterioles

Decreased resistance of Efferent arterioles

MAINLY AFFERENT DILATIONS

Lead to :

Increased GFR

^^Increased RBF ( Significant (

MAINLY AFFERENT DILATION ( OPPOSE ANG 2 EFFECT ON AFFERENT ARTERIOLES )

Vasodilation of renal vessels and increased GFR , Basal level of NO is REQUIRED for vasodilation of kidneys , IN HYPERTENSIVE PATIENTS AND IN ATHEROSCLEROSIS CUZ OF DAMAGE TO ENDOTHELIUM —–> LESS NO is produced leads to increased RENAL VASOCONSTRICTIONS and elevation in BP

decrease GFR eventually and this is one of the mechanism of atherosclerosis leads to hypertension

Question 10

what is the effect of endothelin on GFR?

Answer 10

VASOCONSTRCTIONS :

MAINLY AFFERENT CONSTRICTIONS

^^^Increased afferent resistance

Increased efferent resistance

leads to :

DECREASE GFR

^^Decreased RBF ( SIGINIFCANT )

Produced by damaged endothelial cells in conditions like chronic kidney disease and uremia , causing VASOCONSTRICTIONS and a reduction in BOTH GFR AND RBF

Question 11

what does the kidney need to regulate?

Answer 11

kidneys need to regulate the GFR and renal blood flow, but of course , GFR more

if one is affected , the other is affected, so changes in blood pressure will affect both

Question 12

what is autoregulation of GFR?

Answer 12

despite marked changes in BP, feedback mechanism inside the kidneys keep GFR at nearly constant

Question 13

what is the significance of AUTOREGULATION OF GFR?

Answer 13

maintain a relatively constant GFR for the precise control of renal excretion of water and solutes

crucial for urine productions ensuring the body effectively eliminates waste and maintain water and electrolytes balance

each day approximately 180 liters of filtrate are produced without this process toxin substances would accumulate and fluid and electrolyte balance would be disrupted .

the kidneys have intrinsic regulations of auto regulation of GFR which is very tightly regulated kidneys need to regulate even with slight changes

Question 14

How does autoregulation work on BP and GFR?

Answer 14

Bp drops —-> GFR decreases —> fluid retention

BP rise —-> GFR increase —> potentially dehydration

Mean arterial pressure range of 70-180 mmhg, kidneys is able to keep the GFR constant and allowing it to change by 10% up or down despite changes in BP

Question 15

how is autoregulation achieved?

Answer 15

myogenic mechanism ( Smooth muscle response )

Macula densa feedback ( TUBULOGLOMERULAR FEEDBACK ) –> macula densa in juxtaglomerular apparatus sense sodium chloride levels and signals adjustments —> this communication between the tubular fluid in distal convoluted tubule and arterial blood in afferent and efferent nephrons

angiotensin 2

Question 16

describe the myogenic mechanism ?

Answer 16

blood vessels can resist stretching

when BP increases

Vessels respond to increased wall tension by contraction of vascular smooth muscles

this contraction prevent excessive stretch of vessels wall and help prevent increase in RBF and GFR

intrinsic property of smooth muscles cells that helps regulate blood flow - when blood vessels are stretched beyond limit due to increased blood flow, the smooth muscle contracts automatically restrict the blood flow

Increased arterial pressure —->

Increased stretch of blood vessel —>

Increased Cell Calcium permeability —->

Increased intracellular calcium —->

Increased vascular resistance and contraction —->

The increased pressure will increase the flow

and then the increased resistance and contraction will reduce the blood flow counteract the increase

IF MAP is high then renal afferent arterioles constrict and resistance increase = RBF AND GFR flow remains constant Q = delta P/ R

Resistance is most important and significance

Question 17

what are the 2 components of macula densa feedback mechanism?

Answer 17

tubuloglomerular feedback mechanism by macula densa has 2 components :

1— > afferent arteriolar feedback mechanism

2—-> efferent arteriolar feedback mechanism

Question 18

what causes macula densa feedback mechansim?

Answer 18

special anatomical arrangement of JG apparatus when macula densa come in contact with AFFERENT AND EFFERENT ARTERIOLES

decrease in arterial blood pressure —–> less blood reaches the afferent arterioles ——> GFR decreases —-> RATE OF FLOW OF FLUID IN A LOOP OF HENLE DECREASE —-> MORE TIME TO INCREASE REABSORPTION OF SODIUM AND CHLORIDE

and by the time it reaches the Juxtaglomerular apparatus + distal convoluted tuble will sense REDUCED levels of NaCl by MACULA densa cells and WILL LEAD TOOO :

1- Afferent arteriolar vasodilation (less resistance )

2- angiotensin efferent arteriolar vasoconstriction ( more resistance )

increasing the GFR

both will help return of GFR towards normal

Question 19

why does Efferent constrict ?

Answer 19

less sodium and chloride

macula densa signals the juxtaglomerular cells release renin activating RAAS system to raise to BP, where ANG 2 will constrict EFFERENT

Question 20

is the afferent arteriole dilation part of myogenic mechanism?

Answer 20

it can be part of it

Myogenic mechanism is more potent when theres too much blood coming in , but this mechanism is more helpful when theres less blood flow and low blood pressure

Question 21

describe the regulation of GFR by ang 2?

Answer 21

Decreased GFR —->

decreased macula densa NaCl —-?

Increased Renin release —->

Increased ANG 2 —->

Increased efferent arteriolar resistance —-?

increased blood pressure —>

Increase GFR

When bp and blood volume are low , macula densa sense low SODIUM CHLORIDE —> ang 2 level increases due to renin release —> increase efferent resistance —->

Causes the blood to pool in the glomerulus , this increases capillary hydrostatic pressure thereby raising the GFR

also due to efferent arteriolar constriction , blood flow in the peritubular capillaries decreases , giving more time for reabsorption of sodium chloride into the ECF, further contributing to the increase in blood volume and GFR

ang 2 is a potent vasoconstrictor of systemic vessels which help raise blood pressure

Question 22

what are the effects of ang 2 ?

Answer 22

multiple effects :

stimulates ADH/vasopressin

promotes water reabsorption

trigger thrist

potent vasoconstrictor

release aldosterone

retain sodium and water

Question 23

describe renal blood flow?

Answer 23

22-25% of cardiac output

1.2L/min

much in excess of metabolic demands of kidneys

90% of this CO is used by the kidneys in The cortex

1-2% of it is going to the medulla

Question 24

why does the less blood goes to the medulla?

Answer 24

juxtamedullary nephrons do not need much blood

if it too much blood reaches the medulla , it could wash the essential solutes disrupting the necessary hyposomotic environent

Question 25

why does most of the blood goes to the cortex?

Answer 25

majority of urine forming nephrons are located in the cortex

Question 26

what happens when the blood enters the afferent arterioles ?

Answer 26

blood will flow into the glomerulus plasma is filtered while blood cells are retained ( Blood cells stays ) so renal plasma flow is more accurate for assessing filtration of the renal plasma entering the glomerulus , only 20% is filtered with remaining flowing through the efferent and peritubular capillaries so only 20% is filtered and doesnt go to efferent arterioles

Question 27

how to calculate filtration fraction ?

Answer 27

divide GFR by renal plasma flow GFR / RPF if GFR is 125 and RPF is 625 ---> 125/625 = 0.2 the filtration fraction is approximately 20% and should be 20% resistance has more significant impact on blood ( Q = pressure / resistance )

Question 28

what causes vasodilation ?

Answer 28

PGE 2 PGI2 NO Bradykinin dopamine arterial natriuretic peptide ( ANP )

Question 29

what causes vasoconstrictions ?

Answer 29

sympathetic nerves ---> catecholamines ang 2 Endothelin

Question 30

what is peritubular cap pressure ?

Answer 30

small capillaries originating from the efferent arterioles if flow is high is in efferent arterioles = increase peritubular cap flow and pressure

Question 31

what happens if you constrict efferent ?

Answer 31

Increased glomerular cap pressure DECREASED peritubular cap pressure Decreased nephron plasma flow

Question 32

what happens if u dilate efferent arterioles?

Answer 32

decrease glomerular cap pressure Increase peritubular cap pressure Increased plasma flow

Question 33

what happens if u constrict afferent arterioles?

Answer 33

Decreased glomerular cap pressure Decreased peritubular cap pressure Decreased nephron plasma flow

Question 34

What happens if u dilate the afferent arterioles?

Answer 34

Increased glomerular cap pressure Increased peritubular cap pressure Increased nephron flow

Question 35

What mainly regulates renal blood pressure ?

Answer 35

mean arterial pressure ( MAP )

Question 36

describe autoregulation of renal blood flow ?

Answer 36

renal autoregulatory mechanism prevent large changes in GFR and RBF and renal excretion of water and solutes that would otherwise occur with BP MAP can vary from 80 to 200 mmhg but RENAL FLOW IS CONSTANT CUZ OF CHANGES IN ARTERIOLAR DIAMTER by : Myogenic hypothesis Tubuloglomerular feedback

Question 37

describe urine output relation with BP?

Answer 37

although there are control mechanism yet when the BP changes the renal excretion of WATER AND NA is affected ---> to get rid of excess water and electrolytes like excretion of excessively large amounts of Na and water in the urine

Question 38

through which mechanism does BP affect urine?

Answer 38

Pressure diuresis Pressure natriuresis

Question 39

what is renal clearance ?

Answer 39

Clearance of substance is : Volume of plasma from which the substance was completely cleared by the kidneys per unit time C = Us x V / P Us = urine concentration V = urine flow rate ml per min P = plasma concentration

Question 40

how to we asses kidney function?

Answer 40

we need to evaluate both renal plasma flow and GFR GFR is the rate of which substances are filtered through the glomerulus to accurately measure GFR , we need to use substances that is neither secreted nor reabsorbed by the kidneys ---> SHOULD ONLY BE FILTERED this is to ensure that we can accurately check its concentration in both urine and plasma and calculate GFR which is equal to clearance as long as it is neither secreted nor absorbed IF substance is secreted or reabsorbed , it will affect the calculation of GFT keep in mind that 20% of renal plasma flow is filtered through the glomerulus and the remaining goes to peritubular capillaries

Question 41

what is the significance of clearance in GFR?

Answer 41

assess glomerular function clearance of substance freely filtered at the glomerulus but not REABSORBED OR secreted in tubules is the VALUE OF GFR

Question 42

what is the significance of clearance in Renal plasma/ blood flow?

Answer 42

not routinely performed the clearance of a substance filtered at glomerulus and COMPLETELY SECRETED BY THE TUBULES IS THE SAME AS RENAL FLOW Complicated cuz : Only 20% of the renal blood flow is filtered through glomerulus while the remaining flows into the peritubular capillaries TO accurately measures renal plasma flow , we need a substance that is freely filtered and completely secreted so that it is removed from the plasma and excreted in urine While theres no such substance there are substances that are close --> para aminohippuric acid

Question 43

where does each process happen ?

Answer 43

Filtration ---> glomerular capillaries Reabsorption in the TUBULES ---> with peritubular capillaries Secretion to the TUBULES ---> with peritubular capillaries 4---> excretion to the urethra excretion = filtration - ( reabsorption + secretion )

Question 44

describe what happens in case of substance that is filtrated only ?

Answer 44

substance is filtered through the glomerulus NEITHER REABSORBED OR SECRETED IN THE TUBULES The amount of this substance in urine reflects GFR like creatinine

Question 45

describe what happens in case of substances that is filtered and partially reabsorbed ?

Answer 45

substance is filtered into glomerulus and some of it gets reabsorbed in tubules like sodium

Question 46

describe what happens in the case of substances that is filtered and completely reabsorbed?

Answer 46

Substance gets filtered into the glomerulus but are entirely reabsorbed in the tubules meaning none of it appears in the urine like nutrients and glucose

Question 47

describe what happens if substance is filtrated and secreted ?

Answer 47

substance is filtered into glomerulus and then completely SECRETED INTO URINE from the PERITUBULAR CAPILLARIES Getting the 80% ( 20% is filtered ) went to peritubular capillaries ----> RENAL BLOOD FLOW

Question 48

describe renal clearance of albumin?

Answer 48

not filtered ---> ZERO Doesnt go to the tubules to begin with

Question 49

describe renal clearance of Glucose ?

Answer 49

Zero filtered BUT COMPLETELY ABSORBED IN THE TUBULES

Question 50

describe renal clearance of Na, urea, phosphate, chloride ?

Answer 50

filtered but partially reabsorbed

Question 51

describe clearance of Insulin , creatinine ?

Answer 51

filtered neither reabsorbed or secreted Measures glomerular filtration rate very reliable marker for determining GFR Can measure it in both plasma and urine its exogenous (NOT FOUND IN BODY ) and need to be given IV to avoid exogenous effect/ RISKS AND LIMIATION --> WE USE CREATININE

Question 52

describe clearance of para aminohippuric acid?

Answer 52

highest clearance because its both filtered and secreted it is used for renal plasma flow due to 90% of it getting secreted after being filtered making it ideal for plasma flow determination

Question 53

what are the properties of ideal GFR substance ?

Answer 53

Freely filtrated at glomerulus not reabsorbed by tubules Not secreted in tubules not metabolised by nephrons not toxic to the body doesnt affect renal function , particularly glomerular function Easily measured in the plasma and urine Found in body Creatinine is byproduct of muscles metabolism produced naturally by body

Question 54

describe clearance and plasma creatine concentration as measure of GFR?

Answer 54

Creatinine --> byproduct of muscle metabolism cleared from the body by glomerular filtration and estimation of GFR it is not a perfect marker as: some of it is secreted by tubules in the plasma over estimated in plasma these two errors cancel each other giving reasonable estimate if urine sample collection is not feasible , it can be just measured in plasma which is inversely proportional to GFR

Question 55

what is the law of plasma p creatinine ?

Answer 55

Plasma P cr - GFR = C cr = U x V / P

Question 56

what happens if GFR decreases by 50%?

Answer 56

half of the creatinine will be excreted plasma creatinine concentration rises until filtered load ( P x GFR ) and excretion ( U x V ) Return to normal and a balance is established , this will happen when plasma creatinine increases to twice normal We measure both Plasma lvl and urine lvl of creatinine if the plasma creatinine level increases , it means kidneys are not clearing it if it doubles then the kidney function is lost by 50%

Question 57

what happens if GFR decreases to 1/8?

Answer 57

plasma Creatinine increases 8 times

Question 58

what happens if GFR decreases to 1/4?

Answer 58

Plasma Creatinine lvl increases 4 times

Question 59

what is ficks principle ?

Answer 59

amount of a substance entering organ Equals amount leaving the organ Substance is neither synthesized nor degraded by organ IF substance is completely cleared from plasma its clearance rate is equal to RPF GFR is only 20% total plasma flow substances must be filtered and secreted by the tubules ( no such one ) Paraamino hippuric acid --> used to measure RBF because filtered and secreted by kidneys ( 90% cleared from plasma ) so nearly all of it enters the kidneys will be excreted in the urine ITS EXOGENOUS BUT WE DONT HAVE ALTERNATIVES

Question 60

Describe PAH clearance as estimate of Renal plasma flow?

Answer 60

PAH is freely filtered completely secreted in the tubules the amount of substances excreted comes from entire plasma flowing through kidneys ( all of it ) amount in urine = amount in the entire plasma flowing through kidney

Question 61

is the clearance of PAH = RPF?

Answer 61

no some blood may bypass the nephrons Clearance of PAH = effective RPF Total RPF is about 5-10% more than ERPF ( PAH CLEARANCE)

Question 62

what is the calculation process of substance clearance of PAH?

Answer 62

Renal plasma flow = U ( urine conc ) x V (urine flow rate ) / P ( plasma conc ) P = conc in artery - conc in vein Renal plasma flow = U pah x V / RA- RV Pah ( artery - vein ) renal plasma flow = 5.85 x 1 / 0.01 -0.001 RPF = 5.85 / 0.009 - 650 ml /min Theres no known substance which is completely cleared from the plasma PAH is 90% cleared and is called the EXTRATCTION RATIO ( ER) can be calculated as: R arterial pah - R venous pah / R arterial ph = 0.9 total RPF = PAH clearance / PAH ER

Question 63

How do we calculate renal blood flow from plasma flow?

Answer 63

the plasma only constitutes 55% so we do 1-45 or 55 Renal blood flow = RPF/ 1-PCV ( plasma % in blood ) So RBF = 650 / 1-0.45 = 1182