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SM Renal > Physiology 3 > Flashcards

Physiology 3 Flashcards

(73 cards)

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1
Q

What is the equation to calculate GFR

A

Kf x net filtration pressure

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2
Q

What are the 3 physical barriers to the process of filtration

A

1 - the wall of the capillary
2 - Basement Membrane (Basal lamina for plasma protein barrier)
3 - Slit processes of podocytes (Glomerular epithelium)

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3
Q

What is the difference between capillaries in the nephron to capillaries elsewhere in the body

A

the pores between adjacent endothelial cells are about 100 times larger than those found in capillaries elsewhere in the body

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4
Q

What forms the slit processes of the podocytes

A

The interdigitations between podocytes

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5
Q

What are the 2 main substances that do not cross from the blood into the lumen of the Bowman’s capsule

A

RBC

plasma proteins

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6
Q

Describe the basement membrane of the Bowman’s capsule

A

Acellular layer

rich in glycoproteins and collagen

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7
Q

What do the glycoproteins do to the basement membrane

A

Causes a net negative charge which then acts to repel the negatively charged plasma proteins in the filtrate

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8
Q

What is the filtrate that is initially formed

A

Modified filtrate of the blood - it lacks RBC and large plasma proteins
it does contain small solutes and salts that can cross the glomerular membrane

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9
Q

Active transport is the main way in which molecules move in the glomerular membrane. True or False

A

It is an entirely passive process

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10
Q

What are Starling Forces

A

The balance of hydrostatic pressure and osmotic forces

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11
Q

How can we calculate the net filtration

A

Add the pressures that favour filtration and subtract those that oppose it

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12
Q

What is the most important pressure in the glomerular filtration

A

Glomerular capillary blood pressure

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13
Q

What is the value of the glomerular capillary blood pressure

A

55mmHg

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14
Q

Why does the glomerular capillary blood pressure remain the same throughout the length of the capillary

A

The diameter of the afferent arteriole is larger than the efferent arteriole and therefore this causes a back pressure of blood that will be maintained

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15
Q

What is the pressure of the Bowman’s capsule hydrostatic pressure

A

15mHg

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16
Q

How does the Bowman’s capsule hydrostatic pressure occur

A

As the fluid enters the lumen, it builds up to eventually cause a pressure opposing filtration

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17
Q

What is another term for oncotic pressure

A

colloid osmotic pressure

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18
Q

What are oncotic pressures related to

A

plasma proteins

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19
Q

How does capillary oncotic pressure occur

A

plasma protein concentration acts across the membrane

They exert an osmotic effect and act to attract fluid from the Bowman’s capsule back into the blood

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20
Q

What is the value of the capillary oncotic pressure

A

30mmHg

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21
Q

What is the pressure of the Bowman’s capsule oncotic pressure
Why is this

A

0mmHg

we shouldn’t have any plasma proteins in the Bowman’s capsule and therefore it cannot pull any negative charges through

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22
Q

What pressures make up the Starling forces

A

Glomerular capillary blood pressure
Bowman’s capsule hydrostatic pressure
capillary oncotic pressure
Bowman’s capsule oncotic pressure

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23
Q

What does the net filtration do overall

A

it drives the movement of fluid and its constituents across the membrane

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24
Q

What is GFR

A

the rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time

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25
What is Kf ?
The filtration coefficient | How holy the glomerular membrane is
26
What is the normal GFR rate
125ml/min
27
How can we change the pressure of blood flowing through the glomerular capillary
Vasodilation or vasoconstriction
28
What happens if we increase the GFR
We increase the rate at which the kidneys are filtering and therefore increases the urine production
29
What are the intrinsic regulations of GFR
myogenic mechanism Tubuloglomerular These require no hormonal or nervous stimulation
30
What is the primarily role of extrinsic regulation of GFR
sympathetic control via baroreceptors | increase in the sympathetic nerve activity causes an activation of the baroreceptor reflex
31
Describe what happens to GFR in vasoconstriction
Decrease blood flow into the glomerulus | Decreases the glomerular capillary blood pressure and decreases the net filtration pressure which then decreases GFR
32
What happens to GFR in vasodilation
Increase blood flow into the glomerulus | Increases the glomerular capillary blood pressure and Increases the net filtration pressure which then increases GFR
33
Describe why the urine output decreases when a patient has a drop in blood volume e.g. Haemorrhage
``` Decreased arterial BP Detected by aortic and carotid sinus baroreceptors Increases sympathetic activity Generalised arteriolar vasoconstriction constriction of afferent arterioles Decrease BP in capillaries Decrease GFR Decrease urine output This then helps to compensate for the blood loss ```
34
Why does changes in systemic arterial blood pressure not result in changes in GFR
autoregulation prevents short term changes in systemic arterial pressure affecting GFR
35
What is the mean arterial Blood pressure if the BP is 120/80
93 mmHg
36
Why is the fact that GFR is relatively constant important
avoid unintentional shifts in the glomerular filtration rate that could lead to an imbalance of salts and fluid or solutes
37
What is the myogenic auto regulation
If vascular smooth muscle is stretch (e.g exercise increasing the arterial BP) it contracts thus constricting the arteriole It is related to the amount of stress caused to the smooth muscle found within the wall of the afferent arteriole
38
What does the tubuloglomerular feedback involve
The juxtaglomerular apparatus | If the GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles
39
What do the macula densa cells do
Sense the NaCl content of the tubular fluid
40
Where is the juxtaglomerular apparatus
The part of the distal tubule passes between the afferent and efferent arterioles
41
What happens if an increase in salt has been detected by the macula densa
Vasoactive chemical messengers are released which will bring about a contraction of the smooth muscle which will bring about a reduced amount of blood flowing into the capillary and GFR will decrease.
42
What type can over ride the other type of control
Extrinsic control of GFR can override the 2 mechanisms that control the intrinsic control
43
What happens to GFR in a patient that has a kidney stone and how
It decreases - blockage downstream in the nephron causes a build up of fluid which will increase the hydrostatic fluid pressure - this causes an increase in the pressures opposing filtration
44
What happens to GFR in a patient that has diarrhoea and how
Patient is dehydrated and this increases the concentration of plasma proteins. This then increases the capillary oncotic pressure which opposes filtration. This then decreases the net filtration pressure and therefore decreases GFR
45
What happens to GFR in a patient that has severe burns and how
Los plasma proteins from the site of injury which causes a decrease in capillary oncotic pressure which results in an increase in GFR
46
What is plasma clearance
a measure of how effectively the kidneys can clean the blood of a substance It equals the volume of plasma completely cleared of a particular substance per minute
47
How can we calculate the clearance of a substance
Rate of excretion / plasma concentration
48
What are the normal units for plasma clearance
ml/min
49
What is inulin
exogenous compound that is not produced naturally by the body found in onions and garlic
50
Inulin is metabolised by the kidney. True or False
False
51
Why is inulin important in terms of calculating GFR
As it is not metabolised, absorbed or secreted, we can calculate the GFR based on the inulin clearance. all inulin would leave the body in urine
52
What is the normal level of inulin clearance
125ml of inulin-free plasma is returned to the circulation per minute
53
What is the draw back of measuring inulin
we have to infuse it into the subject and is therefore not ideal
54
What substance can be measured instead of inulin
creatinine - it gives us a close approximation of GFR level
55
What is the clearance rate of glucose
0 | All glucose is reabsorbed and none should be in the urine
56
What is the clearance for substance which are filtered, partly reabsorbed and not secreted. Give an example of this type of substance
Less than GFR (we excrete less than what was initially filtered) Urea
57
What is the clearance for substance which is filtered, secreted but not reabsorbed. Give an example of this type of substance
More than GFR. More ions are added to the initial tubular fluid H+ ions
58
What happens to the substance if the clearance is less than GFR
substance is reabsorbed
59
What happens to the substance if the clearance is more than GFR
Substance is secreted into the tubule
60
What happens to the substance if the clearance is equal to the GFR
The substance is not reabsorbed or secreted
61
How can we calculate the clearance
concentration of substance in urine x urine flow rate all divided by the concentration of substance in plasma
62
What is Para-amino hippuric acid (PAH)
exogenous organic anion
63
Why is PAH used clinically
To measure renal plasma flow
64
How is PAH cleared
it is freely filtered at the glomerulus secreted into the tubule from the blood (not reabsorbed) completed cleared from the plasma
65
How is PAH unique
all the PAH in the plasma that escapes filtration is secreted from the peritubular capillaries into the tubular fluid
66
What is the normal clearance value of PAH | What does this also equal
650ml/min | Renal plasma flow (RPF)
67
What criteria does a substance have to make in order for it to be used as a clearance marker
Non-toxic Inert (i.e. not metabolised or broken down in the kidney) Easy to measure in urine and plasma
68
What should a GFR marker also be
Filtered freely | NOT secreted or reabsorbed as it passes along the nephron
69
What should a RPF marker also be
filtered and completely secreted
70
What is the filtration fraction
The fraction of plasma flowing through the glomeruli that is filtered into eh tubules
71
How can we calculate the filtration fraction
GFR/ Renal plasma flow
72
What is the filtration fracture in healthy individuals
20% 20% of the plasma that enters the glomeruli is filtered. The remaining 80% moves on to efferent arterioles and then the peritubular capillaries
73
How much of the cardiac output do the kidneys receive
24%

SM Renal (23 decks)

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