Final Exam - Renal/Biophysics Flashcards
(84 cards)
1
Q
What is pressure described as in mmHg?
A
The force it takes to move a column of Hg 1 mm
2
Q
What is the most important determinant for blood flow?
Describe the determinant’s function.
A
- Vascular resistance
- Higher resistance = decreased blood flow after resistance and higher pressure before resistance
- Determines blood pressure
- Regulated by arterioles
3
Q
Describe the pressures found before and after a point of resistance?
A
- Between source of force and resistance = high pressure
- After source of resistance = low pressure
4
Q
What is the inverse of vasular resistance?
Describe it’s characteristics?
A
- Vascular Conductance
- Describes ease of blood flow
- Very easy to drive blood = high conductance
- Hard to drive blood = low conductance
5
Q
Where is the vast mojority of blood found?
A
- Systemic veins
6
Q
Describe a system in series and its resistance?
A
- A system that has tubes or pathways arranged end to end
- The resistance is equal to the sum of each tubes individual resistance
7
Q
Describe a system in parallel and its resistance?
A
- Tubes of equal length, size, and resistance in parellel
- This decreases resistance because of the increase in number of potential pathways
8
Q
What does cross sectional area describe?
A
The area inside the cross-section of a vessel
9
Q
Describe the cross sectional area in different vessels and how it relates to velocity?
A
The smaller the cross sectional area, or fewer pathways, the higher the flow
The larger the cross sectional area and number of pathway the slower the flow
The capillaries have the lowest velocity because there is many, many of them, and therefore have a large cross sectional area.
They are also after the resistance arteries, causing them to have slower velocity.
The further away from the heart, the slower the velocity
10
Q
Explain the dip in pressure when blood arrives are the small arteries and arterioles?
What drug works on these vessels?
A
The small arteries and arterioles are high resistance vessels, and are primary determinants of our blood pressure.
This means before the resistance pressure is high and after the resistance pressure is low.
There is also an increased number of pathways the further from the heart.
Phenylephrine squeezes resistance vessels causing an increased pressure in the large vessels before the “choke point”, and decreased resistance after the “choke point”
11
Q
How is the amount of blood flow to a tissue determined?
A
Blood flow is increased or decreased based upon a tissue’s metabolic demands.
12
Q
Describe laminar flow?
A
Flow of blood where all blood is moving in the same direction, very efficient
Blood closest to the vessels walls have more resistance and have lower velocity than the blood furthest from the walls
13
Q
Describe turbulent/disorderly flow?
What are its adverse effects?
What can cause it?
A
Blood is flowing in many different directions including into the vessel wall
Cholesterol and calcium is being deposited more because blood is being slammed into the vessel wall, leads to vessel remodeling
Typically caused by a resistance or choke point in the vessel disturbing flow and causing blood to spray onto the walls after the choke point (like finger over a water hose)
14
Q
How much blood do the kidneys get?
Why is this important?
A
- ~20% of cardiac output or 1100 mL/min
- The kidneys recieve more blood than they metabolically need, but require a larger flow of blood in order to adequately filter
15
Q
What is Ohm’s Law?
When used for vasculature?
A
V=IR
For the vasculature: Delta Pressure = flow x vascular resistance
16
Q
What does Poiseuille’s Law tell us regarding blood flow?
A
That a very small change in vessel diameter can cause a large change in flow
17
Q
How can you determine vascular resistance in the kidney?
A
Rewrite Ohm’s Law: R = Delta P/F
F = 1100 mL/min (20% of 5L CO)
18
Q
How could you calculate peripheral vascular resistance?
A
R= delta P/F
Delta P = difference is pressure between Aorta and R atria
F = cardiac output
19
Q
How could you calculate vascular conductance?
A
Vascular conductance = 1/Resistance
20
Q
What is normal pressures are the end and begining of a capillary?
A
Beginning: 30 mmHg
End: 10 mmHg
21
Q
Define filtration and reabsorption?
A
Filtration: Fluid moving out of the capillaries
Reabsorption: Fluid moving into the capillaries
22
Q
What is the primary cause of pressure drop from large arteries to capillaries?
A
High vascular resistance from arterioles
Not due to the increased number of pathways
23
Q
What controls the blood flow through the capillaries?
A
Arterioles - they have lots of smooth muscle that can increase or decrease blood flow to the capillaries
24
Q
How many capillaries are in the body?
How much surface area do they make up combined?
A
> 10 Billion
500-700 square meters
25
Compare diameter, cross-sectional area, and blood flow in the aorta and vena cavae?
**Aorta**: internal diameter is relatively small and there is only one path for all the blood to take, making the cross sectional area low and therefore the velocity very high.
**Vena cavae**: There are 2 pathways (inferior and superior) and the internal diameter is slightly larger. Because there are 2 paths with larger diameters, the cross sectional area is larger than the aorta, causing a lower velocity of blood flow.
26
Describe the strucuture of the arterioles and it's function?
* Very thick walls with smooth muscles allowing for regulation of vascular resistance
* Controls flow of blood to capillaries
* Small internal diameter
* High wall thickness:internal diameter ratio
27
Describe the structure of the capillaries and it's function?
* Wall is only 1 layer thick comprised of only endothelial cells
* Cannot contract or relax
* This allows for nutrient exchange
28
How does the cross sectional area of the capillaries relate to blood flow?
Because the are billions of capillaires, the cross sectional area is very high leading to a slow velocity of blood flow
29
What is the normal arterial blood pressure (MAP)?
100 mmHg
30
What are the 4 capillary starling forces?
1. Pcap: Capillary Hydrostatic Pressue
2. Pisf: Interstitial fluid hydrostatic pressure
3. πcap: Caillary colloid osmotic pressure; oncotic pressure
4. πisf: Interstitial fluid colloid osmotic pressure
31
Describe systemic Pcap?
* The hydrostatic or physical fluid pressure inside of the capillary
* 30mmHg at arterial end
* 10mmHg at the venous end
32
Describe systemic Pisf?
* Physical fluid pressure of contained outside of the capillary (interstitium)
* If pressure was positive, will oppose filtration at arterial end and promote reabsorption at venule end.
* Normal pressure is -3 mmHg, due to pull of fluid from interstitium by the lymphatics
33
Describe πcap?
* The pressure contributed by the protiens within the capillary
* Plasma proteins are normal impermeable and help to retain fluid within the CV system (oppose filtration)
* Normal is 28 mmHg
34
Describe what occurs when capillary becomes leaky?
* The cell walls are more porous allowing fluid and proteins to leak out
* This reduces the oncotic pressure of proteins within the capillary because the semipermeable membrane has been lost
* This makes it difficult to keep fluids within the CV system
* Occurs during sepsis or hemmorhage
35
What are the contributing structures for πisf?
What is the normal pressure for πisf?
* Proteoglycan filaments
* Hyaluronic acid
* Collagen
* These components stay within the interstitium and create πisf
* Normal is 8 mmHg
36
Describe the mechanism of tissue swelling with cell damage?
* Cells are damaged and destroyed, releasing their contents into the interstitium
* This increases the amount of proteins in the ISF and therefore increasing the πisf
* This increase in oncotic pressure pulls fluid from the capillary to the area leading to tissue swelling/edema
37
Describe the mechanism of tissue swelling in sepsis?
* Capillary wall permeability is increased in sepsis leading to an increase in the amount of fluid and protein leakage
* Eventually the capillaries go back to normal but all of the proteins are now stuck in the ISF, causing edema which is hard to remove
38
Desribe how the body can remove excess fluid and proteins from the interstitium?
* The lymphatic system is specialized to remove fluid from the intersititum and return it to the plasma.
* This process is slow and its rate is dependent on movement
* It is not specialized for absorbing protiens, although it can over time slowly
39
What is Kf?
* The capillary filtration coefficent
* Related to capillary permeability and surface area
* Larger surface area leads to increased filtration
40
What contributes to πcap?
* Albumin
* Globulins
* Fibrinogen
41
Describe how the lymphatic system works?
* Returns fluid from interstitial fluid to the the vasculature
* Fluid is moved up to the top of the chest via muscle movement
* Works like the veins, consisting of one way valves keeping the fluid moving in one direction
* Flow can be increased 20 fold during movement
42
What starling forces favor and oppose filtration at the arterial end of capillary?
What is the net filtration pressure here?
* Favor: Pcap + Pisf + πisf
* Oppose: πcap
* Net filtration force: Favors - opposes = 13 mmHg
A positive NFP promotes filtration
43
What starling forces favor and oppose filtration at the venous end of capillary?
What is the net filtration pressure here?
Favors: Pcap + Pisf + πisf
Oppose: πcap
Net filtration pressure: Favors - opposes = -7 mmHg
A negative NFP promotes reabsorption
44
Describe the difference in rate of filtration and absorption in the capillaries?
What keeps the difference in balance?
The filtration pressure (13mmHg) is greater than the reabsorption pressure (7mmHg), meaning more fluid is being filtered than reabsorped.
This excess in filtered fluid must be scavenged by the lymphatic system, keeping fluid within the interstitium in balance
45
What is the average overall capillary blood pressure?
Why?
* 17.3 mmHg
* The capillary gets larger from arterial to venous end
46
What is the average net filtration pressure (NFP) in an individual capillary?
* 0.3 mmHg in each individual capillary
* Although this number is low, remember there are many many capillaries that in summation can filter a lot of fluid
47
What are some things that are permeable and impermeable in the capillary?
What about in the blood brain barrier?
* Water and small ions can pass easily
* Glucose passes but a lower rate because its larger
* Albumin is massive in comparison and only a very small amount is filtered
The blood brain barrier has tight junctions that prevent the movement of even small ions. So ions and glucose require specialized transporters to cross into the brain.
48
What causes the large drop in pressure from the blood that enters to the blood that exits the kidney?
There is a lot of vascular resistance within the kidney, dropping the pressure as it moves through.
49
Describe the path of blood flow into and through the kidneys?
Renal artery - arterial branches - afferent arteriole - glomerular capillaries - efferent arteriole - paratubular capillaries
50
What is the difference in pressure from the afferent arteriole to the glomerular capillaries?
What causes this?
Afferent arteriole: 100 mmHg
Glomerular capillaries: 60 mmHg
There is a lot of resistance within the afferent arterioles
51
The systemic capillaries have a pressure of 30 mmHg and the renal capillaries have a pressure of 60 mmHg. Explain why this is important?
The pressure is doubled in the glomerular capillaries which drives the high rate of filtration, which is what it is specialized to do.
52
What is the net filtration rate for the glomerular capilllaries?
125 mL/min
53
How do the kidneys autoregulate their blood pressure in response to changes in systemic blood flow?
What does this help maintain?
When blood flow is decreased to the kidneys, the afferent arteriole relaxes to increase perfusion.
When blood flow is increased to the kidneys, the afferent arteriole constricts to prevent overperfusion.
This helps to maintain GFR at a semi-constant rate.
54
GFR autoregulation is represented by the red line, why is the slope important?
It means that GFR is not maintained perfectly, but allows the kidneys to get rid of more fluid when pressures are high and retain more fluid when pressures are lower.
This helps manage blood pressure long-term.
55
What is oncotic pressure in the afferent arteriole, glomerular capillaries, and efferent arteriole?
Why is this different than systemic capillaries?
Afferent arteriole: 28 mmHg
Glomerular capillaries: 32 mmHg
Efferent arteriole: 36 mmHg
The plasma is becoming more concentrated as it moves through the glomerulus due to fluid loss from filtration
In systemic capillaries, filtration and reabsorption are happening at the same capillary.
In the kidneys, filtration and reabsorption occur at different capillaries
56
What is the hydrostatic pressure and oncotic pressure within the tubule?
Hydrostatic pressure (P): 18 mmHg
πtubule: 0
If we are healthy, we should not be filtering much protein
57
What is the NFP at the glomerular capillaries?
NFP = 60 mmHg - 32 mmHg - 18 mmHg = 10 mmHg
NFP = Pglomerulus - πglomerulus - Ptubule
This is a high NFP that drives the 125 mL/min filtration of the kidneys
58
How do you determine filtration rate?
What is the filtration coefficient in the kidneys?
Filtration rate = Kf (NFP)
125 mL/min = Kf (10 mmHg)
Kf = **12.5 mL/min/mmHg**
59
What is the role/function of the efferent arteriole?
What is normal pressure at the end of the efferent arteriole?
Helps *fine-tune GFR* by increasing or decreasing its vascular resistance, which increases or decreases the pressure within the glomerulus - leading to increased/decreased filtration.
P = 18 mmHg
60
Which arteriole has the highest vascular resistance?
Efferent arteriole: causes a change in pressure of 42 mmHg (60mmHg in glomerulus and 18mmHg at end of efferent arteriole) while the afferent arteriole causes a change in pressure of 40 mmHg (100mmHg at renal artery and 60mmHg at glomerulus)
61
How much of the filtrate is reabsorbed normally?
99% of all filtrate is reabsorbed
62
What two routes can solutes take to be reabsorbed from the tubule?
Transcellular - Directly through the cells lining the tubule through a specialized channel
Paracellular - Small compounds can move *in between* cells via diffusion
63
What is the πPTcap?
Why is there a difference from the πefferent?
* 32 mmHg
* The oncotic pressure is lower here than in the efferent arteriole because the plasma is now more dilute from reabsorption
64
What is the P in the middle of the PT capillaries?
πPTisf?
PPTisf?
P middle of PT capillaries: 13 mmHg
πPTisf: 15 mmHg
PPTisf: 6 mmHg
65
What is the NFP/NRP in the paratubular capillaries?
What does this mean?
NFP: PPTcap +πPTisf - πPTcap - PPTisf
NFP = 13 mmHg + 15 mmHg - 32 mmHg - 6 mmHg = -10 mmHg
NRP: πPTcap + PPTisf - PPTcap - πPTisf
NRP = 32 mmHg + 6 mmHg - 13 mmHg - 15 mmHg = 10 mmHg
Starling forces at the paratubular capillaries favor reabsorption
66
How much of the plasama that moves through the kidneys is filtered?
About 1/5
67
What is excretion?
How can we determine how much is being excreted?
What units can this be measured in?
Excretion = removal of fluids/filtrate from the body as urine
Exrection = filtration - reabsorption + secretion
Volume: mL's per min
Quanity: mols or mg per min
68
What is secretion?
The movement of compounds/solutes from the paratubular capillaries to the tubules
69
Describe what happens to the oncotic pressure in the glomerular capillaries with changes in filtration rate?
How does this occur?
When filtration rate is increased, more fluids are bring filtered, increasing the concentration of proteins (blue line)
When filtration rate is decreased, less fluid is being filtered, diluting and decreasing the concentration of proteins (green line)
The change is filtration rate is accomplished by the efferent arteriole constricting/relaxing, which increases/decreases the golmerular pressure, changing the filtration rate
70
How do you determine filtration fraction?
What is a normal filtration fractions?
GFR/RPF = FF
125 mL/min / 660 mL/min = 0.19 or ~ 20%
71
How do we obtain RPF of 660 ml/min?
RBF = 1100 mL/min
Hct = 0.40
Plasma = 0.60
RPF = 0.60 x 1100 mL/min
RPF = 660 mL/min
72
What effects would you observe if the resistance in the afferent arteriole were increased?
* Decreased renal blood flow
* Decreased pressue in the glomerulus
* Decreased GFR
73
What effects would you observe if the resistance in the efferent arteriole were increased?
* Decreased renal blood flow
* Increased pressure in the glomerulus
* Increased GFR
74
What effects would you observe if the resistance in the afferent arteriole was decreased?
* Increased renal blood flow
* Increase pressure in glomerulus
* Increased GFR
75
What effects would you observe if the resistance in the efferent arteriole were decreased?
* Increase renal blood flow
* Decreased pressure in the golmerulus
* Decreased GFR
76
At what pressures do the kidneys autoregulate?
What can alter this?
* 50 mmHg - 150 mmHg
* In sick patients with comorbidities, their afferent arteriole cannot relax normally, so there LLA is increased and they need more perfusion to maintain autoregulation.
77
Describe autoregulation of renal blood flow, GFR, and urine output at high and low pressures?
GFR is more tightly autoregulated than renal blood flow - preventing unwanted fluid losses.
Because renal autoregulation is imperfect, the body will favor increased urine output and fluid loss at higher pressures (helping decrease BP)and decreased urine output and fluid retention at lower pressures (helping to increase BP).
78
What is normal urine output in health adults?
1 mL/min
79
Explain these different routes through the kidney and examples of things that take each route?
A. Filtration only - compound is completely filtered and not reabsorbed
B. Filtration with partial reabsorption - Na+
C. Filtration with complete reabsorption - Glucose in non-diabetics and amino acids
D. Filtration with full secretion - Para amino hippuric acid (PAH) - compound used to estimate renal blood flow because removal from blood is entirely dependent on renal blood flow. The lower amount in the body = higher renal blood flow, higher amount in the body = lower renal blood flow.
80
What specialized structure allows for increased filtration in the renal capillaries?
Fenestrations in the endothelium
81
Describe the structure that provides support to the glomerular capillaries?
Podocytes, which have extensions with openings called slit pores
82
How does the glomerular capillaries prevent proteins from being filtered?
The basement membrane and endothelium are negatively charged and repels proteins which are negatively charged.
83
How does size and charge of a compound affect renal filtration?
Large and negative compounds compounds are less filterable
Small and positve compounds are more filterable
84
What synthetic compound can be used to estimate GFR?
Inulin - it is completely filtered and not reabsorbed or secreted. It can be measured in the blood and urine to determine GFR
