FINAL EXAM - Lecture 3 Flashcards
Control point that the body manipulates to control blood flow and filtration in the glomerular capillaries
Afferent arteriole
If kidney sees that blood flow is too low, what happens?
Afferent arteriole relaxes to allow more blood flow
If kidney detects blood flow is too much, what happens?
Afferent arteriole constricts more to reduce blood flow
Characteristics of blood flow auto regulation?
Imperfect, it is not a flat line like brain and spinal cord. It is slightly increased along the regulated portion.
The “imperfect” significance of the slanted line in renal auto regulation is because of what?
It’s how the kidney gets rid of fluid when blood pressure is high, or retains fluid when blood pressure is low.
Plasma oncotic pressure in the Afferent arteriole
28mmHg
How does the glomerular capillary plasma oncotic pressure differ from general capillaries?
The pressure changes throughout the capillaries due to the filtration. In a healthy patient, there shouldn’t be any plasma colloids lost. Although, there is a lot of fluid lost, therefore the oncotic pressure goes up.
What the is the beginning and end plasma oncotic pressure of glomerular capillaries? Middle?
28 and 36. 32.
Hydrostatic pressure of container that fluid is initially being filtered into
It fills up until it reaches 18mmHg
Oncotic pressure of container initially being filtered into
Should be 0 in a healthy patient.
Net FILTRATION pressure of glomerular capillaries
60mmHg (capillary blood pressure)
- 32mmHg (average oncotic pressure opposing filtration)
- 18 mmHg (physical fluid pressure opposing fimtrstion)
= 10mmHg, drives filtration to a tune of 125mL/min
Kf means? What are the calculations?
Filtration coefficient that goes along with NFP.
Filtration rate = Kf (NFP)
125mL/min = Kf (10mmHg)
= 12.5mL/min/mmHg(?)
Efferent arteriole characteristics
Sits post-glomerular capillaries.
Kidney uses this to fine-tune GFR by constricting or relaxing.
How can the kidney increase GFR?
Contract efferent arteriole to increase upstream capillary blood pressure, increases filtration forced out.
Blood pressure at end of efferent arteriole is
18mmHg
Where is the greatest blood pressure drop in the blood vessels kidneys?
Efferent arteriole has the highest vascular resistance.
Blood pressure in the Afferent arteriole goes from 100 to 60 (40 point drop). But after the glomerular capillary, it drops to 18. Therefore, efferent arteriole has the highest drop of 42.
Second set of capillaries, directly after efferent arteriole
Peritubular capillaries
Role of PT capillaries
Reabsorption of fluid that was filtered in the tubule that the kidney decided to hang onto.
What % of everytning filtered will be re-absorbed?
99%
What is the route of re-absorption?
Through or between cells that make up wall of tubule. Some parts of kidneys have wide gaps that allow water and small ions to go in between the cells to be reabsorbed
What sits between tubule and the PT capillaries?
Matrix that makes up the renal interstitium. Made of proteins and ions. When things are reabsorbed, it has to pass through this.
Plasma oncotic pressure average of PT capillaries
32mmHg
Blood pressure of PT capillaries
Beginning: 18mmHg
Middle: 13mmHg
End: something lower than 13mmHg lol
PIEisf of renal interstitium
Lots of proteins in there, it’s 15mmHg
Physical fluid pressure of renal interstitium (Pisf)
6mmHg
NFP of PT capillaries
-10mmHg
NRP of peritubular capillaries
10mmHg
What is the 125mL/min being filtered?
Not the blood, it’s plasma. RBCs shouldn’t be filtered.
What % of plasma is filtered when it goes through glomerular capillary?
1/5th or 20% of the plasma
Excretion is the process of
removing things from the body via the urine
Equation for excretion
Filtration - reabsorption + secretion = Excretion
What is secretion
Typically toxins that the kidney really wants to get rid of, are actively pumped into the tubule.
Can also be excessive ions such as potassium, if the body has too much of it.
What is the path for secretion?
specialized transport system that is the reverse path of reabsorption, through or between the cells/interstitium, into the tubule.
How is excretion measured? (Units)
in volume (mL’s) or quantities of substances (mol or mg)
If the filtration fraction is higher than normal, what happens to the glomerular colloid osmotic pressure from beginning to end?
Becomes more concentrated, resulting in higher blood pressure. More fluid is being filtered and proteins do not get filtered.
If the filtration fraction is lower than normal, what happens to the glomerular colloid osmotic pressure from beginning to end?
Lower pressure.
What are total effects of excess contraction of efferent arteriole?
Increased GFR, increased glomerular colloid osmotic pressure.
Filtration fraction equation, what is a normal number, and what percent of the plasma is that?
GFR/Renal plasma flow (e.g. 125/660 = 0.19) which is 19%
Renal blood flow mL/minute
1100mL/min
What percent of cardiac output is renal blood flow?
22% or 1100mL/min
Renal plasma flow equation
Assuming 0.4 HCT, the equation is 0.6 x RBF
0.6 x 1100mL/min = 660mL/min
If hematocrit is 55%, what is the RPF in an otherwise healthy patient?
0.45 x 1100mL/min = 495mL/min
If we need to adjust renal blood flow, what is adjusting?
Afferent arteriole
If we need to adjust GFR, what is adjusting?
Efferent arteriole
If we have a relaxed afferent and efferent arteriole, what are the effects?
Increased blood flow.
Afferent arteriole increases blood flow and increases GFR and capillary pressure, but the relaxed efferent arteriole will decrease GFR/cap pressure, so it counteracts. The end result is just increased blood flow.
If someone is sick in the ICU, what can happen with their autoregulation?
Afferent arteriole cant relax as well as it normally does in order to increase blood flow, so they need a bit higher of total blood pressure to prevent lack of perfusion to kidneys.
This is why patients in ICU wouldn’t pee when they were hypotensive and we had to watch their urine output!
When we are hypertensive beyond autoregulation, how does GFR react?
It increases, but doesnt increase at the same rate of increasing hypertension. Kidneys are generally good at not increasing GFR too much with extreme hypertension.
When we are hypotensive beyond autoregulation, how does GFR react?
GFR is directly correlated with hypotension, so as blood pressure tanks, so does GFR (unlike with hypertension)
Why is the GFR not going up too high with extreme hypertension a good thing?
Its good because the body may be purposely causing extreme hypertension, such as when the brain had a stroke and the body is trying to compensate by increasing brain perfusion. It would suck if the kidneys just started dumping urine and losing volume.
What is a normal urine output in this class?
1mL/min
Sodium follows which filtration/secretion/reabsorption?
Filtration with partial reabsorption, partial urine excretion.
Typically, body keeps excessive amounts of sodium
Glucose follows which filtration/secretion/reabsorption process?
Filtration with complete reabsorption. None should be present in the urine, if healthy.
When can glucose be present in urine?
Extremely high blood sugar, or something is wrong with transport system with reabsorption.
What is the max amount of substance that can be filtered when it passes through glomerular capillary?
1/5th, cause thats how much of the plasma gets filtered each pass through. So 4/5ths of the substance doesnt get filtered.
If something needs to be completely excreted, how does it get it out of the blood circulation?
1/5th was filtered, then the rest was secreted into the tubule.
Diagnostic compound that follows complete excretion via filtration and secretion, and what is used to test?
PAH - Para amino hippuric acid
Renal blood flow. if there is a low amount of PAH excreted compared to what went in the body, that means the renal blood flow is low.
GFR + Reabsorption = Urine numbers
125mL/min -> 124mL/min = 1mL/min excreted
Innermost layer of glomerular capillaries and what are their characteristics?
Endothelial cells, much more permeable to stuff than generic capillary, because they have special openings called fenestrations.
Fenestrations
Specialized openings in renal glomerular endothelium lining that make it extra permeable to stuff.
Middle layer of glomerular capillary
Basement membrane, just connective tissue.
Outer layer of glomerular capillaries
Epithelium lining, specialized to provide support to capillary bed because of the extra pressure.
Podocytes keep frame of capillary supported.
Podocytes
Supportive structure in glomerular capillaries to keep them open against the high pressure. They have slit pores , which are openings between their feet. It also prevents swelling of glomerular capillaries.
What is the basement membrane in the glomerular capillary charged with?
A ton of negative charges, to oppose negatively charged compounds from slipping through fenestrations.
If people have super high chronic blood pressure, how does this affect the kidneys?
Glomerular capillary pressure is also extremely high, and the capillaries will be swollen and nasty. The podocytes help prevent this from happening at a faster rate.
Dextran
synthetic sugar that chemists can make larger or smaller if they want to. They have different charges on their compounds.
In comparing filterability, a polyanionic dextran wont filter as well, while the polycationic dextran will filter much better. A neutral dextran will be in between as far as filterability. This is due to the negatively charged basement membrane in the wall of the capillary. As far as size, the larger = the less filterability.
What will be the best filterable dextran?
Small and positively charged.
What will be the worst filterable dextran?
Large and negatively charged.
What are the 4 compounds that have equal filterability in the glomerular capillary?
H2O, Na+, Glucose, Inulin (NOT INSULIN) should all have 1.0 filterability.
This is also the increasing order in size. H2O being the smallest, inulin largest.
What is a substance used to check GFR levels?
A synthetic compound called Inulin.
inject into patient, and then check the clearance of inulin.
We also use creatinine, but it isnt as accurate.
what are large compounds that have filterability?
Myoglobin (0.75) and Albumin (only 0.005 filterability)
