couple questions about kidney

[akimhaneul]

1) In the kaplan bio book, it says that the filtrate in the bowman's capsule is isotonic to the blood in glomerulus. Why is this important and how does this happen?

2) Also, it says that cardiovascular system can vasoconstrict or vasodilate in order to maintain blood pressure and that constriction of afferent arteriole will lead to a lower pressure of blood reaching glomeruli, which allows the juxtaglomerular cells to release renin and help increase blood pressure.
I'm confused about this. I thought vasoconstriction leads to increase in blood pressure.

Thanks!

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[wizzed101]

1. The filtrate is just plasma minus big molecules. It's important because we if the plasma in a glomerulus is hypertonic to that inside a bowman's capsule, it will reduce filtrate flow rate and impair a kidney's function.
2. The order of events is wonky here. But the point is that vasoconstriction of a section will reduce the pressure of out flow at the end of said section. Blood reaching a glomerulus is downstream to the one after the choke point and therefore, has reduced pressure.

Vasoconstriction will certainly NOT lead to an increase in blood pressure in the affected section. That just defies physics. A systematic stress response involves vasoconstriction to certain organs and vasodilation to others directly involved in fight-or-flight response. It usually accompanies with increases heart rate. The overall effect of this channeling of blood is a systematic increase in blood pressure.

When people say vasoconstriction leads to increase BP, they either refer to overall effect of a systematic stress response or the pressure upstream to the point of constriction.

 

[akimhaneul]

1. The filtrate is just plasma minus big molecules. It's important because we if the plasma in a glomerulus is hypertonic to that inside a bowman's capsule, it will reduce filtrate flow rate and impair a kidney's function.
2. The order of events is wonky here. But the point is that vasoconstriction of a section will reduce the pressure of out flow at the end of said section. Blood reaching a glomerulus is downstream to the one after the choke point and therefore, has reduced pressure.

Vasoconstriction will certainly NOT lead to an increase in blood pressure in the affected section. That just defies physics. A systematic stress response involves vasoconstriction to certain organs and vasodilation to others directly involved in fight-or-flight response. It usually accompanies with increases heart rate. The overall effect of this channeling of blood is a systematic increase in blood pressure.

When people say vasoconstriction leads to increase BP, they either refer to overall effect of a systematic stress response or the pressure upstream to the point of constriction.

Could you please explain #2 more? Does pressure decrease because vasoconstriction reduce the flow of liquid?


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[wizzed101]

See Poiseuille's law.

 

[victorias]

1. It is important to note that filtrate is isotonic to blood, meaning that when the filtration process happens at the glomerulus, it is least selective process and everything except for large proteins and red blood cells passes through. And when this filtrate passes through the different sections of the nephron, it becomes with more concentrated or more diluted depending on the needs of the body at the time, resulting in final urine exiting from the collecting ducts.

2. Vasoconstriction of the afferent arteriole will reduce the amount of blood coming into the glomerulus so as a result, the amount of filtrate formed will decrease and the pressure in the glomerulus and efferent arteriole will decrease. You are correct in saying that pressure in the afferent arteriole will increase due to vasoconstriction.

 

[akimhaneul]

1. It is important to note that filtrate is isotonic to blood, meaning that when the filtration process happens at the glomerulus, it is least selective process and everything except for large proteins and red blood cells passes through. And when this filtrate passes through the different sections of the nephron, it becomes with more concentrated or more diluted depending on the needs of the body at the time, resulting in final urine exiting from the collecting ducts.

2. Vasoconstriction of the afferent arteriole will reduce the amount of blood coming into the glomerulus so as a result, the amount of filtrate formed will decrease and the pressure in the glomerulus and efferent arteriole will decrease. You are correct in saying that pressure in the afferent arteriole will increase due to vasoconstriction.

Thank you! So are you saying that since everything except for large proteins and cells become filtrated at the glomerulus, the filtrate in the bowman' capsule has to be isotonic to the blood?




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[victorias]

Yes