Glomerular filtration part 1

Kidney 11



Kidney 12


Glomerular filtration

Glomerular filtration is a passive process in which hydrostatic pressure forces fluids and solutes through a membrane. The glomeruli can be viewed as simple mechanical filters because filtrate formation does not consume metabolic energy.

The glomerulus is a much more efficient filter than other capillary beds. One reason is that its filtration membrane has a large surface area and is thousands  of times more permeable to water and solutes. Furthermore, glomerular blood pressure is much higher than that in other capillary beds (approximately 55 mmHg as opposed to 18 mmHg or less), resulting in  a much higher net filtration pressure.  As a result of these differences, the kidneys produce about 180 L of filtrate daily, in contrast to the 2 to 4 L formed daily by all other capillary beds of the body combined.

Molecules smaller than 3 nm in diameter such as water, glucose. amino acids, and nitrogenous wastes pass freely from the blood into thr glomerular capsule. As a result, these substancesusually show similar concentration in the blood and the glomerular filtrate. Larger molecules pass with greater difficulty, and those larger than 5 nm are generally barred from entering the tubule. Keeping the plasma proteins in the capillaries maintains the colloid osmotic (oncotic) pressure of the glomerular blood, preventing the loss of all its water to the renal tubules. The presence of proteins or blood cells in the urine usually indicates a problem with the filtration membrane.


Net filtration pressure

The net filtration pressure, responsible for filtrate formation, involves forces acting at the glomerular bed. Glomerular hydrostatic pressure, which is essentially glomerular blood pressure, is the chief force pushing water and solutes out of the blood and across the filtration membrane. Although theoretically the colloid osmotic pressure in the capsular space of the glomerular capsule “pulls” the filtrate into the tubule, this pressure is essentially zero because virtually no proteins enter the capsule.


Glomerular filtration rate

The glomerular filtration rate is the volume of filtrate formed each minute by the combined activity of all 2 million glomeruli of the kidneys. Factors governing filtration rate at the capillary beds are :

  • Total surface area available for filtration
  • Filtration membrane permeability
  • Net filtration pressure

In adults the normal glomerular filtration rate in both kidneys is 120-125 ml/min. Because glomerular capillaries are exceptionally permeable and have a huge surface area (collectively equal to the surface area of the skin), huge amounts of filtrate can be produced even with the usual modest net filtration pressure.  The opposite side of this “coin” is that a drop in glomerular pressure of only 18% stops filtration altogether.

The glomerular filtration rate is directly proportional to the net filtration pressure, so any change in any of the pressures acting at the filtration membrane changes both the net filtration pressure and the glomerular filtration rate. In the absence of regulation, an increase in arterial (and glomerular) blood pressure in the kidneys increases the glomerular filtration rate.




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12 Responses to Glomerular filtration part 1

  1. This reminds of my work. Oh well, it has way too many medical terms, and sometimes I have to invent new when it comes to new medical devices and genetic research, etc. GFR is an important value, indeed. It never stops amazing me how such tiny things can do so much. I am basically taken away by a complexity of human body.

    Liked by 1 person

  2. I look forward to when you post because they are so interesting!

    Liked by 2 people

  3. I’m not sure I understand exactly how this works, but it is amazing nonetheless. All of this happens and a person isn’t even aware of it. Incredible!

    Liked by 2 people

  4. Learnography says:

    Physiology of Bowman’s capsule well explained

    Liked by 2 people

  5. Diana says:

    You have such an interesting blog! As I work in healthcare my reading is mostly not of this type, but you are fascinating and what you post is cool. Thank you for liking my poetry, you are very kind. 💜
    PS- I imaged a horseshoe kidney today. Quite rare 😊

    Liked by 2 people

  6. Bloggerjosh says:

    Cheers my guy. This will come in handy with my human physio module

    Liked by 2 people

  7. anne leueen says:

    This is new information for me! Very interesting!

    Liked by 2 people

  8. Reblogged this on By the Mighty Mumford and commented:

    Liked by 1 person

  9. Anand says:

    Solute is such an interesting word. Glomerular filters–are they in cells ? I am trying to get a perspective about hierarchy and levels. We name things to use them. The use becomes the name. Thanks for following my blog and visiting. Have a lovely day 🙂 ❤

    Liked by 2 people

  10. lkwatts67 says:

    What are your best suggestions for someone having kidney dysfunction in her early sixties? A friend is trying to deal with this but has a lot of reflux and numbness in her fingers.

    Liked by 1 person

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