Physiology 3120 Lecture Notes - Lecture 40: Basal Lamina, Podocyte, Nephron
2 May 2018
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Human Physiology Lecture 40
Renal Physiology Part 2
Glomerular Filtration
- Process of filtering fluid is important
o If kidneys can not filter the fluid, they can not process the filtrate and producing the right
urine
- 20% of all the blood that travels through the glomerulus is filtered into the capsular space
- For filtration to happen, you need a lot of blood going to the kidneys so that blood can get to the
nephrons
o Although we have a lot of blood going to the kidney; of the blood that passes through the
glomerular bed, only 20% is filtered 20% of fluid moving from blood into the capsular
space (A LOT OF FLUID)
o 20% EFFICIENCY
- The rate of fluid filtration is carefully regulated to prevent filtering too much into nephrons or TOO
little
- Since the blood continues to cycle throughout the body all day long, it adds up
- Important to filter a large volume to achieve homeostasis
o To ensure ions are at the right concentration, proper pH and osmolality, excrete toxins
- How much fluid should you filter a day?
o 180 LITERS OF FLUID
- How much urine do you excrete?
o 1.5-2L OF FLUID
o Note: some people with diabetes insipidus produce 20-25 L of urine a day
▪ Upper limit where you can still survive
▪ They have to drink a lot of fluid or get their condition treated
- Consequences of filtering too much or too little fluid into the capsular space?
o Your kidneys NEED to filter 180L
o Filter too much dehydration, lose fluid volume, ruptures and damaging barriers to
filtration, body tries to compensate and make scar tissue
▪ Nephrons die if you filter too much
o Too little filtration can not balance things out well if you do not have product to work with
▪ Have to generate a good amount of filtrate in order for the tubule to perfect the
filtrate composition
▪ If do you not filtrate enough, you can not maintain homeostasis
- Kidneys do not have a great regenerative capacity
o Can not make more juxtamedullary nephrons if you are very dehydrated– you would die
before that happens
▪ Body compensates in other ways makes hormones to regulate fluid balance
o Once you start losing nephrons you can not replace them
o What you got is what you got!
o There is a little bit of ability to correct tubule disruption if there are any cuts in lumen,
damage to kidney
▪ Corrected by local cells
o ONCE U LOSE NEPRHON = ITS OVER
▪ Cant proliferate new nephron
o Example of a regenerative organ = liver, skin
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▪ Skin regenerates well when you’re young, but as you get older it loses its capacity
- The glomerular filtration rate (GFR) is due to the net of the forces in the corpuscle
o Rate you filter fluid tells us how functional your kidneys are (how much fluid is filtered in a
period of time)
o 180L/day is normal
o Reason why you have fluid being filtered at a certain rate – it is because there are pressures
that surround the corpuscle
▪ Forces impact how much fluid moves
▪ There are 4 forces results in net filtration pressure
- GFR = amount of fluid/solutes that are filtered per unit time into Bowman’s space from the
glomerular capillaries
o Rate is due to forces in the nephron
Forces at the Corpuscle
- 1. Hydrostatic Pressure of Glomerular Capillaries (PGC)
o Pressure created due to the presence and movement of fluid (blood) through the glomerular
capillaries
o Pressure caused by the fact that there is fluid in the glomerular capillary
▪ Fluid is blood!
▪ Blood travels each of the nephrons in the first capillary bed b/c the heart is pushing
the blood through the body
o Capillaries are leaky – fluid pushed through, and pushes out
o GOOD FORCE FOR FILTRATION
▪ Generally, the largest force that contributes to filtration
- . Hydrostatic Pressure of Bowman’s Capsule (PBC)
o Pressure created due to the presence of fluid filtrate in Bowman’s space
o Pressure of fluid that sits in the Bowman’s capsule
▪ Fluid wants to move into the space, fluid is in the space – those two pressures fight
against each other
o INHIBITS FILTRATION
▪ Fluid is in the capsular space – causes a back pressure that inhibits filtration
▪ Fluid in the capsular space can only leave via proximal tubule; there is a fluid that
builds up in the capsular space
▪
- . Colloid Osmotic Pressure of Glomerular Capillaries (πGC)
o Pressure created due to the presence of proteins in the fluid (blood) in the glomerular
capillaries
o In the blood, there are many proteins
▪ Pressure due to the proteins
o Proteins have a high affinity for water
▪ WHEREVER THERE ARE PROTEINS, THERE WILL BE AFFINITY FOR THE FLUID
o Fluid wanting to leave and get into the space is coming back toward the proteins
o INHIBITS FILTRATION
▪ Since proteins are in the blood, they will not let go of the water – want the water to
stay by
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- . Colloid Osmotic Pressure of Bowman’s Capsule (πBC)
o Pressure created due to the presence of proteins in the fluid filtrate in Bowman’s space
o IF there were proteins that made it into the capsular space, those proteins would create a
pressure
▪ That pressure would draw fluid toward proteins
o Proteins in the capsular space would promote filtration
▪ Have a force in the direction of the capsular space
o PROMOTE FILTRATION
Net Filtration Pressure
Net Filtration = (PGC + πBC)- (PBC + πGC)
- Net Filtration = 10 mm Hg
o If you are healthy and normal
o Promotes fluid filtration at a rate of 180L/DAY
▪ Normal value
o Usually, the net result is that you filter fluid into your corpuscle space = GOOD
o IF higher than 10 = more filtration
▪ Higher the net filtration pressures the more fluid you will filter
o IF lower than 10 =
▪ Lower the net filtration pressure, the less fluid you will filter per fluid time
- Two pressure in the direction of filtration
o Hydrostatic pressure of the glomerular capillaries
o Colloid osmotic pressure of Bowman’s capsule
- Two pressures against filtration
o Hydrostatic pressure of Bowmans capsule
▪ Having fluid in the capsular space prevents fluid from filtering
o Colloid osmotic pressure of glomerular capillaries
- NET = FILTRATION – AGAINST FILTRATION
- LARGEST CONTRIBUTOR TO THE NET FILTRATION PRESSURE = BLOOD PRESSURE EXPERIENCED
IN KIDNEY
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find more resources at oneclass.com
Document Summary
If kidneys can not filter the fluid, they can not process the filtrate and producing the right urine. 20% of all the blood that travels through the glomerulus is filtered into the capsular space. The rate of fluid filtration is carefully regulated to prevent filtering too much into nephrons or too little. Since the blood continues to cycle throughout the body all day long, it adds up. Important to filter a large volume to achieve homeostasis: to ensure ions are at the right concentration, proper ph and osmolality, excrete toxins. How much fluid should you filter a day: 180 liters of fluid. If do you not filtrate enough, you can not maintain homeostasis. The glomerular filtration rate (gfr) is due to the net of the forces in the corpuscle: rate you filter fluid tells us how functional your kidneys are (how much fluid is filtered in a.
