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Lecture 16

LECTURE 16 Notes. Happy studying

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Department
Biological Sciences
Course Code
BIOC33H3
Professor
Stephen Reid

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Lecture 16
The Renal System and Kidney Function
Hydrostatic Pressure Gradient
Diagram of a general capillary bed
Several pressure involved in forcing fluid across capillary wall from inside to the ECF and
forces that work in reverse that draw fluid from ECF into capillary bed
First pressure is the hydrostatic pressure (blood pressure in blood vessels) and the other
is the oncotic pressure
Capillary attached to artery and vein
Two hydrostatic pressure important in regulating the direction of fluid movement:
oCAP (within the capillary)
oISF (pressure within the interstitial fluid)
ISF: small hydrostatic pressure of ~1 mmHg
oOccurs in the ECF in general (doesnt matter where in the circulatory system).
This pressure occurs relatively constantly everywhere
Pressure in blood vessel will change as we go from artery to venous side: Because
capillary bed resist flow, pressure will drop from arterial side of capillary bed to the
venous side
Arterial to capillary bed: 38 mmHg in arterioles in the beginning of capillary as the bed is
beginning to form
From inside to outside of capillary, theres a pressure difference of ~37 mmHg across the
capillary wall on the arterial side of capillary bed
As we go across capillary bed and end up in the venous side, theres a pressure drop
such that the hydrostatic pressure at end of capillary bed is only 16 mmHg
Venous side, hydrostatic pressure differential of 15 mmHg
We have a larger pressure gradient in terms of hydrostatic pressure gradient on the
arterial side
Hydrostatic pressure is first important pressure that will cause fluid movement
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oForce that pushes fluid in one pressure down their gradient (forcing fluid out of
vessel)
Hydrostatic pressure can be countered by the oncotic pressure gradient
Oncotic Pressure Gradient
Osmotic pressure caused by presence of proteins in the plasma
ISF (ECF fluids surrounding tissues and capillary bed) has no protein in it
Oncotic pressure is ~0 (no protein present in ECF) but there are proteins in the plasma
and the oncotic pressure exerted by them is ~25 mmHg
Proteins are too large to move across capillary wall so they dont leak out into ECF.
Thats why there are no protein and hence no oncotic pressure in the ISF
Oncotic pressure is constant going from arterial side to the venous side
Oncotic pressure is ~25 mmHg across the length of the entire capillary bed
Hydrostatic pressure changes but oncotic pressure dont change
Small solutes (like ions), glucose, and amino acids do manage to leak across capillary
beds and found in similarly concentrations in plasma but proteins are high in blood and
negligible in interstitial fluid
Net Filtration Pressure
Balance of forces between hydrostatic pressure and oncotic pressure that will lead to
driving force of movement
Varying pressure between the capillary and ISF across the length of the capillary
oHigh capillary pressure = forcing blood out
oHigh interstitial pressure = forcing blood in
oOncotic pressure gradient within the blood vessel will drive blood in
oIn theory, there will be an oncotic pressure gradient in ISF that will drive blood out
(IF IT EXIST) this is 0 so this variable only exist in theory
Slide 5
Gradient for fluid movement out of capillary and into ISF on arterial side but on venous
side, theres gradient for movement from ISF into the capillary
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Arterial side:
onet hydrostatic pressure of 37 mmHg pushing fluid outward
oOncotic pressure of 25 mmHg pushing fluid in
oNet filtration pressure (NFP): 37 pushing out, 25 pushing in = 12 mmHg pushing
fluid out into the ISF
Venous side
oOncotic pressure of 25 mmHg pushing fluid in
oHydrostatic pressure of 15 mmHg pushing fluid out
oNet filtration pressure will draw fluid into the capillary bed. (absorption)
Slide 6
From a whole person perspective: 20 litres of fluid filtered from capillary out into ISF
Every day: 17 litres reabsorbed back from ISF into the capillary bed
On balance, there is a net movement of fluid of 3 litres/day (more fluid going out then
coming back in)
3 litres is ultimately returned to circulatory system (not by capillary but into the lymphatic
system)
Lymphatic system
Consist of blind-ended lymph capillary thats juxtaposed amongst capillary bed
Main role is to reabsorbed fluid that has been filtered across capillary bed and returned
into the vena cava
Excess fluid thats leak across the systemic capillary will move into lymphatic capillary
and dumb back into vena cava
Filtered return to right atria and it becomes part of the plasma again
Oncotic and hydrostatic pressure gradient are the same forces involved in filtering
plasma at the kidney in the first stages of pre-urine formation
Kidney Function
The kidney filters the plasma volume every 22 minute
Major organ for keeping blood and ECF at a constant [ionic]
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Description
Lecture 16 The Renal System and Kidney Function Hydrostatic Pressure Gradient Diagram of a general capillary bed Several pressure involved in forcing fluid across capillary wall from inside to the ECF and forces that work in reverse that draw fluid from ECF into capillary bed First pressure is the hydrostatic pressure (blood pressure in blood vessels) and the other is the oncotic pressure Capillary attached to artery and vein Two hydrostatic pressure important in regulating the direction of fluid movement: o CAP (within the capillary) o ISF (pressure within the interstitial fluid) ISF: small hydrostatic pressure of ~1 mmHg o Occurs in the ECF in general (doesnt matter where in the circulatory system). This pressure occurs relatively constantly everywhere Pressure in blood vessel will change as we go from artery to venous side: Because capillary bed resist flow, pressure will drop from arterial side of capillary bed to the venous side Arterial to capillary bed: 38 mmHg in arterioles in the beginning of capillary as the bed is beginning to form From inside to outside of capillary, theres a pressure difference of ~37 mmHg across the capillary wall on the arterial side of capillary bed As we go across capillary bed and end up in the venous side, theres a pressure drop such that the hydrostatic pressure at end of capillary bed is only 16 mmHg Venous side, hydrostatic pressure differential of 15 mmHg We have a larger pressure gradient in terms of hydrostatic pressure gradient on the arterial side Hydrostatic pressure is first important pressure that will cause fluid movement www.notesolution.com
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