10. Write the equation used to define and calculate net filtration pressure (NFP). You may use words or the standard symbols for the terms of the equation. NFP = GHP (6cop +CAP) & Capsulan by droderic pussun glomemton v hydratric pressur 11. In Ila and Ile below you are asked to calculate a numerical value for net filtration pressure first at the afferent end of the glomerular capillaries (1 la) and then at the efferent end of the glomerular capillaries (1 lb). In 1le you are asked to average these two pressures to determine the average net filtration pressure across all of the glomerular capillaries. Don’t forget to include units with your answer. a. At the afferent end of the glomerular capillaries: glomerular capillary blood (hydrostatic or hydraulic) pressure is 60 mm Hg: hydrostatic (hydraulic) pressure in Bowman’s capsule is 15 mm Hg, colloid osmotic pressure of blood in the glomerular capillaries at the afferent end is 21 mm Hg; and colloid osmotic pressure in Bowman’s capsule is 0 mm Hg. Please show your work. b. Does your answer to the above question indicate that filtration or reabsorption is occurring across the glomerular capillaries at their afferent end? c. At the efferent end of the glomerular capillaries: glomerular capillary blood (hydrostatic or hydraulic) pressure is 58 mm Hg; hydrostatic (hydraulic) pressure in Bowman’s capsule is 15 mm Hg; colloid osmotic pressure of blood in the glomerular capillaries at the efferent end is 33 mm Hg; and colloid osmotic pressure in Bowman’s capsule is 0 mm Hg. Please show your work.
The correct answer and explanation is:
Net Filtration Pressure (NFP): Equation
The equation for calculating the net filtration pressure (NFP) across the glomerular capillaries is: NFP=(GHP−CHP)−COP\text{NFP} = (\text{GHP} – \text{CHP}) – \text{COP}
Where:
- GHP = Glomerular hydrostatic pressure (the blood pressure within the glomerular capillaries)
- CHP = Capsular hydrostatic pressure (the pressure exerted by the fluid in Bowman’s capsule)
- COP = Colloid osmotic pressure (the osmotic pressure due to proteins in the blood plasma)
1a. NFP at the Afferent End of the Glomerular Capillaries
Given values:
- GHP = 60 mm Hg
- CHP = 15 mm Hg
- COP = 21 mm Hg (colloid osmotic pressure in blood)
- Colloid osmotic pressure in Bowman’s capsule = 0 mm Hg (negligible)
Substitute values into the formula: NFP=(60−15)−21\text{NFP} = (60 – 15) – 21 NFP=45−21\text{NFP} = 45 – 21 NFP=24 mm Hg\text{NFP} = 24 \, \text{mm Hg}
1b. Filtration or Reabsorption at the Afferent End?
Since the NFP at the afferent end is positive (24 mm Hg), it indicates filtration is occurring. Filtration happens when the outward force (GHP – CHP) exceeds the inward force (COP).
1c. NFP at the Efferent End of the Glomerular Capillaries
Given values:
- GHP = 58 mm Hg
- CHP = 15 mm Hg
- COP = 33 mm Hg (colloid osmotic pressure in blood)
- Colloid osmotic pressure in Bowman’s capsule = 0 mm Hg (negligible)
Substitute values into the formula: NFP=(58−15)−33\text{NFP} = (58 – 15) – 33 NFP=43−33\text{NFP} = 43 – 33 NFP=10 mm Hg\text{NFP} = 10 \, \text{mm Hg}
1d. Average NFP Across the Glomerular Capillaries
The average NFP is the mean of the afferent and efferent NFP values: Average NFP=NFP at afferent end+NFP at efferent end2\text{Average NFP} = \frac{\text{NFP at afferent end} + \text{NFP at efferent end}}{2} Average NFP=24+102\text{Average NFP} = \frac{24 + 10}{2} Average NFP=17 mm Hg\text{Average NFP} = 17 \, \text{mm Hg}
Explanation
The net filtration pressure (NFP) determines the movement of fluid and solutes across the glomerular capillaries into Bowman’s capsule. It reflects the balance between forces favoring filtration (glomerular hydrostatic pressure, GHP) and opposing forces (capsular hydrostatic pressure, CHP, and colloid osmotic pressure, COP).
At the afferent end, GHP (60 mm Hg) is significantly higher than CHP (15 mm Hg) and COP (21 mm Hg). This creates a positive NFP of 24 mm Hg, which drives filtration. Filtration occurs when the pressure pushing fluid out of the glomerular capillaries (GHP – CHP) exceeds the inward osmotic pull (COP).
As blood progresses to the efferent end, the COP increases due to the higher concentration of proteins in the plasma (because water is filtered out). GHP slightly decreases (58 mm Hg), while CHP remains constant (15 mm Hg). These changes result in a reduced NFP of 10 mm Hg at the efferent end, meaning filtration still occurs, but at a slower rate.
The average NFP (17 mm Hg) represents the net driving force for filtration across the glomerular capillaries. Positive NFP throughout the capillary length ensures continuous filtration, which is crucial for removing waste products and maintaining fluid and electrolyte balance in the body.
The calculations highlight the dynamic nature of pressures in the glomerular capillaries, reflecting the kidney’s efficiency in maintaining filtration while preventing excessive loss of blood plasma.