Sistema Excretor / Renal / Urinário 06 - Filtração Glomerular P2 (Fisiologia) - vídeo-aula

Summary

In this video, Vinícius Jesus explains the crucial process of glomerular filtration and its regulation in the renal system. He discusses the factors that influence glomerular filtration pressure, including hydrostatic and oncotic pressures, and how various diseases can alter these forces. The video also explores the mechanisms of renal autoregulation, particularly the tubuloglomerular feedback system, and the role of hormones and neural inputs in maintaining filtration. Practical examples are given to illustrate how changes in blood pressure, resistance, and renal blood flow affect glomerular filtration, highlighting the body's ability to regulate these processes under different conditions.

Takeaways

• 😀 Glomerular filtration is the process where blood is filtered through the glomerulus to form urine, and it is influenced by various forces like hydrostatic and oncotic pressures.
• 😀 The effective filtration pressure is the sum of the forces that either promote or oppose filtration through the glomerular capillaries.
• 😀 Hydrostatic pressure in the glomerular capillaries is the primary force driving filtration, while hydrostatic pressure in the Bowman's capsule and oncotic pressure in glomerular capillaries oppose it.
• 😀 Under normal conditions, the concentration of proteins in the filtrate is very low, making the oncotic pressure in the Bowman's capsule negligible.
• 😀 Conditions like kidney stones or urinary tract obstructions can increase the hydrostatic pressure in the Bowman's capsule, leading to decreased filtration.
• 😀 Oncotic pressure in glomerular capillaries is affected by plasma protein concentration and the fraction of plasma filtered. High oncotic pressure reduces filtration.
• 😀 Renal blood flow influences glomerular filtration rate (GFR). Changes in arterial pressure or afferent/efferent arteriolar resistance can increase or decrease filtration.
• 😀 The kidneys maintain stable filtration rates even with blood pressure fluctuations through autoregulation mechanisms, such as the juxtaglomerular apparatus.
• 😀 The renin-angiotensin system plays a key role in autoregulation. When filtration drops, renin is released, leading to the formation of angiotensin II, which constricts the efferent arteriole and increases filtration.
• 😀 Hormones like epinephrine, norepinephrine, and endothelin can cause vasoconstriction of renal vessels, reducing renal blood flow and filtration, especially in response to stress or injury.

Q & A

What is glomerular filtration and how is it determined?

Glomerular filtration is the process of plasma being filtered from the blood into the kidney's Bowman's capsule. It is determined by the net effect of hydrostatic and oncotic pressures across the glomerular membrane.

What does 'effective filtration pressure' mean in glomerular filtration?

Effective filtration pressure refers to the net pressure that drives the filtration of plasma from the capillaries into the Bowman's capsule. It is calculated by subtracting the opposing pressures (hydrostatic in the Bowman's capsule and oncotic in the glomerular capillaries) from the favorable ones (hydrostatic in the glomerular capillaries and oncotic in the Bowman's capsule).

What is the role of oncotic pressure in glomerular filtration?

Oncotic pressure, caused by proteins in the plasma, opposes filtration by attracting water back into the glomerular capillaries. It plays a crucial role in regulating the amount of fluid filtered into the Bowman's capsule.

How does the pressure in Bowman's capsule affect filtration?

Increased pressure in Bowman's capsule opposes filtration by pushing the filtrate back into the glomerular capillaries, reducing the overall glomerular filtration rate (GFR). Conversely, a decrease in pressure in the capsule increases GFR.

What happens if there is obstruction in the urinary tract?

Obstruction in the urinary tract, such as the formation of kidney stones, can increase pressure in Bowman's capsule. This can decrease glomerular filtration rate and lead to conditions like hydronephrosis, where the kidney becomes swollen due to urine buildup.

How do changes in the filtration fraction affect oncotic pressure in glomerular capillaries?

An increase in the filtration fraction (the proportion of plasma filtered through the glomeruli) increases the concentration of proteins in the remaining plasma in the capillaries, raising oncotic pressure and decreasing the glomerular filtration rate.

What factors influence glomerular filtration rate (GFR)?

GFR is influenced by factors such as the glomerular hydrostatic pressure, the resistance of afferent and efferent arterioles, and the oncotic pressure in the capillaries. These factors are affected by blood pressure, blood volume, and the vasoconstriction or vasodilation of renal arterioles.

What is the effect of sympathetic nervous system activation on renal blood flow?

Sympathetic nervous system activation can constrict the renal arterioles, reducing renal blood flow and glomerular filtration rate. However, under normal conditions, this effect is usually mild unless there is significant sympathetic stimulation.

How does the renin-angiotensin system contribute to regulating GFR?

The renin-angiotensin system helps regulate GFR by adjusting the diameter of the afferent and efferent arterioles. Angiotensin II constricts the efferent arteriole more strongly, increasing glomerular hydrostatic pressure and maintaining filtration despite low blood pressure.

What role does nitric oxide play in regulating glomerular filtration?

Nitric oxide is a vasodilator that reduces the resistance in renal blood vessels, increasing glomerular filtration rate. It is important for maintaining normal sodium and water excretion by the kidneys.