Kidney as a filter Flashcards
Q: What are the six general functions of the kidneys?
A: The six general functions of the kidneys are:
Regulation of extracellular fluid (ECF) and blood pressure.
Regulating osmolarity.
Maintaining ion balance.
Regulating pH.
Waste excretion.
Hormone production.
Q: What is the path of blood flow through the nephron?
A: Blood flows from the renal artery into the portal system: Afferent arteriole > Glomerulus > Efferent arteriole > Peritubular capillaries (vasa recta) > Venules.
two types of nephrons
the two types of nephrons are cortical nephrons and juxtamedullary nephrons.
A: Cortical nephrons are located primarily in the renal cortex.
A: Juxtamedullary nephrons are located close to the boundary between the renal cortex and the renal medulla, with longer loops of Henle extending into the medulla region
A: Juxtamedullary nephrons play a crucial role in concentrating urine by creating an osmotic gradient in the medulla, whereas cortical nephrons are primarily involved in the reabsorption and secretion processes in the cortical region.
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cortical nephrons
A: Cortical nephrons primarily handle the filtration of blood to form urine, reabsorption of essential nutrients, ions, and water back into the bloodstream, and secretion of waste products into the urine. They have glomeruli located in the outer cortex and shorter loops of Henle, which only dip slightly into the medulla, making them less involved in urine concentration.
A: Cortical nephrons primarily handle the filtration of blood to form urine, reabsorption of essential nutrients, ions, and water back into the bloodstream, and secretion of waste products into the urine. They have glomeruli located in the outer cortex and shorter loops of Henle, which only dip slightly into the medulla, making them less involved in urine concentration.
juxtamedullary nephrones
A: Juxtamedullary nephrons are crucial for concentrating urine. They have glomeruli near the corticomedullary junction and longer loops of Henle that extend deep into the medulla. These long loops create a high osmotic gradient in the medulla, which helps in reabsorbing water from the collecting ducts, thereby concentrating the urine.
A: The vasa recta, straight capillaries that parallel the loops of Henle in juxtamedullary nephrons, play a vital role in maintaining the medullary osmotic gradient. They participate in the countercurrent exchange mechanism, which helps preserve the gradient necessary for water reabsorption and urine concentration.
Q: What are the basic renal processes?
A: The basic renal processes are:
Glomerular filtration. (blood -> afferent arteriole –> glomerulus –> filtered across bowmans capsule –> kidney tubules)
Tubular reabsorption == reabsorbed from kidney tubules to back to the body
Tubular secretion. == transport specifically additionaly substances that were not filtered initally due to size, charge or they were bound to protein
==> highly specific, adds substances from blood to tubules
These processes lead to urine production.
tubular reabsorption
selective movement of filtered substances from the tubular lumen into the peritubular capillaries
aim to regulate body fluid
- Na+ is reabsorbed by active transport from tubule lumen to ECF
- electrochemical graident drives anions reabsorption, Na+ and Cl- makes salt which drives H2O
- movement of Na+ creates osmotic gradient => H2O follow by osmosis
- concentrations of solutes (K+, Ca2+, urea) increase as fluid volume in lumen decrease
- solutes are reabsorbed by diffusion through membrane transporters or by the paracellular pathway (between cells)
all can go through the paracellular pathway except for Na+ because they’re all passive diffusion
all go transepithelial (across a cell)
tubular secretion
selective movement of non filtered substances from peritubular capillaries into the tubular lumen
Q: What are the three filtration barriers substances must pass through before entering the tubule?
A: The three filtration barriers are:
Glomerular capillary endothelium == fenestrated/ have pores for fluid to move through more easily
Basement membrane.
Epithelium of Bowman’s capsule.
Q: What are podocytes and their function?
A: Podocytes are cells that lines capillaries in the Bowman’s capsule that contain long cytoplasmic extensions called foot processes, which leave narrow filtration slits essential for the filtration process.
A: Mesangial cells hold capillaries in close association, allowing them to provide structural support. They can contract to move capillaries closer together, which can change how podocytes line the capillaries and alter the surface area available for filtration. This contraction and adjustment help regulate the glomerular filtration rate (GFR).
Q: What drives the filtration in the kidneys?
A: Filtration is driven by net driving force, which pushes fluid out of the capillary and into the Bowman’s capsule. Key pressures involved are:
Hydrostatic pressure in capillaries (pressure with glomerular capillaries): 55 mm Hg.
–> increase = increase in GFR
Osmotic pressure in capillaries (conc of solutes/proteins in blood): 30 mm Hg.
–> increase and increase solutes, decrease in GFR
Fluid pressure in capsule (fluid already filtered): 15 mm Hg.
=> increase, decreases GFR
how does fluid pressure affect GFR
fluid pressure = fluid already filtered
increase in fluid pressure will decrease GFR
Essentially, higher fluid pressure in the capsule makes it more difficult for additional fluid to enter, lowering the overall rate of filtration.
Q: How does hydrostatic pressure in the glomerular capillaries affect the GFR?
Hydrostatic pressure in the glomerular capillaries
increase in hydrostatic pressure will increase GFR
drives the filtration of plasma into the Bowman’s capsule. An increase in hydrostatic pressure increases the net filtration pressure
- increase renal arterial pressure (increases blood flow into glomerulus, blood moving faster, more blood flowing at faster rate)
- afferent arteriole vasodilation
- efferent arteriole vasoconstriction
= more blood accumulates, higher net filtration pressure
Q: How does osmotic pressure in the glomerular capillaries affect the Glomerular Filtration Rate (GFR)?
A: Osmotic pressure in the glomerular capillaries (conc of solutes/proteins in blood)
increase in osmotic pressure decreases GFD
high osmotic pressure opposes filtration by pulling water back into the capillaries (formed from afferent arterioles) due to the presence of plasma proteins so less is getting fitlered by bowman’s capsule. Higher osmotic pressure reduces the net filtration pressure and, therefore, decreases the Glomerular Filtration Rate (GFR). Lower osmotic pressure would have the opposite effect, increasing the GFR.
Q: What is the GFR and its normal value?
A: GFR (glomerular filtration rate) is the volume of fluid that filters into the Bowman’s capsule per unit time, typically around 125 mL/min or 180 L/day. It is altered by net filtration pressure, surface area, and permeability.
