Renal Physiology 2
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What is the macula densa?
The point at which the afferent and efferent arterioles of the nephron come into contact with the distal tubule.
What is the function of the macula densa?
Specialized cells make up this site and can detect levels of NaCl in the filtrate. These levels correspond to the GFR. The macula densa communicates with the juxtaglomerular cells of the afferent arteriol in the process of autoregulation.
(It is the site where the decision is made to change resistance in the afferent arteriol in order to control fluid levels through the nephron)
Describe the location and function of the podocytes.
Podocytes surround and anchor the glomerular capillaries to the inside face of Bowman's capsule in order to prevent them from flapping around (due to hydrostatic pressure).
What characteristic of the glomerular capillaries allows for filtration?
Fenestrations in the capillary walls.
What percent of cardiac output is sent to the kidneys?
Of the blood sent to an individual glomerulus:
1.) What percentage is filtered?
2.) What percentage remains in the plasma?
3.) What percentage is reabsorbed?
4.) What percentage is ultimately excreted?
- 1.) 20%
- 2.) 80%
- 3.) > 19%
- 4.) < 1%
The movement of fluid (plasma) from glomerular capillaries into Bowman's space and the tubule system.
Movement of water or solutes (ions, AA's, glucose) from tubular fluid back into the peritubular capillaries.
What term describes the movement of solutes (ex. creatinin catecholamines) from peritubular capillaries into the tubular fluid for excretion?
(Only solutes are secreted)
What term describes the movement of water and solutes from the bladder through the urethra to the exterior?
Rapid filtration in the kidneys allows us to filter our entire body plasma up to 60 times per day.
Why is this important?
It gives our body numerous chances to remove toxins from circulation.
What is the greatest contributer to colloid osmotic pressure in capillaries?
Describe the function of the glomerular basement membrane.
- The glomerular basement membrane is a loose mesh of negatively charged collagen.
- This serves as an additional barrier to proteins, since the two negative charges repel each other.
Though what barriers must plasma pass through in order to be filtered?
- 1.) Fenestrations in the glomerular capillaries
- 2.) The negatively charged glomerular basement membrane
- 3.) Slit pores created by the podocytes
What characteristics of solutes determine how well it will pass through the filtration barriers of the glomerulus?
- 1.) Molecular size
- 2.) Charge
What four molecules were given as examples of things that pass the glomerular filters 100% of the time?
- 1.) Water
- 2.) Sodium (Na+)
- 3.) Glucose
- 4.) Insulin
*Others exist as well (for ex. other ions)
What protein was given as an example of a molecule that passes glomerular filters 0.5% of the time?
What pressure-related factors favor the flow of plasma through the glomerular capillaries out into Bowman's space and into the tubule?
1.) Glomerular capillary hydrostatic pressure PGC (from MAP)
*Since proteins can't pass the barriers of filtration, there is a negligible IIBC
What pressure-related factors oppose the flow of plasma through the glomerular capillaries out into Bowman's space and into the tubule?
- 1.) IIGC
- 2.) PBC (the inelastic capsule surrounding the kidney exerts a pressure on Bowman's capsule, resulting in a pushing force back into the glomerular capillaries)
What are the two overall determinants of glomerular filtration?
- 1.) Balance of hydrostatic and colloid osmotic forces
- 2.) (Ultra) filtration coefficient
What is the (ultra) filtration coefficient?
The (ultra) filtration coefficient, Kf describes the porosity of a glomerular capillary structure.
How do you calculate Kf?
Kf = GFR / Net Filtration Pressure
True or False?
In a normal capillary (ex. a muscle capillary), colloid osmotic pressure remains constant along the length of the vessel.
True or False?
Colloid osmotic pressure remains constant along the length of the glomerular and peritubular capillaries.
- As 20% of fluid is filtered out of the glomerular capillaries, the concentration of the proteins that remain increases. This larger concentration of proteins results in a substantially larger IIgc, which will ultimately cause the reabsorption of nearly all the fluid that was initially filtered.
Define glomerular filtration rate.
The quantity of filtrate formed each minute in all nephrons in both kidneys.
How do you calculate GFR?
GFR = NFP (Net filtration pressure) x Kf
How do you calculate filtration fraction?
Filtration fraction = GFR / Renal Plasma Flow
If the filtration fraction decreases, what happens to the concentration of proteins in the glomerular and peritubular capillaries?
The [protein] will decrease relative their concentration before the FF decreased.
What is the primary driving force for glomerular filtration?
Mean arterial pressure, directly resulting Pc.
What is Key Concept # 2?
Substances become concentrated due to water abstraction.
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