Clearance and renal blood flow Flashcards
Explain the blood flow to the kidneys and the names of the veins/arteries involved
After entering the kidney at the hilus, the renal artery branches into interlobar arteries which pass outward to the junction of cortex and medulla. At that point they turn horizontally, forming the arcuate arteries, which branch to form interlobular arteries. The interlobular arteries run outward through the cortex giving off short afferent arterioles, which carry blood to the glomeruli. These arterioles break up into numerous glomerular capillaries, where ultrafiltration of the blood occurs (~ 20% gets filtered). The capillaries coalesce to form efferent arterioles, some of which redivide into a network of capillaries around the proximal tubule of superficial nephrons. However, efferent blood flow from the glomeruli of juxtamedullary nephrons flows through vessels called vasa recta, which descend into the medulla and follow a course similar to the loops of Henle.
Explain the venous and lymphatic system in the kidneys.
The venous and lymphatic systems generally parallel the arterial network and have the same terminology (i.e., interlobular - arcuate - interlobar - renal vein). The only exception is the most superficial region of the cortex, which is drained by superficial veins and lymphatics that run immediately beneath the renal capsule
Which nerves are in the kidneys and what do they innervate?
Cholinergic and adrenergic nerve fibers lie adjacent to the arteries, afferent arterioles, juxtaglomerular apparatus and efferent arterioles of juxtamedullary nephrons and innervate them. There appears to be little direct innervation of the epithelium, although catecholamines do bind to specific receptors on the proximal tubule and modulate transport
Describe the renal blood flow. Is it high? How much of the cardiac output?
Renal blood flow (RBF) is high relative to the flow in many other parts of the body. It amounts to nearly 1/4 of the cardiac output even though the kidneys constitute less than 1% of the body weight. Blood is forced through the kidney by the hydraulic pressure developed by the heart, against resistances located in two types of arterioles that are arranged in series.
What is the formula for absorption?
(GFR • Ps) = Us • V + Ts
Ts = (GFR • Ps) – Us • V
What does the formula for absorption not provide as an information?
Not sure if active or passive absorption, do not know where it is occurring –> doesn’t say anything about mechanistic information
Explain the titration curve of glucose
Plasma glucose vs glucose in kidneys
- Increased G in plasma more filtered by glomerulus. If GFR remains constant, more glucose = more filtered. Straight line
- Clearance is usually 0 under normal conditions unless disease
- Increased G in plasma More and more is reabsorbed none of it is excreted, until threshold (transport maximum)
o Absorption of glucose has a maximum rate
- As reabsorption decreases, excretion increases
What is the formula for secretion?
Us • V = (GFR • Ps) + Ts
Ts = Us • V - (GFR • Ps)
Describe the titration curve of PAH
For PAH, filtered load is also linear with plasma concentration. More plasma PAH, more excreted (also saturating capabilities though. Very high concentrations saturate transport process and reaches plateau.
What is the GFR?
Measure of renal function
Depends on the number of functional nephrons
What is used to determine GFR in the lab? In clinical settings?
In the lab, GFR is determined by injection of inulin. (inulin clearance)
In clinics, injections are not favored and thus they use creatinine clearance or plasma creatinine concentration
What happens to the creatinine filtered and excreted when GFR drops?
then filtered load of creatinine drops initially, then recovers and comes back to the same initial level
Cumulative creatinine balance and serum creatinine concentration increases though (since not filtered as much), and reach a new plateau when filtration comes back to normal.
New, higher steady state is achieved – to be able to excrete the same amount of creatinine as before.
In which category does creatinine belong in terms of excretion?
Creatinine is filtered and excreted
How is renal plasma flow calculated?
By using PAH
- It is a secreted solute (filtered + secreted)
- Its excretion is flow-limited
- Clearance provides a measure of fluid delivery to the kidneys
UPAH x V ~ PPAH x RPF
Describe the changes in pressure in the glomerulus
As the fluid flows through the capillary of the glomerulus, the hydrostatic pressure stays relatively constant (only slightly drops)
Due to large surface area of the capillaries (low resistance of capillary beds)
Colloid osmotic pressure increases
- Afferent arteriole is a resistance vessel (drop in pressure)
- Fairly constant in glomerular capillary
- Further decrease in efferent arteriole
- Both the afferent and efferent arterioles are the main sites of resistance in the vasculature
The resistance to flow offered by the afferent and efferent arterioles causes nearly all of the drop in pressure between the renal artery and renal vein.
Kind of a portal system (From glomerular capillaries to peritubular capillaries)
