Unit V: The Body Fluids and Kidneys - Glomerular Filtration and Renal Blood Flow

Practice questions regarding glomerular filtration rate factors, arteriolar resistance effects, and renal blood flow determinants.

How does constriction of afferent arterioles affect the glomerular filtration rate (GFR)?

Constriction of afferent arterioles reduces the GFR.

What are the biphasic effects of efferent arteriolar constriction on GFR?

Modest constriction raises the GFR, but severe constriction (more than a 3-fold increase in resistance) tends to reduce the GFR.

Why does GFR eventually decrease during severe efferent arteriolar constriction?

Severe constriction reduces renal plasma flow, which increases the filtration fraction and glomerular colloid osmotic pressure ($\pi_g$); this rise eventually exceeds the increase in glomerular capillary hydrostatic pressure ($P_g$).

According to Table 27.2, what are some physiological causes that decrease the glomerular filtration coefficient ($K_f$)?

Renal disease, diabetes mellitus, hypertension, and aging.

What is a common clinical cause of increased Bowman capsule hydrostatic pressure ($P_b$) leading to decreased GFR?

Urinary tract obstruction, such as kidney stones.

In a healthy $70\,kg$ adult, what is the combined blood flow through both kidneys?

Approximately $1100\,mL/min$, or about $22\%$ of the cardiac output.

What is the relationship between renal oxygen consumption and sodium reabsorption?

Renal oxygen consumption varies in proportion to renal tubular sodium reabsorption, which is closely related to the GFR and the rate of sodium filtered.

To what level does renal oxygen consumption decrease if glomerular filtration and sodium reabsorption cease completely?

It decreases to about one-fourth of its normal level, which reflects the basic metabolic needs of the renal cells.

What is the formula for calculating Renal Blood Flow ($RBF$)?

$$RBF = \frac{\text{Renal artery pressure} - \text{Renal vein pressure}}{\text{Total renal vascular resistance}}$$

Which vessels account for most of the renal vascular resistance?

Interlobular arteries, afferent arterioles, and efferent arterioles.

What is autoregulation in the context of renal function?

The capacity of the kidneys to maintain relatively constant renal blood flow and GFR over an arterial pressure range between $80\,mm Hg$ and $170\,mm Hg$.

What percentage of total renal blood flow is received by the renal medulla?

Only $1\%$ to $2\%$.

What are the vasa recta?

Specialized peritubular capillaries that descend into the medulla parallel to the loops of Henle; they supply the medulla and help the kidneys form concentrated urine.