Thanks.
The ability to concentrate urine varies among animal species. The max urine conc that can be produced by an animal is MOST closely relate to which of the foll:
a. renal blood flow
b. total number of nephrons
c. gfr
d. length of loop of henle
e. diameter of distal tubule
ANS: RENAL BLOOD FLOW
I see a lot of different choices of ans have been chosen for this question. BUT the right ans is -Renal blood flow.
*There about 500,000 nephrons in each kidney under normal conditions.
*GFR depends on the renal blood flow (glomerular filtrate is formed by squeezing fluid through the glomerular capillary bed by the driving hydrostatic pressure (head of pressure) controlled by the afferent and efferent arterioles, and provided by arterial pressure)
*Agreed that the highest osmolar conc of the urine occurs in the loop of henley - Vasa recta and henley work together to conc the urine by counter current mech -which depends on the amount and osmolality of blood flowing through the peritubular capillaries surrounding the tubules.
*Inside the distal and collecting tubules, the filtrate is either diluted or concentrated to form urine regulated by ADH- which again depends on the osmolality.
The ability of the kidneys to selectively clear waste products from the blood and simultaneously maintain the bodys essential water and electrolyte balances is controlled in the nephron by the following functions: renal blood flow, glomerular filtration, tubular reabsorption, and tubular secretion
Mechanisms for urinary conc or dilution depend on counterflow processes, both tubular and vascular, within the renal medulla.The regulation of plasma osmolality is accomplished by varying the amount of water excreted by the kidneys. It is due to the response to water deprivation or to water intake. When the osmolality is too low, nervous and hormonal feedback mechanisms cause the kidneys to excrete a great excess of water in urine causing a dilute urine, but removes water from the body to increase the body fluid osmolality back to normal. When the osmolality of body fluids is too great, the kidneys excrete an excess of solutes to reduce the body fluid osmolality again back to normal, but at the same time excreting a concentrated urine.
Maintenance of water balance is tightly regulated by renal functions such that water intake precisely match water loss from the body. Low water intake or increased water loss results to small vol of conc urine produced by the kidneys to conserve water. Human kidneys have powerful capability to retain water such that the vol of urine excreted may represent less than 1% of the volume of glomerular filtrate. In cases of increased water intake or over hydration, large vol of dilute urine is produced. Water reabsorption occurs passively in several parts of the nephron. Permeability to water by the distal tubule and collecting ducts is regulated by ADH. The rate of release of this hormone from the posterior pituitary gland is in turn affected by changes in fluid intake, or fluid loss from the body, consequently changing the rate of water excretion