Vander's Ch. 1 Renal Functions, Anatomy, and Basic Processes Flashcards
What percentage of the blood entering the kidney flows directly into the medulla without passing through the cortex?
*None* Most medullary blood is supplied by efferent arterioles near the corticomedullary border. A small fraction may be supplied from cortical radial arteries. All of these vessels are in the cortex.
True or False: The difference between superficial and juxtamedullar nephrons is that superficial nephrons have their glomeruli in the cortex whereas the glomeruli of juxtamedullary nephrons are in the medulla.
*False* All glomeruli are in the cortex
Substance T is present in the urine. Does this prove that it entered the renal tubule by filtration at the glomerulus?
*No* It is possible that substance T was filtered, but substance T might also enter tubules by secretion into the tubules.
Substance V is not normally present in the urine. Does this mean that it does not enter the kidney at all (in the blood), or is neither filtered nor secreted?
All substances in the general circulation enter the kidneys via the renal arterial system and flow through the renal microvasculature. It is possible that it was neither secreted nor filtered, accounting for its not being in the urine, but it is more likely that whatever substance V reaches the lumen via filtration or secretion is completely reabsorbed. Many substances fall into this category
A substance is filtered into Bowman’s space and excreted in the urine. How many cell plasma membrane barriers must it cross in order to move from the blood to outside the body?
*None* In glomerular filtration, the filtered substances pass around the endothelial cells (through fenestrations) and around the podocytes. Topologically, Bowman’s space is continuous with the external environment; thus, a filtered substance can move from blood to the bladder and be excreted without crossing through any plasma membrane.
A substance is freely filtered. Does this mean that it is all filtered?
*No* Freely filtered means the substance is filtered in the same proportion that volume is filtered. If 20% of the volume is filtered then 20% of a freely filtered substance is filtered, meaning that 80% is not filtered and passes on to the efferent arterioles and peritubular capillaries.
If you immunologically labeled cells of the macula dense with label X, and labeled cells of the thick ascending limb with label Y, would you find labels X and Y in the cortex, medulla, or both?
X in cortex. Cells of macula dense are part of juxtaglomerular apparatus, just next to the glomeruli that are all in the cortex. Y in the cortex and outer medulla. This ascending limbs of all nephrons begin in the outer medulla and continue back to the glomerulus from which that nephron arose.
Given the generalizations about transport events in the medulla (secretion, reabsorption), can you say that blood flow into the medulla is in anyway different in volume from blood flow out of the medulla?
*Yes* under all circumstances, there is net volume reabsorption in the medulla. By mass balance, this requires that the reabsorbed volume leave the medulla. The only way out for reabsorbed substance is in the blood. Thus blood flow out is slightly greater than blood flow in.
