Flashcards in Renal Chapter 1: Renal Functions, Anatomy, and Basic Processes Deck (55)
What is filtration?
process by which water and solutes in the blood leave the vascular system through the filtration barrier and enter Bowman's space (space that is topologically outside the body)
The filtrate contains substances X, Y, and Z in the same concentrations as the plasma (ie, each one is freely filtered).
The filtrate enters the proximal convoluted tubule and begins its flow through the rest of the tubule. Simultaneously, the remaining 80% of the plasma, with its substances X, Y, and Z in the same concentrations as they had when entering the
kidney, leaves the glomerular capillaries via the efferent arterioles and enters the
What is secretion?
the process of moving substances into the tubular lumen from the cytosol of epithelial cells that form walls of the nephron
What is re-absorption?
re-absorption is the process of moving substances from lumen across epithelial layer into the surrounding interstitum
In most cases, reabsorbed substances then move from the interstitium into surrounding
blood vessels, so that the term reabsorption implies a 2-step process of removal
from the lumen followed by movement into the blood.
What is excretion?
exit of the substance from the body... substance present in the final urine
What does synthesis and catabolism refer to?
means a substance is constructed from molecular precursors
catabolism means a substance is broken down into smaller component molecules.
What does it mean for a substance to be "freely filtered"?
substances found in filtrate at same concentration as found in plasma (doesn't mean all filtered)
many low-molecular weight components of blood are freely filtered. Na, K, Cl, bicarbonate, glucose, urea, amino acids, peptides like insulin and ADH found in freely filtered substances
glomerular filtration (fluid from glomerular capillaries into Bowman's capsule) is very much like blood plasma but contains little protein... (large proteins like plasma and globulin can't get through filtration barrier)
What is the GFR? What can cause reductions?
volume of filtrate formed per unit time
young adult male GFR is 180L/ day
(fluid across other capillaries in body is approx 4L/day)
...aging and renal pathologies can cause reduction in GFR
GFR is 125mL/min
Draw ex. of substance X being filtered and secreted but not reabsorbed. Substance Z is filtered but completely reabsorbed.
p. 28 Vander's
screenshot or pic.
Describe how products like urea and glucose and water, electrolytes might be reabsorbed.
re-absorption of waste products like urea is incomplete, so large fractions of their filtered amounts are excreted in urine
"useful" plasma components like water, electrolytes, and glucose vary from essentially complete reabsorption to complete so urine concentrations should be mostly undetectable
Describe metabolism by tubules.
tubular cells may extract organic nutrients from glomerular filtrate or peritubular capillaries and metabolize them as dictated by cell's own nutrient requirements
other metabolic functions are to alter composition of urine and plasma (synthesis of ammonium from glutamate and production of bicarbonate)
Describe signals that regulate the kidney. From where do they originate?
signals arise from both neural and hormonal input.
neural signals originate in sympathetic celiac plexus. exert control over renal blood flow, glomerular filtration and release of vasoactive substances (renin-angiotensin system)
hormonal signals originate in adrenal gland, pituitary gland and heart... adrenal cortex secretes steroid hormones aldosterone and cortisol
adrenal medulla secrets catecholamines epi and NE
(all hormones, esp aldosterone, are regulators of Na and K excretion by kidney)
pituitary gland- vasopressin (ADH) ...water excretion/Na excretion
heart secretes peptides too
At what site does the greatest mass of excreted substances enter the nephron?
Where would penicillin most likely be secreted?
proximal convoluted tubule
As a whole, how much Na and Cl and water does the loop of Henle reabsorb? What are the consequences of these proportions?
reabsorbs 20% of filtered Na and Cl and 10% of filtered water
by reabsorbing relatively more salt than water, the luminal fluid becomes diluted relative to normal plasma and the surrounding interstitum.
During periods when the kidneys excrete dilute final urine, the role of the loop of Henle in diluting the luminal fluid is crucial
What is the macula densa?
the end of the loop of Henle contains cells of the macula densa, which senses or assays the Na and Cl content of the lumen and generates signals that influence other aspects of renal function (specifically the renin-angiotensin system)
What will happen with large amounts of ADH present? With little ADH present?
with large amounts of ADH present- most water remaining in the lumen is reabsorbed, leading to concentrated, low-volume urine
With little ADH present, most of the water passes on to final urine, producing dilute, high-volume urine.
Is the following statement true or false? The difference between superficial and
juxtamedullary nephrons is that superficial nephrons have their glomeruli in the cortex whereas the glomeruli of juxtamedullary nephrons are in the medulla.
all glomeruli are in the cortex
What percentage of the blood entering the kidney flows directly into the medulla
without passing through the cortex?
The correct answer is 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
Substance T is present in the urine. Does this prove that it entered the renal tubule
by filtration at the glomerulus?
The correct answer is 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?
Book: The answer is 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.
Webber: filtered substances pass not only through fenestrae (pores) but also across basement membrane which is thicker than those found in other capillaries. And the basement membrane constitutes part of the endothelial cells which must be traversed for substances to reach Bowman's space
A substance is freely filtered. Does this mean that it is all filtered?
The answer is 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
If you immunologically labeled cells of the macula densa 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?
You would find label X in the cortex. Cells of the macula densa are part of the juxtaglomerular apparatus, just next to the glomeruli that are all
in the cortex. You would find label Y in the cortex and outer medulla. Thick 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 any way different in
volume from blood flow out of the medulla?
The answer is 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 substances is in the blood. Thus blood flow out is slightly greater than
blood flow in.