Renal Physiology - Quiz 2 Flashcards
Work unit of kidneys for excretion of wastes; purpose is to form an ultrafiltrate of plasma
Glomerulus
regulates flow through the glomerulus
afferent arteriole muscle tone
What is the charge of the basement membrane in the glomerulus? Why?
negative
because of the glycoproteins which compose it
What impact does the charge of the glomerular basement membrane have on filtration?
Proteins cannot be filtered through the membrane (unless the kidneys are injured)
define glomerular filtration rate (GFR)
total volume per unit time (mL/min) which leaves the capillaries and enters Bowman’s Space
what is normal GFR in mL/min and L/day?
120 mL/min
180 L/day
what % of CO is renal blood flow?
20 %
1200 mL/min
What is the only organ that gets a higher percentage of CO than the kidneys?
Liver
True or False. The vast majority of filtered blood/plasma is reabsorbed.
True
4 factors that determine GFR
- Ultrafiltration coefficient
- Oncotic pressure
- Net hydraulic pressure
- Capillary plasma flow rate
What 2 factors determine the ultrafiltration coefficient?
- capillary permeability
2. surface area available for filtration
Does oncotic pressure in Bowman’s Space favor or oppose filtration? Why?
Opposes filtration
b/c there should be no free protein in bowman space; all the proteins are in the blood.
where does net hydraulic pressure push fluid
into Bowman’s space from the capillaries
How does capillary plasma flow rate affect filtration?
Higher flow = greater filtration
Net filtration pressure (10 mmHg) = ______ - ______ - ______
Glomerular hydrostatic pressure (60 mmHg) - Bowman’s capsule pressure (18 mmHg) - Glomerular oncotic pressure (32 mmHg)
Why does filtration slow as plasma moves towards the end of the glomerular capillary?
increase in oncotic pressure within the capillaries
As fluid (but not proteins) is removed from the blood, the protein concentration increases in the blood, pulling water back into the blood
what drops significantly at the level of the efferent arteriole, resulting in maximal reabsorption into the vasa recta and peritubular plexi?
Capillary hydrostatic pressure
term that reflects the kidney’s ability to regulate GFR over a range of conditions
autoregulation
2 mechanisms that enable autoregulation in the kidneys
- constriction and dilation of pre capillary spinsters in the afferent and efferent arterioles (allow more or less fluid into the glomerulus)
- Increased Na delivery to the macula densa decreases GFR
part of the basement membrane of the distal tubule that lies against the afferent and efferent arterioles; senses Na levels/concentration and decreases GFR if Na levels are increased/more concentrated
Macula densa
Volume of plasma from which all of a given substance is removed per unit time in one pass through the kidney
renal clearance
if renal clearance > GFR, there must be net secretion or reabsorption?
secretion
IF renal clearance is < GFR, there must be net secretion or reabsorption?
reabsorption
if renal clearance = GFR, there must be net secretion or reabsorption?
neither
What is used clinically to estimate GFR?
Renal clearance of creatinine
What is creatinine? Is it a normal component of blood?
byproduct of sk musc protein
yes
Where is Cr secreted?
proximal tubule (it is excreted in a very small act and then ignored)
Best way to evaluate creatinine clearance
24 hour urine
if renal function is normal (100% of nephrons are fx-ing), what is the GFR?
If renal fx is reduced (10-40% of nephrons fx-ing)?
In renal failure (<10% of nephrons fx-ing)?
Normal (100% nephron fx) = GFR 125 mL/min
Reduced (10-40% nephron fx) = GFR 12-80 mL/min
Renal failure (<10% nephrons fx) = GFR <12
3 mechanisms of transport for reabsorption and secretion in the kidney
- Active transport (uses energy)
- Passive transport
- simple
- facilitated
- Secondary active transport (indirectly uses energy)
what is secondary active transport?
Moves a solute against a concentration gradient coupled to movement of another solute
Diffusion of lipid soluble agents or gasses would utilize which type of transport?
Simple (passive) transport
transport route that uses a protein channel or carrier to transport a substance
Facilitated (passive) transport
2 substances moved by sodium co-transport
- Na
2. Glucose
in renal tubules, reabsorption and secretion of substances (e.g. glucose and amino acids) are coupled with the secondary active transport of which electrolyte?
Na
Until the transport mechanism is saturated, the rate of secretion or absorption of a substrate is proportional to:
- concentration of the substrate
2. affinity of the carrier for the substrate
limit to the rate at which a solute which is actively reabsorbed or secreted can be transported
transport maximum
main reabsorptive area of nephron
proximal tubule
True or False: ALL reabsorption in the proximal tubule is ISO-OSMOTIC
TRUE
Which part of the renal tubule system has extensive microvilli on the luminal membrane?
Proximal tubule
proximal tubule contains many intracellular channels for reabsorption of which 3 substances?
Na, Cl, water
only region of the nephron where carbonic anhydrase is present on the luminal membrane
proximal tubule
What part of the Proximal tubule is loaded with NaK pumps (therefore lots of active transport occurs)
Basolateral membrane
What is reabsorbed in the proximal tubule?
- 2/3 of all Na and water
- amino acids (all)
- glucose (all)
- HCO3 (via carbonic anhydrase)
- Vitamin K
- Cl
- K
What substances are secreted into the proximal tubule?
- Organic acids (via anion pumps in basolateral membrane)
- Organic bases
- Ammonia (important to acid-base function)
location where diuretics work and ABX get excreted
Proximal tubule basolateral membrane
segment of the loop of Henle that is highly permeable to water and moderately permeable to most solutes; function is to allow simple diffusion of substances through its walls
descending thin segment
portion of the loop of Henle that is virtually impermeable to diffusion of water; has some reabsorptive capacity for ions (Ca, HCO3, Mg)
thin ascending segment
Key feature of the TAL
it is IMPERMEABLE TO WATER while solutes are pumped out of the tubular fluid
target site of Lasix
luminal membrane of the TAL
Only nephron segment where Cl is actively transported. What transports it?
luminal membrane of the TAL
1Na 1K 2Cl transporter pump
is the tubular fluid in the TAL hyper-, iso-, or hypo-tonic?
Hypotonic and dilute
The TAL is impermeable to water, and many of the solutes are being pumped out
What drives the reabsorption of Mg and Ca in the TAL?
positive intraluminal charge
which segment controls the degree of dilution or concentration of urine?
late distal tubule
water permeability of the later distal tubule is controlled by the presence or absence of what?
ADH (vasopressin)
what controls the rate or reabsorption of Na and K in the later distal tubule?
aldosterone
What happens to hydrogen in the later distal tubule?
hydrogen is secreted into the tubule against a large concentration gradient by the H-ATPase pump
2 cell types that perform H and K regulation
Principal cells
Intercalated cells
cells in the distal tubule through which reabsorb Na and H2O from the lumen and secrete K into the lumen
Principal cells
cells in the distal tubule which reabsorb HCO3 and K ions and secrete H into the tubular fluid
Intercalated cells
cells that are important for acid-base regulation by the kidneys
Intercalated cells
final site for processing urine; place where urine is first called urine
medullary collecting duct
where is urea filtered out of the urine?
collecting duct
What portion of the nephron is capable of secreting H ions against a large concentration gradient to regulate acid-base balance
collecting duct
