Renal physiology- week 2 Flashcards
Production of urine begins w water and solute filtration from plasma flowing into the _____ via the _____ _____
glomerulus via the afferent arteriole
what is the role and function of the glomerulus?
form an ultrafiltrate of plasma
-muscle tone of the afferent arteriole influences the flow through the glomerulus
what are the features of the glomerular capillary membrane?
3 layers:
1.) endothelium of the capillary
2.) basement membrane
3.) epithelia cells (podocytes)
The basement membrane is _____ charges d/t ______ that compose it
NEGATIVELY charges d/t glycoproteins
-negatively charged proteins are repelled and can’t pass through it
- molecules greater than 50-100 angstroms can not pass
What is GFR?
total volume per unit time (ml/min) which leave the capillaries and enter the bowman’s space
What’s a normal GFR?
120 ml/min
180L/day
What are the 2 major determinates of filtration pressure?
-Glomerular capillary pressure (PGC)
(directly related to renal artery pressure and heavily influenced by arteriolar tone- afferent and efferent arteriolar)
-Glomerular oncotic pressure (pgc)
what organ get a higher percentage of CO than the kidneys?
liver
what is the amount of renal plasma flow?
660 ml/min
the vast majority of what is filtered is:
reabsorbed
What causes a rapid fluid filtration?
high hydrostatic pressure in glomerular capillaries
what causes rapid fluid reabsorption?
low hydrostatic pressure in the peritubular capillaries
how do the kidneys regulate hydrostatic pressure?
adjusting the resistance in the afferent and efferent arterioles - can regulate hydrostatic pressure in glomerular and peritubular capillaries =
-changes rate of glomerular filtration, or tubular reabsorption
what % of what’s filtered becomes actual urine?
1%
-what’s filtered is ultimately reabsorbed
the renal vasculature is unusual because:
The arrangement of 2 capillary beds joined in series by arterioles
blood supply to the entire tubular system comes from:
efferent arteriole
What are the 4 factors that determine GFR?
1.) the ultrafiltration coeficient (Kf)
2.) Glomerular Oncotic pressure (pgc)
3.) Glomerular capillary pressure (PGC)
4.) Capillary plasma flow rate
what is the net filtration pressure?
10 mmHg
What is glomerular hydrostatic pressure determined by?
1.) arterial pressure
2.) afferent arteriolar resistance
3.) efferent arteriolar resistance
increased arterial pressure =
increased GFR
increase arteriolar resistance=
decreased GFR
How does the body get back filtered plasma?
reabsorbption in the vasa recta and peritubilar plexi
What is the normal glomerular capillary hydrostatic pressure?
60 mmhg- biggest determinant of GFR
Over what range of systolic BP is renal blood flow maintained via autoregulation?
80-200 mmhg
what is autoregulation?
the kidney’s ability to regulate GFR over a range of conditions
what are the mechanisms of autoregulation?
-constriction and dilation of precapillary sphincters in the afferent and efferent arterioles
-increases na+ delivered to the macula densa = decreased GFR via adenosine-induced vasoconstriction of afferent arteriole
what is the macula densa?
specialized group of epithelial cells in the distal tubule that comes in close contact with the afferent and efferent arterioles. Contains the Golgi apparatus which are intracellular secretory organelles
What happens when the macula densa senses decreased sodium chloride?
1.) decreases resistance to blood flow in the afferent arterioles = increase hydrostatic pressure = increased GFR
2.) Increases renin release from juxtaglomerular cells
constriction of efferent arterioles=
increased hydrostatic pressure = increase GFR
what other things affect autoregulation?
myogenic reflex theory
tubuloglomerular feedback
tubular ____ is more important than tubular _____ in the formation of urine
reabsorption is more important than secretion
secretion plays an important role in determining:
the amounts of potassium and hydrogen ions that are excreted in the urine
which produces are poorly reabsorbed and therefore excreted in the urine?
urea
creatinine
uric acid
urates
what is renal clearance?
Volume of plasma from which all of the given substance is removed per unit of time in one pass through the kidney
if a substance is not secreted or reabsorbed then its clearance is
= GFR (insulin)
if a substance is completely reabsorbed then its clearance is:
0
if clearance is greater than GFR=
secretion
if clearance is less than GFR=
reabsorption
what is renal clearance of creatinine used for clinically?
to estimate GFR
- creatinine is a normal component of blood, a byproduct of skeletal muscle protein
- 24 hr urine is best to evaluate this
What is considered a reduced GFR?
12-80ml/min
10-40% of functioning nephrons
What is considered renal failure?
GRF <12ml/min
<10% functioning nephrons
what are the 3 mechanisms of reabsorption and secretion?
- active transport
-passive transport (simple and facilitated)
-secondary active transport - (moves solute against a concentration gradient coupled to movement of another solute- uses energy indirectly
what is an example of secondary active transport?
reabsorption of glucose
amino acids, ions, metabolites
What is pinocytosis?
some parts of the tubule, especially the proximal tubule, reabsorb large molecules such as proteins via pinocytosis
- requires energy- considered form of active transport
What is the transport maximum?
The limit dt saturation of the specific transport system involves when the amount of solute delivered to the tubule (tubular load) exceeds the capacity of the carrier proteins and specific enzymes involved in the transport process
PCT:
-Sodium (65%) is actively transported from the proximal tubule and into the peritubular intersititum. this consumes a large amount of o2
-Water (65%) follows sodium by osmosis
-K+, Cl-, and HCO3- follow sodium in direct proportion by the sodium co-transport mechanism. (65% of these ions absorbed in PCT)
-organic bases, acids and H+ are secreted into the proximal tubule via the sodium counter-transport mechanism
ex of organic acids and bases: bile salts, uric acid, catecholamines, toxins and certain drugs
- all reabsorption in the proximal tubule is iso-osmotic
-only region of nephron where carbonic anhydrate is present on the luminal membrane
Descending loop of Henle:
-Primary function is to participate in forming concentrated or dilute urine- separates sodium and water
- the ability of the kidneys to produce concentrated or dilute urine depends on the presence of a gradual hyperosmotic peritubular interstitium
- countercurrent systems: countercurrent multiplier system creates osmotic gradient, - vasa recta- countercurrent exchanger system maintains medullary osmotic gradient
-highly permeable to water (concentrates NaCl –> delivered to TAL)
Ascending Loop of Henle
not permeable to water
-ions pumped from the tubular fluid to the peritubular interstitium.
-the most important pump is the sodium-potassium (2)chloride co-transporter (target for loop diuretics), which removes 20% of tubular sodium
-tubular fluid becomes dilute, peritubular interstitium becomes concentrated
- juxtamedullary nephrons play a more significant role in the countercurrent multiplier
-H+ excreted via sodium-hydrogen exchange mechanism
DCT:
- 5% of Na+ reabsorbed, potassium, Cl-, and bicarb follow via sodium co-transport mechanism
-impermeable to water except w ADH and aldosterone - fine tube final urine concentration
- home to JGA- lies at the junction of the thick ascending limb and distal tubule
- adjusts urea concentration
collecting duct:
regulates final concentration of urine
-reabsorbs sodium (5%)
- ADH and aldosterone also work here
- Atrial natriuretic peptide inhibits water and sodium reabsorption
-adjusts H+ concentration
Where is the preferential site of HCO3- reabsorption?
PCT (using carbonic anhydrase)
What is the site of ammonia secretion?
PCT- important for acid-base function
What are the 3 functional distinct segments of the loop?
descending thin segment
the ascending thin segment (reabsorption of ca2+, mg+, and bicarb)
thick ascending segment (most important)
what happens in the TAL?
DILUTING SEGMENT OF NEPHRON
-impermeable to water –> solute pumped out= hypertonic intersititium = hypotonic dilute fluid in tubule
POSITIVE CHARGE
Movement of sodium across the luminal membrane is mediated by the 1-sodium, 1-potassium, 2-chloride co-transporter (target site of lasix)
-only segment where Cl is actively transported.
- this co-transport protein carrier uses the potential energy released by downhill diffusion of sodium into the cell to drive reabsorption into the cell against the concentration gradient
in the collecting duct- permeability to water is controlled by:
level of ADH
where in the nephron is permeable to urea?
collecting duct
The collecting duct is capable of secreting ______ ions against a large concentration gradient which is important for regulating acid-base balance
