Lecture 1 & 2- Introduction Flashcards
Cortex
Outer region, located under the kidney capsule
has interstitial osmolarity close to plasma
Medulla
central region, divided into an outer and inner medulla
has HIGH interstitial osmolarity, which allows kidney to generate concentrated urine
Papilla
innermost tip of the inner medulla (extension of the ureter)
Nephron order
Fluid filtered at glomerulus -> Bowman’s capsule -> proximal tubule -> thin descending -> thin ascending -> thick ascending -> distal tubule -> collecting duct
Filters
the blood to generate a fluid free of cells and most proteins
(plasma minus proteins)
Reabsorbs
certain solutes and water from tubular fluid (Na, Cl, glucose)
Secretes
other solutes from tubular fluid (uric acid)
Excretes
in the urine the water and solutes that remain in the tubular fluid after passing through the renal tubule
How much of plasma gets filtered?
20%
How much plasma exits through efferent arteriole?
80%
Cortical nephrons (90%)
- Glomeruli in outer cortex
- Short loops of Henle
- Efferent arterioles that form peritubular capillaries
Juxtamedullary nephons (10%)
- Glomeruli at the borderof the cortex and medulla
- Long loops of Henle
- Efferent arterioles that form peritubular capillaries and also vasa recta
Macula Densa
functions to monitor the renal fluid composition
juxtaglomerular cells
produce renin and help control constriction of the afferent and efferent arterioles
glomerular filtration
filtration of a fraction of plasma (minus proteins) into Bowman’s Space
tubular reabsorption
transport of solutes from blood into renal fluid
excretion
elimination of water and solutes in urine
excretion =
filtration- reabsorption + secretion
capillary membrane
- capillary endothelial cells
- basement membrane- contains fixed negative charges that selectively filter proteins
- podocytes- final barrier
nephrin
transmembrane protein embedded in the podocyte membrane
-localizes to diaphagms covering the filtration silts
nephrotic syndrome
mutations in nephrin
loss of protien in urine, edema, and eventually renal failure
GFR
rate at which fluid is filtered through the glomerulus
= Kf x (net filtration pressure)
increased Pbs
indicates tubular obstruction (e.g. kidney stones)
RPF
the rate at which plasma is delivered to the kidneys
= RBF (1-Hct)
Glomerulonephritis
- renal disease initiated by immune response
- antigen-antibody complexes accumulate in the glomerular basement membrane, cause REDUCED GFR
- WBC aslo accumulate so can lead to proteinuria
Filtration Fraction
fraction of plasma filtered through the glomerulus
20%
=GFR/RPF
can be used to solve for GFR by moving around equation
Renal Clearance
=U(x)V/P(x)
volume of plasma per unit time from which x has been completely removed and excreted
Measurement of GFR
- freely filtered
- not reabsorbed or secreted
- not metabolized or produced by the kidney
- does not alter GFR
measure by the clearance of INULIN or CREATININE
Measurement of RPF
- freely filtered
- efficiently secreted
- not reabsorbed
measuring clearance of PAH
-extraction efficiency is 90% (only about 90% of PAH that enters the kidney is secreted into the tubule
Measurement of tubular secretion rate
for a compound that is freely filtered, secreted, but not reabsorbed:
secretion = excretion rate - filtration rate
Measurement of Tubular Reabsorption Rate
for a compound that is freely filtered and reabsorbed, but not secreted
reabsorption = filtration rate -excretion rate
properties of glucose reabsorption
glucose is completely reabsorbed if Pglucose < 2
2-3: glucose appears in urine since some glucose escapes uptake
>3 glucose uptake is saturated and glucose appears in urine
Diabetes Mellitus
failure to produce insulin in Beta cells or failure to respond to insulin lead to excess blood sugar levels
- excess glucose appears in urine
- glucose that remains in tubule acts to retain water in tubule, leading to polyuria
Clearance Ratio
CR(x)= C(x)/GFR
Cx = GFR; CR =1, no net reabsorption or secretion (inulin)
Cx < GFR; CR>1, reabsorption must be occurring (glucose)
Cx > GFR; CR<1, secretion occurring (PAH)
how are RBF and GFR regulated?
constriction or dilation of the afferent and efferent arterioles
vasoconstrictors
norepinephrine
- Released by renal nerves in response to decreased blood pressure or volume
- Constricts afferent and efferent arterioles
- Decreases GFR and RBF; helps to restore blood pressure and conserve fluid
vasodilators
nitric oxide
Released by endothelial cells in response to increased intake of NaCl
-Dilates afferent and efferent arterioles
-Increases GFR and RBF; helps to increase excretion of water and NaCl and reduce blood pressure
Myogenic mechanism
Constriction of smooth muscle of afferent arteriole when stretched
Tubuloglomerular feedback
increased Tubular flow sensed by macula densa –> signal from juxtaglomerular apparatus –> constriction of afferent arteriole
A patient has a urinary glucose concentration of 100 mg/ml and a urine flow rate of 1.25 ml/min. Assuming a reabsorption rate for glucose of 375 mg/min and a plasma glucose concentration of 5 mg/ml, what is this patient’s GFR?
100 ml/min
A patient being treated with penicillin has a plasma penicillin concentration of 0.10 mg/ml, a urinary penicillin concentration of 20 mg/ml and a urine flow rate of 2.5 ml/min. Measurement of creatinine gives values of Pcreat = 0.025 mg/ml and Ucreat = 1 mg/ml. What is the secretion rate of penicillin?
40 mg/min
