Lecture 1 & 2- Introduction Flashcards by Alexis Villacampa

Cortex

Outer region, located under the kidney capsule

has interstitial osmolarity close to plasma

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Medulla

central region, divided into an outer and inner medulla

has HIGH interstitial osmolarity, which allows kidney to generate concentrated urine

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Papilla

innermost tip of the inner medulla (extension of the ureter)

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Nephron order

Fluid filtered at glomerulus -> Bowman’s capsule -> proximal tubule -> thin descending -> thin ascending -> thick ascending -> distal tubule -> collecting duct

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Filters

the blood to generate a fluid free of cells and most proteins

(plasma minus proteins)

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Reabsorbs

certain solutes and water from tubular fluid (Na, Cl, glucose)

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Secretes

other solutes from tubular fluid (uric acid)

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Excretes

in the urine the water and solutes that remain in the tubular fluid after passing through the renal tubule

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How much of plasma gets filtered?

20%

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How much plasma exits through efferent arteriole?

80%

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Cortical nephrons (90%)

Glomeruli in outer cortex
Short loops of Henle
Efferent arterioles that form peritubular capillaries

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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

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Macula Densa

functions to monitor the renal fluid composition

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juxtaglomerular cells

produce renin and help control constriction of the afferent and efferent arterioles

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glomerular filtration

filtration of a fraction of plasma (minus proteins) into Bowman’s Space

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tubular reabsorption

transport of solutes from blood into renal fluid

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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

1. freely filtered 2. not reabsorbed or secreted 3. not metabolized or produced by the kidney 4. does not alter GFR measure by the clearance of INULIN or CREATININE

Measurement of RPF

1. freely filtered 2. efficiently secreted 3. 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