Structure and Function of Kidney

Question 1

1. Describe the anatomy of the kidney and its vasculature.

Answer 1

cortex includes the glomerular structures while the medulla contains the tubular segments

blood supply to the glomerulus enters and exits as a artery

vascular follows: renal artery- segmental artery- inter lobar artery- arcuate artery- interlobar artery, afferent arteriole- glomerulus- efferent arteriole- peritubular capillaries and vasa recta lead to inter lobar, arcuate, inter lobar then renal vein

Question 2

2. Describe the structure and function of the glomerulus.

Answer 2

bowman’s capsule contains a parietal and visceral layer (podocytes) of glomerular capsule

blood enters and exits through the afferent and efferent arterioles

filtrate leaves via the proximal convoluted tubule

Question 3

3. Explain the juxtaglomerular apparatus and tubuloglomerular feedback.

Answer 3

low volume state serves as a stimulus sensed by macula densa cells (sense low Na and Cl and stretch) and sympathetic nerve endings in JG apparatus

causing release of renin by juxtaglomerular apparatus of renin leading to vasoconstriction and increased Na and water retention

Question 4

4. Identify the factors that regulate glomerular filtration.

Answer 4

hydrostatic pressure of blood arterioles is only opposed by fluid pressure within the glomerulus and the oncotic pressure of the blood

due to compensation of the arterioles, there is a fairly consistent level of renal blood flow for a wide range of MAP, very high or low BP can lead to changes in filtration

Question 5

5. Explain the major transport functions of the different segments of the nephron.

Answer 5

proximal tubule: reabsorption of solutes and water (66% Na, 100% glucose, 90% phosphate), water is reabsorbed passively leaving isotonic filtration

loop of Henle: descending limb removes water w/o salt, ascending limb transports NaCl w/o water resulting in countercurrent multiplication

distal convoluted tubule: further reabsorption of sodium and dilution of ultra filtrate

collecting duct: cortical (Na reab, K excretion); medullary reabsorption of water

Question 6

6. Describe the endocrine functions of the kidney with regard to the production of renin.

Answer 6

1. juxtaglomerular signal
2. efferent constriction
3. juxta release of renin (converts angiotensiongen to angiotensin I, leads to aldeosterone and ADH release action in collecting duct

Question 7

6. Describe the endocrine functions of the kidney with regard to the production of 1,25-dihydroxy vitamin D3. (which cells, when and to what effect)

Answer 7

kidney converts to active form of vit D by alpha 1 hydroxylase

produced when Ca or Phos are low, promoting healthy bone formation, inhibiting PTH

Question 8

6. Describe the endocrine functions of the kidney with regard to the production of erythropoietin. (which cells, when and to what effect)

Answer 8

produced when tissue have low oxygenation,

produced by the proximal tubular epithelial cells and cortical interstitial cells

increases RBC production, maturation and lifespan

Question 9

7. [How would you] assess kidney function with the measure of creatinine clearance?

Answer 9

memorize equation:
clearance = (U x V)/ P (don’t forget units)
U= urinary concentration of substance
V= urine flow rate (mL/min)
P= plasma concentration of substance (mg/mL)

inulin(exogenous) and cystatin C (proteinase inhibitor) are expensive to test but creatinine (muscle produces) is a endogenous substance that is cheap to test but requires a 24hr. collection

Question 10

7. [How would you] assess kidney function with the Cockcroft-Gault equation to estimate creatinine clearance? (What are the benefits)

Answer 10

avoid 24h collection
uses weight for a surrogate of muscle mass (potential for error)
and accounts for age and center

good estimate when kidneys function at a high level (measured in chronic not acute disease)

Question 11

7. [How would you] assess kidney function with the Modification of Diet in Renal disease and CKD-EPI formulae to estimate the glomerular filtration rate?

Answer 11

MDRD is a more complex formula that is useful when the kidney is functioning at lower levels of filtration and stable creatinine (not AKI)

CKD-Epi is the newest formula (not used in AKI)

Question 12

2. Describe the make up of the glomerular basement membrane.

Answer 12

fenestrated endothelium lines vessel

GBM acellular matrix includes type IV collagen, laminin and negatively charged glycoproteins

potocytes form visceral layer of glomerular capsule (interdigitated- adjacent cells connected by slit diaphragm 40nm) are anchored to GBM

Question 13

Name 3 important components of podocytes that can be effected by mutation and cause leakage of proteins.

Answer 13

podocin, nephrite and actinin 4

Question 14

Describe the transporters of the proximal tubule.

Answer 14

Na+ reabsorbed with glucose, phos and AA or exchanged for H+

basolaterally Na+ and bicarbonate are transported together; Na/K ATPase sets up sodium gradient

Question 15

What is the action of anhydrase inhibitors?

Answer 15

acetazolamide

disable CA inside the cell which decreases Na/H activity, blocks transport of H+ and therefore Na reabsorption

cause diaeresis and also decreased bicarb reabsorption (acidosis)

Question 16

Where is the action of loop diuretics? (what channels are effected and what electrolytes are effected?)

Answer 16

in thick ascending limb: decreases action of NaCLK transporter, disabling channel lease to low Na reabsorption (volume loss) but also loss of Ca, Mg and K

Question 17

What is the site of action of ADH

Answer 17

reduces aquaporins in the medullary collecting ducts

Question 18

Contrast the properties of the principal cells vs. the intercalated cells.

Answer 18

principle cells: site of action of aldosterone and ANP; key channel includes ENaC

intercalated cells: site of action of ADH, contains aquaporins for the movement of water out of hypotonic urine

note ANP decreases ENaC channel activity
Hyperaldosterone will cause HTN due to Na+ retention and hypokalemia