Kidney Function 1 Flashcards
(52 cards)
What are the major functions of the kidney?
- water and sodium homeostasis
- acid-base balance
- control of ECF ion concentration (K, Ca, Mg, Cl, HPO4)
- excretion of waste products and xenobiotics
- endocrine secretions (EPO, renin, VitD3, PGI2)
- formation of concentrated (1200mOs/L) or dilute urine (30mOs/L)
What are the features of superficial cortical glomeruli (SCG)?
- 85% of glomeruli
- short LOH; penetrate short distance into medulla
- efferent arterioles give rise to cortical capilaries surrounding PCT & DCT
What are the features of juxtamedullary glomeruli (JMG)?
- 10-15% of glomeruli
- at junction of medulla and cortex
- long LOH; penetrate deeply into medulla to papilla
- efferent arterioles become vasa recta around LOH
- responsible for the concentration gradient of the kidney that allows formation of concentrated urine
- 300mOs at junction
- 1200mOs at papilla
Normal renal blood flow in a 70kg human is
1L/min (total including both kidneys) ~20% of CO
What percentage of cardiac output flows through the renal vasculature per minute?
20%
What is normal haematocrit (packed cell volume)?
(% of RBCs in blood)
40% - women
45% - men
What is filtered from the renal blood flow?
plasma
Renal plasma flow to the kidney is
~600mL/min
Normal glomerular filtration rate (GFR) is
120mL/min (both kidneys)
60mL/min (each kidney)
approximately 180L/day of plasma is filtered
What volume of plasma is filtered per day?
approximately 180L/day of plasma is filtered
Average urine output is
1-2L/day
What is the function of the peritubular capillaries?
- come from efferent arteriole
- surround nephron closely
- take up 178L of 180L of plasma that is filtered per day
- maintains ~1-2L/day urine output
What comprises the juxtaglomerular apparatus (JGA)?
- terminal thick ascending LOH
- afferent and efferent arterioles
- macula densa cells in thich ascending LOH
What is the formula for MAP?
MAP = DP + 1/3(SP - DP)
What is the blood pressure range for which renal autoregulation can function?
70-180mmHg
Glomerular pressure is
constantly ~50mmHg
What are the functional roles of the JGA and macula densa cells?
function in autoregulation and tubuloglomerular feedback
What is tubuloglomerular feedback?
- part of autoregulatory function of glomerulus
- macula densa cells detect NaCl in thich ascending LOH/DT junction
- feedback via paracrine mediators (eg adenosine released from MD cells) to alter tone of afferent (only) arteriole
- adenosine causes vasoconstriction
- other mediators eg prostaglandins cause dilation
What are the two components of autoregulation?
tubuloglomerular feedback and the myogenic reflex
What is the myogenic reflex (renal)?
- afferent arteriole responds to stretch by contracting - it resists change by mitigating the dilating force
- helps maintain glomerular pressure of ~50mmHg
What are the roles of the macula densa?
- functions in tubuloglomerular feedback
- functions in renin release from epithelial cells of the afferent arteriole
- these are independent functions - renin release is NOT involved in tubuloglomerular feedback
What is clearance?
- amount of plasma removed per unit time
- clearance of a specific plasma constituent eg Na is the volume of plasma which is cleared of Na over time
- eg rate of urinary excretion of Na/plasma concentration of Na
- renal clearance = UV/P
- U = urinary concentration of substance
- V = rate of urine, usually per day
- P = plasma concentration
What is excretion?
urine concentration of substance x urine volume
UV
Why is creatinine clearance used to approximate GFR?
- net reabsorbtion and secretion of creatinine are equal
- therefore it is effectively all filtered and all cleared (no reabsorption) and the rate is equal to GFR



