Pathology of the urinary system

nephron (functional unit)

 (each human kidney has an estimated 10

6

 nephrons; dog, ~400,000; cat, 

~200,000.): 

- glomerular corpuscle: glomerulus, uriniferous space, Bowman’s capsule 

- proximal convoluted tubule (the longest part of the nephron) (pars convoluta, pars recta 

[synonym with thick descending limb of loop of Henle]): metabolically very active because 

of its important function in reabsorbing much of the glomerular filtrate (~65% of sodium and 

water present in the glomerular filtrate) 

- loop of Henle: thin descending limb, thick ascending limb 

- distal convoluted tubule 

 

Proximal and distal convoluted tubules are normally tightly packed, with little intervening 

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2

 

connective tissue, in order to favour their close apposition to blood vessels and thus easy 

exchange of material between glomerular filtrate and blood.  Connective tissue is normally 

visible microscopically in the cortex only near blood vessels. 

 

collecting tubule 

 

collecting system 

collecting ducts 

calyces, pelvis 

ureter 

 

The glomerular capillaries, derived from the glomerular afferent arteriole, are perfused at high 

pressure, which favours production of the glomerular filtrate, whereas the capillary bed arising from 

the glomerular efferent arteriole and supplying the rest of the nephron is at low pressure, thus 

favouring exchange of material between glomerular filtrate and blood. 

 

Only a small proportion of the total renal blood flow, about 1-2%, flows through the vasa recta 

which supply the medulla.  In other words, blood flow through the medulla of the kidney is sluggish 

in contrast to the rapid blood flow in the cortex. 

 

Nephrons of newborn animals are functionally immature, and their loops of Henle are short and 

therefore do not dip deeply into the medulla, thus reducing their ability to concentrate urine.  For this 

reason, newborn animals, especially piglets, are particularly susceptible to dehydration. 

 

 

RENAL FAILURE

 

 

   ∙ 

renal disease = any deviation from normal renal structure or function, without necessarily implying 

clinical significance. 

 

   ∙ 

renal failure = inability of the kidney to maintain normal function with consequent loss of 

homeostasis → affects many body systems. 

 

   ∙ 

because of the substantial renal functional reserve, there can be significant (subclinical) renal disease 

before renal failure occurs; renal failure requires a loss of ~75% of renal function; in human patients, 

however, in whom more subtle clinical signs can be recognized, some of the features of uremia 

associated with renal failure may be present to a lesser degree in people with a glomerular filtration 

rate that is barely below 50% of the normal rate.  

 

   ∙ 

through renal filtration, many metabolic waste products are eliminated in the urine: 

  - 

mainly urea and creatinine → plasma concentrations are used to detect renal malfunction; 

  -