Urinary System – BIOL 302
Excretion of waste
Production of urine – 180L/day. Filtration, resorption and secretion.
Endocrine glands depend on kidneys
Consists of renal corpuscles (glomerulus and Bowman’s capsule)
Medullary rays break up the cortex into segments.
Pyramidal areas that tubules and blood vessels pointing in one
direction that empty into the papilla
Outer, more dense, darker layer consists of proximal and distal
Inner, looser lighter layer consists of loop of Henle, collecting
ducts, papillary ducts
The kidney is divided into lobes. Lobes are defined as a pyramidal shape Calyxes
at the small end of the pyramid join to form the renal pelvis.
The renal artery and renal vein supply blood to the kidney.
Nephron is the functional unit of the kidney. The glomeruli and the tubular system are
both parts of the functional unit. It consists of the renal corpuscle, proximal convoluted
tubule, loop of Henle, and distal convoluted tubule.
The uriniferous tubule is divided into the proximal tubule, the intermediate (thin)
tubule, the distal tubule and the collecting duct.
o Blood supply
o Big afferent arteriole
o Small efferent arteriole
o Proximal convoluted tubule continuous with the parietal layer of
Bowman’s capsule Bowman’s capsule:
o Visceral layer is against capillaries with podocytes (supporting cells)
Podocytes have pedicels (end feet that interdigitate with filtration
Basal lamina is thick, shared endothelium, and acts as a filter
o Parietal layer against Bowman’s (urinary) space
Simple cuboidal epithelium, microvilli in lumen, small lumen
o In cortex
o Coils close to the glomerulus in the cortex.
o Their walls are formed by a simple cuboidal/columnar epithelium, with
o The eosinophilic cells of the epithelium have a wide brush border and are
active in endocytosis. They almost completely resorb substances of
nutritional value from the glomerular filtrate (glucose, amino acids,
protein, vitamins etc.).
o In the proximal tubules the volume of the glomerular filtrate is reduced by
about 75%. Sodium ions are actively resorbed from the glomerular filtrate. They are followed by passively diffusing chloride ions and the osmotic
absorption of water.
o The straight portion of the proximal tubule descends towards the medulla.
o In medullary ray and medulla
o The straight portion of the proximal tubule merges with the intermediate
tubule (thin segment of the loop of Henle).
o A flattened, only ~1-2 µm high epithelium forms the intermediate tubule,
which is only ~15 µm wide.
o Descending parts of the straight proximal and intermediate tubules are
permeable to water but not to solutes.
Loops of Henle
Simple squamous epithelium
For osmotic balance and to create a sodium gradient
Consists of a descending thin segment, a loop, and a ascending thin segment
Simple cuboidal epithelium, low or flattened nuclei on apical side, large lumen
o In medulla and medullary ray
o The straight portion of the di