Urinary system
General outline
 component
urinary organs: kidneys
micturition organs: ureter, bladder and urethra
 function
 discharge metabolite
 regulate the balance of water and electrolyte
 endocrine function: renin, erythropoietin,
prostaglandin
Renal anatomic structure
 Fibrosa
Cortical labyrinth
Cortex
Medullary ray
 Parenchyma
Renal pyramids
Medulla
Renal columns
Renal histological structure
Glomerulus
Renal corpuscles
 nephron
Renal tubules
 collecting duct
 juxtaglomerular apparatus
Bowman’s capsule
Kidney
Renal cortex
Renal medulla
Structure of Renal corpuscle:
afferent arteriole
efferent arteriole
capillary network
Glomerulus
mesangial cells
parietal layer: simple squamous
Epi.
Bowman’s
capsular cavity: filtrate
capsule
visceral layer: podocytes
(primary and secondary processes, slit membrane)
Renal
corpuscle
Podocyte
Renal corpuscle
Glomerulus
Functions of Renal corpuscle:
 Produce filtrate (primary urine)
fenestrated endothelium
 Filtration membrane basement membrane
(filtration barrier)
slit membrane of podocyte
 relevant factors of filtrate
molecular weight
charges
Filtration
membrane
Renal tubules:
convoluted tubule
proximal
straight tubule
thin segment
straight tubule
distal
convoluted tubule
Henle’s loops
Proximal tubule
 Location: cortical labyrinth
 LM: simple cuboidal or pyramid Epi.
acidophilic cytoplasm
no discrete cell margin;
brush border;
longitudinal striation
Convoluted segments of proximal
and distal tubules
EM: apical canaliculi and vesicles
numerous lysosomes, Mi.
many lateral interdigitations
microvilli on the surface
membrane invaginations
abundant Na+-K+ATPase
 Function
 reabsorb water, glucose, amino acid,
protein, vitamin and inorganic salts etc.
 secrete ammonia and some metabolic
substances
thin segment
 location: medullary ray and renal pyramids
 LM: simple squamous Epi.; pale cytoplasm,
 EM: a few microvilli; less organelles
 Function: water, and ions pass through easily
Thin segment and straight
segment of distal tubule
Distal tubule
 location: medullay ray and renal pyramids
 LM: simple cuboidal Epi;
clear cell boundary;
pale cytoplasm;
nuclei near lumen;
without brush border;
have longitudinal striation
 EM: a few microvilli;
many membrane invagination;
many mitochondria;
abundant Na+-K+ATPase
 Function: reabsorb Na+ and water;
excrete K+; secrete NH3
Distal straight tubules and
collecting tubules
Convoluted segments of proximal
and distal tubule
Collecting tubules:
 location: medullary ray and renal pyramids
 components: arched collecting tubules;
straight collecting tubules;
papillary ducts
 simple cuboidal Epi simple columnar Epi.,
papillary ducts line tall columnar Epi;
pale staining; distinct borders;
rare microvilli and Mi.
 function: similar to that of distal convoluted
tubules
Straight segment of distal
tubule and collecting tubule
Juxtaglomerular apparatus:
 located in a triangle area at the vascular pole of
the renal corpuscles
 consist of juxtaglomerular cells, macular densa
and extraglomerular mesangial (polar cushion)
cells
 function: control water and electrolyte balance;
regulate blood pressure;
produce erythropoietin
Juxtaglom
-erular
apparatus
Juxtaglomerular cells
 smooth muscle cells of the afferent arteriole
transform into the epithelial cells
 cytoplasm: a few myofibrils;
PAS-positive granules contained renin;
abundant RER, ribosomes and
well developed Golgi apparatus;
 function: secrete renin and erythropoietin
Juxtaglomerular
cell
Macular densa
 transformed from the cells of distal tubule
which near the vascular pole of the renal corpuscle
 the cells become taller and narrow, arranged
compactly; pale cytoplasm; nuclei located at the
apex
 a chemical (Na+ ) sensor
Macular densa
Extraglomerular mesangial cells
 resemble the intraglomerular mesangial cells
 gap junctions between the component of the
juxtaglomerular apparatus
 transmit information
Features of renal blood circulation
 blood flow is large
 two sets of capillary network
 the diameter of afferent arterioles is larger
than that of efferent, so as to facilitate filtration
 the vasa recta are parallel to the Henle’s loop, so
aid water reabsorption and urine concentration
Blood vessels
of kidney
Micturition organs
(ureter, bladder,)
 mucosa
Epi: transitional Epi
Lamina propria: L.C.T.
 muscle layer: smooth muscle
 adventitia: fibrosa
serosa
Bladder
Ureter