The Urinary System
Th is general role of the kidneys involves a
complex combination of renal functions:
1. Regulation of the balance between
water and electrolytes (inorganic
ions) and the acid-base balance
2. Excretion of metabolic wastes along
with excess water and electrolytes
in urine
3. Excretion of many bioactive
substances, including many drugs
4. Regulation of arterial blood pressure by secretion of renin
5. Secretion of erythropoietin
6. Conversion of vitamin D the active form (1,25-dihydroxyvitamin D3 or calcitriol)
7. Gluconeogenesis
Kidneys:
o Hilum has ureter exiting, and blood and lymph vessels entering.
o Renal pelvis at the hilum divides into 2 or 3 major calyces, which then branch out into minor calyces.
o Renal medulla consists of 8-12 renal pyramids separated by renal columns
o Medullary rays: striations projecting from the medulla into the cortex.
o The tip of pyramid has a renal papilla which projects into the minor calyx that collects urine formed by the tubules
in the pyramid.
o The functional unit is nephrons (around 1 million in each kidney) that consists of :
Renal corpuscle
Proximal tubule
Loop of henle
Distal tubule
Connecting tubule
These tubules join to form the collecting ducts that converge in the renal papilla where they deliver
urine to the minor calyx
- Each nephron originates in the cortex, at the renal corpuscle surrounding a small tuft of glomerular capillaries.
, Extending from the corpuscle is the long proximal convoluted tubule which leads to short proximal straight tubule that enters
the outer medulla.
This tubule continues as the thin
descending limb and the thin
ascending limb of the nephron’s
loop of Henle in the medulla.
The loop of Henle ends with a thick
ascending limb, a straight tubule
that reenters the cortex and ends at
its thickened macula dense area
where it contacts the arterioles
entering the glomerulus.
Beyond the macula densa this
tubule is the distal convoluted
tubule, the end of which is the short
connecting tubule.
Connecting tubules from many
nephrons merge into cortical
collecting tubules and a collecting
duct that transports urine to the
calyx.
Blood circulation:
o Each renal artery divides into 2 or more segmental arteries at the hilum which branch further into interlobar
arteries at the renal pelvis. These divide further into arcuate arteries that run at the base of each renal pyramid.
Smaller interlobar arteries run into the cortex.
o From the interlobar arteries arise the afferent arterioles which divide to form a plexus called the glomerulus
(Where blood is filtered)
o Blood leaves the glomerulus through efferent arterioles (not venules) which branch again to form another capillary
network called the peritubular capillaries in the cortex.
o Vasa recta are capillary loops that penetrate deep into the medulla in association with the loops of Henle and
collecting ducts.
o Cortex receives 10 times more blood than the medulla.
Th is general role of the kidneys involves a
complex combination of renal functions:
1. Regulation of the balance between
water and electrolytes (inorganic
ions) and the acid-base balance
2. Excretion of metabolic wastes along
with excess water and electrolytes
in urine
3. Excretion of many bioactive
substances, including many drugs
4. Regulation of arterial blood pressure by secretion of renin
5. Secretion of erythropoietin
6. Conversion of vitamin D the active form (1,25-dihydroxyvitamin D3 or calcitriol)
7. Gluconeogenesis
Kidneys:
o Hilum has ureter exiting, and blood and lymph vessels entering.
o Renal pelvis at the hilum divides into 2 or 3 major calyces, which then branch out into minor calyces.
o Renal medulla consists of 8-12 renal pyramids separated by renal columns
o Medullary rays: striations projecting from the medulla into the cortex.
o The tip of pyramid has a renal papilla which projects into the minor calyx that collects urine formed by the tubules
in the pyramid.
o The functional unit is nephrons (around 1 million in each kidney) that consists of :
Renal corpuscle
Proximal tubule
Loop of henle
Distal tubule
Connecting tubule
These tubules join to form the collecting ducts that converge in the renal papilla where they deliver
urine to the minor calyx
- Each nephron originates in the cortex, at the renal corpuscle surrounding a small tuft of glomerular capillaries.
, Extending from the corpuscle is the long proximal convoluted tubule which leads to short proximal straight tubule that enters
the outer medulla.
This tubule continues as the thin
descending limb and the thin
ascending limb of the nephron’s
loop of Henle in the medulla.
The loop of Henle ends with a thick
ascending limb, a straight tubule
that reenters the cortex and ends at
its thickened macula dense area
where it contacts the arterioles
entering the glomerulus.
Beyond the macula densa this
tubule is the distal convoluted
tubule, the end of which is the short
connecting tubule.
Connecting tubules from many
nephrons merge into cortical
collecting tubules and a collecting
duct that transports urine to the
calyx.
Blood circulation:
o Each renal artery divides into 2 or more segmental arteries at the hilum which branch further into interlobar
arteries at the renal pelvis. These divide further into arcuate arteries that run at the base of each renal pyramid.
Smaller interlobar arteries run into the cortex.
o From the interlobar arteries arise the afferent arterioles which divide to form a plexus called the glomerulus
(Where blood is filtered)
o Blood leaves the glomerulus through efferent arterioles (not venules) which branch again to form another capillary
network called the peritubular capillaries in the cortex.
o Vasa recta are capillary loops that penetrate deep into the medulla in association with the loops of Henle and
collecting ducts.
o Cortex receives 10 times more blood than the medulla.
