Download The Urinary System - Ms. Zhong`s Classes

The Urinary System
Kidney
The urinary system
• The urinary system provides
temporary storage reservoirs
for urine or serve as
transportation channels
• The organs involved in the
urinary system are:
- Kidney
- Ureter
- Bladder
- Urethra
Kidneys
• Locations:
- The kidneys extend from
T12 to L3
- Because it is crowded by the
liver, the right kidney is
positioned slight lower than
the left
• An adult kidney is about the
size of a large bar of soap
Kidney Structure
• A fibrous, transparent
renal capsule encloses
each kidney:
- In a living person, a
fatty mass, the
adipose capsule,
surrounds each
kidney and helps hold
it in place against the
muscles of the trunk
wall
Kidney Structure
• The kidney has 3 distinct regions:
1. Renal cortex: The outer region, light in color
2. Renal medulla: Deep to the cortex, darker reddish-brown
area
- It is made of many triangular regions with a striped
appearance, the medullary pyramids
- The pyramids are separated by extensions of cortical
tissue, the renal columns
Kidney Structure
3. Renal pelvis: medial to the cortex, a basin-like
cavity
- Extensions of the pelvis, calyces, form cup
shaped areas that enclose the tips of the
pyramid
Blood Supply
• The kidneys continuously cleanse the blood and
adjust its composition:
- Approximately ¼ of the total blood supply of the
body passes through the kidneys each minute
Renal Arteries
• Renal Arteries
(from large to
small):
- Renal artery
- Segmental
artery
- Lobar artery
- Interlobar
artery
- Arcuate artery
- Interlobular
artery
Renal Veins
• Venous blood
draining from the
kidney flows
through veins that
trace the pathway
of the arterial
supply but in a
reverse direction:
- Interlobular veins
 arcuate viens
interlobar veins
 renal veins
- There are no lobar
or segmental
veins
Nephrons
• Nephrons: the
structural and
functional units of the
kidneys and are
responsible for
forming the urine
product
- Each nephron consists
of two main
structures:
1. Glomerulus: knot of
capillaries
2. Renal tubule
Tubules
• Bowman’s capsule: the
closed end of the renal
tubule that is enlarged
and cup-shaped and
completely surrounds the
glomerulus
• Tubules (from bowman’s
capsule to renal pelvis):
Proximal convoluted tubule
Loop and Henle  Distal
convoluted tubule 
Collecting ducts
Tubules
• The lumen surfaces of the
tubule cells in the
proximal convoluted
tubules are covered with
dense microvilli
• Microvilli also occur on
the tubule cells in other
parts of the tubule but in
much reduced numbers
Types of nephrons
• Most nephrons are called cortical
nephrons because they are
located almost entirely within
the cortex
• Some nephrons are called
juxtamedullary (juxta- nearby)
nephrons because they are
situated close to the cortexmedulla junction and their loops
of Henle dip deep into the
medulla
Capillaries
• Each and every nephron is
associated with 2 capillary
beds:
- The glomerulus
- Peritubular capillaries
(peri- around)
• The glomerulus is both fed
and drained by arterioles:
- The afferent arteriole:
feeder vessel
- The effector arteriole:
receives blood that has
passed through the
glomerulus
Capillaries
• The peritubular
capillaries:
- Arise from the
efferent arteriole that
drains the glomerulus
- Drain into interlobular
veins leaving the
cortex
Urine Formation
• Urine formation is a result of
3 processes:
1. Filtration
2. Reabsorption
3. Secretion
• Filtration:
- non-selective, passive
process
- Water and solutes smaller
than proteins are forced
through the capillary walls
and pores of the glomerular
capsule into the renal tubule
Urine Formation
• Reabsorption:
- Water, glucose, amino
acids and needed ions
are transported out of
the filtrate into the
tubule cells and then
enter the capillary
blood
Urine Formation
• Secretion:
- It is essentially
reabsorption in reverse
- H+ , K+, and
breakdown product of
the body are removed
from the peritubular
capillaries to the
tubules