Download The Urinary System Chapter 18

The Urinary System
Chapter 18
Overview of Urinary Anatomy
Play Urinary Anatomy movie
The organs of the urinary system include:
Functions of the urinary system (all done by
kidneys):
 Regulate the volume, concentration, pH
and content of blood
 Eliminate metabolic wastes as urine
3 processes occur within the kidneys to accomplish
these goals
Filtration (F) – Pressure (blood pressure) forces some fluid (plasma) and
small substances from blood to renal (kidney) tubules. Results in the
formation of “filtrate” in the renal tubules; approx. 180 liters filtrate/day
Reabsorption (R) – Movement (by passive & active means) of most
fluid & many solutes from renal tubules back into the blood; approx.
99% filtate reabsorbed
Secretion (S) – Selective movement of specific substances (e.g. H+, K+)
from blood to tubules
blood
Blood vessels (capillaries)
F
filtrate
R
Renal tubules
Filtered
blood
S
urine
Gross Anatomy of the Kidneys
 Retroperitoneal organs
 Left kidney more superior than right (due to liver)
 Notch at medial border (hilus) for renal artery & vein, ureter
Each kidney surrounded by 3
layers of CT:
 renal capsule – innermost layer
of dense CT
 adipose capsule – middle layer
protecting & insulating kidneys
 renal fascia – outer layer
holding kidneys in place in
abdominal cavity
Internal Anatomy of the Kidneys
 Cortex
 Medulla
where urine
formation
occurs
 pyramids
 renal papillae
 renal columns
 Pelvis - collecting basin
 minor calyces
 major calyces
 renal pelvis
Microscopic Anatomy of the Kidneys
Functional unit of the kidneys is the “Nephron”
Nephron = renal corpuscle + renal tubules
Renal corpuscle – 1st part of the
nephron; site of filtration;
comprised of
 glomerulus – capillary network
 Bowman’s capsule – double
layered capsule of epithelial
tissue (inner visceral (podocyte)
layer/outer parietal layer),
surrounding glomerulus
Bowman’s capsule
(parietal (capsular)
layer)
Filtration occurs across
“endothelial capsular (filtration)
membrane” – junction
between glomerular
endothelium & podocytes;
results in formation of “filtrate”
in capsular space
capsular space
glomerulus
Visceral layer of
Bowman’s
capsule
(podocytes)
Representative
Nephron
proximal convoluted tubule
distal convoluted tubule
reabsorption
Filtrate from
renal corpuscle
will move into
PCT  loop of
Henle DCT;
and then into a
collecting
system of tubes
 minor calyx)
NEPHRON
Secretion, some
reabsorption
COLLECTING
SYSTEM
renal
corpuscle
filtration
collecting duct
variable
secretion &/or
reabsorption
Loop of Henle
H2O
solutes
filtrate
more
reabsorption
Connecting
tubule
papillary duct
delivery of
urine to minor
calyx
Blood supply to Kidneys
Renal artery
Renal artery 
afferent arterioles 
glomerulus  efferent
arterioles
Renal
vein
Efferent
arteriole
glomerulus
Afferent arteriole
Efferent arterioles branch into a second capillary network, the peritubular
capillaries, which surround the renal tubules
Reabsorption & secretion occur between the renal tubules & peritubular
capillaries
Peritubular capillaries  venules renal vein
Juxtaglomerular Apparatus (JGA)
Extremely important to regulate the rate of filtration that occurs at the
glomerulus (glomerular filtration rate “GFR”)
GFR directly related to glomerular blood pressure –
increased BP  increased GFR
decreased BP  decreased GFR
To regulate glomerular BP, we have a feedback system – the
juxtaglomerular apparatus (JGA)
JGA =
 juxtaglomerular cells of the afferent arteriole – recognize if renal BP is
too low & then can respond
 macula densa cells of the distal convoluted tubule – recognize if
decreased filtrate produced or too many solutes within filtrate & then can
respond
Once urine is formed, it will move from the pelvis of the kidneys
into the ureters
 retroperitoneal, muscular tubes running from kidneys to urinary
bladder
 lined with transitional epithelium
 transports urine primarily by peristalsis
 Hollow muscular organ that
temporarily stores urine prior to
“micturition”
 Lined with mucosa of transitional
epithelium with rugae
 Muscularis of 3 layers of smooth
muscle known as “detrussor muscle”
 Internally have “trigone” – triangular
area formed by openings of ureters &
urethra
 Micturition reflex – stretch receptors
in wall of bladder stimulate smooth
muscle of detrussor muscle
(involuntary); stimulation of external
urethral sphincter of skeletal muscle
(voluntary) & of internal urethral
sphincter (involuntary)
Urinary bladder
Urethra
 Transports urine out of body
 Inner urethral sphincter of smooth muscle; external urethral sphincter
of skeletal muscle
 Anatomically different in men & women