The Urinary System
Chapter 23
• Consists of: 2 kidneys, 2 ureters, 1 urinary bladder, 1
urethra
• Major function: kidneys filter blood and restore water and
solutes to bloodstream. Remaining water and solutes are
voided of body.
Function
• Regulates blood volume and composition
– Removes wastes such as protein wastes
(ammonia, urea), nucleic acid waste (uric
acid), excess water, and other ions to form
urine.
• Regulation of blood pressure
– Kidney secretes renin, an enzyme that
increases blood pressure and volume.
Other Functions
• Produces erythropoietin
– a hormone that stimulates red blood cell
production in bone marrow.
• Metabolizes vitamin D to its active form.
Kidney enclosed in 3 layers
Renal capsule – tough fibrous tissue that adheres
directly to kidney surface and is continuous with
outer coat of ureter.
Kidney enclosed in 3 layers
Adipose capsule – provides protection from
trauma and keeps kidney in place
Kidney enclosed in 3 layers
Renal fascia – thin outer layer of dense, irregular
C.T. that anchors kidney to abdominal wall,
peritoneum, and other structures.
2 distinct regions of the kidney are: cortex and renal medulla
Cortex – outer edge of kidney, delineated by renal pyramid
Medulla – deep inner portion of kidney
Renal pyramid – cone-shaped structures, the apex of each points toward the
renal sinus, where its papilla communicate with minor calyx.
Renal pelvis – ureter expands and widens into kidney to form funnel shaped sac.
Subdivided into minor and major calyx.
These structures collect urine from the renal papilla located in the renal pyramids.
renal
artery
segmental
artery
lobar
artery
interlobar
artery
arcuate
artery
interlobular
artery
afferent
arteriole
glomerulus
(capillaries)
renal
vein
interlobar
vein
arcuate
vein
interlobular
vein
peritubular
capillaries
and vasa
recta
efferent
arteriole
1. Arterial flow – renal artery, segmental artery, lobar artery, interlobar artery,
arcuate artery, interlobular artery, afferent arteriole.
2. Glomerular tubular flow – glomerular capillaries, efferent arteriole, peritubular
capillaries/vasa recta
3. Venous flow – interlobular veins, arcuate veins, interlobar veins, renal vein
Nephrons
• Urine producing units of the kidney
• 2 components:
– renal corpuscle
• glomerulus surrounded by thin-walled sac called the
glomerular (Bowman’s) capsule.
– renal tubule
Nephrons Perform 3 Functions
Overall net effect is to allow wastes to be excreted in
concentrated urine and needed materials returned to blood.
Juxtaglomerular Apparatus
•
•
The collection of cells near the glomerulus.
These cells secrete renin as decreased delivery of water, sodium, and
chlorine are detected. This triggers a hormonal response to raise blood
pressure, increase blood volume, and blood solute concentration.
Summary of Filtration
•
•
•
•
•
Renal corpuscles
– filter fluid into tubule containing all solutes in blood
• e.g. water, ions, glucose, amino acids, etc.
PCT
– reabsorption of water, glucose and amino acids, ions
– secretion of H+, ammonium ion, urea
Loop of Henle
– reabsorption of water, ions
– secretion of urea
DCT
– reabsorption of water and ions
Late DCT and Collecting Duct
– reabsorption of water
– secretion of ions
Elimination of Urine
Ureters & Urinary Bladder
• Urine drains into ureters from the renal pelvis and connects
to urinary bladder.
• Urinary bladder - A hollow, distendable, muscular organ
located behind the symphysis pubis in the pelvic cavity.
Urethra – small tube leading
from the internal urethra orifice
in the floor of the bladder to the
exterior of the body.
Females – urethera about 4cm
long and passes posteriorly to
the pubic symphysis and opens
to the exterior between the
clitoris and the vagina.
Males – urethra functions as the urinary canal and
reproductive canal for sperm and associated
secretions.
Prostatic urethra – about 2.5 cm long and passes
through the prostate gland. Ducts from reproductive
structures also pass through the prostate and join
urethra.
Membranous urethra – about 2cm long and passes
through the urogenital diaphragm and is surrounded
by external urethral sphincter.
Penile (spongy) urethra – about 15 cm long and
passes through the corpus spongiosum of the penis,
surrounded by erectile tissue.
External urethral orifice – where the urethra opens
to the outside.
Urine Flow
• The order of structures urine passes through on its
way to the outside world:
• Glomerular capsule, PCT, descending limb of loop
of Henle, ascending limb of loop of Henle, DCT,
collecting tubule, papillary duct of renal papillae,
minor calyx, major calyx, renal pelvis, ureter,
bladder, urethra.