urinary system sanjaya adikari department of anatomy
TRANSCRIPT
Urinary System
Sanjaya Adikari Department of Anatomy
• Urinary system
comprises of
– Two kidneys
– Two ureters
– Bladder
– Urethra
Position and size of the kidneys
Retro-peritoneal
Size 12 x 6 x 3 cm
Weighs about 130 g
Hilum is 5 cm from midline
12
6
Position and size …
Hilum of right Kidney
is just below
transpyloric plane
Hilum of left Kidney
is just above
transpyloric plane
Slight movement
with respiration
Back
Renal fascia
Perinephric fat
Renal capsule
Ureter
Renal vessels
Renal fascia separates the kidney from the suprarenal gland and surrounding tissues.
Limits the spread of a perinephric abscess
Structures at the hilum of the kidney
• Three structures enter each kidney via the hilum, from front to back
– the vein
– the artery
– the ureter
Renal vein
Renal artery
Ureter
Functions of the kidney
• Filtration
• Selective reabsorption
• Secretion
• Control of renin-angiotensin-aldosterone mechanism
• Secretion of erythropoietin
• Production of 1,25-dihydroxycholecalciferol
Structure of the kidney
• Capsulated
• Outer cortex and inner medulla
• Medulla is arranged into medullary
pyramids
• Apices of pyramids are called renal
papillae
• Papillae project into calyces
• Calyces converge to form the renal
pelvis
Minor Calyces
Renal Papilla
Structure of the kidney…
• Functional unit is the nephron
• Approximately 1.3 million nephrons
in each kidney
• Part of a nephron is in cortex and
part in medulla
Nephron
Nephron
Renal corpuscle
Renal tubule
Glomerulus
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting tubule
Nephron…cont.
Location of nephrons
Cortical nephrons
Juxtamedullary nephrons
Renal corpuscle(Bowman’s space)
of the visceral layer
Vascular pole
Urinary pole
Bowman’s capsuleSingle layer of flattened cells resting on a basement membrane
GlomerulusCoiled network of anastomosing capillaries
MesangiumSupporting connective tissue
Renal corpuscle – microscopic view
Glomerular filtration barrier
• Capillary endothelium– Contain pores (fenestrations) large enough to permit
passage of all non-cellular elements of blood
• Common basement membrane (glomerular basement membrane)– Non-fenestrated, continuous layer. Allows passage of
molecules <65000 molecular weight. Eg. Free Hb. Albumin with mw of 68000 and other lager molecules are retained
• Podocyte layer– Has primary and secondary processes (pedicles).
There are slit pores between pedicles. Function of slit pores ?
Components of
glomerular filter
Proximal convoluted tubule (PCT)
• Longest section of the tubule
• Most convoluted section
• Makes up the bulk of cortex
• Simple cuboidal epithelium
• Brush border fills the lumen
• Cytoplasm is pink stained due to mitochondria
• >75% of GF is reabsorbed
Proximal convoluted tubule…
PCT
DCT
Loop of Henle
• Has thin and thick limbs
• Descending limb is lined by simple squamous epithelium (thin walled)
• Ascending limb is lined by simple cuboidal epithelium (thick walled)
• Closely associated with parallel capillary loops called vasa recta (forms a counter-current multiplier system)
• Generates a high osmotic pressure in the ECF of medulla
Loop of Henle…
Distal convoluted tubule (DCT)
• Shorter and less convoluted than PCT
• Found in the cortex
• No brush border
• Larger, clear lumen
• Cells smaller, so more cells than in PCT in section
• Na+ ions absorbed under the influence of aldosterone
Collecting tubule
• This is the terminal part of the DCT
• Opens into collecting ducts
• Together with collecting ducts form ‘medullary rays’
• Collecting tubules and ducts are not normally permeable to water
• Becomes permeable to water in the presence of ADH
• Site of reabsorption of water
Collecting ducts• Formed by fusion of collecting tubules
• They fuse with adjacent ducts and form larger ducts called ducts of Bellini
• Ducts of Bellini convey urine into the calyceal space through renal papillae
• Lined by tall, pale stained columnar cells
• No brush border
• Water reabsorption under ADH control
Collecting ducts…
Minor Calyces
Renal Papilla
Calyces and renal pelvis
Ureter
• About 25cm long
• In X-ray seem to lie
over the transverse
processes of L2 – L5
veterbrae
• Comprises the pelvis,
abdominal, pelvic and
intravesical portions
Course of the ureter• Abdominal part lies on medial edge of psoas
muscle
• Psoas muscle separates it from the tips of transverse processes of L2-L5
• Crosses into the pelvis at the bifurcation of common iliac artery in front of sacroiliac joint
• Pelvic part runs on the lateral wall of pelvis towards the ischial spine
• At ischial spine turns forwards and medially to enter the bladder
• Intravesical part runs obliquely through the bladder wall for 2 cm. This creates a valvular effect
Narrow parts in the ureter
• Ureter is relatively narrowed at three sites
– Junction between the renal pelvis and abdominal
part
– At the pelvic brim
– At the ureteric orifice (narrowest of all)
• A ureteric stone can get lodged at one of these
places
• Usually stones <5mm in diameter tend to pass
naturally
Ureter…
• Lined by transitional epithelium
• Muscular tube
– Inner longitudinal
– Outer circular
• Urine is propelled by peristalsis
Transitional epithelium
• Also called urinary epithelium/
urothelium
• Plasma membrane of superficial cells
are thicker
• Impermeable to urine (potentially toxic)
• Prevents water leaking out towards
concentrated urine
• Allows greater stretching of epithelium
Transitional epithelium…
Bladder• Lined by transitional epithelium• Wall has three smooth muscle layers (Detrusor
muscle)
Urethra• In males, has three parts
– Prostatic urethra
– Membranous urethra
– Spongy urethra (penile urethra)
• Prostatic urethra is lined by urinary epithelium
• Urethral meatus is lined by stratified squamous epithelium
• Other parts are lined by stratified or pseudostratified columnar epithelium
• External orifice is the narrowest part
UrethraCompare the distance between the anus and the urethral opening in male with that of female. In females the urethra opens into the vestibule of vulva where the vagina is also opened.
Females are more prone to get urinary tract infections (UTI)
Juxtaglomerular apparatus (JGA)
Juxtaglomerular apparatus…
• Has 3 components:
– Juxtaglomerular cells
• Derived from smooth muscle cells of afferent arteriole
– Macula densa
• Modified DCT cells
– Lasis cells
• Modified extraglomerular mesangial cells
Juxtaglomerular cells
• Derived from smooth muscle cells of afferent
arteriole. Cytoplasm contains granules of
enzyme renin. Directly sensitive to BP in the
afferent arteriole
Macula densa
• Modified DCT cells. Closely associated with
juxtaglomerular cells. Has taller cells with
prominent nuclei. Sensitive to [Na+] within
DCT. When [Na+] is low stimulates the release
of renin from juxtaglomerular cells
Lasis cells
• Modified extraglomerular mesangial
cells. Lie between macula densa
and Bowman’s capsule. Produce
the hormone erythropoietin
Blood supply of the kidney
Five segments of the kidney
Apical
Upper
Middle
Inferior
Anterior view
Posterior
Posterior view
They are supplied by five segmental branches of the renal artery.
In the region of the hilum, the artery divides into anterior and posterior branches
The posterior branch supplies the posterior segment of the kidney.
The anterior branch further divides into four branches and supply the remaining 4 segments
Both renal arteries give off a suprarenal branch and a
ureteric branch before they enter the kidneys.
The pattern of
branching of
vessels may vary,
but always five
segmental arteries
are present.
Branches of renal
arteries do not
have collateral
circulations
between them.
Each segmental artery gives several interlobar arteries.
They ascend between the pyramids of the renal medulla.
At the corticomedullary junction, they branch to form the arcuate arteries.
Arcuate arteries give rise to interlobular arteries.
Afferent arterioles of the glomeruli originate from these interlobular arteries.
Efferent arterioles give rise to peritubular
capillaries and vasa recta
Vasa recta are found in association with the
loops of Henle of juxtamedullary nephrones
that extend down into the medulla
The cortical and medullary capillaries drain
via interlobular veins to arcuate vein at the
corticomedullary junction and through
interlobar veins to the renal vein
Afferent
arteriole
Efferent
arteriole Peritubular
Capillaries.