3. Renal Function
• Regulation of water and electrolyte balance and acid-base balance
• Excretion of metabolic wastes, water and electrolytes in urine
• Excretion of many bioactive substances, including many drugs
• Regulation of arterial blood pressure by secretion of renin
• Secretion of erythropoietin, a glycoprotein growth factor that stimulates
erythrocyte production in red marrow when the blood O2 level is low
• Conversion of the steroid prohormone vitamin D, initially produced in the
epidermis, to the active form (1,25-dihydroxyvitamin D3 or calcitriol)
• Gluconeogenesis during starvation or periods of prolonged fasting,
making glucose from amino acids to supplement this process in the liver
4. Kidney
• Each kidney has a thick outer cortex, surrounding a medulla that is
divided into 8 to 12 renal pyramids; each pyramid and its associated
cortical tissue comprises a renal lobe.
• The apical papilla of each renal pyramid inserts into a minor calyx, a
subdivision of two or three major calyces extending from the renal
pelvis.
• The ureter carries urine from the renal pelvis and exits the renal
hilum, where the renal artery and vein are also located.
• Striations extending from the medulla into the cortex are called
medullary rays; these plus the attached cortical tissue are considered
lobules.
5.
6. Nephron
• Each kidney contains around 1 million functional units called nephrons
that consist of simple, single-layered epithelium along their entire lengths.
• Cortical nephrons are located almost completely in the cortex while
juxtamedullary nephrons (about one-seventh of the total) lie close to the
medulla and have long loops of Henle.
• Major Divisions:
• Renal corpuscle, an initial dilated part enclosing a tuft of capillary loops and the site
of blood filtration, always located in the cortex;
• Proximal tubule, a long convoluted part, located entirely in the cortex, with a shorter
straight part that enters the medulla;
• Loop of Henle (or nephron loop), in the medulla, with a thin descending and a thin
ascending limb;
• Distal tubule, consisting of a thick straight part ascending from the loop of Henle
back into the cortex and a convoluted part completely in the cortex; and
• Connecting tubule, a short final part linking the nephron to collecting ducts.
7.
8. Cortical vs. Juxtamedullary Nephrons
• The cortical nephrons make up 85% of the kidney nephrons and are
contained entirely in the cortex and almost don’t reach the medulla.
Their function is to filter the plasma, reabsorb critical ions and
molecules, and send their filtrate to the collecting ducts.
• The juxtamedullary nephrons make up 15% of the nephrons. They
have long loops of Henle that extend deep into the medulla.
• They create the concentration gradient in the medulla necessary to
either dilute or concentrate urine. (Countercurrent multiplication)
9. Blood Supply
• Renal artery divides into two or more segmental arteries at hilum
• Renal artery
• Interlobar arteries
• Arcuate arteries
• Smaller interlobular arteries radiate from the arcuate arteries
• Afferent arterioles
• Plexus of capillary loops (glomerulus)
• Efferent arterioles
• Peritubular capillaries
• From the juxtaglomerular corpuscles near the medulla, efferent
arterioles do not form peritubular capillaries, but instead branch
repeatedly to form parallel capillary loops called the vasa recta that
penetrate deep into the medulla in association with the loops of Henle
and collecting ducts.
12. Renal Corpuscle
• Contains a tuft of glomerular capillaries, surrounded by a double-walled epithelial
capsule called Bowman capsule
• The internal or visceral layer of this capsule closely envelops the fenestrated
capillaries. The visceral layer consists of stellate epithelial cells called podocytes
which together with the capillary endothelial cells compose the apparatus for renal
filtration.
• Podocytes extend large primary processes that curve around a capillary and
extend short, interdigitating secondary processes or pedicels, between which are
narrow spaces called slit pores.
• The outer parietal layer has a simple squamous epithelium and forms the surface
of the capsule.
• Between the two capsular layers is the urinary space
• Each renal corpuscle has a vascular pole, where the afferent arteriole enters and
the efferent arteriole leaves, and a tubular pole, where the proximal convoluted
tubule (PCT) begins
13.
14.
15.
16. Mesangial Cells
• Physical support of capillaries within the glomerulus;
• Adjusted contractions in response to blood pressure changes
• Phagocytosis of protein aggregates adhering to the glomerular filter
• Secretion of several cytokines, prostaglandins, and other factors
important for immune defense and repair in the glomerulus.
17.
18. Proximal Convoluted Tubule
• The first tubular part, the proximal convoluted tubule (PCT), is mainly
cortical, has simple cuboidal cells with long microvilli in the lumen,
abundant mitochondria, and large, interdigitating basolateral folds.
• The cells of the proximal tubules have central nuclei and very
acidophilic cytoplasm because of the abundant mitochondria.
• Cells show prominent vacuoles.
• The long brush border may be disorganized and give the lumens a
fuzz-filled appearance
• In the PCT, all glucose and other organic nutrients, all small proteins
and peptides, and much water and electrolytes are reabsorbed from
the filtrate and transferred to the peritubular capillaries.
19.
20.
21. Loop of Henle
• From the PCT filtrate flows into the loop of Henle, located in the
medulla, which has squamous thin descending and ascending
limbs; the latter extends as a thick ascending limb (TAL) back
into the cortex.
• In the cortex the TAL contacts the arterioles at the vascular
pole of its parent renal corpuscle and there thickens focally as
the macula densa.
• Tall epithelial cells of the macula densa and specialized smooth
muscle cells in the adjacent afferent arteriole called
juxtaglomerular cells, which secrete renin, comprise a
juxtaglomerular apparatus (JGA) that is an important regulator
of blood pressure.
22.
23. The thin ascending and descending limbs
have simple squamous epithelium while
the thick ascending limb has simple
cuboidal epithelium
26. Distal Convoluted Tubule
• Beyond the macula densa, the tubule continues as the distal
convoluted tubule (DCT), where electrolyte levels of the filtrate are
adjusted further and which lead to short connecting tubules.
• The simple cuboidal cells of the distal tubules differ from those of the
proximal tubules in being smaller and having no brush border and
more empty lumens.
• Common to see luminal nuclei.
27.
28. Juxtaglomerular Apparatus
• Cells of the macula densa typically have apical nuclei, basal Golgi
complexes, and a more elaborate and varied system of ion channels
and transporters.
• Adjacent to the macula densa, the tunica media of the afferent
arteriole is also modified. The smooth muscle cells are modified as
juxtaglomerular granular (JG) cells, with a secretory phenotype
including more rounded nuclei, rough ER, Golgi complexes, and
zymogen granules with
• Also at the vascular pole are lacis cells which are extraglomerular
mesangial cells that have many of the same supportive, contractile
and defensive functions as these cells inside the glomerulus
29.
30. Macula Densa
• Higher GFR leads to higher luminal concentrations of Na+ and Cl- in
the TAL of the nephron, which are monitored by cells of the macula
densa. Increased ion levels in the lumen cause these cells to release
ATP, adenosine, and other vasoactive compounds that trigger
contraction of the afferent arteriole, which lowers glomerular pressure
and decreases the GFR. This lowers tubular ion concentrations,
which turns off the release of vasoconstrictors from the macula densa.
31. JG Cells
• Decreased arterial pressure leads to increased autonomic stimulation
to the JGA as a result of baroreceptor function. This causes the JG
cells to release renin into the blood. Renin angiotensinogen into
angiotensin I. Angiotensin-converting enzyme (ACE) on lung
capillaries clips this further to angiotensin II, a potent vasoconstrictor
that directly raises systemic blood pressure and stimulates the
adrenals to secrete aldosterone. Aldosterone promotes Na+ and
water reabsorption in the distal convoluted and connecting tubules,
which raises blood volume to help increase blood pressure. The
return of normal blood pressure turns off secretion of renin by JG
cells.
32. Collecting Tubule
• The last part of each nephron, the connecting tubule, carries the filtrate
into a collecting system that transports it to a minor calyx
• A connecting tubule extends from each nephron and several join together
in the cortical medullary rays to form collecting ducts of simple cuboidal
epithelium
• In the apex of the pyramid, several collecting ducts merge further as a
papillary duct which delivers urine to the minor calyx
• Collecting ducts are composed mainly of pale-staining principal cells with
few organelles, sparse microvilli, rich with aquaporins and distinct cell
boundaries
• Scattered among the principal cells are variably darker intercalated
cellswith more abundant mitochondria and projecting apical folds.
Intercalated cellshelp maintain acid-base balance by secreting either H+
or HCO3-.
33.
34.
35. Antidiuretic hormone (ADH) makes
collecting ducts more permeable to water
and increases the rate at which water
molecules are pulled osmotically from the
filtrate.
36. Ureter
• The ureters are lined by urothelium, or transitional epithelium, which
protects underlying cells from hypertonic or toxic effects of urine.
• Large, bulbous superficial cells of the urothelium, called umbrella
cells, have apical membranes consisting of hinged regions with dense
plaques of uroplakin proteins that protect the cytoplasm.
• Characteristic pattern of longitudinally folded mucosa, surrounded by
a thick muscularis that moves urine by regular waves of peristalsis.
38. Bladder
• Urothelium is surrounded by a folded lamina propria and submucosa,
followed by a dense sheath of interwoven smooth muscle layers and
adventitia
• The bladder's lamina propria and dense irregular connective tissue of
the submucosa are highly vascularized.
• As the urinary bladder fills its highly folded mucosa unfolds, the
urothelium gets somewhat thinner by cell movements, and the hinged
membrane plaques of umbrella cells partially unfold.
• The muscularis consists of three poorly delineated layers, collectively
called the detrusor muscle
• All the urinary passages are covered externally by an adventitial layer,
except for the upper part of the bladder that is covered by serous
peritoneum.
39.
40. Urethra
• The urethra drains the bladder and is lined by unusual stratified
columnar and pseudostratified columnar epithelium.
• In males the urethra has three regions: the prostatic urethra in the
prostate gland; the short membranous urethra passing through the
urogenital diaphragm, and the long penile urethra.
• In women, the urethra is 4- to 5-cm-long, lined initially with transitional
epithelium, then by stratified squamous epithelium and some areas of
pseudostratified columnar epithelium
43. Kidney Position
• The left kidney is related to ribs 11 and 12. Its upper pole is located at
vertebral level T11, and it is also located higher than the right kidney.
•
• The right kidney is only related to rib 12. Its upper pole is located at
T12. The presence of the liver is the reason the right kidney is lower
down.
•
• The kidneys are retroperitoneal organs, which lie on the ventral
surface of the quadratus lumborum muscle, lateral to the psoas
muscle and vertebral column, and superior to the iliacus.
44. Kidney Injury
• Fracture of the lower ribs,
• Fracture of the transverse processes of lumbar vertebrae,
• Gunshot or knife wound over the lower rib cage,
• And after a car accident when seat belt marks are present.
• Right kidney trauma is associated with liver trauma, whereas left
kidney trauma is associated with spleen trauma.
• Clinical findings include flank mass and/or tenderness, flank
ecchymosis, hypotension, and hematuria.
• One of the absolute indications for renal exploration is the presence
of a pulsatile or expanding retroperitoneal hematoma found at
laparotomy.
45. Renal Capsule and Renal Fascia
• The kidneys are directly covered by a fibrous renal
capsule (aka true capsule).
• This can be readily stripped from the surface of the kidney except
in pathologic conditions where scarring makes it strongly adherent
to the kidney.
• The kidneys are further surrounded by the perirenal fascia
(of Gerota, aka false capsule).
• The fascia defines the perirenal space (aka perinephric space),
which contains:Kidney, adrenal gland, ureter, gonadal artery and
vein, and perirenal fat.
• Note that the fascia is important in the staging of renal cell
carcinoma.
• Also any fat located outside the perirenal space is called pararenal
fat, and is best seen posterolaterally.
46.
47. Nutcracker Syndrome
• Nutcracker syndrome (NCS) refers to the wide spectrum of clinical
presentations caused by compression of the left renal vein between
the abdominal aorta and the superior mesenteric artery.
• Can lead to hematuria and left flank pain.
• Because the left gonadal vein drains to the left renal vein, the condition can
also result in left testicular pain or left lower quadrant pain in women.
• The right gonadal vein drains directly to the inferior vena cava
48. Horseshoe Kidney
• Normally, between the 6th and 9th weeks of development, the
kidneys ascend to a lumbar site immediately inferior to the suprarenal
glands, following a path just on either side of the dorsal aorta.
• Horseshoe kidney occurs when the inferior poles of both kidneys fuse
during fetal development. The horseshoe kidney gets trapped behind
the inferior mesenteric artery as the kidney attempts to ascend toward
the normal adult location.
49. Accessory renal arteries
• During its ascent, the kidneys are progressively revascularized by a
series of arterial sprouts from the dorsal aorta. As new, more
superiorly located blood vessels are produced, the older, inferiorly
located vessels degenerate.
• Accessory renal arteries develop as sometimes one or more of the
transient inferior renal arteries fail to regress.
50. Oligohydramnios
• Oligohydramnios - A deficiency (lack of) in amniotic fluid due to a
congenital abnormality of fetus.
• One of the causes is a lack of kidney formation (renal agenesis) or
malformations (renal dysplasias like multicystic dysplastic kidney) and
therefore lack of urine production that would contribute to amniotic
fluid.
• Therapy: dialysis and transplantation in first years of life
51. Ureteral Constriction and Urolithiasis
• Ureter constriction locations
• Ureteropelvic junction
• Ureteral crossing of iliac vessels
• Ureterovesical junction
• Proximal ureter - Upper limit of T12-L2/L3 regions of spinal cord
• Middle ureter - Lower limit of T12-L2/L3 regions of spinal cord
• Distal ureter - PS neurons from S2-S4 regions of spinal cord
• In general a renal calculus will refer ureter pain from flank, down the
abdomen and into the perineum, thigh and genitalia
52. Male vs. Female Ureter
• Male ureters -- pass posterior to ductus deferens to reach bladder
• Female ureters -- pass posterior and inferior to uterine artery to reach
bladder
• Ureter injury is rarely due to external trauma because they are well
protected. The more common causes of injury are iatrogenic. Most
commonly, the abdominal hysterectomy in females.
• The uterine arteries run across the anterior side of the ureters. These
arteries are ligated during hysterectomies, putting the ureters at risk.
53.
54. Duplicated Ureters and Renal Pelvis
• If ureteric bud splits prematurely duplication of ureters can result.
• The splitting can occur partially or completely and metanephric tissue
can be divided into two parts, each with its own renal pelvis and
ureter.
• In normal development, during the fifth week ureteric buds sprout
from distal portion of mesonephric region.
• The intermediate mesoderm and ureteric buds interact with one
another and cause the following formations:
• Ureteric bud collecting duct system and ureters
• Intermediate mesoderm nephrons
55. Pelvic Spaces
• Rectovesical pouch - most inferior aspect of peritoneal cavities in
males; posterior surface of the bladder in males
• Rectouterine pouch - most inferior aspect of peritoneal cavities in
females; superior to the bladder in females
• Excess peritoneal fluid flows to these locations when one is in a
standing or sitting position.
• When supine, excess fluid flows to the hepatorenal recess (in either
sex) instead.
• Retropubic space (of Retzius) - fat-filled space posterior to pubis that
is continuous with deep perineal space; defines the anterior surface of
the bladder
• Rupture of the bladder or urethra results in an extraperitoneal extravasation of
urine within this space
60. Congenital Malformations
• Urachal cyst/Urachal sinus
• Remnant of the allantois persists in the urachus
• Urachal fistula
• Persistence of the entire lumen of the intraembryonic portion of the allantois.
• May cause urine to drain from the umbilicus
• Rectovesical fistula
• Various congenital defects are associated with improper partitioning of the
cloaca. A rectovesical fistula is an improper communication between the
rectum and the urinary bladder
62. Urine Leakage
• Type II
• Posterior urethra is torn above the urogenital diaphragm
• Can be caused by a fractured pelvis, or improperly inserted catheter
• Urine leaks within the retropubic space
• Type III: Most Common
• Anterior urethra is torn below the urogenital diaphragm. The membranous urethra is also torn due to
disruption of the urogenital diaphragm
• Caused by a saddle injury
• Urine leaks extraperitoneally into the superficial perineal space
• Type IV
• Neck of bladder and proximal prostatic urethra are injured
• This injury is especially serious if the internal urethral sphincter is injured
• Extraperitoneal leakage into the retropubic space
• Type V
• Penile urethra is torn
• Caused by a crushing injury to the penis
• Extraperitoneal leakage beneath the deep fascia. Will be confined to the penis if the fascia is intact.
• If fascia is damaged, leakage can occur in the superficial perineal space
67. Contrast
• CT contrast media: Iodine (very nephrotoxic)
• MRI contrast media: Gadolinium
• The use of contrast for CT scans is contraindicated if the patient is
allergic or in the event of contrast induced nephropathy, or if the
patient has kidney disease.
71. Renal Size and Location
• The normal longitudinal dimension of the right kidney is 11 cm ± 1 cm,
and that of the left kidney is 11.5 cm ± 1 cm
• The contours of the kidneys are usually smooth; occasionally, some
slight nodularity is present as a result of fetal lobulation.
• The kidneys are located in the retroperitoneum surrounded by a layer
of renal fascia and perinephric fat.
• The upper pole of the left kidney occurs at the level of the T11
vertebra, whereas the upper pole of the right kidney occurs at the
level of the T12 vertebra.
• The left kidney is related to rib 11 and rib 12. The right kidney is
related only to rib 12.
72.
73. Ureters
• The ureters pass posterior to the gonadal vessels and anterior to the
psoas major muscle.
• They cross anterior to the common iliac (or external iliac) arteries and
veins and the pelvic brim to enter the lesser pelvis.
• In the lesser pelvis the ureters run posteroinferiorly on its lateral walls.
Opposite the ischial spine they curve anteromedially to enter the
urinary bladder.
74. Cortex and Medulla on US
Terms used in US
• Hyperechoic
• Hypoechoic
• Isoechoic
85. Common indications
US:
• Hydronephrosis
• Renal Size
CT
• Stone
• Mass
MRI
• Mass
• Low renal function
86. Advantages and disadvantages
US:
• No radiation
• Bed side
• Obesity/Bowel/Operator dependent
CT:
• Good anatomic overview
• Good for stone evaluation
• Radiation
MRI:
• No radiation
• Not good for stones
• Expensive
Circumaortic left renal vein: The left renal vein splits into two, one part goesg in front of aorta and other behind the aorta to drain into the inferior vena cava.
* Aorta
