Anatomy, physiology and pathology of the kidney
Dr Andrew PotterRegistrar
Department of Radiation OncologyRoyal Adelaide Hospital
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Anatomy
Overview Retroperitoneal, paired
organs Posterior abdominal wall,
largely under cover of costal margin
Key organ of urinary system
Filtration/ concentration of urine
Biochemical balance, hormone production
Structure - macro Enclosed in a strong fibrous capsule which passes over the lips
of the sinus and becomes continuous with the walls of the calices.
Kidney + capsule are surrounded by pararenal fat Each kidney has superior and inferior poles, medial and lateral
borders/margins and anterior and posterior surfaces Reddish-brown in colour when fresh – colour varies between
cortex and medulla Measure ~12x6x3cm (left often slightly longer than right) Weigh ~130g each Ovoid in outline but indented medially (the renal sinus) bean-
shaped appearance
Structure - macro
Hilum At the concave part of each kidney Renal vein exits (anteriorly) Renal artery enters (posterior to renal vein) Renal pelvis exits (posterior to artery)
Structure - macro
Renal pelvis Funnel-shaped Lined with transitional epithelium with a smooth
muscle and connective tissue wall Continuous inferiorly with ureter Divides into major and minor calyces
Urine collecting tubule minor calyx major calyx renal pelvis ureters bladder
Structure - macro
Cortex Beneath capsule, extends towards the pelvis as
renal columns lying between pyramids of medulla
Apices of several pyramids open together into a renal papilla, each of which projects into a renal calyx
Structure - macro
Strcuture - micro Nephrons
Functional and histological subunit ~106 per kidney = glomerulus + tubules glomerulus
tuft of capillaries surrounded by podocytes projects into Bowman’s capsule
tubule system epithelium continuous with Bowman’s capsule proximal convoluted tubule Loop of Henle distal convoluted tubule
collecting tubule and collecting duct glomeruli and convoluted tubules are in cortex ducts lie in the medulla glomerular capillaries supplied by afferent arteriole and drained by efferent arteriole
Structure - micro
Structure - micro
Structure - nephron
Position and relations Lie in a mass of fat (perinephric fat) and fascia, retroperitoneally
against posterior abdominal wall Fatty renal capsule is covered by fibroareaolar tissue – the renal fascia Renal fascia
encloses kidney, its surrounding fibrous and fatty capsules helps maintain organ position superiorly, is continuous with fascia of inferior diaphragm medially the left and right fascia blend with each other anterior to
abdominal aorta and IVC posterior layer of fascia blends with fascia overlying psoas
Extraperitoneal fat outside the renal fascia is located between peritoneum of posterior abdominal wall and renal fascia
Position and relationsLeft Right
Posterior Diaphragm (postero-superiorly) Quadratus lumborum (postero-laterally) Psoas major postero-medially Transversus abdominis postero-laterally Subcostal nerve and vessels Iliohypogastric and ilioinguinal nerves descend diagonally across
posterior surfaceAnterior Lies with pancreas and spleen in
the stomach bed Adrenal gland Stomach Spleen Pancreas (tail) Jejunum Descending colon Posterior wall of omental
bursa Peritoneum
Superiorly related toinferior surface of liver
Descending part ofduodenum
Right colic (hepatic)flexure lies anterior tolateral border and inferiorpole
Small intestine (inferiorly) Peritoneum
Medial L adrenal gland Right adrenal gland –wedged between superiorpole and IVC
IVC
Surface anatomy
Superior poles protected by 11th and 12th ribs Extend from T12 to L3 vertebral bodies Move ~2cm superior-inferior during respiration Right – just below transpyloric plane, 5cm right of
midline. Inferior pole ~ finger-width superior to right iliac crest
Left – just above transpyloric plane, 5cm left of midline.
Arterial supply
Renal arteries branches of aorta at L1/L2 lie behind pancreas
and renal veins Enter at hilum, giving rise to
Anteriorly – apical, upper, middle and lower segments
Posteriorly – posterior segment
No communication between segments
Venous drainage
Renal veins Communicate widely Eventually form 56 vessels that unit at the
hilum Drain into IVC
Lymphatic drainage
Para-aortic nodes at L1/L2 Surface of upper kidney drains through
diaphragm into nodes in the posterior mediastinum
Innervation
Sympathetic Preganglionic cells in spinal cord T12/L1
fibres to thoracic and lumbar splanchnic nerves Postganglionic cells in coeliac, renal and
superior hypogastric plexuses Vasomotor function
Development Arises from mesoderm Pronephros
Transitory, non-functional structures consisting of a few ducts which persist Mesonephros
Large elongated organs that function as interim kidneys Glomeruli + tubules open into mesonephric ducts
Metanephros Permanent kidneys Begin to develop in ~5th week Arises caudal to mesonephros Induces a bud from caudal end of mesonephric duct (ureter)
Ureteric bud divides into calyces of pelvis and collecting tubules and medullary pyramids
Develops in anatomic pelvis and migrates to adult position and the new single definitive artery forms
Physiology
Physiology - overview
Regulation of the water and electrolyte content of the body
Retention of substances vital to the body such as protein and glucose
Maintenance of acid/base balance Excretion of waste products, water soluble toxic
substances and drugs Endocrine functions
Water and electrolyte regulation Renal blood supply is approx 20% of cardiac
output 99% to cortex 1% to medulla
2 capillary beds,arranged in series: Glomerular
High pressure for filtering Peritubular
Low pressure for absorption
Water and electrolyte regulation
Urine formation - 3 phases Simple filtration Selective and passive
resorption Concentration
Filtration Takes place through the semipermeable walls of the glomerular
capillaries almost impermeable to proteins and large molecule
Glomerular filtrate is formed by squeezing fluid through glomerular capillary bed
Hydrostatic pressure (head of pressure) is controlled by afferent and efferent arterioles, and provided by arterial pressure
About 20% of renal plasma flow is filtered each minute (125 ml/min). This is the glomerular filtration rate (GFR). Autoregulation
With a change in arterial blood pressure, there is constriction or dilatation of the afferent and efferent arterioles, the muscular walled vessels leading to and from each glomerulus
Juxtaglomerular apparatus
Macula densa cells Detect chloride concentration
Juxtaglomerular cells Modified smooth muscle cells Produce renin
Converts angiotensin to angiotensin I Angiotensin I converted to angiotensin II by
Angiotensin converting enzyme (ACE) Causes systemic vasoconstriction and increase in BP
Tubular reabsorption 60% of solute is
reabsorbed inproximal tubule
Different partsof tubule systemoptimised to absorb differentcomponents of urine
Distal tubule and collecting duct determines final urine concentration Regulated by ADH production by posterior pituitary
Acid-base balance
Tubular acid secretion Ammonia secreted by
tubules (combines withH+ to form NH4
+
and passed in urine)
Hormones Renin
Increases production of angiotensin II Aldosterone
Stimulates water and sodium ion resorption in distal tubule Atrial natriuretic hormone (ANP)
Produced when atrial pressure increases (eg heart failure) Promote Na+, Cl- and water loss
Antidiuretic hormone Increases permability of distal tubule to water, to cinrease water resorption
(therfore increases concentration of urine) 1,25 dihydroxy vitamin D3
Promotes calcium absorption from gut Erythropoietin (EPO)
Stimulates marrow to produce red blood cells
Pathology
Benign pathology Vascular disease
Hypertension, diabetes, deposition of immune complexes (eg amyloidosis), coagulation
Inflammatory/autoimmune conditions SLE
Infective Pyelonephritis, tuberculosis
Idiopathic Nephrotoxic drugs - eg. platinum chemotherapy, aminoglicoside antibiotics
Congenital/structural Polycystic kidney, horseshoe kidney, renal agenesis/hypoplasia
Metabolic/biochemical Renal calculi
Benign tumours
Frequent incidental findings (up to 20%) Renal adenoma
Bening epithelial tumours arising from tubular epithelium
Difficult to distinguish from renal cell carcinoma - similar histology
Distinguished on size (<3cm)
Benign tumours
Oncocytomas Variant of adenoma
Angiomyolipoma Smooth muscle, fat and vessels
Renal fibroma Common small tumours 3-10mm Arise in medulla
Malignant tumours
90% are renal cell adenocarcinoma (RCC) About 3% of all adult cancers
Usually seen >50 years of age Present with haematuria, pain, loin mass Paraneoplastic syndrome
Hypercalcaemia, hypertension, polycythaemia, Cushing’s syndrome or other hormonal disturbances
Renal cell carcinoma
Rounded masses, yellowish colour with haemorrhage and necrosis
Most commonly the ‘clear cell’ variant Clear cytoplasm
because of high lipid and glycogen content
Renal cell carcinoma Spread by local extension/expansion through
capsule Blood borne metastases
Bone, lung, brain Lymphatic metastases
Para-aortic chain Prognosis depends on stage
70% ten-year survival of confined to renal capsule Poor prognosis if metastatic disease at presentation
Nephroblastoma(Wilms’ tumour)
Common childhood malignancy Embryonal tumour from primitive
metanephros Peak incidence 1-4 years of age Presents as abdominal mass or haematuria Rounded mass largely replacing kidney
Solid, fleshy white with necrosis Prognosis related to stage at presentation
Summary Paired retroperitoneal/post abdominal organ Cortex, medulla, nephron
Glomerulus, tubule, duct Water/biochemical regulation
Filtration, reabsorption Hormone production Many benign pathological conditions Malignancies predominantly RCC in adults,
nephroblastoma in children
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