Anatomy, physiology and pathology of the kidney

Dr Andrew Potter Registrar Department of Radiation Oncology Royal Adelaide Hospital

Medical ppt http://hastaneciyiz.blogspot.com

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 between cortex and medulla – colour varies 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  major calyx  renal pelvis  minor calyx  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 ~10 6 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 tubule   Loop of Henle  collecting tubule and collecting duct glomeruli and convoluted tubules are in cortex distal convoluted 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 relations

Posterior Anterior Medial Left       Diaphragm (postero-sup eriorly) Quadratus lumborum (postero-laterally) Psoas ma jor postero-media lly Transversus abdominis postero-laterally Subcostal nerve and vessels Right Iliohypog astric and ili oingu inal ne rves descend dia gona lly ac ross posterior surface Lies with panc reas and spleen in the stomach bed  Adrena l gland  Stomach      Spleen Panc reas (tail) Jejunum Descend ing colon Posterior wall of omental bursa   Peritoneum L adrena l gland       Supe riorly rela ted to inferior surface of liver Descend ing part of duodenu m Right colic (hepa tic) flexur e lies anterior to lateral border and inferior pole Small intestine (infe riorly) Peritoneum Right adrenal gland – wedged between superior pole and IVC  IVC

Surface anatomy

     Superior poles protected by 11 th and 12 th 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 – segments apical, upper, middle and lower  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 ~5 th 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

Angiotensin converting enzyme (ACE)  by Causes systemic vasoconstriction and increase in BP

Tubular reabsorption

   60% of solute is reabsorbed in proximal tubule Different parts of tubule system optimised to absorb different components 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 with H + to form NH 4 + 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 D 3  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

Medical ppt http://hastaneciyiz.blogspot.com