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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