Kidney

KIDNEY

DR.K.SARAVANAN

PAIR OF EXCRETORY ORGANSExcrete the end products of metabolism and

excess waterMaintaining electrolyte and water balance in

the tissue fluidsEndocrine functions- erythropoietin, renin

and 1,25-di-hydroxycholecalciferol

INTRODUCTION

Reddish-brown in colour. Situated posteriorly behind the peritoneum

on each side of the vertebral column

Superiorly -upper border of the T12, inferiorly– center of body of L3

The right is usually slightly inferior to the left.

Left is a little longer and narrower.Left lies nearer the median plane.

Location

Bean shaped 11 cm in length, 6 cm in breadth and 3 cm

in antero-posterior dimension The left kidney may be 1.5 cm longer weight -150 g in men and 135 g in women In fetus and newborn, the kidney normally

has 12 lobules.

Dimensions & Gross features

1. Fibrous capsule: Thin membraneClosely invests the kidney and renal sinusCan be easily stripped off2. Perirenal fatAdipose tissue outside the capsuleThickest at the borders

Coverings of kidney

Dense, elastic connective tissue sheath enveloping kidney and suprarenal gland together with perirenal fat.

Posterior fascia of zuckerkandl and the anterior fascia of gerota, fuse laterally forming lateral conal fascia

Lateral conal fascia continues anterolaterally behind the colon to blend with the parietal peritoneum.

Perirenal fascia

Single multilaminated structure which is fused posteromedially with the muscular fasciae of psoas major and quadratus lumborum.

Extends anteromedially behind the kidney as a bilaminated sheet

Divides into a thin anterior lamina, passing around the front of the kidney -anterior perirenal fascia

Thicker posterior lamina which continues anterolaterally as the lateral conal fascia, fusing with the parietal peritoneum.

In the midline superiorly - anterior and posterior renal fasciae fuse and attached to the crura of their respective hemidiaphragms

Superior aspect of the perirenal space is open and in continuity with the bare area of the liver on the right and the subphrenic extraperitoneal space on the left.

The posterior fascial layer blends bilaterally with the fascia of psoas major and quadratus lumborum as well as the inferior phrenic fascia

Right - anterior fascial layer blends with the right inferior coronary ligament at the level of the upper pole of the kidney and bare area of the liver

Left - anterior layer fuses with the gastrosplenic ligament at the level of the suprarenal gland.

Anterior perirenal fascia extends across the midline in front of the great vessels

Below this level the two fasciae merge and attached to the great vessels or iliac vessels

Laterally the anterior and posterior leaves fuse with the iliac fascia, and medially with the periureteric connective tissue.

Inferior apex of the cone is open anatomically towards the iliac fossa

Two poles, superior and inferior Sup- broad, inf- pointed.

Two surfaces- anterior and posterior. Anterior – irregular and posterior surface –

flat.

Lateral borders- convex Medial borders- convex adjacent to the

poles, concave between them showing a depression, the hilum and slope inferolaterally.

PARTS

Hilum renal vein (anterior) renal artery (intermediate) pelvis of the kidney (posterior).

Right kidney – anterior relations Right suprarenal gland Below this - right lobe of the liver Narrow medial area - descending part of the

duodenum Inferiorly –Laterally with the retroperitoneal right colic

flexureMedially with part of the intraperitoneal small

intestine(jejunum).

relations

Lateral border – Rt lobe of liver Hepatic flexure of the colon

Left kidney Medial area of the superior pole - left

suprarenal gland Lateral half of the anterior surface – spleen Central quadrilateral area - retroperitoneal

pancreas and splenic vessels Between the suprarenal and splenic areas -

stomach separated by a layer of peritoneum

Below the pancreatic and splenic areas, a narrow lateral strip -retroperitoneal left colic flexure and the beginning of the descending colon.

extensive medial area - intraperitoneal loops of jejunum.

Embedded in fat and devoid of peritoneum. Superiorly are the diaphragm and the medial

and lateral arcuate ligaments. More inferiorly, from medial to lateral Psoas major Quadratus lumborum Aponeurotic tendon of transversus abdominis, Subcostal vessels Subcostal, iliohypogastric, and ilioinguinal

nerves.

Posterior surface

The upper pole of the right kidney is level with the 12th rib, and that of the left with the 11th and 12th ribs.

The diaphragm separates the kidney from the pleura, which descends to form the costodiaphragmatic recess.

Internal pale medulla and external reddish brown cortex.

Renal medulla consists of striated, conical renal pyramids, their bases peripheral, their apices converging to the renal sinus which is the space around the renal pelvis extending to the interior.

At the renal sinus they project into minor calyces as papillae.

Internal macrostructure

Renal cortex is subcapsular. Arching over the bases of the pyramids-

cortical arches or lobules and extending between them towards the renal sinus as renal columns

Pyramid + cortical arch forms a lobe of the kidney

The cortex close to the medulla is sometimes termed the juxtamedullar cortex.

Hilum of the kidney leads into a central renal sinus, lined by the renal capsule

Renal pelvis, vessels and fat. Within the renal sinus, collecting tubules open

onto the summits of the renal papillae to drain into minor calyces, which are funnel-shaped expansions of the upper urinary tract

Each minor calyx surrounds either a single papilla or rarely, groups of two or three papillae.

The minor calyces unite with their neighbours to form two to three major calyces

Renal pelvis and calyces

Calyces drain into the infundibula Renal pelvis is normally formed from the

junction of two infundibula, from upper and lower pole calyces

There may be a third draining the calyces in the mid-portion of kidney.

Funnel-shaped renal pelvis tapers as it passes inferomedially, traversing the renal hilum to become continuous with the ureter

Renal arteries About 20% of the cardiac output Arises from abdominal aorta Near the renal hilum, each artery divides into

an anterior and a posterior division, and these divide into segmental arteries supplying the renal vascular segments.

Accessory renal arteries are common (30%) and usually arise from the aorta above or below (most commonly below) the main renal artery and follow it to the renal hilum

Vascular supply

Subdivisions of the renal arteries are described sequentially as

1. Segmental, 2. Lobar, 3. Interlobar, 4. Arcuate5. Interlobular arteries 6. Afferent and efferent glomerular arterioles

Five arterial segments have been identified Apical segment - anteromedial region of the

superior pole. Superior (anterior) segment - rest of the

superior pole and the central anterosuperior region.

Inferior segment -whole lower pole. Middle (anterior) segment - between

anterior and inferior segments. Posterior segment - whole posterior region

between the apical and inferior segments.

Branches of segmental arteries are lobar, usually one to each renal pyramid.

Each lobar artery subdivide into two or three interlobar arteries, extending towards the cortex around each pyramid.

At the junction of the cortex and medulla, interlobar arteries dichotomize into arcuate arteries which diverge at right angles over the base of pyramid

Lobar, interlobar, arcuate and interlobular arteries

Divides further into interlobular arteries which diverge radially into the cortex.

Terminations of adjacent arcuate arteries do not anastomose but end in the cortex as additional interlobular arteries

End arteries

lateral rami of interlobular arteries Efferent glomerular arterioles from most

glomeruli (except at juxtamedullary and, sometimes, at intermediate cortical levels) soon divide to form a dense peritubular capillary plexus around the proximal and distal convoluted tubules

Two sets of capillaries – glomerular and peritubular.

Afferent and efferent glomerular arterioles

vascular supply of the renal medulla is largely from efferent arterioles of juxtamedullary glomeruli

Efferent glomerular arterioles passing into the medulla divides into 12–25 descending vasa recta close to henle’s loop and collecting duct.

Venous ends of capillaries converge to the ascending vasa recta, which drain into arcuate or interlobular veins.

Proximity of descending and ascending vessels with each other and adjacent ducts provides the structural basis for the countercurrent exchange and multiplier phenomena

Renal veins Venous ends of the peritubular plexuses

converge to join interlobular veins, one with each interlobular artery.

Interlobular veins pass to the corticomedullary junction end in arcuate veins (which accompany arcuate arteries), and anastomose with neighbouring veins.

Arcuate veins drain into interlobar veins, which anastomose and form the renal vein.

Collecting vessels from the intra-renal plexus form four or five trunks which follow the renal vein to end in the lateral aortic nodes

INNERVATION Rami from the coeliac ganglion and plexus,

aorticorenal ganglion, lowest thoracic splanchnic nerve, first lumbar splanchnic nerve and aortic plexus form a dense plexus of autonomic nerves around the renal artery.

LYMPHATIC DRAINAGE

Kidney is composed of 1 to 3 million uriniferous tubules, bounded by a delicate connective tissue with blood vessels, lymphatics and nerves.

Two embryologically distinct parts Nephron-produces urine Collecting duct-concentration of urine

MICROSTRUCTURE

1.Renal corpuscle - filtration from the plasma,2.Renal tubule - selective resorption from

the filtrate to form the urine

Nephron

Small rounded structures 0.2 mm in diameter Each has a central glomerulus of vessels and

a glomerular (bowman's) capsule, from which the renal tubule originates.

Glomerulus A glomerulus is a collection of convoluted

capillary blood vessels supplied by an afferent arteriole.

An efferent arteriole emerges from the same point, the vascular pole of the corpuscle

Renal corpuscle

Blind expanded end of a renal tubule deeply invaginated by the glomerulus. lined by a simple squamous epithelium on its

outer (parietal) wall glomerular, juxtacapillary (visceral) wall is

composed of specialized epithelial podocytes branch to form secondary or tertiary

processes and give rise to terminal pedicels separated by narrow (25 nm) gaps, the

filtration slits

Bowman's capsule

Luminal membrane and the slit diaphragm are covered by a dense surface coat rich in sialoglycoproteins – negative charge.

Proximal convoluted tubule is connected to the capsule by a short neck

This straightens as it approaches the medulla-becomes descending thick limb of loop of henle and then ascending limb by an abrupt u-turn.

Loop of henle are narrower and thin-walled in medulla - descending and ascending thin segments.

Renal tubule

The tubule wall shows a focal thickening, the macula densa, where it comes close to the vascular pole of its parent glomerulus at the start of the convoluted part of the distal tubule.

The nephron finally straightens once more as the connecting tubule, which ends by joining a collecting duct

PROXIMAL CONVOLUTED TUBULE Lined by cuboidal or low columnar

epithelium Brush border of tall microvilli on its luminal

surface Cytoplasm of proximal tubular cells is

eosinophilic and nuclei are euchromatic and central.

Cytoplasm is rich in mitochondria

LOOP OF HENLE Thin segment (30 μm in diameter), lined by

low cuboidal to squamous cells Thick segment (60 μm in diameter)

composed of cuboidal cells Cells of the DISTAL TUBULE are cuboidal and

resemble those in the proximal tubule. They have few microvilli COLLECTING DUCTS Simple cuboidal or columnar epithelium

1 in 1200 individuals and results from failure of metanephric blastema to join with a ureteric bud on the affected side

absence of the ipsilateral vas deferens and/or epididymis with other congenital anomalies including imperforate anus, cardiac valvular anomalies and oesophageal atresia

Absent kidney

Failure of the kidney to ascend into the renal fossa in utero 

1 in 2500 live births CROSSED RENAL ECTOPIA normal location of the ureteric orifices

within the bladder two renal masses are on the same side

Ectopic kidney

1 in 400 individuals. A transverse bridge of renal tissue, the

isthmus, connects the two renal masses. lies between the inferior poles anterior to

the great vessels

Horseshoe kidney

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