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The kidney

Are retroperitoneal organs found in theabdomen

each kidney is bean shaped

It has a convex lateral border and a concavemedial border with a hilum

Functions

excretion of waste products

production of renin (regulation of blood pressure

mantainance of fluid balance

production of erythropoietin

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Kidney cont

Each kidney is invested by a thin looselyadhering capsule consistin of dense irregularcollegenous connective tissue

It is divided into an inner medulla and an outercortex

The cortical region appears dark brown and

granular whilst the medulla contains 12-18 coneshaped medullary pyramids

From the hilum of the kidney exits a ureterwhose expanded upper part is known as a renal

pelvis

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kidney

Each renal pelvis is divided into two or threemajor calyces which further divide into severalminor calyces

Each renal pyramid is has an overlying portionof the cortex >> the cortical arch

Longitudinal striations of continuation of

material located in the pyramids into the cortexare known as medullary rays

Lobe = medullary pyramid + cap of corticaltissue

Lobule = medullary ray + cortical larbyrinth

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Kidney cont

Functional unit of the kidney >> nephron

There are about 4million nephrons in eachkidney

Parts of a nephron>> renal corpuscle, proximalconvoluted tubule, loops of Henle, distalconvoluted tubule, collecting tubules and ducts

Two types of nephrons are found in the humankidneu >> cortcal nephron and juxtaglomerularnephron

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Kidney cont

Renal corpuscle( abt 200um in diameter)

composed of a tuft of cappillaries, the glomeruluswhich is invaginated into a pouch like proximal

end of nephron, the Bowman's capsule

Glomerulus

arise from afferent glomerular arteriole which

divides into a tuft of cappilariesmade of fenestrated capillaries with no diaphragm

lying on a basement membrane(abt 0,1umthick)

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Kidney cont

Mesangial cells

are specialised Ct cells found in the glomerulus

have receptors for agiotensin II (when activateddecrease glomerular flow) and natriuretic acid(cause increase in blood flow and increasesurface area for filtration)

Other functions:structural support toglomerulus, synthesise Ecmatrix, endocytoseand dispose of pathological molecules trappedby basement membrane and produce chemical

mediators e.g prostaglandins

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Kidney cont

Basement membrane has 3 regions>> 2 outerlamina rarae(electronlucent) and a middlelamina densa (electron dense)

Lamina densa is made of type iv collagen whilstlamina rarae are made of laminin,fibronectinand positively charged proteoglycan to give aphysical and ionic barrier

Bowman's capsule

double layer of epithelium( visceral and parietallayer)

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Kidney cont

Visceral layer

consists of podocytes( cells with feet likeprocesses)

podocytes have a cell body, primary andsecondary processes(pedicels)

pedicels are in direct contact with basal lamina at

a periodic distance of 25nm (filtration slits)a diaphragm of about 6nm brides filtration slits

Parietal layer

simple squamous epithelium supported by

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Kidney cont

Basal lamina and athin layer of reticular fibres

Urinary space>> space between the parietaland visceral layer

Urinary pole>> region where the proximaltubule begins

Proximal convoluted tubule

drains from the capsular space of the renalcorpuscle approx 14mm long, 60um diameter

has a turtuous course in the cortex, small lumen

has cuboidal yo low columnar cells

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Kidney cont

Cells are eosinophilic, broad, have manymicrovilli on internal surface( brush border)

Have basal oval nuckei

Have basal prominent elongated villi

Basal membrane has invaginations with asodium pump

When distended the lumen is wider and theepithelium is lower

PCT reabsorbs all the glucose and amino

acids,85% NaCl and water , phosphate and

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Kidney cont

Loops of Henle

consist of a thick descending, thin descending,thin ascending and thick ascending loops

greater part lies in the medulla

descending limb is a continuation of PCT withouter diameter of 60um, cells of 1st part are

similar to PCTin more distal portion epithelium is simple

squamous and lumen is narrower

nuclei may protrude into lumen

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Kidney cont

1/7th of nephrons are juxtamedullary nephrons

these establish a gradient of hypertonicity inmedullary interstitium giving kidney the ability to

produce hypertonic urine Distal covoluted tubule

lies in the cortex

shorter and less turtuous than PCT(abt 5mm)

cells are flatter and smaller ie more nuclei areseen. Lumen is wider. Plasma membrane is

indistinct. Notrue brush border (small no. Of

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Kidney cont

DCT cont

have basal invaginations and associatedmitochondria

when DCTnakes contact wiyh vascular pole ofrenal corpuscle of parent artery the DCT ismodified>> cells are columnar, nuclei areclosely packed and smaller and these cells are

jnown as macula densa. These cells aresensitive to ionic content and produce signals toincrease the liberation of renin

Juxtaglomerular apparatus

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Kidney cont

Juxtaglomerular apparatus

is formed by macula densa of DCT,juxtaglomerular cells(JG cells) of adjacent

afferent arteriole and extraglomerular mesangialcells

JG cells are modified smooth muscle cells intunica media of afferent arterioles. Containspecific granules which contain renin. JG cellssecrete renin which helps to control bloodpressure. Internal elastic lamina of afferentarteriole disappears in the area of JG cells

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Kidney cont

Collecting tubules and ducts

running in medullary rays in the centre of eachrenal lobule are collecting tubules. Collecting

tubules drain several DCTscollecting tubules are made of pale staining

cuboidal cells, with small round nuclei and feworganelles. They have well defined cellmembranes

collecting tubules unite to become largermedullary ducts of Belliniwhich oprn onto the

surface of the renal papillae

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Kidney cont

Renal papillae have a covering of low columnarepithelium

The epithelium of ducts is responsive to ADH.

ADH is secreted when water intake is low. Itallows the uptake of water by duct cells from theglomerular filtrate by making them morepermeable to water.

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Kidney cont

Blood circulation

renal artery enters at the hilum an d divides into 2primary branches (anterir and posterior)

frm the primary branches arise several interlobararteries which ascend btwn individual pyramidsto give rise to vessels which fork towards thecortex(arcuate arteries)

arcuate arteries are formed at thecorticomedullary junction and branching off atright angles to these arcuate vessels are

interlobular arteries

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Kidneys cont

Interlobular arteries form lobular boundariesand alternate with medullary rays

Afferent glomerular arterioles arise from

interlobular arteries and supply blood toglomerulus

Blood passes from afferent to efferent arterioleswhich branch further to form peritubularcapillary network to supply proximal and distaltubules to carry away absorbed ions and lowmolecular weight materials

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Kidney cont

Vasa recta>> peritubular capillaries whichfollow a straight course into medulla then loopback towards corticomedullary junction

descending vessels>> continous type capillaryascending vessel>> fenestrated endothelium

these vessels provide nourishment and oxygen to

the medulla Capillaries of outer cortex and capsule

converge to form stellate veins which empty intinterlobar veins. Veins follow same course as

arteries

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Kidney cont

Renal interstitium

occupies space between nephrons, blood andlymph vessels

contains small amount of CT>> fibroblasts, somecollagge fibres, hydrated substance pich inprostaglandins

interstitial cells (found in medulla) containcytoplasmic lipid droplets. Are thought tosecrete prostaglandins and prostacyclins

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Kidney cont

The glomerulus

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The kidney cont

The glomerulus