Git the Kidney
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Transcript of Git the Kidney
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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