Download Juxtaglomerular cells

Urinary System
Shiping Ding
Zhejiang University
[email protected]
• In many texts this is considered as part
of the Excretory System.
• It is the system involved with cleaning
the blood of the end products of
metabolic activities.
• Also functions to adjust the
composition of body fluids by
selective re-absorption and secretion.
• secrete some bioactive factors-renin,
erythropoietin.
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The outside covering of the kidney is the renal
capsule.
Kidney is comprised of an outer region, the
renal cortex and an inner region, the renal
medulla.
Renal medulla also contains the cup or funnellike connective tissue calyces which open into
the renal pelvis and exit by way of the ureter.
---hilum: BV, LV, N and ureters enter or out
*renal pelvis: funnel-shaped expension of upper
end of ureter
*calyx: branches of renal pelvis
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Cortex contains all of the structure of cortical
nephrons and part of the structure of juxtamedullary nephrons.
Renal medulla contains parts of descending and
ascending tubules and loops of juxta-medullary
nephrons and the collecting tubules of all
nephrons. Collecting tubules are arranged in
bundles called pyramids.
Spaces between pyramids called renal columns.
Nephrons are the structural and functional unit
of the kidney.
Cortical nephrons have short tubules and loops
of Henle and are retained within the cortex
layer
Juxta-medullary nephrons have much longer
tubules and extend deep into medulla layer.
Nephron
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Major components of the nephron include:
Renal corpuscle consists of glomerulus and capsules
Proximal convoluted tubule
Distal convoluted tubule
Peritubular capillaries
Nephron
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Renal Corpuscle consists of the glomerulus and
the capsule.
Glomerulus is a capillary ball. Blood is supplied
to the glomerulus by way of the afferent arteriole
and leaves the glomerulus by the efferent
arteriole.
This is different in that blood travels from
arteriole to capillary bed back to arteriole.
The capsule consists of two layers of epithelium.
The visceral layer fits like a glove over the
glomerulus. This can not be seen with light
microscope.
Outer layer the parietal layer can be seen with
light microscope.
Podocyte：
cells with many processes
( primary and secondary processes-foot processes)
Foot processes: interdigitated with each other and embraced the capillaries
slit pore:
-narrow intercellular space between foot processes
-25 nm, with 4-6 nm diaphragm-slit membrane
---function: produce filtrate by filtration
* filtration barrier or membrane: the structure for filtration is called filtration barrier or
membrane, including:
fenestrated endothelial cell: negative ions
basal lamina: type IV collagen, proteoglycan, laminin-negative ions (sulphate heparin)
slit membrane-nephrin(size selective filter: negative ions
*intraglomerular mesangium:
/mesangial cell:
-small, irregular, with processes
-small dark N
-EM: RER, Golgi, lysosome, phagocytic vesicles, cytoskeleton-MF, MT,IF and secretory
granules
-functions:
i. produce ground substance
ii. phagocytosis
iii. contract
iv. secrete renin and enzymes
Renal tubule:
a. proximal tubule: 50-60um in D, 14 mm long
---structure
L/M:
E/M:
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pyramidal cuboidal
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eosinophilic
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round N
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brush-liked border -------- microvilli(apical canaliculi)
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longitudinal striation------- plasma membrane infolding
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no clear boundary ------- lateral extension(rich in Na+ K+ ATPase)
-------Function:
Re-absorption and secretion:
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All glucose, all amino acids and 85% of mineral ions are reabsorbed by active
transport from the filtrate to the tissue fluid. They then diffuse into the
blood capillaries.
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Small proteins are reabsorbed by pinocytosis, digested, and the amino acids diffuse
into the blood.
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80% of the water is reabsorbed to the blood by osmosis.
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As urea molecules are so small and carry no charge that they diffuse passively
through the cell membrane. In part this explains why not all urea is excreted as
blood passes through the kidney.
b. thin segment:
/10-15 um, simple squamous epi,
/facilitate the passage of water and ions
/reabsorb Na+ and Cl- and 5% water
c. distal tubule:
---structure:
L/M
E/M
• cuboidal
• slight-stained
• round N
• no brush-liked border --------------------------------- less microvilli
• well-developed longitudinal striation -------plasma membrane infolding
---function:
i. reabsorption of 8% water, Na+ ions
ii. excretion of K+, H+,NH3
iii. regulated by aldosterone(adrenal gland) and antidiuretic hormone (vasopressin)
(pituitary gland)
Collecting tubule:
• -simple cuboidal epi. to simple columnar epi.
-slight –stained
-have clear boundary
-reabsorb 4% water
Juxta-glomerular apparatus
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Is consists of following components:
Juxtaglomerular cells: the tunica media of the afferent arteriole has modified smooth
mucle cells.
Macula densa – a specialized segment of distal tubule, a ion sensor
Extraglomerular mesangial cells:a signal sender
Function:
• Allows to sample the composition of blood as it enters nephron and as it is ready to
leave.
• Plays important role in regulation of sodium excretion by kidney.
• Secretes hormone renin which then trigers the angiotensin II pathway.
a. juxtaglomerular cell:
---a groups of modified SM cell of afferent arterioles
---structure:
-larger, cuboidal in shaped, with round N
-contain secretory granules
---function:
i.secrete renin→adrenal gland→aldosterone→blood pressure↑
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angiotensinogen→angiotensin I→angiotensin II→contraction of
SM of BV
ii. secrete erythropoietin to promote erythropoiesis
b. macula densa
---a group of cells derived from epi. of distal tubule
---cell becomes taller, narrow, with round N apical part arranged
---cells have processes connecting with other cells
---function: chemoreceptors- feel the Na+ ions concentration
c. extraglomerular mesangial cell(polar cushion cell)
---similar to intraglomerular mesangial cell
---transfer the information
d. peripolar cell
---structure:
EM: -microvilli
-junctional complexes
-RER, Golgi, and granules
---function: regulate the reabsorption and secretion of renal tubule
Renal interstitial: CT
---fibers: type I,III,IV collagen
---matrix
---cell:
• fibroblast
• macrophage
• lipid-laden interstitial cell:
-stellate cell with processes
-osmiophilic lipid droplets:
-function:
i. involve in formation of F and matrix
ii. secret prostaglandin
Blood supply to the kidney
i. Very large blood flow (1.2L/min)
ii. To form cap.two times
iii. Glomerular cap. have a high blood
pressure
iv. Form vasa recta loop near medullary
loop
v. More larger blood flow in renal
cortex
Interlobar arteries → Arcuate arteries →Interlobular arteries →Capsular cap.
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Renal artery
Afferent arterioles
Afferent arterioles
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Juxtamedullary nephron Cortical nephron
glomerulus
glomerulus
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Efferent arterioles Efferent arterioles
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Vasa recta(artery and vein)← Capillary network Capillary network
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Renal vein←Interlobar vein← Arcuate vein ← Interlobular vein ← Stellate vein
Questions:
1. Describe the fine structure of renal corpuscle in detail.
2. Draw the ultra-structures of the filtration barrier of kidney and
describe it in detail.
3. Compare the structures and functions of the proximal convoluted
tubule with that of distal convoluted tubule.
4. Compare the structure and function of the juxtaglomerular cells
with that of the macula densa.
5. Describe the blood supply of the kidney.
Thank you for your attention!