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Describe the renal cortex. What is located there? What are the 2 parts of it? What is located in each?

One cm thick​
Covers base, sides (Columns of Bertin) of medulla pyramids​
Contains glomeruli, convoluted and straight tubules, cortical collecting ducts

Cortical labyrinth: glomeruli, proximal, distal convoluted tubules, interlobular vessels, capillaries, connecting tubules, initial collecting tubules.​

Medullary ray: parallel striations, straight part of proximal, distal tubules, collecting ducts. ​


Describe the renal medulla. What are the different layers and what is located there?

Internal to cortex, divided into 8-12 conical pyramids​
Base faces cortex (corticomedullary junction)​
Tip (papilla) faces minor calyx.

Outer juxtacortical medulla (next to cortex) ​
Corticomedullary junction ​
Inner and outer stripe ​

Inner medulla includes papilla (pyramid apex) ​
Mostly collecting ducts​
Papilla perforated by collecting ducts, protrudes into a minor calyx


What is the functional unit of the kidney? What are the components? How many are there in the kidney?

Functional unit of kidney​
1,000,000 nephrons/kidney​
Includes renal corpuscle, attached tubule with 3 segments​
Proximal tubule​
Loop of Henle​
Distal tubule


What are the two steps in urine formation?

Ultrafiltration of blood plasma across semi-permeable filtration barrier in glomerulus ​
Reabsorption and secretion in tubules.


What are the parts of the renal corpuscle?

Bowman’s Capsule​
Bowman’s (Urinary) Space​
Glomerulus – “the filter”


What is a glomerulus? How are glomerular capillaries unique? What tonic control are they under? What does their unique anatomy insure?

Ball of 10-20 interconnected capillaries wrapped around central mesangium ​
Glomerular capillaries are unique ​
Capillary bed between 2 muscular arterioles: afferent + efferent arterioles (not arteriole + venule). ​
Under tonic control by vasoactive substances (eicosanoids, nitric oxide, etc.) ​
Anatomy insures high capillary hydrostatic pressure, drives filtration.


What is Bowman's capsule? What is its function? What cells is it made up of? Describe its poles.

Pouch of proximal tubule around glomerular capillary loops​

Captures filtrate; sends it to proximal tubule ​
Simple squamous parietal epithelium​
Two poles ​
Vascular pole: Afferent and efferent arterioles ​
Urinary (tubular) pole: Proximal tubule attachment


What is Bowman's space? What cells are located their?

Between glomerulus and capsule​
Continuous with proximal tubule lumen​
Lined by ​
Parietal epithelial cells ​
Visceral epithelial cells (VEC, podocytes)


How does the structure of the glomerulus relate to its function? What are its 4 components?

Maximum surface area for filtration ​
13 km capillary length; 1.6 m2 surface area​
High permeability to water, small solutes​
Low permeability to plasma proteins the size of albumin (MW 68,000) and larger, cells

Visceral epithelium (podocyte)​
Glomerular basement membrane​
Endothelium ​


What is the mesangium? What are the two parts? Subparts?

In center of glomerulus ​
Mesos middle + angeion vessel​
Structural support for capillary network​
Includes ​
Mesangial matrix​
Mesangial cells​
Phagocytic cells derived from circulating monocytes​
Contractile cells – modified smooth muscle cells


What is the mesangial matrix made up of?

Mesangial cells synthesize and are surrounded by extracellular matrix. ​
Matrix has a similar (but not identical) composition to GBM ​
Type IV collagen, fibronectin, laminin, decorin, tenascin, proteoglycans


Describe the two types of mesangial cells and their function. Overall, what are their functions?

Specialized pericytes/smooth muscle cells​
Vasoactive hormone receptors ​
Angiotensin II, atrial natriuetic peptide, prostaglandins ​
Actin-myosin filaments ​
Receptors + filaments allow contraction, response to hormones, vasoactive agents ​
Capillary closure, change in filtration surface area, filtration volume.

“Clean” GBM of “junk” accumulated during filtration. ​
Phagocytize, catabolize filtered/trapped macromolecules (e.g., lipoproteins, immune complexes) ​
Make inflammatory, fibrogenic cytokines with role in glomerular injury response​
IL-1, PDGF, TNF, TGF-, prostaglandins, metalloproteinases

Structural support ​
Regulate GBF, GFR​
Respond to injury​


Describe the structure and function and other names of podocytes.

Cover outer surface of capillary loops​
Large cells with cytoplasmic foot processes (pedicels) attached to outer GBM, provide structural support ​
Foot processes adhere to GBM​
Produce most of GBM

GBM synthesis​
Maintenance of permselectivity ​
Negative charge, slit diaphragm​
Structural support for capillary


Describe the specialized intercellular junctions between podoctyes including the proteins involved and its function.

Foot processes attach to each other by 6-nm-thick, 25-60 nm wide filtration slit diaphragm across slit pore​
Nephrin, podocin, -actinin,CD2AP ​

Cytoskeletal filaments regulate slit pore size ​
Actin, tubulin, cytokeratin, synaptopodin

Restricts macromolecule passage​
Slit proteins interact with VEC actin cytoskeleton​
Cytoskeleton rearrangement occurs in proteinuria


What is the anatomy of the GBM? What is the composition? What is its function?

300-350 nm thick​
Made by VEC​
Three layers​
Lamina Rara interna​
Lamina Densa​
Lamina Rara externa

Type IV collagen, sialoglycoproteins, noncollagenous glycoproteins (laminin, fibronectin, nidogen), glycosaminoglycans (heparin sulfate)​

Restricts filtration based on molecule size, charge and configuration


Describe the structure and function of glomerular endothelial cells.

Line capillaries ​
Fenestrated (perforated) ​
70-100 nm fenestrae without diaphragm​
Larger, more numerous than in other organs​
Negative charged surface ​
Polyanionic glycoproteins contribute to charge selective barrier of GCW ​
Prevent filtration of RBC, WBC, platelets.


Where does urine formation begin? What percent of plasma flowing through glomerulus is filtered? What passes through? What doesn't pass through? Explain what causes this selective filtration.

Urine formation begins at GCW ​
20% of plasma that flows thru glomerulus is removed by filtration across GCW ​
GCW permeable to H2O, small MW molecules, electrolytes.
Impermeable to proteins, larger molecules, cells

Two size pores​
A few large pores – minimal large proteins​
Lots of small pores – water, electrolytes, small proteins ​

Negative charge also important​
Negatively charged sialoglycoproteins on GCW impede filtration of anionic proteins


What is the function of the tubules? Generally, How do they tubular segments differ? What are 3 different ways to differentiate them?

Tubule reabsorbs (water, sodium, bicarbonate, glucose), secretes (creatinine, organic acids and bases, drugs)​

Divided in segments with different functions ​

Epithelial cells in each segment have unique morphology, correlates with function.

Course – Convoluted or straight​
Location – Proximal or distal ​
Wall thickness – Thick or thin ​


Describe the tight junctions of the tubular cells.

Near lumen​
Bind cells together​
“Tightness” varies with segment​
Early tubules more “leaky” than late


Describe the different tubular segments including where they are located.

Proximal thick segment​
Proximal convoluted tubule (PCT, pars convoluta) in cortex​
Proximal straight tubule (pars recta, thick descending limb) in outer medulla​

Thin segment - thin limb of loop of Henle​ in medulla (outer and inner)

Distal thick segment​
Distal straight segment (pars recta, thick ascending limb, TAL) ​in outer medulla
Distal convoluted tubule (DCT, pars convoluta) in cortex


Contrast the short vs. long loop nephrons. Why are long loop nephrons important?

Based on length of thin limb of Henle ​

Short loop nephron (cortical nephron)​
Glomeruli in superficial/mid-cortical region. ​
80-90% of nephrons​

Long loop nephron (juxtamedullary nephron)​
Juxtamedullary glomeruli, deep in cortex at corticomedullary junction.
“Juxtamedullary nephron” ​
Thin limbs are long, descend to tip of papilla ​
10-20% of nephrons ​
Glomeruli slightly larger than those in superficial cortex ​Important for urinary concentration


What is the JGA? Where is it located? Describe it. What are its components?

Juxtaglomerular Apparatus

Where they all come together:
Thick ascending limb (TAL)​
Parent glomerulus​
Afferent arteriole

Association of distal TAL epithelium, arteriole, extraglomerular mesangial cells at vascular pole of one nephron.

Macula densa​
Granular cells (JG Cells)​
Extraglomerular mesangial (Goormaghtigh) cells ​


What Macula Densa cells? What are they like histologically? What is their function?

Modified TAL epithelium. ​
Narrow, tall cells ​
Closely packed nuclei “macula densa”​
Sensitive to ions, flow in tubule​
Promotes signal from adjacent mesangial cells ​
Regulates GFR, renal blood flow

“Tubuloglomerular feedback”​


What are JG cells like? What is their function?

Modified afferent arteriole media ​

Smooth muscle (JG) cells have ​ Myoepithelioid appearance​

No elastic lamina ​

Cytoplasmic renin granules​

When BP falls, JG cells produce, secrete protease renin into arteriole, which leads to increased vasoconstrictor, angiotensin II, increased BP