Two Flashcards
(24 cards)
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
Mesangium
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
Phagocytosis Structural support Secretion 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
