Renal Histology Flashcards
What are the kidney functions?
- Regulate volume & composition of body fluids
- Produce ultrafiltrate of blood plasma
- Endocrine activities
What is renin made/secreted by? What does it do? What does it control?
- Synthesized and secreted by juxtaglomerular cells
- Cleaves circulating angiotensinogen to make angiotensin I
- Controls blood pressure and volume
What are the endocrine activities of the kidney?
–Erythropoietin (EPO), a glycoprotein hormone
–Renin, an acid protease
–Vitamin D3
Describe the structure of the stroma
–Thin capsule with 2 layers
•Outer: collagen fibers + fibroblasts
•Inner: myofibroblasts
–Sparse interstitial connective tissue consisting of reticular fibers
What structures pass through the hilum?
: renal pelvis (becomes ureter), nerves, vessels, lymphatics
In the parenchyma, most tissue is functional… What do the epithelial cells that are arranged to form urniferous tubules do?
Drain urine into the renal pelvis
What is the renal pelvis?
–the expansion of the proximal ureter, lies within the renal sinus, and is supported in a bed of fat
What is the renal sinus?
–(aka hilum) is the central cavity that opens medially
______________________…
–Vertical striations that appear to emanate from the medulla
–Contains straight tubules of the nephron and collecting ducts
Medullary rays
_______________:
–The regions between medullar rays that contain the renal corpuscles, convoluted tubules of the nephrons, and the collecting tubules
Cortical labyrinths
______________:
–Each nephron and its collecting tubule
•Uriniferous tubule
What is a kidney lobe?
•each medullary pyramid and one half of each adjacent renal column
_______________:
•central medullary ray and surrounding cortical material (only found in cortex)
–Made up of the collecting duct for a group of nephrons that drain into that duct
Lobule
What are the components of the renal corpuscle?
–Bowman’s capsule (double-layered epithelial cup)
–Glomerulus (10-20 capillary loops)
What are the four components of the tubule system?
–Proximal convoluted and straight tubule
–Thin descending and ascending limbs of the loop of Henle
–Distal straight (thick ascending limb) tubule
–Distal convoluted tubule
What are the two types of nephrons?
Juxtamedullary nephron
Cortical nephron
Juxtamedullary nephrons are very important in creating…
Concentrated urine
What are the cell populations of the renal corpuscle?
- squamous cells of parietal epithelium
- endothelial cells of capillaries
- mesangial cells (and matrix)
- squamous cells of visceral epithelium (podocytes)
__________________
•Double-walled epithelial structure
–Blind end of the uriniferous tubule reflected onto the capillary tuft
–Parietal epithelium – squamous outer wall; continuous with the cuboidal epithelium of the proximal convoluted tubule
–Visceral epithelium – reflected tubular epithelium
•Modified epithelial cells called podocytes
–Bowman’s space (urinary space) - between parietal and visceral layers
•Receives glomerular filtrate
Bowman’s capsule
_____________________:
•Tufts of capillaries that indents into Bowman’s capsule
–Vascular pole – where vessels enter and leave capsule
•Afferent arteriole enters and ramifies into capillaries that recombine to form efferent arteriole
–Urinary pole – where ultrafiltrate exits corpuscle
Glomerulus
How does one differentiate between distal and proximal convoluted tubules?
PC: thick walled, with a fuzzy bordered lumen that may have “stuff” in it
DC: thin walled, clean shaven lumen, not much detritus inside
Nephrin is an important structural and functional component, and mutations in the gene encoding neprhin are associated with congenital nephrotic syndrome – characterized by
massive proteinuria and edema.
_______________________:
–Possesses numerous fenestrations (70-90 nm)
–The endothelial cells possess a large number of aquaporin channels
–Endothelial cells secrete NO and prostaglandins, as well as a sialic acid-rich glycocalyx that adds negative charge to the filtration apparatus
•Endothelium of glomerular capillaries
________________:
–Thick (300-370 nm) basal lamina that is a joint product of the endothelium and podocytesEndothelium of glomerular capillaries
–
–Prominent in sections stained with the periodic acid-Schiff (PAS) procedure
–Consists of Type IV collagen, laminin, nidogen, entactin, proteoglycans, multiadhesive glycoproteins
•Glomerular basement membrane (GBM)
_____________________:
–Contains specialized cells called podocytes (visceral epithelial cells)
–These cells extend processes around the glomerular capillaries and develop numerous secondary processes called pedicels (foot processes)
•Foot processes interdigitate and create filtration slits (40 nm wide), which are covered by an ultrathin filtration slit diaphragm
•Visceral layer of Bowman’s capsule
What type of barrier is the Type IV collagen in the filtration apparatus of the kidney?
Size exclusion
___________________:
•rich in polyanions (heparan sulfate) that impede the passage of negatively charged molecules
Lamina rara externa of glomerular basement membrane
__________:
•: similar to lamina rara externa
Lamina rara interna of glomerular basement membrane
________________:
•overalapping portion of the two basal laminae, containing type IV collagen organized into a physical barrier; type XVIII collagen, perlecan, and agrin are responsible for the bulk of anionic charges found in the GBM
Lamina Densa of glomerular basement membrane
What are the layers of the glomerular basement membrane?
Lamina rara externa
Lamina rara interna
Lamina densa
What size particles are restricted by the glomerular basement membrane?
•Restricts the movement of particles larger than 70 kDa, or 3.6 nm radius (including albumin or Hb)
•The polyanionic glycosaminoglycans of laminae rarae have strong negative charges and restrict the movement of even
small, negatively charged molecules
In diabetic nephropathy, what is going on?
the number of anionic sites in the glomerular basement membrane is reduced
Add mesangia stuff
__________________:
•Includes the macula densa, juxtaglomerular cells, and the extraglomerular mesangial cells
•Adjacent to afferent/efferent arterioles at the vascular pole of the renal corpuscle
•Regulates the body’s salt and water balance by monitoring Na+ levels (distal tubule), blood pressure (afferent arteriole)
–Renin is released when levels are low
Juxtaglomerular apparatus
_________________:
–In the distal tubule, adjacent to afferent arteriole
–Monitor Na+ concentration in tubular fluid
–When Na+ is low, these cells stimulate renin release from JG cells and contraction of afferent arteriolar smooth muscle
Macula densa of juxtaglomerular apparatus
_______________:
–Modified smooth muscle cells of afferent arteriole
–Secrete the protease renin
Juxtaglomerular cells of juxtaglomerular apparatus
______________:
–AKA cells of lacis or polkisson
–Fusiform/flat cells provide support
•Extraglomerular mesangial cells of Juxtaglomerular Apparatus
3 cell types of Juxtaglomerular Apparatus?
macula densa
juxtaglomerular cells
extraglomerular mesangial cells
Why so many mitochondria in the proximal tubule cells?
To drive Na/K-ATPase pumps
_________________________:
•Initial and major site of reabsorption
–Reabsorbs ~65% of glomerular filtrate (water, salt, amino acids, glucose, proteins)
•Cuboidal cells with:
–Brush border with many microvilli
–Tight junctions between neighboring cells
–Plicae (folds) on lateral surfaces
–Basal striations, consisting of elongate mitochondria concentrated in the basal processes and oriented vertically
Proximal convoluted tubule
________________:
- AKA thick descending limb of the loop of Henle
- Found in the cortex and medullary rays
- Morphology is similar to PCT cells, but the cells are shorter with less microvilli, and fewer basal infoldings with mitochondria
Proximal straight tubule
What does the loop of Henle do?
•Establishes a hypertonic medullary interstitium
In the loop of henle, what is the thin descending limb permeable to?
–Thin descending limb is highly permeable to water, and less permeable to solutes
In the loop of henle, what is the thin ascending limb permeable to?
–Thin ascending limb is highly permeable to NaCl and impermeable to water
In the loop of henle, what is the thick ascending limb permeable to?
–Thick ascending limb produces an 85 kDa protein called uromodulin (Tamm-Horsfall protein) that influences NaCl reabsorption and urinary concentration ability
http://www.colorado.edu/intphys/Class/IPHY3430-200/countercurrent_ct.html
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What is the most important structure in concentrating urine?
The loop of henle
__________________:
•Continuous with the thick ascending limb of the LOH
•Impermeable to water; transports ions from tubular lumen into interstitium
•Cuboidal epithelium with basolateral interdigitations
–Round, smooth lumen; apically-placed nuclei; numerous basal mitochondria; paler staining than PCT in H&E stain
Distal straight tubule
_____________:
•Found only in the cortex
–Returns to renal corpuscle of origin
–Simple cuboidal epithelium, round/smooth lumen, paler staining than PCT, numerous mitochondria
Distal convoluted tubule
Under the influence of aldosterone, the distal convoluted tubule…
–Reabsorbs Na+ (secretes K+), reabsorbs bicarbonate (secretes H+), secretes ammonia
__________________________:
- Composed of simple epithelium with a flattened (squamous-cuboidal) shape
- Receives urine from several nephrons
- Duct runs in center of medullary ray towards medulla
Collecting Tubules and Cortical Collecting Ducts
__________________:
•Simple epithelium: cuboidal cells with a transition to columnar cells as the ducts increase in size
•Site of final concentration of urine
•H2O is lost to increasingly hypertonic medullary interstitium
–Antidiuretic hormone (ADH) makes duct more permeable to H2O
Medullary Collecting Ducts
____________:
–AKA ducts of Bellini
–The ducts open at the area cribrosa of papilla
large papillary ducts
What are the two distinct cell types present in the collecting tubules and ducts?
-principle cells (light cells)
intercalated cells (dark cells)
__________:
•Pale-staining cells; possess a single primary cilium and relatively few short microvilli; small, spherical mitochondria; have an abundance of ADH-regulated water channels (aquaporin-2)
–Principal cells (light cells)
_______________:
- Considerably fewer in number; many mitochondria; dense cytoplasm with numerous vesicles present
- α-intercalated cells secrete H+
- β-intercalated cells secrete HCO3-
–Intercalated cells (dark cells)
What renal cells are responsible for renal compensation to pH disturbances?
–Intercalated cells (dark cells)
What are the two cell types of the renal interstitium cortex?
–Fibroblast-like cells: found between the basement membrane of the tubules and the adjacent peritubular capillaries; secrete collagen and glycosaminoglycans of the extracellular matrix
–Macrophages
What is the 1 cell type of the renal interstitium medulla?
–Myofibroblast-like cells: oriented to the long axes of the tubular structures and may have a role in compressing these structures; an abundance of actin filaments, rough endoplasmic reticulum, Golgi complex, lysosomes
segmental arteries are important because?
they are functional end arteries, no collateral blood supply. Occlude one and the kidney segment that is supplied will die.
What is the path of urine through the kidney structures?
collecting ducts à minor calyx à major calyx à renal pelvis à ureter à bladder
What are the layers of the lower urinary tract?
–Mucosa: transitional epithelium and lamina propria (attaches epithelium to smooth muscle)
–Muscularis: inner longitudinal layer of smooth muscle, outer circular layer of smooth muscle
–Adventitia: attaches organs to surrounding structures and may be covered with serosa
