Flashcards in Renal Histology Deck (57):
What is the functional significance of the cortex? What is in the cortex?
Outer part of the kidney, between capsule and medulla
Where ultrafiltration occurs
Epo is produced here
straight tubules of the nephron
What is the functional significance of the cortical/renal columns?
Medullary extension of the cortex in between renal pyramids
- allows for better anchoring of the cortex
What is the functional significance of the medullary rays?
Contain the straight tubules of the nephron and collecting ducts.
-look like vertical striations that emanate from medulla
What is the functional significance of the medulla?
straight tubules of nephrons - form pyramids
What is the functional significance of the renal lobe?
Lobe contains a whole medullary pyramid and half of each adjacent renal column
What is the functional significance of the renal papillae?
Papilla = apical portion of each medullary pyramid
Perforated (cribrosa) projection into minor calyx of renal pelvis, allows for passage of filtrate
What is the functional significance of the renal pelvis?
Collecting duct for urine
Exits kidney via hilum
What is the functional significance of the renal lobule?
Made up of the collecting duct for a group of nephrons that drain into duct
Lobule: central medullary ray and surrounding cortical material (only found in cortex)
What 2 general parts make up a nephron?
What is the function of the renal corpuscle?
Initial blood filtering component of a nephron
What cells make up the renal corpuscle?
Squamous cells - from parietal epithelium
endothelial cells - from capillaries
mesangial cells and matrix
squamous cells of visceral epithelium - AKA podocytes
What is a Bowman's capsule?
Beginning of a nephron
A sac-like covering for the capillary glomerulus - collects fluid from blood going through glomerulus
What are the cellular parts of the structure of a Bowman's capsule?
Double walled epithelial structure
Uriniferous tubule - leads away from glomerulus/capillary tuft
Parietal epithelium - squamous outer wall
Visceral epithelium - covers glomerulus, has podocytes
Bowman's space - urinary space between parietal and visceral layers, receives glomerular filtrate
What is the glomerulus?
'Tuft' of capillaries that indents into Bowman's capsule
What are the 2 poles of the glomerulus?
- where vessels enter and leave capsule
- afferent arteriole enters and splits off into capillaries
- capillaries recombine to make efferent arteriole
Urinary pole - where ultrafiltrate exits corpuscle
In a general sense, what are the 3 filtration components found in the nephron?
Endothelium of glomerular capillaries
Glomerular basement membrane
Visceral layer of Bowman's capsule
What 4 features of the glomerular capillary endothelium contribute to it's filtration capacity?
1. Numerous fenestrations
2. Large numbers of aquaporins
3. Secreted NO and prostaglandins
4. Glycocalyx that adds negative charge to the filtration apparatus
What makes up the glomerular basement membrane?
Type IV collagen mostly
- also additional adhesive molecules - laminin, nidogen, entactin, proteoglycans, multiadhesive glycoproteins
What part of the visceral layer of Bowman's capsule helps with glomerular filtration?
Podocytes - AKA visceral epithelials
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
What are the three layers of the glomerular basement membrane?
Lamina rara externa
Lamina rara interna
What features of glomerular basement membrane allow it to filter blood?
Lamina rara externa
- rich in polyanions - heparin sulfate - that impede passage of negatively charged molecules
- type IV collagen makes a physical barrier
- type XVIII collagen, perlecan, & agrin are responsible for most of anion charges in GBM
Anions allow for a charged 'net' or boundary that won't allow negatively charged blood proteins to pass
- Cellular components of blood too large, platelets too negative
How does diabetic nephropathy reduce the filtering capacity of the GBM?
Greatly reduces number of anionic sites
What 4 things do mesangial cells do?
1. Phagocytosis and endocytosis
- Remove trapped residues and proteins from the GBM and filtration slit diaphragm; endocytose immune complexes
2. Structural support for podocytes
3. Secretion of molecules in response to glomerular injury
4. Modulation of glomerular distension
What makes up the juxtaglomerular apparatus?
Extraglomerular mesangial cells
What does the juxtaglomerular apparatus do?
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
Where is the juxtaglomerular apparatus?
Adjacent to afferent/efferent arterioles at the vascular pole of the renal corpuscle
What is the function of the macula densa?
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
Where is the macula densa located?
In the distal tubule, adjacent to afferent arteriole
What are the juxtaglomerular cells made out of? What is an important endocrine function that they do?
Modified smooth muscle cells of afferent arteriole
Secrete the protease renin
What do the extraglomerular mesangial cells do?
Fusiform/flat cells provide support
AKA cells of lacis or polkisson
What is the function of the proximal convoluted tubule?
Initial and major site of reabsorption
Reabsorbs ~65% of glomerular filtrate (water, salt, amino acids, glucose, proteins
What cells make up the proximal convoluted tubule? What are some histological features?
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
Why do proximal convoluted tubule cells have so much mitochondia?
Run Na/K-ATPase pumps
Where are the proximal straight tubules formed?
Found in the cortex and medullary rays
AKA thick descending limb of the loop of Henle
What is the morphology of the proximal straight tubules like?
Morphology is similar to PCT cells, but the cells are shorter with less microvilli, and fewer basal infoldings with mitochondria
Where is the loop of Henle found?
In the medulla
What does the loop of Henle do?
Establishes a hypertonic medullary interstitium
List the different portions of the loop of Henle in relation to Na and water retention.
Thin descending limb is highly permeable to water, and less permeable to solutes
Thin ascending limb is highly permeable to NaCl and impermeable to water
Thick ascending limb produces an 85 kDa protein called uromodulin (Tamm-Horsfall protein) that influences NaCl reabsorption and urinary concentration ability
Where is the distal straight tubule?
Continuous with the thick ascending limb of the LOH
What are the filtering characteristics of the distal straight tubule?
Impermeable to water; transports ions from tubular lumen into interstitium
What is the cell type of the distal straight tubule?
Cuboidal epithelium with basolateral interdigitations
Round, smooth lumen; apically-placed nuclei; numerous basal mitochondria; paler staining than PCT in H&E stain
Where is the distal convoluted tubule found?
Found only in the cortex
Returns to renal corpuscle of origin
What is the cell type of the distal convoluted tubule?
Simple cuboidal epithelium, round/smooth lumen, paler staining than PCT, numerous mitochondria
What is the impact of aldosterone on the distal convoluted tubule?
Reabsorbs Na+ (secretes K+)
reabsorbs bicarbonate (secretes H+)
What do the collecting tubules do?
Receives urine from several nephrons
Where do the collecting ducts run?
Duct runs in center of medullary ray towards medulla
Receives urine from several nephrons
What is the epithelium of the collecting ducts like?
Composed of simple epithelium with a flattened (squamous-cuboidal) shape
What is the epithelium of the medullary collecting ducts like?
Simple epithelium: cuboidal cells with a transition to columnar cells as the ducts increase in size
What is the function of the medullary collecting ducts?
Site of final concentration of urine
H2O is lost to increasingly hypertonic medullary interstitium
Antidiuretic hormone (ADH) makes duct more permeable to H2O
How do the medullary collecting ducts change as they merge into ductal cells?
Medullary portion (renal papilla region)
Ductal cells become tall cuboidal to columnar
These combine to form large papillary ducts
AKA ducts of Bellini
The ducts open at the area cribrosa of papilla
What are the 2 cell types of the collecting ducts and tubules?
What are some characteristics of principal 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)
What are some characteristics of intercalated cells?
Considerably fewer in number; many mitochondria; dense cytoplasm with numerous vesicles present
α-intercalated cells secrete H+
β-intercalated cells secrete HCO3-
What is the renal interstitium?
Interstitial tissue that surrounds the nephrons, ducts, and blood and lymphatic vessels
Present in greater amounts in medulla (20% volume) compared to cortex (7% volume)
What is a special consideration for the segmental arteries that supply the kidney?
They're functional end arteries, with no collateral blood supply. If compromised, the kidney they feed is SOL.
What are the vasa recta? Where are they located and what do they drain to?
Arterioles/capillaries that run in the renal columns of the medulla
Located in juxtamedullary region
Descend into medulla and parallel loops of Henle
Loop and return to corticomedullary boundary
Bypass interlobular veins, drain into arcuate veins arcuate veins drain to segmental veins