Lecture 10: Renal Histology Flashcards
What is a glomerulus?
Tuft of capillaries
- afferent arteriole feeds into it (higher pressure)
- efferent arteriole drains it (lower pressure)
What are the two type of peritubular capillaries?
Cortical: surrounds proximal and distal convoluted tubules Long medullary (vasa recta): surrounds loop of Henle
*What type of endothelium is found in the cortical peritubular capillary?
Fenestrated endothelium
*What type of endothelium is found in the long medullary peritubular capillary?
Ascending: Fenestrated
Descending: Continuous
What is a renal corpuscle?
Blood filtering component of nephron
- Glomerulus (capillaries) - filters
- Bowman’s capsule - collects
*From deep to superficial (from capillary to capsule), what are the layers of the Bowman’s capsule?
Visceral: layer of podocytes that cover capillaries
Glomerular space: contains the primary filtrate
Parietal layer: simple squamous EPIthelium
Is the vascular pole of renal corpuscles endothelium or epithelium?
What does this pole contain?
Endothelium
afferent and efferent arterioles
Is the urinary pole of renal corpuscles endothelium or epithelium?
What does this pole contain?
Epithelium (continuous with external envt)
origin of the PCT
Mesangial cells
Function
Type of cells?
- hold the “ball of yarn” glomerulus and ECM of podocytes and prevent distension of the glomerulus due to high BP required for filtration (stop the pop)
- Phagocytic cells that secrete GFs and cytokines when there is injury
What are the characteristics of the glomerular endothelium?
- Open fenestrations = leaky
- Thick luminal glycocalyx
- Large number of aquaporins
- Can promote vasodilation by generation NO and prostaglandins
What does the glomerular basement membrane do?
keeps large molecules >70kD (e.g. RBCs) and anions (e.g. proteins) in capillaries
-not good if urine has blood or albumin = indicates damage to GBM
What are podocytes?
have foot like processes that wrap around the capillaries and form slits (interlocked toes analogy) leading to selective permeability
*What layers of the capillaries do filtrates have to cross to reach Bowman’s capsule?
1) Capillary endothelium
2) Basement membrane
3) Podocytes
Where is the filtration membrane located? What does it allow through?
Between capillary and bowman’s capsule
Water, Ions, Glucose, Amino Acids, Urea»_space;» to urine
*no blood or protein goes through
What type of cells make up the parietal layer of Bowman’s capsule?
Simple squamous epithelium
Proximal convoluted and straight tubule: Found where? Epithelium? Contains? What transporters are here?
- Cortex only
- Simple cuboidal to columnar epithelium
- highly folded basal and lateral membranes to increase surface area (star shaped lumen) and many microvilli (brush border) and mitochondria
- Na+/K+ pumps, aquaporins, gluts and AA transporters
*PST less so than PCT, but also has high sensitivity to Na+ and gluts
Thin loop of henle
epithelium?
features
- simple squamous epithelium
- no brush border
Thick ascending loop of henle
epithelium?
features
- Simple cuboidal epithelium
- Many microvilli but no brush border
Distal convoluted tubule: Found where? Epithelium? Features What hormone acts at the DCT?
- Cortex only
- Simple cuboidal epithelium
- Sparse microvilli, smooth/more open luminal surface
- Aldosterone (secondary to angiotensin II action)
What is the significance of the juxtoglomerular cells in the jxtg apparatus?
Mechanosensory cells within afferent arterioles that secrete renin when BP is low
Specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole
What is the function of the macula densa in the jxtg apparatus?
-located at the distal end of Thick Ascending Limb, it senses Na+ levels and tells jxtg cells whether to make renin or not
Describe the “track” of urine from DCT out of the kidney
DCTs form collecting tubules that merge to form the collecting duct > drain into papillary ducts > renal minor calyx > major calyx > renal pelvis > ureter
Collecting tubules/ducts:
Epithelium?
What hormones act on these?
What two cell types are here and how are they significant?
- simple cuboidal with simple columnar at the ends
- ADH and aldosterone (water and Na+ retention)
- principal cells (target of aldosterone) and intercalated/dark cells (transports HCO3-)
What does the cortex contain?
What does the medulla contain?
renal corpuscles, cortical tubules
renal columns, pyramids, medullary tubules and loop of henle
*all these parts aggregate to form the Cortical rays
Urinary tract:
Epithelium?
Why is this type of epithelium significant?
transitional epithelium/urothelium
-surface changes depending on body condition (eg distended when full of urine)
What are the layers of transitional epithelium (deep to superficial)?
1) Deep: single layer of basal cells on basement membrane
2) Intermediate: layers of cuboidal/columnar
3) Superficial: Umbrella cells (that stretch/relax)
What are umbrella cells and how do they relate to bladder urine content?
Full bladder: thicker membrane with visible uroplakin proteins on the surface
Empty bladder: uroplakin gets endocytosed into fusiform vesicles (basically flatten when urine is emptied)
What are the layers of the ureters? (deep to superficial)
Superficial: adventitia
Middle: muscularis - three layers
Innermost (lumen side): transitional epithelium
What muscle controls flow in the ureter and how does this happen?
Muscularis muscle does peristalsis that allows urine flow
also has valves that prevent backflow
Urinary bladder:
Location?
Which muscle controls it?
- Anterior to uterus and rectum and sits in the pelvis
- Detrusor muscle
What are the components of the urinary bladder?
- Trigone (inferior part where ureter and urethra open to)
- Bladder wall
What comprises the bladder wall?
Urothelium
Smooth muscle (detrusor)
Fibrous adventitia
Why is UTI higher risk in women?
-female urethra is shorter (higher risk for UTI due to shorter bacteria traveling distance)
What are the 3 regions of the male urethra and what epithelium covers it?
Prostatic (transitional)
Membranous (PSC and stratified squamous)
Spongy/penile (stratified squamous)
Epithelium changes in the urethra (same in female and male)?
-Transitional (bladder) > Pseudostratified columnar (most of the urethra) > stratified squamous (distal)
What is the difference between the internal and external urethral sphincters?
External urethral sphincter is under voluntary control
Polycystic kidney disease
Cause
Clinical
- PKD1 or 2 mutations
- cysts form that impede drainage and leads to renal failure and impaired BP regulation
What is urinary incontinence?
-inability to control urine, more common in women
What is most common cause of UTI?
Symptoms?
E. coli
Pelvic pain, dysuria, fever
What is schistosoma haematobium?
Parasitic blood flukes that lead to fibrosis or calcification of bladder and higher risk for bladder cancer
