10. Histology of The Urinary Tract Flashcards
What are the components of the unrinary system?
- Kidneys
- Ureters
- Urinary Bladder
- Urethra
What are the structural components of the kidneys?
Function?
Kidneys - Structure
- Fibrous capsule - Outer visceral mesothelium!
-
Cortex = Location of filtration units
- Nephrons or glomeruli
- Medulla = Medullary pyramid/rays of parallel tubules & vessels (vasa recta)
- Pelvis = Calyces/papillae emptying of large collecting ducts
- Hilum = entry and exit of Vessels & nerves & Ureter by way of renal sinus leads to bladder
- Ureter
What are the functions of the kidneys?
- Remove soluble waste
- Regulate blood pressure
- Stimulate red cell production
- Concentration of electrolytes
- Conservation of water
- Blood pH - acid/base balance/ pH homeostasis
Label this histological section of the renal cortex.
What is labelled here?
What is a Kidney lobe?
Kidney Lobe
–Tubules & collecting ducts of medullary ray and cortical segment
–Sometimes each lobe is delineated on kidney surface, known as “fetal lobulations” – most mature kidneys have a smooth surface
What comprises the kidney cortex?
Renal Cortex
- Filtration units known individually as either - Nephron, Glomerulus or Renal [Malpighian] corpuscle
- Are 2x106 per kidney
- Tubules - Short segments only
- Blood vessels of various calibres
Label this.
Label this.
Black arrows?
Blue arrows?
Black arrows = Tubules
Blue arrows = Glomeruli
Basement membranes = black
What is the bowmans capsule?
Structure?
Glomerulus
- Ball of a fine fenestrated capillary
- Enters and exits at the hilum of Bowman capsule
- Afferent capillary (enter)
- Efferent capillary (exit)
- Bowman Capsule - Separated by the urinary space or Bowman space
What are the Glomerular capillaries?
- Where do they come from?
- What function do they perform?
- Where does the filtrate collect?
Glomerular Capillaries
- Origin of glomeruli – Interlobular arteries
- Bud-off glomeruli or
- Branch-off intralobular arteries, which then bud-off glomeruli
- Are fenestrated capillaries to reduce filtration distance
- Filtrate collects in Bowman (urinary) space
What is the Mesangium?
- Where are they found?
- 5 specialised functions?
Mesangium
- Mesangial cells are pericyte-like (also known as polkissen lacis cells or polar cushions)
- Found between glomerular capillaries
- Specialized cell function:
- Physical support
- Contraction to modify glomerular blood flow (angiotensin II receptors) (filtration rate)
- Phagocytosis
- Make the extracellular matrix
- Monitor capillary lumen glucose concentration
What is the Extraglomerular Mesangium?
Extraglomerular Mesangium
- Considered a type of smooth muscle cell
- Through the renin-angiotensin system
- Autoregulate blood flow
- Systemic blood pressure
What are the Juxtaglomerular Cells and what is their function?
- What type of cell are they?
- What are they also known as?
- Where are they located in the kidney?
- What do they release when stimulated bu the macula densa cells?
- Function - role in BP regulation?
Juxtaglomerular Cells
- ‘Juxta’ means ‘near’ or ‘adjacent’ in Latin
- Are modified smooth muscle cells (also known as granular cells) of afferent arteriole
- In the media of the afferent arteriole, though similar - function differently to mesangium
- Release renin granules in response to stimulation from the macula densa (distal tubule)
- Contain angiotensin-converting enzymes
- Monitor blood pressure by detecting arterial wall stretch
What are the Macula Densa Cells?
- Where are they?
- What do they do?
Label the glomerulus.
Macula Densa
- Specialized epithelial cells of the distal tubule
- Adjust glomerular filtration rate by responding to sodium chloride (NaCl) concentrations within the distal tubule
Purple = macula densa (DT)
light blue = central glomerulus
dark blue = tubules
green = basement membrane
teal = mesangial cells
What is the Juxtaglomerular apparatus?
- Function?
- 3 components?
Juxtaglomerular Apparatus
- Regulates renal blood flow & glomerular filtration rate
- Combines ALL three components:
- Macula Densa
- Juxtaglomerular cells
- Extraglomerular mesangial cells
Label this.
(HIGH YIELD)
What type of epithelium lines the:
- Bowman’s capsule?
- PCT?
- Thin descending limb of LOH?
- Thin ascending limb of LOH?
- Thick ascending limb of LOH?
- What are they permeable to?
- DCTs?
- CTs?
Lining & Absorptive Epithelium
Epithelium although continuous is regionally specialized
- Bowman capsule = parietal epithelium – Simple squamous epithelium
- Incomplete, visceral epithelium “podocytes” covering the capillary ball
- Epithelium of tubules which further specialized
What are Podocytes?
- Where are they found?
- Shape?
- Function?
Podocytes
- Incomplete sheet of epithelium over glomerular capillary OUTER surface
- Cells have foot-like processes resembling a ‘starfish’
- Each cell foot process branched into pedicels extending into the BM of glomerular capillary
- Creating filtration slits 25nm or 0.025μm in width
- Nephrin forms the slit diaphragm, a zipper-like protein that allows sugar and water through, not proteins
SEM of Podocytes
BS? P? CL?
- BS =Bowman space
- P = Pedicel
- CL = Capillary lumen
Label this.
What feature of the tubule is labeled here?
What is the Arterial Blood Supply to the kidneys?
Arterial Blood Supply
- Renal artery
- Arcuate artery supplies:
-
Cortex (vessel in descending diameter)
- Interlobular arteries (between)
- Intralobular arteries (within)
- Afferent & Efferent arterioles
- Glomerular Tuft
-
Cortex (vessel in descending diameter)
-
Medulla
- Vasa Recta = Straight vessels of the medulla
Vasculature of Kidney
What is the renal medulla composed of?
Medulla
• Segmented in to calyces (calyx singular)
– Are pyramidal segments of tubules and collecting ducts
What are the 2 cell types of the collecting ducts?
What are they each involved in?
Collecting Ducts
Collecting duct system contains two cell types:
1 - Intercalated cells = dark flask-shaped with a broad base, narrow surface
– α and β varieties participate in acid-base homeostasis
2 - Principal cell = pale cuboidal, with superficial shallow scant microvilli – Involved in sodium and potassium balance
What is the renal pelvis?
Pelvis
• Cavity into which the filtrate (urine) – Empties from individual calyces
How can you tell the difference between the PCT and DCT?
Shape of epilelium in CT?
PCT = Bigger & Cuboidal cells with lots of microvilli
DCT = Smaller & cuboidal cells with few it any microvili
CT = cuboidal to columnar
What is Urothelium? Where is it found
Urothelium – transitional epithelium
- Lines renal pelvis, ureter, urinary bladder, upper urethra.
- Stratified or pseudostratified.
- Adapts to contraction or dilation of organ they line.
- Columnar: 5-7 cells thick – empty bladder.
- Squamous & cuboidal: 2-3 cells thick – full bladder.
What is the histology of the ureters?
- Diameter?
- Where does it empty into the bladder?
- Shape of lumen?
- Structure of muscularis?
- How many cells thick?
Ureter Histology
- Large bore tube (3-4mm in diameter)
- Empties into bladder at the trigone
- Flap like valves of mucosa
- Consists of folded mucosa = Distinctive STAR shaped lumen
- 2 layer muscularis (smooth muscle) and Fibrous connective tissue coat covered by mesothelium
- Mucosa lined by transitional (stratified) epithelium like the bladder
- 3-5 cells thick
What is the histology of the Urinary Bladder?
Urinary Bladder Histology
- Muscular sac collects urine
- Wall of smooth muscle
- Arranged in bundles (3 interlaced layers)
- Lined by a transitional (stratified) epithelium
- Can expand and contract with filling of the bladder (folded in empty state, with mucous glands at urethral orifice)
- Outer visceral surface of:
- Collagen & elastin
- Covered by mesothelium continuous with abdominal cavity
What are Umbrella/Dome cells?
Where are they found?
Bladder (Urothelium)
Superficial cells – dome/ umbrella/ facet cells.
- Assist in distention (interplaque regions) & protection (plaque region).
- Plaques: invaginate into cytoplasm when bladder empties; impermeable to water.
What is the Histology of the Urethra?
- What type of epithelium lines it?
- Length variation?
- What are the mucous secreting glands called? Function?
- Difference for females?
Urethra Histology
- Vary in length – Male 15-20cm – Female 4-6cm
- Close to the bladder lined by urothelium
- Lower down lined by stratified non-keratinized epithelium
- Both genders have mucus secreting glands of Littre in wall
- Protect against concentrated urine
- In the female there is a thin layer of erectile tissue similar to the penile corpus spongiosum
