10. Histology of The Urinary Tract

Question 1

What are the components of the unrinary system?

Answer 1

1. Kidneys
2. Ureters
3. Urinary Bladder
4. Urethra

Question 2

What are the structural components of the kidneys?

Function?

Answer 2

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

Question 3

What are the functions of the kidneys?

Answer 3

1. Remove soluble waste
2. Regulate blood pressure
3. Stimulate red cell production
4. Concentration of electrolytes
5. Conservation of water
6. Blood pH - acid/base balance/ pH homeostasis

Question 4

Label this histological section of the renal cortex.

Answer 4

Question 5

What is labelled here?

Answer 5

Question 6

What is a Kidney lobe?

Answer 6

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

Question 7

What comprises the kidney cortex?

Answer 7

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

Question 8

Label this.

Answer 8

Question 9

Label this.

Black arrows?

Blue arrows?

Answer 9

Black arrows = Tubules

Blue arrows = Glomeruli

Basement membranes = black

Question 10

What is the bowmans capsule?

Structure?

Answer 10

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

Question 11

What are the Glomerular capillaries?

• Where do they come from?
• What function do they perform?
• Where does the filtrate collect?

Answer 11

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

Question 12

What is the Mesangium?

• Where are they found?
• 5 specialised functions?

Answer 12

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

Question 13

What is the Extraglomerular Mesangium?

Answer 13

Extraglomerular Mesangium

• Considered a type of smooth muscle cell
• Through the renin-angiotensin system
  
  • Autoregulate blood flow
  • Systemic blood pressure

Question 14

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?

Answer 14

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

Question 15

What are the Macula Densa Cells?

• Where are they?
• What do they do?

Label the glomerulus.

Answer 15

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

Question 16

What is the Juxtaglomerular apparatus?

• Function?
• 3 components?

Answer 16

Juxtaglomerular Apparatus

• Regulates renal blood flow & glomerular filtration rate
• Combines ALL three components:

1. Macula Densa
2. Juxtaglomerular cells
3. Extraglomerular mesangial cells

Question 17

Label this.

(HIGH YIELD)

Answer 17

Question 18

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?

Answer 18

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

Question 19

Answer 19

Question 20

What are Podocytes?

• Where are they found?
• Shape?
• Function?

Answer 20

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

Question 21

SEM of Podocytes

Answer 21

Question 22

BS? P? CL?

Answer 22

• BS =Bowman space
• P = Pedicel
• CL = Capillary lumen

Question 23

Label this.

Answer 23

Question 24

What feature of the tubule is labeled here?

Answer 24

Question 25

What is the Arterial Blood Supply to the kidneys?

Answer 25

**Arterial Blood Supply** * Renal artery * Arcuate artery supplies: * ***Cortex*** (vessel in descending diameter) * Interlobular arteries (between) * Intralobular arteries (within) * Afferent & Efferent arterioles * Glomerular Tuft * ***Medulla*** * Vasa Recta = Straight vessels of the medulla

Question 26

Vasculature of Kidney

Answer 26

Question 27

Answer 27

Question 28

What is the renal medulla composed of?

Answer 28

**Medulla** • Segmented in to calyces (calyx singular) – Are pyramidal segments of tubules and collecting ducts

Question 29

What are the 2 cell types of the collecting ducts? What are they each involved in?

Answer 29

**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

Question 30

Answer 30

Question 31

What is the renal pelvis?

Answer 31

**Pelvis** • Cavity into which the filtrate (urine) – Empties from individual calyces

Question 32

How can you tell the difference between the PCT and DCT? Shape of epilelium in CT?

Answer 32

PCT = Bigger & Cuboidal cells with lots of microvilli DCT = Smaller & cuboidal cells with few it any microvili CT = cuboidal to columnar

Question 33

What is Urothelium? Where is it found

Answer 33

**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.

Question 34

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?

Answer 34

**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

Question 35

What is the histology of the Urinary Bladder?

Answer 35

**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

Question 36

What are Umbrella/Dome cells? Where are they found?

Answer 36

**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.

Question 37

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?

Answer 37

**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