Microscopic anatomy of the urinary tract Flashcards
Describe the vascularisation of the kidney
- Supplied by single branch of aorta (renal artery)
- Splits into interlobar artery within kidney
- Then arcuate artery
- Then interlobar artery
- Into vasa recta
- Into arcuate vein, then interlobar vein and then renal vein out into caudal vena cava
What is the reason for the gross appearance of cat kidneys?
The subscapular veins run towards the hilum of the kidney, givign a grooved appearance
What is meant by end arteries?
- Vessels that do not have anastomoses with a back up blood supply
- Closed blood supply
What is the relevance of end arteries to renal function?
- Renal arteries are end arteries
- Damage to an artery will lead to a whole section losing its blood supply and dying off
What is the nephron?
The functional unit of the kidney
What is the nephron made up of?
- The renal corpuscle (glomerulus)
- And the tubular system
What are the components of the tubular system of the nephron? (in order)
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct (drains into pelvis)
What components are found in the renal cortex
- Proximal and distal convoluted tubues
- Glomeruli
What components are found in both the inner and outer medulla of the kidney?
- The thin loops of Henle
- Collecting ducts
What is found in the outer medulla?
- Straight proximal tubule (S3)
- Thick ascending loop
- Collecting ducts
- Thin tubules
- Vasa recta
What is found in the inner medulla?
- Collecting ducts
- Thin tubules
- Vasa recta
What can be seen in the cortex of the kidney on histology?
- Renal corpuscles
- Convoluted tubules
- Medullary rays
Describe the glomerulus
- Aka renal corpuscle
- Vascular tuft/ capillary bundle
- Fneestrated so filtrate drains out
- Pressure difference between afferent and effect arteriole to facilitate filtration
Which has higher pressure, the afferent or the efferent arteriole in the kidney?
- The efferent
- Facilitates filtration through the glomerulus
Describe Bowman’s capsule
- Inner (visceral) layer made up of podocytes
- Outer (parietal) layer
- Not directly in contact with blood
- Podocytes between vascular tuft and inner of capsule
What are the filtration mechanisms found in the glomerulus?
- Physical
- Electrical
What is the function of the podocytes in Bowman’s capsule?
- Filter to keep proteins in the blood
What are the mesangial cells?
- Mesothelium of the capillary tuft (glomerulus)
What are the functions of the mesangial cells?
- Properties of immune and smooth muscle cells
- Assist filtration barrier
- Provide structural support
- Phagocytose foreign material
List the filtration apparatus of the glomerulus
- Fenestrated capillary endothelium
- Charge of the glomerular basement membrane (-ve charge, repels anions)
- Podocytes
- Physical action of glomerular basement membrane
How do podocytes act to filter the blood?
- Have primary and secondary processes
- Pedicels
- Filtration slite between pedicels
- Anything larger than slit will not pass through
Describe the structure of the proximal tubule
- Made up of 3 segments
- S1, S2, S3
- S1,2 are convoluted, S3 is straight
- Brush border
- Basal striation
- Interdigitation of basal processes
- Infolding of basal cell membrane to increase SA
What is the function of the proximal tubule?
- Majority of transport
- Bulk absorption
- Reabsorption from filtrate e.g. glucose
How does the proximal tubule carry out its function?
- Enzymatic system
- Abundant Na/K ATPase
Why are there many mitochondria present in the proximal tubule cells?
- Reabsorption is an enzymatic process
- Active process, lots of ATP needed
- Mitochondria supply this ATP
What is the disadvantage of the enzymatic system in the proximal tubule?
- Can be overloaded
- osmotically active substances can get into the loop of Henle
- E.g. glucose
What are the different segments of the Loop of Henle? (in order)
- Thick descending limb
- Thin segment
- Thick ascending limb
What is the function of the loop of Henle?
- Concentration of urine
How does the Loop of Henle carry out its function?
- Countercurrent multiplier
- Water out of descending loop, ions out of the ascending loop
Describe the concentration of ions in the loop of Henle
- Increasing ion concentration down the loop, decreasing up the loop
- 2 isotonic regions
- Highest concentration of salts at the bottom of the loop
What is medullary wash out and how does this occur?
- Too much fluid
- Unable to produce concentrated urine
Describe the structure of the distal tubule
- Straight segment
- Convoluted segment
- Basal striation
What is the function of the distal tubule?
- Ion transfer
- Balances amount of water in teh body
How does the distal tubule carry out its function?
- Pumps sodium chloride
- Controls K, Cl, Na to balance water
- Isotonic solution of these ions
What is the juxtaglomerular apparatus?
- Terminal portion of straight distal tubule comes into contact with the afferent and efferent arterioles of its “own” glomerulus
- Macula densa where in contact
What is the function of the juxtaglomerular apparatus?
Rate and concentration of sodium going past measured here
Describe the structure of the collecting ducts
- Inner medulla
- Flat cylindrical cells
- Each individual duct coalesces to a larger duct to open to renal papilla
What is the function of the collecting ducts?
- Bring urine together
- Alter amount of water in urine
How do the collecting ducts carry out their function?
- Use concentration gradient set up by loop of Henle
- ADH inserts aquaporins to allow more absorption into tissues
Where do the collecting ducts connect to the papilla?
- At area cribrosa of the papilla, into the renal pelvis
What is unique about the horse renal pelvis?
- Contain low numbers of mucus glands
- Referred to as pelvis renalis and uretericae glands
- Simple branched tubualveolar glands present in mucosa and produce viscous mucinous material
What is the vasa recta?
- Capillary network around the loop of Henle
- Reabsorbs water from interstitium and carries back to venous sytem
Describe the microscopic structure of the ureters
- Transitional epithelium - Thick, fibroelastic lamina propria
- Upper 2/3rds smooth muscle, 2 layers inner (longitudinal) and middle (circular)
- Lower 1/3rd only has outer longitudinal smooth muscle
What is the function of transitional epithelium?
- Stretchable and impermeable, can adjust to distension
- Can stretch until appears squamous
Describe the microscopic structure of the bladder
- 3 layers of smooth muscles
- Transitional epithelium
- Underlying mucosa heavily folded to accomodate volume changes
- As expands, folds disappear
Describe the microscopic structure of the urethra
- Mainly transitional epithelium
- Some parts with stratified epithelium
- Erectile tissue in both sexes (endothelial lined vascular spaces)
