Renal Hist Flashcards
What projects out of the hilum of the kidney?
Ureter
What are the two zones of the kidney?
Outer - Cortex
Inner - Medulla
What is located at the border between the medulla and cortex?
The arcuate vessels (they form the boundary)
How many nephrons are in each kidney?
Between 0.3 and 1.5 million
What is located on the outside of the kidney?
Thin connective tissue capsule
What is located in the cortex?
- Blood vessels
- Tubules
- Renal corpuscles
Where are the vessels located in the cortex?
They are jammed in between the tubules and the corpuscles. It is a highly vascularised structure
Where are the renal corpuscles located?
All of them are in the cortex
Where does part does the tubule follow?
The first part always runs in the cortex (it is usually quite a tortuous path) it then turns and runs into the medulla (loop of Henle) before turning and upwards and returning to the cortex and eventually connecting to the collecting duct
What are the two types of nephrons?
- Juxta medullary
2. Cortical
What is distinctive about the juxta medullary corpuscle?
The renal corpuscle is very close to the boundary of the medulla
AND
The tubule goes the furthest down into the medulla
Percentage juxta medullary vs Cortical?
15 vs 85
What is distinctive about the cortical nephron?
More superficial renal corpuscle
Loop which descends only part way into the medulla
How much connective tissue is found in the kidney?
Very little connective tissue
It is mainly just nephrons and blood vessels packed in together as tightly as possible
What is a glomerulus?
It is a tuft of capillaries connected to an arteriole
It doesn’t penetrate into the lumen of the tubule but is rather wrapped up in it
What are the cells of the outermost layer of the corpuscle called?
The parietal layer
What are the cells of the punched in section of the corpscle called?
Podocytes
What is Bowman’s space?
A space which is continuous with the lumen of the tubule and is wrapped around the capillaries
What do mesangial cells do?
They are a little like connective tissue - they provide the mechanical tension which pulls the base of the tuft of capillaries together
Where does the ultrafiltrate accumulate?
In Bowman’s space crosses the capillaries, across the podocytes and enters into Bowman’s space
What is Bowman’s space continuous with?
The lumen of the tubule
Where are the vascular and urinary poles of the corpuscle?
180 degrees away from each other
What type of cells are the parietal cells of Bowman’s capsule?
Squamous cells
What type of cells are the tubules composed of?
Cuboidal epithelium
What do podocytes do?
They branch (a lot) Eventually they interdigitate (there are little cracks here) Much of the surface is covered by the arms and processes of the podocytes
Where is the ultra-filtrate formed?
The cracks in the interdigitations of the filtrate
Glycocalyx and slit membranes
What happens to the basal lamina of the podocytes and that of the capillary?
They fuse to form a thick basal lamina
What is the biggest molecule that is able to cross the basal lamina?
Basal lamina traps molecules above 69kD
What is in the slit membrane?
Tiny pores - only a few nm across, this also acts as a filter
Describe the steps of movement from the capillary to Bowman’s space?
Cross the fenestrations in capillary
Cross the basal lamina (less than 69kD in size)
Cross the slit membrane (3-5nm)
Enter Bowman’s space
What type of epithelium is seen in the proximal tubule?
Cuboidal epithelium
What is seen on the surface of the cuboidal epithelium?
Microvilli
What is seen at the boundaries between cells
Complex interdigitating cell boundaries.
Presumably to prevent the ultrafiltrate from entering into the intracellular space
What transporters are seen on the basal surface of the cells of the proximal tubule?
Na+K+ATPases (pumps)
What effect do the Na+K+ATPases have on the movement of Na+, Cl- and Water out of the lumen?
Na+K+ATPases move sodium out of the cell making the concentration of Na+ low.
Sodium thus moves by diffusion across the apex of the cell (down the concentration gradient) into the cytoplasm before it it pumped out.
Their is now an electrotonic imbalance and chloride follows passively.
The movement of Cl- and Na+ then drives water across the membrane as well
What is a prominent feature of cells of the proximal tubule?
They have lots of mitochondria (i.e. they require a lot of energy to perform their function)
What types of epithelial cells are seen in the loop of Henle?
Squamous cells
What is the loop of Henle permeable to?
Permeable to urea and water
Are the cells of the loop of Henle using any active processes to move water and urea?
No - it is all passive
Also the permeability changes in different regions of the loop
What type of cells make up the distal tubules?
Cuboidal cells
Are the cells of the distal tubule active?
Yes - lots of mitochondria (even more)
The concentration gradients are harder to deal with so even more energy is required to get work done
Do the cells of the distal tubule have microvilli?
No
What is recovered in the distal tubule?
Chloride and sodium
Impermeable to water and urea
What are the distinctive features of the collecting duct?
Cuboidal cells
Very large lumen
What is the function of the collecting duct normally?
It is merely a conducting tube
It is impermeable to water and urea
What happens to the collecting duct when there is body wide dehydration?
Under the action of vasopressin the wall can become permeable to water
Which nephrons can make urine more osmotically concentrated then the blood?
Only the juxtamedullary nephrons
What dos the efferent arteriole form?
A network of fine capillaries called the vasa recta
What is the role of the vasa recta?
They carry away all of the products which have been recovered from the tubule
What is seen in cross section of the medulla?
Tubules everywhere and blood vessels
• Thin and thick walled loops of Henle
• Collecting ducts
• Capillaries of vasa recta
What is the role of the ureter?
Conducts urine from kidney to bladder
What type of epithelium lines the UT after the kidney?
Transitional epithelium
It is stratified and the apical cells have a balloon like shape
What is the role of the transitional epithelium?
It is designed to keep it well away from the rest of the body - it can be a dangerous substance if it comes into contact with the rest of the body
What moves urine from the kidney to the bladder?
The ureter has a thick muscularis of smooth muscle which moves urine in peristaltic waves
Does the kidney like backpressure?
Nah it hates it :) need thus need to move urine away and do so in peristaltic waves
What lines the bladder?
Transitional epithelium
What controls the bladder?
ANS
Two modes:
Filling mode
Emptying mode
What happens in the bladder in ‘filling mode’?
Relax the smooth muscle
Constrict the sphincter
This minimises the pressure in the bladder as it fills
What happens to the bladder in ‘emptying mode’?
Smooth muscle contraction
Sphincter relaxation
Micturitional voiding
Where does the urethra penetrate?
The pelvic floor, which acts as a sphincter
What type of epithelium lines the urethra?
Initially transitional and then stratified squamous
