Renal microanatomy Flashcards
1
Q
Parts of nephron and their location in the kidney
A
- Glomerulus and proximal tubule are both in the cortex
- Loop of henle (descending, thin ascending and thick ascending) in medulla
- Macula densa, distal tubule and cortical collecting tubule in the cortex
- Medullary connecting tubule and collecting duct in medulla
2
Q
Renal corpuscle and flow of filtrate
A
- Bowman’s capsule + glomerulus, glomerulus supplied by capillaries that are btwn afferent and efferent arteriole
- Proximal convoluted tubule extends from glomerulus to eventually become LOH
- LOH terminates at the MD and then tubule becomes distal tubule, which turns into collecting system
3
Q
Blood supply
A
- Renal arteries-> interlobar arteries (btwn pyramids)-> arcuate arteries (perpendicular to pyramids)
- Arcuate arteries give off cortico-radial arteries which travel parallel to a pyramid on both sides to feed the two pyramids adjacent to it
- Cortico-radial arteries give off afferent arterioles which form capillary beds in the glom and blood exits thru efferent arterioles
- Efferent arterioles become peritubular capillaries of the cortex and the vasa recta
4
Q
Supplying blood to different regions of the nephron
A
- Glomerular capillaries only for filtration, O2 and nutrients supplied by cortico-radial arteries and vasa recta
- 90% of nephrons are mostly in the cortex, so they are supplied by cortico-radial arteries for nutrients
- But juxtamedullary nephrons (those w/ glomeruli near the medullar/cortical junction) are supplied by vasa recta
- Some of the LOH and collecting systems in normal nephrons are also supplied by vasa recta
5
Q
Vasa recta vs glomerular capillaries
A
- Glomerular capillaries is high pressure (btwn two arterioles) and vasa recta is low pressure
- Ascending vasa recta has fenestrated capillaries, descending vasa recta is continuous capillaries
- Vasa recta helps establish counter current exchange system
6
Q
Functions of various parts of nephron
A
- Proximal tubule: reabsorption
- LOH: thin segment permeable to Na and H2O, thick (TAL) pumps Na but impermeable to H2O (counter current system)
- Distal tubule: pumps Na, responds to aldo
- Collecting tubules: H20 permeable (responds to ADH), Na pumps (respond to aldo)
7
Q
Glomerular barrier for filtration
A
- 3 layers, from in to out (direction of fluid flow):
- Endothelial layer, not continuous, excludes based on charge
- Basal lamina layer, continuous, excludes based on charge and size
- Podocyte spaces/slit diaphragm: spaces btwn the feet of podocytes (visceral layer of bowman’s capsule) filled in w/ protein nephrin
- Nephrin over laps w/ other nephrin molecules to create a sieve, filters based on size
8
Q
Overview of glomerulus
A
- Located in cortex
- Afferent arteriole most important for controlling resistance
- 3 layers to filtration/glomerulus, the last being the podocyte/slit diaphragm
9
Q
Proximal tubule
A
- Longest part of nephron, contains a brush border and microvilli for endocytotic mechanisms
- Tight junctions present btwn epithelial cells that can be changed to alter permeability
- Basal surface infoldings, baso-lateral membrane w/ abundant Na/K ATPase activity (lots of mito)
- Capillaries (fenestrated) very close to epithelia
- Capillary hydrostatic pressure low, oncotic pressure high (albumin) to facilitate reabsorption
10
Q
Loop of Henle
A
- Establishes and maintains counter current system: Na reabsorbed from TAL (thick ascending) enters ISF btwn the two limbs (ascending and descending)
- The Na gradient in the ISF stimulates H2O reabsorption from the descending limb
- Na also reabsorbed in descending limb, but mainly TAL
- TAL is impermeable to H2O to maintain this system
- Descending limb: no active transport (freely permeable to H20 and Na)
- TAL: not permeable, but does actively transport Na across membrane
- TAL is “diluting segment” since the osmolality is lowest form pumping out Na and keeping H2O
11
Q
Distal tubule
A
- Structurally identical to LOH, but different in that it is permeable to H2O (still actively pumps Na)
- Main action site of aldo and ADH
- Aldosterone will stimulate Na reabsorption
- ADH will stimulate H2O reabsorption (by increasing AQP)
12
Q
Collecting tubules
A
- Dominant cell is principal/light cells
- These cells have a single motile cilium on luminal surface and are responsible for NaCl reabsorption and adjustments of H2O reabsorption
- Dark cells/intercalated cells are also found and specialize in acid-base balance by using H+ transporters
- Main jobs of collecting tubules: conducts urine into calyces, modifies urine to final adjustments in Na and H2O retention
13
Q
Role of primary cilia
A
- The central cilium is present on the luminal surface of all cells lining the nephron (except intercalated cells)
- They have a sensory role detecting tubular fluid flow
- Defects are associated w/ cystic kidney disease
14
Q
Hormonal influences on collecting tubule system
A
- ADH will stimulate H2O reabsorption, but it needs an osmotic gradient to do this
- The Na osmotic gradient in the medullar interstitium established by the LOH is the osmotic force behind H2O retention
- Since this gradient is always present, the amount of H2O reabsorption depends on the permeability of the collecting tubule to H2O
- ADH increase AQPII on the membranes of principal cells thus making the collecting tubules more permeable to water and increasing H2O reabsorption
- Aldosterone acts mostly on cortical collecting tubules to stimulate Na pumping and Na reabsorption
15
Q
Juxtaglomerular apparatus (JGA) and macula densa (MD) 1
A
- Juxtaglomerular cells are modified SMCs within the media of the afferent arteriole that secrete renin (store in granules)
- Macula densa: cell plaque at the end of the TAL associated w/ the JG cells (final portion of TAL located btwn afferent and efferent arterioles)
- MDCs detect NaCl movement thru the apical membrane (using NKCC) to modify renin release from JG cells
- When NKCC activity is low (not enough NaCl making it to the MD- indicating a low NaCl in plasma and low ECF) the MD stimulates JG cells to release renin to increase NaCl/H2O reabsorption and increase ECF
