Basic Anatomy and Histology Flashcards
Glomerulus (5 major components)
- Vascular pole = Afferent arteriole –> capillary (large fenestrae) –> efferent arteriole (portal system)
- Urinary pole - where proximal tubule begins
- Bowman’s Capsule
- Visceral epithelium surrounds caps (simple squamous)
- Parietal epithelium makes up outer wall of urinary space (cont w/ proximal tubule)
- Glomerular basement membrane - collagen type IV (mesh-like web) that limits filter size (keep proteins out) & include laminins (linkers) & sulfate-rich, neg-charged glycoproteins (neg filter)
- Mesangial Cells (support capillaries)
- Some smooth-muscle like = contractile, sensitive to angio-II, make ECM, make PGE for vasodilation
- Macrophages = phag anything that is opsonized or coated in antibody; MHC-II so can be APCs
What are the 3 glomerular filtration barriers?
1- fenestrated endothelium of capillary
2- glomerular BM (sulfates, laminin, mesh)
3- foot processes/pedicels w/ slits b/n
Podocytes (what do they do? how are their processes organized?)
- Along basement membrane of glomerulus
- Podocytes also make VEGF
- Have individual processes called pedicels w/ filtration slit diaphragms between pedicels
- Nephrin is linked to pedicels - linkage proteins (podocin, ZO-1, alpha-actinin4) - actin anchor
- Pedicels coated in neg glycoproteins (contribute to overall neg charged filter)
Proximal Tubule Basics
(REABSORPTION WORKHORSE)
- Only place w/ transporters for glucose, AA, citrate, small peptides
- ISOMOTIC; so Osm of filtrate coming in is same as Osm of filtrate going out; water and ions/proteins leave in equal proportions
- Apical - Simple cuboidal epithelium w/ single, central nucleus and tall brush border (microvilli) - SA for mult transporters on surface
- Less tight junctions and claudin –> leaky epithelium for water b/n cells and in aquaporins
- Apical endocytic apparatus - vesicles so recover small proteins that were filtered out (blocked by statins)
- Basolateral - active Na/K pumps to maintain Na gradient to power other active transport (accompanied by mitochondria)
Megalin
- Specific endocytosis receptor on proximal tubule apical membrane
- down-regulated by TGF-beta in inflammation (proteinuria)
Loop of Henle (compare 3 main segments)
- Thin descending (simple squamous) - water permeable/salt impermeable
- Thin ascending (simple squamous)- water impermeable/salt permeable (claudin tight junct & no aquaporins)
- TAL (thick = cuboidal)- also water impermeable/sale permeable (“diluting segment”)
- Only part of loop w/ ACTIVE transport (Na-K on basolateral; Na-Ca-2Cl symporter on apical)
- Result = makes hypertonic interstitium and yield hypotonic tubular fluid to distal tubule
- Contains macula densa
Distal Tubule (+ 3 major pumps)
(fine-tuning - in cortex)
- Cuboidal epithelium w/ no microvilli so smooth lumen
- Still impermeable to water (sealed w/ claudins)
1- Basolateral - Na-K pump and mitochondria provides energy for following hormone-reg pumps…
2-Basolateral parathyroid-sensitive Na/Ca antiporter
3-Apical thiazide-sensitive symporter to reclaim Ca
Collecting Duct (+ 2 cell types)
- Controlled by vasopressin, aldosterone to fine-tune tonicity and volume
- Simple cuboidal –> columnar –> pseudostratified
- 1- Principle/light cells - HORMONE regulation
- Aldosterone –> reabsorb Na+ an secrete K+
- Vasopressin –> inc permeability of lumen to water (new water channels) - 2- Intercalated/dark cells - acid/base regulation
What is the overall goal of the juxtaglomerular apparatus? How does it achieve this (sensors and effectors)?
-Goal = Control GFR so that it does not flood the distal tubule and collecting ducts where fine-tuning occurs
- Afferent arteriole stretch receptors - sense BP
- Inc BP - constrict AA- block renin release
- Dec BP - JG cells release renin granules
- Macula Densa (end of TAL)- use Cl- sensors as a measure of amount of flow
- Low Cl flow - inc COX-2 –> PGI1 and PGE2 –> inc cAMP in JG cells –> inc renin
- Low Cl flow - inc NO –> afferent arteriole vasodilation
- High Cl flow - inc adenosine –> inc JG cell Ca++ –> JG vasoconstriction–> dec renin
Renal Interstitium (in cortex v. medulla)
- Not usually seen or noticed in histo/EM unless something wrong
- In cortex… fibroblast-like cells that can contract, make ECM components and secrete erythropoiten & phagocytic cells
- In medulla … fibroblast-like cells that can make PGE to vasodilate/inc flow & supportive cells in BM of vasa recta that act as source of stem cells to replace capillary endo cells
How is renal circulation distributed?
- Flow to outer cortex»_space; inner cortex»_space; medulla (5-10%)
- So medulla vulnerable to ischemia
- If hypovolemic state - divert flow to inner areas
Basic Renal Circulation Circuit
- Renal arteries –> interlobar arteries –> arcuate arteries (divide cortex and medulla) –> interlobular arteries (b/n lobules or medullary rays) –> afferent arterioles –> glomerular capillary –> efferent arterioles
Efferent arterioles –> 1 of 2 cap networks
- If superficial - peritubular capillary plexus forms to assimilate reabsorbed material
- If juxtamedullary - vasa recta (series of straight capillaries in medulla) - Both of these capillary networks –> arcuate veins –> intra-lobar veins –> renal veins
What is a renal lobule?
Medullary ray (straight prox, TAL, collecting duct) from give glomerulus that all travel together from cortex to/from medulla
