1 Renal Anatomy & Histology

Question 1

General functions of the kidney

• Most important
• Excretion
  
  • Responsibilities
  • Filtration
  • Reabsorption
  • Secretion
• Endocrine
• Metabolic

Answer 1

• Most important
  
  • Maintain salt & water balance (aqueous homeostasis)
• Excretion
  
  • Responsibilities
    
    • Form urine
    • Remove metabolic wastes
    • Balance internal ion concentrations
    • Eliminate exogenous substances (drugs, pesticides, & other chemicals)
  • Filtration
    
    • Passive process based on size & charge of plasma components
    • Removal of breakdown products of protein metabolism
    • Occurs in glomeruli
  • Reabsorption
    
    • Retention of essential substances (water, glucose, amino acids, sodium, bicarbonate) from the filtrate back into the blood
    • Occurs in the tubules
  • Secretion
    
    • Cellular transport into the tubular lumen of substances/drugs too large or charged to enter the filtrate of the glomerulus
      
      • Ex. penicillin, contrast dyes
    • ATP binding cassette (ABC) trasnporters shuttle lipophilic substances across tubular membranes
• Endocrine
  
  • Kidney releases secretions into circulation
  • –> systemic effects
    
    • Renin –> retain Na & water
    • Erythropoietin –> RBC maturation
  • –> local effects
    
    • Prostaglandins & kinins affect local blood flow through the kidney
• Metabolic
  
  • Peptide hormone degradation (PTH, insulin)
  • Vitamin D –> 1,25 dihydroxyvitamin D3 (active form)
  • Hypoglycemia –> gluconeogenesis
  • Citrulline –> arginine as urea cycle processes NH4
    
    • All components of the uric cycle except the last step (arginase enzyme) so citriulline –> arginine
    • Severe kidney disease: arginine –> essential amino acid

Question 2

Light microscopy

• H&E
• PAS
• Mallory’s trichrome stain
• Silver stain

Answer 2

• H&E
  
  • Highlights overall kidney morphology (rare)
• PAS
  
  • Highlights thickness of basement membrane & ECM
  • Bright pink = proteoglycans / carbohydrates
• Mallory’s trichrome stain
  
  • Highlights degree of collagen deposits in interstitial matrix
  • Blue = collagen I (& II & III)
• Silver stain
  
  • Highlights fine collagen III in the matrix
  • Black = collagen III (reticulin fibers)

Question 3

Electron & immunofluorescence microscopy

Answer 3

• EM
  
  • Ultrasound that looks at the glomerular filtration membrane
  • For diagnosis (esp glomerular disorders)
• IM
  
  • Antibodies labeled w/ fluorescein bind to immunoglobulins (ex. IgG, IgA), C3, or C4 which may accumulate in certain renal pathologies
  • IM visualizes the locaiton of these molecules

Question 4

Renal biopsy

Answer 4

• 4 phsycial elements / histological areas examined for involvement in disease processes
  
  • GLomeruli
  • Tubules
  • Interstitium
  • Blood vessels
• Visible interstitium –> too much (normally souldn’t see)
• Enlarged blood vessels –> renal vascular disease

Question 5

Gross histology (A-Q)

Answer 5

• A: Capsule
  
  • Thick, strong, w/ capsular veins
• B: Hilus
  
  • Blood vessel entrance/exit
  • Ureter exit
• C: Renal artery & vein
• D: Cortex (outer)
  
  • W/ glomeruli & tubules
  • Darker reddish brown due to richer blood supply
• E: Medulla (inner)
  
  • W/ straight tubules
  • Shaded zones due to thickness of tubules
• F: Medullary rays
  
  • Bundles of straight tubules in cortex which travel to & from the medulla (not part of the medulla)
• G: Medullary pyramids
  
  • Conical shaped w/ their apex toward the renal hilus
  • Lighter & striated appearance
• H: Renal papilla
  
  • Apex of the renal pyramid
• I: Renal lobes
  
  • Medullary pyramid + cap of cortex (8-14 in humans)
  • Interlobar arteries
• J: Renal lobules
  
  • Medullary ray + associated nephrons
  • Interolobular arteries
• K: Minor calyx (8-14)
  
  • Receives tips of each medullary lobe
• L: Major calyx (3-4)
  
  • Receives tips of minor calyces
  • Empties into the renal pelvis
• M: Renal pelvis
  
  • Continuous w/ ureter
  • Once urine gets here, we lose the capacity to make alterations to the urine
• N: Nephron
• O: Interlobular artery
• P: Arcuate artery
• Q: Ureter

Question 6

Nephron

• Bowman’s capsule
• Proximal tubule
• Thin limbs of the loop of henle (descending & ascending)
• Thick ascending limb of the loop of henle
• Distal convoluted tubule
• Collecting duct
• Number of nephrons
• Classification

Answer 6

• Bowman’s capsule
  
  • ​Associated w/ the glomerulus (a tuft of capillaries) –> filtration
• Proximal tubule
  
  • Integrated w/ peritubular capillaries –> reabsorption & secretion
• Thin descending, thin ascending & thick ascending limbs of the loop of henle
  
  • Interaction w/ surrounding vasa recta –> hypertonic interstitium for altering the tonicity of excreted urine
• Distal convoluted tubule
  
  • Integrated w/ peritubular capillaries for reabsorption & secretion
• Collecting duct
  
  • Close association w/ the vasa recta –> final assimilation of water & ions from the urine back to the blood
• Number of nephrons
  
  • ~1 million per kidney
• Classification
  
  • Based on the location of the glomerulus (filtration unit)
    
    • Superficial: outside
    • Juxtamedullary: inside (near the medulla)
    • Midcortical: in between
  • Based on the length of the loop of henle
    
    • Short loop: superficial
    • Long loop: juxtamedullary

Question 7

Glomerulus

• Function
• Location
• Components
• Vascular pole
• Urinary pole
• CO, filtrate, & excreted urine

Answer 7

• Function
  
  • Filtration unit of the kidney
  • aka renal corpuscle
• Location
  
  • Cortex
  • Surrounded by coiled tubules
  • B/n medullary rays
• Components
  
  • Blood vessels (glomerular capillaries)
  • Epithelium of the nephron tube (bowman’s capsule)
  • Intervening basement membrane b/n the endothelial layer of capillary & bowman’s capsule
  • Stalk of intraglomerular support cells (mesangial cells)
• Vascular pole
  
  • Entering afferent arteirole & exiting efferent arteriole cluster here
• Urinary pole
  
  • Continuation of the nephron tubule exits the glomerulus here
• CO, filtrate, & excreted urine
  
  • ~20% of blood volume leaving the heart (CO) is filtered through the kidney (1 L/min of the total CO of 5 L/min)
  • Kidneys produce 180 L of filtrate / day but only excrete 1-2 L urine / day

Question 8

Glomerulus: blood vessels

• Afferent arteriole
• Capillary endothelium
• Efferent arteriole
• Both arterioles
• Portal system

Answer 8

• Afferent arteriole
  
  • Incoming, larger
  • Branches to form a tuft of glomerular capillaries where filtration ocurs
• Capillary endothelium
  
  • Fenestrated w/ no diaphragms spanning the pores
    
    • Capillaries are riddled w/ holes in endothelial cells
    • Gaps keep cellular elements out but can let large proteins in based on damage
  • Patent capillary loops: histological landmark where filtration occurs
• Efferent arteriole
  
  • Outgoing, smaller
  • Formed from merged glomerular capillaries
• Both arterioles
  
  • Surrounded by smooth muscle that contracts & relaxes to affect filtration pressure in the glomerular capillaries
• Portal system
  
  • 2 capillary beds + 1 loop of circulation
  • Occurs in the liver, kidney, & pituitary

Question 9

Glomerulus: bowman’s capsule

• General
• Parietal epithelium
• Visceral epithelium
• Vascular pole
• Urinary pole

Answer 9

• General
  
  • Blind beginning of tne nephron tube
  • Bulbous expansion
• Parietal epithelium (outermost)
  
  • Simple squamous epithelium
  • Forms the outer wall of the urinray space
  • Where provisional urine accumulates
• Visceral epithelium (innermost)
  
  • Reflects over the glomerular tuft of capillaries
  • Coats capillaries
• Vascular pole
  
  • Parietal epithelium is continuous w/ the visceral epithelium
  • Where incoming afferent arterioles, capillaries, & efferent arterioles exist
• Urinary pole
  
  • Parietal epithelium is continuous w/ the proximal tubule
  • Where extra filtrate exits

Question 10

Glomerulus: podocytes

• General
• Foot processes (pedicels)
• Filtration slit diaphragm
• Nephrin
• Intracellular linkage molecules
• Minimal change disease

Answer 10

• General
  
  • Specialized cells that form the visceral epithelium of bowman’s capsule that covers glomerular capillaries
  • 2 podocyte cells coat capillaries
• Foot processes (pedicels)
  
  • Formed by podocyte processes or trabeculae interdigitating w/ processes from neighboring podocytes
  • Coated w/ podocalyxin (a glycoprotein rich in negatively charged sialic acid)
    
    • Provides repulsion b/n adjacent podocytes
  • Spacing is essential for proper glomreular filtration
    
    • Fusion of adjacent pedicles only occurs in pathologcial states
• Filtration slit diaphragm
  
  • Specialized juncitonal complex that spans spaces b/n foot processes
• Nehprin
  
  • Transmembrane protein of the immunoglobulin superfamily (ex. cadherins)
  • Forms homodimers to link neighboring foot processes
  • Maintains podocyte integrity to regulate filtration
  • Ca depending binding
  • Actin: fibers that nephrins connect to
• Intracellular linkage molecules
  
  • Interface b/n nephrin & actin cytoskeleton
  • Ex. ZO-1, alpha-actinin4, podocin
• Minimal change disease
  
  • 3 hallmarks: diffuse loss podocyte foot processes, vacuoles, microvilli
  • Foot process fusion

Question 11

Glomerulus: basement membrane

• General
• 3 layers
• Interna & externa
• Diabetes

Answer 11

• General
  
  • 320-33 nm thick
  • Lies b/n the glomerular capillary endothelium & the podocyte foot processes
• 3 layers
  
  • Lamina rara externa: contacts glomerular podocytes
  • Lamina densa: central dense layer
    
    • Collagen IV limits porosity of the BM to small substances
    • Some albumin can get through (anything smaller: yes, anything larger: no)
  • Lamina rara interna: contacts capillayr endothelium
• Interna & externa
  
  • Contain anchoring proteins laminin & fibronectin + heparan sulfate-rich anionic proteoglycans
    
    • Laminin: linker molecule b/n collagen, proteoglycans, & integrins found in all layers except right underneath filtration slit membranes
  • Repel negativley charged plasma proteins (anions)
  • Allow positivley charged proteins (cations) to pass through more easily
• Diabetes
  
  • Decrease in BM heparan –> proteinuria

Question 12

Glomerulus: filtration barrier

• 3 layers that comprise the glomerular filtration barrier
• Factors that determine glomerular filtration rate (GFR) through these layers
• Histological structures that fine tune GFR

Answer 12

• 3 layers that comprise the glomerular filtration barrier
  
  • Fenestrated endothelium
  • Glomerular basement membrane
  • Foot processes w/ filtration-slit diaphragm
• Factors that determine glomerular filtration rate (GFR) through these layers
  
  • Hydrostatic pressure: BP within the glomerular capillaries
  • Oncotic pressure: created by plasma proteins
• Histological structures that fine tune GFR
  
  • Smooth muscle in the media of afferent & efferent arterioles
  • Contractile intraglomerular mesangial cells

Question 13

Glomerulus: intraglomerular mesangial cells

• General
• Smooth muscle-like mesangial cells
• Bone marrow-derived macrophages
• Glomerular sclerosis

Answer 13

• General
  
  • Connective tissue cells that support the tuft of capillaries
• Smooth muscle-like mesangial cells
  
  • Contractile (express alpha-actin) –> decreaes surface area for filtration
  • Sensitive to AII –> constrict cells –> limit area for filtration
  • Synthesize & degrade extracellular matrix components
    
    • Collagen: mainly IV & V, more I & III when activated by cytokines
    • Fibrinonectin, thrombospondin, laminin, vitronectin, proteoglycans
  • Synthesize enzymes for turnover of ECM
    
    • Metalloproteinases, serine-proteinases
  • Secrete prostaglandins –> vasodilate glomerular arterioles –> counteract AII
  • Secrete & sensitive to hormones, cytokines, growth factors, & paracrine agents
• Bone marrow-derived macrophages
  
  • Phagocytose apoptotic cells in the basement membrane
    
    • Utilize C3b or Fc receptors to bind opsonized particles
  • Express MHC class II antigens –> act as antigen presenting cells
• Glomerular sclerosis
  
  • Normal glomeruli: minimal intraglomerular mesangial CT
  • Glomerular sclerosis: increased mesangial expansion at the expsne of open capillary loops

Question 14

Proximal tubule

• General
• Osmoticity of absorption
• Physiological segments
• Anatomical segments

Answer 14

• General
  
  • First portion after leaving bowman’s capsule
  • Reabsorptive workhorse
  • Reabsorbs…
    
    • All gluocse, amino acids, citrate, & small peptides
    • Most water, Na, K, bicarbonate, Ca, & PO4
• Osmoticity of absorption
  
  • Isomotic: absorptoin of solutes is proportional to that of water
  • For any solute that is reclaimed, water can come w/ it
• Physiological segments
  
  • Based on the distribution of transporters: S1, S2, & S3
• Anatomical segments
  
  • Proximal convoluted tubules: coil & occupy most of hte cortex around glomeruli
  • Proximal straight tubules
    
    • In the cortex: in a medullary ray
    • In the medulla: by itself

Question 15

Proximal tubule: histology

• Lining
• Lumen
• Peritubular capillaries

Answer 15

• Lining
  
  • Simple cuboidal epithelium w/ a large, central, prominent nucleus
• Lumen
  
  • Collapsed & star-shaped w/ fuzzy edges
• Peritubular capillaries
  
  • Carmmed into spaces b/n tubules

Question 16

Proximal tubule: apical plasma membrane

• Brush border
• Apical tight junctions & desmosomes
• Junctional complexes
• Claudins
• Aquaporins
• Megalin

Answer 16

• Brush border
  
  • Tall, regular microvili that increase surface area
  • Carriers are inserted for secondary active transport of reabsorbed amino acids, glucose, citrate, & bicarbonate
  • Molecules are coupled w/ Na in positively charged carrier complexes
• Apical tight junctions & desmosomes
  
  • Tight junctions aka zonula occludens
  • Less frequent & thinner than in other tissues
• Junctional complexes
  
  • Provide large pores for water to go through freely
• Claudins
  
  • Create leaky epithelium in tight junctions to permit paracellular movement of water & Ca from the lumen to the interstitial space below the epithelium
• Aquaporins
  
  • Water channels for water to move through the apical membrane
• Megalin
  
  • Wedge of small vesicles w/ different shapes & sizes
  • Clathrin-mediated receptor anaglogous to the LDL receptor
  • Binds to amino acids & small peptides to clear small peptides

Question 17

Proximal tubule: apical cytoplasm

• Endocytic apparatus
• Megalin
• Inhibition

Answer 17

• Endocytic apparatus
  
  • Consists of vesicular invaginations b/n the bases of microvilli, clathrin coated vesicles, large vacuoles, lysosomes, & condensing vacuoles
  • Here, peptides from teh filtrate are endocytosed & degraded before release outside the basolateral aspect of the cells
• Megalin
  
  • Specific endocytosis receptor for albumin & small proteins recovered in the proximal tubule
    
    • Clathrin-mediated receptor analogous to the LDL receptor
  • Wedge of small vesicles w/ different shapes & sizes
  • Binds to amino acids & small peptides to clear small peptides
• Inhibition
  
  • TGF-beta downregulates meglain during inflammatory conditions contributing to proteinuria
  • Inhibitors of 3-hydroxy-3 methylglutary-CoA (statins) also inhibit this & endocytosis & can contribue to proteinuria

Question 18

Proximal tubule: basolateral plasma membrane

• Na/K ATPase
• Mitochrondia

Answer 18

• Na/K ATPase
  
  • Extensive folding provides surface area for Na/K ATPase transporters
  • Na/K ATPase pumps Na out of the cell & into the basolateral extracellular space
  • Na electrochemical gradient powers secondary active transport at the apical border
• Cytoplasmic mitochondria
  
  • Occupy folds b/n basolateral invaginations providing ATP for the energy demands of active transport

Question 19

Loop of henle

• 4 portions
• Length
• Interstitium tonicity

Answer 19

• 4 portions
  
  • Thin descending limb
  • Thin ascending limb
  • Medullary thick ascending limb
  • Cortical thick ascending limb
• Length
  
  • Varies w/ location
  • Short loops: superficial glomeruli
  • Long loops: juxtamedullary glomeruli
    
    • Extend to the tips of the medullary papillae
• Interstitium tonicity
  
  • long LOHs establish a hypertonic interstitium in the medulla to produce hypertonic urine
  • Countercurrent exchange b/n the tubules & vasa recta establishes & maintains the hypertonic interstitium
  • 13% of nephrons contain long LOHs to produce hypertonic urine

Question 20

Loop of henle: thin descending limb

• General
• Permeability
• Water movement
• Tubular fluid

Answer 20

• General
  
  • Simple squamous epithelium
  • Variations in the # of interdigitations & mitochondria
• Permeability
  
  • Permeable to water & urea (passive process)
  • Impermeable to Na & Cl
• Water movement
  
  • Water & urea passively move from the tubular fluid into the interstitium as the thin limb descends into the hypertonic interstitium of the medulla
  • Water moves paracellular through shallow tight junctions & intracellularly through aquaporin channels
• Tubular fluid
  
  • In equilibrium w/ interstitial mileu throughout its descent

Question 21

Loop of henle: thin ascending limb

• Main function
• Permeability
• Salt movement
• Water movement
• Active transport of Na or Cl

Answer 21

• Main function
  
  • maintain & stabilize the hyperotnic gradient of the medullary interstitium
• Permeability
  
  • Permeable to Na & Cl (passive process)
  • Impermeable to water
• Salt movement
  
  • Salt exits the tubule as flow ascends into less hypertonic regions of the medulla
• Water movement
  
  • Water movement is prevented by more extensive tight junctions w/ claudins that seal & the lack of aquaporins
• Active transport of Na or Cl
  
  • No active transport of Na or Cl anywhere laong the thin limb of the LOH

Question 22

Loop of henle: thick ascending loop (TAL)

• Location
• Tonicity
• Basolateral plasma membrane
• Mitochondria
• Apical plasma membrane
• Net result
• Inhibition

Answer 22

• Location
  
  • Near the hairpin turn in short looped nephrons
  • At the transition from the outer to inner medullayr zones in long looped nephrons
• Tonicity
  
  • TAL aka diluting segment b/c the lumenal contents are hypotonic when they exit
• Basolateral plasma membrane
  
  • Simple cuboidal epithelium displays numerous invaginations
  • Folds extend almost to the apical end of TAL cells
  • Site of Na/K ATPase active transport pumps
• Mitochondria
  
  • Contained within cytoplasm b/n the folds
  • More round than the elongated ones of the proximal tubule
• Apical plasma membrane
  
  • Slightly irregular
  • Contains a Na/K/2Cl symporter
  • Extensive tight junctions block the paracellular movement of water
  • No aquaporin channels –> impermeable to water
  • Claudins permid passage of Mg, Ca, & Na
• Net result
  
  • Movement of Na & Cl from the lumen into the interstitium
  • Ion pumping produces the hypertonic medulary interstitium & delivers hypotonic, dilute tubular fluid to the distal convoluted tubule
• Inhibition
  
  • Loop diuretics (ex. furosemide) inhibit the apical co-transporter

Question 23

Loop of henle: macula densa

Answer 23

• Last segment of the cortical TAL
• Each macula densa returns to its glomerulus of origin
• Component of the juxtaglomerular apparatus that’s responsible for renin secretion

Question 24

Distal convoluted tubule

• Location
• Length, lining, coiling, & tight junctions vs. proximal tubules
• Apical surface
• Basolateral surface
• Response to aldosterone & parathyroid hormone (PTH)

Answer 24

• Location
  
  • In the cortex intermingled w/ the proximal convoluted tubules
• Length, lining, coiling, & tight junctions vs. proximal tubules
  
  • Length: shorter w/ fewer sections per area
  • Lining: lower cuboidal epithelium
  • Coiling: not as much b/c doesn’t do as much work
  • Tight junctions: broader w/ sealing claudins to prevent paracellular water movement
• Apical surface
  
  • Devoid of microvilli –> smooth lumen
• Basolateral surface
  
  • Highly folded w/ Na/K ATPase pumps & mitochondria
  • Pumps drive reabsorption of Na & Cl
• Response to aldosterone & parathyroid hormone (PTH)
  
  • Aldosterone: reabsorb Na
  • PTH: reabsorb Ca

Question 25

Collecting duct

• 3 segments
• Function
• Under the control of…
• Lining
• Principal (light) cells
• Intercalated (dark) cells

Answer 25

• 3 segments
  
  • Connecting segment
  • Cortical collecting duct
  • Medullary collecting duct
• Function
  
  • Final adjustments to volume & tonicity of excreted urine
• Under the control of…
  
  • Vasopressin (antidiuretic hormone, ADH)
  • Aldosterone
• Lining
  
  • Initially: simple cuboidal epithelium
  • Toward the medullary papilla: tall, columnar, & pseudostratified at the exiting papillary ducts
  • Full length: distinct lateral cell borders
• Principal (light) cells
  
  • Pale cytoplasm, small random mitochondria, few basal infoldings, few microvilli, & a single cilium
  • Cilium: flow sensor linked to a Ca channel
  • Response to aldosterone: reabsorb Na & secrete K
  • Response to ADH: increase luminal permeability to wtaer
• Intercalated (dark) cells
  
  • More electron dense
  • Secrete H for acid/base balance & urine acidification

Question 26

Juxtaglomerular apparatus

• Where it fits in w/ the other parts of the nephron
• Function
• Structures
• Sensors

Answer 26

• Where it fits in w/ the other parts of the nephron
  
  • Proximally: reabsorb filtrate
  • Distally: fine-tuning
  • In b/n: juxtaglomerular apparatus provides feedback about what the nephron is doing
• Function
  
  • Control GFR to not flood out the capacity of the distal nephron
  • Prevents excessive salt & water loss
  • Adjusts renal hemodynamics during increased or decreased perfusion
  • Activates renin, AII, & aldosterone
• Structures
  
  • Afferent arteriole
  • Efferent arteriole
  • Macula densa
  • Extraglomerular mesangial cells
• Sensors
  
  • Afferent arteriole stretch receptors
  • Macula densa Cl/osmolality receptors

Question 27

Juxtaglomerular apparatus: juxtaglomerular (JG) cells in the afferent arteriole

Answer 27

• Specialized cells that comprise smooth muscle in the media
• Contain intracellular actin, myosin, dense bodies, RER, golgi, & secretory vesicles
• Decrease BP –> decrease arteriorlar stretch –> JG cells secrete renin
• Increase BP –> JG cells vasoconstrict the AffA

Question 28

Juxtaglomerular apparatus: macula densa

• Location
• Base
• Nuclei
• Response to flow related alterations in levels of Cl (osmolality) in the fluid being delivered from the thick ascending limb

Answer 28

• Location
  
  • Where the cortical thick ascending limb returns to its glomerulus of origin
• Base
  
  • Interdigitate w/ underlying extraglomerular mesangial cells & JG cells
• Nuclei
  
  • Forced apically toward the luemn
• Response to flow related alterations in levels of Cl (osmolality) in the fluid being delivered from the thick ascending limb
  
  • High Cl flow rates –> high glomerular perfusion rate –> macula densa releases adenosine & NO (directly) & AII & thromboxane (indirectly) –> blocks JG cell renin release

Question 29

Juxtaglomerular apparatus: extraglomerular mesangial cells

Answer 29

• Lie b/n the AffA & EffA, macula densa, & glomerulus
• Interact w/ macula densa & JG cells
• Regulate renin secretion & vasoconstriction

Question 30

Juxtaglomerular apparatus: efferent arteriole

Answer 30

• EffA smooth muscle contraction increases hydrostatic pressure within the glomerulus
• Low pressure/flow: AII–> EffA constriction –> preserve GFR
• High pressure/flow: local synthesis of prostaglandins –> EffA vasodilation –> preserve blood flow to medulla

Question 31

Renal interstitium

• General
• Cortex
• Medulla
  
  • Type I
  • Type II
  • Type III

Answer 31

• General
  
  • Minor component of connective tissue cells b/n tubular & vascular elements of the kidney
• Cortex
  
  • Fibroblast-like interstitial cells
    
    • Secrete ECM & contain contractile filaments
    • May secrete erythropoietin
  • Phagocytic interstitial cells
    
    • Derived from monocytes
• Medulla
  
  • Type I interstitial cells
    
    • Fbroblast-like w/ lipid droplets, SER, & mitochondria w/ vesicular cristae
    • Site of prostaglandin synthesis to maintain blood flow in the medulla
  • Type II interstitial cells
    
    • Rounded cells w/ free ribosomes & lysosomes but no lipid droplets
  • Type III interstitial cells
    
    • Similar to pericytes, found in the BM of the vasa recta
    • Source of regenerative cells to support the wall when secreting new endothelial cells

Question 32

Renal circulation

• Distribution of blood flow
• Ischemia
• Hypovolemic states

Answer 32

• Asymmetrical distribution of blood flow
  
  • 80% –> outer cortex (where 85% of glomeruli are located)
  • 10-15% –> inner cortex (where 15% of glomeruli & juxtamedullary nephrons are located)
  • 5-10% –> medulla
• Ischemia
  
  • Greater risk to low flow areas
• Hypovolemic states
  
  • Blood flow from the outer cortex is diverted to the inner cortex

Question 33

Renal circulation pathway

Answer 33

1. Renal artery
2. Interlobar artery
   
   • Located b/n renal lobes
   • Branch from renal arteries at the base of the medullary pyramids
   • Penetrate the medulla b/n renal lobes
3. Arcuate arteries
   
   • Flow along the junction b/n cortex & medulla
   • Don’t anastomose (each is responsible for supplying a specific portion of cortex)
4. Interlobular arteries
   
   • Located b/n lobules
   • Arise from the arcuate & penetrate the cortex b/n medullary rays
   • Give rise to AffAs directly or to short intralobular arteries first
5. Intralobular arteries (sometimes)
6. Afferent arterioles
   
   • Come off intralobulra arteries & go to glomeruli
7. Glomerular capillaries (capillary tufts)
   
   • Superficial glomeruli –> peritubular capillary plexus to assimilate reabsorbed materials
   • Juxtamedullary glomeruli –> vasa recta –> medulla to accompany LOH to the papillary tips
8. Efferent arterioles
9. 2nd capillary bed
   
   • Follows its nephron of origin
   • Superficial nephron –> short LOH –> peritubular capillaries
   • Juxtamedullary nephron –> long LOH –> vasa recta
10. Arcuate veins
11. Interlobar veins (sometimes)
12. Renal vein
    
    • Exits renal pelvis

Question 34

Summary

• Bowman’s capsule
• Proximal tubule
• LOH
• Distal convoluted tubule
• Collecting duct
• Internal regulation/feedback

Answer 34

• Bowman’s capsule
  
  • Glomerular capillaries
• Proximal tubule
  
  • Peritubular capillaries b/n proximal tubules
• LOH
  
  • Vasa recta
• Distal convoluted tubule
  
  • Peritubular capillaries
• Collecting duct
  
  • Vasa recta in the inner medulla
• Internal regulation/feedback
  
  • Afferent arteriole
  • Macula densa