Glomerular Filtration I Flashcards
What are the two types of glomerular mesangial cells and their functions?
Phagocytic - keeps glomerular membranes clean and functional
Nonphagocytic - functions as a contractile cell to regulate the surface area for filtration
What are the three layers of the glomerular membrane?
Endothelium - fenestrated capillary freely permeable even to large molecules
Basement membrane - Barrier to large proteins and lipids
Epithelium - composed of specialized cells called podocytes that form filtratio slits
What is glomerulonephritis?
Renal disease with bilateral inflammatory changes in the glomeruli
Characterized by decreased urine production, presence of blood and protein in urine, and edema
What is nephrotic syndrome?
Nonspecific disorder
Severe proteinuria, hypoalbuminemia, hyperlipidemia, generalized edema
Caused by various disorders that damage the glomeruli
What are the slit diaphragm proteins?
Nephrin, NEPH-1, P-Cad, FAT, Podocin
Mutations in encoding genes can cause nephrotic syndrome
What is nephritic syndrome?
Clinical syndrome characterized by:
Edema, Hypertension, Hematuria
Elevated serum creatinine, Azotemia, Oliguria
What is the structure of the tubule?
Made up of a single layer of epithelial cells with tight junctions between adjacent cells
What is the structure of the proximal tubule and its functions?
Connected to Bowman’s Capsule
Major site of reabsorption of filtered fluid
Apical membrane has extensive, non-motile brush border
Basolateral membrane consists of multiple infoldings and lined with mitochondria
Interdigitation with neighboring cells not tight, allows for large lateral intercellular spaces or channels
What is the structure and function of Henle’s loop?
Hairpin loop that allows fluid in the descending and ascending portions to influence each other
Configuration results in countercurrent direction of flow of the tubular fluid
Loops are close together and can influence electrolyte and water transport
What is the structure and function of the distal tubule?
Returns to cortex and makes contact with the afferent and efferent arterioles of the parent renal corpuscle
Site of the juxtaglomerular apparatus (JGA)
Shorter than the proximal tubule
What are the three cell types of the juxtaglomerular apparatus?
Macula densa cells
Granular cells
Extraglomerular mesangial cells
What are macula densa cells?
Specialized epithelial cells in the thick ascending limb of the loop of Henle/early distal tubule
Provide information on flow, volume, or NaCl concentration of tubular fluid to the JGA
Interdigitate with the other two cell types of the JGA
What are granular cells?
Differentiated smooth muscle cells in the walls of the afferent (predominantly) and efferent arteriole
Secretes Renin
What are extraglomerular mesangial cells?
Aka lacis or polkissen cells
Phagocytic activity, continuous with the intraglomerular mesangial cells
Communicate with granular cells via gap junctions
Impermeable to water
What is the collecting tubule system?
Connecting tubule, initial portion of cortical collecting duct, and cortical and medullary collecting duct
Receives tubular fluid from distal tubules on its course from the cortex to the inner medulla
Sit of “fine tuning” of tubular fluid composition which results in fine control of the ECF fluid composition
What types of cells line the collecting tubule system?
Principal cells
Intercalated cells
What is the function of principal cells?
Responsive to hormones:
ADH
ANP
Aldosterone
What is the function of intercalated cells?
a intercalated cells - H+ secretion
B intercalated cells - HCO3 secretion
What are the two types of nephrons?
Coritcal (or superficial)
Juxtamedullary
Describe cortical nephrons
7/8 of all nephrons
Glomeruli lie in outer 2/3 of cortex
Short Loops of Henle, rarely penetrate the medulla
Have no thin ascending loop of Henle
Describe juxtamedullary nephrons
1/8 of all nephrons
Glomeruli lie in inner 1/3 of cortex and are larger
Loops of Henle are long; thin segment of loop may reach the tip of the papillae
Number of JM nephrons and their Loops of Henle directly correlates with the capacity to make concentrated urine
What is the nerve supply to the kidney?
NO vagal innervation
Sympathetic innervation to:
Smooth muscle of efferent and afferent arterioles (vasoconstriction
Granular cells - increase renin secretion
Basement membrane - enhances Na reabsorption
Describe the organization of the blood supply in the kidneys
Renal artery –> Interlobar artery –>arcuate artery –>Interlobular artery
Veins accompany arteries
What is glomerular filtration?
The bulk-flow of esentially protein-free plasma from the glomerular capillaries into Bowman’s capsule
No active transport
Permeability selective
What is tubular secretion?
Transfer of materials from the peritubular-capillary plasma to the tubular lumen
Highly selective
Both active and passive transport processes
Occurs throughout the length of the nephron
What is tubular reabsorption?
Transfer of materials from the lumen of the tubule to the peritubular-capillary plasma
Highly selective
Both active and passive transport processes
Occurs throughout the length of the nephron
How much blood flow do the kidneys get?
About 1200ml/min
Represents about 20% of cardiac output
What glomerular filtration rate?
How much blood passes through the glomeruli each minute
Normal GFR is about 90-130ml/min
Best overall index of kidney function
Significant decrease indicates renal insufficiency or renal failure
What is the filtration fraction?
GFR divided by the renal plasma flow
FF = GFR/RPF
What factors affect GFR?
Ultrafiltration coefficient
Glomerular capillary pressure
Pressure in Bowman’s space
Average colloid osmotic pressure in the glomerular capillaries
What factors increase the ultrafiltration coefficient (Kf)?
ANP - causes relaxation of the mesangial cells, increasing surface area and therefore Kf
What factors decrease the ultrafiltration coefficient?
ADH - contraction of mesangial cells, decreased surface area, lower Kf
ANG II - see above
Pathologic changes - thickening of the filtration barrier, destruction of the glomerular capillaries
How does the pressure in Bowman’s space affect GFR?
Increase in Bowman’s pressure decreases urine flow
Pb increases with increases urine flow or in pathological obstruction of the tubules
What two mechanisms are responsible for autoregulation in the kidneys?
Myogenic mechanism
Tubuloglomerular feedback mechanism
