Renal Histology Flashcards
Functions of the urinary system
-Elimination?
Eliminates urine and toxic metabolites from the blood
Functions of the urinary system
-Conservation?
Conserves salts, glucose, proteins, and water
Functions of the urinary system
-Regulation?
Regulates blood pressure, hemodynamics, and acid-base balance
Functions of the urinary system
-Endocrine?
Produces vitamin D, renin, erythropoietin, and prostaglandins (hormonal control of other tissues/organs)
Kidney blood supply
- As a blood filtering organ, the kidney’s blood supply is critical to its function
- Supplied by renal arteries which branch directly from the aorta
Blood supply of the kidney
-Renal artery splits off into?
-Renal a–>segmental (lobar) a–>interlobar a–>arcuate a–>interlobular a (cortical radial a)–>afferent arteriole–>glomerulus capillary–>efferent a–>peritubular capillary/vasa recta–>interlobular v–>arcuate vein–>interlobar vein–>renal vein
What is significant about segmental arteries?
Segmental arteries are end arteries
The nephron
Functional unit of the kidney
The nephron-functional unit of the kidney
- Parts are modified for specific physiological functions
- Renal corpuscle function?
- Tubular portion function?
- Renal corpuscle filters fluid from blood
- Tubular portion modifies filtrate into urine
Afferent arteriole leads into?
Glomerulus-a capillary bed which leads to the efferent arteriole
Types of nephrons?
-The type depends on?
- Two types of nephrons-cortical (short) and juxtamedullary (long)
- Depends on location of their Henle loop
Types of nephrons
-Cortical (short)-Two types?
- superficial
- midcortical
Whole renal pathway summary on slides 12 and 13
look at them
Renal corpuscle
-Glomerulus?
Tuft of fenestrated capillaries
Renal corpuscle
-Glomerulus is surrounded by?
-The glomerulus is surrounded by urinary (Bowman’s) capsule
Renal corpuscle
- Capillaries invaginate into Bowman’s capsule
- Capillaries are in contact with the visceral layer (podocytes)
- Parietal layer is simple squamous epithelium
- Separate by the urinary space
Mesangial cells
-What are they?
- Supporting cells
- Modified smooth muscle
Mesangial cells
-Functions?
- Contractile
- Supportive
- Phagocytic
- Secretory
Mesangial cells
-Functions-contractile?
-Reduce/increase blood flow through capillaries
Mesangial cells
-Functions-supportive?
Supportive in area where the visceral layer of the renal corpuscle is absent
Mesangial cells
-Functions-Phagocytic?
Resorption and maintenance of the basal lamina
Mesangial cells
-Functions-secretory?
Secrete prostaglandins and endothelins (induce constriction of afferent and efferent arterioles)
Glomerular filtration barrier
- Fluid from capillaries leaks into the urinary space through a complex filtration barrier
- Fenestrated capillary endothelium
- Basal lamina (basement membrane)
- Podocytes of the visceral layer of Bowman’s capsule
- High polyanionic charge on some components of both basal lamina and surface of podocyte processes
Glomerular capillaries
-Characteristics?
- Fenestrated
- Large pores not covered by a diaphragm
- Permeable to water, urea, glucose, and small proteins
- Barrier only to formed elements in blood and large maccromolecules
Basal lamina
-Lamina rarae contains:
- Type 4 collagen
- Laminin
- Fibronectin
- Negatively charged proteoglycans
Pedicels and filtration slits
- Pedicels?
- Filtration slits?
- Covered by?
- Each pedicel has a glycocalyx of negatively charged podocalyxin
- Separated by clefts-filtration slits
- Covered by a porous slit diaphragm
Filtration slit diaphragm
-contains what protein? what does this protein do?
- Diaphragm contains the protein nephrin
- Nephrin seems to halt passage of molecules through the fenestrations and basal lamina
Mutations in gene for nephrin are associated with what disease?
Congenital nephrotic syndrome
Filtration process
- Blood enters glomerulus via afferent arteriole
- Arteriole pressure forces fluid through fenestrae of capillary endothelium
- Large molecules are trapped by the basal lamina
- Negatively charged molecules are stopped by the basal lamina and podocytes
- Fluid passes through pores in slit diaphragm to enter the urinary space
Proximal convoluted tubule
- Site of “bulk operations”, it begins at urinary pole
- Lined by cuboidal/low columnar epithelium
- Microvilli and well-defined brush border
Proximal tubule
-Bulk operations?
- Extensive reabsorption of glomerular filtrate
- Na (active transport), Cl (passive diffusion), water (aquaporin-1) (small transmembrane channel)
- Reduction in fluid volume
- Proteins and small peptides are endocytosed in PCT
Loop of henle concentration
Concentration of the interstitium
Loop of Henle function?
To assist in forming hypertonic urine by establishing an osmotic gradient in the interstitial fluid of the medulla
Loop of Henle structure?
- U-shaped epithelial tube
- Consists of a thick (PCT) and thin descending limb and a thick and thin descending limb
Loop of Henle structure
-Difference between thick and thin portions in both the ascending and descending limbs?
Epithelial change
- Thick-cuboidal
- Thin-squamous
Thin ascending is really only found in what type of nephron?
Juxtamedullary nephrons
Loop of Henle: descending portion
- Permeable to both water and salt
- As filtrate (isotonic) in the lumen passes deeper into the medulla, it loses water to the interstitium
- Filtrate becomes more hypertonic
- Filtrate volume also decreases with loss of water
Loop of Henle: Ascending portion
- Plays a more active role in setting up the osmotic gradient required to make the interstitium hypertonic
- Contains an Na/K/Cl pump-symporter
- Constantly pumps these ions from the filtrate into the interstitium
Loop of Henle: Ascending portion cont.
- Impermeable to water (water cannot follow salt into the interstitium)
- Loss of salt, but not water, causes the filtrate in Loop of Henle to become isotonic or even hypotonic
- Filtrate ascends toward the DCT in the cortex
Distal convoluted tubule
- Lined by?
- Compared to proximal convolute tubule?
- Lined by low cuboidal epithelium
- Fewer microvilli in comparison to PCT (lumen looks larger)
Distal convoluted tubule
-2 cell types?
- Principal cells
- Intercalated cells
Distal convoluted tubule
-Principal cells-function?
Resorb Na and secrete K
Distal convoluted tubule
-Intercalated cells-function?
Secrete H+ or HCO3-
Macula Densa
- Modified segment at transition between the thick ascending loop of Henle and the DCT wall
- Sensitive to Cl- ion or NaCl content of tubular fluid
- Produces molecular signals promoting constriction of afferent arteriole
- Regulate the rate of glomerular filtration (GFR)
Juxtaglomerular apparatus
- Involved in maintaining blood pressure and volume through production of renin
- Juxtaglomerular cells of afferent arteriole (produce renin)
- Extraglomerular mesangial cells (lacis, polkissen)
- Macula densa of Loop of Henle/DCT transition
Juxtaglomerular apparatus
-Macula densa function?
-Macula densa acts as a sensor, regulating juxtaglomerular function by monitoring Na+ and Cl- levels in the DCT
Juxtaglomerular apparatus
-Decrease in blood volume/pressure elicits what reaction by JG cells?
JG cells secrete renin–>angiotensinogen–>active angiotensin–>aldosterone
Aldosterone is secreted by?
Suprarenal glands
Angiotensinogen–>?
- Angiotensinogen converted to angiotensin I by renin
- Angiotensin I converted to ang II by ACE
- Ang II stimulates aldosterone production by suprarenal glands
- Reabsorption of Na and water by DCT, CT, and CD
Treatment of chronic hypertension?
ACE inhibitor
DCT and aldosterone
- Crucial to acid-base balance and urine concentration
- Aldosterone (adrenal cortex) cause DCT cells to resorb remaining Na
- Pump H+ and K+ ions into lumen
- Control body’s extracellular K+ level and urine acidity
- Atrial Natriuretic factor
- secreted by?
Atrial myocytes
Atrial Natriuretic factor
-Function?
- Increases Na (natriuresis) and water (diuresis) EXCRETION
- Opposes action of aldosterone, inhibits the release of ADH
Urodilatin
-Secreted by?
DCT and CD cells
Urodilatin
-Function?
-Inhibits NaCl and water reabsorption by the medullary part of the collecting ducts
Collecting tubules
-Function?
Receive isotonic urine from DCT
Collecting ducts
-Function?
- Receive isotonic urine from collecting tubules
- Play important role in final concentration of urine (interstitium and vasa recta)
Collecting ducts
-pathway?
- Leave cortex in medullary rays and enter medulla
- Collecting ducts open at papilla into minor calyx
Collecting ducts
-Epithelium responsive to?
ADH
ADH is released by?
Neurohypophysis
Collecting ducts
-How are they affected by presence of ADH?
Water is lost from collecting ducts–>hypertonic urine
Collecting ducts
-How are they affected by absence of ADH?
Ducts remain impermeable to water–>iso-/hypotonic urine
Pathway of urine in kidney?
Minor calyces–>major calyces–>renal pelvis–>ureter
Urothelium
-Histology?
- Stratified
- Surface layer of umbrella cells linked by desmosomes and tight junctions
- Possibly impermeable to water and salt
- Forms osmotic barrier
Functions of the urinary system?
- Elimination
- Conservation
- Regulation
- Endocrine
