Lecture 2: Renal Histology Flashcards
What is the functional unit of the kidney and how many of them are there?
Nephron, around 1 million
Give an overview of nephron function tying together location and function:
Renal corpuscle: Filtration
Proximal tubule: Bulk reabsorption (some secretion)
Desc and Asc: Water extraction
Distal conv. tubule: Salt fine tuning
Collecting duct: Reabsorption of water
What is reabsorbed in the PT and whats the function of the rest of the nephron after that?
PT = 65% filtrate reabsorbed
Remaining segments fine tune salt levels, pH and/or extract water
Describe the renal corpuscle:
- Capillary tuft
- Surrounded by epithelial cells (podocytes and parietal epithelial cells)
- Podocytes envelope the capillaries
- Parietal epithelial cells form the outside later (Squamous epithelium)
Note: Podocytes and parietal epithelium are continuous at the vascular pole (look at picture illustrating parietal vs visceral epithelium)
What makes the glomerular filtration barrier and what sort of barrier is it?
- 3 Mjr components; Endothelium, GBM, Podocytes
- Physical barrier
- Charge selective barrier
What does the glomerular filtration barrier restrict?
- Restricts cells, albumin and other large proteins
Describe the endothelium of the glomerular capillary:
- Fenestrations (holes), permeable to small moleculares, restrict cells.
- Negatively charge glycocalyx coat (repells proteins in the plasma, most of which are -ive charged)
Describe the glomerular basement membrane:
- Thick
- Made up of collagen and negatively charged proteoglycans
- Has a dense core and less dense outer layers
- Acts as physical (inner layer) and charge barrier (outer layers)
Describe the structure of podocytes at the glomerulas;
- Adhere to the GBM
- Primary and secondary processes that interdigitate
- Form slits linked by protein bridge (slit membrane)
- Covered in a negatively charged glycocalyx coat
What do defects in the 3 components of the golmerular filtration barrier lead to?
Leaky glomerular filter -> Proteinuria
What are mesangial cells?
- They are smooth muscle cells packed inside the capillary tuft
What are the role of mesangial cells?
- Supportive/contractile role (maintain tuft shape)
- Produce ECM
- Involved in glomerulosclerosis (glomerular scarring)
What happens to mesangial cells in high BP?
High glomerular pressure increases mesangial proliferation which can lead to glomerulosclerosis
What makes up the Juxtaglomerular apparatus? JGA
JGA:
- JG cells; Modified SM cells in wall of afferent arteriole (Secrete renin)
- Macula dense cells: Special cells in the wall of the TAL that sense salt Conc. in the filtrate
- Extraglomerular mesangial cells
What are the major regulatory functions of the JGA?
1) High distal tubular NaCl induces afferent arteriole vasoconstriction (mesangial cells)
2) Low tubular NaCl induces renin release (increase BP)
Describe the features of the proximal tubule cells that make it good for bulk reabsorption:
- Cuboidal epithelium
- Prominent brush border (microvilli) (inc. SA)
- Pinocytosis (proteins)
- Lateral processess and infoldings (interdigitations) to increase SA
Describe the features of the thin limb cells:
- Thin squamous epithelium
- Role in water reabsorption as part of loop of henle
- Nuclei bulge into the lumen
Describe the features of the distal tubule cells:
- Cuboidal epi.
- Interdigitating lateral processes and in foldings
- NO brush border (short microvilli instead)
- NO pinocytosis
What is the functions of the distal tubule cells:
Fine tuning salts, pH (DCT and CNT) Urine concentrations (TAL)
Describe the features of the collecting duct:
- Final modifier of water, salt and pH of the urine
- Cubiodal to columnar epithelium
Describe the tissues of the ureter and bladder:
- Transitional epithelium
- Mucous membrane (lube, protection)
- Subepithelial CT/Lamina propria (elastic)
- Smooth muscle layers (in;long,out;circ)
- Outside layer of adventitia (elastic)
Describe the epithelium of the urethra:
Initially transitional that becomes stratified columnar and then stratified squamous.
Describe the journey of blood through the kidney:
Renal art -> Interlobar art -> Arcuate art -> Interlobular art -> Afferent art. / glomerulus -> Efferent art. / pertitubular cap. -> Interlobular vein -> Arcuate vein -> Interlobar vein -> Renal vein
Whats found in the cortex?
Renal corpuscles
Portions of the proximal and distal tubules
(Nephrons lie from deep to outer locations and this determines loop depth)
What are medullary rays?
Straight bundles containing a collecting duct and prox. and dist. tubules going to and from the medulla. Centre of lobule.
