Functional Histology of the Kidney Flashcards
How is plasma composition maintained?
By regulated excretion of water, ions and organic waste products into urine.
How is blood pressure maintained?
Through the enzyme renin.
How is RBC content maintained?
Through the secretion of erythropoietin.
How much of the cardiac output do the kidneys receive?
25%
What does high blood pressure do?
It destroys glomeruli and they are replaced by masses of clear ‘hyaline’ material.
What is the function of the proximal convoluted tubule?
Reabsorption from the ultrafiltrate
How does reabsorption occur in the PCT?
- By active transport across the membrane into cell: small molecules like Na+, glucose, amino acids
- By pinocytosis: macromolecules, especially proteins. These broken down in lysosomes and returned to the blood.
- By passive flux: water, Cl-
What is the structure of the PCT epithelial cells?
- Long microvilli for a high surface area for reabsorption, also lytic enzymes on the surface to break down macromolecules
- Many lysosomes to break down and recycle macromolecules
- Many mitochondria to fuel active transport (seen especially near the basolateral sodium pumps)
What are the functions of the (thin) Loop of Henle?
Reabsorption of water and salts from filtrate - passive flux across the epithelium, by osmosis & concentration gradients.
What is the structure of the Loop of Henle?
- Thin, squamous epithelium to allow passive fluxes
- A minimum of organelles
What are the functions of the DCT and the thick ascending loop of Henle?
Homeostasis by regulated active transport & exchange of ions
(Na+/K+, H+/HCO3-)
What are the structures of the DCT and the thick ascending loop of Henle?
- Cuboidal epithelium – thicker than squamous, to reduce passive fluxes and accommodate organelles
- Few, short microvilli (unlike PCT)
- Many mitochondria to fuel active transport. These are mainly basal and can show as a pale or striped basal area in H&E-stained sections.
What is the function of the collecting duct?
- Transport of urine to the ureter.
- Water homeostasis: passive reabsorption of water, regulated through epithelial permeability.
What is the structure of the collecting duct?
- Cuboidal to columnar epithelium, to prevent passive flux of water (and urea etc)
- Specialized dense membranes at cell contacts [red]. Function unclear – probably also helping to prevent passive flux.
What is the juxtaglomerular apparatus?
Where DCT loops back to meet arterioles of the same nephron.
What does the macula densa?
sensing [Na+] in the DCT fluid. Appears to signal to the glomerular cells telling them how much renin to release
What do juxtaglomerular cells do?
They release renin – more so in response to lower [Na+] in DCT. Renin indirectly increases vascular tone and sodium resorption.
What do the Lacis cells do?
Function unknown. (Signalling between the other two?) Also called extraglomerular mesangial cells.
What are the parts of the ureter?
Transitional epithelium
Dense connective tissue (lamina propria)
Layers of smooth muscle
Adventitia
What are the properties of transitional epithelium?
Specialized to be impermeable to urine.
Changes appearance on stretching
Somewhat like stratified squamous epithelium (SSE) when distended, but apical cells are biggest and have much apical cytoplasm
(in SSE, basal cells are biggest, apical cells very flat).
