functional histology of the kidney Flashcards
functions of the urinary system
homeostasis of:
- Plasma composition by regulated excretion of water, ions and organic waste products into urine
- Blood pressure through the enzyme renin
- RBC content through secretion of erythropoietin
Medullary rays
anatomy of kidney on slide
lines within the cortex, they are part of the medulla but they extend into the cortex
Renal corpuscle
bowman’s capsule and glomerulus
glomerulus is the site of what?
ultrafiltration
The basement membrane of podocytes fuses with what?
the basement membrane of the endothelial cells
function of proximal convoluted tubule
(selective) reabsorption from the ultra filtrate
how are molecules reabsorbed back into the bloodstream in the proximal convoluted tubule?
Active transport across membrane into cell: small molecules like Na+, glucose, amino acids
Pinocytosis: macromolecules, especially proteins - these are broken down in lysosomes and returned to blood
Passive flux: water, Cl-
how is the structure of the proximal convoluted tubule adapted for its function
Structure:
- Long microvilli for high surface area for reabsorption, also lytic enzymes on surface to break down macromolecules
- Pinocytotic vesicles carrying macromolecules to lysosomes - they break down and recycle macromolecules
- Many mitochondria to fuel active transport (seen especially near the basolateral sodium pumps)
Loop of henle thin limb function
Reabsorption of water and salts from filtrate - passive flux across epithelium, by osmosis & concentration gradients
what is the structure of the thin limb of the loop of henle similar to?
proximal convoluted tubule
why are the cells thin in the thin LOH limb?
because there is a lot of passive flux going on
why is here a hypertonic extracellular environment in the thin LOH limb?
so water will flow out of the tubule
Thin loop of Henle - epithelial cell structure
- Thin, squamous epithelium to allow passive fluxes
- A minimum of organelles
functions of the distal convoluted tubule and thick ascending loop of Henle
Homeostasis by regulated active transport & exchange of ions
(Na+/K+, H+/HCO3-)
why is pumping ions necessary in the thick limb of the loop of henle?
needed to set up the hypertonic environment towards the bottom (hairpin bend)
Distal convoluted tubule (DCT) epithelial cell structure
- 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.
Collecting duct and collecting tubule function
- Transport of urine to ureter
- Water homeostasis: passive reabsorption of water, regulated through epithelial permeability
- the epithelium can make itself more or less permeable partly through specialized molecules on the membrane
Collecting duct epithelial cell structure
- Cuboidal to columnar epithelium, to prevent passive flux of water (and urea etc)
is the proximal or distal convoluted tubule thicker?
proximal
why is the lumen clearer in the DCT?
because it hasn’t got as many microvilli
PCT doesn’t have much lumen
what type of epithelium is the thin loop?
squamous
what happens to the collecting duct as you go down?
gets taller and thicker as you go down (starts off as cuboidal)
what is renin involved in?
controlling BP (indirectly increases vascular tone and sodium resorption)
Macula densa
involved in sensing [Na+] in the DCT fluid. - signals to the juxtaglomerular cells
