Functional histology of the kidney Flashcards
How does homeostasis of plasma composition occur?
→ By regulated excretion of water, ions and organic waste products into the urine
How does homeostasis of blood pressure occur?
→ Through the enzyme renin
How does homeostasis of RBC content occur?
→ secretion of EPO
How much of the cardiac output do the kidneys receive?
→ 25%
What happens at the nephron?
→ blood is filtered at the molecular level (dialysis) to produce urine, while retaining cells and large proteins
How many nephrons are there in each kidney?
→ About 1 million
What is the glomerulus the site of?
→ site of ultrafiltration
What is ultrafiltration?
→Filtration/dialysis of blood through an extremely fine molecular filter
→A knot of capillaries
What capillaries are there in the glomerulus?
→ fenestrated capillaries
What happens during nephrotic syndrome?
→Glomerular basement membranes become damaged and more leaky
→So proteins are lost in the urine (proteinuria)
What happens to glomeruli during high pressure?
→Some glomeruli are destroyed and replaced by masses of clear “hyaline” material (H)
What is the function of the renal tubule?
→ adjust the composition of the ultrafiltrate, to recover nutrients, water etc, and to regulate plasma composition
What is the function of the proximal convoluted tubule?
Reabsorption from the ultrafiltrate
By active transport across the membrane into the cell
→Small molecules like Na+, glucose and amino acids
By pinocytosis: macromolecules, especially proteins
→These are broken down in lysosomes and returned to the blood
By passive flux
→Water, Cl-
What is the structure of the PCT?
→Long microvilli
→For high surface are for reabsorption
→Many mitochondria to fuel active transport
→Seen especially near the basolateral sodium pumps
What enzymes does the PCT have and what is this for?
→Lytic enzymes on the surface to break down macromolecules
→Has many lysosomes to break down and recycle macromolecules
What is the function of the loop of Henle?
→Reabsorption of water and salts from the filtrate
→Passive flux across the epithelium, by osmosis & concentration gradients
What is the function of epithelial cells in the loop of Henle?
→Thin, squamous epithelium to allow passive fluxes
A minimum of organelles
What is the function of the distal convoluted tubule?
→Homeostasis by regulated active transport & exchange of ions
→(Na+/K+, H+, HCO3-)
What is the structure of the DCT?
→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 ducts?
→Transport of urine to ureter
→Water homeostasis, passive reabsorption of water, regulated through epithelial permeability
What is the structure of the collecting ducts?
→Cuboidal to columnar epithelium
→To prevent passive flux of water (and urea etc)
→Specialised dense membranes at cell contacts (RED)
→Function is unclear – probably also helping to prevent passive flux
As you go down the collecting duct what happens to the cells?
→cells get taller and taller
→ more impermeable to the water crossing them
Where is the juxtaglomerular apparatus found?
→Is found where the DCT loops back to meet arterioles of the same nephron
What does the macula densa do?
→Senses [Na+] in the DCT fluid
→Signals to the juxtaglomerular cells
What do the juxtaglomerular cells release?
→Release renin
→More release of renin in response to lower [Na+] in DCT
What does renin indirectly increase?
→Renin indirectly increases vascular tone and sodium resorption
What are Lacis cells also known as?
→ extraglomerular mesangial cells
What is transitional epithelium?
→special stratified epithelium, found only in ureters and bladder
What is the transitional epithelium specialized for?
→Specialised to be impermeable to urine
When does the transitional epithelium change appearance?
→It changes appearance on stretching
What is transitional epithelium similar to?
→It is similar to stratified squamous epithelium (SSE) when distended
What cells are the bigger in the transitional epithelium
?
→But apical cells are the biggest and have a lot of apical cytoplasm
→In SSE, basal cells are the biggest, and apical cells are very flat
What cells are biggest in stratified squamous epithelium?
→In SSE, basal cells are the biggest, and apical cells are very flat
What is present in the apical cells of epithelium?
→There are plaques of specialised (urine-resistant) plasma membrane in the apical cells of transitional epithelium
What do the rigid membrane patches in apical cells in the TE do?
→These impermeable, rigid membrane patches (plaques) protect apical cells from toxic urine
What happens to the rigid membrane patches when the bladder is empty?
→rigid plaques are invaginated
→ forming pits and vesicles in the cell
→ allowing the cell surface are to decrease
Why are urinary infections quite common?
→Transitional epithelium is highly impermeable
→The leukocytes of the immune system cannot readily penetrate
Why are urinary infections common in women?
→The female urethra is shorter
→More risk of contamination
E.g. from anal region
How do you prevent urinary infections?
→ Drinking water
