Histology of the Kidney Flashcards
Relate the main structure of the urinary system to its function
Regulates plasma composition by regulated excretion of water, ions and organic waste products into urine
Regulates BP through the enzyme renin
Regulates Erythrocyte/RBC content by erythropoietin secretion.
Label this kidney
What is the nephron?
The functional unit of the kidney - where blood is filtered at the molecular level (dialysis), to produce urine, while retaining cells and large proteins, also reabsorbing valuable small molecules.
About 1 million nephrons in each human kidney
What do each of these numbers represent?
Label this histological kidney section
Label this and use it to explain the filter stages of the kidney
Explain this
What is the function of the proximal convuluted tubule?
Function is reabsorption from ultrafiltrate by 3 ways:
- By active transport across membrane into cell, for small molecules like Na+, glucose, aa.
- By pinocytosis, for proteins. These are broken down in lysosomes and returned to blood.
- By passive flux, for water, Cl-
Describe the structure of the proximal convuluted tubule
Long microvilli= high SA for reabsorption.
Also hay lytic enzymes on surface to break down macromolecules
Pinocytotic vesicles to carry macromolecules to lysosomes which break them down
Many mitochondria to fuel a.transport (esp near the basolateral Na pumps)
What is the structure and function of the loop of Henle?
Function is water and salts reabsorption from filtrate by: passive flux across epithelium, by osmosis & concentration gradients.
Structure: thin, squamous epithelium to allow passive fluxes. A minimum of organelles
Describe the structure and function of the DCT
Functions: homeostasis by regulated active transport & exchange of ions (Na+/K+, H+/HCO3-)
Structure:
- Cuboidal epithelium – thicker than squamous, to reduce passive fluxes and accommodate organelles
- Few, short microvilli (unlike PCT)
- Many mitochondria to fuel a.transport.
Describe the structure and function of the collecting duct
Functions: Transport urine to ureter. Water homeostasis: passive reabsorption of water, regulated through epithelial permeability.
Structure: cuboidal epithelium, to prevent passive flux of water (and urea etc). Specialized dense membranes at cell contacts also helps prevent passive flux.
Label and describe this
Where is the juxtaglomerular aparatus?
Where DCT loops back between glomerular arterioles of same nephron. Involved in the regulation of blood pressure
Hay 3 parts to the juxtaglomerular apparatus. Where and what are they?
The 3 parts are marked by 3 stars
- Macula densa - senses [Na+] in the DCT fluid. Signals to juxtaglomerular cells
- Juxtaglomerular cells - release renin in response to lower [Na+] in DCT. Renin increases bp and Na resorption.
- Lacis cells – Maybe for signalling between the other two? Aka extraglomerular mesangial cells.
Label this, what is it?
What is transitional epithelium?
A special stratified epithelium, found only in ureters and bladder
- Specialized to be impermeable to urine (noxious)
- Changes appearance on stretching
- apical cells (shown in green) are biggest, and dome-shaped when not stretched:
What specialised features are found in apical cells of transitional epithelium?
Specialized (urine-resistant) plasma membrane plaques
When the bladder is distended, the plaques protect apical cells from toxic urine. They are made of transmembrane proteins called uroplakins.
When the bladder is contracted the plaques are invaginated, forming irregular pits in the cytoplasm, decreasing SA
What is the disadvantage of transitional epithelium?
Cystitis= infections of the bladder
Transitional epithelium highly impermeable - immune leukocytes cannot readily penetrate, so UTIs are common
More common in females bc their shorter urethra has more risk of contamination, e.g. from anal region.
