Functional Histology of The Kidney Flashcards
What are the functions of the urinary system?
Blood homeostasis
What role does the urinary system play in blood pressure homeostasis?
Using renin
What role does the urinary system play in plasma homeostasis?
Excretion of water, ions and organic waste products into the urine
What role does the urinary system play in RBC homeostasis?
Synthesise and secrete erythropoietin
Briefly, describe the nephron.
Functional unit of the kidney
Describe the function of the nephron.
Where blood is filtered to produce urine while retaining cells and large proteins.
What is the function of the renal tubule?
- Adjusts the composition of the ultrafiltrate to recover nutrients, water, etc.
- Regulate plasma composition.
What is the function of the proximal convoluted tubule?
Reabsorption from the ultrafiltrate
Give examples of molecules reabsorbed by the PCT using active transport.
Na+
Glucose
Amino acids
Give examples of molecules reabsorbed by the PCT using pinocytosis.
Macromolecules i.e proteins
What happens to molecules reabsorbed by pinocytosis?
Hydrolysed by lysosomes and returned to blood
Give examples of molecules reabsorbed by the PCT using passive flux
Water
Chloride ions
Describe the adaptations of a cell of the proximal convoluted tubule. Give a brief explanation why it has these adaptations.
- Microvilli - high surface area for reabsorption
- Lytic enzymes on the surface - hydrolyse macromolecules.
- Lysosomes - hydrolyse recycle macromolecules.
- Mitochondria - fuel active transport
What are the functions of the Loop of Henle?
- Reabsorption of water and salts from the filtrate
- By passive flux across the epithelium, by osmosis and concentration gradients.
Describe the structure of an epithelial cell in the thin Loop of Henle.
Thin, squamous epithelium to allow passive fluxes
What are the functions of the distal convoluted tubule and the thick ascending Loop of Henle?
Homeostasis by regulated active transport and exchange of ions
Describe the structure of an epithelial cell of the distal convoluted tubule. Give brief explanations why they have these structural features.
- Cuboidal epithelium - reduce passive fluxes and accommodate organelles.
- Few, short, microvilli (unlike the PCT).
- Many basal mitochondria to fuel active transport
What are the functions of the collecting duct and the collecting tubule?
- Transport of urine to the ureter.
- Water homeostasis as the passive reabsorption of water, regulated through epithelial permeability.
Describe the structure of an epithelial cell of the collecting duct. Give brief explanations why they have these structural features.
- Cuboidal to columnar epithelium - prevent the passive flux of water (and urea, etc.).
- Specialised dense membranes at cell contacts (red) - possibly to prevent passive flux.
What does the macula densa do?
- Senses [Na+] in the DCT fluid.
- Signals to juxtaglomerular cells.
What do juxtaglomerular cells do?
- Release renin - more so in response to lower [Na+] in the DCT.
What does renin do?
- Increases vascular tone and sodium reabsorption
What do Lacis cells do?
We don’t know what they do.
What are Lacis cells known as?
Extraglomerular mesangial cells
Describe the transitional epithelium.
- Specialised stratified epithelium found only in ureters and the bladder.
- Specialised to be impermeable to urine.
What structural changes occur to transitional epithelium upon stretching?
- Large apical cells
- Apical cytoplasm
There are plaques in specialised (urine-resistant) plasma membrane in the apical cells of the transitional epithelium.
Describe their function in a distended bladder.
Protect apical cells from the toxic urine.
There are plaques in specialised (urine-resistant) plasma membrane in the apical cells of the transitional epithelium.
Describe their function in a contracted bladder.
- Plaques are invaginated, forming pits and vesicles in the cell
- Allows the cell surface area to decrease.
What is cystitis?
Inflammation of the bladder
- Usually caused by a bladder infection.
Why are UTIs (urinary tract infections) quite common?
- Transitional epithelium is highly impermeable
- Leukocytes cannot readily penetrate it.
Why are UTIs commoner in females?
- Female urethra is shorter
- More risk of contamination
What is the most common advice doctors give regarding UTI prevention?
Increase fluid intake
What is the glomerulus the site of?
Ultrafiltration
What is ultrafiltration?
→Filtration of blood through a molecular filter
What capillaries are there in the glomerulus?
Fenestrated capillaries
What happens during nephrotic syndrome?
→Glomerular basement membranes become damaged
→Proteins lost in the urine (proteinuria)
What happens to glomeruli during high pressure?
Some glomeruli are destroyed and replaced by masses of hyaline material
As you go down the collecting duct what happens to the cells?
→ cells become 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
