Functional Histology of the Kidney Flashcards
State the basic functions of the kidney
- Kidney is needed for blood homeostasis e.g maintenance of:
- Plasma composition via regulated secretion of water, ions and waste into urine
- Blood pressure via renin secretion
- Red blood cell number via secretion of erythropoietin
Draw the nephron structure and state the collective names of regions of it
- Bowman’s capsule + glomerulus = renal corpuscle
- Proximal convoluted tubule to the collecting tubule = renal tubule
- Bowman’s capsule to the collecting tubule = nephron
- Nephron (in order of structures)
- renal artery (afferent arteriole)
- glomerulus in the bowmans capsule
- efferent arteriole
- proximal convoluted tubule
- descending limb of loop of Henle
- ascending limb of loop of Henle
- distal convoluted tubule
- collecting tubule
- collecting duct
- ureter
Describe the glomerulus including the stages of filtration that occur within it
- A knot of capillaries
- Afferent arteriole (higher pressure) enters the glomerulus and the efferent arteriole (lower pressure) exits it
- Specialised epithelial cells coat the glomerulus - called the podocytes - have cell bodies with branches that surround the cells - eventually called feet - they are indigitating so interlock and create thin slits between them that helps to filter blood
Stages of filtration -
1. Fenestration - between the capillary endothelial cells of glomerulus
2. Through the thick, fused basement membrane of capillary endothelial cells and podocytes
3. Filtration slit membrane - between podocyte foot processes
State the function of the proximal convoluted tubule, what mechanisms it uses and the structure of the cells
Acts to reabsorb from the ultrafiltrate
Mechanisms used -
- Active transport- small molecules reabsorbed against their concentration gradient - glucose, amino acids, Na+ ions
- Pinocytosis- macromolecules reabsorbed particularly proteins - lysosomes break down into amino acids and these enter the blood
- Passive flux- small molecules reabsorbed down their concentration gradient e.g. H2O, Cl- ions
Cell type - (PCT)
- On the luminal side of the proximal convoluted tubule is the microvilli which have a high surface area where lytic enzymes on the surface break down macromolecules
- Pinocytic vesicles in these cells carry macromolecules to lysosomes and there are many lysosomes present to ensure macromolecules are recycled
- Also contains many mitochondria to fuel active transport
State the function of thin arms of the loop of henle, the mechanism used and the type of cells present
- Functions to reabsorb from the ultrafiltrate
- This occurs by passive flux only such as osmosis
- Contains thin squamous epithelial cells to allow for passive flux and the cells have a minimal number or organelles also to facilitate this
State the function of thick arms of the loop of henle (ascending loop and distal convoluted tubule), the mechanism used and the type of cells present
- Function in blood homeostasis
- There is regulated active transport and ion exchange (Na+/K+ and H+/HCO3-)
- Distal tubule epithelial cells have a cuboidal shape which is thicker than squamous to reduce passive fluxes and accommodate organelles - also has many mitochondria to fuel active transport with a few short microvilli
State the function of thin arms of the collecting duct and collecting tubule, the mechanism used and the type of cells present
- Transports urine to the ureter
- Water homeostasis - there is passive reabsorption of water regulated by the epithelial permeability
- Epithelial cells are cuboidal to columnar to prevent unregulated passive flux of water - also have dense membranes at the cell contacts - may also help prevent passive flux
State 2 conditions related to the kidney and include how they affect the histology
- Nephrotic syndrome -
- Glomerular basement membranes become damaged and more leaky so proteins are lost in the urine
- This is called proteinuria
- Basement membrane is thickened
- High blood pressure -
- Some glomeruli are destroyed and replaced by masses of clear hyaline material
- Hyaline looks glassy in H&E stain
Proximal and distal convoluted tubules histology
- Note that distal convoluted tubules are lighter so can be distinguished from proximal tubules
- The lumen of the distal tubules is also smaller and the surface is smoother
- Proximal tubule is bigger and has fixed proteins in the lumen
Describe the juxtaglomerular apparatus (where it is, what cells are present and the functions of those cells)
- A set of cells present between the distal convoluted tubule, afferent and efferent arterioles
- The afferent and efferent arterioles pass very close to the cells of the distal convoluted tubule which allows the apparatus to form
- Contains several cell types - juxtaglomerular cells containing renin granules (on the surface of the afferent arteriole), lacis cells (in between afferent and efferent arterioles) and the macula densa in the distal convoluted tubule
- Functions -
- Macula densa- senses [Na+] in the distal convoluted tubule fluid - appears to signal the juxtaglomerular cells
- Juxtaglomerular cells can then release renin in response to lower [Na+] in the distal convoluted tubule - renin indirectly increases vascular tone and sodium reabsorption
- Lacis cells have an unknown function - speculated that it helps signal between the other cell types
The ureter (from the centre outwards) histology
- The lumen (star shaped)
- Surrounded by transitional epithelium
- This is surrounded by lamina propria (dense connective tissue)
- There is then longitudinal and circular smooth muscle layers
- This is finally surrounded by the adventitia
Describe the structure of transitional epithelium
- Unique to the genitourinary system
- Consists of specialised stratified epithelium - bigger cells on the apical surface (normal stratified cells have big basal cells and flat apical cells)
- It is impermeable to urine and can change appearance once it has stretched
- The epithelium has plaques on the apical surface (in contact with the urine)
- These plaques are urine resistant - are impermeable and rigid which protects apical cells from toxic urine when the bladder is distended
- When the bladder is contracted and empty the plaques are invaginated forming pits to allow the bladder volume to decrease
(When the bladder is distended the transitional epithelium is not as thick)
What is a disadvantage of the transitional epithelium?
NOTE - a disadvantage of this is that because the transitional cells are impermeable it makes the area poorly accessible to leukocytes so the urinary tract is common for infections
