Functional histology of the kidney Flashcards
List all the different parts of the nephron
- Bowman’s capsule
- Glomerulus (blood capillaries)
(Latin: glomerulus, little ball.) - Proximal convoluted tubule
- Loop of Henle - thin arms (descending & ascending)
- Loop of Henle - thick arm (ascending)
- Distal convoluted tubule
6a. Collecting tubule (straighter, epithelium is like 7). - Collecting duct
- Papilla
1-2 = Rena
Describe the glomerulus
A knot of capillaries
Seen here by SEM (scanning
electron microscopy)
Describe the glomerulus and bowman’s capsule
SEM, higher
magnification
(false colour)
Showing part of the filter
formed by the specialized
epithelial cells coating the
capillaries: podocytes
What are three stages of filtration
1) Fenestration between capillary endothelial cell of glomerulus
2) thick, fused basement membranes of capillary endothelial cells and podocytes
3) filtration slit membrane between podocyte food processes
Explain molecules involved in pinocytosis and passive flux
pinocytosis- macromolecules, especially proteins are degraded within lysosomes and amino acids recycled to blood
Passive flux- small molecules with a concentration gradient
Explain the structure of the proximal CT epithelial cell
Microvilli (high surface area); lytic enzymes
on surface to break down macromolecules Pinocytotic vesicles carrying macromolecules to lysosomes
Many lysosomes to recycle macromolecules
Many mitochondria to fuel active transport
(especially near the basolateral Na+ pumps)
What is the function of the loop of henle
-reabsorption from ultrafiltrate
-by passive flux only
Explain the structure of the thin loop of henle
-thin squamous epithelium to allow passive fluxes
-a minimum of organelles
What is the function of the thick ascending loop of henle and distal convoluted tubule
Function: Blood homeostasis
Regulated active transport and ion exchange
(Na+/K+, H+/HCO3-)
Explain the structure of distal epithelial cell
Cuboidal epithelium – thicker than
squamous, to reduce passive fluxes and
accommodate organelles
Many mitochondria to fuel active
transport. Can show as a pale or striped
basal area in H&E-stained sections.
Few, short microvilli (unlike PCT)
What are the functions of the collecting duct and collecting tubule
Functions:
Transport of urine to ureter
Water homeostasis: passive reabsorption of water, regulated through epithelial permeability
what is the structure of collecting ducts in the epithelial cells
Cuboidal to columnar epithelium, to
prevent unregulated passive flux of water
(and urea)
Dense membranes at cell contacts.
Function unclear – probably also helping to prevent passive flux.
Explain what happens in kidney disease
Glomerular basement
membranes become damaged and
more leaky – so proteins lost in
urine (proteinuria).
In one type, the basement
membranes (B, pink) become
visibly thickened, thought to be
through deposition of
immunoglobulins (autoimmunity).
Some glomeruli
destroyed and replaced
by masses of clear
“hyaline” material (H).
Hyaline = “glassy” in an H&E
stain and usually indicates
proteinaceous material rather
than cells.
What is the juxtaglomerular apparatus
-where DCT loops back to meet arterioles of same nephron
What are functions of the juxtaglomerular apparatus cell
-Macula densa - senses [Na+] in the DCT fluid. Appears to signal to….
- Juxtaglomerular cells - release renin – more so in response to lower [Na+] in DCT. Renin indirectly increases vascular tone and sodium resorption.
- Lacis cells – function unknown. (Signalling between the other
two?) Also called extraglomerular mesangial cells.
What are characteristics of transitional epithelium
A SPECIAL STRATIFIED EPITHELIUM, FOUND ONLY IN URETERS AND
BLADDER
-Specialized to be impermeable to urine
(full)
* Changes appearance on stretching
* Appearance is like stratified squamous
epithelium, except biggest cells are apical
(Stratified squamous epithelium = big
basal cells, flat apical cells)
Explain what happens when the bladder is full or empty
Distended (bladder full):
These impermeable, rigid
membrane patches (plaques)
protect apical cells from toxic
urine.
Contracted (bladder empty):
The rigid plaques are invaginated
forming pits, allowing bladder
volume to decrease.
