Functional histology of the kidney Flashcards
What are the functions of the urinary system?
It is involved with the homeostasis of:
- Plasma composition - by regulated excretion of water, ions and organic waste products into urine.
- Blood pressure - through the enzyme renin;
- RBC content - through secretion of erythropoietin.
Describe the structure of the kidney and low power histology section of whole human kidney
This is revision from the previous lecture
Describe the structure of what it is seen on a low power histological section of the kidney
On image
Describe the parts of the nephron
- Bowmans capsule
- Glomerulus
- Proximal convoluted tubule
- Loop of Henle - thin arm
- Loop of Henle - thick arm
6 Distal convoluted tubule
6a Collecting tubule (straighter, epithelium like 7) - Collecting duct
- Papilla
Renal corpusule = 1+2
Renal tunile = 3-6a
Nephron = 1-6a
Describe the structures seen as a cross-section of a kidney cortex
- Renal corpuscle (glomerulus and Bowman’s capsule)
- Proximal convoluted tubules
- Distal convoluted tubules (paler)
- Collecting ducts in medullary ray
Describe the structure of the glomerulus
What can it be seen by?
- A knot of capillaries
2. Can be seen on an SEM
Look at the structure of the glomerulus and Bowmans capsule
Can it been seen on an SEM and with what magnification?
SEM can be used to see them
High magnification
What does P show on the diagram of the glomerulus and Bowmans capsule?
showing part of the filter formed by the specialized epithelial cells coating the capillaries, the podocytes (P)
What makes up the first part of the glomerulus filter?
What is the size of these structures?
What can they be seen by?
- Capillary fenestrations
- 50-100nm
- SEM
Describe the diagram showing the movement of fluid in ultrafiltration
2nd and 3rd stages of filter: Basement membrane & Podocytes
On image
What are the three layers of the glomerular filtrate?
Show these on the diagram
- The cytoplasm of the capillary endothelial cell of the glomerulus
- Thick, fused basement membranes of capillary and podocytes
- Filtration slit membranes (with = 4nm pores)
What is the filter cut - off of the glomerular filter?
70Kda (albumin)
This size and larger molecules retained in the blood. Many proteins, nutrients (e.g) sugars and ions come through
Describe the views of the 3 layers of the glomerular filtration (3D view)
On image
Describe the parts of a podocyte seen on an SEM
- Podocyte cell body
2. Filtration slits
What can be seen on a Histological section of a normal glomerulus (H&E), “longitudinal”
refer to image
A: afferent arteriole
BC: Bowman’s capsule
PC: beginning of proximal convoluted tubule
White = fluid: blood or filtrate.
What is the function of the renal tubule?
In short, adjusting composition of ultrafiltrate, to recover nutrients, water etc, and to regulate plasma composition
What are the functions of the proximal convoluted tubule?
Reabsorption from ultrafiltrate:
- By active transport across membrane into cell: small molecules like Na+, glucose, amino acids
- By pinocytosis: macromolecules, especially proteins. These broken down in lysosomes and returned to blood.
- By passive flux: water, Cl-
Describe the structure of the proximal convoluted tubule (PCT) epithelial cell, as seen by TEM
- Long microvilli for high surface area for reabsorption, also lytic enzymes on surface to break down macromolecules
- Pinocytotic vesicles carrying macromolecules to lysosomes
- Many lysosomes to break down and recycle macromolecules
- Many mitochondria to fuel active transport (seen especially near the basolateral sodium pumps)
What is the function of the Loop of Henle, thin limb?
Reabsorption of water and salts from filtrate - passive flux across epithelium, by osmosis & concentration gradients.
Describe the structure of the thin loop of Henle, epithelial cell
- Thin, squamous epithelium to allow passive fluxes
- A minimum of organelles
What is the function of the Distal convoluted tubule and thick ascending loop of Henle
Homeostasis by regulated active transport & exchange of ions :
(Na+/K+, H+/HCO3-)
What is the function of the Collecting duct and collecting tubule?
Functions:
- Transport of urine to ureter.
- Water homeostasis: passive reabsorption of water, regulated through epithelial permeability
Describe the structure of the collecting duct epithelial cell
Structure:
- Cuboidal to columnar epithelium, to prevent passive flux of water (and urea etc)
- Specialized dense membranes at cell contacts [red].
Function unclear – probably also helping to prevent passive flux.
Describe the Sketch of differential appearance of parts of the renal tubule & collecting ducts
On image
Describe the structure of the proximal & distal convoluted tubules in cortex - H&E
Describe the structure of the Medulla, section of various tubules
On image
Have a look at the the juxtaglomerular apparatus (and regulation of blood pressure)
This is where the DCT loops back to meet arterioles of same nephron
What is the function of the Macula densa?
Macula densa - sensing [Na+] in the DCT fluid. Appears to signal to….
What is the function of the juxtaglomerular cells?
Juxtaglomerular cells - release renin – more so in response to lower [Na+] in DCT. Renin indirectly increases vascular tone and sodium resorption.
What is the function of the Lacis cells?
Lacis cells – function unknown. (Signalling between the other two?) Also called extraglomerular mesangial cells.
Describe the Section showing juxtaglomerular apparatus (H&E)
On image
Describe the structure of the Ureter (transverse section, Masson’s trichrome, low magnification)
On image
What is Transitional epithelium?
Where is it found?
How is it specialised?
Describe its structure
A special stratified epithelium, found only in ureters and bladder
- Specialized to be impermeable to urine.
- Changes appearance on stretching.
- Somewhat like stratified squamous epithelium when distended,
- but apical cells are biggest and have much apical cytoplasm.
- (In stratified squamous epithelium, basal cells are biggest, apical cells very flat.)
What is an an oddity?
Describe its structure when distended and contracted
Plaques of specialized (urine-resistant) plasma membrane in apical cells of transitional epithelium
On image
What is the downside of the transitional epithelium?
Cystitis
Why are urinary infections quite common?
Transitional epithelium highly impermeable - leukocytes of immune system cannot readily penetrate.
Why commoner in females?
Female urethra shorter. More risk of contamination, e.g. from anal region.
Advice on prevention?
Plenty of fluids.
