Functional Histology of Kidney and Renal Tubule Flashcards
What is the Renal corpuscle and Renal tubule?
Describe the structure of the Glomerulus
Renal Corpuscle - Bowman’s capsule and glomerulus
Renal Tubule - from end of Bowman’s capsule to Collecting duct
Glomerulus: Ultrafiltration
The glomerular filter has 3 layers - fenestrated capillaries, basement membrane, and filtration-slit membranes formed by Podocytes
Describe the structure of the PCT, Loop on Henle (LoH), DCT, and Collecting Duct (CD)
PCT:
• Reabsorption occurs here - by active transport, passive flux, and pinocytosis.
• Long microvilli - large surface area for reabsorption
• Pinocytic vesicles - carry macromol. to lysosomes
• Many lysosymes - break down macromolecules
• Many mitochondria - active transport
Thin LoH:
• Passive flux of ions and water by osmosis and conc. gradients
• Squamous Epithelium
• Ascending portion is impermeable to water
Thick LoH:
• Na+ and Cl- reabsorption
• Cuboidal Epithelium with short microvilli
DCT:
• Ion exchange
• Cuboidal epithelium with less and short microvilli
• Many mitochondria - active transport.
CD:
• Used to transport the urine to ureter, and for water homeostasis
• Cuboidal epithelium - prevent passive flux of water/urea.
• Dense membranes between neighbouring cells - prevent water passage between cells
• Permeability controlled by ADH
What is the Juxtaglomerular Apparatus and what’s its function?
Where the DCT loops back in between the afferent and efferent arterioles. The important cells is called the MACULA DENSA.
The Macula Densa senses the concentration of Na+ in the DCT, and sends signals to the juxtaglomerular cells to release Renin. This will activate the RAAS = ↑vascular tone and Na+ reabsorption.
The Lacis cells are between the macula densa and arterioles, and have an unknown function.
Describe the structure of the ureter and bladder, in relation to water retention
Why are UTI’s so common, in relation to permeability?
- • TRANSITIONAL epithelium - impermeable to urine
• Dense connective tissue
• Smooth muscle
• Adventitia layer
When distended (full bladder), the epithelium stretches to look more like squamous epithelium. The epithelium has impermeable, rigid patches/plaques to protect it from toxic urine.
When contracted (empty bladder), the rigid plaques become invaginated to form pits and vesicles.
- High impermeability so WBCs can’t pass through.
How is the filtrate modified to produce urine?
What is Active Transport, Passive Transfer, and Secondary Active Transport/Cotransport?
- It is modified as it moves along the renal tubule via reabsorption and secretion.
- Active transport: movement against its concentration/electrochemical gradient
Passive transfer: movement down its concentration gradient
Secondary Active Transport/Cotransport: movement of a substance down
its concentration gradient, which produces energy for the transport of another substance against its concentration gradient. Is a SYMPORTER/ANTIPORTER.
How do they transfer process work to reabsorb substances, like Na/Glucose, in the tubule?
What are the techniques used to investigate renal tubule function?
- There is transcellular transport over the luminal and basolateral membranes
- Clearance studies, Micropuncture/Isolated, Perfused tubule, Electrophysiology
What are the 2 types of nephrons?
- Cortical nephrons: short LoH, and has many capillaries surround the entire tubule.
- Juxta-medullary nephrons: long LoH, and the efferent arterioles extend into capillaries, called the VASA RECTA, which lie side-by-side with the LoH.
What is the function of the PCT?
Is highly metabolic/active and has an extensive brush border - large amount of reabsorption occurs here.
- Lots of water, and 100% of glucose and AA are taken back up.
- Any small proteins in the filtrate are taken up by the epithelial cell and broken down into AAs and sugars - can then move into the blood.
What are the 3 segments of the LoH? What are their structural differences?
- Thin descending limb
- Thin ascending limb - no microvilli, few mitochondria
- Thick ascending limb - large epithelial cells, some microvilli, lots of mitochondria
What is the main role of the LoH and how does it achieve this?
Main role is to concentrate/dilute the urine by altering the rate of water secretion and reabsorption.
- The LoH ↑osmolality (attracts water) in the medullary interstitium and creates a medullary osmotic gradient through the accumulation of solutes.
- Countercurrent Multiplication is where the filtrate flows down into the medulla and then back upwards out of the medulla - fluid in the descending limb has the same osmolarity as the blood plasma.
- The thick ascending limb is impermeable to water but NaCl can still be moved out = dilute filtrate - has to actively pump it out.
- As the filtrate becomes more dilute, solutes accumulate in the interstitium = ↑osmolality.
- The descending limb is permeable to water, so the high osmolarity in the interstitium causes water to move out of the descending limb.
*This whole effect is multiplied by the continuous entry of new fluid into the top of the LoH, as the osmotic gradient is maintained.
How does the vasa recta work?
As it descends into the medulla, it takes water IN and pumps salt OUT. Water moved into the interstitium by the descending limb is removed by the vasa recta.
*This keeps the medullary osmotic gradient unaffected.
What are the functions of the DCT?
Role is solute reabsorption without any water reabsorption. 1st part is the Macula dense and the 2nd part is highly convulated.
- ↑Na/K ATPase activity in the basolateral membrane
- Low water permeability - further dilutes the filtrate
*ADH can work in this region to affect water reabsorption.
What are the functions of the CD?
It has 2 cell types:
- Intercalated cells - urine acidification
- Principal cells - Na balance and ECF volume regulation
This region is the final area for the processing of urine, and is permeable to water and urea.
*ADH/Vasopressin action = ↑↑↑water permeability in the CD.
How does ADH (Vasopressin/AVP) concentrate/dilute the urine in the CD?
LOOK AT PICTURE IN NOTES!
Hypothalamus produces ADH, which works to conserve body water, and its secretion is regulated by osmoreceptors (plasma osmolarity), volume receptors, and arterial baroreceptors.
- ↑Plasma osmolarity = ↑ADH secretion
- ADH binds to V2 receptors on principal cells of CD = ↑Aquaporin synthesis and ↑cAMP/PKA in cell
- ↑cAMP = AQ moves to luminal membrane
- V2 activation also activates urea transporters to aid in urea reabsorption.
What is Polycystic Kidney Disease (PKD)
What is Glomerulonephritis (GN)
What is Diabetic Nephropathy
What are some abnormal urinary constituents?
- Genetic disorder with the growth of many cysts in the kidney.
- Inflammation of the glomerulus/nephrons due to e.g. diabetes. This can obstruct the tubules and impair transport functions.
- Consequence of diabetes as the filtering system is destroyed over time.
- Glucose (Diabetes), Protein, Ketone bodies (DKA), Blood (Trauma/stones/infection), Bile pigments (Liver disease), Pus (UTI).
