Function and description of the kidneys
Bean shaped organ the size of your fist that sits retroperitoneal in the body cavity.
- Filter the blood and produce urine.
- Major homeostatic regulator of blood, salt and pH (acid-base balance) in the body.
- Regulate BP
- Produce hormones/enzymes (epo, renin, vit D)
Label this Diagram
Cortex: outer layer/rind
Renal Large cavity lined with epithelium
Urine flows from this to urethra eventually.
What is a Nephron
- Functional unit of the kidney.
- There are ~1 million per kidney
- Comprimised of a blood filter attached to a tubular epithelium
"blood filter" = Renal corpuscle (capillary tuft surrounded by tubule)
Proximal, thin and distal tubules.
- Drain to collecting ducts
Label this Diagram
Shaded Segments: Make up loop of Henle
Allows urine to be concentrated so that we can conserve water!
What is the function of the nephron at the?
Thick and thin ascending limb:
Distal convoluted and connecting tubules:
Renal Corpuscle: Blood filtration
Proximal Tubules: Bulk reabsorption (66% of filtrate, eg: glucose, salts aa, water), secretion (drugs)
Thick and thin ascending limb: Urine concentration
Distal convoluted and connecting tubules: Fine tuning of salts, pH
Collecting Duct: reabsorption of water
The Renal Corpuscle, what makes it up? Podocytes vs parietal cells
Corpuscle= Bowmans capsule + Glomerulus
Glomerulus: Capillary Tuft: Usually fills but cells shrink post-mortum
Bowman's capsule: Podocytes envelope capillaries, whereas parietal cells form outside layer (squamous epi). Podocytes and parietal epithelium are actually continuous with urinary space between.
The Renal Corpuscle, how does it work?
Blood comes in via the afferent arteriole into the capsule via the vascular pole, passes through the loops (capillary tuft made of podocytes), and exits via an efferent arteriole
Vascular vs urinary pole?
Vascular Pole: Where the vessels enter the capsule
Urinary pole: Where the filtered urine flows into the next bit of the nephron, the proximal tubule
Urinary Space/ Bowman's capsule.
Cup-like sac enclosing a glomerulus at the begining of the tubular component of a nephron. Lined by parietal epithelium and podocytes.
Visceral Layer: Podocytes
Parietal Layer: Parietal epithelium
Formed by embryonic primitive Renal tubule invaginating around the glomerulus.
The glomerular Filtration Barrier, with its 3 layers.
- Endothelial Layer: Fenestrated (holes)
- Glomerular Basement Membrane: Quite thick
- Podocytes: with foot processes that form 'interdigitations' with other cells
Therefore the Glomerular filtration barrier is not only a Physical Barrier (holes and slits), and a Charge-Selective Barrier (lots of negative charge on the filter, so many things are stopped)
Restricts Cells, albumin (most abundant plasma protein) and other larger proteins.
What defines the 'Glomerular Capillary Endothelium' and what special substance is it involved with?
In cross-section you can see the holes (fenestrations), like swiss cheese. The fenestrations are coated in a negatively charged glycocalyx coat (repels proteins in the plasma, most of which are negatively charged)
The Glomerular Basement Membrane
Thick, made up of collagen and lots of negatively charged proteogycans.
Dense core and less dense outer layers.
Acts as a Physical (inner core) Barrier and charge barrier (outer core layer)
Have Primary and secondary processes, that lock into cones of other podocytes.
- Adhere to GBM
- Primary and secondary processes that interdigitate
- Form slits linked by a protein bridge (slit membrane)
- Convered in negatively charged glycocalyx
The Slit Membrane
- Fine Filter, a protein bridge between foot processes
- Covered in a glycocalyx coat (negatively charged)
As you cansee there's a lot a molecule has to pass through!
What happens if any of the GF layers are defected? What would this look like?
A defect would lead to a 'leaky' glomerular filter. There is no nice foot processes, it is 'effaced' and flattened.
This happens in diabetes.
Smooth Muscle cells packed inside capillary tuft.
- Have supportive/contractile role for capillary tuft
- Produce ECM (needed in diabetic nephropathy where mesangial cells aren't enough)
- Involved in glomerulosclerosis
Diabetic Nephropathy: damage to kidneys due to diabetes → lots of sclerosis in the nephron, "focal segmental glomerulosclerosis'.
Mesangial cells are doing there best to hold everything together and they do that by producing/pumping out ECM, but that actually constricts capillaries in that region, and the filtration is compromised. (defective Nephron > renal failure or high BP)
- JG cells: modified SM cells in the wall of the afferent arteriole that secrete renin (ezyme that generates angiotensin)
- Macula Densa Cells: Special cells in the walls of TAL that sense salt conc of filtrate
- Extraglomerular Mesangial cells
High salt hits TAL, macula densa stimulates JG cells, they constrict.
Proximal Tubule cells: for bulk reabsorbtion
Prominant Brush border (microvilli): increase SA on apical side
Pinocytosis (uptake of droplets with macromolecules eg proteins)
Lateral processes and infoldings (interdigitation) to increase SA
Thin desc/asc Limb Cells
- Thin squamous Epithelium
- Role in water reabsorption as a part of the loop of henle
- Nuclei bulge into lumen
Distal Tubule Cells
No longer for bulk reabsorption, now just for fine tuning!
- Fine tuning salt, pH (DCT, CNT) and urine concentration
- Interdigitating lateral processes and infoldings (like proximal)
- No brush border
- No pinocytosis