1 - Renal Histology Flashcards
4 functions of the kidney?
- Filters blood and removes waste as urine
- Produces hormones and enzymes (vit d, erythropoietin, renin)
- Regulates body water, salt and acid-base balance and so regulated BP
- Homeostatic regulation
Ureter vs urethra
Ureter exits kidney urethra exits body
The kidney is made up of lots of …. called nephrons
Filtering tubules
What is the centre of the kidney called and what does it contain?
Sinus/ cavity that is full of fat (even in cachexic people)
Where does the urine go once it exits the kidney
Ureter > bladder > urethra
What are nephrons
- the functional unit of the kidney
- there are approx 1 million per kidney
- they are a blood filter (renal corpuscle/glomerulus/capillary tuft enveloped by the tubule) and proximal, thin and distal tubules which then drain to the collecting ducts
What is the order of the structures in a nephron?
Renal corpuscle (containing glomerulus) Proximal convoluted tubule Proximal straight tubule Thin descending limb Thing ascending limb Thick ascending limb Distal convoluted tubule Collecting tubule Collecting duct
What makes up most the cortex?
The proximal convoluted tubules
What makes up the loop of henle?
Proximal straight tubule
Thin descending loop
Thin ascending loop
Thick ascending loop
Where does the filtration occur
Renal corpuscle
- salts proteins etc filtered out. The glomerulus doesn’t discriminate well - most needs to be reabsorbed
Where does bulk reabsorption occur
Proximal tubules (convoluted and straight)
- 65% of filtrate is reabsorbed in the proximal convoluted/straight tubules
- all of the glucose and salt, aa’s and water (bulk reabsorption of filtrate - secretion also occurs)
What occurs in the thin limbs and thick ascending limb?
Water extraction - IF required to make the urine more conc and retain water.
Distal convoluted, connecting tubule?
Fine tuning of salt levels, pH and water
Collecting ducts?
Water reabsorption
Renal corpuscle?
Contains a capillary tuft/glomerulus. Is surrounded by epithelial cells - podocytes which sit on the endothelial cells of the capillaries and parietal epithelial cells line the capsule
What is the vascular pole?
Where the afferent arteriole enters while the urinary pole is where the proximal convoluted tubule exits the renal corpuscle
Where does the filtrate go?
Urinary space
Where are podocytes and parietal epithelial cells continuous?
The VASCULAR pole
Describe the embryonic development of the renal corpuscle
The developing glomerulus invaginates into the tubule lining cells of the primitive renal tubule - the layer touching the glomerulus/endo cells will become the podocytes (visceral layer) while the outer layer is the parietal layer of the renal corpuscle
What dies the glomerular filtration barrier consist of?
3 major components
- Fenestrated endothelium of glomerular capillary
- Glomerular basement membrane
- Podocytes
- is a physical barrier, charge-selective barrier (negative charges such as albumin are repelled)
- restricts cells and large proteins
Glomerular Capillary Endothelium
- fenestrated; permeable to small molecules but restricts cells
- has a negative glycocalyx coat that is also IN the fenestrations
Glomerular BM
- thick
- the glomerular basement membrane is made up of collagen and negatively charged proteoglycans
- has a dense core and 2 less dense outer layers
- dense inner layer acts as a physical barrier (meshwork of fibres acts like a sieve)
- less dense layers act as a charge barrier as are negative and repel
Podocytes
The podocytes adhere to the GBM of the capillaries. Primary processes give off secondary processes that interdigitate that form slits and are linked by a protein bridge called a slit diaphragm (the slits form a physical filter). The podocytes are also covered in a glycocalyx coat.
Describe the slit membrane
Protein complexes that link adjacent secondary processes (covered in a glycocalyx)
What is podocyte effacement?
- podocyte effacement is the breakdown of foot processes
- is a common feature of glomerular pathology/disease
- results in albumin ‘leaking’ into the nephron which can be toxic/pro-inflam and so damages the kidney
What are mesangial cells?
Mesangial cells are smooth muscle cells that are packed inside the capillary tuft but not inside the BVs. They have a supportive/contractile role which acts to maintain the capillary tuft shape and also produces ECM that acts as glue to hold everything together - means they are involved in glomerularsclerosis (glomerular scaring) where if BP increases the mesangial cells proliferative and deposit more matrix to try and stabilise the apparatus
Cells involved in the juxtaglomerular apparatus?
- macula densa cells
- JG cells
- extraglomerular mesangial cells
Extraglomerular mesangial cells?
Transmit the signal from macula densa cells in TAL to the afferent arteriole
Macula densa cells
Cells in the thick ascending limb that sense the salt conc in the filtrate i.e. proxy for renal BF through the renal corpuscle
JG cells
SM cells in the wall of the afferent arteriole that SECRETE renin
What cells secrete renin?
JG cells in the wall of the afferent arteriole
What are the 2 major regulatory functions performed by the JG apparatus?
- the high distal tubular/TAL concentration of NaCl induces afferent arteriolar vasoconstriction (tubularglomerular FB)
- low tubular NaCl induces renin release ( will increase BP via PERIPHERAL vasoconstriction and so renal BF)
Features of the proximal tubule cells?
- bulk reabsorption
- cuboidal epithelium
- prominent brush border (microvilli) to increase SA for transporters
- pinocytosis (uptake of droplets with macromolecules like proteins)
- lateral processes and infoldings (interdigitation) to also increase SA
Thin limb cells?
- thin squamous cells
- water reabsorption (LOH)
- nuclei bulge into the lumen
Distal tubule cells?
- fine tuning of salt, pH, urine conc
- cuboidal cells
- lateral processes that interdigitate like the proximal tubule cels
- BUT no microvilli and no pinocytosis (less material to reabs)
Collecting duct cells?
Final modifier of salt, water and pH of urine. Cuboidal to columnar epithelium.
Describe the higher organisation of the kidney
- kidney is contained within the renal capsule
- consists of lobes which are divided into the medulla and the cortex
- the medulla is organised into conical structures called medullary pyramids
What is the apex of a medullary pyramid called?
Renal papillae which is enveloped by minor and then major calyces which fed into the renal pelvis (dilated end of the ureter)
The cortex consists of structures called … …
Medullary rays
Lobule?
In the centre consists of medullary rays which are parallel straight collectings ducts, surrounded by proximal and distal convoluted tubules, the lobule is bordered by BVs
Journey pf urine?
Glomerulus/renal corpuscle into the urinary space Prox convoluted tubule Proximal straight tubule Thin descending limb Thin asc limb TAL Distal convoluted tubule Connecting tubule Collecting duct Renal papillae at apex of medullary pyramid Minor and major calcyes Renal pelivs Ureter Bladder Urethra
Renal BVs?
Enter and exit at hilum (w/ureter) - Renal a - Interlobar a - Arcuate A - Interlobular A - afferent arteriole - glomerulus - efferent .... 2 paths
Where are the arcuate arteries formed?
At the boundary of the cortex and the medulla
What is the blood pathway for OUTER renal corpuscles? Superficial corpuscles that are close to the renal capsule?
The efferent arteriole forms peritubular capillaries which wrap around the proximal tubules and distal convoluted tubules and then enters the venous sytem that reflects the arteries (interlobular v > arcuate v…)
Blood pathway for deep renal corpuscles that are next to the cortical/medullary junction?
Efferent arteriole dives into the medulla where it formed the arterial vasa recta (parallel looped capillaries running down) which are bundled with the collecting ducts and LOHs. Venous return occurs via the venous vasa recta which are also bundled
> these vasa recta act by counter current to reabsorb water
What would happen if the vasa recta weren’t looped?
Then the vasa recta would take all the salt with it due to the gradient and so it would be hard to maintain the salt concentration in the medulla. We need to conc our urine in order to retain water. The vasa recta takes the salt and puts it back to preserve the gradient
