lecture 29 - the nephron Flashcards
How many nephrons are found in each kidney?
1 million
What are the 2 types of nephron?
Cortical and juxtamedullary nephrons
What is the major type of nephron, making up 85% of all nephrons?
Cortical nephrons
Where do cortical nephrons mainly lie?
The cortex of the kidneys
Where do juxtameduallry nephrons sit?
Glomerular capsule and tubules in the cortex, but the nephron loop extends deep into the medulla
What are juxtamedullary nephrons important for?
The formation of concentrated urine
What are the 3 key components of a nephron?
A glomerular capsule, renal tubules and a collecting duct
What blood vessels are each nephron associated with?
A glomerulus and peritubular capillaries
What are glomerular capillaries specialised for?
Filtration
What is the structure of glomerular capillary walls?
Single layer of fenestrated endothelial cells
What regulates glomerular capillary blood pressure?
Input and output via the afferent and efferent arteriolar sphincters
What are the peritubular capillaries specialised for?
Absorption - are fenestrated
Where are the peritubular capillaries located?
Wrapped around the renal tubules
What blood do the peritubular capillaries receive?
Filtered blood from the glomerulus via efferent arterioles
How do peritubular capillaries remove unwanted solutes?
Some solutes that were unfiltered in the glomerulus and need to be excreted can pass into the nephron via secretion
What are the vasa recta?
Extensions of the peritubular capillaries that follow juxtamedullary nephron loops deep into the medulla
What type of nephrons have vasa recta?
Only juxtamedullary nephrons - not cortical nephrons
What is the renal corpuscle?
The first part of a nephron, where the glomerulus sits, enclosed by the glomerular capsule. Where the capillary and nephron meet, and where filtration occurs
What is the site of the filtration barrier in the kidneys?
The renal corpuscle of nephrons
What are the 2 layers of the glomerular capsule?
Outer parietal layer of simple squamous cells, and an inner visceral layer of podocytes
What sits between the 2 layers of the glomerular capsule?
The capsular space/urinary space
What is the function of the capsular space in the glomerular capsule?
Receives filtrate from the filtration of blood in the glomerular capillaries
Where are podocytees located?
Make up the inner layer of the glomerular capsule in the renal corpuscles of the kidneys
What is the structure of a podocyte?
Highly branched, specialised epithelial cell that has branches that form intertwining foot processes called pedicels with filtration slits between them.
What is the name for the intertwining foot process of podocytes?
Pedicels
What is the name for the gaps between pedicels?
Filtration slits
What is the function of filtration slits in the glomerulus?
Filtered blood (filtrate) goes though these slits and passes into the capsular space
What does the kidney filtration barrier allow the passage of?
water and small molecules
What does the kidney filtration barrier restrict the passage of?
Most proteins, and red blood cells
What are the 3 layers of the filtration barrier?
Fenestrated endothelium of glomerular capillary, fused basement membrane, filtration slits between the pedicels of the podocytes
What are the 2 tubules in a nephron?
Proximal convoluted tubule and distal convoluted tubule
What is the function of the proximal convoluted tubules?
Bulk reabsorption of filtered solutes
What type of epithelium makes up the proximal convoluted tubule?
Simple cuboidal epithelium
What feature of proximal convoluted tubule increases the surface area within the lumen?
Dense microvilli brush border on the luminal membrane
What feature of proximal convoluted tubule increases the surface area on the outside of the tube?
Highly folded basolateral membrane
What organelle is very prevalent in the epithelium of the proximal convoluted tubules, and why?
Mitochondria - because the active transport required for bulk reabsorption requires a lot of energy
Why is the epithelium of the proximal convoluted tubules leaky?
To allow for diffusion across the tight junctions between cells - paracellular transport
What does the length of a nephron loop determine?
The concentration of urine
What are the 4 parts of the nephron loop?
Thin descending limb, thick descending limb, thin ascending limb, thick ascending limb
What is the main function of the distal convoluted tubule?
‘Fine tuning’ of absorption - reabsorption if necessary
What type of epithelium makes up the distal convoluted tubule?
Simple cuboidal epithelium
Does the distal or proximal convoluted tubule have a thinner epithelial wall?
Distal
What is the structure of a distal convoluted epithelial cell?
Few microvilli - so no brush border. Fewer mitochondria than the PCT
What is reabsorption by the distal convoluted tubule influenced by?
Aldosterone & ADH
What is the process of drainage from collecting ducts?
Filtrate from several nephron DCTs drain into one collecting duct, which empty at papilla.
What epithelium type makes up collecting ducts in the kidneys?
Simple cuboidal
What is the cellular structure of the collecting ducts in the kidneys?
Wall of simple cuboidal epithelium, with principal and intercalated cells
What is the function of principal cells in the collecting duct?
Reabsorption of solutes in the filtrate
What is the function of intercalated cells in the collecting duct?
Acid/base balance
What hormones influence reabsorption in the collecting duct?
Aldosterone and ADH (anti-diuretic hormone)
