Lecture 29: The nephron Flashcards
How many nephron approximately are in each kidney?
about 1 million per kidney
What are the two types of nephron?
Cortical nephrons
Juxtamedullary nephrons
What type of nephron is more common?
Cortical nephrons
- about 85%
- Lie mainly in cortex
What is the main role of juxtamedullary nephrons?
They Extend deep into medulla
Important for the formation of concentrated urine
What is each nephron comprised of?
– A Glomerular capsule
– Renal tubules:
- Proximal Convoluted Tubule, nephron loop, Distal Convoluted Tubules
– A collecting duct
What is each nephron associated with?
– A glomerulus (capillary bed)
– Peritubular capillaries
Is blood pressure regulated in the glomerular capillaries?
- Fed and drained by arterioles
- Blood pressure here is tightly regulated
How are glomerular capillaries specialised for filtration?
- Thin walled single layer of FENESTRATED endothelial cells
What are vasa recta and where can they be found?
- Extensions (of peritubular capillaries) that follow nephron loops deep into the medulla
- Only found with juxtamedullary nephrons
What is the role of peritubular capillaries?
- Specialised for re-absorption
- Wrap around renal tubules
- Receives filtered blood from glomerulus via efferent arterioles
- Receives reabsorbed filtrate from nephron
- Some non-filtered solutes that need to be excreted can pass from here into nephron
What is the renal corpuscle and what is its function?
- First part of nephron
- Glomerulus enclosed by the Glomerular capsule
- Where capillary and nephron meet
- Site of filtration barrier (encapsulates filtrate)
What are the outer (parietal) and inner (visceral) layers of the glomerular capsule made of?
- Outer parietal layer of simple squamous cells
- Inner visceral layer of podocytes
Where is filtrate initially captured?
Between the two layers is the capsular space which
receives filtrate (glomerular capsule)
What specialised cell covers glomerular capillaries and what is their role?
Podocytes
- Specialised epithelium with many branches
- Branches form intertwining foot processes called pedicels
- Filtration slits form between pedicels
- Filtered blood (filtrate) goes through these slits and passes into capsular space
What does the filtration barrier let through and what does it keep in the blood?
- Allows free passage of water and small molecules
- Restricts passage of most proteins
- RBCs are not filtered into nephron
What are the three layers of the filtration barrier (in to out)?
– Fenestrated endothelium of glomerular capillary
– Fused basement membrane
– Filtration slits between the pedicels of the podocytes
Which of the following is not a component of the
blood-urine barrier:
A. Fused basement membrane
B. Filtration slits
C. Pedicels
D. Sinusoidal endothelium
D
What happens after blood is filtered?
- Not everything that is filtered is excreted
- Some filtrate is reabsorbed
- And some of what wasn’t filtered is secreted into the nephron
Where does bulk reabsorption occur?
Proximal convoluted tubule (PCT)
What is the structure of proximal convoluted tubules that allow their function?
Function: bulk reabsorption
– Cuboidal epithelial cells
– Dense microvilli (brush border) on luminal membrane
– Highly folded basolateral membrane
– Many mitochondria for active transport
– Leaky epithelium
Where does fine tuning reabsorption occur and how is it influenced?
Distal convoluted tubules (DCT) and Collecting duct
Reabsorption influenced by hormones
What type of epithelium do distal convoluted tubules have and what does their structure lack?
Cuboidal epithelium, but thinner than PCT
Structure:
- Few microvilli = no brush border
- Fewer mitochondria (less active transport)
How does the length of the nephron loop affect its function?
Loops down into the medulla:
Length is important in production of dilute/concentrated urine. Longer = more concentrated
What is the structure of the thick/thin descending limb and thick/thin ascending limb of the nephron loop? (epithelium)
Thick descending limb
- Similar to PCT structure
Thin descending limb (thin segment cells)
- Simple squamous epithelium
Thin ascending limb
- Simple squamous epithelium (thin segment cells)
Thick ascending limb
- Similar to DCT structure
