Lecture 29: The nephron

Question 1

How many nephron approximately are in each kidney?

Answer 1

about 1 million per kidney

Question 2

What are the two types of nephron?

Answer 2

Cortical nephrons

Juxtamedullary nephrons

Question 3

What type of nephron is more common?

Answer 3

Cortical nephrons
- about 85%
- Lie mainly in cortex

Question 4

What is the main role of juxtamedullary nephrons?

Answer 4

They Extend deep into medulla

Important for the formation of concentrated urine

Question 5

What is each nephron comprised of?

Answer 5

– A Glomerular capsule

– Renal tubules:
- Proximal Convoluted Tubule, nephron loop, Distal Convoluted Tubules

– A collecting duct

Question 6

What is each nephron associated with?

Answer 6

– A glomerulus (capillary bed)
– Peritubular capillaries

Question 7

Is blood pressure regulated in the glomerular capillaries?

Answer 7

• Fed and drained by arterioles
• Blood pressure here is tightly regulated

Question 8

How are glomerular capillaries specialised for filtration?

Answer 8

• Thin walled single layer of FENESTRATED endothelial cells

Question 9

What are vasa recta and where can they be found?

Answer 9

• Extensions (of peritubular capillaries) that follow nephron loops deep into the medulla
• Only found with juxtamedullary nephrons

Question 10

What is the role of peritubular capillaries?

Answer 10

• 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

Question 11

What is the renal corpuscle and what is its function?

Answer 11

• First part of nephron
• Glomerulus enclosed by the Glomerular capsule
• Where capillary and nephron meet
• Site of filtration barrier (encapsulates filtrate)

Question 12

What are the outer (parietal) and inner (visceral) layers of the glomerular capsule made of?

Answer 12

• Outer parietal layer of simple squamous cells
• Inner visceral layer of podocytes

Question 13

Where is filtrate initially captured?

Answer 13

Between the two layers is the capsular space which
receives filtrate (glomerular capsule)

Question 14

What specialised cell covers glomerular capillaries and what is their role?

Answer 14

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

Question 15

What does the filtration barrier let through and what does it keep in the blood?

Answer 15

• Allows free passage of water and small molecules
• Restricts passage of most proteins
• RBCs are not filtered into nephron

Question 16

What are the three layers of the filtration barrier (in to out)?

Answer 16

– Fenestrated endothelium of glomerular capillary
– Fused basement membrane
– Filtration slits between the pedicels of the podocytes

Question 17

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

Answer 17

D

Question 18

What happens after blood is filtered?

Answer 18

• Not everything that is filtered is excreted
• Some filtrate is reabsorbed
• And some of what wasn’t filtered is secreted into the nephron

Question 19

Where does bulk reabsorption occur?

Answer 19

Proximal convoluted tubule (PCT)

Question 20

What is the structure of proximal convoluted tubules that allow their function?

Answer 20

Function: bulk reabsorption

– Cuboidal epithelial cells
– Dense microvilli (brush border) on luminal membrane
– Highly folded basolateral membrane
– Many mitochondria for active transport
– Leaky epithelium

Question 21

Where does fine tuning reabsorption occur and how is it influenced?

Answer 21

Distal convoluted tubules (DCT) and Collecting duct

Reabsorption influenced by hormones

Question 22

What type of epithelium do distal convoluted tubules have and what does their structure lack?

Answer 22

Cuboidal epithelium, but thinner than PCT

Structure:
- Few microvilli = no brush border
- Fewer mitochondria (less active transport)

Question 23

How does the length of the nephron loop affect its function?

Answer 23

Loops down into the medulla:

Length is important in production of dilute/concentrated urine. Longer = more concentrated

Question 24

What is the structure of the thick/thin descending limb and thick/thin ascending limb of the nephron loop? (epithelium)

Answer 24

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

Question 25

What does the collecting duct do?

Answer 25

Filtrate from several DCTs drains into one collecting duct, which empty at papilla

Question 26

What is the structure of the collecting duct and what are the two types of cells and their roles present?

Answer 26

Structure:
Wall of simple cuboidal epithelium

Principal cells - Reabsorption (flat cells in duct)

Intercalated cells - Acid/Base balance (spikey cells in duct)

Question 27

The cells that form the visceral layer of the Glomerular capsule are called:
A. Pedicels
B. Podocytes
C. Filtration slits
D. Peritubular

Answer 27

B