Lecture 29: The Nephrons Flashcards
What is a nephron?
A microscopic functional unit of the kidney
Approximately how many nephrons are there per kidney?
1 million
What are nephrons responsible for the formation of?
Urine
What are the 2 types of nephrons?
- Cortical nephrons
- Juxtamedullary nephrons
What % of nephrons are cortical nephrons?
85%
Where do cortical nephrons lie?
In the cortex
Where do Juxtamedullary nephrons extend?
Deep into the medulla
What are Juxtamedullary nephrons important for?
Formation of concentrated urine
What are the 3 functions of the nephron?
- Selectively filter blood
- Return to blood anything to be kept
- Carry waste away for expulsion
What is each nephron comprised of?
5
- Renal corpuscle
- Proximal convoluted tubule
- Nephron loop
- Distal convoluted tubule
- Collecting duct
What is each nephron associated with?
2
- A glomerulus
- Peritubular capillaries
What are glomerular capillaries specialised for?
Filtration
What are glomerular capillaries?
Thin walled single layer of fenestrated endothelial cells
What are glomerular capillaries fed/drained by?
Arterioles
What is tightly regulated around glomerular capillaries?
Blood pressure
What are peritubular capillaries specialised for?
Absorption
What do peritubular capillaries wrap around?
Renal tubules
What do peritubular capillaries receive blood from/via?
From the glomerulus via efferent arterioles
What do the peritubular capillaries receive reabsorbed filtrate from?
Nephron
Some non-filtered solutes that need to be excreted can pass from the peritubular capillaries to where?
Into the nephron
What are vasa recta?
Extensions of pertibular capillaries that follow nephron loops deep into the medulla
Where are vasa recta found?
Only with juxtamedullary nephrons
What are renal corpuscles?
A glomerulus enclosed by the glomerular capsule
The renal corpuscle is where what meet?
The capillary and nephron
The renal corpuscle is the site of what?
The filtration barrier
What is the glomerular capsule?
The first part of the nephron
What 2 layers make the glomerular capsule?
- Outer parietal layer
- Inner visceral layer
What is the parietal layer of the glomerular capsule made from?
Simple squamous cells
What is the visceral layer of the glomerular capsule made from?
Podocytes
What is between the outer parietal layer and the inner visceral layer of the glomerular capsule?
Capsular space
What does the capsular space receive?
Filtrate
What do podocytes surround?
The glomerular capillaries
Podocytes are very branched, very specialised what?
Epithelium
Podocyte branches form intertwining what?
Foot processes called pedicels
What forms between pedicels?
Filtration slits
What happens to filtered blood going through filtration slits?
It passes into capsular space
Where does the filtration barrier lie?
Between blood and capsular space
What does the filtration barrier allow the free passage of?
Water and small molecules
What does the filtration barrier restrict?
The passage of most proteins
What is not filtered through the filtration barrier into the nephron?
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
Urine is waste fluid and what?
Solutes filtered from the blood
Not everything that is filtered is what?
Excreted
What happens to some filtrate?
It is reabsorbed
Some of what isn’t filtered, is secreted where?
Into the nephron
Urine = ?
Filtered - Reabsorbed + secreted
What is the function of the proximal convoluted tubule?
Carry out the bulk of reabsorption
What are proximal convoluted tubules surrounded by?
Peritubular capillaries
What cells make up the proximal convoluted tubule?
Cuboidal epithelial cells
There is a dense what on the luminal membrane of the proximal convoluted tubule?
Microvilli (brush border)
The proximal convoluted tubule has a highly folded what?
Basolateral membrane
The proximal convoluted tubule has many mitochondria for what?
Active transport
Where does the nephron loop extend down into?
The medulla
What is the length of the nephron loop important for?
Production of dilute/concentrated urine
What is the nephron loop in juxtamedullary nephrons surrounded by?
Vasa recta
What are the 4 regions of the nephron loop?
- Thick descending limb
- Thin descending limb
- Thin ascending limb
- Thick ascending limb
What is the structure of the thick descending limb of the nephron loop?
Similar to PCT structure
What is the structure of the thin descending limb of the nephron loop?
Simple squamous epithelium
What is the structure of the thin ascending limb of the nephron loop?
Simple squamous epithelium
What is the structure of the thick ascending limb of the nephron loop?
Similar to DCT structure
The nephron loop has different permeabilities to what?
Water and sodium
What is the function of the distal convoluted tubule?
Fine tuning/regulated absorption (hormonal regulation)
What cells make up the distal convoluted tubule?
Cuboidal epithelium, but thinner than PCT
Because there are only a few microvilli on the distal convoluted tubule there is no what?
Brush border
there are fewer what at the distal convoluted tubule?
Mitochondria
What is reabsorption mainly influenced by in the distal convoluted tubule?
Aldosterone
What is the function of the collecting duct?
Fine tuning/regulated absorption
Filtrate from several DCT’s drain into what?
One collecting duct
What is the structure of collecting ducts?
Wall of simple cuboidal epithelium
What 2 cells are found in Collecting duct walls?
- Principal cells
- Intercalated cells
What is the role of principle cells?
Reabsorption
What is the role of intercalated disks?
Acid/base balance
What is reabsorption in the collecting duct influenced by?
2
- ADH
- Aldosterone
What is the juxtaglomerular apparatus?
A specialised zone in every nephron
Where is the juxtaglomerular apparatus located?
Where DCT lies against afferent arterioles
What are the specialised cells of the DCT in the juxtaglomerular apparatus?
Macula densa cells
What are the specialised cells of the afferent arterioles in the juxtaglomerular apparatus?
Juxtaglomerular cells
What are macula densa cells?
Chemoreceptors detecting sodium levels
What are Juxtaglomerular cells?
Mechanoreceptors that detect blood pressure
What does the juxtaglomerular apparatus control?
The glomerular filtration rate
What does the juxtaglomerular apparatus ensure?
The system is working at full capacity
What does the juxtaglomerular apparatus stabilise?
Blood pressure