Lecture 28: THE NEPHRON Flashcards
How many nephrons per kidney?
Approximately 1 million
What is the nephron responsible for?
Urine formation
What are the two types of nephrons?
Cortical and juxtamedullary
What portion of nephrons are cortical?
85%
Where are cortical nephrons found?
Lie mainly in the cortex
Where are juxtamedullary nephrons found?
Extend deep into the medulla
What are juxtamedullary nephrons important for?
The formation of concentrated urine
What are the functions of the nephron and its associated structures?
Selectively filter blood, return to blood anything to be kept and carry waste away for storage and expulsion
What is each nephron comprised of?
A glomerular capsule, renal tubules and a collecting duct
What is each nephron associated with?
A glomerulus and peritubular capillaries
What are glomerular capillaries specialised for?
Filtration
What is the structure of glomerular capillaries?
Thin walled single layer of fenestrated endothelial cells
What are glomerular capillaries fed and drained by?
Arterioles
What is tightly regulated at the glomerular capillaries?
Blood pressure
What are peritubular capillaries specialised for?
Absoprtion
Where are peritubular capillaries found?
Wrapped around the renal tubules (proximal and distal)
What do the peritubular capillaries receive?
Filtered blood from the glomerulus via efferent arterioles
What can pass from the peritubular capillaries into the nephron?
Some non-filtered solutes that need to be excreted
What are vasa recta?
Extensions that follow the nephron loop deep into the medulla
Where are vasa recta found?
Only with juxtamedullary nephrons
What is the renal corpuscle?
The glomerulus enclosed by the glomerular capsule
What meets at the renal corpuscle?
The capillary and nephron
What is the renal corpuscle the site of?
The filtration barrier
What is the first part of the nephron?
The glomerular capsule
How many layers of the glomerular capsule?
Two
What is the layers of the glomerular capsule?
Outer parietal layer of simple squamous cells and inner visceral layer of podocytes
What is between the layers of the glomerular capsule?
The capsular space which receives the filtrate (primary urine)
Where are podocytes found?
Surrounding the glomerular capillaries
What is the structure of podocytes?
very branched, very specialised epithelium
What do the branches of podocytes form?
Intertwining foot processes called pedicels
What forms between pedicels?
Filtration slits
What goes through the filtration slits into the capsular space?
Filtered blood (filtrate)
Where is the filtration barrier found?
Between the blood and capsular space
What does the filtration barrier allow?
Passage of water and small molecules
What does the filtration barrier restrict?
Passage of most proteins
What isn’t filtered into the nephron?
RBC’s
How many layers are there to the filtration barrier?
Three
What are the layers of the filtration barrier?
fenestrated endothelium of glomerular capillaries, fused basement membrane and filtration slits between the pedicels of the podocytes
What is urine?
Waste fluid and solutes filtered from the blood
What happens to what 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
What does urine =?
Filtered-reabsorbed+secreted
What occurs at the PCT?
Bulk reabsorption
What is the PCT surrounded by?
Peritubular capillaries
What is the cells of the PCT?
Simple cuboidal epithelial
What is on the luminal membrane of the PCT cells?
Dense microvilli which forms a brush border to increase the surface area for reabsorption
How is the basolateral membrane of the PCT cells?
Highly folded
What does the PCT have lots of?
Mitochondria for active transport
How is the epithelium of the PCT?
Leaky (tight junctions aren’t very tight)
Where does the nephron loop go?
Down into the medulla
Why is the length of the nephron loop important?
For production of dilute/concentrated urine
What is the nephron loop surrounded by?
Vasa recta in juxtamedullary nephrons
What are the components fo the nephron loop?
Thick descending limb, thin descending limb, thin ascending limb, thick ascending limb
What is the structure of the thick descending limb?
Similar to the PCT
What is the structure of the thin descending limb?
Simple squamous epithelium
What is the structure of the thin ascending limb?
Simple squamous epithelium
What is the structure of the thick ascending limb?
Similar to the DCT
What does the nephron loop have different permeabilities to?
Water and sodium
What happens at the DCT?
Fine tuning (regulated reabsorption)
What is the epithelium of the DCT?
Cuboidal but thinner than the PCT
What is in the structure of the DCT?
Few microvilli - no brush border, fewer mitochondria
What is reabsorption at the DCT influenced mainly by?
Aldosterone
What happens at the collecting duct?
Fine tuning - regulated reabsorption
What drains into a collecting duct?
Filtrate from several DCT’s
Where does the collecting duct empty into?
The papilla
What is the structure of the collecting duct?
Wall of simple cuboidal epithelium, principal cells and intercalated cells
What is the role of principal cells?
Reabsorption
What is the role of intercalated cells?
Acid/base balance
What is reabsorption at the collecting duct influenced by?
ADH and aldosterone
What is the juxtaglomerular apparatus (JGA)?
A specialised zone in every nephron
Where is the JGA?
Where the DCT lies against the afferent arteriole
What are the specialised cells of the DCT at the JGA
Macula densa cells
What are macula densa cells?
Chemoreceptors which detect sodium levels in the filtrate in the DCT
What are the specialised cells of the afferent arteriole of the JGA?
Juxtaglomerular cells
What are juxtaglomerular cells?
Mechanoreceptors which detect blood pressure
What does the JGA control?
Glomerular filtration rate, ensuring the system is working at full capacity
What does the JGA stabilise?
Blood pressure
