Lecture 29 Flashcards
What is the nephron?
A microscopic functional unit of the kidney
How many nephrons are there per kidney?
~1 million
What is the nephron responsible for?
Urine formation
What are the two types of nephron?
Cortical and juxtamedullary nephrons
What are cortical nephrons?
Shallow nephrons that lie mainly in the cortex
What are juxtamedullary nephrons?
Nephrons that extend deep into the medulla
What are juxtamedullary nephrons import for?
The formation of concentrated urine
What is the function of the nephron?
To selectively filter blood, return specific filtrate to blood and carry waste away for storage and expulsion
What is the nephron composed of?
A glomerular capsule, renal tubules and a collecting duct
What is each renal tubule comprised of?
PCT, nephron loop, DCT
What is each nephron associated with?
A glomerulus and the peritubular capillaries
What are the glomerular capillaries?
They form the glomerulus and are specialised for filtration
What is the structure of the glomerular capillaries?
Thin-walled single layer of fenestrated endothelial cells
What feeds into and drains the glomerular capillaries?
Arterioles
What is tightly regulated around the glomerular capillaries?
Blood pressure
What are the peritubular capillaries?
Capillaries that wrap around the renal tubules that are specialised for absorption
What do the peritubular capillaries receive?
Filtered blood from the glomerulus via efferent arterioles and reabsorbed filtrate from nephrons
Can non-filtered solutes pass through the peritubular capillaries?
Yes
Why would non-filtered solutes enter the nephron from the peritubular capillaries?
To be excreted
What is the vasa recta?
Extensions from the peritubular capillaries that follow nephron loops deep into the medulla
Where are the vasa recta found?
Only in juxtamedullary nephrons
What is the renal corpuscle?
The glomerulus enclosed by the glomerular capsule, where capillary and nephron meet
What happens at the renal corpuscle?
Filtration
What is the glomerular capsule?
The first part of the nephron
What are the two layers of the glomerular capsule?
Outer parietal and inner visceral
What is the outer parietal layer of the glomerular capsule made of?
Simple squamose cells
What is the inner visceral layer of the glomerular capsule made of?
Podocytes
What is between the two glomerular layers?
The capsular space that receives filtrate
What are podocytes?
Specialised epithelium that wraps around the glomerular capillaries
What do podocytes form?
Pedicels from the branches foot processes intertwining
What is between the pedicels?
Filtration slits
What is the filtration barrier?
A selective barrier that lies between the blood and capsular space
What is the function of the filtration barrier?
To allow the passage of water and small molecules, restrict the passage of most proteins and completely inhibit RBCs from filtering into the nephron
What are the three layers of the filtration barrier?
- Fenestrated endothelium of glomerular capillary
- Fused basement membrane
- Filtration slits between the pedicels of the podocytes
What happens after filtration?
Not everything that is filtered is excreted, some filtrate is reabsorbed and some of what wasn’t filtered is secreted into the nephron
What is urine?
+ equation
Combination of waste fluid and solutes filtered from the blood
Urine = Filtered - Reabsorbed + Secreted
What happens in the proximal convoluted tubule?
Bulk reabsorption
What is the structure of the proximal convoluted tubule?
Cubodial epithelial with a dense microvilli brush boarder, highly folded basolateral membrane, many mitochondria and leaky epithelium
Is length of the nephron loop important?
Yes - in production of dilute or concentrated urine
What is the nephron loop?
The section of the nephron that extends into the medulla of the kidney
What is the nephron loop surrounded by?
Vasa recta in juxtamedullary nephrons
What are the four sections 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?
Cuboidal epithelial cells, similar to PCT
What is the structure of the thin descending limb?
Simple squamose epithelium
What is the structure of the thin ascending limb?
Simple squamose epithelium
What is the structure of the thick ascending limb?
Cuboidal epithelium, similar to DCT
What happens in the distal convoluted tubule?
Fine-tuning absorption
What is the structure of the distal convoluted tubule?
Cuboidal epithelium (thinner than PCT) with few microvilli so no brush boarder and fewer mitochondria
What is reabsorption in the DCT influenced by?
Hormones
What is the collecting duct?
The final part of the nephron that empties urine into the papilla, where many DCTs drain into one collecting duct
What happens in the collecting duct?
Fine-tuning reabsorption
What is the structure of the collecting duct?
A wall of cuboidal epithelial cells
What are the two types of epithelial cells in the collecting ducts?
Principal cells and intercalated cells
What are principle cells involved in?
Reabsorption
What are the intercalated cells involved in?
Acid/base balance
What is reabsorption in the collecting ducts influenced by?
Hormones
