The Nephron Flashcards
What are the two types of nephron?
- microscopic functional unit of the kindeys
- approx 1 million per kidney
- responsible for urine formation
Cortical nephrons:
- make up 85% of all nephrons
- lie mainly in cortex
Juxtamedullary nephrons:
- (nephron loop) extend deep into medulla
- important for the formation of concentrated urine
- renal corpuscle sits right on the boarder of the medulla
describe the function of the nephron and associated structures
Function:
- selectively filter blood
- return to blood anything to be kept
- cary waste away for storage and expulsion
Each nephron is comprised of:
- a glomerular capsule
- renal tubes (PCT, nephron loop, DCT)
Each nephron is associated with:
- a glomerullus
- peritubular capillaries
describe glomerular capillaries
- forms glomerulus
- specialised for filtration
- thin walled single layer of fenestrated endothelial cells
- fed and drained by arterioles
- blood pressure here is tightly regulated
describe peritubular capillaries
- specialised for absoption
- wrap around renal tubes
- receives filtered blood from glomerulus vis efferent arterioles
- receives reabsorbed filtrate from nephron
- some non-filtered solutes that need to be excreted can pass from here into nephron
- vasa recta (extensions that follow nephron loops deep into the medulla, only found with juxtamedullary nephrons)
describe the renal corpuscle
- glomerulus enclosed by the glomerular capsule
- where capillary and nephron meet
- site of filtration barrier
describe the glomerular capsule
- first part of nephron
- aka bowman’s capsule
- two layers:
- outer parietal layer of simple squamous cells
- inner visceral layer of podocytes - between the two layers is the capsular space which receives filtrate
describe podocytes
- wrap around the glomerular capillaries
- specialised epithelium with many branches
- branches form intertwining foot processes called pedicels
- filtration slits for between pedicels (do NOT merge, the cells are still separate structures)
- filtered blood (filtrate) goes through these slits and passes into capsular space
describe the filtration barrier
- aka. blood-urine barrier/glomerular capsular membrane
- lies between blood and capsular space
- allows free passage of water and small molecules
- restricts passage of most proteins
- RCSs are not filtered into nephron
Three layers:
- fenestrated endothelium of glomerular capillary
- fused basement membrane
- filtration slits between the pedicels of the podocytes
what happens after filtration?
- urine is waste fluid and solutes filtered from the blood
- not everything the is filtered is excreted
- some filtrate is reabsorbed
- and some of what wasn’t filtered is secreted into the nephron
- so, urine = filtered - reabsorbed + secreted
describe features of the proximal convoluted tubule (PCT)
Bulk reabsorption
Surrounded by peritubular capillaries
Structure:
- cuboidal epithelial cells (not enough space for columnar)
- dense microvilli (rush boarder) on luminal membrane
- highly folded basolateral membrane
- many mitochondria for active transport
- leaky epithelium
describe the features of the nephron loop
Aka loop of Henle
Loops down into the medulla:
- length is important in production of dilute/concentrated urine
Surrounded by vasa recta (juxtamedullary nephrons only)
Structure:
- thick depending limb (similar to PCT structure, cuboidal epithelium)
- thin depending limb (simple squamous epithelium)
- thin ascending limb (simple squamous epithelium)
- thick ascending limb (similar to DCT structure, cuboidal epithelium)
Different permeabilities to water and sodium
describe the features of the distal convoluted tubule (DCT)
- fine tuning
- cuboidal epithelium, but thinner than PCT (don’t ned as much surface area bc less absorption)
Structure:
- few microvilli = no brush boarder
- fewer mitochondria
- reabsorption influenced by hormones
describe the features of the collecting duct
- fine tuning
- filtrate from several DCTs drains into one collecting duct, which empty at papilla
- reabsorption influenced by hormones
structure:
- wall of simple cuboidal epithelium
- principal cells (reabsorption)
- intercalated cells (acid/base balance)
what does understanding the epithelium throughout the nephron help you do?
understand the function of each section
brief overview of urine/filtrate through the nephron and kidney
Nephron:
- glomerular capsule (vascular pole is the end where blood vessels go in and out of, urinary pole is where the tubular part of the nephron starts)
- capsular space
- PCT
- Nephron loop
- DCT
- collecting duct
Kidney:
- papilla
- minor calyx
- major calyx
- renal pelvis
- ureter
