HUBS192 Lecture 29 - Urinary System II, The Nephron Flashcards
approximately how many nephrons per kidney?
approx. 1 million per kidney
what does the juxtamedullary nephron describe?
describes where the renal corpuscle and the glomerulus meet where they are located
what are the 2 types of nephrons?
1) cortical nephrons
2) juxtamedullary nephrons
where are cortical nephrons located?
lie mainly in the cortex with some parts in the medulla
how many percent does the cortical nephrons make up of the nephrons in the body?
85%
where is the renal corpuscle of juxtamedullary nephrons located?
renal corpuscle right at the border between the medulla and the cortex above it
where are juxtamedullary nephrons located?
extend deep into the medulla
what are juxtamedullary nephrons important for?
important for the formation of concentrated urine
what are the 3 functions of the nephron?
1) selectively filter blood
2) return to blood anything to be kept/wanted
3) carry waste away for storage & explusion
what 3 parts are each nephron comprised of?
1) a glomerular capsule
2) renal tubules
3) a collecting duct
what 2 capillaries are each nephron associated with?
1) a glomerulus (glomerular capillaries)
2) peritubular capillaries
what are glomerular capillaries?
thin walled single layer of fenestrated endothelial cells
how is blood fed and drained through fenestrated endothelial cells?
fed by afferent arterioles and drained by efferent arterioles
what is tightly regulated at the glomerular capillaries?
blood pressure is tightly regulated
what are the glomerular capillaries specialised for?
specialised for filtration
why are peritubular capillaries called peritubular capillaries?
because they wrap around renal tubules
what are peritubular capillaries specialised for?
specialised for absorption
what do peritubular capillaries carry?
carries filtered blood from the efferent arterioles
what do peritubular capillaries receive?
receives reabsorbed filtrate from the nephron
where can the peritubular capillaries secrete into?
secrete into the nephron
what are vasa recta?
extensions that follow loops deep into the medulla and are only found in juxtamedullary nephrons
where are vasa recta only found with?
only found with juxtamedullary nephrons
what is the glomerulus?
bundle of glomerular capillaries
what is the glomerulus capsule enclosed by?
enclosed by the glomerular capsule
what is the renal corpuscle the site of?
site of the filtration barrier
what is the first part of the nephron?
the glomerular capsule
why is the outer parietal layer of the glomerular capsule made up of simple squamous cells?
to stop whatever is filtered from leaking back out
what is filtrate?
what is taken out of the blood that may become urine before it travels down the nephron tubes
what are the 3 layers of the glomerular capsule from outer to inner?
1) outer parietal layer composed of simple squamous cells
2) capsular space which receives filtrate
3) inner visceral layer composed of podocytes
what is the outer parietal layer of the glomerular capsule made up of?
simple squamous cells
what is the inner visceral layer of the glomerular capsule made up of?
podocytes
what does the capsular space receive?
receives filtrate
what are filtration slits?
gaps formed between the pedicels
how do podocytes wraps around capillaries?
by interdigitating and surrounding the glomerular capillaries
what is the function of pedicels?
pedicels interdigitate and sit over the fenestrations making filtration more selective
what are pedicels?
branches that have formed intertwining foot processes
what forms between pedicels?
filtration slits
how does blood pass through the filtration slits?
filtered blood (filtrate) goes through the filtration slits and passes into the capsular space
what is the main function of the filtration barrier?
restrict what passes through mainly based on size
-mostly proteins and RBC’s are too large to be filtered into the nephron
what is the filtration barrier?
blood-urine barrier or glomerular capsular membrane
where does the filtration barrier lie between?
lies between the blood and the capsular space
what does the filtration barrier allow?
allows the free passage of water and small molecules
what are the 3 layers of the filtration barrier?
1) fenestrated endothelium of the glomerular capillary
2) fused basement membrane
3) filtration slits between the pedicels of the podocytes
what happens after filtration?
- not everything that is filtered is excreted
- some filtrate is absorbed
- some of what wasn’t filtered is secreted into
what is urine in terms of filtration?
urine = filtered - reabsorbed + secreted
what is the proximal convoluted tubule (PCT)?
the bulk reabsorption site
where is the proximal convoluted tubule (PCT) located?
located in the cortex surrounded by peritubular capillaries
what are the 5 components that make up the structure of the proximal convoluted tubule (PCT)?
- cuboidal epithelial cells
- dense microvilli (brush border) on the luminal membrane
- highly folded basolateral membrane
- many mitochondria for active transport
- leaky epithelium
where does the nephron loop always loop down into?
loops down into the medulla
what is the relationship between length of the nephron loop and urine?
length is important in the production of dilute/concentrated urine
what is the nephron loop surrounded by?
surrounded by vasa recta (juxtamedullary nephrons only)
what are the 4 parts of the structure of the nephron loop?
1) thick descending limb
- like the proximal convoluted tube
2) thin descending limb
- composed of simple squamous epithelium
3) thin ascending limb
- composed of simple squamous epithelium
4) thick ascending limb
- like the distal convoluted tube
what are the thin descending limb and the thin ascending limb made up of?
simple squamous epithelium
what is the relationship between different areas of the nephron loop and permeability?
different areas have different permeabilises to water and sodium
what is the function of the distal convoluted tube (DCT)?
fine tuning
what is the distal convoluted tube (DCT) composed of?
cuboidal epithelium but thinner layer than in the proximal convoluted tube (PCT)
what are the 3 structures that make up the distal convoluted tube (DCT)?
1) no bush order because of few microvilli
2) fewer mitochondria
3) reabsorption regulated mailing by aldosterone
what occurs at the collecting duct?
receive filtrate from several distal convoluted tubes (DCTs) that drain into one collecting duct which empty at a papilla
what is the function of a collecting duct?
fine tuning
what 3 structures is the collecting duct made up of?
1) wall of simple cuboidal epithelium
2) principal cells for absorption
3) intercalated cells for acid/base balance
what is the function of principal cells?
reabsorption
what is the function of intercalated cells?
acid/base balance
what is reabsorption regulated by in the collecting duct?
regulated by antidiuretic hormone (ADH) and aldosterone
what is the juxtaglomerular apparatus (JGA)?
specialised zone in every nephron
where is the juxtaglomerular apparatus (JGA) located?
located where the distal convoluted tube (DCT) lies against the afferent arteriole
what are the macula densa cells
chemoreceptors in the distal convoluted tube (DCT) that detect sodium levels
what are juxtaglomerular cells?
mechanoreceptors in the afferent arteriole that detect blood pressure through stretch
what are mechanoreceptors?
stretch receptors that detect blood pressure
what is the function of the juxtaglomerular apparatus (JGA)?
controls glomerular filtration rate ensuring that system is working at full capacity and stabilises blood pressure
what term is used when passing through the nephron?
filtrate
what term is used when passing through the kidney?
urine
what are the cells that form the visceral layer of the glomerular capsule called?
podocytes
what are the cells of the juxtaglomerular apparatus (JGA) on the afferent arteriole called?
juxtaglomerular
what type of epithelial cells would you find in nephron loop?
cuboidal with microvilli brush border at part closest to the proximal convoluted tube (PCT), simple squamous, cuboidal with few microvilli at part closest to distal convoluted tube (DCT)
what are the 2 capillary beds associated with the nephron?
glomerular and peritubular
which type of nephron is important for the production of concentrated urine?
juxtamedullary
