Lecture 29 Nephron Flashcards
whats the nephron?
Microscopic functional unit of the kidney
Approx. 1 million per kidney
Responsible for urine formation
what are the types of nephrons?
Cortical nephrons
Juxtamedullary nephrons
whats Cortical nephrons?
85%
Lie mainly in cortex
whats Juxtamedullary nephrons?
Extend deep into medulla
From renal corpuscle
Important for formation of concentrated urine
Not much water, other solutes remain
whats the function of nephron?
- Selectively filter blood
- Return to blood anything to be kept
- Carry waste away for storage & expulsion
what is Each nephron comprised of?
– A Bowman’s (glomerular) capsule
– Renal tubules
– A collecting duct
what is Each nephron associated with?
– A glomerulus
– Peritubular capillaries
whats Glomerular capillaries specialised for?
filtration
whats Glomerular capillaries?
Thin walled single layer of fenestrated endothelial cells
Fed and drained by arterioles
Blood pressure here is tightly regulated
what are Peritubular capillaries specialised for?
absorption
whats Peritubular capillaries?
Wrap around renal tubules
Carries filtered blood from efferent arteriole
Receives reabsorbed filtrate from nephron
Can secrete into nephron
Vasa recta
whats Vasa recta?
Extensions that follow loops of Henle deep into the medulla
Only found with juxtamedullary nephrons
whats the renal corpuscle?
Glomerulus enclosed by the Bowman’s capsule
Where capillary and nephron meet
Site of filtration barrier
whats the Bowman’s capsule?
First part of nephron
Between the 2 layers is the Bowman’s space (aka capsular space/urinary space) which receives filtrate
whats the 2 layers of Bowman’s capsule?
Outer parietal layer of simple squamous cells
Inner visceral layer of podocytes
whats the outer parietal layer made of in the bowmans capsule?
simple squamous cells
whats the Inner visceral layer made of in the bowmans capsule?
podocytes
whats the bowmans space (aka capsular space/urinary space)?
space between the outer parietal layer and inner visceral layer which receives filtrate.
whats podocytes?
Surround the glomerular capillaries
Very branched, very specialised epithelium
Branches form intertwining foot processes called pedicels
whats filtration slits?
form between pedicels
Filtered blood (filtrate) goes through these slits and passes into Bowman’s space
whats the Filtration barrier (blood-urine barrier/glomerular capsular membrane)?
- Lies between blood and Bowman’s space
- Allows free passage of water and small molecules
- Restricts passage of most proteins
- RBCs are not filtered into nephron
whats the 3 layers of Filtration barrier?
– Fenestrated endothelium of glomerular capillary
– Fused basement membrane
– Filtration slits between the pedicels of the podocytes
Which two structures form the renal corpuscle?
Glomerulus and bowman capsule
Which of the following is not a component of the blood-urine barrier: A. Fused basement membrane B. Filtration slits C. Podocytes D. Pedicels E. Sinusoidal endothelium
E. Sinusoidal endothelium
What happens after filtration?
Not everything that is filtered is excreted.
Some filtrate is reabsorbed.
Some of what wasn’t filtered is secreted into the nephron
urine =
filtered - reabsorbed + secreted
whats the Proximal convoluted tubule (PCT)?
Bulk reabsorption
Surrounded by peritubular capillaries
whats the structure of the Proximal convoluted tubule (PCT)?
Cuboidal epithelial cells Dense microvilli (brush border) on luminal membrane Highly folded basolateral membrane Many mitochondria for active transport Leaky epithelium
whats the loop of henle?
Only part of tubule to penetrate the medulla.
Different permeabilities to water and sodium
Length is important in production of highly concentrated or very dilute urine
Surrounded by vasa recta (juxtamedullary nephrons only)
for the loop of henle
what epithelium makes up... the thick descending limb? the thin descending limb? the thin ascending limb? the thick ascending limb?
- similar to PCT structure
- Simple squamous
- simple squamous
- similar to DCT structure
whats the Distal convoluted tubule (DCT)?
Fine tuning
Cuboidal epithelium, but thinner than PCT
whats the structure of the Distal convoluted tubule (DCT)?
Few microvilli = no brush border
Fewer mitochondria
Reabsorption influenced mainly by Aldosterone
whats the Collecting duct?
Fine tuning
Filtrate from several DCTs drains into one collecting duct, which empty at papilla
whats the structure of the Collecting duct?
Wall of simple cuboidal epithelium Principal cells (Reabsorption) Intercalated cells (Acid/Base balance)
whats reabsorption of the collecting duct influenced by?
ADH, through use of aquaporins
what are principal cells of the collecting duct used for?
Reabsorption
what are Intercalated cells of the collecting duct used for?
Acid/Base balance
histology of the nephron
what does the renal corpuscle consist of?
squamous epithelium of parietal layer of bowmans capsule
bowmans capsular space
Glomerulus
histology of the nephron
proximal convoluted tubule
fuzzy lumen due to long microvilli
histology of the nephron
distal convoluted tubule
clear lumen
whats the Juxtaglomerular apparatus (JGA)?
Specialised zone in every nephron
Controls glomerular filtration rate, ensuring system working at full capacity
Stabilises blood pressure
wheres the JGA located?
where DCT lies against afferent arteriole
what specialized cells does DCT have and what do they do?
Macula densa cells.
Chemoreceptors.
Detect Na levels in filtrate
what specialized cells does JGA have and what do they do?
Afferent arteriole:
juxtaglomerular cells.
Mechanoreceptors.
Detect blood pressure
what are JGA cells?
- Detect pressure
- No stretch - low pressure
- Sends signal to cause changes on filtration rate
The cells that form the visceral layer of the Bowman’s capsule are called: A. Pedicels B. Podocytes C. Mesangial cells D. Filtration slits E. Macula densa
B. Podocytes
The cells of the JGA on the afferent arteriole are called: A. Juxtamedullary B. Macula densa C. Mesangial cells D. Juxtaglomerular E. Podocytes
D. Juxtaglomerular
What type of epithelial cells would you find in the Loop of Henle?
cuboidal with microvilli brush border at part closest to PCT, simple squamous, cuboidal with few microvilli at part closest to DCT
Name the two capillary beds associated with the nephron.
Glomerular and peritubular
Which type of nephron is most important for the production of concentrated urine?
juxtamedullary
