L33 - The Nephron Flashcards
What is a Nephron
Microscopic functional unit of the kidney
Approx 1 million per kidney
Responsible for urine format
Types of Nephron
Cortical Nephron
- 85% of all nephrons
- lie mainly in the cortex
- short nephron loop
- Glomerulus further from junction
Juxtamedullary nephron
- Extend deep into the medulla
- Important for the formation of concentrated urine
- long nephron loop
- Glomerulus closer to junction
Functions of the Nephron
Selectively filter blood
Return to blood anything we want to keep
Carry waste for storage and removal
Components of the nephron
Bowmans capsule
Renal Tubules
Collecting duct
Each nephron is associated with
Glomerulus
Peritubular capillaries
Glomerular Capillaries
Specialised for filtration
Thin walled single layer of fenstrated endothelial cells
Fed and drained by arterioles
high pressure and tightly regulated
Peritubular Capillaries
Specialised for absorption
Adjacent to renal tubes
Arise from efferent arteriole draining glomeruli
After filtration the blood is viscous and protein/cell rich
Low Pressure
Vasta Recta
Long Straight Vessels
associated with loop of hence in juxtamedullary nephrons
Renla Corpuscle
- Glomerulus is enclosed by bowman’s capsule
- Site of filtration - blood/urine barrier
- Where blood and nephron meet
- Site of filtration barrier
Bowman’s Capsule
2 Layers
1) Outer parietal layer of simple squamous epithelium
2) Inner visceral layer of podocytes
- Between two layers is Bowman’s space (aka capsular space/urinary Space)
Podocytes
- Surround glomerular capillaries
- Very branched, specialised epithelium
- Branches form intertwining foot process called pedicels
- Filtration slits form between pedicels
- Filtered blood goes through these slits and passes into Bowman’s space
Filtration Barrier
- Lies between blood and Bowman’s space
- Allows free passage of water and small molecules
- Restricts passage of most proteins
- RBC’s are not filtered into nephron
3 layers of filtration barrier
- Fenestrated endothelium of glomerular capillary
- Fused basement membrane
- Filtration slits between the pedicels of podocytes
After Filtration
- Urine is waste fluid and solutes filtered from blood
- Not everything is excreted
- Some is reabsorbed
- And some of what wasn’t filtered is secreted in
Proximal Convoluted tubule
Bulk Reabsorption
Surrounded by peritubular capillaries
Structure of proximal convoluted tubes
- Cuboidal epithelial cells!
- Dense microvilli (brush border) on luminal membrane
- Highly folded basolateral membrane
- Many mitochondria for active transport
- Leaky epithelium
Loop of Henle
- Part of it is in the medulla
- Length is important in production of highly concentrated or very dilute urine
- Surrounded by vasa recta
- Only tubule to penetrate the medulla
Descending limb of loop of henle
- Reabsorption of water from filtrate
- Structure:
○ Thick - similar to PCT
○ Thin - simple squamous epithelium
Ascending limb
- Reabsorption of water from filtrate
- Structure:
○ Thick - similar to PCT
○ Thin - simple squamous epithelium
Distal Convoluted tube
- Fine tuning
- Cuboidal epithelium, but thinner than PCT
- Few microvilli = no brush border
- Fewer mitochondria
- Reabsorption influenced by Aldosterone
Collecting Duct
- Fine tuning
- Filtrate from several DCTs drains into one collecting duct, which empty at papilla
- Wall of simple cuboidal epithelium
○ Principal cells - Reabsorption!
○ Intercalated cells - Acid/Base balance! - Reabsorption influenced by ADH, through use of aquaporins
Juxtaglomerular apparatus JGA
- Specialised zone in every nephron
- Located where DCT lies against afferent arteriole
- Controls glomerular filtration rate, ensuring system working at full capacity
Stabilises blood pressure!
Afferent arteriole:
- Juxtaglomerular cells!
- Mechanoreceptors!
- Release renin in response to BP!
Renin stimulates angiotensin II formation!
DCT:
- Macula densa cells
- Chemoreceptors
Detect Na+ conc in filtrate
