Lecture 29- The nephron Flashcards
How big are nephrons and approximately how many are there per kidney?
- Microscopic (roughly 3 cm long)
- Approx. 1 million per kidney
What is the basic function of a nephron?
Urine formation via…
- Selectively filter blood
- Return to blood anything to be kept
- Carry waste away for storage & expulsion
What are the two types of nephrons and how do they differ?
Basic structure is the same between the two types, difference is in location:
- Cortical nephrons lie mainly in the cortex. Also more numerous (85% of nephrons)
- Juxtamedullary nephrons have the nephron loop extending deep into medulla. They are Important for the formation of concentrated urine
What is each nephron composed of (the basic parts)?
Made of... -A Glomerular capsule -Renal tubules (proximal and distal) -A collecting duct Associated with... -A glomerulus -Peritubular capillaries
What are glomerular capillaries specialized for and what does this require of their structure?
- Specialized for filtration
- Thin walled single layer of fenestrated endothelial cells
What are glomerular capillaries fed and drained by and why?
- Fed and drained by arterioles
- Because blood pressure here needs to be tightly regulated
A ball of glomerular capillaries=
The glomerulus
What are peritubular capillaries specialized for and what does this require of their structure/placement?
-Specialised for absorption
-Wrap around renal tubules
-Receives filtered blood from glomerulus via efferent
arterioles
-Receives reabsorbed filtrate from nephron
-Some non-filtered solutes that need to be excreted can pass from here into nephron
What are vasa recta?
- Straight blood vessel extensions of the peritubular capillaries that follow nephron loops deep into the medulla
- Only found with juxtamedullary nephrons
What is the structure of the renal corpuscle? What occurs there?
- The glomerulus enclosed by the Glomerular capsule is collectively called the renal corpuscle
- Where capillary and nephron meet
- Site of filtration barrier
What is the first part of the nephron?
Glomerular capsule
What are the two layers of the glomerular capsule?
- Outer parietal layer of simple squamous cells
- Inner visceral layer of podocytes
- Between the two layers is the capsular space which receives filtrate
What are podocytes? What does their structure allow?
-Surround the glomerular capillaries
-Very branched, very specialized epithelium
-Branches form intertwining foot processes called
pedicels
-Filtration slits form between pedicels
-Filtered blood (filtrate) goes through these slits and passes into capsular space
What is the filtration barrier?
- Also called the blood-urine barrier
- Lies between blood and capsular space
What can freely past through the filtration barrier and what cannot?
- Allows free passage of water and small molecules
- Restricts passage of most proteins and RBCs. These are not filtered into the nephron as they are too big.
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
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
Its fenestrated not sinusoidal (this is found in the liver)
Is everything that is filtered into the nephron excreted as urine?
- No, some filtrate is reabsorbed (2/3 water, 100% glucose)
- And some of what wasn’t filtered is secreted into the nephron
- Urine = Filtered – Reabsorbed + Secreted
What is the structure of the proximal convoluted tubule (PCT) like and how does this relate to its function?
- Bulk reabsorption
- Surrounded by peritubular capillaries
Structure:
- Cuboidal epithelial cells
- Dense microvilli (brush border) on luminal membrane to increase surface area
- Highly folded basolateral membrane
- Many mitochondria for active transport (provides energy)
- Leaky epithelium as allows things to pass through via the paracellular pathway (between cells)
What is the structure of the nephron loop like and how does this relate to its function?
- Loops down into the medulla
- Length is important in production of dilute/concentrated urine
- Surrounded by vasa recta (juxtamedullary nephrons only)
Structure:
- Thick descending limb which is similar to PCT structure
- Thin descending limb made of Simple squamous epithelium
- Thin ascending limb made of Simple squamous epithelium
- Thick ascending limb similar to DCT structure
- Different permeabilities to water and sodium
What is the structure of the distal convoluted tubule(DCT) like and how does this relate to its function?
-Fine tuning
Structure:
- Cuboidal epithelium, but thinner than PCT
- Few microvilli = no brush border (not as vital to have large surface area as not being used for bulk transport)
- Fewer mitochondria (not as much energy required)
- Reabsorption influenced mainly by the hormone Aldosterone
What is the structure of the collecting duct like and how does this relate to its function?
- Fine tuning
- Filtrate from several DCTs drains into one collecting duct, which empty at papilla
Structure:
- Wall of simple cuboidal epithelium
- Principal cells specialized for reabsorption
- Intercalated cells keep an Acid/Base balance
- Reabsorption influenced by ADH (antidiuretic hormone) and Aldosterone
What is the Juxtaglomerular apparatus (JGA)? What is its function?
- Specialised zone in every nephron
- Located where DCT lies against afferent arteriole
Both vessels have specialized
cells:
-DCT: Macula densa cells. Chemoreceptors. Detect sodium levels
-Afferent arteriole: juxtaglomerular cells. Mechanoreceptors. Detect blood pressure
-Controls glomerular filtration rate, ensuring system working at full capacity
-Stabilizes blood pressure
