Lecture 34 Flashcards
Nephron - basics, functions
- Approximately 1 Million in each kidney
- Production of ultrafiltrate from blood
- Conservation of water, electrolytes and metabolites
- Removal of metabolic waste
- Control of blood pressure
- Nephron is ep structure
- uriniferous tubule is a nephron with diff parts that hook up to collecting duct. All ep ducts that carry urine in the kidney are called uriniferous tubule
Kidney anatomy
Capsule
Cortex
Medulla
Renal papilla
Calyx
Renal vein and renal artery
Renal pelvis
Ureter
Renal cortex
- urine mostly made in cortex, and then sent towards tip of pyramids (going more inwards)
- produces filtrate of blood
- To recognize renal cortex, there are renal corpuscles surrounded by convoluted tubules
Renal medulla
- Composed of pyramidal structures and each pyramid is a lobe of the kidney
- Pyramid = lobe
- has no renal corpuscles
- re-absorption of electrolytes and water
- The parts of the nephron, which are ep tubules, all run in parallel. You get a diff view depending on how the section cuts through it.
- In cross sec, can see diff tubules
- In long sec, can see ep tubules mostly cuboidal tubules, sometimes squamous, are running in parallel
- For the nephrons to recover material, there is transport of material across. This material is delivered into capillaries that also run parallel to the tubules, and they are called vasa recta (straight vessels), which are leaky capillaries that take in material
Renal papilla
- tip of the lobe/pyramid, where lots of collecting ducts for urine open up to deliver the urine into the calyx
- Urine leaves the renal medulla at the renal papillae, and then travels to the Urinary Bladder through the Ureter
- there are various openings that deliver the content into the space that is made up of the ureter
- there are papillary ducts (of Bellini) in the renal papilla
- renal papilla is right above the minor calyx
Renal calyx
- The spaces in which urine flows
- There are larger spaces called major calyxes. Also minor calyxes that communicate within each lobe
Renal vein and renal artery
- Where the ureter enters, renal arteries and renal veins travel into too. They supply the nephrons in the lobes with blood in order to
filter material out of it
Ureter
- ep lined tube that opens up in the funnel.
- each part of the funnel caps the pyramids/lobes
- funnel-like space (inwards after pyramid) is where the urine is delivered into
- Urine leaves the renal medulla at the renal papillae, and then travels to the Urinary Bladder through the Ureter
- lined by transitional epithelium
Renal lobe and lobule
Lobule
- all nephrons that drain into a common collecting duct
- medullary ray in cortex = centre of a lobule = parallel tubules in the cortex
Lobe
- contains many lobules
- lobe = pyramid
The nephron - parts and pathway
Nephrons are highly surrounded by blood supply, which enters via vessels that run parallel to border b/w cortex and medulla. These vessels form an arch, and are called arcuate vessels (arcuate artery, arcuate vein)
Within the lobule, there are arterioles and venules (interlobular vessels connect arcuate vessels to afferent arteriole) that run up into the cortex. They branch off to supply each individual renal corpuscle, which is the part of the ep derived nephron that interacts with blood supply. Glomerulus is capillary network within renal corpuscle that interacts with ep cells to create urine or an ultrafiltrate of the blood. Afferent arteriole contacts the glomerulus.
The filtrate will flow through proximal convoluted tubule (in cortex), which is highly coiled, is first part of the nephron and is adjacent to renal corpuscle.
The urine or filtrate then enters medulla through Loop of Henle, which has 3 parts: thick descending limb, thin segment, thick
ascending limb. Thin segment cells are
squamous ep, thick segment cells are cuboidal ep.
Thick ascending limb goes back up into cortex. Then, it transitions to distal convoluted tubule in the cortex. Then, it empties into a collecting duct partially in cortex, which extends into medulla. Then, it empties urine at renal papillae further down.
Medullary ray
- wherever you see medullary ray in cortex of kidney, it is centre of lobule, and adjacent renal corpuscles and tubules will feed
into collecting ducts that run down into the medulla - medullary ray is where the tubules collect the urine that is collected from one lobule
- go from medulla to cortex
Blood vessels in cortex and medulla
Cortex
- Glomerular capillaries of the glomerulus are everywhere in cortex
- Peritubular vessels
- Interlobular vessels
Arcuate vessels bw cortex and medulla
- sends blood into cortex
- arcuate artery with lots of smooth muscle
- arcuate vein with very little smooth muscle
Medulla
- Interlobar vessels
Morphogenesis of the renal corpuscle
During development, we have blind ending tubule that forms primitive renal tubule/ kidney that induces formation of glomerulus. Glomerulus is fed by afferent arteriole and the blood has high BP. The blood flows out of glomerulus as efferent arteriole. This is arteriole portal system
The glomerulus forms indentation at tip of primitive tubule, then the cells that make up the blind ending tip will differentiate depending on where they are located. They form cup-like structure surrounding the glomerulus. Invagination forms visceral layer of Bowman’s capsule. Parietal layer of Bowmans’ capsule also forms
Bowman’s capsule
Ep cells of primitive renal tubule bend around and on top of glomerulus.
The space where the glomerulus indents into the blind ending tip to make a cup-like structure is called urinary space, where urine is delivered into the kidney tubule
Entire cup is called Bowman’s capsule. Parietal layer is outside. Visceral layer is inside. The middle b/w these 2 is the urinary space
Glomerulus is formed by afferent arteriole that branches into many branches. Each branch forms a loop and the loops are
interconnected. Then they are all collected as efferent arteriole. Efferent arteriole supplies blood to convoluted tubule
Bowman’s capsule is squamous ep.
Vascular pole and urinary pole
Vascular pole
- afferent arteriole goes in
- efferent arteriole goes out
- next to distal convoluted tubule that has macula densa
- next to juxtaglomerular cells
Urinary pole
- where proximal convoluted tubule starts
Convoluted tubule is cuboidal ep
Podocyte and endothelial cell - structures that allow filtration
Processes of the podocyte have a thick basement membrane that fuses with the thin basement membrane of the fenestrated endothelium. They merge their basement membrane.
Diff layers of basement membrane: lamina lucida, lamina densa. b/c it is a sandwich, we have 2 lamina lucidas and 1 big lamina densa
- lamina lucida externa (closer to process)
- lamina densa
- lamina lucida interna
There is molecular network called filtration slit diaphragm that are transmembrane proteins that hold the secondary processes tgt to allow filtration.
How secondary processes attach to basement membrane
Adhesion molecules (i.e. integrin alpha 3 beta 1) connect the basement membrane to the actin cytoskeleton that is within the secondary process (pedicel)
Filtration slit diaphragm protein
Filtration slit diaphragm is made up of 1 type of protein only found in the kidney. The protein is nephrin.
Nephrin is also anchored to actin cytoskeleton within the secondary processes (pedicels)
