the amazing nephron workshop Flashcards
what is the functional unit of the kidney
the nephron
how many nephrons are in the canine kidney
400,000 - 600,000
in basic terms (in/out) what does the nephron do
filter plasma and produce urine
can the body regenerate nephrons
no - damages due to normal ageing loss, renal injury or renal disease
the medulla is composed of
entirely of straight tubules - appears striated in transverse section
what are the classifications of nephrons
by their location of their glomeruli in the cortex:
- superficial (near the capsule)
- cortical
- juxtamedullary (near medulla)
the cortex of the kidney is made up of
glomeruli as well as straight and convoluted tubule segments
what are juxtamedullary nephrons
long and due to this are adapted to resorb a lot of water back into the blood. this is really useful in animals that need to minimise the amount of water that they lose in urine
the ability to produce very concentrated urine is associated with
a greater percentage of juxtamedullary nephrons
a filtrate is formed when:
blood passes through the glomerulus which acts like a sieve
outline the journey of blood through the kidney to make urine
- glomerulus
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule
- collecting duct
what is the function of the tubular components of the nephron
adjust the make up of the urine by moving things in or out
the renal corpuscle is made up of
made up of a ball of capillaries (glomerulus) where blood flows in and is filtered towards a double walled capsule (bowmans capsule)
what structures are included in the nephron
- glomerulus
- bowmans capsule
- efferent and afferent arterioles
- proximal convoluted and straight tubule
- loop of henle
- distal convoluted tubule
what is the venous supply/drainage of the glomerulus
The glomerulus is formed by an afferent arteriole that divides into looping capillaries in a ball, which then join back up on the opposite side to make the efferent arteriole carrying the blood away. Intraglomerular mesangial cells and matrix occupy the spaces between capillary loops within the glomerulus.
The arterioles (afferent and efferent) enter and exit at one end of the ball of the glomerulus (the “vascular pole”) and the ultrafiltrate is created and enters the Bowman’s capsule at the other end (the ‘urinary pole”).
what happens to blood entering the glomerulus through the afferent arteriole
pushed through the walls of the glomerular capillaries with a filtration effect towards bowmans capsule. the capsule is cup shaed with inner and outer laters separated by a cavity (urinary space)
the renal filter is made up of
- Endothelial cells of the glomerulus
Endothelial cells have large fenestrations (pores) which allow many products to pass through. However, a lot of the material that makes up the pores is negatively charged and so there is a charge-barrier as well as a physical space restriction when passing through.
Blood cells and most proteins are too large to pass through this layer. - Glomerular Basement Membrane (GBM)
This is the main filtration barrier to cells and large molecules. It is also negatively charged. - Podocytes of the visceral layer of Bowman’s capsule
The podocyte projections don’t completely cover the GBM as there are some gaps. They therefore make a discontinuous layer on the urinary space side of the GBM.
The spaces between the foot projections are called filtration slits. Filtration of smaller molecules is blocked by the presence of a thin negatively charged membrane within the filtration slits.
passage through the renal filter is dependent on
molecular size and charge
Blood cells and most proteins are stopped at the endothelial fenestrations and negatively charged macromolecules are repelled by the negatively charged components of all layers of the filter.
which is wider: the afferent of efferent arteriole
afferent, but both are regulated to maintain GFR
where is the juxtaglomeruluar apparatus located
vascular pole of glomerulus
the juxtaglomerular apparatus is made of which 3 types of cells
- juxtaglomerular cells
- macula densa cells
- extraglomerular mesangial cells
what are juxtaglomerular cells
Juxtaglomerular cells are modified smooth muscle cells in the wall of afferent (and more rarely, efferent) arterioles. The cells contain renin (see ENI module) granules and may be called “granular cells”.
what are macula cells
The macula densa are specialised epithelial cells in the wall of the TAL of the Loop of Henle and/or distal tubule. This area sits close to the afferent and efferent arterioles of the glomerulus. Macula densa cells detect changes in luminal sodium chloride (NaCl) concentration.
The macula densa can signal changes in arteriolar resistance and so affect the blood flow to the glomerulus. The MD also signals the release of renin, causing a cascade of physiological reactions that result in increased systemic blood pressure. Increasing systemic BP also increases glomerular perfusion.
what are extraglomerular mesangial cells
bridge the afferent and efferent arterioles and the MD cells and help coordinate the messages and effects of the JGA.
what happens to the urinary filtrate once it enters the urinary spece of bowmans capsule
it begins to flow towards the tubule. The volume and contents of the urinary filtrate will be adjusted by reabsorption and secretion as it passes through the different areas of the tubule. The different areas of the tubule are highly adapted to do specific jobs in the production of urine.
what is the proximal convoluted tubule
coiled area of the nephron that makes up much of the renal cortex.
- one of the most active areas of the nephron and is where most solute reabsorption occurs
describe the cells of the proximal convoluted tubule
- Cuboidal epithelial cells
- Apical intercellular tight junctions (try to stop “leakage” of molecules between cells but allow easy movement of water and some small ions)
- Intercellular gap junctions (evidence of intercellular communication).
- A layer of microvilli (brush border) – a modification to increase surface area for absorption and intracellular transport of luminal material.
- Basolateral intercellular interdigitations: increase the surface area between cells to maximise transcellular transport of materials.
- Lots of mitochondria, especially close to all of the transport pumps on cell membranes
what is the loop of henle
the part of the tubule which descends into the medulla and then ascends back into the cortex
list and describe the parts of the loop of henle
The thick descending Limb
- Often described with the PCT as it is active in reabsorption. Simple cuboidal cells with less extensive cellular modifications than the PCT.
The thin descending and thin ascending limbs
- Changes abruptly to flatter cells: simple squamous epithelium.
- No brush border or lateral interdigitations (or very underdeveloped)
- Few organelles
- The thin limbs, in combination with the surrounding vascular network (the vasa recta) play an important role in concentrating urine.
The thick ascending limb
- Thicker again: simple cuboidal epithelium
- Rises up towards the cortex and ends up next to the glomerulus and macula densa.
discuss the blood vessels associated with the loop of henle
The efferent arterioles in cortical nephrons go on to form a second capillary bed – the peritubular capillaries – which surround the rest of the tubular system.
The efferent arterioles from juxtamedullary nephrons are a bit different. They first form vascular bundles which give rise to both peritubular capillaries and straight vessels that form the vasa recta. The descending vasa recta follow the LoH down into the inner medulla and once down there divide to make a capillary bed before joining up and rising as the ascending vasa recta. The vasa recta are the sole blood supply to the medulla and are very important in creating a concentration gradient
what is the distal convoluted tubule
This part of the nephron is after the macula densa.
It is shorter in length and has less developed microvilli than the PCT. However, it has lots of basolateral interdigitations and even more mitochondria than the PCT.
what are the sections of the collecting duct (in order according to their depth in the kidney)
- Cortical collecting duct
- Outer medullary collecting duct
- Inner medullary collecting duct
in what part of the kidney is the nephron primarily located
renal cortex
what are the key components of glomerular ultrafiltrate
- electrolytes
- glucose
- plasma protein
what component of the kidney is primarily involved in maintaining fluid homeostasis
nephron
what structural feature distinguishes the renal medulla from the renal cortex
presence of straight tubules
what type of cells occupy the spaces between capillary loops in the glomerulus
mesangial cells
what is the primary role of podocytes in the nephron
to create a filtration barrier with specialized processes
which layer of the renal filter is primarily responsible for creating a charge barrier
glomerular basement membrane
what prevents blood ccells and most proteins from passing through the endothelial cells of the glomerulus
The large fenestrations in endothelial cells allow certain products to pass, but blood cells and most proteins are too large to pass through.
where does ultrafiltrate first collect in the nephron
bowmans capsule
what effect do mesangial cells have on the glomerular basement membrane
keep clean by phagocytosing debris
which type of cells is responsibel for detecting changes in sodium chloride concentration
macula densa cells
what role do extraglomerular mesangial cells play in the juxtaglomerular apparatus
they bridge and coordinate signals between other cell types in the JGA
why are negatively charged macromolecules repelled by the renal filter
the layers of the filter contain negatively charged components
what tyoe of epithelial cells predominanty line the thick ascending limb of the loop of henle
simple cuboidal epithelium
what feature of the proximal convoluted tubule enhances its ability to reabsorb solutes
brush border formed by microvilli
what happens to the blood vessels in juxtamedullary nephrons
efferent arterioles form straight vessels called vasa recta
