ICL 1.1: Histology of the Kidneys Flashcards
what are the functions of the kidney?
- filters blood by excreting metabolic waste products like creatinine, urea, uric acid
- homeostasis: maintaining constant pH, blood volume, osmolarity etc.
- produces erythropoietin
- activates vitamin D
how does the kidney maintain homeostasis?
by precisely regulating:
- extracellular fluid osmolarity
- body fluid volume (via water excretion/absorption)
- acid-base balance
where is the interlobar artery? what is a lobe?
in-between lobes; each kidney has about a dozen lobes
a lobe includes a pyramid and some adjacent area as well – each lobe involves 1/2 a renal column and a pyramid and the overlying cortex
the peripheral tissue under the capsule is the cortex while the tissue in-between pyramids is called renal columns
what is the medulla?
the area between the cortex and the inner part of the artery
so it includes the pyramids and renal columns
what is the blood supply of the kidney?
the renal artery splits in the sinus and gives off the segmental artier
the interlobar arteries then come off the segmental arteries
the interlobar artieries give off the arcuate artery which are parallel to the capsule and run along the base of the pyramid
interlobular arteries come off the arcuate arteries and is in-between lobules in the cortex
interlobular artery then gives off the afferent arteriole which heads towards the glomerulus
how does blood leave the kidney?
efferent arterioles carry blood away from the glomerulus into the peritibular capillaries which are associated with the convoluted tubules
the peritubular capillaries drain into the vasa recta which are associated with the nephron loop
blood can sometimes go straight from the efferent arteriole to the vasa recta; this allows for blood that has been fully filtered to go straight into the vasa recta
then blood drains into an interlobular vein –> arcuate vein –> interlope vein –> renal vein –> IVC
what is a nephron?
its the functional unit of the kidney
what are the components of a nephron?
- Bowman’s capsule
- proximal convoluted tubule
- loop of Henle = thick descending limb, thin descending limb, thing ascending limb, thick ascending limb
- distal convoluted tubule
- collecting tubule
- collecting duct of Bellii
what is Bowman’s capsule?
the part right around the glomerulus; it’s in the cortex
what is the proximal convoluted tubule?
receives ultra-filtrate from the Bowman’s capsule; it’s in the context
when it turns, it becomes the loop of Henle which extends into the medulla
how does the osmolarity differ between the cortex and medulla?
osmolarity in the cortex is lower than in the medulla
so the increased osmolarity in the medulla allows for absorption of water into the interstitial and blood vessels!
where does filtration occur in the nephron?
glomerulus and Bowman’s capsule = renal corpuscle
where does reabsorption and secretion occur in the nephron?
proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting tubule and collecting duct
where does excretion occur in the nephron?
tubular filtrate is no longer being processed
you’ve produced urine and the tubular filtrate is going to enter a minor papilla
it’s also used to refer to the urine being exreted through the urethra
what is glomerular vs. tubular filtrate?
they’re both subcategories of ultra-filtrate
glomerular filtrate is in the area of the renal corpuscle; when it first enters Bowman’s space it’s called glomerular filtrate
once it’s in the proximal convoluted tubule it’s called a tubular filtrate
you can just call both of them an ultra-filtrate
what happens when you’re totally hydrated? what about dehydrated?
in a hydrated state, it will allow water to bypass and we don’t need vasopressin
in the absence of vasopressin, the distal convoluted tubule, collecting tubule and collecting duct are impermeable to water so you’re hydrated and producing diluted urine –> however, water is happening in proximal convoluted tubule
but in a dehydrated state, the presence of vasopressin (ADH) makes the distal convoluted tubule, collecting tubule and collecting duct permeable to water! you’ll have concentrated urine because you’re reabsorbing urine
what is the % reabsorption of Na+ and Cl- in Bowman’s capsule, PCT, descending limb, ascending limb, DCT, collecting tubule and collecting duct?
Bowmans: no reabsorption, only filtration
PCT: 65%
descending limb:0%
ascending limb: 20%
DCT:10%
collecting tubule and collecting duct: 5%, depends on angiotensin II and aldosterone
what is the % reabsorption of water in Bowman’s capsule, PCT, descending limb, ascending limb, DCT, collecting tubule and collecting duct?
Bowmans: no reabsorption, only filtration
PCT: 65%
descending limb: 20%
ascending limb: 0%
DCT: 10%, depends on vasopressin
collecting tubule and collecting duct: 5%, depends on vasopressin
what cell type is in the proximal convoluted tubule?
simple cuboidal
what cell type is in the thick segment of the loop of henle?
simple cuboidal
what cell type is in the thin segment of the loop of henle?
simple squamous
what cell type is in the distal convoluted tubule?
simple cuboidal
what cell type is in the collecting tubule?
simple cuboidal
what cell type is in the collecting duct of Bellini?
simple cuboidal
how can you differentiate between the medulla and cortex histologically?
cortex has corpuscles which look like little purple dots and has a capsule at the periphery
the medulla doesn’t have renal corpuscles! it’s the inner portion where the vasa recta and the straight portions of the nephron are
we’re parallel to the loops of henle and vasa recta
there’s also medullar rays which are an extension of the medulla into the cortex! they literally look like sun rays composed of medullar tissue into the cortex and contain the straight portions of the loop of henle and interlobular arteries
what do you see at the corticomedullary junction in histology of the kidney?
lumens with veins and arteries = arcuate veins and arteries!
in the medullary rays you’ll see interlobular arteries!
what is the cortical labyrinth?
area of the cortex inbetween the medullar rays
it has convoluted tubules and parts of the collecting tubules and looks very windy
so cortex = cortical labyrinth + medullary rays
what is a lobule?
a single, central medullary ray plus adjacent cortical labyrinth
which structures are in the renal pyramids?
- loop of henle
- collecting tubules
- collecting ducts
- vasa recta
they contain the straight portions of the nephron plus the associated vessels
collecting tubules look like cuboidal cells with purple circles; organized and very circular
thick part of the loops of henle also have purple circles but surrounding cytoplasm is pink; looks messier
vasa recta can be identified by looking for red blood cells!
where does filtration occur?
renal corpuscle!
it’s made of 3 parts:
1. glomerulus
- Bowman’s capsule
- Mesangial cells
what is the glomerulus?
small coiled cluster of capillaries line by fenestrated endothelial cells
what is the structure of Bowman’s capsule?
it has 2 layers: parietal and visceral and Bowman’s space is the space between these two layers
parietal layer is simple squamous epithelium and lines outside of the capsule
visceral layer has podocytes which are directly adhered to the basement membrane and this is where filtration happens!
Bowman’s space contains glomerular filtrate –> so filtration happens from the lumen of a glomerulus to Bowman’s space
what are mesangial cells?
part of the renal corpuscle that:
- structural support of glomerulus and macula densa
- maintenance of the basement membrane
- phagocytosis
how do you differentiate proximal vs. distal convoluted tubule?
distal has a larger lumen and the cells aren’t as big
the proximal has a small lumen and the cells are taller; almost look columnar
what is the function of the proximal convoluted tubule?
irregular shaped lumen with simple cuboidal epithelium that have brush border formed by long microvilli on apical side; frequently seem
there’s basolateral folds to increase surface area for transport of solutes and water
you’ll also see eosinophilic striation created by stacking of mitochondria
typical site of acute tubular necrosis
site of reabsorption for:
1. 65% of Na+, Cl-
- 100% of glucose and amino acids
- majority of bicarbonat ions
what is the function of the distal convoluted tubule?
circular shaped lumen with shorter cuboidal epithelial cells; fewer of them seem because they’re shorter in lengthen than the PCT
fewer, short microvilli because not as much absorption happens here
target of thiazide diuretics!
site of reabsorption of:
1. 10% of Na+ and Cl-
- 10% of water, depending on vasopressin
compare and contrast proximal vs. distal convoluted tubule appearance
PCT
- long microvilli
- irregularly happen lumen
- more numerous in light micrographs due to longer length
DCT
- shorter microvilli
- circular lumen
- less numerous in light micrographs due to shorter length
where is the descending limb of the loop of henle? what cell type is it made of?
it’s in the medulla, we’re not in the cortical labrynth anymore! you can’t distinguish it from the ascending limb
there will be a thick and thin portion that you can tell the difference between
it’s simple squamous portion that is highly permeable to water
20% of water reabsorption happens here
what is the cell type and function of the loop of henle?
you can’t distinguish it from the ascending limb but you can identify thick vs. thin
the entire ascending limb is impermeable to water!!!
reabsorption of 20% Na+ and Cl- happens at the ascending limb
thick ascending limb is the site of action of loop diuretics
where do thiazide diuretics act on?
distal convoluted tubule?
where do loop diuretics act on?
loop of henle
what is the cell type and function of the collecting tubule?
simple intercalated cells and principal cells
principal cells reabsorb water via aquaporin in response to vasopressin
they’re the site of pH regulation! alpha intercalated cells secrete H+ while B-intercalated cells secrete HCO3-
what is the cell type and function of the collecting duct of bellini?
simple columnar cells!
collecting ducts lack intercalated cells and have only principal cells
principal cells reabsorb water via aquaporin in response to vasopressin
aldosterone stimulates insertion of Na+/K+ pump on basolateral membrane, creating a favorable gradient for water reabsorption
what are the components juxtaglomerular apparatus?
three subcomponents:
1. macula dense of the distal convoluted tubule
- juxtaglomerular cells = specialized smooth muscle cells in afferent arteriole
- mesangial cells
what is the function of juxtaglomerular apparatus?
- decreased salt concentration in the distal convoluted tubule stimulates release of renin and contraction of the efferent arteriole
macula densa senses decreased concentration of NaCl in tubular filtrate and stimulate juxtaglomerular cells to secrete renin – renin causes production of angiotensin II
- decreased blood volume in the afferent arteriole stimulates release of renin and contraction of the efferent arteriole
juxtaglomerular cells sense decreased blood volume in afferent arteriole and secrete renin which then causes production of angiotensin II
- sympathetic stimulation of the juxtaglomerular cells causes release of renin
simulation of juxtaglomerular cells by sympathetic nerve fibers causes release of renin; renin causes production of angiotensin II
what does angiotensin II do?
increases BP!!
- angiotensin II constricts efferent arterioles which increases the glomerular filtration rate
- constricts peripheral vessels
- increases aldosterone secretion
- stimulates epithelial cells of proximal convoluted tubule to increase their salt and water reabsorption
- angiotensin II stimulates ADH release from the posterior pituitary gland, which in turn increases aquaporin insertion in principal cells
