ICL 1.1: Histology of the Kidneys

Question 1

what are the functions of the kidney?

Answer 1

1. filters blood by excreting metabolic waste products like creatinine, urea, uric acid
2. homeostasis: maintaining constant pH, blood volume, osmolarity etc.
3. produces erythropoietin
4. activates vitamin D

Question 2

how does the kidney maintain homeostasis?

Answer 2

by precisely regulating:

1. extracellular fluid osmolarity
2. body fluid volume (via water excretion/absorption)
3. acid-base balance

Question 3

where is the interlobar artery? what is a lobe?

Answer 3

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

Question 4

what is the medulla?

Answer 4

the area between the cortex and the inner part of the artery

so it includes the pyramids and renal columns

Question 5

what is the blood supply of the kidney?

Answer 5

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

Question 6

how does blood leave the kidney?

Answer 6

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

Question 7

what is a nephron?

Answer 7

its the functional unit of the kidney

Question 8

what are the components of a nephron?

Answer 8

1. Bowman’s capsule
2. proximal convoluted tubule
3. loop of Henle = thick descending limb, thin descending limb, thing ascending limb, thick ascending limb
4. distal convoluted tubule
5. collecting tubule
6. collecting duct of Bellii

Question 9

what is Bowman’s capsule?

Answer 9

the part right around the glomerulus; it’s in the cortex

Question 10

what is the proximal convoluted tubule?

Answer 10

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

Question 11

how does the osmolarity differ between the cortex and medulla?

Answer 11

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!

Question 12

where does filtration occur in the nephron?

Answer 12

glomerulus and Bowman’s capsule = renal corpuscle

Question 13

where does reabsorption and secretion occur in the nephron?

Answer 13

proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting tubule and collecting duct

Question 14

where does excretion occur in the nephron?

Answer 14

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

Question 15

what is glomerular vs. tubular filtrate?

Answer 15

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

Question 16

what happens when you’re totally hydrated? what about dehydrated?

Answer 16

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

Question 17

what is the % reabsorption of Na+ and Cl- in Bowman’s capsule, PCT, descending limb, ascending limb, DCT, collecting tubule and collecting duct?

Answer 17

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

Question 18

what is the % reabsorption of water in Bowman’s capsule, PCT, descending limb, ascending limb, DCT, collecting tubule and collecting duct?

Answer 18

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

Question 19

what cell type is in the proximal convoluted tubule?

Answer 19

simple cuboidal

Question 20

what cell type is in the thick segment of the loop of henle?

Answer 20

simple cuboidal

Question 21

what cell type is in the thin segment of the loop of henle?

Answer 21

simple squamous

Question 22

what cell type is in the distal convoluted tubule?

Answer 22

simple cuboidal

Question 23

what cell type is in the collecting tubule?

Answer 23

simple cuboidal

Question 24

what cell type is in the collecting duct of Bellini?

Answer 24

simple cuboidal

Question 25

how can you differentiate between the medulla and cortex histologically?

Answer 25

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

Question 26

what do you see at the corticomedullary junction in histology of the kidney?

Answer 26

lumens with veins and arteries = arcuate veins and arteries!

in the medullary rays you’ll see interlobular arteries!

Question 27

what is the cortical labyrinth?

Answer 27

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

Question 28

what is a lobule?

Answer 28

a single, central medullary ray plus adjacent cortical labyrinth

Question 29

which structures are in the renal pyramids?

Answer 29

1. loop of henle
2. collecting tubules
3. collecting ducts
4. 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!

Question 30

where does filtration occur?

Answer 30

renal corpuscle!

it’s made of 3 parts:
1. glomerulus

2. Bowman’s capsule
3. Mesangial cells

Question 31

what is the glomerulus?

Answer 31

small coiled cluster of capillaries line by fenestrated endothelial cells

Question 32

what is the structure of Bowman’s capsule?

Answer 32

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

Question 33

what are mesangial cells?

Answer 33

part of the renal corpuscle that:

1. structural support of glomerulus and macula densa
2. maintenance of the basement membrane
3. phagocytosis

Question 34

how do you differentiate proximal vs. distal convoluted tubule?

Answer 34

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

Question 35

what is the function of the proximal convoluted tubule?

Answer 35

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-

2. 100% of glucose and amino acids
3. majority of bicarbonat ions

Question 36

what is the function of the distal convoluted tubule?

Answer 36

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-

2. 10% of water, depending on vasopressin

Question 37

compare and contrast proximal vs. distal convoluted tubule appearance

Answer 37

PCT

1. long microvilli
2. irregularly happen lumen
3. more numerous in light micrographs due to longer length

DCT

1. shorter microvilli
2. circular lumen
3. less numerous in light micrographs due to shorter length

Question 38

where is the descending limb of the loop of henle? what cell type is it made of?

Answer 38

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

Question 39

what is the cell type and function of the loop of henle?

Answer 39

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

Question 40

where do thiazide diuretics act on?

Answer 40

distal convoluted tubule?

Question 41

where do loop diuretics act on?

Answer 41

loop of henle

Question 42

what is the cell type and function of the collecting tubule?

Answer 42

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-

Question 43

what is the cell type and function of the collecting duct of bellini?

Answer 43

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

Question 44

what are the components juxtaglomerular apparatus?

Answer 44

three subcomponents:
1. macula dense of the distal convoluted tubule

2. juxtaglomerular cells = specialized smooth muscle cells in afferent arteriole
3. mesangial cells

Question 45

what is the function of juxtaglomerular apparatus?

Answer 45

1. 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

2. 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

3. 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

Question 46

what does angiotensin II do?

Answer 46

increases BP!!

1. angiotensin II constricts efferent arterioles which increases the glomerular filtration rate
2. constricts peripheral vessels
3. increases aldosterone secretion
4. stimulates epithelial cells of proximal convoluted tubule to increase their salt and water reabsorption
5. angiotensin II stimulates ADH release from the posterior pituitary gland, which in turn increases aquaporin insertion in principal cells