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Where does pee come from?. Rachel Boggus Boggusrl@email.uc.edu. The Kidney. Pretty kidney But of course you need to know more about it than this. The kidney in detail. Why does the cortex have a granular appearance? Why does the medulla have a striated appearance?. The kidney in detail.

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where does pee come from

Where does pee come from?

Rachel Boggus


the kidney
The Kidney
  • Pretty kidney
  • But of course you need to know more about it than this
the kidney in detail
The kidney in detail
  • Why does the cortex have a granular appearance?
  • Why does the medulla have a striated appearance?

The kidney in detail

  • Why does the cortex have a granular appearance?
    • Because of the presence of renal corpuscles
  • Why does the medulla have a striated appearance?
    • Because of the radially oriented tubules that it is composed of.
more kidney fun
More Kidney fun
  • In your notes, Dr. Michaels talks about the ureter expanding into the renal pelviscalyx, etc. In the REVERSE order of the flow of urine. I’m presenting it here in the order that urine flows through it. Because I think that makes more sense.

More Kidney fun

  • Formed urine passes through large collecting ducts in the papilla and into the minor calyx
So go over the flow of formed urine
    • Formed urine begins in the large collecting ducts in the renal papilla. From there it enters the minor calyces which come together forming the major calyces which come together forming the renal pelvis which constricts forming the ureter.
more gross kidney
More GROSS kidney
  • Lobes and lobules
    • Each lobe has a medullary pyramid (the papilla is at the tip of the pyramid) and a cortex that sits on top of the medullary pyramid
    • Renal columns (of Bertin, if you will) are cortical tissue that extend beyond the pyramid
  • Are cylindrical and have a central core, a medullary ray/pars radiata consisting of radially-oriented tubes
  • Peripheral to medullary rays are the proximal and distal convoluted tubules (PCT and DCT) in the pars convoluta/cortical labyrinth
What is contained in the medullary rays?
  • What is contained in the pars convoluta?
What is contained in the medullary rays?
    • Descending and ascending thick limbs and collecting ducts
  • What is contained in the pars convoluta?
    • Proximal and distal convoluted tubules, the connecting tubules and the renal corpuscles
blood supply
  • Renal arteryinterlobar arteriesarcuate arteriesinterlobular arteriesafferent arteriolesglomerular capillariesefferent arterioleseither peritubular plexus or vasa recta



Proximal end of nephronrenal corpuscle
  • 2 parts of a renal corpuscle?
    • Glomerulus and bowman’s capsule
    • Remember that between the bowman’s capsule and the glomerulus is the bowman’s space – filled with pee
The rest of the nephron is tubular
  • Begins with proximal convoluted tubule (PROXIMAL to the glomerulus)
    • Extends to medullary ray where it descends toward the medulla as the straight portion of the proximal tubule or descending thick limb
Proximal convoluted tubulestraight portion/thick descending limbin the medulla abrupt transition to the thin descending limb
Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limb
  • Hairpin loop upwards towards cortex as thin ascending limb
Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limb
  • Straight portion of the distal tubule/thick ascending limb
Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limbthick ascending limb/straight portion of the distal tubule
  • Enters medullary ray, extends to pars convoluta, crosses vascular pole and becomes distal convoluted tubule
Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limbthick ascending limb/straight portion of the distal tubule distal convoluted tubule
  • Connecting tubule (branch of collecting duct) which extend from pars convoluta to medullary ray
Collecting ducts descend in medullary ray in cortex all the way through the medulla and the papilla papillary ducts
What regions of the nephron are in the pars convoluta?
    • Renal corpuscle, PCT, DCT, connecting tubule
  • What regions of the nephron are located in the pars radiata (medullary ray)?
    • Portions of the straight proximal (descending thick limb) and straight distal tubule (ascending thick limb), part of collecting duct
What parts of the nephron are located in the medulla?
    • Descending thick limb, descending and ascending thin limbs of the loop of Henle, and ascending thick limb
    • Collecting ducts, papillary ducts

Simple cuboidal epithelium

  • Irregular apical surface
  • Lots of mitochondria acidophilic
  • Lateral cell membranes not visible
    • because of interdigitation
  • 3 segements, s1, s2, s3
Another EM of a proximal convoluted tubule… note the brush border
  • Also notice the crap-load of mitochondria
What are the functions of the proximal convoluted tubules?
    • Reabsorption of 60-80% of the glomerular filtrate
    • Active transport of Na
    • Removal of virtually all glucose and proteins from provisional urine

*** If people are confused, REABSORPTION is from the pee tube into the interstitium, SECRETION is from interstitium to the pee tube ***

straight proximal tubule
Straight proximal tubule
  • Mostly segment S3
  • When tubule enters medullary ray
  • Interdigitations less pronounced
  • Brush border more variable
  • When epithelium changes to squamousthin descending limb of the loop of henle
how do i tell pct from straight pt
How do I tell PCT from straight PT?
  • BECAUSE you are a genius and you know that PCTs are in the cortex in the pars convoluta and that the straight PT is in the medullary ray
thin segments
Thin segments
  • Located in the medulla
  • Simple squamous epithelium
  • Lateral interdigitations present
  • Yellowthick descending limbs
  • Joins thin ascending limb at junction of inner and outer medulla
  • Also located in the pars radiata/medullary rays
distal convoluted tubule
Distal Convoluted tubule
  • When it enters the pars convoluta
  • Macula densa is adjacent to afferent arteriole (we’ll talk about this later)
  • No brush border
  • Has lots of lateral interdigitations
  • Primary function is reabsorption of ions
macula densa1
Macula densa
  • Where the DCT crosses the vascular pole
  • Cells of DCT adjacent to arteriole become tall and narrow, nuclei look close together
  • Helps distinguish DCT
  • Is part of the juxtaglomerular apparatus
connecting duct tubule whatever
Connecting duct/tubule/whatever
  • Connects the DCT to the collecting duct
  • Within the pars convoluta
  • Gradual transition of epithelium from DCT Collecting duct
Epithelium transition:
  • DCT—cuboidal, lots of interdigitations, mitochondria
  • Connecting tubule cells—many small mito
  • Intercalated cells—have microplicae on lumenal surface, vesicles in apical cytoplasm, little interdigitation with adjacent cells – note these for a possible EM
  • Principal (light cells)—collecting duct cells, have short microvillae, fewer mitochondria
As collecting duct descends in medullary ray, the epithelium becomes progressively taller, less interdigitation between lateral cells, and less mitochondria  able to see the lateral plasma membranes
  • Unite to form papillary ducts of bellini
  • Permeability responsive to ADH/vasopressin
cortical vs juxtamedullary nephron
Cortical vs. Juxtamedullary nephron
  • Cortical—short loops of henle, only in medulla for a little bit
    • Supplied by peritubular plexus of capillaries
    • Venous return is via interlobular vein
  • Juxtamedullary—long loops of henlemedulla
    • Create a concentration gradient that you love to hate in physiology
    • Efferent arterioles form vasa recta
    • Venous return is via arcuate vein or interlobular vein
lets love the renal corpuscle
Lets love the renal corpuscle
  • Bowman’s capsule and urinary pole
    • Capsule
      • Two layers
      • Between them is the urinary space (US)
    • Urinary pole
      • Continuous with PCT (TP) and

Also on the opposite side is a vascular pole (EA AND AA)

vascular pole
Vascular pole
  • 2—bowmans capsule – parietal layer
  • 3—vascular pole
  • 4—urinary pole – can see leading to PCT
vascular pole1
Vascular pole
  • Region where afferent and efferent arteriole enter and leave glomerulus
  • Blood enters the glomerular capillaries from the afferent arteriole
  • Efferent arteriole leads away from renal corpuscle carrying blood that was NOT filteredsecond capillary network
  • This is an arteriole portal system!
  • From efferent arterioles, the peritubular plexus and the vasa recta are formed (depending on the location of the nephrons—cortex/medulla)
green arrow arcuate artery blue arrow arcuate vein
Green arrow—arcuate arteryBlue arrow—arcuate vein
  • Remember the lumen size and wall size differences from last block?
gross feature of the kidney you need to know
  • Cortex
  • Medulla – including papilla (papilla drains into MINOR CALYCES
  • Hilum – where all the shiznit comes together
  • Renal sinus – fat here, along with renal pelvis
  • Renal pelvis – the “expanded ureter”
  • Calyces – minor calyces together = major calyces. major calyces together = renal pelvis. Fun!
  • Renal artery – branches into interlobar, arcuate, interlobular
    • Don’t mess up lobar and lobular!!!!!!!
only need to know interlobar arcuate interlobular in this pic
Only need to know interlobar, arcuate, interlobular in this pic
  • Follow renal artery to interlobar arteries to arcuate arteries to interlobular arteries. A kidney lobule lies between two interlobular arteries.
    • Convoluta = convoluted tubules (PCT and DCT) and glomeruli and connecting tubule
    • Radiata = medullary ray = straight portions of tubules = thick ascending and descending limbs and collecting ducts
    • Also look for INTERLOBULAR ARTERIES in convoluta

MEDULLA = renal pyramids + papilla = thick tubes, thin tubes, collecting ducts




So in the cortex you have convoluta and radiata, and the RADIATA is the CENTER of the lobule. So each lobule has a radiata center with the edges formed by convoluta. Remember the interlobular arteries are between lobules so they will be where?
  • In the convoluta! This should be obvious b/c they have to give off the afferent arterioles which clearly need to be by the glomerulus
  • So they can label a variety of things in the convoluta:
    • Glomerulus
    • Renal corpuscle = glomerulus plus bowmans
    • Interlobular arteries
    • DCT – light colored, can see cell borders
    • PCT – CANNOT see lateral membranes, fuzzy



Proximal and distal convoluted tubules (EM). Distal has no brush border. capillaries lie in the connective issue between tubules.



  • The medullary ray is composed of proximal and distal tubules going to and from the medulla, and collecting ducts. These tubules serve the adjacent glomeruli
Bowman's capsule: Squamous epithelium forming a double-walled cup surrounding the glomerular capillaries. The portion of the wall applied to the capillaries is termed the visceral epithelium. The visceral epithelium is separated from the outer wall by Bowman's space. Bowman's space is continuous with the lumen of the proximal tubule at the urinary pole .
  • Vascular pole: The point of entry of the afferent arteriole into Bowman's capsule. The arteriole immediately forms the tuft of glomerular capillaries and exits as the efferent arteriole.
Juxtaglomerular cells: Myoepithelioid cells replace typical smooth fibers in the wall of the afferent arteriole as it approaches the glomerulus. These cells secrete a hypertensive factor, renin.
Cell types make up the glomerulus: endothelial (red), mesangial (blue) and the visceral epithelial cell, and podocyte (yellow). Squamous epithelial cells of the Bowman capsule are easily seen(green). The macula densa (black) is part of the distal tubule.
So if they label a cell IN the glomerulus and it is roundish and not part of any form of vasculature = mesangial cell.
  • If they label a very even looking row of nuclei pressed all up on the glomerulus’ shit then it’s the macula densa
  • If they label a nice gathering of cells in the afferent arteriole = JG cells

Here are some longitudinal cuts of pale collecting tubules. Epithelium of collecting tubules is regular, block-like, simple cuboidal, with clear cell walls. Other tubules in the field are thick and thin limbs of loops of Henle.

  • So if you know you are in the medulla (i.e. you see ZERO glomeruli) it can be descending limb (fuzzy like PCT), ascending limb (NOT as fuzzy, looks like DCT and can see lateral cell borders), thin limb (squamous epithelium), or collecting duct (really pale)
  • DO NOT confuse thin limbs with blood vessels – blood vessels will have RBCs in the lumen
Do not let them trick you. They can cut medulla in cross section so it looks like pars convoluta, but you know its not because of no glomeruli

Ascending thick limb

Collecting duct

the innermost zone of the medulla (lowest section of the picture) contains only thin limbs of the loop of Henle, plus collecting ducts. This is the area where the counter-current mechanism for urine concentration (carried out between the tubules and the surrounding peritubular capillaries) is most active.
Appreciate the Collecting ducts of papilla open into minor calyx, with transitional epithelium and muscularis in its wall.

So this is the lowermost part of the medulla, right????

You know this, you do

    • Border?
    • Can you see lateral cell borders?
    • What part of the kidney are we in?
  • Answer: PCT
  • Blue arrow is a DCT – note the macula densa
Hints: What type of epithelium?
  • Where in the kidney are we?
  • Answer:
    • Thin limb of loop of henle – NOT a capillary because NO RBC
    • Blue arrow is a collecting duct because you can see the lateral cell borders
Well it comes right from the urinary pole of the glomerulus
  • So you would say “proximal convoluted tubule”
  • Remember the GROSS anatomy, helps with the microscopic
Arcuate vein. You know that the arcuate vessels are found in between the cortex and medulla so what else could it be? From there just decide if it is an artery or a vein. You know this from last block. Collapsed lumen = vein, thick wall and nice round lumen = artery.
what 3 things can they label in the medullary ray
What 3 things can they label in the medullary ray?
  • Don’t let the cross section fool you, we are still in the cortex. You see glomeruli, DON’T YOU???
1. Collecting duct
  • 2. Ascending thick limb
  • 3. Descending thick limb
  • For extra credit is the ray the peripheral part or the center of the lobule?
  • Cortex plus interlobular vessels are in the periphery


Q? C? boggusrl@email.uc.edu