Where does pee come from?

Rachel BoggusBoggusrl@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

• 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

• In your notes, Dr. Michaels talks about the ureter expanding into the renal pelviscalyx, 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

•Several minor calyxes come together to form a major calyx.

•The major calyces come together forming the renal pelvis which then forms the ureter

• So go over the flow of formed urine

• 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

• 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

Dr. Michaels thinks its like an ice cream cone… whatever

Lobules

–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 arteryinterlobar arteriesarcuate arteriesinterlobular arteriesafferent arteriolesglomerular capillariesefferent arterioleseither peritubular plexus or vasa recta

Interlobar arteries

Nephron

• Proximal end of nephronrenal 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 tubulestraight portion/thick descending limbin the medulla abrupt transition to the thin descending limb

• Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limb

• Hairpin loop upwards towards cortex as thin ascending limb

• Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limb

• Straight portion of the distal tubule/thick ascending limb

• Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limbthick ascending limb/straight portion of the distal tubule

• Enters medullary ray, extends to pars convoluta, crosses vascular pole and becomes distal convoluted tubule

• Glomerulusproximal convoluted tubulestraight portion of proximal convoluted tubule/thick descending limbthin descending limbthin ascending limbthick 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

Down and dirty with the PCT

• Simple cuboidal epithelium

• Irregular apical surface

• Lots of mitochondria acidophilic

• Lateral cell membranes not visible

•because of interdigitation

•3 segements, s1, s2, s3

EMs of proximal and distal convoluted tubules

• 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 Portion of Proximal tubule

Straight proximal tubule

• Mostly segment S3• When tubule enters medullary ray• Interdigitations less pronounced• Brush border more variable• When epithelium changes to

squamousthin descending limb of the loop of henle

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 segment descending and ascending

Thin segments

• Located in the medulla • Simple squamous epithelium• Lateral interdigitations present

Thick Ascending Limbs

• Blue• Yellowthick descending limbs

• Joins thin ascending limb at junction of inner and outer medulla

• Also located in the pars radiata/medullary rays

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

DCT

Macula densa

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

• Connects the DCT to the collecting duct

• Within the pars convoluta• Gradual transition of epithelium

from DCT Collecting duct

Cortical 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

Just beautiful

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 henlemedulla– 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

•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

• 2—bowmans capsule – parietal layer

• 3—vascular pole

• 4—urinary pole – can see leading to PCT

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 filteredsecond 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)

Interlobar artery – wow, its SO big ;)

Lobule separated by interlobular arteries

Green arrow—arcuate arteryBlue arrow—arcuate vein

• Remember the lumen size and wall size differences from last block?

LAB STUFF

This is all you need to know:

KIDNEY

HAHAAHA. You wish.

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!!!!!!!

Nice gross kidney

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.

• CORTEX = PARS CONVOLUTA + PARS RADIATA– 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

cortex radiata convoluta

• 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

Notice the interlobular arteries in the convoluta

cortex

• 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

DCT

PCT

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

NO BRUSH BORDER

NICE BRUSH BORDER

radiata

• 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.

• JG CELLS THE AFFERENT ARTERIOLE vs. MACULA DENSA IN DCT

Love the glomeruli

What are these podocytes you speak of?

• 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

Say hi to the macula densa

medulla

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.

medulla

• 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

Collecting duct

Ascending thick limb

• 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

• Now for a REALLY short quiz because I am getting sick of this material

Identify

Identify Green arrow

•Hints:–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

Identify—green arrow

• 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

Grey arrow

• 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?• 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?

• Center

• Cortex plus interlobular vessels are in the periphery

Done.

Q? C? boggusrl@email.uc.edu