comparative microanatomy of the urinary systems

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Last updated 12:54 PM on 5/21/26

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20 Terms

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regions of the kidney

Cortex

Pars convolute (proximal tubule): Renal corpuscles, proximal and distal tubules, peritubular capillaries, and portions of collecting tubules

Pars radiata: Collecting tubules/ducts and portions of the loop of Henle

Medulla

Collecting tubules, thick and thin segments of the loops of henle and the vasa recta (peritubular capillaries)

<p><span style="color: rgb(7, 7, 7);"><strong>Cortex</strong></span></p><p><span style="color: purple;">Pars convolute (proximal tubule): </span>Renal corpuscles, proximal and distal tubules, peritubular capillaries, and portions of collecting tubules</p><p><span style="color: purple;">Pars radiata:</span> Collecting tubules/ducts and portions of the loop of Henle</p><p></p><p><span style="color: rgb(1, 1, 1);"><strong>Medulla</strong></span></p><p>Collecting tubules, thick and thin segments of the loops of henle and the <span style="color: purple;">vasa recta (peritubular capillaries)</span></p>

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renal nephrons

The functional units within the kidney are known as nephrons

Each nephron consists of a blood supply and a specialized network of ducts called a tubule

Vascular parts of the nephron include afferent arteriole, glomerulus, efferent arteriole and peritubular capillaries

Tubular parts include bowman’s capsule, proximal tubule, loop of henle, distal tubule and collecting duct

<p>The functional units within the kidney are known as <span style="color: purple;">nephrons</span></p><p></p><p>Each nephron consists of a <strong>blood supply </strong>and a <span style="color: purple;">specialized network of ducts called a <strong>tubule</strong></span></p><p></p><p><strong>Vascular </strong>parts of the nephron include<span style="color: purple;"> afferent arteriole, glomerulus, efferent arteriole and peritubular capillaries</span></p><p></p><p><strong>Tubular </strong>parts include <span style="color: purple;">bowman’s capsule, proximal tubule, loop of henle, distal tubule and collecting duct</span></p>

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renal corpuscle

The renal corpuscle: Glomerulus, Bowman’s capsule/renal capsule, Bowman’s space

The glomerulus and its epithelial covering together will make the renal corpuscle

Once the ultrafiltrate is formed, the fluid enters Bowman’s space (the space between the capillary tuft and Bowman’s capsule)

Renal or Bowman’s capsule has two parts: parietal (squamous epithelial cells) and visceral layer (podocytes)

Blood enters the convulusions called glomerular tuft via the afferent arteriole at the vascular pole and leave via efferent arteriole

These two vessels are immediately adjacent to one another at the vascular pole (VP), which is at the opposite end of the glomerulus from the urinary pole (UP)

They can contract or dilate, changing the amount of blood that flows into the glomerular tuft

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glomerulus

Each nephron begins with a blind expansion that is invaginated by a cluster of capillaries known as glomerulus

The glomerulus is a complex web of capillaries derived from the afferent arteriole

Glomeruli can be located in the cortex of the kidney or the corticomedullary junction

The glomerulus filters blood to produce a fluid, called filtrate

The major structures of the glomerular filtration barrier include: endothelium/pores, glomerular basement membrane (basal lamina), and podocytes

The glomerular endothelial cells are fenestrated

Another important feature of the endothelial cell is the glycocalyx, which covers the luminal surface of the cell - for a strong and functional vascular endothelium

Filtering out negatively charged molecules, leukocytes, red blood cells, platelets and larger proteins

The glomerular basement membrane is a product of the fusion of the basement membrane produced by endothelial cells and podocytes

<p>Each nephron begins with a blind expansion that is invaginated by a cluster of capillaries known as <span style="color: purple;">glomerulus</span></p><p></p><p>The glomerulus is a complex web of capillaries <span style="color: purple;">derived from the afferent arteriole</span></p><p></p><p>Glomeruli can be located in the <span style="color: purple;">cortex of the kidney</span> or the <span style="color: purple;">corticomedullary junction</span></p><p></p><p>The glomerulus filters blood to produce a fluid, called <span style="color: purple;">filtrate</span></p><p></p><p>The major structures of the glomerular filtration barrier include: <span style="color: purple;">endothelium/pores, glomerular basement membrane (basal lamina), and podocytes</span></p><p></p><p>The glomerular <span style="color: purple;">endothelial </span>cells are <span style="color: purple;">fenestrated</span></p><p></p><p>Another important feature of the endothelial cell is the <span style="color: purple;"><strong>glycocalyx</strong></span>, which covers the <span style="color: purple;">luminal surface </span>of the cell - for a s<span style="color: purple;">trong and functional vascular endothelium</span></p><p></p><p>Filtering out<span style="color: purple;"> negatively charged </span>molecules, <span style="color: purple;">leukocytes, red blood cells, platelets and larger proteins</span></p><p></p><p>The<span style="color: purple;"> glomerular basement membran</span>e is a product of the <span style="color: purple;">fusion of the basement membrane</span> produced<span style="color: purple;"> by endothelial cells and podocytes</span></p>

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glomerulus-mesengial cells

Extraglomerular mesangial cells (not in pic):

(Juxtaglomerular apparatus)

Intraglomerular mesangial cells (MC in pic) for:

Phagocytosis

Vasoconstriction

Histologically, there are 2 to 3 mesangial cell nuclei beneath each capillary loop

Collectively, the mesangial cells and the glomerular extracellular matrix that they produce constitute the mesangium

they’re basically immune cells

specialized, smooth muscle-like cells in the kidneys that support the structure of the glomerulus and help regulate blood filtration.

<p><strong>Extraglomerular mesangial cells (not in pic):</strong></p><p><span style="color: purple;">(Juxtaglomerular apparatus)</span></p><p></p><p><strong>Intraglomerular mesangial cells (MC in pic) for:</strong></p><p><span style="color: purple;">Phagocytosis</span></p><p><span style="color: purple;">Vasoconstriction</span></p><p></p><p>Histologically, there are 2 to 3 mesangial cell nuclei beneath each capillary loop</p><p></p><p>Collectively, the mesangial cells and the glomerular extracellular matrix that they produce constitute the <span style="color: purple;">mesangium</span></p><p></p><p>they’re basically<span style="color: purple;"> immune cells</span></p><p>specialized, smooth muscle-like cells in the kidneys that support the structure of the glomerulus and help regulate blood filtration.</p>

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podocytes

Podocytes are specialised epithelial cells

Located on the “abluminal” surface of the capillary loop

Podocytes have numerous processes, like tentacles, that surround the capillaries

Foot processes (FP) of podocytes (epithelial cell in inner layer of Bowman’s capsule) devoid of organelles except microtubules/ microfilaments

Podocyte FPs comprise a functioning slit diaphragm (SD) in between, a meshwork of proteins actively participating in podocyte signaling

visceral layer of bowman’s capsule

Support glomerular capillaries and are part of the glomerular filtration barrier

The filtration barrier: endothelial cells/pores, basal lamina, podocytes-slit pores (slit diaphragm) between podocyte foot processes

Podocytes respond to hormones and growth factors that are present in the circulation

Podocytes work with mesangial cells to support the structure and function of the glomerulus

the yellow wiggles around the pink circles are the slits

<p><span style="color: purple;">Podocytes are specialised epithelial cells</span></p><p></p><p>Located on the “abluminal” surface of the capillary loop</p><p></p><p>Podocytes have numerous processes, like tentacles, that surround the capillaries</p><p></p><p><span style="color: purple;"><strong>Foot processes</strong></span> (FP) of podocytes (epithelial cell in i<span style="color: purple;">nner layer of Bowman’s capsul</span>e) devoid of organelles except m<span style="color: purple;">icrotubules/ microfilaments</span></p><p></p><p>Podocyte FPs comprise a functionin<span style="color: purple;">g <strong>slit diaphragm </strong>(SD)</span> in between, a meshwork of proteins actively participating in <span style="color: purple;">p<strong>odocyte signaling</strong></span></p><p></p><p><strong>visceral layer of bowman’s capsule</strong></p><p>Support glomerular capillaries and are part of the <span style="color: purple;">glomerular filtration barrier</span></p><p></p><p><strong>The filtration barrie</strong>r: endothelial cells/pores, basal lamina, podocytes-slit pores (slit diaphragm) between podocyte foot processes</p><p></p><p>Podocytes respond to <span style="color: purple;">hormones and growth factor</span>s that are present in the circulation</p><p>Podocytes <span style="color: purple;">work with mesangial cells</span> to support the structure and function of the glomerulus</p><p></p><p>the yellow wiggles around the pink circles are the slits</p>

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urinary system

Filtration, resorption, secretion and concentration

so the glomerulus is the ultumate filtrate but now its part of the rest of the nephron

we have the

proximal convoluted tubule

loop henle - descending and ascending

distal convoluted tubule - v close to glomerulus

then collecting duct

many glomeruli give to collecting duct (many glomeruli for one collecting duct)

then papillary duct

then papillary

renal pelvis (major calyces converge to form the renal pelvis-large funnel shaped cavity in central part of kidney)

<p><strong>Filtration, resorption, secretion and concentration</strong></p><p></p><p>so the glomerulus is the ultumate filtrate but now its part of the rest of the nephron</p><p>we have the</p><p><span style="color: purple;">proximal convoluted tubule</span></p><p><span style="color: purple;">loop henle - descending and ascending</span></p><p><span style="color: purple;">distal convoluted tubule - v close to glomerulus</span></p><p><span style="color: purple;">then collecting duct</span></p><p><span style="color: purple;"><strong>many glomeruli give to collecting duct (many glomeruli for one collecting duct</strong>)</span></p><p><span style="color: purple;">then papillary duct</span></p><p><span style="color: purple;">then papillary</span></p><p><span style="color: purple;">renal pelvis (major calyces converge to form the renal pelvis-large funnel shaped cavity in central part of kidney)</span></p>

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urinary system

PCT

abundant dark pink cytoplasm-mitochondria
prominant brush border (microvilli) for increased SA
simple cuboidal epithelium

Loop of henle

thick descending portion resembling PCT -simple cuboidal
thick ascending portion resemble distal convoluted tubule - simple cuboidal
thin segments are squamous epithelium

DCT

Smaller cells with less cytoplasm-giving impession of more nuclei
lack brush border microvilli
simple cuboidal epithelium

Collecting tubule/duct

no active reabsorption
simple cuboidal epithelium without brush border
ADH influence

<p><span style="color: purple;">PCT</span></p><ul><li><p>abundant dark pink cytoplasm-mitochondria</p></li><li><p>prominant brush border (microvilli) for increased SA</p></li><li><p>simple cuboidal epithelium</p></li></ul><p></p><p>Loop of henle</p><ul><li><p>thick descending portion resembling PCT -simple cuboidal</p></li><li><p>thick ascending portion resemble distal convoluted tubule - simple cuboidal</p></li><li><p>thin segments are squamous epithelium</p></li></ul><p></p><p>DCT</p><ul><li><p>Smaller cells with less cytoplasm-giving impession of more nuclei</p></li><li><p>lack brush border microvilli</p></li><li><p>simple cuboidal epithelium</p></li></ul><p></p><p>Collecting tubule/duct</p><ul><li><p>no active reabsorption</p></li><li><p>simple cuboidal epithelium without brush border</p></li><li><p>ADH influence</p></li></ul><p></p>

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urinary system

Lying just outside Bowman’s capsule and the glomerulus is the juxtaglomerular apparatus (JGA)

JGA includes macula densa, juxtaglomerular cells, mesangial cells

juxta = next to

<p>Lying just outside Bowman’s capsule and the glomerulus is the <span style="color: purple;">juxtaglomerular apparatus (JGA)</span></p><p></p><p>JGA includes <span style="color: purple;">macula densa, juxtaglomerular cells, mesangial cells</span></p><p></p><p>juxta = next to</p>

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macula densa

Macula densa(like dense black structures)

short segment of the distal convoluted tubule that is next to the afferent and efferent arterioles
the macula densa cells sense sodium chloride concentration
in the lumen and stimulates the juxtaglomerular cells to synthesize and release renin into the bloodstream

Juxtaglomerular cells

are within the interstial tissue between the macula densa and the vascular pole
This is a modified, smooth muscle cell lining the afferent arteriole that can contract or relax in response to the macula densa

<p><strong>Macula densa(like dense black structures)</strong> </p><ul><li><p><span style="color: purple;">short segment of the distal convoluted tubule</span> that is next to the afferent and efferent arterioles</p></li><li><p>the macula densa cells sense<span style="color: purple;"> <strong>sodium chloride concentration</strong></span></p></li><li><p>in the lumen and<span style="color: purple;"> stimulates the juxtaglomerular cells</span> to <span style="color: purple;">synthesize </span>and <span style="color: purple;">release <strong>renin </strong>into the bloodstream</span></p></li></ul><p></p><p><span style="color: rgb(8, 7, 7);"><strong>Juxtaglomerular cells </strong></span></p><ul><li><p>are within <span style="color: purple;">the interstial tissue between the macula densa and the vascular pole</span></p></li><li><p>This is a<span style="color: purple;"> modified, smooth muscle cell lining the afferent arterio</span>le that can <span style="color: purple;">contract or relax in response to the macula densa</span></p></li></ul><p></p>

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histology

white space on 14 is bowman’s space, 14 points to the superficial cell layer i.e. bowmans capsule

14 - bowmans capsule

2- afferent arteriole

7 - macula densa

6- renal corpuscle

in second pic u see renal corpuscles (the blue dots scattered) ….check. radiata/tubules giving striated appearance (right pic shows straight vertical lines running towards centre are the straight tubules and collecting duct towards medulla)

<p>white space on 14 is bowman’s space, 14 points to the superficial cell layer i.e. bowmans capsule</p><p>14 - bowmans capsule</p><p>2- afferent arteriole</p><p>7 - macula densa</p><p>6- renal corpuscle</p><p>in second pic u see renal corpuscles (the blue dots scattered) ….check. radiata/tubules giving striated appearance (right pic shows straight vertical lines running towards centre are the straight tubules and collecting duct towards medulla)</p>

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reptile kidney

Unusual glomerular appearance and renal portal system

urinary pole = bowmans space

reptile kidney lack loop of henle

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fish kidney

Unusual glomerular appearance and renal system

Interstitial cells have endocrine and haematopoietic function

No loops of Henle

Fresh water fish – few, small glomeruli

<p>Unusual glomerular appearance and renal system</p><p></p><p>Interstitial cells have endocrine and haematopoietic function</p><p></p><p><span style="color: purple;">No loops of Henle</span></p><p></p><p>Fresh water fish –<span style="color: purple;"> few, small glomeruli</span></p>

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bird kidney

Cortical tissue dominates

There are two types of nephrons (most nephrons do not contain a loop of Henle) (reptillian and mammalian)

Cortical (reptilian) type is plenty and lacks loop of Henle (located entirely in the cortex)

Medullary type is mammalian type and less numerous and It has loop of Henle

16-bowmans space

11-proximal convoluted tubule

5-erythrocytes

7- mesengial cells

4- distal convoluted tubule

they have both two types of nephrons - mammalian (loop of henle) and reptilian

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renal pelvis- transitional epithelium

Transitional epithelium, smooth muscle

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histology of cortex kidney of horse

9 - Bowman's space

2- Bowmans capsule parietal layer (oh so its parietal layer, bowmans space, then visceral layer, then glomerulus)

7- Macula densa

4- Collecting tubule

5- Distal convoluted tubule (because macula densa on here)

8- Proximal convoluted tubule — has brush border

<p>9 - Bowman's space</p><p>2- Bowmans capsule parietal layer (oh so its parietal layer, bowmans space, then visceral layer, then glomerulus)</p><p>7- Macula densa</p><p>4- Collecting tubule</p><p>5- Distal convoluted tubule (because macula densa on here)</p><p>8- Proximal convoluted tubule — has brush border</p>

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basal lamina made from 2 layers - podocytes + endothelium - protect against loss of leukocytes, erythrocytes, large molecules

mesangial cells-rovide structural support, regulate blood filtration, and perform immune-like cleanup

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juxtaglomerular cells produce renin

podocytes are in the visceral layer of the bowmans capsule

bowman capsule is ultra filtrate

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to summarise

juxtaglomerular apparatus: is just on the side, it is macular densa, distal convoluted tubule

renal corpuscle: is the main filtering blob thing we were talking about in this slidedeck, in the urinary system

bowman’s capsule: This is the outer, tan/blue "cup" or shell that forms the perimeter of the circle. It catches the fluid filtered from the red blood capillaries (the glomerulus) inside it.

Renal Corpuscle: The complete, entire filtering unit.
Bowman’s Capsule: Just the double-walled outer shell.

<p><strong>juxtaglomerular apparatus: </strong>is just on the side, it is macular densa, distal convoluted tubule</p><p></p><p><strong>renal corpuscle</strong>: is the main filtering blob thing we were talking about in this slidedeck, in the urinary system</p><p></p><p><strong>bowman’s capsule</strong>: This is the outer, tan/blue "cup" or shell that forms the perimeter of the circle. It catches the fluid filtered from the red blood capillaries (the <strong>glomerulus</strong>) inside it.</p><p></p><ul><li><p><span><strong>Renal Corpuscle</strong>: The complete, entire filtering unit.</span></p></li><li><p><span><strong>Bowman’s Capsule</strong>: Just the double-walled outer shell.</span></p></li></ul><p></p>

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structures that make up the major filtration barrier

a. slit pore diaphragm

b. glomerular basal membrane

c. podocyte foot process

d. endothelial cell from the renal glomerulus

e. fenestrate or endothelial cell pore