ANAT 261 Lecture Notes - Microvillus, Lamina Propria, Adrenal Gland

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Naveen Sooknanan McGill Fall 2011
1
Urinary System (Kidneys):
The urinary system is made up of the kidneys, ureters, urinary bladder and the urethra
In this course, we will only study the kidneys and the urinary bladder
The urinary system contributes to:
o Excretion of metabolic waste products (such as urea)
This is done through a filtration process, during which proteins such as
albumin are recovered
o Regulation of total body water
Highly regulated and can vary greatly depending on how much water you
consume
o Regulation of electrolyte balance
Retains sodium and other ions to a constant level
o Endocrine secretion of Renin and Erythropoietin
Renin is an enzyme released into the blood which controls blood pressure
Erythropoietin stimulates RBC production (modern name is Erithrogenin)
The kidney is shaped like a kidney bean (which was named after it)
It has two borders:
o The concave border, called the hilium, is where the renal pelvis is located
This structure is funnel shaped and is continuous with the ureters
At this level, there is also the entrance of renal arteries and the exit of
renal veins
o There is a convex lateral portion
The human kidney is big enough to
be divided into lobes and lobules
o A mouse’s kidney is
unilobar
The capsule is made of tough dense
irreg. CT rich in collagen fibers and
fibrocytes
o Very eosinophilic, easy to
identify
The cortex is located immediately
below the capsule, and looks grainy
due to the presence of tiny little
spheres
The cortico-medullary junction is
where the cortex stops and the next part, the medulla begins
The medulla is a striated structure which have straight ducts travelling all the way to the
draining points (called calices, or calix in singular)
o Each lobe contains a group of straight ducts making the a medullary pyramid (a
mouse only has one pyramid)
o The medulla can also be separated further into lobules
Medullary rays are projections of the medulla into the cortex
o They have the exact same structure as the upper medulla, as we will look at later
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Naveen Sooknanan McGill Fall 2011
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Dividing each lobe are columns of Bertin, which is the equivalent of interlobular CT in
other structures (it is made of CT)
All of these medullary pyramids drain through openings known as the area cribosae
o There are around 25 of these regions in each renal pyramid
These collections then get dumped into the minor calix, which are small pockets in front
of the AC
These minor calices then converge to form the major calix, which turns into the renal
pelvis
o The renal pelvis is continuous with the ureters
The ureter will go all the way to the urinary bladder
The main filtration unit of the kidney is called the nephron, and is located between the medulla
and cortex
Each kidney is comprised of 1-4 million nephrons
Blood comes into the nephron and gets filtered into urine through a series of tubules
o In the cortex, blood enters the renal corpuscle, which is a dilated tuft, and gets
filtered
o Still in the cortex, the urine then enters the proximal convoluted tubule (PCT)
which is very twisted
o The PCT then penetrates into the medulla and straightens out, becoming the
straight thick descending limb (SD)
It is structurally identical to
the PCT except it’s straight
and in the medulla
o Next, the SD turns into the thin
limb, which does a U turn in the
lower medulla and starts coming
back up (towards the cortex)
o The TL then turns into the straight
thick ascending limb (SA) which
penetrates back into the cortex
o The SA, once in the cortex,
becomes the distal convoluted
tubule, which is very twisted like
the PCT
The SA and DCT are structurally the same as well
o The SD, TL and SA together are known as the loop of Henle (because of the U
turn)
This point marks the END of the nephron, from here on, the urine is no longer inside the
nephron
o The DCT is connected to a collecting tubule, which collect urine from different
nephrons and merge as they penetrate into the medulla
o In the deeper medulla, the collecting tubules begin to thicken and become
collecting ducts of Bellini
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Naveen Sooknanan McGill Fall 2011
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o The CD of B then drain into the area cribosa, through the minor and major
calices, and to the ureters
The renal corpuscle consists of a double walled-epithelium containing a glomerular tuft of
capillaries
The unit is surrounded by a capsule called Bowman’s capsule, which contains two layers:
the inner visceral layer and the outer parietal layer
o These layer do not touch, the space between them is known as Bowman’s space
or capsular space
o The visceral layer has cells called podocytes with a lot of indentations and
processed, whereas the parietal layer is similar to a simple squamous epithelium
resting on a BM
The parietal layer is also surrounded by reticular fibers (type III collagen)
The squamous cells and podocytes are embryologically related
The renal corpuscle is polarized (not electrically). This just means is has two different
poles: the vascular pole and the urinary pole
o The vascular pole contains afferent and afferent arterioles
Like the portal venule in the liver, these BVs are functional (get filtered)
and are not for nutrition
o The afferent arteriole contains a region of modified SMCs in the media which are
called juxtaglomerular cells
These cells are located very close to the renal corpuscle and secrete Renin
They are endocrine cells
o The efferent arteriole leaves the renal corpuscle, still at the vascular end, with
clean blood that has been filtered
The afferent arteriole enters the capsule and
divided into 5 or more capillaries, called
glomerular capillaries
o All of the capillaries together is
referred to as the glomerulus
Eventually, all of these capillaries will merge
into the efferent arteriole
The filtered produce then travels out of the
urinary pole, which marks the beginning of
the PCT
o The PCT is lined with 1 layer of
columnar cells with microvilli
pointing into the lumen
o The microvilli are immobile and have
absorptive functions
In a section of the renal corpuscle, the DCT can also be seen as it comes back from the
medulla
o The DCT contains a thickened portion called the macula dense
This region is located just as the vessel leaves the corpuscle, and is made
of thin columnar cells as opposed to the normal cuboidal ones
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