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Terms in this set (27)
There are two key components of the urinary system:
A pair of organs that performs the primary functions of the kidneys.
The urinary tract includes paired ureters that drain urine from the kidneys into the
where it is temporarily stored until it is voided through the
to the exterior.
The primary functions of the kidneys include:
1. Regulation of the
of sodium, potassium, chloride, calcium and other ions.
2. Long term regulation of
3. Long term regulation of *plasma pH
4. Excretion of
5. Assists the liver in
of toxins and
The kidneys are located lateral to the vertebral column between the last thoracic vertebra (T12) and the third lumbar vertebra (L3) with the right kidney slightly inferior to the left.
The kidneys are
in position with the kidneys and associated structures located between the muscles of the dorsal body wall and the parietal peritoneum
In addition to the parietal peritoneum and nearby organs, three layers of connective tissue stabilize and protect the kidneys:
- A fibrous layer on the surface of the kidney.
- Adipose tissue that surrounds each kidney
- A sheet of connective tissue that anchors the kidney to surrounding structures
Superficial Anatomy of the Kidney
Each kidney has a prominent medial indentation called the
which serves as the entry point of blood vessels, nerves and ureter.
At the hilus an inner layer of the renal capsule extends into an internal cavity of the kidney called the
. This cavity is filled with blood vessels, nerves, and the tributaries of the collecting system that eventually form the ureters
Sectional Anatomy of the Kidneys
When the kidney is cut open three distinct regions become visible:
The renal cortex is the outermost layer that is contact with the capsule
The renal medulla is internal to the cortex and contains 6-18 conical structures called
. The base of each pyramid rests on the cortex and the tip, called the
, projects into the renal sinus. Adjacent pyramids are separated by bands of tissue called
which are essentially extensions of cortical tissue.
is a segment of the kidney centered around the renal pyramid. It includes the renal pyramid, the overlying renal cortex, and a share of the adjacent renal colums
Each renal papilla that projects into the renal sinus is surrounded by a cup-shaped drain called a
. Four or five minor calyces merge to form a
. The major calyces fuse to form a large, funnel shaped chamber, the
The renal pelvis tapers to form the
which exits at the hilus.
Blood Supply to the Kidneys
Each kidney receives blood from the
which enters at the hilus. The renal artery divides into the
within the renal sinus. The segmental arteries divide into
that penetrate the renal columns.
These arteries then divide into the
that course along the boundary between the cortex and medulla. Each arcuate artery divides into
cortical radiate arteries also called interlobular arteries
that supply the adjacent renal cortex. Numerous
branch off the interlobular arteries.
Blood drains from the kidney in a sequence of veins that reverse the pathway of the arteries and includes,
cortical radiate veins also known as interlobular veins, arcuate veins, interlobar veins, and a
Histology of the kidney
Each kidney contains over a million microscopic tubules called
which are the basic structural and functional units of the kidneys.
Each nephron begins at the *renal corpuscle* which contains a capillary network called the *glomerulus*. Blood arrives at the glomerulus via the *afferent arteriole* and leaves by an *efferent arteriole*. Filtration occurs at the
begins at the *renal corpuscle* which contains a capillary network called the *glomerulus*. Blood arrives at the glomerulus via the
and leaves by an
. Filtration occurs at the
and the filtrate flows through the tubule which is divided into the
proximal convoluted tubule, loop of Henle, and distal convoluted tubule
There are two types of nephrons:
About 85% of nephrons are located almost entirely within the cortex. These nephrons perform most of the absorptive and secretory functions of the kidney.
These nephrons are located close to the cortico-medullary border and have long loops of Henle that extend deep into the pyramids. These nephrons create the conditions necessary to produce a concentrated urine.
The filtrate formed by each nephron is finally collected by a shared system of tubules called the
The collecting system consists of a
that connects each nephron to a collecting duct; the
that descend toward the renal papilla; and the
that result from the fusion of the collecting ducts in the renal papillae.
The renal corpuscle consists of the expanded, blind end of the renal tubule called
and the capillaries of the
The glomerulus extends into Bowman's capsule without entering into the tubule. As a result, two layers of tubular epithelium come to surround the capillaries and create a capsular space between them
The two layers are:
Parietal (capsular) epithelium
- This is an outer layer of simple squamous epithelium
Visceral (glomerular) epithelium
- The cells of this layer come into direct contact with the endothelial cells of the capillaries and are called
Filtration occurs in the renal corpuscle across the filtration membrane formed by:
This layer is formed by the glomerular capillaries which are
The basal lamina of the endothelial cells is distinct in having a
that is thicker than normal. The lamina densa often encircles more than one capillary with
between adjacent capillaries.
The functions of the mesangial cells include:
for the capillaries
Engulf organic materials
that could accumulate and clog the filtration membrane
Regulate the diameter
of the capillaries
The podocytes that form the glomerular epithelium have cellular processes that wrap around the lamina densa.
These processes have smaller finger-like processes called
that interdigitate with those of a neighboring cell's process to form narrow
Proximal Convoluted Tubule (PCT)
The PCT begins at the
of the renal corpuscle which is opposite the
where the afferent and efferent arterioles enter and leave
The primary function of the PCT is
The simple cuboidal epithelium of the PCT has numerous microvilli on the apical surface which increases the surface area for absorption.
Over 60% of water, sodium and chloride
is reabsorbed from the filtrate in the PCT. All the
There is also active reabsorption of various ions including
calcium, potassium, magnesium, and bicarbonate
Loop of Henle
When the PCT straightens out it forms a tubule that descends toward the renal papilla of the pyramid.
This descending limb then turns in a hair-pin fashion and ascends toward the renal corpuscle. This loop is called
loop of Henle
The loop of Henle is the portion of the renal tubule responsible for creating an
in the pyramid in which the osmotic pressure increases from the base of the pyramid towards the renal papilla
The osmotic pressure gradient enables the kidney to produce urine that is more concentrated than the body fluid
Distal Convoluted Tubule (DCT)
When the ascending limb of the loop of Henle reaches the renal corpuscle it passes by the vascular pole in between the afferent and efferent arterioles and becomes the DCT.
The DCT performs
both absorption and secretion
and is the primary location where secretion occurs. The DCT is the part of the tubule where regulation of
sodium, potassium, calcium and pH
The location where the ascending limb passes in between the afferent and efferent arterioles
The Juxtaglomerular apparatus consists of:
(dense spot) At this location, which is next to the arterioles, the epithelial cells are taller and more concentrated
These are modified smooth muscle cells in the wall of the
Extraglomerular Mesangial Cells
These cells occupy the space between the glomerulus, afferent and efferent arterioles and the macula densa
The Juxtaglomerular apparatus monitors
in the filtrate of the tubule at this point and uses this information to regulate the production of filtrate to maintain consistency
This is also the site of production of the hormones
red blood cell production
Structures for Urine Transport, Storage, and Elimination
The ureters are muscular tubes that transport urine from the tapering tip of the renal pelvis to the urinary bladder.
The ureters are
in position like the kidneys
The wall of the *ureters consists of:
- This epithelium accommodates the cycles of expansion and contraction without changes in the impermeability of the epithelium
-There is an inner longitudinal and an outer circular layer
- Connective tissue that surrounds and stabilizes the position of the ureters
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