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Munirah binti Shaban
Department of Basic Health Sciences
Kulliyyah of Allied Health Sciences
International Islamic University Malaysia
09 December 2009, Wednesday, AHS 1023
OBJECTIVES
1. To identify the components of the urinary system
2. To characterize the general organization of the
kidney
3. To examine the histological structure of the nephron
and the collecting ducts
4. To correlate structure of various components with
function
Introduction The functions of the urinary system include
i. eliminating organic waste products
ii. regulating blood volume and pressure by adjusting the
volume of water lost and releasing erythropoietin and renin
iii. regulating plasma concentrations of ions by controlling
the
quantities lost in urine and calcium by calcitrol.
iv. helping stabilize blood pH by controlling loss of
hydrogen
and bicarbonate ions.
v. conserving nutrients, eliminates urea and uric acid
vi. assisting the liver in detoxification, and during
starvation,
deaminating amino acids so that they can be catabolized by
other tissues.
Organization of the Urinary System
The urinary system includes the kidneys, the ureters,
the urinary bladder and the urethra.
The kidneys produce urine - a fluid that contains
water, ions and soluble compounds.
Urine leaving the kidneys travels along the paired
ureters to the urinary bladder for temporary storage.
During urination (micturition) urine is forced out of
the body. This occurs when the contraction of the
muscular urinary bladder forces urine through the
urethra and out of the body.
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KIDNEY
URETER
BLADDER
URETHRA
highly vascular (25% cardiac
output)
produces urine (water and
electrolytes, urea, uric acid,
creatinine), initially an
ultrafiltrate of the blood
The Kidneys The kidneys are located on either side of the
vertebral column
between vertebrae T12 and L3. The left kidney extends
superiorly slightly more than the right kidney.
The superior surface of each kidney is capped by adrenal
gland; lie in a retroperitoneal position.
Each kidney is protected by three layers of connective
tissue:
the renal capsule (collagen fibers), adipose capsule
(adipose
tissue), renal fascia (anchors the kidney to surrounding
structures).
Each kidney hangs suspended by collagen fibers from the
renal
fascia and packed in as oft cushion of adipose tissue.
Floating kidney.
Kidneys Each kidney has the shape of a kidney bean. It is about
10
cm in length and weighs 150 g. The hilus provides entry for
the renal artery and renal nerves and exit for the renal
vein and the ureter.
The renal capsule has outer and inner layers.
The renal cortex is the outer layer in contact with capsule.
The renal medulla consists of 6-18 conical or triangular
structures called pyramids. The base faces cortex and tip-
the renal papilla.
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Kidneys Adjacent pyramids separated by renal columns.
A renal lobe consists of a renal pyramid, the overlying area
of
renal cortex, and adjacent tissues of the renal columns.
Urine production occurs in the renal lobes. Ducts within
each
renal papilla discharge urine into a cup-shaped drain called
minor calyx. Four or five merge to form-major calyx and two
or
three of these-renal pelvis.
Urine production occurs in microscopic structures called
nephrons present in the cortex of each lobe.
There are roughly 1.25 million nephrons in each kidney with
a
combined length of 85 miles.
KIDNEY
1) EXOCRINE PORTION
2) ENDOCRINE PORTION
- synthesis and secretion of erythropoietin (regulation of red
blood cell formation)
- synthesis and secretion of renin (hormone necessary for
control of blood pressure and blood volume)
KIDNEY (ORGANIZATION)
- RENAL HILUM, PELVIS, AND
SINUS
- RENAL CAPSULE
GROSS STRUCTURE:
- RENAL CORTEX
- RENAL MEDULLA
MM
CC
MM
CC
KIDNEY (ORGANIZATION)
- region immediately beneath renal
capsule
- composed of two distinct regions:
(1) CORTICAL LABYRINTH
(2) MEDULLARY RAY
- located immediately beneath renal
cortex
- consists of triangular blocks of
tissue called the PYRAMIDS
- RENAL COLUMNS are strands of cortical
tissue that extend down between
adjacent pyramids
RCRC
PP
PPPP
PP
PP
PPPP
CORTEXCORTEX
MEDULLAMEDULLA
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KIDNEY (ORGANIZATION)
PP
PPPP
PP
PP
PPPP
RENAL LOBERENAL LOBE
- a single pyramid with its
associated overlying cortex
RENAL LOBULERENAL LOBULE
- defined within cortex and
involves a single medullary
ray (central axis of lobule)
with adjacent cortical
labyrinth
- defined as a functional unit that consists of a
collecting duct and all the nephrons that it drains
Cortical Labyrinth
with
interdigitating
Medullary Rays
Supplementary notes: Kidney
Supplementary notes: Kidney Supplementary notes: Kidney
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Supplementary notes: Kidney Supplementary notes: Kidney
Supplementary notes: Kidney THE NEPHRON
& COLLECTING
DUCTS
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The Nephron The nephron is the basic functional unit of the
kidney.
It consists of a renal corpuscle and renal tubule.
The renal tubule begins at the renal corpuscle. It includes
a
knot of intertwined capillaries called the glomerulus
surrounded by Bowmans capsule. Blood arrives at the
glomerulus via the afferent arteriole and departs in the
efferent
arteriole. Filtrate is produced at the renal corpuscle and
then
enters the tubule.
The renal tubule is divided into proximal convoluted tubule,
loop of Henle and distal convoluted tubule.
The nephron empties tubular fluid into the collecting system
through a connecting tubule, a tributary of a collecting
duct.
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The Nephron Nephrons are responsible for the production of
filtrate, the
reabsorption of organic nutrients, the reabsorption of
water and ions, and the secretion into the tubular fluid of
waste products missed by filtration.
Roughly 85% of the nephrons are cortical nephrons found
in the cortex. These perform most of the reabsorptive and
secretory functions of the kidneys.
The juxtamedullary nephrons are found in the medulla,
with their loops of Henle extending deep into the renal
pyramids. These are responsible for the ability to produce
a concentrated urine.
The Nephron The proximal convoluted tubule (PCT) made of
cuboidal
cells with microvilli actively reabsorbs nutrients,
plasmaproteins, and ions from the filtrate.
The loop of Henle made of low cuboidal or squamouscells includes
a descending limb, and an ascending limb.Each limb contains a thin
segment and a thick segment.
The ascending limb made of cuboidal cells with very
littlemicrovilli delivers fluid to the distal convoluted
tubule(DCT) which actively secretes ions, toxins, and drugs and
reabsorbs sodium ions from the tubular fluid.
The collecting system The DCT opens into the collecting
system.
This consists of connecting tubules, collecting ducts,
papillary
ducts.
Individual connecting tubules connect each nephron to a
nearby
collecting duct. Each collecting duct receives tubular fluid
from
many connecting tubules.
Several collecting ducts converge to empty into a larger
papillary duct, which in turn empties into a minor calyx.
The epithelium lining the connecting tubule is cuboidal and
changes to columnar in the collecting and papillary ducts.
Besides transport, this adjusts composition and final
osmotic
concentration and volume of urine.
1) THE NEPHRON1) THE NEPHRON
2) COLLECTING DUCTS2) COLLECTING DUCTS
a) RENAL CORPUSCLE
- distributed throughout cortex
and various zones of medulla
BOWMANS CAPSULE + GLOMERULUS
b) PROXIMAL TUBULECONVOLUTED AND STRAIGHT
PORTIONS
c) HENLES LOOP
THICK AND THIN PORTIONS
d) DISTAL TUBULESTRAIGHT AND CONVOLUTED
PORTIONS
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CORTICAL LABYRINTH
1- RENAL CORPUSCLES
2- PROXIMAL CONVOLUTED
TUBULES
3- DISTAL CONVOLUTED
TUBULES
MEDULLARY RAY
1- STRAIGHT PORTIONS OF
PROXIMAL TUBULE (THICK DESCENDING)
2- STRAIGHT PORTIONS OF DISTAL
TUBULE (THICK ASCENDING)
3- COLLECTING DUCTS
CORTEX:
OUTER ZONE
INNER ZONE
MEDULLA:
1- STRAIGHT PORTIONS OF PROXIMAL
TUBULE (THICK DESCENDING)2- STRAIGHT PORTIONS OF DISTAL
TUBULE (THICK ASCENDING)
4- COLLECTING DUCTS
3- THIN SEGMENTS OF LOOP OF
HENLE (DESCENDING & ASCENDING)
2- COLLECTING DUCTS
1- THIN SEGMENTS OF LOOP OF
HENLE (DESCENDING & ASCENDING)
The Blood and Nerve Supply to the
Kidneys 1200 mL of blood flows through the kidneys each
minute.
Each kidney receives from a renal artery.
The vasculature of the kidneys includes the segmental,
interlobar, arcuate, and interlobular arteries, afferent
arterioles
and the venules, interlobular, arcuate, interlobar and
segmental veins.
Blood travels from the efferent arteriole to the peritubular
capillaries and the vasa recta.
The renal nerves that innervate the kidneys and ureters are
dominated by sympathetic postganglionic fibers. Functions
regulation of glomerular blood flow and pressure,
stimulation
of renin release, direct stimulation of water and sodium
reabsorption.
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BLOOD FLOW (KIDNEY)
AORTA
RENAL ARTERY
INTERLOBAR ARTERIES
INTERLOBULAR ARTERIES
ARCUATE ARTERIES
AFFERENT ARTERIOLES
GLOMERULAR CAPILLARY BED
EFFERENT ARTERIOLES
RENAL LOBULE
- run between lobes in medulla
- run parallel to bases of pyramids at the corticomedullary
junction
- delineate lateral limits of renal lobules
- supply blood to glomerulus
- drain blood from glomerulus and form either peritubular
capillary plexus (cortex) or vasa recta system (medulla)
BLOOD FLOW (KIDNEY)
VENA CAVAVENA CAVA
RENAL VEINRENAL VEIN
INTERLOBAR VEINSINTERLOBAR VEINS
INTERLOBULAR VEINSINTERLOBULAR VEINS
ARCUATE VEINSARCUATE VEINS
RENAL LOBULE
- run between lobes in medulla
- run parallel to bases of pyramids at the corticomedullary
junction
- delineate lateral limits of renal lobules
PERITUBULAR
CAPILLARY
PLEXUS
VASA RECTA
SYSTEM
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IAIA
GG
GG
BLOOD FLOW (KIDNEY)
injection of colored colloidin in renal artery
IA = interlobular artery
Aging and the urinary system
Age related changes include:
declining numbers of functional nephrons: drops by 30-
40%
reduced GFR: this results form decreased numbers of
glomeruli. Damage to filtration apparatus, reduction in
renal blood flow.
reduced sensitivity to ADH: distal portion of nephron
and collecting system less responsive to ADH. More
sodium ions lost in urine.
problems with the micturition reflex: sphincter muscles
lose muscle tone.
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Integration with other systems
The urinary, integumentary, respiratory, and
digestive systems are sometimes considered an
anatomically diverse excretory system, whose
component work together to perform all the
excretory functions that affect the composition
of the body fluid.
HISTOLOGICAL STRUCTURE
AND FUNCTION OF THE
NEPHRON & COLLECTING
DUCTS
*the epithelial changes that
occur along the uriniferous
tubules (reflects function)
RENAL CORPUSCLE
BOWMANS CAPSULE +
GLOMERULUS
1. BOWMANS CAPSULE:
- the beginning of the
nephron that consists of a
blind sac lined with simple
squamous epithelium that is
continuous with the PCT
- parietal layer & visceral
layer (specialized)
FILTRATION APPARATUS
OF KIDNEY
RENAL CORPUSCLE
BOWMANS CAPSULE +
GLOMERULUS
2. GLOMERULUS:
- specialized tuft of capillaries
which housed in the capsular
space (10-20 capillary loops)
- blood flowing through
glomerulus capillaries
undergoes a filtration
process to produce the initial
urine filtrate
FILTRATION APPARATUS
OF KIDNEY
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GLOMERULUS (FILTRATION
MEMBRANE):
1- fenestrated capillaries; discontinuous endothelium; fenestrae
have a diameter of 500-1000 and lack a diaphragm
2- continuous basal lamina
3- podocytes of visceral layer; processes contact basal lamina
and are separated by slits measuring approximately 250
GLOMERULUS (FILTRATION MEMBRANE):
prevents RBCs and large MW proteins from leaving circulation,
while most other blood constituents pass easily into the capsular
space
prevents RBCs and large MW proteins from leaving circulation,
while most other blood constituents pass easily into the capsular
space
MESANGIAL CELLS
phagocytic cells with a surrounding matrix that lend structural
support to the glomerulus
phagocytic cells with a surrounding matrix that lend structural
support to the glomerulus
GLOMERULUS (FILTRATION
MEMBRANE):
1- fenestrated capillaries
2- continuous basal lamina
3- podocytes
PODOCYTEPODOCYTE
1 process1 process
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