‫‪THE URINARY SYSTEM‬‬
‫‪PHYSIOLOGY 2‬‬
‫‪PHL-226‬‬
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The Urinary System
The urinary system is a group of organs that
are responsible for excretion of excess fluid
and other substances from blood stream in
the form of urine.
Organs of the Urinary system :
 Paired kidneys
 A ureter for each kidney
 Urinary bladder
 Urethra
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THE KIDNEY
 Kidneys are retroperitoneal organs that is located in the
superior lumbar region of the posterior abdominal wall
 The lateral surface of the kidney is convex
 The medial surface of the kidney is concave
 Hilum is cleft in the medial surface of the kidney where
vessels, ureters and nerves enter and leave through it
 Adrenal gland lies superior to each kidney
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 Kidney has two regions:
 Cortex: outer
 It lies under the capsule and contains:
a. Cortical tissue
b. Renal columns which divide the medulla into “pyramids
c. Nephron”
 Medulla: inner
 Darker, cone-shaped medullary or renal pyramids
 Parallel bundles of urine-collecting tubules
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 The human kidney has lobes
 Each lobes formed from renal pyramid and
cortical tissue surrounding it
 There are 5-11 lobes per kidney
 Renal pelvis (=basin)
 It is the expanded, funnel shaped and superior
part of ureter
 Branches to form two or three major calyces
(plural of calyx )
 Each of these divides again, to form minor
calyces: collect urine from papillae of pyramids
 NB; Renal calyx(minor and major calyces and Renal
pelvis are called (renal cavities)
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 Uriniferous tubule is the main structural
and functional unit of the urinary system
A uriniferous tubule is the main structural
and functional unit of the urinary system
Each kidney contains :
1- More than a million of uriniferous
tubules are present in each kidney
and act together to form the urine
2- The urine is formed by three main
mechanisms:
a. Glomerular filtration
b. Tubular reabsorption
c. Tubular secretion
3- A uriniferous tubule has two major
parts:
1. A urine-forming nephron
2. A collecting duct which concentrates
urine by removing water from it
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Uriniferous tubule
 Uriniferous tubule (anatomical unit for
forming urine) consists of
 Nephron which is formed of :
 Renal corpuscle (in cortex) which consists of:
– Glomerulus (tuft of capillaries)
– Glomerular (Bowman’s) capsule
 Tubular section that consists of :
– Proximal convoluted tubule
– Loop of Henle
– Distal convoluted tubule
 Collecting duct
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function of uriniferous tubule
a. Glomerular filtration
Fluid is squeezed out of the
glomerular capillary bed
b. Tubular reabsorption
Most nutrients, water and
essential ions are returned to
the blood of the peritubular
capillaries.
c. Tubular secretion
Moves additional undesirable
molecules into tubule from
blood of peritubular capillaries
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Nephron
Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of
capillaries)
Glomerular (Bowman’s)
capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
1) Renal corpuscle:
 Present only in the renal
cortex
 It consists of :
 Tuft of capillaries called
glomerulus
 Surrounded by cup-shaped,
hollow glomerular
(Bowman’s) capsule
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Classes of
nephrons
1) Cortical nephrons
 85% of all
nephrons
 Almost entirely
within cortex
2) Juxtamedullary
nephrons
 Renal corpuscles
near cortexmedulla junction
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Glomerular (Bowman’s)
capsule:
Bowman‘ s capsule consists of two layers:1.Parietal layer of the capsule: which is the
outer layer .
2.Visceral layer of capsule which has
podocytes
WHAT IS PODOCYTES?
 They are unusual branching epithelial
cells
 They have foot processes with slit
processes between them
WHAT IS THE BOWMANS SPACE?
It is the space between two layers of the
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bowman‘s capsule
GLOMERULAR FILTERATION BARRIER
1) The capillary endothelial cells which contain slits (fenestrations)
FUNCTION: They restrict the passage of the largest elements such as blood
cells and most protein
2) The basement membrane which is the main filtration barrier that
FUNCTION: 1. it prevents any large molecules from being filtered.
2. it contain heparin sulphate proteoglycans which repels
negatively charged protein such as albumin
3) Slit diaphragm ( filtration slits or processes ) between processes of podocytes
which hold back large molecules and proteins while letting through small
molecules such as water, ions, glucose, amino acids, and urea
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Uriniferous tubule (anatomical unit for forming urine)
Tubular section of the
Nephron
1. the tubular section consists of
 Proximal convoluted tubule
 Loop of Henle
 Distal convoluted tubule
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
2. The tubular section ends by
joining collecting duct.
FUNCTION :
It is responsible for reabsorption
and secretion of solutes
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Uriniferous tubule (anatomical unit for forming urine)
Proximal convoluted
tubule
 Confined to renal
cortex
 FUNCTION:
Reabsorption of
water, ions and
solutes
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries
Glomerular (Bowman’s) capsu
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
*
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Uriniferous tubule (anatomical unit for forming urine)
Nephron
Loop of Henle
1. Confined to renal
medulla
2. It consists of :
 Descending limb
 Ascending limb
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
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Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Distal convoluted tubule
 It is confined to
the renal cortex
FUNCTION:
 It is responsible
for selective
secretion and
reabsorption of
ions
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Uriniferous tubule (anatomical unit for forming urine)
Nephron
Renal corpuscle (in cortex)
Glomerulus (tuft of capillaries)
Glomerular (Bowman’s) capsule
Tubular section
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct
Collecting Ducts
Collecting Duct
 Each receives
urine from
several DCT of
nephrons
 Run straight
through cortex
into the deep
medulla 18
Uriniferous tubules
1. Nephron
2. Collecting ducts
Collecting Ducts
*
 At papilla of pyramid,
collecting ducts join to
form larger papillary
ducts
 Empty into minor
calices
 Role: conserve body
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fluids
The collecting ducts
Role of ADH in maintaining the volume of urine:
The most important role of ADH is to conserve body
fluids.
1- When the body must conserve water, the posterior
pituitary gland secretes ADH (antidiuretic hormone).
2- ADH increases the permeability of the collecting
tubules and distal tubules to water so more water is
reabsorbed into blood.
3- This decreases the total volume of urine.
4- Alcohol inhibits the release of ADH, so less water is
reabsorbed producing copious amounts of dilute urine
(can cause dehydration).
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Vessels

Afferent and efferent arterioles associated with glomerular capillaries
 Allows high pressure for forcing filtrate out of blood
 About 20% of renal plasma flow is filtered each minute (125 ml/min): this is the
glomerular filtration rate (GFR), an important clinical measure of renal function
 This is about one liter every 8 minutes (only 1% ends up as urine)

Peritubular capillaries arise from efferent arterioles
 Absorb solutes and water from tubule cells
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(vascular supply of the kidney )
1- Aorta gives off right and left renal arteries
2- Renal arteries divides into 5 segmental arteries as enters
hilus of kidney
3- Segmental arteries branch
into lobar arteries.
4- Lobar artery divide into
interlobar arteries
5- Interlobars give rise
arcuate artery at the junction
between medulla and cortex
6- Arcuate arteries
send
interlobular
arteries
into
cortex.
7Cortical
interlobular
arteries
give
rise
to
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glomerular arterioles
Vasculature of the kidney
 The glomerular capillary bed is unusual in
having arterioles going both to it and away from
it (afferent and efferent arteriole), instead of a
vein going away as most
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(vessels, continued)
The Vasa recta
1)The Vasa recta is a portion
of the peritubular capillary
system which enters the
medulla where the solute
concentration in the
interstitium is high. 2) It acts
with the loop of Henle to
concentrate the urine by a
complex mechanism of
counter current exchange
using urea. If the vasa recta
did not exist, the high
concentration of solutes in
the medullary interstitium
would be washed out.
____vasa recta
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Juxtaglomerular apparatus
 Juxtaglomerular apparatus is formed of :
1) Mesangial cells
2) Macula densa cells:3) Juxtaglomerular cells
(granular cells)
FUNCTION :
Regulation of blood pressure.
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Juxtaglomerular apparatus
1) Mesangial cells:- that are located between glomerular
capillaries. They are supportive cells.
2) Macula densa cells:- which line the wall of distal
convoluted tubule facing the glomerular capillaries
afferent and efferent arteriole
FUNCTION: It act as chemoreceptors by monitor
salts (Na Cl) concentration in the distal convoluted
tubule.
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Juxtaglomerular apparatus
The macula densa cell response to the drop of
blood pressure by 2 mechanisms:
1) It dilates the afferent arteriole of the glomeruli
to increase the volume of blood and pressure
inside the glomeruli
2) Releases prostaglandin from adrenal glands
which stimulate the juxtaglomerular cells to
release renin in the blood stream
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Juxtaglomerular apparatus
3) Juxtaglomerular cells (granular cells) : –
Juxtaglomerular cell is a modified smooth muscle
cell
Function :
1) They act as mechanooreceptor which monitor
the change in blood pressure in the arteriole
2) They secrete renin in response to falling blood
pressure in afferent arteriole.
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Juxtaglomerular apparatus
 Juxtaglomerular cells secrete renin in
response to :
1) A decrease in the blood pressure in
afferent arteriole.
2) Signals from macula densa.
3) Sympathetic nervous system activity
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