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TOPICS
• Anatomy of the urinary system
• Renal physiology
– Renal functions
– Nephron
– Blood supply
– Urine formation
– Counter-current mechanism
– Body water regulation
– Sodium ion regulation
– Micturition
1
2
URINARY SYSTEM
RENAL SYSTEM
EXCRETORY SYSTEM
• Water content of the body ~ 42 liters
– Made up of
• Intracellular fluid ~ 30 L – 70%
(Intra=Inside)
• Extracellular fluid ~ 12 L (Extra = outside)
– Blood plasma ~ 3 L
– Interstitial fluid ~ 9 L (Interstitial =
between cells)
3
URINARY SYSTEM
• Plasma and interstitial fluid have similar
ionic composition
– Mainly Na, Cl ions
– Lesser amounts of K, Ca, Mg, HCO3, PO4
ions
• Intracellular fluid
– Mainly K ions
–Lesser amount of Na, Cl ions
4
KIDNEYS
FUNCTIONS
• Filter 200 liters of blood daily
– allowing toxins, metabolic wastes, and
excess ions to leave the body in urine
• Regulate volume and chemical makeup
of the blood
5
KIDNEYS
FUNCTIONS
• Regulation of acid-base (pH) homeostasis
• Other functions:
– Production of erythropoietin to stimulate
RBC production
– Activation of vitamin D
–Gluconeogenesis during prolonged fasting
– Production of rennin to help regulate blood
pressure
6
KIDNEYS
GROSS ANATOMY
• Kidneys
–lie in the loin, alongside the vertebral column
– just under the lower ribs
– Surrounded by protective fat
– Lie outside the peritoneal cavity
• Hilus
– Point of entry (into) and exit (out) of the
kidneys:
• Ureters, renal blood vessels, lymphatics,
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and nerves
• The urine
– Is formed in the nephrons
– Flows and collects in the pelvis
– Leaves the kidneys via the ureter
– Is stored in the bladder
– Is discharged thru the urethra
8
Urinary System Organs
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Figure 25
...
Glomerular filtration
• Occurs in the renal corpuscle – the glomerulus
b
...
Secretion
• Mostly in the distal tubule and the collecting
duct
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Mechanism of Urine Formation
Glomerular Filtration
• Is the first step in urine formation
• Water and most solutes move across the
glomerular wall into the glomerular capsule
and then into the renal tubule
– Substances filtered
• Water, ions – Na, Cl, HCO3, K
• Glucose, amino acids
• Urea, uric acid, creatinine
44
Mechanism of Urine Formation
Glomerular Filtration
•The filtered fluid is then known as the
filtrate
• Blood cells and protein are too large to
pass thru the capillary wall
• Glomerular Filtration Rate (GFR)
–The total amount of filtrate formed per
minute by the kidneys
– Kidney (renal) function test
45
Mechanism of Urine Formation
Tubular Reabsorption
• Occurs along the renal tubule and the
collecting duct
• In the proximal tubule
– 99 % water reabsorbed
– Glucose, amino acids and K ions are
completely absorbed
– Most Na ions are also absorbed
– Water and these substances are returned to
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the blood
Mechanism of Urine Formation
Tubular Reabsorption
• Urea is absorbed by DCT
• Uric acid is also filtered, some reabsorbed
• Creatinine is filtered but none is
reabsorbed
47
Mechanism of Urine Formation
Tubular Secretion
• Usually occurs in the distal convoluted
tubule (DCT)
• Substances secreted
– K, acid (H), NH4 ions
– Urea
– Certain drugs
48
Glucosuria
• When the blood glucose is above 200
mg/ml (threshold level)
– The extra glucose is not reabsorbed
but remains in the urine
• A condition known as glucosuria ( ~
glucose in urine)
– The common cause being
diabetes mellitus
49
Mechanism of Urine Formation
Countercurrent Mechanism
• Involves the movement of Na ions in the loop
of Henle
• As the filtrate flows down the descending limb
– water leaves the tubule by osmosis
– the filtrate becomes more hypertonic (less
water) as it goes down the descending limb
50
Mechanism of Urine Formation
Countercurrent Mechanism
• As the fluid travels up the ascending limb
– Na ions are pumped out of the tube by
active transport into the medulla
– The fluid becomes less and less hypertonic
as it goes up the tube
• So the condition creates high osmotic
pressure in the medulla
–Which is important for the collecting duct
function to produce concentrated urine 51
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Countercurrent Mechanism
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Mechanism of Urine Formation
Distal Convoluted Tubule
• Reabsorption occurs:
– Water, Na ions, H ions
– Some urea – most tends to stay in the urine
– Certain drugs
• Reabsorption of water is under the control of
hormones:
– Antidiuretic hormone (ADH) from the
posterior pituitary
– Aldosterone from the adrenal cortex
55
Mechanism of Urine Formation
Collecting duct
• The filtrate from the distal collecting tubule
passes on to the collecting duct
– where further reabsorption of water and
Na ions takes place
• According to the need of the body to
maintain internal homeostasis
• The urine then travels down the ureter
– to be stored in the urinary bladder
• before passing thru the ureter to the
outside during micturition (urination)
56
process
KIDNEYS
Regulation of Body Water
• Important to maintain blood volume and consequently
the blood pressure
• A decrease of blood volume and an increase in the
osmotic pressure in the plasma provoke the following
events:
– Increase of ADH secretion
– ADH acts on the distal and collecting tubules
• to increase water reabsorption
• to prevent water loss
– This leads to the formation of a concentrated
urine
57
KIDNEYS
Regulation of Body Water
• An increase of blood volume and a
decrease of the osmotic pressure
provokes the opposite:
– Decreased ADH secretion
• decreased water reabsorption
• increased water loss
• formation of a dilute urine
58
KIDNEYS
Regulation of Na Ions
• Important to maintain osmotic pressure in the
body fluids, including plasma
• A decrease of Na ions in the blood plasma
provokes the following events:
– Increase of aldosterone secretion
– Aldosterone acts on the distal and
collecting tubules
• To increase Na ion reabsorption
• Water follows Na reabsorption
59
• This prevents water loss
KIDNEYS
Regulation of Na Ions
• An increase of Na ions in the blood
plasma provokes the opposite:
– Decreased aldosterone secretion
– Decreased Na ion reabsorption
– Increased water loss
60
JUXTAMEDULAARY APPARATUS
• Located at the point where the distal
convoluted tubule comes close to the
glomerular afferent arteriole
• Secretes a hormone renin
– which responds to low sodium in the
body
• to stimulate aldosterone secretion
61
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Renin-Angiotensin System
• Regulates blood pressure and water
(fluid) balance
...
• Plasma renin then carries out the
conversion of angiotensinogen
released by the liver to angiotensin I
...
• Angiotensin II causes blood vessels
to constrict, resulting in increased
blood pressure
...
• Aldosterone causes the tubules of the
kidneys to increase the reabsorption
of sodium and water into the blood
...
65
Rennin-Angiotensin-Aldosterone System
• If the renin-angiotensin-aldosterone
system is too active, blood pressure will
be too high
...
• These drugs are one of the main ways
to control high blood pressure
(hypertension), heart failure, kidney
failure, and harmful effects of diabetes
...
• In medicine, diuretics are used to treat
heart failure, liver cirrhosis,
hypertension and certain kidney
diseases
71
DISORDERS OF THE RENAL
SYSTEM
• Kidney stones
• Bladder stones
• Drug toxicity
This is occasionally responsible for
kidney complications
• Renal Failure
• Infections of kidneys
72
RENAL FAILURE
• Diseases of the kidneys often produce
temporary or permanent changes to the
kidney
...
• Acute renal failure has an abrupt onset and is
potentially reversible
...
RENAL FAILURE
DIALYSIS MACHINE
Artificial kidney
• Dialysis is a procedure that is performed
routinely on persons who suffer from acute
or chronic renal failure
...
• Kidney transplant
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Peritoneal Dialysis
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Nephrons
Cortical nephrons – 85% of nephrons; located in
the cortex
Juxtamedullary nephrons:
Are located at the cortex-medulla junction
Have loops of Henle that deeply invade the medulla
Have extensive thin segments
Are involved in the production of concentrated urine
79
Nephrons
• Cortical nephrons – 85% of nephrons;
located in the cortex
• Juxtamedullary nephrons:
– Are located at the cortex-medulla junction
– Have loops of Henle that deeply invade the
medulla
– Have extensive thin segments
– Are involved in the production of concentrated
urine
80
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• Juxtaglomerular Apparatus (JGA)
• Where the distal tubule lies against the
afferent (sometimes efferent) arteriole
• Arteriole walls have juxtaglomerular (JG)
cells
– Enlarged, smooth muscle cells
– Have secretory granules containing renin
– Act as mechanoreceptors
83
Mechanisms of Urine Formation
• The kidneys filter the body’s entire plasma
volume 60 times each day
• The filtrate:
– Contains all plasma components except
protein
– Loses water, nutrients, and essential ions to
become urine
• The urine contains metabolic wastes and
unneeded substances
84
Mechanisms of Urine Formation
• Urine formation
and adjustment
of blood
composition
involves three
major
processes
– Glomerular
filtration
– Tubular
reabsorption
85
Figure 25
...
8
Osmotic Gradient in the Renal
Medulla
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Diuretics
• Chemicals that enhance the urinary output
include:
– Any substance not reabsorbed
– Substances that exceed the ability of the renal
tubules to reabsorb it
– Substances that inhibit Na+ reabsorption
111