Transcript Kidney

Kidney & Urinary System
Kidney & Urinary System
Location and Structure of Kidney
 Lie against the dorsal body wall in a retroperitoneal position in the superior lumbar
region.
 Receive some protection from lower part of the rib cage.
 Right kidney positioned slightly lower than the left due to its location near liver.
 Above each kidney is adrenal gland, it’s a part of endocrine system and separate
organ.
 Other structure include ureters, renal blood vessels and nerves enter or exit the
kidney at the hilus.
 Kidney enclosed by a fibrous, transparent renal capsule.
 Adipose capsule, a fatty mass surrounds each kidney and helps hold it in place
against the muscles of the trunk wall.
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Listed here are other structures which forms human kidney system :
Renal cortex : outer region contains blood vessels, glomeruli and urine tubes.
Renal pyramids : The conical segments within the internal medulla. They contain the
secreting apparatus and tubules.
Renal column : structures which support the cortex, consist of lines of blood
vessels and urinary tubes and a fibrous material. It separates the renal pyramids.
Renal artery : Two renal arteries come from the aorta, each connecting to a kidney.
The artery divides into five branches, each of which leads to a ball of capillaries.
The arteries supply (unfiltered) blood to the kidneys. The left kidney receives about
60% of the renal blood flow.
Renal vein : The filtered blood returns to circulation through the renal veins which
join into the inferior vena cava.
Renal pelvis : accepts the urine and channels it out of the hilus into the ureter.
Kidney & Urinary System
Kidney & Urinary System
Nephrons
 Each kidney contains million of tiny structures called nephrons.
 It’s the structural and functional units of the kidneys.
 Responsible for forming urine.
 Two types of nephrons : cortical and juxtamedullary.
 They are classified based on location : cortical located almost entirely within the
cortex, juxtamedullary situated close to cortex-medulla junction.
 Consists of two main structures : glomerulus and renal tubule.
 Glomerulus is a knot of capillaries which receives blood supply from an afferent
arteriole of renal circulation.
 Renal tubule the portion of the nephron of the kidney containing the tubular fluid
filtered through the glomerulus. After passing the tubule, the filtrate continues to
the collecting duct system.
Kidney & Urinary System
Kidney & Urinary System
Kidney & Urinary System
Kidney & Urinary System
Kidney & Urinary System
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Glomerular or Bowman’s capsule is a portion of renal tubule which completely
surrounds the glomerulus.
Inner layer of capsule made up of cells called podocytes.
Podocytes have long branching processes called foot processes.
Podocytes form a porous membrane around glomerulus because filtration slits
exists between their extensions.
From glomerular, renal tubule forms several other structure where each structure
forms a region with different name.
They are proximal convoluted tubule, loop of Henle and distal convoluted tubule.
As tubule extends from glomerular, it coils and twists before forming a hairpin loop,
then again become coiled and twisted before entering collecting ducts.
Collecting ducts receives urine from many nephrons and run downward through
medullary pyramids.
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Kidney & Urinary System
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Glomerulus is feed and drained by arterioles.
Afferent arteriole is the feeder vessel.
Efferent arteriole receives blood that has passed through glomerulus.
These arterioles are high resistance vessels.
Afferent arteriole has larger diameter than efferent.
Blood pressure in glomerular capillaries is higher than other capillary beds.
This extremely high pressure forces fluid and solutes out of the blood into the
glomerular capsule.
Collecting ducts receives urine from many nephrons and run downward through
medullary pyramids.
Peritubular capillaries arises from efferent arteriole that drain the glomerulus.
These capillaries are low-pressure porous vessels that are adopted for absorption.
Kidney & Urinary System
Kidney & Urinary System
Urine Formation
 Urine formation is a result of three processes : filtration, tubular reabsorption and
tubular secretion.
Filtration
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A nonselective, passive process.
Glomerulus acts as a filter.
Filtrate that is formed is blood plasma without blood proteins.
Proteins and blood cells too large to pass through filtration membrane.
But if either of these appear in urine, there might be problem with glomerular
filters.
As long as systemic blood pressure is normal, filtrate will be formed.
If arterial blood pressure drop too low, glomerular pressure becomes inadequate to
force substances out of blood into tubules, thus filtrate formation stops.
Kidney & Urinary System
Kidney & Urinary System
Tubular Reabsorption
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Filtrate contains useful substances besides wastes that must be removed.
These substances must be returned to the blood.
Tubular reabsorption begins as soon as the filtrate enters the proximal convoluted
tubule.
Tubule cells are transporters, taking up needed substances from the filtrate.
The substances are passed out into extracellular space from which they are
reabsorbed into peritubular capillary blood.
Reabsorption mostly depends on active transport which uses membrane carriers
and very selective.
Example of needed substances that entirely removed from filtrate are glucose and
amino acids.
Nitrogenous waste products are poorly reabsorbed.
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These include urea formed by liver as end product of protein breakdown.
Tubular secretion
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Reabsorption in reverse.
Some substances (e.g. hydrogen, potassium ions) move from blood of peritubular
capillaries through tubule cells or from tubule cells into filtrate to be eliminated in
urine.
Important for getting rid of substances not already in filtrate or as additional
means for controlling blood pH.
Kidney & Urinary System
Renal Circulation
 In a resting adult, kidney receive 1.2 – 1.3 liters of blood per minute.
 Just under 25% of cardiac output.
 Renal blood flow can be measured with EM flowmeter or other type of meter.
 Renal plasma flow equals amount substance excreted per unit time divided by renal
arteriovenous difference.
 Renal plasma flow commonly measured by infusing para-aminohippuric acid (PAH)
or iodopyracet and determining their urine and plasma concetrations.
 These substances filtered by glomeruli and secreted by tubular cells so that their
extraction ratio is high.
 Extraction ratio = (CA – CRV/CA) where CA is arterial concentration and CRV is renal
venous concentration.
 Effective renal plasma flow (ERPF) is amount of PAH in urine divide by amount of
PAH in plasma.
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Example
Given concentration PAH in urine = 14 mg/ml , concentration PAH in plasma = 0.02 mg/ml , urine
volume = 0.9 ml/min
ERPF 
U PAH  V
PPAH
14  0.9
0.02
 630 ml / min
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