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The Mammalian Kidney
The human kidneys are two bean-shaped
organs, located against the dorsal body
wall on either side of the backbone
The principal functions of the kidneys are:

· Excretion ­ the removal of toxic nitrogenous
waste products from the blood; these include
urea and creatine…

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The Renal
System vena cava aorta
adrenal gland

renal artery left kidney
renal vein


The urethra carries urine
away from the bladder

Kidney Section

Pelvis Pelvis


The kidney is composed of three distinct regions

Kidney Section

The renal pelvis ­ a The outer cortex
large chamber…

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The Kidney Tubule (Nephron)
The kidney tubule or nephron is the
functional unit of the kidney
Each kidney tubule receives its own small supply of
blood from the extensive arteriole branches arising
from the renal artery; each human kidney contains
approximately 1 million tubules
Each kidney tubule is responsible for…

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Convoluted tubules of
the nephron

Collecting duct

Bowman's (renal)

of proximal

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Urine formation begins with the filtration of
blood at the glomeruli of the renal corpuscles

Glomerular Filtration
The first step in the formation of urine is
glomerular filtration
The afferent arteriole, which provides the blood
supply to the glomerulus, branches to form a
network of capillaries which reunite to form…

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proximal convoluted

outer (parietal)
layer of the renal
cavity of
(renal) capsule

glomerulus capillary

podocyte nucleus

The afferent arteriole is larger in diameter
than the efferent arteriole

Blood tends to back up in the the glomerular capillaries
due to the high resistance to the outflow of blood…

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Podocytes are the cells that form the inner layer
of Bowman's capsule; this layer is moulded
around the capillaries of the glomerulus
The capillary walls are only one cell thick and made up of
endothelial cells; these cells rest on the basement membrane
Small molecules, present in the blood, are…

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This electron micrograph
shows the components of the
capillary/capsular membrane

nucleus of podocyte

foot process of podocyte

slit pore
basement membrane
fenestrated capillary

red blood cell

High blood pressure within the
glomerular capillaries forces
molecules out of the blood (GBHP)
The hydrostatic pressure of the filtrate
(CHP) tends to…

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Typical values for these pressures are:
GBHP = 60 mm Hg
CHP = 15 mm Hg
OP = 27 mm Hg
Therefore the Net Filtration Pressure
that promotes glomerular filtration
equals 18 mm Hg

The high blood pressure
(hydrostatic pressure) in
the glomerular capillaries
forces small molecules out
of the…

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Three terms are used to describe the
relative concentrations of solutions on
either side of membranes; these are
isotonic, hypotonic and hypertonic
Isotonic solutions have the same concentration and
therefore the same water potentials
When two solutions are separated by a cell
membrane such that one of the solutions…


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