Kidney Function

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  • Created on: 30-03-13 21:26
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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 (a waste product of muscle
· Homeostasis ­ the kidneys regulate the water
content, ion composition and pH of the body
fluids; their role in the regulation of water
content is described as osmoregulation
of the

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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 that Kidney tubule
collects urine from (nephron) where
the kidney tubules blood is filtered
and funnels it into and urine is
the ureter formed ­ about
one million in
each kidney
The medulla
consisting of…read more

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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 urine formation
and this involves three basic processes:
· Ultrafiltration of blood
· Selective tubular reabsorption of filtered
· Tubular secretion; the secretion of
substances from the blood capillaries into
the kidney tubules
glomerulus…read more

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Convoluted tubules of
the nephron
Collecting duct
Bowman's (renal)
of proximal
tubule…read more

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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 the
outgoing or efferent arteriole
Ultrafiltration of the blood takes place at the
glomerulus producing a fluid that enters the cavity
of Bowman's (renal) capsule; this filtered fluid is
called the glomerular filtrate
The driving…read more

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(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
This creates a high blood pressure within the glomerular capillaries that
forces water and solutes out of the blood into the cavity of Bowman's
capsule; this is ultrafiltration and produces a filtrate that contains all
the molecules present in blood plasma except the larger plasma proteins
The…read more

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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 forced through the endothelial layer,
the basement membrane and the slit pores of the podocyte foot processes
The glomerular capillaries are fenestrated (possess pores); larger molecules
can therefore pass through this endothelial layer
The ACTUAL…read more

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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 push fluid back into the
glomerular capillaries
Osmotic pressure tends to pull water
out of the filtrate back into the blood
The osmotic potential of the blood is more
negative than that of the filtrate…read more

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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 blood into the cavity
of Bowman's capsule
Opposing this hydrostatic
pressure is the hydrostatic
pressure of the glomerular
filtrate together with a
tendency for some of the
filtered fluid to move back
into the capillaries…read more

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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 has a lower
water potential than the other, then this more
concentrated solution is described as being
hypertonic to the weaker solution
The weaker solution, with a higher water potential, is
described as being hypotonic…read more


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