2. Human Excretory System
functions to remove waste
from the human body;
this system consists of
specialized structures and
capillary networks that
assist in the excretory process;
this system includes the
4. The kidneys are two small organs
located near the vertebral column at
the small of the back.
The left kidney lies a little higher than
the right kidney.
They are bean-shaped, about 4 in.
(10 cm) long and about 21/2 in.
(6.4 cm) wide.
7. Renal Vein
This has a large diameter and a thin wall.
It carries blood away from the kidney and
back to the right hand side of the heart.
Renal Artery
This blood vessel supplies blood to the kidney
from the left hand side of the heart. This
blood must contain glucose and oxygen
because the kidney has to work hard
producing urine.
Blood in the renal artery must have sufficient
pressure or the kidney will not be able to filter
the blood.
8. Medulla
The medulla is the inside part of the kidney.
This is where the amount of salt and water
in your urine is controlled.
It consists of billions of loops of Henlé.
These work very hard pumping sodium ions.
Ureter
The ureter carries the urine down to
the bladder.
9. Cortex
The cortex is the outer part of the
kidney.
This is where blood is filtered. We call
this process “ultra-filtration” or “high
pressure filtration” because it only
works if the blood entering the kidney
in the renal artery is at high pressure.
Billions of glomeruli are found in the
cortex. A glomerulus is a tiny ball of
capillaries.
10. Nephron
The basic structural and functional unit of the
kidney.
Its chief function is to regulate the
concentration of water and soluble substances
like sodium salts by filtering the blood,
reabsorbing what is needed and excreting the
rest as urine.
A nephron eliminates wastes from the body,
regulates blood volume and blood pressure,
controls levels of electrolytes and metabolites,
and regulates blood pH.
a normal kidney contains 800,000 to 1.5 million
nephrons
11. T h e Ne p h r o n
(P a r t s a n d S t r u c t u r e )
13. 1. FILTRATION
Urine formation begins with the process
of filtration, which goes on continually in the
renal corpuscles. As blood courses through the
glomeruli, much of it is fluid, containing both
useful chemicals and dissolved waste
materials, soaks out of the blood through the
membranes (by osmosis and diffusion) where it
is filtered and then flows into the Bowman's
capsule. This process is called glomerular
filtration.
14. The water, waste products, salt, glucose,
and other chemicals that have been filtered
out of the blood are known collectively as
glomerular filtrate. The glomerular filtrate
consists primarily of water, excess salts
(primarily Na+ and K+), glucose, and a waste
product of the body called urea. Urea is
formed in the body to eliminate the very toxic
ammonia products that are formed in the liver
from amino acids.
15. Since humans cannot excrete ammonia,
it is converted to the less dangerous urea and
then filtered out of the blood. Urea is the
most abundant of the waste products that
must be excreted by the kidneys.
The total rate of glomerular filtration
(glomerular filtration rate or GFR) for the
whole body (i.e., for all of the nephrons in
both kidneys) is normally about 125 ml per
minute. That is, about 125 ml of water and
dissolved substances are filtered out of the
blood per minute.
16. 2. REABSORPTION
It is the movement of substances out of
the renal tubules back into the blood
capillaries located around the tubules (called
the peritubular copillaries). Substances
reabsorbed are water, glucose and other
nutrients, and sodium (Na+) and other ions.
Reabsorption begins in the proximal
convoluted tubules and continues in the loop
of Henle, distal convoluted tubules, and
collecting tubules.
17. Large amounts of water - more than
178 liters per day - are reabsorbed back into
the bloodstream from the proximal tubules
because the physical forces acting on the
water in these tubules actually push most of
the water back into the blood capillaries. In
other words, about 99% of the 180 liters of
water that leave the blood each day by
glomerular filtration returns to the blood
from the proximal tubule through the
process of passive reabsorption.
18. The nutrient glucose (blood sugar) is
entirely reabsorbed back into the blood from
the proximal tubules. In fact, it is actively
transported out of the tubules and into the
peritubular capillary blood. None of this
valuable nutrient is wasted by being lost in the
urine. However, even when the kidneys are
operating at peak efficiency, the nephrons can
reabsorb only so much sugar and water. Their
limitations are dramatically illustrated in cases of
diabetes mellitus, a disease which causes the
amount of sugar in the blood to rise far above
normal.
19. 3. SECRETION
Secretion is the process by which
substances move into the distal and collecting
tubules from blood in the capillaries around
these tubules. In this respect, secretion is
reabsorption in reverse. Whereas
reabsorption moves substances out of the
tubules and into the blood, secretion moves
substances out of the blood and into the
tubules where they mix with the water and
other wastes and are converted into urine.
20. These substances are secreted through
either an active transport mechanism or
as a result of diffusion across the
membrane. Substances secreted are
hydrogen ions (H+), potassium ions (K+),
ammonia (NH3), and certain drugs.
Kidney tubule secretion plays a crucial
role in maintaining the body's acid-base
balance, another example of an
important body function that the kidney
participates in.
23. KIDNEYS
The kidneys are two brownish, bean shaped
organs about the size of a fist, they weigh
about 5 ounces.
They are located in the upper right and left
back part of the abdominal cavity.
Each kidney contains about 1,200,000
microscopic filters called nephrons.
The main function or the kidneys are to
maintain the water balance and to
eliminate waste materials from the blood.
24. URETERS
The left and the right ureters are long
muscular tubes.
They are about 12 inches long with a
diameter 2 to 3 millimeters.
The ureters connect pelvis of each
kidney to urinary bladder. They
carry urine from each kidney to
the urinary bladder.
25. URINARY BLADDER
The urinary bladder is a muscular
sac that holds urine.
It is located in front the pelvis and
behind the pubis.
As the bladder fills walls stretch
signaling the desire to urinate.
26. URETHRA
The urethra is a muscular tube which
carries urine from the bladder to the
outside part of the body.
In the female, it is a one inch long from
the bladder to the cleft of the labia.
In the male, it is several inches long from
the prostate gland to the penis.
When one is about to urinate, a value in
the urethra relaxes to allow the urine
to flow out.
