Transcript Excretion

Excretion
Section 38-3
Do Now
Your Body’s Filter
•Have you ever seen a water-purification system
attached to a faucet?
This system removes impurities from the water such as
arsenic or other chemicals that can be harmful to
people. As water passes through the filters contained in
the system, the impurities are trapped on the surface of
the filters. Eventually, the water that comes out of this
purifier is free of the impurities.
1. Your body has its own system for filtering blood. Why might the blood
in your body need to be filtered?
2. What organ(s) do you think filters your blood?
3. How do you think the filtered materials leave your body?
Checks and Balances
• Your body is amazingly maintaining
homeostasis through an intricate system
of checks and balances to satisfy your
body’s needs and remove waste products
that are not useful or toxic
Excretion
• Excretion = the process by which wastes
are eliminated from the body
• The excretory system includes:
– Lungs: excrete gaseous carbon dioxide from
cellular respiration
– Rectum: excrete solid undigested remains
from food
– Skin: excretes excess water, salts, urea
– Kidneys and accessory organs
The Urinary System
• The urinary system rids the blood of wastes
produced by the metabolism of nutrients and
controls blood volume by removing excess water
produced by body cells.
• The urinary system includes:
– Kidneys
– Urinary bladder
– Connecting tubules:
• Ureter
• Urethra
Section 38-3
The Urinary System
Vein
Kidney (Cross Section)
Kidney
Cortex
Medulla
Ureter
Urinary bladder
Urethra
Artery
Kidneys
• Most people have 2 kidneys located on either
side of the spinal column on your lower back
• Ureters = tubes that carry urine from each
kidney to the urinary bladder
• Urinary bladder = saclike organ that stores urine
until it can be excreted
• The kidneys filter blood by removing urea,
excess water and other wastes collected as
urine and the clean filtered blood returns to
circulation
Kidney Structure
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Inner part = renal medulla
Outer part = renal cortex
Functional units of the kidney = nephrons
About 1 million nephrons in each kidney
Each nephron has its own arteriole (small
artery), venule (small vein), and network of
capillaries to filter blood
Figure 38–17 Structure
of the Kidneys
Section 38-3
Kidney
Nephron
Bowman’s
capsule
Cortex
Capillaries
Glomerulus
Medulla
Renal
artery
Renal vein
Ureter
Collecting
duct
Vein
To the bladder
Artery
Loop of Henle
To the ureter
Filtration
• Blood enters a nephron through the
glomerulus (network of capillaries) in
Bowman’s capsule (cup-shaped structure)
• Blood is under high pressure causing fluid
to flow from the blood into Bowman’s
capsule = filtration
• The filtrate contains water, urea, glucose,
salts, amino acids, and some vitamins
Reabsorption
• Most of the material removed from the
blood at Bowman’s capsule makes its way
back into the blood = reabsorption
– 99% of water is reabsorbed into blood
Secretion
• Some materials, including hydrogen ions
(H+) are transferred from the blood into
the filtrate = secretion
Figure 38–18 The Nephron
Reabsorption
Filtration
Most filtration occurs in the
glomerulus. Blood pressure forces
water, salt, glucose, amino acids,
and urea into Bowman’s capsule.
Proteins and blood cells are too
large to cross the membrane; they
remain in the blood. The fluid that
enters the renal tubules is called
the filtrate.
As the filtrate flows through the
renal tubule, most of the water
and nutrients are reabsorbed into
the blood. The concentrated fluid
that remains is called urine.
Secretion
Substances such as hydrogen
ions are transferred from the
blood to the filtrate.
Urine
• The material that remains = urine
containing urea, salts, water and other
substances
• The loop of Henle conserves water and
minimizes the volume of urine
• Urine is stored in the urinary bladder until
it can be released from the body through a
tube = urethra
Kidney Function
• The kidneys maintain homeostasis by:
– Regulating the water content of the blood
(blood volume)
– Maintaining blood pH
– Removing waste products from the blood
Dialysis
• Although you are born with two kidneys,
you can live with only one kidney.
• If both kidneys malfunction, a kidney
dialysis machine can artificially filter blood
Figure 38–19 Kidney Dialysis
Section 38-3
Blood in tubing flows
through dialysis fluid
Blood pump
Vein
Artery
Used dialysis fluid
Shunt
Air detector
Dialysis
machine
Fresh
dialysis
fluid
Compressed
air