The document discusses excretion and homeostasis in animals. It explains that excretion involves filtering wastes from blood and extracellular fluids through cell membranes in excretory structures like the kidneys. The kidneys filter blood, selectively reabsorb nutrients, and excrete excess water, nutrients, and dissolved wastes as urine. This helps regulate substances in cells and their environments to maintain homeostasis. The human urinary system involves the kidneys filtering waste from the bloodstream, reabsorbing nutrients, and excreting urine through the ureters, urinary bladder, and urethra to remove cellular wastes from the body.

1. EXCRETION
It’s not only to get rid of wastes, it’s the maintenance of
constant equilibrium to preserve health.
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2. How do we keep ourselves in
equilibrium?
HOMEOSTASIS: Includes the processes by which organisms
maintain their internal environment within a narrow range of
conditions necessary for cells to function properly under
changing conditions.
These changes include
• Temperature
• Water and salt concentrations
• Glucose concentrations
• pH
• Oxygen and carbon dioxide concentration
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3. Excretion=filtering
Cell membranes in excretory structures serve as filters for
extracellular fluids. In animals it helps filtering blood too.
Through this process, the system keeps osmolarity which
means proper concentration of substances in cells and their
environment (water balance)
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4. Urinary systems remove wastes from
cellular metabolism
• Water and small molecules are filtered both from blood or
extracellular fluids.
• Nutrients are selectively reabsorbed back from the filtered
fluid.
• Excess of water, nutrients and disolved wastes are excreted
from the body in urine.
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5. EXCRETION IN ANIMALS
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Protonephridia Malphigian tubules Nephridia

6. HUMAN URINARY SYSTEM
What kidneys are for…
• Regulate blood levels of ions such as Na, K, Cl and Ca.
• Maintain pH of blood by regulating H and H2CO3
• Regulate water contents.
• Retain important nutrients such as glucose and aminoacids.
• Eliminate cellular waste such as urea.
• Secreting hormones
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7. HUMAN URINARY SYSTEM
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8. STRUCTURE FUNCTION
RENAL
ARTERY
Transports blood with wastes from the inferior
Aorta.
KIDNEY Filter blood and produces urine.
RENAL VEIN Transports filtered blood from the kidneys to the
Vena Cava.
URETER Transports urine from kidneys.
URINARY
BLADDER
Stores urine from ureters.
URETHRA Tube by which urine is expulsed from the body.
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9. In the
inside…
Renal Capsule: A smooth semitransparent membrane that
adheres tightly to the outer surface of the kidney.
Renal Cortex: The region of the kidney just below the capsule.
Renal Medulla: The region deeper into the kidney, beneath the
cortex layer. It is segregated into triangular regions called the
renal pyramids, which should be striated (or striped) in
appearance due to the collecting ducts running through them,
and columnar regions between the pyramids called the renal
columns in which arteries are located.
Renal Pelvis: A cavity within the kidney that is continuous
with the ureter, which exits from the hilus. The pelvis has
portions that extend towards the apexes of the renal pyramids.
The primary (large) extensions are the major calyces and the
smaller extensions are the minor calyces.
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10. Within the pyramids
FILTRATION: Blood enters the
Bowman’s capsule under relatively
high pressure. 1/5 of plasma is
filtered (water, glucose, vitamins,
salts and urea).
REABSORPTION: Many substances
are reabsorbed selectively in the walls
of the proximal tubule and the distal
tubule by osmosis and active
transport.
The Loop of Henle keeps the high
concentration of Cl and Na ions to
ensure reabsorption of water in the
distant tubule.
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11. Blood vessels make a clustered network
by which blood is filtered. Inside the
Bowman’s capsule, a tangle of
capillaries called glomerulus press blood
to help plasma to be filtered.
Venules collect filtered plasma and
reabsorbed nutrients into the
bloodstream.
Some arterioles secrete substances from
plasma with wastes and toxic materials
into the distal tubule to be dismissed.
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12. ELIMINATION: All collecting tubes from
the pyramids meet at the renal pelvis where
they transport urine. Then, it goes through
a narrow tube called ureter that goes
downwards to a sac-like structure called
urinary bladder.
Contractions of ring-like muscles called
sphincters force urine out of the body
through a tube called urethra.
Usually an adult eliminates from 1.5 to 2.3 L
of urine every day. At least 500 mL of urine
must be eliminated daily.
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