THE EXCRETORY SYSTEM
AND
HOMEOSTASIS
FUNCTION OF THE EXCRETORY SYSTEM
• The excretory system is made up of organs that perform the function
of excretion, which is the discharge of metabolic wastes produced
by homeostasis.
• Major organs:
1. Kidneys
2. Ureters
3. Urinary bladder
4. Urethra
KIDNEYS
• Kidneys filter the blood to remove wastes and form urine.
• Maintain the homeostasis of several important internal conditions:
I.
Discharge/retain water to affect osmosis in cells
II. Discharge/retain water to affect blood pressure (blood volume)
III. Regulate concentration of ions (E.g. Ca2+, NA+, and Cl–) in blood
IV. Affect blood pH by regulating Hydrogen ions (H+) in blood
URINATION
• Products of cellular metabolism must be removed from the bloodstream.
• Kidneys produce urine by a process of filtration, reabsorption, and
secretion. The kidneys extract the soluble wastes from the bloodstream.
• Urine contains high concentrations of urea and other nitrogenous toxins.
Average urine production in adult humans is
around 1.4L of urine per person per day.
ORGANS OF THE URINARY TRACT
1) URETERS: hollow vessels lined with smooth muscle
that move urine from kidneys to urinary bladder.
2) URINARY BLADDER: Elastic organ that collects
and holds urine. Stretch receptors send impulses
to brain when gets too distended.
3) URETHRA: the tube through which urine passes
from the bladder to the exterior of the body
INVERTEBRATE EXCRETORY SYSTEMS
• Diffusion: metabolic waste secreted by external “skin” cells
• Flame cell: specialized excretory cell in flatworms and roundworms.
• Cells function like a kidney, removing waste materials. Bundles of flame cells = protonephridia.
• Nephridia: specialized excretory organs found in mollusks,
annelids, and some arthropods.
• Ciliated funnel leading into duct system and out of body.
• Similar to the vertebrate kidney (paired)
• Malpighian Tubules: excretory system found in most insects.
• branching tubules extending from alimentary canal;
• absorbs solutes, water, and wastes from the surrounding hemolymph.
• wastes released as solid nitrogenous compounds.
VERTEBRATE EXCRETORY SYSTEMS
• Paired kidneys to filter blood/form soluble waste
• Breakdown of amino acids forms nitrogenous waste
• Released as either ammonia, urea, or uric acid.
• Ammonia is highly toxic; requires energy to convert to urea.
• Urea dissolves easily in water, creating urine (dilute waste).
• Uric acid is mostly solid; it is a way of conserving water.
Freshwater fish- excrete excess water w/ some ammonia.
Saltwater fish- constant risk of dehydration; retain water.
• Use energy (ATP) to pump out excess salt
HOMEOSTASIS
• In humans, homeostasis is
the process that maintains
the stability of the body's
internal environment in
response to changes in
external conditions.
HOMEOSTASIS
Principle Homeostatic Processes in Kingdom Animalia:
• Constant body temperature in warm-blooded (endothermic) animals
• Cell number and cell size in organs
• Sleep timing (day/night cycles)
• Blood pH (about 7.4)
• Blood sugar: concentration of glucose.
• Water, ion, waste levels in blood.
• Concentration of oxygen and carbon dioxide in blood.