1. Chapter 44 ~ Regulating the Internal Environment
• KEY POINT! Homeostasis is the maintenance of a constant internal
environment
I.Regulation of Body Temperature
• A. Thermoregulation-Maintenance of body temperature.
• Ectothermic: body heat obtained from the environment
• Endothermic: high metabolic rate generates high body heat
4 physical processes account for heat gain or loss:
• 1.Conduction~transfer of heat between molecules of body and environment
• 2.Convection~transfer of heat as water/air move across body surface
• 3.Radiation~transfer of heat produced by organisms
• 4.Evaporation~loss of heat from liquid to gas
D.Regulation during environmental extremes
• 1. Torpor~ low activity; decrease in metabolic rate
– a.Hibernation long term or winter torpor (winter cold and food scarcity);
bears, squirrels
– B. Estivation short term or summer torpor (high temperatures and water
scarcity); fish, amphibians, reptiles
• II. Osmoregulation and waste disposal
• A. Osmoregulation is the management of the body’s water content and solute
composition, which is critical to survival and homeostasis.

2. B. Nitrogenous waste management is critical…
• 1.Nitrogenous wastes form from the metabolism of proteins and nucleic acids-very
toxic
– Ammonia: formed and removed by most aquatic animals,fish
– Urea: mammals, most amphibians, sharks, some fish
– Uric acid: allows for little water loss-very concentrated form of liquid
waste found in birds, insects, many reptiles, land snails
• C. Methods of osmoregulation
• 1. Osmoconformer: no active adjustment of internal osmolarity (marine animals);
isoosmotic to environment (same)
• 2. Osmoregulator: adjust internal osmolarity (freshwater, marine, terrestrial)
Freshwater fishes (hyperosmotic)- gains water, loses salt; excretes large amounts
of dilute urine.
3.Water balance is critical on Land
• 1.Dessication is deadly (12% drop for human=death)
• 2.Adaptations to retain water:
– Cuticle, shells, exoskeletons, nocturnal behaviors
III. Excretory Systems
• A.Most excretory systems produce urine in 2 steps:

3. • Filtration (nonselective)
– Reabsorption (secretion of solutes)
• B.The Kidney is our organ of excretion
• 1.Renal artery/vein: kidney • 5.Renal cortex (outer region)
blood flow
• 6.Renal medulla (inner region)
• 2.Ureter: urine excretory duct
• 7.Nephron: functional unit of
• 3.Urinary bladder: urine storage kidney
• 4.Urethra: urine elimination
tube
Nephron Function, I Nephron Function, III
•Proximal tubule: secretion and •Collecting duct: reabsorbs water, salt,
reabsorption some urea
Nephron Function, II
•Loop of Henle: reabsorption of water
and salt
•Distal tubule:secretion and reabsorption
Kidney regulation: hormones
• Antidiuretic hormone (ADH) ~ most important hormone for osmoregulation!)
brings H2O back to body; inhibited by alcohol and coffee