Chapter 25 Objectives

1
Chapter 25 Objectives

• Understand homeostasis
• Thermoregulation
• Osmoregulation
• Waste disposal
• Human excretory system
• Liver functions in waste disposal in humans

2
Homeostasis

• Steady-state control mechanisms
• Only allow a narrow range of fluctuations in body
  conditions.
• Temperature thermoregulation
• Water balance osmoregulation
• Nitrogen wastes excretion

3
Thermoregulation

• Heat moves from hot areas to cold areas
• Animals can adjust body temperature
• Involves
• Heat production
• Heat loss
• Heat gain

4
Thermoregulation fig 25.1

• Conduction
• Gain and loss
• Direct from solid surface
• Convection
• Gain and loss
• Direct from liquid or air
• Radiation
• Usually gain
• Not direct
• Evaporation
• Loss only
• Indirect from liquid to gas exchange

5
Specific Examples of Thermoregulation

• Thermogenesis
• Shivering
• Non-shivering
• Sweating
• Insulation
• Fat, fur, or feathers
• Blood flow
• Dilation/Constriction
• Countercurrent heat exchanger

6
Thermoregulation

• Behavior can be used to regulate body temperature
• Relocation
• Migration
• Bathing, wallowing etc.
• Respiration

7
Thermoregulation

• Animals can change their metabolic rates
• Ectotherms can just allow themselves to freeze
• Low energy requirements?basically zero metabolism
• Require glycerol to prevent water crystallization
• Endotherms need to maintain a higher body
  temperature that requires more energy
• Torpor
• Hibernation
• Estivation

8
Osmoregulation

• Metabolism depends on a precise balance of
• Water
• Dissolved ions
• Unequal solute concentrations osmosis or
  diffusion
• Cells cannot survive a net water loss or gain

9
Osmoregulation

• Terrestrial animals are constantly losing water
  through evaporation and excretion
• Aquatic animals are exposed to continuous osmosis
• Osmoconformer vs. osmoregulator
• Salt water vs. fresh

10
Osmoregulation

• Terrestrial animals cannot exchange materials
  directly with the environment
• Gain water by eating and drinking
• Land animals face a risk of dehydration
• Water-proof covering
• Reproductive system
• Excretory system that conserves water

11
Osmoregulation

• Sweating is used for thermoregulation
• Can be a problem for water loss
• Salt loss can also cause problems, but usually
  not
• Drinking water is best when youre sweating

12
Seasonal Dehydration

• Seasonal environments often go from very wet to
  dry
• Some animals can lose large amounts of water and
  go dormant
• Water loss should damage proteins and cell
  membranes
• Use sugars to replace water

13
Waste Disposal fig 25.8

• Metabolism produces toxic by-products
• Nitrogenous wastes
• Excreted wastes variesbetween species
• Amino groups formammonia
• Aquatic animals
• Ammonia excretion
• Diffusion with no energy

14
Waste Disposal fig 25.8

• Terrestrial animals convert ammonia to less toxic
  products
• Can be stored in the body
• Requires energy
• Urea
• Water soluble
• Uric acid
• Crystal
• More energy

15
Waste Disposal

• Kidneys
• 80 km of tubules
• Network of capillaries
• Filters 1100-1200 L per day
• Produce 180 L of filtrate per day
• Water, urea, ions, glucose, amino acids
• Refine the filtrate
• Excrete about 1.5 L of urine

16
Kidneys fig 25.9
17
Kidneys fig 25.9

• Glomerulus
• Blood pressure forces filtrate into glomerulus
• Nephron tubule refines the filtrate
• Proximal tubule
• Loop of Henle
• Distal tubule
• Collecting duct

18
Nephron Function fig 25.10

• Filtration
• Reabsorption
• Secretion
• Excretion

19
Blood Filtration fig 25.11

• Concentration gradient in the medulla
• Active passive transport secretion

20
Nephrons

• Nephrons conserve water
• Also maintain a tight balance of water and
  solutes
• Antidiuretic hormone (ADH)
• Tells nephrons to absorb more water

21
Liver Functions

• Prepares nitrogenous wastes for disposal
• Synthesizes urea from ammonia
• Helps kidney get rid of other toxins
• Hepatic portal system
• Glycogen