Chap. 44: Controlling the Internal Environment

AP Biology

Mr. Orndorff

March 2004

Homeostasis

• External environment tends to vary or be different from the internal environment of:– a cell (cytoplasm) in aquatic environment

– a multicellular organism in aquatic or terrestrial environment:

• an animal (interstitial fluids)

• a plant (apoplast, vascular spaces, and intercellular spaces)

• Homeostasis is the maintainance of a dynamic but relatively stable internal environment.

Heat exchange between organism and environment (Fig. 44.1)

Endotherm vs.

ectotherm (Fig. 44.2)

Thermoregulation in moths

(Fig. 44.5)

Thermoregulation in large active fishes (Fig. 44.6)

Skinas an organ of

thermoregulation (Fig. 44.7)

Feedback in human thermo-

regulation (Fig. 44.8)

Excretory system functions

• Maintains a balance between gain and loss of water needed to maintain proper volume of body fluids.

• Maintains proper concentration of specific ions and other molecules in body fluids.

• Removes by-products of metabolism so they do not build up to toxic levels.

Key functions of excretory system

(Fig. 44.14)

Intercellular junctions in animals (Fig. 7.30)

Salt-excreting glands in

birds (Fig. 44.9)

Nitrogenous wastes

(Fig. 44.10)

Ammonia as a nitrogenous waste

• Ammonia is very soluble in water and pass easily through membranes.

• Extremely toxic and tolerable only in very dilute solutions.

• Used mainly by aquatic organisms to excrete nitrogenous wastes through gills and body surface.

Urea as a nitrogenous waste

• Formed by combining ammonia with carbon dioxide (requires ATP).

• 100,000 times less toxic than ammonia.

• Reduces water loss in excreting nitrogenous wastes.

• Used mainly by mammals, adult amphibians, many marine fish and turtles.

Uric Acid as a nitrogenous waste

• 1000 times less soluble in water than urea or ammonia

• Precipitates out of solution and excreted in pastelike form.

• Used by snails, insects, birds, and many reptiles which reproduce using shelled eggs.

• Shelled eggs are not permeable to liquids.

Osmoconformers vs osmoregulators

• Isoosmotic with saltwater environment

• No energy required to maintain osmolarity

• Includes most marine invertebrates and hagfish (jawless vertebrates).

• Not isoosmotic with environment.

• Requires energy to maintain osmotic gradient.

• Includes all terrestrial animals, freshwater animals, and many marine animals.

Osmoregulation in marine and freshwater bony fish (Fig. 44.11)

Water balance in two terrestrial mammals (Fig. 44.13)

Water loss in human

60%

36%

4%

UrineEvaporationFeces

Water loss in kangaroo rat

23%

73%

4%

UrineEvaporationFeces

Water gain in kangaroo rat

10%

90%

Ingested in food

Derived frommetabolism

Water gain in humans

60%

30%

10%

Ingested in liquid

Ingested in food

Derived frommetabolism

Protonephridia (Fig. 44.15)

Metanephridia (Fig. 44.16)

Malpighian tubules (Fig. 44.17)

Human excretory system (Fig. 44.18)

Nephron and

collecting duct

(Fig. 44.19)

Two solute model

(Fig. 44.20)

Regulating blood osmolarity (Fig. 44.21a)

Regulating blood volume (Fig. 44.21b)

Regulating blood volume (cont.)

• Atrial natriuretic factor (ANF) = hormone released by heart atria in response to increased blood volume (and blood pressure).

• Effects of ANF:– Inhibits release of renin from JGA– Inhibits NaCl reabsorption by the collecting ducts– Reduces aldosterone release from adrenal glands