Which of these animals correctly describe how its nitrogenous waste is related to its phylogeny and habitat? 1. Because I live in water, I excrete urea, a water soluble nitrogenous waste. 2. I need to stay light on my feet for speed, so I excrete a solid nitrogenous waste. 4. My ancestors and I lay shelled eggs, so our embryos are protected from harmful ammonia by converting it to an insoluble precipitate. 3. Living on land, I need to conserve as much water as possible, so I excrete a solid nitrogenous waste.

Regulating the Internal Environment

Learning Objectives: (2/25/09) 1.Discuss the challenges of excretion and osmoregulation for marine, freshwater and terrestrial organisms 2.Compare and contrast the variety of excretory systems in invertebrates 3.Explain the correlation between type of nitrogenous waste product with animal habitat and/or reproductive strategy 4.Describe examples of the relationship between structure and function in excretory systems (esp. the 4 key functions) 5.Discuss the intrinsic and extrinsic regulation of kidney function in water balance 6.Discuss the roles of the hypothalamus in vertebrate water budgets

Most animal cells cannot survive a net gain or loss of water Tardigrades are generally less than ½ mm. They have five body segments, four pairs of legs, and each leg ends in a set of claws. Tardigrades have a ventral nervous system with a brain and eyespots. They have well developed excretory, muscular, digestive, and reproductive systems. A characteristic of the phylum is the lack of both the circulatory and respiratory systems. They breathe through their cuticle and have a hemocoel for circulation. For more info. visit

Osmoregulation in Terrestrial Animals 1.Protective outer layers 2.Drinking fluids and eating moist foods 3.Behavioral adaptations 4.Adaptations to use metabolic water 5.Excretory adaptations Fluid in which body compartment is being regulated? Describe how water may be gained and lost by animals.

The challenge of living in water for osmoregulators Water is the physiological solvent, but how is this volume regulated in most animals, no matter what their environment? Which animals tend to be osmoconformers, and where do they live? p. 936

Is this a countercurrent mechanism? Is NaCl excretion by active or passive transport? Do marine animals have other mechanisms of osmoregulation? p. 939

Nitrogenous waste is related to reproductive strategy and habitat See p. 943 Which of these animal groups excrete nitrogen wastes dissolved in a watery solvent? Explain why.

Key Functions in Animal Excretory Systems 1.Filtration 2.Reabsorption 3.Secretion 4.Excretion Where does each process happen? What is the net direction of movement for each material? Is the movement of material by active or passive transport? Intravenous Pyelogram (IVP)

Protonephridia in Platyhelminthes Identify the fluid that is filtered at the flame bulb. What is the force that drives the production of fluid in the flame bulb system? Is the filtrate modified in the tubule? Explain. What other organ may function in excretion in these animals? How do these animals regain lost fluid?

Metanephridia in Annelids Describe any advances over the protonephridial system. In which direction(s) are materials moving between the blood and the filtrate? …by what mechanisms? How is this system similar to the mammalian nephron in structure and function? Explain.

Malpighian tubules in Arthropods The organs of excretion in arthropods function in both tubular secretion and tubular reabsorption. Where do these processes take place? How is this different than the same processes in the mammalian kidney? Contrast the function of the insect posterior alimentary canal with that of mammals. p. 944

Mammalian Kidney What is the rate- limiting step in urine formation? Which renal mechanisms involve active transport? Why does glucose sometimes appear in the urine of diabetics? See p. 946

Juxtamedullary Nephron Function What materials are initially filtered into the tubule? How would a short loop of Henle affect the ability of an animal to concentrate urine (i.e. conserve water)? Name an alternative water conservation adapatation. What is the target tissue for the hormone ADH (a.k.a. Vasopressin)? See p. 949 PassiveActive

Extrinsic Regulation of the Kidney ADH is also known as Vasopressin. What is the primary target tissue for this hormone? Name the other action of this hormone, and describe how it contributes to homeostasis. Describe the communication between the hypothalamus and the posterior pituitary. Why are aquaporins necessary? See p. 953

Renin-Angiotensin-Aldosterone System Where is the “receptor” in this homeostatic mechanism? Where is the “effector”? Is this intrinsic or extrinsic regulation? What kind of molecule is renin? (hormone, neurotransmitter, enzyme, etc.) How does Aldosterone increase sodium reabsorption at the kidneys?