The process by which animals control solute concentrations and balance water gain and loss.

 Osmoconformers-isoosmotic with their environment, most marine invertebrates  Osmoregulators-regulate internal osmolarity by releasing or taking in water, many marine animals, all freshwater animals, terrestrials animals, and humans

 Most metabolic wastes must be excreted from the body.  Nitrogenous wastes come from the breakdown of proteins and nucleic acids.  Excretion – the removal of nitrogenous wastes from the body

1. Ammonia- very water soluble and toxic. Generally only produced in aquatic animals where water loss is NOT a problem. 2. Urea – Produced in the liver of most vertebrates by combining ammonia with carbon dioxide. Requires energy but urea is less toxic. 3. Uric Acid – Requires more energy to produce than urea; it is insoluble in water and can be excreted as a paste or crystals. Produced by birds and reptiles and can be stored in the egg.

 Protonephridia/Flame-bulb system – Flat worms (Platyhelminthes)  Metanephridia – Annelida (Earthworms)  Malpighian tubules – Insects and terrestrial arthropods  Kidneys – Vertebrates  Fish  Amphibians  Reptiles  Birds  Mammals

 Functional similarities of all excretory systems  Filtration of body fluids  modification of that filtrate by: selective secretion of solutes and selective reabsorption of some of those solutes

 Kidney made of nephrons  nephron-single long tubule and associated capillaries  three processes occur: filtration, secretion, and reabsorption

1. This is the pressure-filtering of body fluids, removing water and solutes. Cells, proteins, and large molecules remain in the body fluid. 2. Occurs in the glomerulus of the kidney.

1. Reabsorption – reclaims valuable substances from the filtrate such as glucose, vitamins and hormones. 2. Occurs in the proximal and distal tubules as well as the loop of Henle. Water continues to be reabsorbed. 3. *** The flow of filtrate in the loop of Henle is an example of a countercurrent system.

1. Adds other substances such as toxins and excess ions to the filtrate by active transport. 2. Occurs in the proximal tubule.

1. Occurs when the altered filtrate leaves the body. 2. Carried by the collecting tubules to the ureters, then to the bladder, then out the urethra.