URINARY SYSTEM Complete Study Guide_ Guaranteed Success.

- Concept and importance of excretion: All biological processes that occur in the bodies of all living organisms are carried out through chemical reactions that leave some waste products. The living organism must get rid of these waste products as soon as they are formed, otherwise it will cause many problems and infections. - Excretion: the process by which the living organisms get rid of these waste products. Excretion in Animals Excretion refers to the materials that leave the body through the plasma membranes. Note: - The undigested food that goes out of the animal body in the form of feces is not considered as excretion. The Nitrogen in the air which enters the lungs in inspiration and leaves them in expiration is not considered as excretion. The important waste products that are produced and excreted from the animal’s body: 1. CO2 and water: that are produced and excreted from organic molecules degeneration. 2. The nitrogenous waste products (Ammonia, Urea, and Uric acid) that are resulted due to protein degradation. N.B. 1. The organs that carry out excretion in higher animals are the skin, the lungs, the liver, and the kidneys. 2. Organs of excretion also regulate the body contents of minerals. 3. Some of the spices that have volatile content leave the body through the lungs, and the rest is excreted through the kidneys. 4. The poisonous materials are transformed into non-poisonous forms in the body or into non-soluble form by the liver or the kidneys. 2 | P a g e Osmoregulation balances the uptake and loss of water and solutes - Just as thermoregulation depends on balancing heat loss and gain, regulating the chemical composition of body fluids depends on balancing the uptake and loss of water and solutes. This process of osmoregulation is based largely on the controlled movement of solutes between internal fluids and the external environment. Because solute movement results in the movement of water by osmosis, the net effect is to regulate both solutes and water. Osmosis and Osmolarity - All animals—regardless of habitat or type of waste produced— face the same need to balance water uptake and loss. If water uptake is excessive, animal cells swell and burst; if water loss is substantial, they shrivel and die. - Water enters and leaves cells by osmosis. The osmosis, a special case of diffusion, is the movement of water across a selectively permeable membrane. It occurs whenever two solutions separated by the membrane differ in osmotic pressure, or osmolarity (total solute concentration expressed as molarity, that is, moles of solute per liter of solution). - The unit of measurement used for osmolarity is milliOsmoles per liter (mOsm/L). Seawater has an osmolarity of about 1,000 mOsm/L (equivalent to a total solute concentration of 1 M), while the osmolarity of human blood is about 300 mOsm/L. - If two solutions separated by a selectively permeable membrane have the same osmolarity, they are said to be isoosmotic. Water molecules continually cross the membrane, but under these conditions they do so at equal rates in both directions. Thus, there is no net movement of water by osmosis between isoosmotic solutions. - When two solutions differ in osmolarity, the one with the greater concentration of solutes is said to be hyperosmotic, and the more dilute solution is said to be hypoosmotic. Water flows by osmosis from a hypoosmotic solution to a hyperosmotic one. 3 | P a g e Osmotic Challenges - Given the chemical principles that govern osmotic flow, an animal can maintain water balance in two ways. • One is to be an osmoconformer: to be isoosmotic with its surroundings. • The second is to be an osmoregulator: to control internal osmolarity independent of that of its environment. - All osmoconformers are marine animals. Because an osmoconformer’s internal osmolarity is the same as that of its environment, there is no tendency to gain or lose water. - Many osmoconformers live in water that has a stable composition and hence have a constant internal osmolarity. - Osmoregulation enables animals to live in environments that are uninhabitable for osmoconformers, such as freshwater and terrestrial habitats. • To survive in a hypoosmotic environment, an osmoregulator must discharge excess water. • In a hyperosmotic environment, an osmoregulator must instead take in water to offset osmotic loss. - Osmoregulation also allows many marine animals to maintain an internal osmolarity different from that of seawater. An animal’s nitrogenous wastes reflect its phylogeny and habitat - Because most metabolic wastes must be dissolved in water to be excreted from the body, the type and quantity of an animal’s waste products may have a large impact on its water balance. In this regard, some of the most significant waste products are the nitrogenous breakdown products of proteins and nucleic acids. • When proteins and nucleic acids are broken apart for energy or converted to carbohydrates or fats, enzymes remove nitrogen in the form of ammonia (NH3). Ammonia is very toxic, in part because its ion, ammonium (NH4+ ), interferes with oxidative phosphorylation. Although some animals excrete ammonia directly, many species expend energy to convert it to less toxic compounds p