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THE EXCRETORY SYSTEM Excretory System- how animals get rid of the nitrogen-containing waste products of metabolism Nitrogenous Waste: Ammonia -very soluble; can only be tolerated at very low concentrations (highly toxic) -can easily pass through membranes and are readily lost by diffusion to the surround water -most aquatic animals, including most bony fishes Urea -substance produced in the vertebrate liver by a metabolic cycle that combines ammonia with carbon dioxide -low toxicity allows animals to transport and store urea safely at high concentrations -the circulatory system carries urea to the excretory organs, the kidneys -mammals, most amphibians, sharks, some bony fishes, turtles Uric Acid -relatively nontoxic; largely insoluble in water and can be excreted as a semisolid paste with very little water loss -great advantage for animals with little access to water: many reptiles, birds, insects, land snails Other Excretory Systems (Invertebrates): Nepridia- found in earthworms Malpighian- found in anthropods Osmoregulation- the general process by which animals control solute concentrations and balance water gain and loss Osmolarity - Used to measure osmotic pressure in a solution - Expressed as moles of solute per liter of solution Osmoconformers- animals are isoosmotic (the same osmolarity) with their surroundings -because their internal osmolarity is the same as their environment, there is no tendency to gain or lose water -often live in water that has a very stable composition and hence have a very constant internal osmolarity (saltwater fish) Osmoregulators- an animal that must control its internal osmolarity because its body fluids are not isoosmotic with the outside environment -an animal must discharge excess water if it lives in a hypoosmotic environment -an animal must take in water to offset osmotic loss if it inhabits a hyperosmotic environment -enables animals to live in freshwater and terrestrial environment, allows many marine animals to maintain internal osmolarities different from that of seawater Stenohaline- animals that cannot tolerate substantial changes in external osmolarity (goldfish) Euryhaline-animals that can survivelarge fluctuations in external osmolarity (white barnacles, Mozambique tilapia) Fish use their gills in order to perform osmoregulation Saltwater Fish: salt ions are excreted from the gills, lose water through their gills Freshwater Fish: salt is taken in through the gills, gain water through their gills ORGANS The kidney gets rid of nitrogenous wastes and reabsorbs water and salt. The skin gets rid of excess salt. Kidney- the major organ that regulates excretion; each kidney is made up of a million tiny structures called nephrons Hormones of the Kidney: Vasopression (antidiuretic hormone) & Aldosterone Nephrons- functional units of the kidney; consists of a single long tubule and ball of capillaries called the glomerulus Bowman’s Capsule: cup-shaped swelling at blind end of tubule which surrounds the glomerulus Three Regions of Nephron: Proximal Convoluted Tubule Loop of Henle: a hairpin turn with a descending limb and an ascending limb Distal Convolute Tubule Collecting Duct: receives processed filtrate from many nephrons Renal Artery: blood vessel which leads to the kidney and branches into arterioles, then tiny capillaries Glomerulus: ball of capillaries “sits” within Bowman’s Capsule Filtrate: blood is filtered as it passed from glomerulus to bowman’s capsule How Nephrons Work 1. Blood enters the nephron at the Bowman’s capsule. 2. Blood is filtered as it passes from the glomerulus to the Bowman’s capsulefluid now called filtrate 3. Filtrate travels from bowman’s capsule, passes through proximal convoluted tubule, then the loop of henle, distal convoluted tubule, then received by the collecting duct 4. Concentrated urine moves from the kidneys into the ureters, then into the bladder, and finally out through the urethra. How Urine is Made Filtration- blood is filtered as it passed from glomerulus to the bowman’s capsule. Small substances such as ions, water, glucose, and amino acids, easily pass through capillary walls. Large substances, such as proteins and blood cells, cannot pass through. Reabsorption- as the filtrate moves through the proximal convoluted tubule, some materials are reabsorbed. The small solutes, such as water, nutrients, and salts, leave the proximal convoluted tubule and are reabsorbed by a network of capillaries, the peritubular capillaries that surround the tubules. The material remaining in t he tubule is urine. Secretion- as the filtrate moves through the convoluted tubules, some substances, such as H+, potassium, and ammonium ions, are secreted from the surrounding capillaries into the tubule Skin - largest organ in the body; contains 2.5 million sweat glands that secrete water and ions in warm weather - sweat glands maintain an optimal salt balance in the body and maintain the body’s temperature Three Layers: Epidermis- covered by a layer of dead cells called the stratum corneum -stratum corneum form a barrier against invading microorganisms Dermis- sweat glands are found here along with blood vessels, nerves, and sebaceous (oil) glands Subcutaneous tissue- mostly fats Multiple Choice Questions: 1. The urinary system (also known as the excretory system) is the principal system responsible for _______. A. removal of carbon dioxide B. water and electrolyte balance C. excretion of toxic nitrogenous compounds D. both "A" and B" E. both "B" and "C" F. "A", "B", and "C" 2. Each kidney is made up of a milllion tiny structures. They are also the functional units of the kidney. What are these structures called? A. nephridia B. malpighian C. renal artery D. nephron 3. The Excretory System includes a lot of organs. What is the major organ(s)? A. urethra B. kidneys C. skin D. "B" and "C" Free Response Question: 1. How does a nephron work? Describe how blood flows through a nephron. Be sure to include where the blood goes after it leaves the nephron. THE EXCRETORY SYSTEM