BIOL 118 1st Edition Lecture 25 Outline of Last Lecture I Introduction II Respiratory Circulatory Systems III O2 CO2 Behavior IV Gills V Insect Trachae VI Vertebrate Lungs VII Blood VIII Circulatory Systems Outline of Current Lecture I Introduction II Osmoregulation Excretion III Kidney Current Lecture Introduction Maintaining water balance is a matter of life death maintains homeostasis o Achieves water balance when its intake of water equals its loss of water Water balance is associated with electrolyte o Dissociates into ions when dissolved in water conduct electrical current o Most abundant are sodium chloride potassium calcium Also associated with excretion o Urination helps expel water Osmoregulation Excretion Electrolytes water move by 2 processes occurs along concentration gradient o Diffusion net movement of substances from regions of higher concentration to regions of lower concentration o Osmosis Net movement of water from regions of higher water concentration to regions of lower water concentration across a selectively permeable membrane o Net movement of ions molecules occurs along concentration gradient These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Selective permeability a membrane that some solutes can cross more easily than others Equilibrium is established when solutes are randomly distributed throughout the solutions on both sides of the membrane Osmolarity concentration of dissolved substances in a solution o Water moves from low osmolarity to areas of high osmolarity Osmotic Stress o Osmotic stress concentrations of the dissolved substances in a cell is abnormal Osmoregulation Process by which organisms control the concentration of water electrolytes in their body o Osmoconformers marine invertebrates that do not encounter osmotic stress because the seawater has the same normal electrolyte concentration as the animals Seawater is isomotic to these species solute concentrations are equal inside outside the body o Osmoregulators bony marine fishes actively regulate their osmolarity Keep osmolarity of tissue lower than seawater Seawater is hyperosmotic to these species solution in body contains less solute than the solution outside o What about freshwater fish Freshwater is hyposmotic they contain more solute than the outside solution Gain water via osmosis over gill epithelium Movement of electrolytes water across membranes o Passive transport driven by diffusion along electrochemical gradient Occurs through channels proteins that form a pore that selectively admits ions Carrier proteins transmembrane proteins that bind to a specific ion or molecule transport it across the membrane by undergoing a conformational change Facilitated diffusion when solutes move from an area of high to low concentration via channels o Active transport Occurs when a source of energy powers the movement of solute to establish the electrochemical gradient Sodium potassium pump important pump in animals Primary active transport A source of energy is used to move ions against their gradients Secondary active transport happens when a pump has established an electrochemical gradient o Cotransporter How water is moved o Cells use pumps to move ions in or out o Water has no known mechanism for movement but generally follows the ions via osmosis o Water balance is related to excretion because the removal of waste products urine require that solutes be dissolved in water Common Molecular Mechanism of salt excretion o In many animal epithelial cells that transport Na Cl have the same membrane proteins as found in the shark rectal gland o These species include Marine birds reptiles that drink salt water excrete NaCl via glands in their nostrils Marine fish that excrete salt from their gills Mammals that transport salt in their kidneys Water Electrolyte Balance in Terrestrial Insects o Insects cope with desert environment in two ways Minimizing water loss from body surface Minimize evaporation on their body surface Exoskeleton consists of chitin a tough polysaccharide and layers of protein Chitin protein are collectively known as cuticle Cuticle is covered with a layer of waterproof wax an adaptation that minimizes evaporative water loss also hydrophobic Carefully regulating the amount of water electrolytes they excrete Helps avoid osmotic stress Malpighian tubules an excretory organ hindgut posterior portion of their digestive tract Water Electrolyte balance in terrestrial vertebrates kidne o Must carefully regulate osmolarity of their tissues o To replace water they lose most terrestrial vertebrates drink ingest electrolytes in food o In land dwelling vertebrates osmoregulation primarily occurs through events that take place in the kidney o Kidney is responsible for water electrolyte balance as well as the excretion of nitrogenous wastes Kidney Four major regions of the nephron o Renal corpuscle filters blood forming a pre urine consisting of ions nutrients wastes water o Proximal tubule epithelial cells reabsorb nutrients vitamins valuable ions water o Loop of Henle establishes a strong osmotic gradient in the tissues outside the loop and osmolarity increases as the loop descends o Distal tubule Ions water are reabsorbed Filtration Renal Corpuscle o Urine formation begins in the renal corpuscle which is made up of the glomerulus the Bowman s capsule Glomerulus Cluster of capillaries that bring blood to the nephron from the renal artery Bowman s capsule Region of the nephron that surrounds the glomerulus o Functions as a filtration device Reabsorption Proximal Tubule o Filtrate containing water waste products valuable nutrients leave Bowman s capsule enters convoluted structure called the proximal tubule o Fluid inside tubule contains water urea glucose amino acids vitamin electrolytes small solutes o Some are waste products others are valuable nutrients Osmotic Gradient Loop of Henle o Has 3 distinct regions Descending limb Thin ascending limb Thick ascending limb o Maintains osmotic gradient because water leaves descending limb salt leaves ascending limb Role of Vasa Recta o Water salt that move out of the loop quickly diffuse into vasa recta Associated network of blood vessels found at bottom of the nephron o Water electrolytes are ten returned to the body Collecting Duct leaks urea o Osmotic gradient is established in part by the nephron s final portion the collecting duct o Urea
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