BIOL 118 1st Edition Lecture 25 Outline of Last Lecture I. IntroductionII. Respiratory & Circulatory SystemsIII. O2 & CO2 BehaviorIV. GillsV. Insect TrachaeVI. Vertebrate LungsVII. Blood VIII. Circulatory SystemsOutline of Current Lecture I. IntroductionII. Osmoregulation & ExcretionIII. KidneyCurrent LectureIntroduction- Maintaining water balance is a matter of life & death- maintains homeostasiso Achieves water balance when its intake of water equals its loss of water - Water balance is associated with electrolyteo Dissociates into ions when dissolved in water & conduct electrical current o Most abundant are sodium chloride, potassium, & calcium - Also associated with excretiono 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 concentrationo Osmosis: Net movement of water from regions of higher water concentration to regions of lower water concentration, across a selectively permeable membraneo Net movement of ions & molecules occurs along concentration gradientThese 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 solutiono Water moves from low osmolarity to areas of high osmolarity- Osmotic Stresso 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 bodyo 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 bodyo 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 outsideo 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 membraneso 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 channelso 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 gradiento Cotransporter- How water is movedo Cells use pumps to move ions in or outo Water has no known mechanism for movement, but generally follows the ions via osmosiso 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 excretiono In many animal epithelial cells that transport Na & Cl have the same membrane proteins as found in the shark rectal glando 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 Insectso 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- kidneo Must carefully regulate osmolarity of their tissues o To replace water they lose, most terrestrial vertebrates drink & ingest electrolytes in foodo In land-dwelling vertebrates, osmoregulation primarily occurs through events that take place in the kidneyo Kidney is responsible for water & electrolyte balance as well as the excretion of nitrogenous wastesKidney- Four major regions of the nephrono Renal corpuscle: filters blood, forming a “pre-urine” consisting of ions, nutrients, wastes & watero Proximal tubule: epithelial cells reabsorb nutrients, vitamins, valuable ions & watero Loop of Henle: establishes a strong osmotic gradient in the tissues outside the loop, and osmolarity increases as the loop descendso Distal tubule: Ions & water are reabsorbed- Filtration: Renal Corpuscleo 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 glomeruluso Functions as a filtration device- Reabsorption: Proximal Tubuleo Filtrate containing water, waste products & valuable nutrients leave Bowman’s capsule & enters convoluted structure called the proximal tubuleo 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 Henleo Has 3 distinct regions: Descending limb Thin ascending limb Thick ascending limbo Maintains osmotic gradient because water leaves descending limb & salt leaves ascending limb- Role of Vasa Rectao Water & salt that move out of the loop quickly diffuse into vasa recta Associated network of blood vessels found
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