Transcript CHAPTER 44
Homeostasis and Excretion (The Kidney) Chapter 44 • Homeostasis - stable internal environment maintained. • Done in three ways. • 1Thermoregulation - maintenance of specific body temperature. • 2Excretion - get rid of wastes. • 3Osmoregulation - maintenance of water and solute balance. http://www.umanitoba.ca/faculties/afs/soil_science/MSSS/links/Images/cartoons/osmoregulation.jpg • Warm-blooded animals (endotherms) – regulators; regulate internal body temperature (mammals). • Conformers - cold-blooded animals (ectotherms); do not have constant internal temperature (lizards) compensate for temperature through behavior (sit in sun if cold). • Temperature of hypothalamus determines body temperature. • Fevers - response to infection alters set-point to higher level than normal to try and slow replication of microorganism that infected individual. Excretion • Cells require water and specific concentrations of salts. • Most organisms have salt concentration equal ocean. • Cells must regulate salt concentration in order for bodies to function. • Cells produce nitrogenous waste must be removed. http://www.theevidence.org.uk/library/science3_3.jpg • Excretory system responsible for balance of water and salt and removal of nitrogenous wastes. • Birds excrete uric acid - semiliquid material. • Vertebrates - different system for excretion. • Primary organ – kidney - forms urine that passes to urinary bladder through ureter. • From bladder, urine passes to exterior of body via urethra. • Kidney filters blood - remove harmful metabolic waste (urea) while retaining cells, proteins, salts, glucose, other essential factors in blood. • Also regulate volume, salt content of extracellular fluids, like blood. http://galileo.phys.virginia.edu/classes/304/kidney.gif • Nitrogen removed from amino acid, released to ammonia - toxic. • Humans - liver converts ammonia to urea - less toxic than ammonia kidneys remove urea from bloodstream. http://www.biologymad.com/Kidneys/liver1.gif The kidney • Basic unit of kidney that performs functions - nephron • Nephron is a small tubelike structure - filters blood, modifies filtrate to produce urine. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Nephron 4 jobs… • 1- Filtration: filter blood • 2- Secretion: secrete material into filtrate • 3- Reabsorption: reabsorb material from filtrate • 4- Excretion: formation of urine http://mcdb.colorado.edu/courses/3280/images/kidney/nephron.gif • Blood filtered enters nephron in ball-shaped cluster of capillaries glomerulus. • The glomerulus is inside a cuplike structure called the Bowman’s Capsule. http://www.biotech.um.edu.mt/home_pages/chris/Renal/Renalhtml/glomerulus.jpg • Pressure of blood in glomerulus squeezes liquid part of blood through filtering structure. • Blood cells - too large to pass through; most proteins retained in blood because of size and charge. • Other smaller molecules (salts, amino acids, glucose, water, urea) pass easily into filtrate. • Filtrate leaves blood, enters structure around glomerulus Bowman’s capsule. • Starting end of nephron. • From Bowman’s capsule filtrate moves down nephron tubule, becoming increasingly modified. http://w3.ouhsc.edu/histology/Glass%20slides/35_08.jpg • Passes through proximal convoluted tubule, loop of Henle, distal tubule, collecting ducts. • Proximal convoluted tubule, active transport pumps glucose, amino acids, sodium, proteins out of filtrate. • Water follows through osmosis, concentrating urine, reducing volume of filtrate. http://library.thinkquest.org/22016/excretion/neph2.gif • Reabsorbed materials reenter blood in capillaries that surround nephron. • Conserves necessary materials that may be wasted in urine • From proximal tubule, filtrate passes to loop of Henle. http://www.ivy-rose.co.uk/Topics/Urinary/Loop_of_Henle_cIvyRose.jpg • Glomerulus and Bowman’s capsule both located in outer region of kidney (cortex), loop of Henle dips into inner kidney region (medulla). • Medulla has high concentration of sodium. (extracellular) http://www.uic.edu/classes/bios/bios100/lecturesf04am/kidney01a.jpg • As filtrate passes down loop of Henle, water drawn out of filtrate due to osmosis, passing from low ion concentration in filtrate to high ion concentration of extracellular fluid in medulla. • When filtrate passes back up loop of Henle, sodium is pumped out into medulla. http://www.ivy-rose.co.uk/Topics/Urinary/Kidney_cIvyRose.jpg • Help further reduce volume of urinary filtrate by drawing water along with sodium; helps to preserve high concentration of sodium in medulla. • After passing through distal tubule, filtrate must pass through collecting duct before passing out to ureter and urinary bladder. http://www.nexavar.com/img/kidney_nephron.gif • Collecting duct passes back down through high ion concentration in medulla. • To make concentrated or dilute urine, vasopressin (antidiuretic hormone or ADH) regulates how permeable walls of collecting duct are. • Determines how much salt actually secreted, how much is retained. • Person needs water - secrete vasopressin, excrete more concentrated urine. • Secreted by posterior pituitary gland when stretch sensors in arteries detect drop in blood pressure. • Vasopressin acts on walls of collecting ducts - make them more permeable to water. • Fluid of medulla very concentrated with ions - water will flow out of collecting ducts if walls of collecting duct are water permeable and allow osmosis. • Saves water, creates concentrated urine. • No vasopressin present - walls of collecting ducts do not permit osmosis, urine will remain dilute. http://www.uic.edu/classes/bios/bios100/lecturesf04am/adh02a.jpg • Regulates urine - aldosterone (steroid) • Secreted in response to low extracellular sodium - distal tubule increases resorption of sodium from urinary filtrate. • Water removed from filtrate by osmosis, reducing urine volume, increasing volume of extracellular fluids - increases blood pressure. http://www.colorado.edu/kines/Class/IPHY3430-200/image/angiotensin.jpg • Secretion of aldosterone helps to conserve water loss.