bs148h 16 October 2007Read: Text ch 42 & 44 • circulation• Membrane Transport• Circulatory Systems: • None• Open• Closed single Loop• Closed Double loop• Hearts & Chambers• Shunting & Diving• Capillaries & Control• Blushing!• BreathingEvery living cell is an open system, importing resources Every living cell is an open system, importing resources & exporting wastes across the lipid plasma membrane. & exporting wastes across the lipid plasma membrane. {ch 7}Hydrophobic (nonpolar) molecules, such as lipids, carbon dioxide, and oxygen, can dissolve in the lipid bilayerof the plasma membrane and cross it by diffusion. The {lipid} core impedes the diffusion of ions and polar molecules such as glucose and even water. Channel & Transport proteins built into the membrane play key roles in regulating transport.hydrophyllic channelsfacilitate diffusion:water & simple solutescarrier proteinsselectively admitglucose & big stuffactive ATP enzymespump ionsup gradient:Na+-K+exchangepumpEndo- & exocytosis viamembrane-bound vessicles{recall secretory epithelial cells}Signals (information) fromwater-soluable hormones &neurotransmitters relayed byreceptor proteins {ch 11} Diffusion is inefficient over distances of more than a few milliDiffusion is inefficient over distances of more than a few millimetersmeters;diffusion time is proportional to the square of the distance: if it takes 1 sec for a given quantity of glucose to diffuse 100 μm, it will take 100 seconds for it to diffuse 1 mm and almost 3 hours to diffuse 1 cm. The branching branching gastrogastrovascularvascularcavitiescavities of colentrates & flatworms → body wall only two cells thick; each cell in direct contact w/ medium; ensuring that ... diffusion distances are short & a circulatory system is unnecessarycirculatory system is unnecessary.In larger In larger multicellularmulticellularanimalsanimals, diffusion is inadequate. The circulatory systemcirculatory system solves this problem by bulk transportbulk transportof the aqueous environment surrounding cells {plasma →interstitial fluid}& the surfaces that exchange gases,nutrients & wastes w/ external env. In unicellular unicellular protistsprotists, each cell is in direct contact w/ external environment& diffusiondiffusion to and from the membrane is adequate For animals with many cell layers, gastrovascular cavities are insufficient.Two types of {mesodermal}circulatory systemscirculatory systems have evolved to overcome the limitations of diffusion: openopen & closedclosed circulatory systems. 3 basic components: a fluid (bloodblood), tubes (blood vesselsvessels), a muscular pumppump (heart).In arthropodsarthropods & most mollusksmost mollusks {except active cephalopods},blood bathes organs directly in an openopencirculatory systemcirculatory system. There is no distinction between blood and interstitial fluidThere is no distinction between blood and interstitial fluid, and the body fluid is more correctly termed hemolymphhemolymph. In arthropods, the heart is an elongated dorsal tube;the heart is an elongated dorsal tube;it pumps hemolymph through vessels out into sinuses. Instead of lungs, insects have trachea insects have trachea that take air directly to cells.Earthworms, squids, octopuses, and vertebratesEarthworms, squids, octopuses, and vertebrateshave closedclosedcirculatory systemscirculatory systems: blood is confined to vessels and is distinct from the interstitial fluid. One or more hearts pump blood into large vessels that branch into smaller ones coursing through the organs, where materials are exchanged across capillaries by diffusion between the blood and the interstitial fluid bathing the cells. Note:earthworm earthworm ‘‘lungslungs’’are just skin capillaries are just skin capillaries {‘single loop’}{amphibians & turtles have some gas exchange through skin}The ‘heart’ of simple chordatessimple chordates like lanceletsis little more than a muscular tubea muscular tubein the main ventral arterythat contracts in peristaltic waves.The closed circulatory system in fishes is a single circuit.The closed circulatory system in fishes is a single circuit.The evolution of gills in fish resulted in blood passing through two capillary beds during each circuit{like hepatic (liver) circulation in mammals}w/ a big drop in pressure across each capillary bed; systemic circulation is quite slow, constraining the delivery of oxygen to body tissues, and hence the maximum aerobic metabolic rate of fishes.A fish heartfish heart is basically just a tube w/ 4 chambers the Sinus Sinus VenosusVenosus & AtriumAtrium collect venus bloodthe VentricleVentricle & ConusConusArteriosusArteriosus pump itin a peristaltic wave to capillary beds in the exchange surfaces.{the SV & CA are ~ muscular vessels (as is ‘heart)}The Sinus Venosus {SV} serves as ‘pacemakerpacemaker’ of perstaltic waves;in mammals homolog is sinoatrial (SA) node CASVThe evolution of lungs in amphibiansamphibians{lost in thin ‘lungless’ salamanders}is associated with two separate circuits:the pulmocutaneouspulmocutaneouscircuitcircuit to the lungs & skin the systemic circuitsystemic circuit to the other tissues {double loop w/ single capillary bed per loop}The pulmonory and systemic blood is mixed in the singlesingleVentricleVentricleMost of the oxygen-rich blood from the left atrium is diverted into the systemic circulation by ridges in the ventricle. Plethodontid(lungless) salamanderAmphibians have a threethree--chambered heart:chambered heart:the Right AtriumRight Atrium (& sinus venosus) collect O2depleted systemic bloodthe Left AtriumLeft Atrium collects O2rich pulmonary blood.Turtles, snakes & lizardsTurtles, snakes & lizardsalso have double circulationalso have double circulationwith pulmonary (lung) and systemic circuits, but one ventricle w/ some mixing.Ridges (septa) & valves allow shunting of bloodfrom one circuit to the other:right aorta captures blood from right pulmonary artery.{note: this shunting from pulmonary to systemichappens in fetuses of placental mammals, but isn’t supposed to happen in adults – later}Evolution: WarmEvolution: Warm--hearted crocs.hearted crocs. AP Summers 2005 Nature 434,833-834Birds and mammals have independently evolved a fourBirds and mammals have independently evolved a four--chambered heartchambered heartThe division of blood flow also allows the pressure to vary betwThe division of blood flow also allows the pressure to