PNB 2250 Lecture Notes - Lecture 8: Circulatory System, Dynamic Structures, Hemolymph
19 Sep 2016
School
Department
Course
Professor
Document Summary
Open circulatory systems: low pressure, fluid (blood or hemolymph) pumped into a container (hemocoel) in which all the organs are suspended. Pump: fluid drained out of hemocoel back to respiratory membrane, cells and tissues in direct contact with blood, disadvantages. Difficult to direct blood to needy tissues: advantages. Closed systems: high pressure, blood contained with pumps or vessels, cells not in direct contact with blood, advantages. High efficiency of diffusion (capillaries: disadvantages. + requires less in terms of control systems. + less able to rapidly change output of system as environmental and internal conditions change. Blood flow returns to pump through a circular pattern. Channels: blood vessels are an example, dynamic structures that change with use. Hagfish: 4 hearts, open and closed blood vessels, 3 hearts circulate blood throughout the body. Heart with 2 chambers in series: cannot generate great deal of pressure. Much energy lost at gills: flow is sluggish but horizontal environment mitigates this somewhat, valves prevent backflow.
