How is bulk transport of extracellular fluid (and interstitial) fluids achieved?Topic 18: INTERNAL CIRCULATION MECHANISMS (CONVECTIVE MOVEMENT OFINTERNAL FLUIDS). (lectures 27-28)OBJECTIVES:1. Be able to differentiate between intracellular, interstitial and extracellularcompartments.2. Know the basic factors that impact blood flow (volume of blood moved per unit time).3. Be able to compare and contrast open vs. closed circulatory systems with respect totheir structures, functional characteristics and in which organisms they are found.4. Be able to describe the evolutionary progression form fish to amphibian tomammalian hearts in terms of structure and functioning.5. Know the overall pathway of blood flow.6. What are the basic events in the cardiac cycle?7. Be able to describe how the rate and force of heart contraction are regulated.8. Understand the functional anatomy of veins.Organisms have three kinds of fluids which can be characterized on the basis of wherethese fluids reside.1. intracellular- fluid found inside of cells; materials here move by passive diffusion2. interstitial – fluid found between cells; materials generally move here by passivediffusion3. extracellular- fluid found is special compartments like tubes (blood and lymphaticvessels; tubes carrying urine; ducts of glands); materials typically move byconvection; that is the bulk movement of fluidHow is bulk transport of extracellular fluid (and interstitial) fluids achieved?Simple organisms- fig. 41.11; Hydra have gastrovascular cavities; bulk movement offluid is by ciliary activity on the epidermal cells.Larger, more complex and active organisms require a specialized circulatory systemconsisting of a pump (usually a heart or heart-like organ) and vessels (or at leastsinuses) through which blood can flow.What are the forces that determine the amount of blood flowing through a tube?Hydrostatic pressure- water is an incompressible substance so that when a force isapplied to it, it does not change in volume but the pressure increases inside; this isknown as hydrostatic pressure. When the fluid is blood we refer to the pressure asblood pressure. Blood pressure is generally expressed in terms of mm Hg.Blood flow (volume of blood transported per unit time) = P/R where1P = the difference in blood pressure between two points; the higher thepressure difference, the greater the blood flowR = resistance to flow; resistance increases as the radius of the vesseldecreases and the length increasesThe heart generates a very high blood pressure by compressing the blood; thisproduces a P which drives the blood forward. Efficient circulatory systems in activeanimals generate very high blood pressures.There are two fundamental types of circulatory systems; fig. 42.2(1) Open – blood is pumped through vessels into large, ill-defined cavities or sinuses; ineffect, the blood is equivalent to the interstitial fluid and is often referred to ashemolymph. Characteristic of all arthropods and most molluscs.(2) Closed- blood is physically contained within specialized vessels and is not in directcontact with the cells. Characteristic of vertebrates, annelids and cephalopdmolluscs (squids, octopus)Functional differences between open vs. closedOPEN CLOSEDBlood volume Large (as much as 50%of the total body volume)Small (8% body volume)Blood pressure Low (1-13 mm Hg) Generally high (50-315mm Hg)Blood flow Sluggish FastWhat this means is that animals cannot be active and achieve large size if they have anopen circulatory system1. vertebrates have closed systems2. squid, the largest and most active of aquatic invertebrates, have a closed systemunlike other molluscs3. insects are an exception; they are small but they achieve the highest activity levels(flight) of any organism yet they have an open system; we’ll see why laterThere is a general correlation between increased activity levels and complexity andperformance of the circulatory (ca. squid vs. clams).Case example- the vertebrate circulatory system.There has been a progressive evolution of the vertebrate circulatory plan toaccommodate and enhance activity levels; fig. 42.3. Basic elements: multi-chamberedheart (atria, ventricles), aorta, arteries, arterioles, capillaries, venules and veins.21. fish- simple circuit in which deoxygenated blood is passed by the branchialcirculation to the gills for oxygenation and returns through the systemic circulationwhere the blood releases oxygen and takes up carbon dioxide. The disadvantage ofthis system is that the capillaries of the gills offer a great deal of resistance to flow.Thus, blood pressure is low after the gills and flow to systemic circulation is sluggish.2. Amphibian- establishment of distinct pulmonary (lung) and systemic circulations;there are two atria and one ventricle so that some oxy- and deoxy blood mix in theventricle which reduces the efficiency of the system.3. Mammals (as well as birds)- four chambered hearts; two separate blood pumps;right side is pulmonary and left side is systemic. No mixing of oxy- and deoxy- blood.Left heart is larger than right heart because it must generate higher pressure to forceblood throughout the body.The functional anatomy of the four chambered heart and circulatory plan.Fig. 42.4- major path of blood flow: right atrium, right ventricle, pulmonary artery, lungs,pulmonary veins, left atrium, left ventricle, aorta, systemic circulation, veins, posteriorand anterior vena cava (REPEAT)Fig. 42.5- valves (AV, semi-lunar) are present which prevent the retrograde (backward)flow of bloodThe cardiac cycle (fig. 42.6)-Diastole- relaxation of a heart chamberSystole- contraction of the walls of the chamber(1) atrial and ventricular diastole- filling of both chambers (AV valve open; semi-lunarvalves closed.(2) atrial systole, ventricular diastole- filling of ventricle (3) atrial diastole, ventricular systole- emptying of the ventricle; semi-lunar valves openand AV valves closeContraction of the ventricle generates a high degree of pressure which ejects the bloodfrom the heart and drives it through the entire circulatory system.Systolic blood pressure- pressure at the peak of ventricular systoleDiastolic blood pressure- pressure during
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