Topic 18 INTERNAL CIRCULATION MECHANISMS CONVECTIVE MOVEMENT OF INTERNAL FLUIDS lectures 27 28 OBJECTIVES 1 Be able to differentiate between intracellular interstitial and extracellular compartments 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 to their structures functional characteristics and in which organisms they are found 4 Be able to describe the evolutionary progression form fish to amphibian to mammalian 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 where these fluids reside 1 intracellular fluid found inside of cells materials here move by passive diffusion 2 interstitial fluid found between cells materials generally move here by passive diffusion 3 extracellular fluid found is special compartments like tubes blood and lymphatic vessels tubes carrying urine ducts of glands materials typically move by convection that is the bulk movement of fluid How is bulk transport of extracellular fluid and interstitial fluids achieved Simple organisms fig 41 11 Hydra have gastrovascular cavities bulk movement of fluid is by ciliary activity on the epidermal cells Larger more complex and active organisms require a specialized circulatory system consisting of a pump usually a heart or heart like organ and vessels or at least sinuses 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 is applied to it it does not change in volume but the pressure increases inside this is known as hydrostatic pressure When the fluid is blood we refer to the pressure as blood pressure Blood pressure is generally expressed in terms of mm Hg Blood flow volume of blood transported per unit time P R where 1 P the difference in blood pressure between two points the higher the pressure difference the greater the blood flow R resistance to flow resistance increases as the radius of the vessel decreases and the length increases The heart generates a very high blood pressure by compressing the blood this produces a P which drives the blood forward Efficient circulatory systems in active animals 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 in effect the blood is equivalent to the interstitial fluid and is often referred to as hemolymph Characteristic of all arthropods and most molluscs 2 Closed blood is physically contained within specialized vessels and is not in direct contact with the cells Characteristic of vertebrates annelids and cephalopd molluscs squids octopus Functional differences between open vs closed Blood volume Blood pressure Blood flow OPEN CLOSED Large as much as 50 Small 8 body volume of the total body volume Low 1 13 mm Hg Generally high 50 315 mm Hg Sluggish Fast What this means is that animals cannot be active and achieve large size if they have an open circulatory system 1 vertebrates have closed systems 2 squid the largest and most active of aquatic invertebrates have a closed system unlike other molluscs 3 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 later There is a general correlation between increased activity levels and complexity and performance of the circulatory ca squid vs clams Case example the vertebrate circulatory system There has been a progressive evolution of the vertebrate circulatory plan to accommodate and enhance activity levels fig 42 3 Basic elements multi chambered heart atria ventricles aorta arteries arterioles capillaries venules and veins 2 1 fish simple circuit in which deoxygenated blood is passed by the branchial circulation to the gills for oxygenation and returns through the systemic circulation where the blood releases oxygen and takes up carbon dioxide The disadvantage of this 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 the ventricle 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 force blood 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 posterior and anterior vena cava REPEAT Fig 42 5 valves AV semi lunar are present which prevent the retrograde backward flow of blood The cardiac cycle fig 42 6 Diastole relaxation of a heart chamber Systole contraction of the walls of the chamber 1 atrial and ventricular diastole filling of both chambers AV valve open semi lunar valves closed 2 atrial systole ventricular diastole filling of ventricle 3 atrial diastole ventricular systole emptying of the ventricle semi lunar valves open and AV valves close Contraction of the ventricle generates a high degree of pressure which ejects the blood from the heart and drives it through the entire circulatory system Systolic blood pressure pressure at the peak of ventricular systole Diastolic blood pressure pressure during ventricular relaxation Fig 42 8 functional anatomy note that veins have unidirectional valves which prevent backflow of blood pressure in veins is quite low Fig 42 14 plasma vs cellular elements red blood cells dominate the cellular elements more when we talk about oxygen transport in blood Control of the heart 3 1 there is an intrinsic automatic rhythm that originates in cells in a pacemaker region known as the sino atrial node SA node 2 this intrinsic rhythm is modified
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