BSC2010 BIOLOGICAL SCIENCE 1 FALL 2012 STUDY GUIDE 19 THE CIRCULATORY SYSTEM Introduction Diffusion is rapid only over small distances o Body size and shape keep cells in direct contact with the environment Each cell can exchange materials directly with the surrounding medium o Circulatory system that moves fluid between each cell s immediate surroundings and the tissues where exchange occurs Animals that lack a circulatory system o Central gastrovascular cavity functions borth in digestion and in the distribution of substances throughout the body A single opening maintains the continuity between the fluid inside the cavity and the water outside As a result both sides are bathed by fluid Only cells in the inner layer have direct access to nutrients but since the body wall is two cells thick nutrients diffuse a short distance to reach the cells of the outer layer o A flat body optimizes diffusional exchange by increasing surface area and minimizing diffusion distances Open and Closed Circulatory Systems The circulatory system connects the aqueous environment of the body cells to the organs that exchange gases absorb nutrients and dispose of wastes A circulatory system has three components o A circulatory fluid o A set of interconnecting tubes o A pump heart that uses metabolic energy to elevate the pressure of circulatory fluid Open circulatory system fluid bathes the organs directly o The circulatory is called hemolymph which is also the interstitial fluid Contraction of the heart pumps the fluid through the system of vessels into interconnected sinuses Relaxation draws it back in through pores o The open circulatory system of larger crustaceans includes more extensive system of vessels as well as an accessory pump Closed circulatory system is when the blood is confined to vessels and is distinct o One hear pumps blood into large vessels that branch into smaller ones o Materials are exchanged between the smallest vessels and the fluid bathes Low hyrostatic pressures are associated with open systems and make them costly from the interstitial fluid through the organs the cells than closed systems Closed systems allow for high BP which enable the effective deliver of oxygen and nutrients to the cells of more active animals Circulatory systems A closed system is also called the cardiovascular system Main types of blood vessels o Arteries which carry blood away from the heart Branch into arterioles small vessels that convey blood to the capillaries o Capillaries are vessels with thin walls Network of these vessels are capillary beds Diffusion between the blood and fluid occurs here o Veins carry blood back to the heart Arteries and veins are distinguished by the way they carry blood not by the oxygen content Portal veins carry blood between capillary beds Heart o Chambers that receive blood entering are called the atria o Chambers responsible for pumping blood out are ventricles Single circulation and ventricle o In fishes rays and sharks the heart consists of two champers and atrium Blood passes through the heart in one complete circuit single Blood entering the heart collects in the atrium before the transfer to circulation the ventricle Contraction of ventricle pumps blood to gills Oxygen goes in the blood and CO2 out As blood leaves the gills capillaries converge into a vessel that carries oxygen rich blood to the beds throughout the body Blood then returns to the heart o Blood that leaves the heart passes through two capillary beds before returning to the heart When flowing through the bed BP drops This drop limits the rate of blood flow Double circulation o Two distinct circuits One pump on the right side delivers oxygen poor blood to the capillary beds of gas exchange tissues Oxygen in CO2 out THIS IS THE PULMONARY CIRCUIT It is called pulmocutaneous circuit if it includes the capillaries in both the lungs and skin After the oxygen enriched blood leaves the gas exchange tissues it enters the pump the left side of the heart Contraction propels the blood to capillary beds in organs Systemic circuit is one full round o Double circulation provides flow of blood to brain muscles and other organs because the hear repressurizes the blood destine for these thissues Adaptations o Amphibians Three chambered heart with two atria and one ventricle Ventricle diverts the oxygen poor blood from the right atrium into the pulmonary circuit Three chambered heart with a spetum that separates the ventricle into right and left chambers o Reptiles o Mammals Two atria two ventricles This four chambered heat supports the endothermic way of life Our hearts deliver ten times as much fuel to tissues Circulatory system in mammals 1 Contraction of right ventricle pumps blood 2 Blood goes to pulmonary arteries 3 Bloof flows through capillaries in the left and right lungs which loads oxygen and unloads carbon dioxide 4 Oxygen rich blood returns from the lungs via pulmonary veins to left atrium 5 Oxygen rich blood flows into the left ventricle blood goes to tissues 6 Blood leaves the ventricle via aorta blood goes to arteries 7 Branches of aorta lead to beds in the head and arms 8 Aorta goes to abdomen which supplies blood to a Oxygen poor blood 9 The arteries leading to the organs and legs 10 Oxygen poor blood is channeled to superior vena cava 11 Inferior vena cava drains blood 12 Blood goes to right atrium and the oxygen poor blood flows to right ventricle The Mammalian heart the heart contract Two atria have thin walls and serve as collection chambers for blood returining to Contraction of the atria transfers the remainder before the ventricles begin to The heart contracts and relaxes in a rhythmic cycle o When it contracts it pumps blood systole o When it relaxes the chambers fill with blood diastole This sequence is called a complete cardiac cycle The volume of blood each ventricle pumps per minute is the cardiac output o Determined by heart rate number of beats per min o Stroke volume amount of blood pumped by a ventricle in one contaction Four valves prevent backflow and keep blood moving in the correct direction o Made of flaps of connective tissure the valves open when pushed from one side and clos ewhen pushed from another The AV vale lives between the atrium and ventricle Its pressure generated by the contraction of the ventricles Keeps blood from back flowing Semilunar valves are located at the two exits where the aorta leaves the left ventricle and where the pulmonary artery leaves the right
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