T RANSPORT AS BY2 W HO N EEDS A T RANSPORT SYSTEM ? Every animal (except those belonging to the phyla Cnidaria (eg jellyfish) and Platyhelminthes (eg flatworms)) possess some form of a specialised internal system for transporting nutrients and respiratory gases** around the body. Cnidaria Platyhelminthes W HO N EEDS A T RANSPORT SYSTEM ? Single-celled organisms, such as bacteria and amoeba ( below ), can obtain nutrients and excrete waste simply by diffusion. nutrients waste products Multi-cellular organisms, such as insects, fish and mammals, require a more specialized transport system. Why is this? S URFACE AREA TO VOLUME RATIO In larger organisms, diffusion of substances would occur far too slowly to enable them to survive. Surface Area to Volume Ratio Single-celled organisms have a very large surface area to volume ratio, because the diffusion path is so short. C OMPONENTS OF CIRCULATORY SYSTEMS Multi-cellular animals overcome the limitations of diffusion by having a specialized circulatory system. This comprises: a heart a medium (blood) in which substances are transported vessels through which the fluid can flow. The two types of circulatory system are open (e.g. molluscs, arthropods) and closed (e.g. vertebrates, a few invertebrates). O PEN CIRCULATORY SYSTEMS An open circulatory system consists of a heart to pump a fluid called haemolymph (blood) short vessels a large cavity called the haemocoel where organs and tissues are bathed by the haemolymph, enabling the diffusion of substances heart haemocoel O PEN S YSTEM IN INSECTS Blood is pumped at low pressure from tube shaped heart running the length of the body. The blood is pumped out of the heart into spaces within the body called haemocoel. The blood bathes the tissue directly. When the heart relaxes, the haemolymph blood flows back to the heart via pores called ostia. Valves help guide this process. C LOSED CIRCULATORY SYSTEMS In a closed circulatory system, blood is fully enclosed within blood vessels at all times. Consists of: A heart (pump) blood (with blood pigments to carry oxygen) ( heamoglobin ) Blood vessels (getting progressively smaller) Capillaries (where diffusion of substances between the blood and tissue cells occurs) Blood returns to the heart via a series of progressively larger vessels. E ARTHWORMS Have a closed circulatory system Blood is under pressure Organs are not in direct contact with the blood Respiratory gases are transported in blood Organs are bathed in tissue fluid O PEN V. C LOSED Video Note: since insects use tracheae to carry oxygen, there is no need for haemoglobin and so the blood is not red. M AMMALS closed, double circulation heart with two atria and two ventricles Blood Blood vessels Heart Respiratory pigments 12 of 33 Boardworks Ltd 2008 Closed circulatory systems 13 of 33 Boardworks Ltd 2008 The mammalian circulatory system 14 of 33 Boardworks Ltd 2008 Circulation: true or false? 15 of 33 Boardworks Ltd 2008 Guide to blood vessels 16 of 33 Boardworks Ltd 2008 Identifying blood vessels VESSELS three main layers in the walls: Outer layer = (tunica adventitia/externa) tough collagen to resist over stretching Middle layer= (tunica media) smooth muscle and elastic fibres to sustain pressure (thicker in arteries) Inner layer = Endothelium (tunica intima) which is one cell thick and smooth to reduce friction A RTERIES V. V EINS Arteries-thick walls to resist pressure Arterioles diameter can be adjusted to change the flow to organs Venules-thin walls, reduced pressure, semi lunar valves Veins-thinner walls, larger lumen C APILLARIES Blood moves slower: the small diameter and friction with the walls to slow blood there are many capillaries in the capillary bed, providing a large total cross-sectional area which further reduces blood flow. Walls one cell thick to exchange materials with the surrounding tissue fluid 20 of 33 Boardworks Ltd 2008 Blood flow in veins semi 21 of 33 Boardworks Ltd 2008 Varicose veins FYI If a vein wall becomes weakened, valves may no longer close properly. This allows backflow of blood, causing the vein to become enlarged and bumpy, and become varicose. This usually happens in superficial veins, near the skin surface in the lower legs, as opposed to deep veins, which lie underneath muscles. Varicose veins can be surgically removed without affecting blood flow, as most blood is returned to the heart by deep veins. 22 of 33 Boardworks Ltd 2008 Draw an artery and vein 23 of 33 Boardworks Ltd 2008 Major Blood Vessels Be sure you can find the following blood vessels: Aorta Vena cava Pulmonary veins Pulmonary arteries Coronary arteries 24 of 33 Boardworks Ltd 2008 Arteries, capillaries and veins 25 of 33 Boardworks Ltd 2008 Blood Pressure and The Heart 26 of 33 Boardworks Ltd 2008 The Heart H EART T HE HEART MAIN FEATURES 4 chambers (separates oxygenated and deoxygenated blood) cardiac muscle- is myogenic (can contract/relax on own) with many mitochondria and myoglobin own blood supply-via coronary arteries variation in thickness of wall- due to pressure valves to prevent backflow of blood Thicker muscle in the ventricular walls given a greater contraction and pressure (left ventrical thicker than right) 29 of 24 Boardworks Ltd 2008 Cardiac muscle The heart mainly consists of cardiac muscle tissue, which like smooth muscle (but not skeletal muscle), contracts involuntarily. Cardiac muscle is made up of cells that are connected by cytoplasmic bridges. This enables electrical impulses to pass through the tissue. It contains large numbers of mitochondria and myoglobin molecules. 30 of 24 Boardworks Ltd 2008 Structure of the heart 31 of 24 Boardworks Ltd 2008 What structure? 32 of 24 Boardworks Ltd 2008 Blood flow through the heart 33 of 24 Boardworks Ltd 2008 35 of 24 Boardworks Ltd 2008 The cardiac cycle CARDIAC CYCLE T HE CARDIAC CYCLE 3 stages: 1. Ventricles relax, atria contract tricuspid and bicuspid valves open and blood flows into the ventricles 2. Atria relax and ventricles contract forcing blood into the aorta and pulmonary artery. Semilunar valves open tricuspid/bicuspid valves close 3. Ventricles relax and pressure in ventricles drops. Blood in the aorta and pulmonary artery is at a higher pressure and causes the semilunar valves to close to prevent the backflow of blood into the ventricles. Blood enters atria from vena cava and pulmonary vein. 39 of 24 Boardworks Ltd 2008 Interactive heart H EART C ONTROL OF HEART Heartbeat initiated within heart (not due to nervous stimulation) 1) SAN = sinoatrial node acts as the pacemaker and starts a wave if electrical stimulation 2) the wave of travels over both atria and causes them to contract together 3) a thin layer of connective tissue between the atria and ventricles prevents the wave from reaching the ventricles 4) The wave reaches the AVN= atrio-ventricular node between the atria 5) the wave is sent down the Budle of His to the apex of the heart 6) the wave travels up the sides of the ventricles along the Purkinje fibres 7) The impulse causes the ventricles to contract from the apex upwards, after the atria have relaxed 43 of 24 Boardworks Ltd 2008 Myogenic stimulation of the heart 44 of 24 Boardworks Ltd 2008 The cardiac cycle 45 of 24 Boardworks Ltd 2008 FYI: Pacemaker cells of the heart The heart can beat without any input from the nervous system as longs as its cells stay alive. This is due to myogenic contraction. Depolarization is initiated in a region of the heart called the sinoatrial node (SAN) also known as the pacemaker which is in the wall of the right atrium. Muscle cells (myocytes) in the heart have a slight electrical charge across their membrane. They are polarized. When the charge is reversed, they are said to be depolarized and this causes them to contract. 46 of 24 Boardworks Ltd 2008 Interactive heart 47 of 24 Boardworks Ltd 2008 FYI: Artificial pacemakers Artificial pacemakers are devices implanted in people whose hearts electrical conduction system is not working properly. Problems include the SAN not firing, and the blockage or disruption of impulses between the SAN and AVN, or in the bundle of His. Pacemakers monitor the hearts electrical activity and stimulate the ventricles or atria to contract when necessary. Impulses are transmitted down electrodes implanted in the muscular walls. 48 of 24 Boardworks Ltd 2008 Cardiac output cardiac output is the amount of blood pumped around the body It depends on two factors: the heart rate the number of times the heart beats per minute. A typical value for an adult at rest is 70 bpm. the stroke volume the volume of blood pumped by the left ventricle in each heart beat. A typical value for an adult at rest is 75 ml. cardiac output = stroke volume heart rate A typical resting cardiac output is 46 litres per minute. This can rise to as much as 40 litres per minute in highly trained endurance athletes. 49 of 24 Boardworks Ltd 2008 Blood Pressure 50 of 33 Boardworks Ltd 2008 Maintaining high blood pressure Blood pressure is the main force that drives blood from the heart around the body. During systole (heart contraction), blood is pumped through the aorta and other arteries at high pressure. The elastic fibres of arteries enable them to expand and allow blood through. During diastole (heart relaxation), the blood pressure in the arteries drops. The elastic recoil of the artery walls help force the blood on. As blood moves through smaller arterioles into capillaries, and then into venules and veins, its velocity and pressure drop continuously. P RESSURE CHANGES arteries show rise and fall of pressure With distance form the heart the pressure falls due to friction with the vessel walls Arterioles have large total surface area and so the pressure drops in each (but they can constrict to increase pressure) Capillaries have low pressure (also large total cross sectional area) Pressure drops more in capillaries as fluid leaks out Veins have low pressure which can be increased as large muscles force blood movement 53 of 33 Boardworks Ltd 2008 BLOOD 55 of 33 Boardworks Ltd 2008 The composition of blood BLOOD 45% cells 55% plasma Cells: Red blood cells/corpuscles (erythrocytes) White blood cells/corpuscles (leucocytes) Platelets (cell fragments) Plasma- mostly water (90%) Contains: dissolved food, waste products hormones plasma proteins vitamins and mineral ions 57 of 33 Boardworks Ltd 2008 Features of erythrocytes What are the specialized features of an erythrocyte? flattened, biconcave disc shape: ensures large surface area to volume ratio for efficient gas exchange diameter (68 m) larger than capillary diameter: slows blood flow to enable diffusion of oxygen no nucleus or organelles: maximises space for haemoglobin, so more oxygen can be transported large amount of haemoglobin: for transporting oxygen F UNCTIONS OF BLOOD Plasma : transport (CO2, digested food, plasma proteins, fibrinogen, antibodies, control pH, heat) Red Blood Cells- transport oxygen- haemoglobin carries oxygen as oxyhaemoglobin. White blood cells fight pathogens/foreign material Phagocytes engulf bacteria (have a lobed nucleus) Lymphocytes- create antibodies H EAMOGLOBIN A RESPIRATORY P IGMENT O XYGEN D ISSOCIATION C URVE (S- SHAPED ) Shows % Hb bound to oxygen (dissociation refers to coming unbound) Normal atmopheric pressure =100 kPa Since O2 is about 21% of air its normal pressure is 21 kPa pO2 is a measure of oxygen conc.) Hb has a high affinity for oxygen when the concentration is high, so it binds the oxygen (i.e at lungs-almost fully saturated) Hb has a low affinity for oxygen where the concentration is low, so it releases the oxygen (i.e. at respiring tissues) S PECIAL ADAPTATIONS The oxygen dissociation curves for llama haemoglobin shows a physiological adaptation for life in oxygen depleted conditions (such as high altitudes) Llama Hb loads oxygen more easily at the lungs when the oxygen conc. (partial pressure) is lower More red blood cells are also produced S PECIAL ADAPTATIONS lugworm haemoglobin also has a high affinity for oxygen at low conc (partial pressure) These worms live in the sand at the seashore and have a low metabolic rate S PECIAL ADAPTATIONS Myoglobin has a dissociation curve far to the left of the normal curve. Found in muscles to take oxygen from blood B OHR E FFECT binding of oxygen is also affected by the amount of CO 2 present lowered pH due to dissolved carbon dioxide reduces the oxygen affinity of haemoglobin (thus releasing it where it is most required) Respiring tissues are high in CO 2, so less oxygen stays bound to Hb CARBON DIOXIDE TRANSPORT Some is transported in red blood cells bound to Hb as carbino-haemoglobin (10%) Some is dissolved in the plasma (5%) most is converted in the red blood cells to bicarbonate (85%) which is then dissolved in the plasma (by enzyme carbonic anhydrase) C HLORIDE SHIFT The chloride shift refers to the influx of chloride ions into the red blood cells to preserve electrical neutrality as the bicarbonate leaves Red blood cell plasma STEPS: C HLORIDE SHIFT CO 2 diffuses into RBC and combines with water to make carbonic acid Carbonic acid dissociates into H + and HCO 3 - (catalyzed by carbonic anhydrase enzyme) HCO 3 - diffuses out into plasma ad binds with Na + (from sodium chloride) H + ions allow oxyhaemoglobin to dissociate in Hb and oxygen H + then binds with Hb to buffer the plasma Oxygen diffuses out of the RBC To balance the negative charge outside (due to HCO 3 - ) Cl - moves into the RBC 68 of 33 Boardworks Ltd 2008 Formation of tissue fluid T ISSUE F LUID Capillary walls are leaky making tissue fluid around the tissue cells (tissue fluid = plasma proteins) M OVEMENT AT TISSUES Water and small solutes pass through the capillary endothelium at the beginning of the capillary beds (due to hydrostatic pressure here (forcing liquid out) being greater than the osmotic pressure (drawing water in) About 99% of the fluid that leaves the blood at the arterial end of the capillary bed returns at the venous end (since pressure is lower in the blood and the blood proteins left behind lower the water potential 71 of 33 Boardworks Ltd 2008 Lymph Not all tissue fluid returns to the capillaries. The excess drains into the lymphatic system, where it forms lymph. Lymph is a colourless/pale yellow fluid similar to tissue fluid but containing more lipids. The lymphatic system drains into the circulatory system near the vena cavae via the thoracic duct. lymphatic capillaries 72 of 33 Boardworks Ltd 2008 FYI: The lymphatic system The lymphatic system is a secondary circulatory system and a major part of the immune system. It consists of: lymphatic capillaries and vein-like lymph vessels, containing valves lymph nodes sac-like organs that trap pathogens and foreign substances, and which contain large numbers of white blood cells lymphatic tissue in the spleen, thymus and tonsils these also contain large amounts of white blood cells and are involved in their development. L YMPHATIC SYSTEM 74 of 33 Boardworks Ltd 2008 Composition of body fluids 75 of 33 Boardworks Ltd 2008 Whats the keyword? 76 of 33 Boardworks Ltd 2008 Multiple-choice quiz