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The Cardiac cycle • Can confidently label internal & external photos of the heart • Can describe the cardiac cycle • Can explain how the heart valves help with the cardiac cycle Bell Task • Label the heart diagram and complete the questions Label the gaps Answer these questions • • • • • • Which side has the thickest muscular wall and why. Where does blood go to from the right side of the heart? Where does blood go to from the left side of the heart? What is the heart made from? What is the function of the valves? What 2 problems would occur with a hole in the wall between the left and right side? Where are the Valves in the heart? • Atrioventricular valves: these valves separate an atrium from a ventricle. • Semilunar valves: found in arteries leaving the heart (pulmonary arteries and aorta). Semilunar Atrioventricular valves • Tricuspid – 3 flaps • Biscuspid – 2 flaps Valves Inside the heart and at the base of the vessels that leave the heart are valves. These valves only open one way, which ensures that there is no backflow of blood. The cardiac cycle • Beats around 70 times a minute. • If you listen to the heart with a stethoscope you hear the sounds often described as “lubb-dupp”. • The cardiac cycle is sequence of events that make up one heart beat. • Continuous Arterial systole • The heart fill up with blood and the muscle in the atrial wall contracts. • Pressure developed is not very big, as muscular atrial walls are only thin. • Forces blood through the atrioventricular valve and into the ventricles. The blood cannot flow back into the vena cava or the pulmonary vein, As these have semilunar valves, to prevent backflow. Instead it is pushed into the ventricles Ventricular systole • About 0.1 second after atrial systole the ventricles contract. • The thick muscular walls of the ventricles squeeze inwards on the blood. • This increases the pressure and pushes it out of the heart As soon as the pressure in the ventricles becomes greater than in the atria. The pressure pushes the atrio-ventricular valves shut, preventing backflow. (‘lubb’) Instead it rushes up into the aorta and the pulmonary artery pushing open the semilunar valves. Ventricular diastole • After about 0.3 seconds, the muscle relaxes and diastole begins. • As pressure drops the semilunar valves snap shut as blood fills their cusps. (‘dubb’) • Whole heart relaxes and blood flows into atria again and the cycle is repeated. The valves are held open or closed by tendons (heart strings), which are attached at the other end to the papillary muscles in the ventricle walls. The valves open to let blood through and then snap shut. This sound of the valves closing is the ‘lub dub’ sound of the heartbeat. • The muscle of the heart is called cardiac muscle and is made of tightly connecting cells. This close contact allows rapid ion transport from cell to cell. This then allows smooth, efficient waves of depolarisation to produce contractions (and repolarisation to bring about relaxation), which pass through the heart. • The tissue is said to be myogenic i.e. it does not need electrical impulses from a nerve to make it contract. If the cardiac muscle is supplied with oxygen and nutrients (a task carried out by the coronary arteries which you can see running over the surface of the heart) it will continue to contract at a steady pace. Nerves supplying the heart, though they are not needed to start the contractions, can bring about an increase or decrease in the rate of contractions when appropriate. Task… • Answer question 5 on page 69 –You will need to draw the graph Heart Action • Can explain how the SAN, AVN & Purkyne tissue coordinate the heart action • Interpret & describe ECG traces in normal & abnormal heart rhythms Task: Describe what is happening at 1,2,3 and 4. Semilunar valve in aorta shuts (aortic valve) 1) Atrio-ventricular valves close because the pressure is higher in the ventricle than in the atria. 2) Semilunar valve in aorta opens due to pressure from the ventricles. 3) Semilunar valves close because the pressure in aorta is higher than in ventricle. (Blood tries to flow back and closes the cups in the valve 4) Atrio-ventricular valves close because the pressure is higher in the atrium than in the left ventricle. The electrical control of the heart • Cardiac muscle is MYOGENIC which means it can contract & relax without receiving signals from nerves • It can control it’s own activity •The heartbeat is initiated in a specialised area of muscle in the right atrium called the sinoatrial node (SAN) or the pacemaker. •The SAN starts the waves of electrical activity, which results in contraction. 1 •There is an area, however, which conducts in the septum, and the waves can pass from here through the ventricles. •This specialised area is called the atrioventricular node (AVN) and will pass on the waves of electrical activity after about 0.1s. 3 •The waves spread out over the 2 atrial walls so that they contract. •There is a band of fibres between the atria and ventricles, which have a high electrical resistance so the waves cannot spread from the atria to the ventricles. 2 The AVN passes the waves on to the Purkinje (also called Purkyne) fibres in the interventricular septum. The excitation is passed to the apex of the heart and then through the ventricle walls. This causes the ventricles to contract from the base upwards ensuring that the blood is forced up and out in the vessels leaving the heart. 4 It would be disastrous if the ventricles contracted at the same time as the atria so that is why there is a short period of delay before the ventricles contract. Task… • With the help of diagrams you must produce a flow chart showing the stages that are involved in the heart beat • Pages 70, 71 & 72 will help you • Use all of the relevant keywords: Myogenic, SAN, AVN, Purkyne tissue… Un-Control of Heart Beat! Put in the correct order SAN contracts and starts off signal Passes to the base of the septum and up through the ventricle wall Wave passes to Purkyne fibres in the septum Fibres between atria and ventricles do not contract Wave spreads to AVN in septum Ventricles contract Atria contract Un-Control of Heart Beat! Put in the correct order SAN contracts and starts off signal Atria contract Fibres between atria and ventricles do not contract Wave passes to Purkyne fibres in the septum Wave spreads to AVN in septum Passes to the base of the septum and up through the ventricle wall Ventricles contract ECG - Electrocardiograph • Doctors can check heart activity by using a machine that records the electrical activity of the heart • The heart depolarises (looses electrical charge) when it contracts • It repolarises (regains charge) when it relaxes • An electrocardiogram allows doctors to assess heart health ECG QRS complex = contraction of ventricles T wave = relaxation (repolarisation) of ventricles P wave = contraction (depolarisation) of atria Time/s 0 0.2 Atrial systole 0.4 Ventricular systole 0.8 Diastole Fibrillation = irregular Tasks • What is fibrillation? • Describe an electrocardiogram showing fibrillation • How do heart monitors save a patient’s life? • What is a defibrillator & when might it be used? • Answer SAQ 6 • Past questions Blood vessels • Can identify veins, arteries & capillaries from diagrams/photos • Can describe how the structure of these vessels relates to their function Which is the ‘normal?’ Regular rhythm of approx 60 bpm Irregular rhythm, heart rate too slow Which is the ‘normal?’ Regular rhythm of approx 60 bpm Irregular rhythm, heart rate too fast Which is the ‘normal?’ Regular rhythm of approx 60 bpm Irregular rhythm, no clear P wave, SA node not initiating beat Which is the ‘normal?’ Regular rhythm of approx 60 bpm Irregular rhythm, Atrial fibrulation, no clear SAN, most of atrium generating own impulses, no clear P wave due to random impulses Which is the ‘normal?’ Regular rhythm of approx 60 bpm AV block, impulse not reacing AVN from SAN, long PR interval Summarising ECG irregularities Irregularity AVN block – problems with the SAN reaching the AVN Fibrillation – irregular heart beat Heart rate too fast or slow How it is shown on ECG Blood vessels Veins Venules Capillary Heart Artery Arteriole Tunica externa Arteries… • Transport blood at high pressure to the tissues • Inner endothelium made of squamous epithelium (smooth cells to reduce friction) • Tunica media containing smooth muscle, collagen & elastic fibres • Tunica externa containing elastic fibres & collagen Externa & collagen & elastic fibres Arterioles… • Smaller branches of the arteries • Walls are similar to arteries but have a greater proportion of smooth muscle • This allows them to contract & narrow the lumen so blood flow can be controlled • For example during exercise they will be dilated to allow maximum blood flow to muscles Capillaries • Smaller branches of the arterioles & will serve every cell in the body • Found in every tissue except the cornea & cartilage • Group together to form capillary beds • The lumen is same size as a RBC to allow efficient diffusion • They are 1 cell thick… made up of endothelial tissue Venules Veins • Capillaries regroup to form venules which them turn into veins • Transports blood back to heart at very low pressure • Contains semi-lunar valves to prevent backflow of blood • The Tunica externa is mostly collagen • The Tunica media is very thin & contains some smooth muscle & elastic fibres • The Tunica intima is the same as the artery with endothelium tissue Questions 1. 2. 3. 4. 5. How do muscles help veins perform their function? Arteries carry oxygenated blood away from the heart, but what is the 1 exception? Why do you think there are no capillaries in the cornea of the eye? What does blood pressure oscillate (go up & down) in the arteries? Why does the blood pressure drop in the arterioles & capillaries? Vein or artery Which one? B A Which one? C Blood plasma, tissue fluid & lymph • Explain the differences between blood, tissue fluid & lymph • Describe how tissue fluid is formed from plasma Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph ! Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph ! Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph ! Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph ! Summarising… Blood/plasma Red blood cells White blood cells Platelets Proteins Water Dissolved solutes Tissue Fluid Lymph ! Blood Lymph 1.List the components that make up the tissue/liquid found in each box 2. Describe what is added or lost on each of the arrows. 3. Include any extra information you think is important. Tissue Fluid Plasma Blood plasma, tissue fluid & lymph • Explain the differences between blood, tissue fluid & lymph • Describe how tissue fluid is formed from plasma The role of haemoglobin • Describe the role of haemoglobin in carrying oxygen & carbon dioxide Oxygen Fact file • Oxygen is transported around the body in combination with haemoglobin (Hb) • Each molecule of haemoglobin can combine with 8 atoms (4 molecules) of oxygen • The resulting compound is named oxyhaemoglobin • Hb will combine with oxygen when concentrations of oxygen are higher • Hb will release it’s oxygen in areas where oxygen is in low concentration How much oxygen can be carried? • Overall each molecule can combine with four oxygen molecules • This means that eight oxygen atoms can be carried by each haemoglobin molecule Hb haemoglobin + 4O2 HbO8 oxyhaemoglobin The binding of oxygen is a reversible reaction. Carbon dioxide fact file • • Carbon dioxide is constantly produced by the respiring tissues & is transported in the blood to the lungs When carbon dioxide diffuses into the plasma 1 of 3 things can happen… 1. Some of it remains as CO2 dissolved in the plasma (about 5%) 2. Some diffuses into the erythrocytes and is converted into Carbonic acid (about 85%) 3. Some combines with the Hb forming carbaminohaemoglobin (about 10%) • When blood reaches the lungs all of these processes are reversed releasing CO2 & leaving the Hb free to go about it’s business! 2. Conversion to carbonic acid 1. 2. 3. plasma Inside the red blood cells are many molecules of an enzyme called carbonic anhydrase *. CO2 It catalyses the reaction between CO2 and H2O. CO2 + carbon dioxide 4. Red cell During respiration, CO2 is produced. This diffuses into the blood plasma and into the red blood cells. H2O water The resulting carbonic acid then dissociates into HCO3- + H+. (Both reactions are reversible). H2O * H2CO3 HCO3- + H+. H2CO3 carbonic acid HCO3- Why is this process important? • The hydrogen ions quickly combine with Hb forming heamoglobinic acid • This makes the Hb release the oxygen it is carrying • The hydrogencarbonate ions diffuse out of the erythrocyte & into the plasma • They remain here in solution • This helps the blood to remain at pH neutral Divide your page in to 4… 1. Hb combining with oxygen 2. CO2 dissolving in plasma 3. CO2 diffusing into erythrocyte & becoming carbonic acid 4. CO2 combining with Hb to become carbaminohaemoglobin Define time 1. Haemoglobin 2. Oxyhaemoglobin 3. Carbonic Anhydrase 4. Haemoglobinic acid 5. Carbaminohaemoglobin CO & O Transport 2 2 • Describe & explain the significance of the haemoglobin dissociation curve • Can use knowledge of Carbon Dioxide transportation to explain the Bohr effect Look at graph 5.26 on page 81… What do you think it shows? Haemoglobin • Oxygen is transported around the body inside red blood cells in combination with the protein haemoglobin • Each haemoglobin is made up of four polypeptides each containing one haem group Haem group What is partial pressure? • The pressure that one component of a mixture of gases would exert if it were alone in a container. • Note: During this topic you will come across the term of partial pressure. Essentially it is a measure of the concentration of oxygen. It is written in shorthand as pO2 and is measured in kilopascals (kPa). How much oxygen can be carried? • Overall each molecule can combine with four oxygen molecules • This means that eight oxygen atoms can be carried by each haemoglobin molecule Hb + haemoglobin 4O2 HbO8 oxyhaemoglobin The binding of oxygen is a reversible reaction. The haemoglobin dissociation curve • The balance can be shown by an oxygen dissociation curve for oxyhaemoglobin. The amount of oxygen held by the haemoglobin, i.e. its saturation level, is normally expressed as a percentage. The haemoglobin dissociation curve At low partial pressures of oxygen, the percentage saturation of haemoglobin is very low, that is the haemoglobin is combined with only a very little oxygen. E.g. In the muscles! At high partial pressures of oxygen, the percentage saturation of haemoglobin is very high. It is combined with large amounts of oxygen. E.g. In the lungs! Answer SAQ 13 on page 81! What determines the loading and unloading of oxygen by haemoglobin? The amount of oxygen that haemoglobin carries is affected by: 1) 2) High pC02 The partial pressure of oxygen and The partial pressure of carbon dioxide The presence of a high partial pressure of carbon dioxide causes haemoglobin to release oxygen. This is called the Bohr effect Haemoglobin releases oxygen The Bohr effect 1. 2. 3. Inside the red blood cells are many molecules of an enzyme called carbonic anhydrase *. It catalyses the reaction between CO2 and H2O. CO2 carbon dioxid e 4. Red cell During respiration, CO2 is produced. This diffuses into the blood plasma and into the red blood cells. + H2O water The resulting carbonic acid then dissociates into HCO3- + H+. (Both reactions are reversible). plasma H2O CO2 * H2CO3 HCO3- + H+. H2CO3 carbonic acid HCO3- The Bohr effect (continued) 5. Haemoglobin very readily combines with hydrogen ions forming haemoglobinic acid. 6. As a consequence haemoglobin releases some of the oxygen it is carrying. 7. By removing hydrogen ions from the solution, haemoglobin helps to maintain the pH of the blood close to neutral. It is acting as a buffer. The Bohr effect Three Oxygen Dissociation curves illustrating the Bohr Effect. Increased carbon dioxide in the blood causes a right-shift in the curves, such that the hemoglobin more easily unloads the oxygen it is carrying. Why is the Bohr effect useful? • High concentrations of carbon dioxide are found in actively respiring tissues, which need oxygen. Due to the Bohr effect, these high carbon dioxide concentrations cause haemoglobin to release its oxygen even more readily than it would do otherwise. How is carbon dioxide transported? • Carbon dioxide is mostly carried as hydrogencarbonate ions in blood plasma, but also in combination with haemoglobin in red blood cells (carbamino-haemoglobin) and dissolved as carbon dioxide molecules in blood plasma. Carbon dioxide transport About 5% of the CO2 produced simply dissolves in the blood plasma. About 85% of the CO2 produced by respiration diffuses into the red blood cells and forms carbonic acid under the control of carbonic anhydrase. The carbonic acid dissociates to produce hydrogencarbonate ions (HCO3-) The HCO3- diffuses out of the red blood cell into the plasma Some CO2 diffuses into the red blood cells but instead of forming carbonic acid, attaches directly onto the haemoglobin molecules to form carbaminohaemoglobin. Since the CO2 doesn’t bind to the haem groups the Haemoglobin is still able to pick up O2. Fetal Haemoglobin • Explain the significance of the different affinities of fetal haemoglobin & adult haemoglobin for oxygen How does a developing fetus obtain it’s oxygen? • A fetus cannot breath therefore is reliant upon it’s mother for a supply of oxygen. • This does happen in the placenta where mother’s & fetus’ blood passes very closely together (without mixing) to allow oxygen to diffuse. Fetal Haemoglobin & partial pressure • Oxygen arrives at the placenta (in mothers blood) combined with Hb in the erythrocytes • The partial pressure of oxygen in the fetal blood is low due to respiration • This causes the mothers Hb to release oxygen which diffuses from her blood into the fetus’ blood Fetal Haemoglobin & partial pressure • The partial pressure of oxygen in the fetus’ blood is only a little lower than that of the mothers blood so oxygen diffusion is slow. However… • The fetal haemoglobin is different from the mothers, it has a greater affinity for oxygen so will bind more readily with available oxygen • The dissociation curve for fetal haemoglobin is to the left of adult haemoglobin. What does this say about the affinity of fetal haemoglobin for oxygen? • Fetal Hb has a higher affinity for O2 than adult Hb at all partial pressures • Why does fetal haemoglobin need a higher affinity than adult? • So when oxygen dissociates from maternal Hb it is picked up by fetal Hb