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Unit 2: The continuation of life

Higher Human Biology. Unit 2: The continuation of life. Chapter 20: Transport Mechanisms: The cardiac cycle. Learning Intentions. Success Criteria.

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Unit 2: The continuation of life

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  1. Higher Human Biology Unit 2: The continuation of life Chapter 20: Transport Mechanisms: The cardiac cycle Mrs Smith Ch19 The need for transport

  2. Learning Intentions Success Criteria To understand the anatomy of the heart, to find out how the heartbeat is controlled and to look at differences in blood pressure in the circulatory system. • Describe the cardiac cycle of the heart • Explain the cardiac cycle of the heart in relationship to pressure changes Mrs Smith Ch19 The need for transport

  3. Image source: www.classes.kumc.edu Cardiac Cycle The cardiac cycle is the pattern of contraction and relaxation of the heart during one heartbeat. The average heart rate is 75 beats/min with a cardiac cycle of 0.8 secs. Systole = contraction Diastole = relaxation

  4. Heartbeat animation

  5. The average human heart rate at rest is 75 beats a minute Each heart beat lasts for approximately 0.8 of a second at rest Each heart beat involves a series of Events referred to as THE CARDIAC CYCLE

  6. Heartbeat: Atria & Ventricular diastole Stage 1: A heartbeat begins with the heart muscle relaxed and valves closed. Blood flows into the two atria and both sides fill up with blood. This blood has to be pushed through the valves to get into the ventricles. How does this happen?

  7. Heartbeat: Atrial systole Stage 2: The atria contract and the blood is squeezed which causes the AV valves leading to the ventricles to open. Blood then flows from the atria into the ventricles. What happens to the open valves when the atria are empty?

  8. Heartbeat: Atrial systole Stage 2 (continued): The AV valves between the atria and the ventricles close. This prevents any backflow. What happens next to the blood in the ventricles?

  9. Heartbeat: Ventricular Systole Stage 3: Almost immediately, the ventricles contractand the blood is squeezed again. The pressure of the blood forces open the SL valves leading out of the heart. Blood is pumped out of the heart. What happens to the open valves when the ventricles are empty?

  10. Heartbeat: Ventricular Systole Stage 3 (continued): When the ventricles are empty, the SL valves leading out of the heart close and the heart muscle relaxes. This completes the sequence of contraction and relaxation in one heartbeat. What will happen next?

  11. Stages of a heartbeat Stage 1 (again): The atria fill up with blood as the heartbeat sequence begins again. Why are the walls of the atria thinner than the walls of the ventricles? Why is the wall of the left ventricle thicker than the right ventricle? Try this Scholar Animation Fig.3.9 http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=dfaf24ad-0021-9d39-4277-e967e919c79f

  12. 2. Heart Valves & Sounds

  13. Pressure Changes during The Cardiac Cycle Throughout the cardiac cycle, pressure changes take place in the atria, ventricles and arteries Pressures in the right and left atrium, right and left ventricle, aorta and pulmonary arteries can be recorded and illustrated in graphical form The graph on the next slide shows pressure changes in the left side of the heart and the aorta A similar graph can be drawn for the right side of the heart and the pulmonary arteries Such a graph is similar in shape to that obtained for the left side of the heart but all the pressures readings are of a lower value

  14. Pressure Changes in the Heart

  15. Pressure Changes in the Left Side of the Heart During One Cardiac Cycle aortic pressure left ventricular pressure The pressure changes in the left ventricle, left atrium and aorta can be related to the phases of the cardiac cycle left atrial pressure

  16. Pressure Changes in the Left Side of the Heart A X Z W A Y aortic pressure left ventricular pressure left atrial pressure Period Z to A represents the phase of Passive Filling of the ventricles when the AV valves are open and the semi-lunar valves are closed DUB Period A to W represents the phase of Atrial Systole when the atria contract and the ventricles are filled to full capacity Period W to X represents the first phase of Ventricular Systole when the ventricles contract in an isometric fashion; the greatest rise in ventricular pressure occurs during this phase and the ventricular volume remains constant Period X to Y represents the second phase of Ventricular Systole when ejection of blood takes place and pressure in the aorta rises LUB Period Y to Z represents relaxation of the ventricles (diastole) when the ventricular pressure drops sharply

  17. Heart Murmur Abnormal cardiac blood flow causes abnormal heart sounds known as heart murmurs. This is often caused by faulty valves that fail to open or close fully. This is often an inherited condition but can be caused by illness e.g. rheumatic fever.

  18. Learning Intentions Success Criteria To understand the anatomy of the heart, to find out how the heartbeat is controlled and to look at differences in blood pressure in the circulatory system. Describe the structures involved in the conducting system of the heart Describe the role of the sino-atrio node in the conductivity of the heart State the sequence of electrical conductivity of the heart.

  19. 3. Conducting System of the Heart • The heart is special in that the electrical stimulation necessary for contraction of its muscles originates from within the heart itself • The sequence of events which occurs during each heartbeat is brought about by the activity of the PACEMAKER and the CONDUCTING SYSTEM of the heart Pace maker (Sino-atrial node (SAN))

  20. As well as the Pacemaker the conduction system consists of... • Atrio-ventricular node or AV node • Bundle of conducting fibres, which divides into left & right branches (Bundle of His) • Dense network of Conduction fibres in the ventricle walls (Purkinje fibres) • The above cells are specialised muscle cells which join in a network called the CONDUCTION SYSTEM • http://www.bbc.co.uk/learningzone/clips/the-human-heart/12225.html

  21. The PACEMAKER AKA – Sino-atrial Node (SAN) • The pacemaker is located in the wall of the right atrium. • The pacemaker is specialised tissue which exhibits spontaneous excitation. • This means that it initiates electrical impulses which make the heart contract at a certain rate. • This rate can then be regulated by other factors to suit the bodies requirements. • The pacemaker works automatically and would continue to function in the absence of nerve connections from the rest of the body. http://www.youtube.com/watch?v=te_SY3MeWys&feature=related

  22. Conduction system of the Heart Understanding these DEFINITION will help with the following slides: SYSTOLE; The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries. (the chambers empty). DIASTOLE; The phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood

  23. Conduction of the heart: step by step! 1.The electrical signal originates from the pacemaker (sino-atrial node) this makes heart muscle cells contract at a certain rate. 2. A wave of excitation (from the SA node) spreads across the muscle cells of the two atria making them contract (atrial systole). 3.The impulse is picked up by the atrio-ventricular node (AV node) located near the base of the atria.

  24. Conducting System of the Heart 4. The impulse passes from the AV node to the bundle of His. This bundle of conducting fibres divides into right and left branches which are continuous with the Purkinjie fibres in the ventricular walls. 5. Stimulation of these fibres causes contraction of the two ventricles (Ventricular systole). The contraction of the ventricles spreads upwards from the apex. • The muscle cells contract in unison, and then relax awaiting the next signal.

  25. Summary: Conduction of the heart with an ECG. Such coordination of the heartbeat ensures each type of systole recieves the combined effect of many muscle cells contracting and that the ventricular systole occurs slightly later the atrial systole allowing time for the ventricles to fill completely before they contract.

  26. & AGAIN Conducting System of the Heart: Explained a little differently. AV node SA node in wall of right atrium Bundle of His with left and right bundle branches Another node of specialised tissue known as the AV node is located in the right portion of the septum between the atria and close to the AV valves The origin of the heartbeat is from within a specialised patch of cardiac muscle tissue, located in the wall of the right atrium, and known as the sino-atrial node or SA node The left and right bundle branches divide into smaller branches called Purkinje fibres that spread throughout the ventricular muscle The AV node connects with a bundle of large fibres called the bundle of His, which divides into left and right bundle branches

  27. CON’T: Conducting System of the Heart: Explained a little differently. Fibrous Tissue As the impulses spread across the atria, they stimulate a wave of contraction within the atrial walls and atrial systole is triggered When the SA node emits spontaneous electrical impulses, they spread rapidly across both atria due to the inter-connecting nature of the cardiac muscle cells When the electrical impulses reach the border between the atria and ventricles they are blocked by a band of non- conducting fibrous tissue Impulses are conducted from AV node along the bundle of His AV Node The bundle fibres divide into numerous Purkinje fibres that permeate throughout the ventricular muscles In order to reach the ventricles, electrical impulses must pass through the AV node, which slows down the speed of electrical transmission This delay, called the AV delay, is extremely important as it allows the atria to complete their contraction before the ventricles begin to contract The spread of electrical impulses throughout the ventricles triggers ventricular systole

  28. Electrocardiogram (ECG) The electrical signals of the heart can be detected by electrodes on the skins surface. They are displayed on an oscilloscope screen to produce a pattern called an electrocardiogram (ECG).

  29. The diagram below shows a normal ECG The ECG trace for each heartbeat displays 3 distinct waves: A P wave, a QRS complex and a T wave

  30. R T wave P wave Q S The waves of an ECG • P wave - Electrical impulses spreading across the atria from the SAN; it coincides with atrial contraction or systole. • QRS complex - Wave of excitation passing through ventricles; coincides with ventricular systole. • T wave - Electrical recovery of the ventricles at the end of ventricular systole.

  31. P – R interval T – P interval R T wave P wave Q S ECG waves : The intervals • The P – R interval time between the events of atrial systole and ventricular systole. This period represents the time taken for the impulse to spread from the SA node through the atria, plus the delay in transmission to the AV node, together with the conduction time through the bundle of His and Purkinje fibres. • The T – P interval is the time spent by the heart in diastole before the next atrial systole begins

  32. A

  33. Abnormal ECGs Heart disease and unusual heart rhythms can be detected by ECG patterns. The diagrams below show identifiable patterns for some common heart conditions. Normal ECG http://www.youtube.com/watch?v=x67vRkooZDc&feature=related

  34. Abnormal ECG: Arterial Flutter • In an arterial flutter the contractions occur much too rapidly than normal but do remain coordinated. • The example shown in the diagram shows several P waves for ever QRS complex.

  35. Abnormal ECG: Fibrillation • In a fibrillation, contractions of different groups of muscle cells occurs at different times making it impossible for coordinated pumping of the heart chambers to take place. • Ventricular fibrillation, for example produces an ECG with an irregular pattern. • This condition is lethal if not corrected.

  36. Abnormal ECG: tachycardia. • During ventricular tachycardia, abnormal cells in the ventricle walls act like pacemakers and make these chambers beat rapidly and independently of the atria. • The P (atrial) waves are absent and the wide QRS waves are abnormal.

  37. Pacemakers Abnormal heart rhythms can be controlled by fitting an artificial pacemaker. This stimulator regulates the heart beat by sending out small electrical impulses to the heart making it beat normally.

  38. Task: Torrance-TYK pg152 Qu’s 1&4 Mrs Smith Ch18 Birth & Post-natal development

  39. Essay Questions:SQA 2010 Discuss the conducting system of the heart and how it is controlled. (10) Mrs Smith Ch19 The need for transport

  40. Learning Intentions Success Criteria To understand the anatomy of the heart, to find out how the heartbeat is controlled and to look at differences in blood pressure in the circulatory system. • Describe the changes in blood pressure as blood flows through the circulatory system. • Explain these changes in blood pressure in reference to peripheral resistance. • Explain the role of elastic walls of the main arteries. Mrs Smith Ch19 The need for transport

  41. 4. Blood Pressure Contraction of the ventricles creates pressure which causes the blood to flow. The pressure in the arteries rises and falls as the heart goes through systole & diastole. Ventricular systole = maximum ~120 mm Hg Ventricular diastole = minimum ~80 mm Hg

  42. Blood Pressure Con’t • During ventricular systole (contraction) the pressure of the blood in the aorta rises to a maximum e.g. 120 mmHg • During ventricular diastole (relaxing) it drops to a minimum e.g. 80 mm Hg

  43. Measurement of the blood pressure Try the Scholar Animation 3.4.7 Measuring Blood Pressure http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=06fbef35-8105-5747-fc89-55365ca328af Systolic and diastolic blood pressures are measured using a sphygmomanometer and varies widely from person to person.

  44. The graph below shows arterial blood pressure trace

  45. The graph below shows arterial blood pressure trace

  46. 5. Role of Elastic walls • Large arteries are elastic • They conduct blood from the heart to medium sized arteries • When the heart contracts and ejects blood, the walls stretch to accommodate the surge of blood. • The stretched fibres store some of the energy. • During the diastole phase the arteries recoil, causing the blood to move forward in a continuous flow.

  47. Diagram of the Elastic walls

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