Biology Homework Chapter 23: The Circulation System
Textbook assignment: Chapter 23: Circulation, sections 1-6.
- Introduction: Note that the circulatory system carries different chemical objects: immunity agents, hormones, and wastes, as well as nutrients and gases.
- 23.1 Circulatory systems allow blood particles to come in contact with all body cells. Some systems have blood simply washing through the body cells, but most circulatory systems have a muscle or heart of one to four chambers that pumps blood through an open or closed network of tubes. Open systems are low pressure, but closed systems have arteries carrying blood away from the heart connected to capillaries which empty into veins carrying blood back to the heart at high pressure, and these systems can move vast amounts of blood quickly.
- 23.2 The network of blood vessels may take the blood directly past the oxygenation membranes on the way to the body cells (single circulation systems, in fish), or send blood on a separate set of vessels for oxygenation (double circulation systems). The number of heart chambers and types of circuits enable animals to live efficiently in their environments.
- 23.3 The flow of blood through a mammalian cardiovascular system goes from the right atria to the right ventricle, to the lungs, back to the left atria, then to the left ventricle, out the heart through the aorta, to other arteries, to capillaries, back to the heart via veins. Pressure is highest in the aorta and lowest in the vena cava just before the blood reenters the heart. Chambers of the heart have valves to prevent back-flow.
- 23.4 During heart contraction (diastole) blood flows through open valves at low pressure; when the heart contracts (systole), valves close and open to direct the flow of blood through the chambers.
- 23.5 Two sets of nerve tissue in the heart act as local controls to synchronize heart beats. The SA (sinoatrial) node in the right atrium wall sends impulses to the muscle and the the AV (atrioventricular) node between the right atrium and right ventricle. The SA signal causes the upper chambers (atria) to contract and empty into the ventricles. The signal to the AV node is delayed, so that the atrium can empty completely before. The AV then signals the ventricles to contract together. If these signals are mixed up or start fluctuation, the heart is said to fibrillate. An automatic external defibrillator (AED) can be used to shock the heart and cause the SA and AV nodes to reset. Pacemakers may also be embedded directly in the heart when a patient has constant fibrillation issues. The pacemaker monitors heart rate and sends small "reset" shocks as needed.
- 23.6 A heart attack (myocardial infarction) can occur when the arteries that feed the heart muscle cardiac muscles become blocked, causing muscle cells to die. The heart can no longer beating efficiently and the body doesn't get sufficient blood. The victim may have trouble breathing, become disoriented, experience pain in the left side, chest, or left arm (or lower back, in women), feel nauseous, or start sweating. Reduced blood flow to the brain can trigger a second problem: stroke that kills brain cells. Familiarity with heart attack symptoms will help you identify an attack and get help in time. Risk of heart disease can be reduced with proper diet and exercise.
Read the following weblecture before chat: The Heart
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Work through the BioCoach activity Cardiovascular
System I: The Beating Heart. Be sure that you can
- identify the chambers of the heart, and the direction of the flow of blood through them.
- explain the sequence of contractions that moves the blood into the chamber.
- identify the electrical signals from the sinoatrial node the trigger contractions.
- locate the valves which must open and close in sequence to prevent backflow.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Written work for discussion in class: See Moodle Assignments.
Lab Exercise: Circulation in Goldfish
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