Topic 6.2:  The Blood System

Essential Idea:  The blood system continuously transports substances to cells and simultaneously collects waste products.

At SHS, Topic 6.2 is taught in the following class unit(s):

• The Heart (unit 44)
• The Circulatory System (unit 45)

​Statements & Objectives:

6.2.U1  Arteries convey blood at high pressure from the ventricles to the tissues of the body.

• State the function of arteries.
• Outline the role of elastic and muscle tissue in arteries.
• State the reason for toughness of artery walls.

6.2.U2  Arteries have muscle cells and elastic fibres in their walls.

• Describe the structure and function of the three layers of artery wall tissue.

6.2.U3  The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

• Describe the mechanism used to maintain blood flow in arteries between heartbeats.
• Define systolic and diastolic blood pressure.
• Define vasoconstriction and vasodilation.

6.2.U4  Blood flows through tissues in capillaries with permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillary.

• Describe the structure and function of capillaries.
• Describe the cause and effect of diffusion of blood plasma into and out of a capillary network.

6.2.U5  Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.

• State the function of veins.
• Outline the roles of gravity and skeletal muscle pressure in maintaining flow of blood through a vein.

6.2.U6  Valves in veins and the heart ensure circulation of blood by preventing backflow.

• Outline the structure and function of a pocket valve.

6.2.U7  There is a separate circulation for the lungs.

• Draw a diagram to illustrate the double circulation system in mammals.
• Compare the circulation of blood in fish to that of mammals.
• Explain the flow of blood through the pulmonary and systemic circulations.
• Explain why the mammalian heart must function as a double pump.

6.2.U8  The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.

• Define myogenic contraction.
• Outline the role of cells in the sinoatrial node.

6.2.U9  The sinoatrial node acts as a pacemaker.

• State the reason why the sinoatrial node is often called the pacemaker.

6.2.U10  The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles.

• Describe the propagation of the electrical signal from the sinoatrial node through the atria and ventricles.

6.2.U11  The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

• Outline the structures and functions of nervous tissue that can regulate heart rate.
• Describe factors that will increase heart rate.
• Describe factors that will decrease heart rate.

6.2.U12  Epinephrine increases the heart rate to prepare for vigorous physical activity.

• Outline conditions that will lead to epinephrine secretion.
• Explain the effect of epinephrine on heart rate.

6.2.A1  William Harvey’s discovery of the circulation of the blood with the heart acting as the pump.

• Outline William Harvey’s role in discovery of blood circulation.

6.2.A2  Causes and consequences of occlusion of the coronary arteries.

• Describe the cause and consequence of atherosclerosis.
• Outline the effect of a coronary occlusion on heart function.

6.2.A3  Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

• Explain the pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.
• Explain the relationship between atrial and ventricular pressure and the opening and closing of heart valves.
• Explain the atrial, ventricular and arterial pressure changes as illustrated on a graph of pressure changes during the cardiac cycle.
• Identify the time of opening and closing of heart valves on a graph o f pressure changes during the cardiac cycle.

6.2.S1  Identification of the blood vessels as arteries, capillaries or veins from the structure of their walls.

• Compare the diameter, relative wall thickness, lumen diameter, number of wall layers, abundance of muscle and elastic fibres and presence of valves in arteries, capillaries and veins.
• Given a micrograph, identify a blood vessel as an artery, capillary or vein.

6.2.S2  Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure.

• Label a diagram of the heart with the following structure names:  superior vena cava, inferior vena cava, pulmonary semilunar valve, aorta, pulmonary artery, pulmonary veins, aortic semilunar valve, left atrioventricular valve, left ventricle, septum, right ventricle, left atrium, right atrium and right atrioventricular valve.

6.2.NOS  Theories are regarded as uncertain- William Harvey overturned theories developed by the ancient Greek philosophy Galen on movement of blood in the body.

• Outline Galen’s description of blood flow in the body.
• Describe how Harvey was able to disprove Galen’s theory.

In the News:

• Computer-designed customized regenerative heart valves (2018-05-09)
• Uncovering secrets of elastin's flexibility during assembly (2016-02-05)
• Building a better valve (2015-06-20)
• Meet the only animal known to pump blood with its guts (2017-07-10)