6.2: The Blood System

State the reason for toughness of artery walls. Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.

Arteries must be able to withstand the pressure of the blood as it moves with each heartbeat. Compared to veins, arteries have a thick, tough tunica media layer containing smooth muscle, elastic fibers and collagen that encircle the vessel.

Explain the effect of epinephrine on heart rate. Understanding: Epinephrine increases the heart rate to prepare for vigorous physical activity.

As a hormone, epinephrine achieves its effects on heart rate by stimulating the adrenergic receptors on the cell membrane of cells throughout the heart tissue. Once stimulated, these receptors activate a second-messenger system that trigger a cascading effect on other substances inside the cell. The overall result of this process is an increase in the heart rate, as well as an increase in the force of each individual heart contraction.

Outline events of ventricular systole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

As the muscles in the ventricle contract (systole), the pressure of the blood within the chamber rises, closing the atrioventricular valves. As ventricular systole continues, the pressure within the ventricle raises to the point that it is greater than the pressures in the pulmonary artery and the aorta. The pressure of the blood pushes open the pulmonary and aortic semilunar valves. Blood is ejected from the heart through the pulmonary artery and the aorta.

Outline events of atrial diastole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). Blood is flowing into the right atrium from the superior and inferior venae cavae. Blood flows into the left atrium from the four pulmonary veins. The left and right atrioventricular valves are both open, so blood flows unimpeded from the atria and into the ventricles. The pulmonary and aortic semilunar valves are closed, preventing backflow of blood into the right and left ventricles from the pulmonary artery on the right and the aorta on the left.

Describe the cause and consequence of atherosclerosis. Application: Causes and consequences of occlusion of the coronary arteries.

Atherosclerosis is the narrowing of arteries due to the buildup of fats, cholesterol and other substances in and on artery walls (plaque). Atherosclerosis begins with damage to the artery endothelial layer (tunica intima) caused by high blood pressure, smoking, or high cholesterol. That damage leads to the formation of plaque on the artery wall. Plaques from atherosclerosis can: - increase blood pressure - block blood flow (causing an aneurysm) - cause the vessel to rupture allowing blood to clot inside the artery (potentially leading to stroke or heart attack).

Explain the pressure changes in the left ventricle during the cardiac cycle. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

Blood flows according to pressure gradients— it moves from regions that are higher in pressure to regions that are lower in pressure. Accordingly, when the heart chambers are relaxed (diastole, A), blood will flow into the atria from the veins and from the atria into the ventricles along the pressure gradient. At the start of ventricular systole (B) , the pressure rises in the ventricle, closing the atrioventricular valves. Pressure continues to increase in the ventricle as it contracts, and eventually the pressure will surpass the pressure in the arteries. The pulmonary and aortic semilunar valves will open and blood will be ejected into the pulmonary artery from the right ventricle and into the aorta from the left ventricle. As the blood leaves the ventricle, the pressure within the ventricle decreases. Once the pressure in the arteries is higher than that in the ventricles, the aortic and pulmonary semilunar valves will close. Although ventricular pressures continues to decrease, volumes do not change because all valves are closed. Once the pressure is again lower in the ventricles than in the atria, the atrioventricular valves will open and blood will again enter the ventricle from the atria. Once the ventricles are completely relaxed, their pressures will slowly rise as they fill with blood from the atria.

Explain the pressure changes in the left atrium during the cardiac cycle. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

Blood flows according to pressure gradients— it moves from regions that are higher in pressure to regions that are lower in pressure. Accordingly, when the heart chambers are relaxed (diastole, A), blood will flow into the atria from the veins and from the atria into the ventricles along the pressure gradient. When the sinoatrial node triggers the muscles in the atria to contract (atrial systole, B), the pressure within the atrial chambers increases, which forces more blood flow across the open atrioventricular valves, leading to a rapid flow of blood into the ventricles. The atria relax and the pressure again decreases (atrial diastole, A).

Outline the roles of gravity and skeletal muscle pressure in maintaining flow of blood through a vein. Understanding: Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.

Blood flows from an area of higher pressure toward an area of lower pressure. If blood is to flow from the veins back into the heart, the pressure in the veins must be greater than the pressure in the atria of the heart. Luckily, the pressure in the atria during diastole is very low. The pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the skeletal muscle pump, helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to the heart. As leg muscles contract, they exert pressure on nearby veins with their numerous one-way valves. This increased pressure causes blood to flow upward, back to the heart against the force of gravity.

Explain how arteries are able to transport the blood under high pressure from the heart to the rest of the body. Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.

Blood leaves the heart through arteries under high pressure as a result of the contraction of the ventricles. The thick muscular walls and narrow lumen of arteries maintains the pressure as the blood moves to the rest of the body. Additionally, the elastic recoil of the arterial walls helps to push blood between contractions of the heart.

Outline the structure and function of a pocket valve. Understanding: Valves in veins and the heart ensure circulation of blood by preventing backflow.

Blood pressure in veins is much lower than that in the arteries. Veins must prevent it from flowing in the wrong direction. Valves in the veins function to keep blood moving in one direction. Theses valves are bicuspid (two) flap like structures made of elastic tissue and are often called "pocket valves" in reference to their shape. As skeletal (especially leg) muscles contract, they exert pressure on nearby veins with their numerous valves. This increased pressure causes blood to flow upward, opening valves superior to the contracting muscles so blood flows through. Simultaneously, valves inferior to the contracting muscles close; thus, blood will not seep backward.

Define "blood pressure." Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Blood pressure is the pressure exerted by blood on the walls of an artery.

Explain the relationship between structure and function of arteries. Skill: Identification of the blood vessels as arteries, capillaries or veins from the structure of their walls.

Blood under the highest pressure (closest to pump from heart) Thickest wall (to withstand high pressure and maintain blood pressure) Three wall layers (tunica intima, media and externa) Smooth endothelium (reduces friction as blood moves through) Smooth muscle (contracts to maintain blood pressure) Elastic fibers (give wall strength and the ability to recoil to propel blood forward) No valves (high pressure maintains blood flow direction) Narrow lumen (maintains high pressure)

Describe the mechanism used to maintain blood flow in arteries between heartbeats. Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Blood will move from areas of higher pressure to areas of lower pressure. During systole, when new blood is entering the arteries, the artery walls stretch to accommodate the increase of pressure of the extra blood. During diastole, the walls return to normal because of their elastic properties. The elastic recoil of the arteries allows the artery to exert an inward force to maintain blood pressure. As the muscles and elastic fibers recoil, they further propel the blood, maintaining blood flow in the arteries between heartbeats.

Describe the structure and function of capillaries. Understanding: 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.

Capillaries are the smallest blood vessels in the body, connecting the arterioles to venules. Capillaries are composed of only two layers of cells; an endothelial layer surrounded by a basement membrane. The capillary lumen is so narrow that red blood cells need to flow through them single file. Capillaries are highly branched to increase the exchange surface area and minimize the diffusion distance. Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). For capillaries to function, their walls must be "leaky", allowing substances to pass through. There are three major types of capillaries, which differ according to their degree of “leakiness:” continuous, fenestrated, and sinusoid capillaries.

Outline events of atrial systole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

Contraction (systole) of the atria is triggered by the firing of the sinoatrial node. As the atrial muscles contract, pressure rises within the atria and blood is pumped into the ventricles through the open atrioventricular valves.

Define diastole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

Diastole is the part of the cardiac cycle during which the the muscle muscle relaxes and allows the chambers to fill with blood There is an atrial diastole and a ventricular diastole.

Define "diastolic blood pressure." Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Diastolic blood pressure measures the amount of pressure that blood exerts on vessels between ventricular contractions, when the heart ventricles are relaxed. Diastolic blood pressure is the second number in a blood pressure reading.

Describe the cause and effect of diffusion of materials into and out of a capillary network. Understanding: 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.

Diffusion is the most widely-used mechanism of transport of materials between the capillary and surrounding tissues. Small molecules diffusion across capillaries such as glucose and oxygen from the blood into the tissues and carbon dioxide from the tissue into the blood. The process depends on the difference of concentration gradients between the blood and the liquid outside the blood vessels, called interstitial fluid. Molecules move from high-concentrated areas to low-concentrated spaces. As a result of this diffusion, the tissue cells are able to receive oxygen and nutrients and remove waste molecules and carbon dioxide.

Outline events of ventricular diastole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

During the early phase of ventricular diastole, as the ventricular muscle relaxes, pressure on the remaining blood within the ventricle begins to fall. The semilunar valves close to prevent backflow into the heart. In late ventricular diastole, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. When this occurs, blood flows from the atria into the ventricles, pushing open the atrioventricular valves. Blood flows from the relaxed atria into the ventricles. Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves are closed.

Explain the pressure changes in the aorta during the cardiac cycle. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

During ventricular systole, pressure increases in the ventricle as it contracts. Eventually the pressure will surpass the pressure in the aorta, causing the aortic semilunar valves to open and blood to be ejected into the aorta from the left ventricle. As the left ventricle ejects blood into the aorta, the aortic pressure increases to a maximum systolic pressure. The greater the force of the ventricular contraction, the greater the change in aortic pressure during ejection. After ventricular contraction, the pressure in the aorta will begin to drop. Once the pressure in the aorta is again higher than that in the ventricle, the aortic semilunar valves will close. Blood will no longer be entering the aorta and its pressure will decrease to a minimum diastolic pressure.

Outline conditions that will lead to epinephrine secretion. Understanding: Epinephrine increases the heart rate to prepare for vigorous physical activity.

Epinephrine (also known as adrenaline) is secreted by the adrenal gland upon activation of sympathetic nerves innervating this tissue. This activation occurs during times of stress (e.g., exercise, heart failure, hemorrhage, emotional stress or excitement, pain). Epinephrine causes an increase in heart rate, muscle strength, blood pressure, and sugar metabolism. This reaction, known as the “Flight or Fight Response” prepares the body for strenuous activity.

Outline Galen’s description of blood flow in the body. Nature of Science: Theories are regarded as uncertain- William Harvey overturned theories developed by the ancient Greek philosophy Galen on movement of blood in the body.

Galen was an ancient Greek whose views on the cardiovascular system were the predominant idea for 15 centuries. Galen claimed that the liver produced blood that was then distributed to the body in a centrifugal manner. Air was absorbed from the lung and carried by vessels to the various tissues of the body. This was an open-ended system in which blood and air simply dissipated at the ends of vessels.

*Describe how Harvey was able to disprove Galen’s theory.* Nature of Science: Theories are regarded as uncertain- William Harvey overturned theories developed by the ancient Greek philosophy Galen on movement of blood in the body.

Harvey (1628) observed the heart in living animals, experimented and used deductive logic to show that arteries and veins are connected in the lung and the peripheral tissues (via capillaries), and that blood circulates with the heart as the pump. Having determined that the quantity of blood issuing from the heart in any given time was too much to be absorbed by the tissues, he was able to show that the valves in the veins permit the blood to flow only in the direction of the heart and to prove that the blood circulated around the body and returned to the heart.

Outline the action of nervous tissue that can regulate heart rate. Understanding: The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

Heart rate is intrinsically determined by the pacemaker activity of the sinoatrial node (SA node) located in the wall of the right atrium. However, the pace of the SA node can be changed by impulses (action potentials) brought to the heart through nerves from the medulla of the brain. Neural input can influence heart rate, cardiac output, and contraction forces of the heart. The vagus nerves (parasympathetic) can reduce the heart rate and the force of contraction of the heart. Cardiac sympathetic nerves (sympathetic) can increase the heart rate and the force of contraction of the heart.

Compare the circulation of blood in fish to that of mammals. Understanding: There is a separate circulation for the lungs.

In fish, there is single pump circulation. The heart only has one atrium and one ventricle. The oxygen-depleted blood that returns from the body enters the atrium, and then the ventricle, and is then pumped out to the gills where the blood is oxygenated, and then it continues through the rest of the body. In mammals there is double pump circulation. The heart has two atria and two ventricles. The right side of the heart receives blood returning back from the body; this “deoxygenated” blood enters the right atrium and then the right ventricle to be pumped to the lungs were the blood will be oxygenated. The oxygenated blood from the lungs enters the left ventricle via the left atrium and is then pumped out into the larger body circulation.

Define "myogenic contraction." Understanding: The heartbeat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.

Myogenic contractions are contractions that are initiated in the heart muscle itself rather than by stimulation from nerve impulses.

Explain the relationship between structure and function of capillaries. Skill: Identification of the blood vessels as arteries, capillaries or veins from the structure of their walls.

One wall layer (tunica intima) Wall has one layer of cells (allowing fast diffusion of substances) Pores and fenestrations (increase permeability for exchange of substances and to allow immune phagocytes to enter tissues) Extensive branching (increases surface area for exchange of materials) Narrowest lumen diameter (allows them to fit between cells and perfuse tissue) Only one red blood cell allowed to pass at a time (for efficient oxygen uptake)

Define systole. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

Systole is the part of the cardiac cycle during which the heart muscle contracts and moves blood out of the chambers. There is an atrial systole and a ventricular systole.

Define "systolic blood pressure." Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Systolic blood pressure measures the amount of pressure that blood exerts on vessels while the heart ventricles are contracting. Systolic blood pressure is the upper number of a blood pressure reading.

Explain the relationship between atrial and ventricular pressure and the opening and closing of the atrioventricular valves. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

The atrioventricular valves are located between the atria and the ventricles of the heart. The atrioventricular valves open and close based on pressure differences between the ventricle and atria. At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). The left and right atrioventricular valves are both open, so blood flows unimpeded from the atria and into the ventricles. As the muscles in the ventricle contract (systole), the pressure of the blood within the ventricle rises above the pressure in the atrium. The greater pressure in the ventricle causes the closing of the the atrioventricular valves and prevents backflow of blood from the ventricle to the atria. When the ventricles relax, the pressure in the ventricle drops lower than the pressure in the atria. The higher pressure of the blood in the atria will cause the opening of the atrioventricular valves, allowing blood to flow from atria into the ventricles.

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

The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. The sinoatrial node (SA node, "pacemaker") starts the sequence by causing the atria to contract. From the SA node, the signal travels to the atrioventricular node (AV node), through the bundle of His, down the bundle branches, and through the Purkinje fibers, causing the ventricles to contract.

Define "cardiac cycle." Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

The cardiac cycle is the action of the heart from the ending of one heartbeat to the beginning of the next. Both the atria and ventricles undergo systole and diastole during one cardiac cycle.

Summarize events of the cardiac cycle. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

The chambers are relaxed (diastole) and both atria collect blood from veins. The sinoatrial node sends impulses initiating contraction of the atria, Blood is pushed into the ventricles by contraction of atria (systole). The atrioventricular valves are open as the atria contract and the semilunar valves are closed so that ventricles fill with blood. When the ventricles contract (systole), the atrioventricular valves close (preventing backflow) and blood is pushed out through the semilunar valves into pulmonary artery and aorta. When the ventricles relax (diastole) the semilunar valves close preventing backflow of blood.

State the function of arteries. Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.

The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Arteries carry blood away from the heart to the capillaries in the tissues of the body.

State the function of veins. Understanding: Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.

The circulatory system is made up of blood vessels that carry blood away from and towards the heart. Veins carry blood towards the heart from the capillaries in the tissues of the body.

Draw a labelled diagram to show the structure of the heart. Skill: 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.

The following structures should be drawn and labeled: Left and right ventricles (drawn below the atria, the left must be thicker walled than right and both must be larger than the atria) Left and right atrium (drawn above the ventricle, both shown with thinner walls than ventricles) Left and right atrioventricular valves (positioned between atria and ventricles) Aortic and pulmonary semilunar valves (shown at the start of the aorta and pulmonary artery, with the cusps facing in the right direction) Aorta (shown connected to the left ventricle) Pulmonary artery (shown connected to the right ventricle) Pulmonary veins (shown connected to the left atrium) Superior and inferior vena cava (shown connected to the right atrium)

Summarize the double pump circulation of the mammalian heart. Understanding: There is a separate circulation for the lungs.

The heart functions as a double pump. Blood moves from the body into the right atrium, and then into the right ventricle where it gets pumped (#1) into the lungs. Blood gets oxygenated in the lungs, moves into the left atrium, and into the left ventricle where it gets pumped (#2) into the body. The double pump allows blood to be pumped at a lower pressure to the lungs (preventing damage of lung tissue) and pumped again at high enough pressure to pump blood to all other body tissues.

Outline the effect of a coronary occlusion on heart function. Application: Causes and consequences of occlusion of the coronary arteries.

The heart muscle requires a constant supply of nutrient and oxygen-rich blood. The coronary arteries provide the heart with this critical blood supply. A coronary occlusion is the partial or complete obstruction of blood flow in a coronary artery. If the heart muscle cells do not receive the blood (nutrients and oxygen) because of the blockage, they can not function properly. This condition may cause a myocardial infarction (heart attack). Within a short time, death of heart muscle cells occurs, causing permanent damage.

Draw a diagram to illustrate the double circulation system in mammals. Understanding: There is a separate circulation for the lungs.

The majority of mammals (including humans) utilize a double circulatory system. It is called a double circulatory system because blood passes through the heart twice per full circuit. The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart. The left pump sends the newly oxygenated blood around the body. By the time this blood returns to the heart, it has returned to a deoxygenated state.

Explain the flow of blood through the pulmonary and systemic circulations. Understanding: There is a separate circulation for the lungs.

The mammalian cardiovascular system has two distinct circulatory paths, pulmonary circulation and systemic circulation. Pulmonary circulation is the movement of blood from the heart to the lungs for oxygenation, then back to the heart again. Systemic circulation is the movement of blood from the heart through the body to provide oxygen and nutrients to the tissues of the body while bringing deoxygenated blood back to the heart.

Label the chambers on a diagram of the mammalian heart. Skill: 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.

The mammalian heart has four chambers: two atria and two ventricles. The right atrium receives oxygen-poor blood from the body via the vena cava and pumps it to the right ventricle. The right ventricle pumps the oxygen-poor blood to the lungs via the pulmonary artery. The left atrium receives oxygen-rich blood from the lungs via the pulmonary veins and pumps it to the left ventricle. The left ventricle pumps the oxygen-rich blood to the body via the aorta.

Explain the relationship between ventricular and arterial pressure and the opening and closing of the semilunar valves. Application: Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

The semilunar valves are located between the ventricles and the arteries leaving the heart. The semilunar valves open and close based on pressure differences between the ventricle and arteries. During ventricular diastole, the semilunar valves are closed to present backflow of blood from the arteries into the ventricles. The pressure is higher in the arteries than the ventricles, which keeps the valves closed. With ventricular systole, the pressure rises in the ventricle and eventually the pressure will surpass the pressure in the arteries. The pulmonary and aortic semilunar valves will open and blood will be ejected into the pulmonary artery from the right ventricle and into the aorta from the left ventricle. As the blood leaves the ventricle, the pressure within the ventricle decreases. Once the pressure in the arteries is higher than that in the ventricles, the aortic and pulmonary semilunar valves will close.

Outline the role of cells in the sinoatrial node. Understanding: The heartbeat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.

The sinoatrial node (SA node) is a group of cells located in the wall of the right atrium of the heart that have the ability to spontaneously and regularly produce an electrical impulse (action potential) that travels through the heart causing it to contract. The SA node is known as the heart's "pacemaker."

State the reason why the sinoatrial node is often called the pacemaker. Understanding: The sinoatrial node acts as a pacemaker.

The sinoatrial node (SA node) is known as the heart's "pacemaker." The main role of a sinoatrial node cell is to initiate action potentials in the cardiac muscle cells at a regular interval, so that the impulse can pass through the heart and cause contraction.

Outline the role of elastic and muscle tissue in arteries. Understanding: Arteries convey blood at high pressure from the ventricles to the tissues of the body.

The tunica media is the middle layer of an artery wall. It is a thick layer containing smooth muscle, elastic fibers and collagen that encircle the vessel. The muscle and elastic fibers assist in maintaining blood pressure between pump cycles. As the blood inside the arteries is being pushed by the heart, the blood pushes against the insides of the artery walls. This pushing is "blood pressure." To cope with this pressure, the muscles and elastin in the artery walls hold them in shape and allow them to to stretch in response to each pulse. This elasticity also helps to maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow.

Given a micrograph, identify a blood vessel as an artery, capillary or vein. Skill: Identification of the blood vessels as arteries, capillaries or veins from the structure of their walls.

The walls of arteries are much thicker than those of veins because of the higher pressure of the blood that flows through them. The artery walls also tend to have a more distinct round shape, held in place by the fibers of the tunica media. Capillaries can be distinguished by the very narrow lumen size (only 1 red blood cell wide).

List factors that will decrease heart rate. Understanding: The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

There are a number of factors that can decrease heart rate, including: Acetylcholine neurotransmitter Decreased thyroid hormones Levels of various ions Decreased body temperature Anticipation of relaxation Reduced oxygen availability in cardiac cells

List factors that will increase heart rate. Understanding: The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

There are a number of factors that can increase heart rate, including: Epinephrine hormone Increased thyroid hormones Levels of various ions Increased body temperature Altitude Exercise Caffeine Nicotine

Explain why the mammalian heart must function as a double pump. Understanding: There is a separate circulation for the lungs.

There must be a double pump in order to create enough pressure to move the blood throughout the entire body. Pressure is needed to move blood through the resistance of a large network of blood vessels like arteries, capillaries, and veins. A single pump (a) would require such a force that the lungs capillaries would be damaged by the high pressure blood moving through or (b) wouldn't supply enough force to move blood through the lung capillaries for oxygenation and then continue on to the tissue capillaries. When the right ventricle contracts (#1), it is able to raises the pressure of the blood to about 25mmHg. After passing through the lungs, the blood pressure is down to about 5mmHg. Then the left ventricle contraction (#2) causes the pressure to rise back up to about 120mmHg. That’s enough pressure to make it through all of the tissue capillaries in the body.

Explain the relationship between structure and function of veins. Skill: Identification of the blood vessels as arteries, capillaries or veins from the structure of their walls.

Three wall layers (tunica intima, media and externa) Thin tunica media with less muscle and elastic fibers (allows skeletal muscles to exert pressure on veins) Widest lumen diameter ( allows great volume of blood to pass while minimizing resistance to blood flow) Valves (prevent backflow of blood)

Describe the structure and function of the three layers of artery wall tissue. Understanding: Arteries have muscle cells and elastic fibres in their walls.

Tunica externa- A tough outer layer of connective tissue the adheres the vessel to the surrounding tissue. Tunica media- A thick layer containing smooth muscle, elastic fibers and collagen that hold arteries in shape and allow them to to stretch in response to each pulse. Tunica intima- A smooth endothelium forming the lining of the artery. Allows blood to flow through the vessel with minimal resistance.

Label the valves on a diagram of the mammalian heart. Skill: 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.

Valves maintain the unidirectional flow of blood through the heart. The atrioventricular (AV) valves are located between the atria and the ventricles of the heart. The right AV valve (tricuspid) is located between the right atrium and the right ventricle. The left AV valve (mitrial) is located between the left atrium and the left ventricle. The semilunar (SL) valves are located between the ventricles and the arteries leaving the heart. The pulmonary SL valve is located between the right ventricle and the pulmonary artery. The aortic SL valve is located between the left ventricle and the aorta.

Outline the cause and effect of vasoconstriction. Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Vasoconstriction is the narrowing of blood vessels resulting from contraction of the muscles in the tunica media layer of the vessel wall. When blood vessels constrict, blood flow to a region is decreased. Vasoconstriction in arteries near the skin surface can occur when the body is exposed to cold. This makes less blood reach the surface, reducing the radiation of heat from the body. Pharmaceutical vasoconstrictors are used in medicine to increase blood pressure.

Outline the cause and effect of vasodilation. Understanding: The muscle and elastic fibres assist in maintaining blood pressure between pump cycles.

Vasodilation is the widening of blood vessels resulting from relaxation of the muscles in the tunica media layer of the vessel wall. When blood vessels dilate, blood flow to a region is increased. Vasodilation in arteries near the skin surface can occur when the body is exposed to heat. This makes more blood reach the surface, increasing the radiation of heat from the body. When exercising, vessels will dilate bringing more oxygen to the metabolically active cells. if there is a localized infection or cut, vessels will dilate, bringing more immune cells and/or clotting factors to to affected tissue. Pharmaceutical vasodilators are used in medicine to decrease blood pressure.

Label the vessels on a diagram of the mammalian heart. Skill: 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.

Veins are vessels that bring blood to the heart. The superior and inferior vena cava bring oxygen-poor blood from the body to the right atrium. The four pulmonary veins bring oxygen-rich blood from the lungs to the left atrium. Arteries are vessels that move blood away from the heart. The pulmonary artery takes oxygen-poor blood from right ventricle to the lungs. The aorta takes oxygen-rich blood from the left ventricle to the rest of the body.

Outline William Harvey’s role in discovery of blood circulation. Application: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump.

William Harvey (1578-1657), observing the heart in living animals, he was able to show that the valves in the veins permit the blood to flow only in the direction of the heart and to prove that the blood circulated around the body and returned to the heart. In his words: "It has been shown by reason and experiment that blood by the beat of the ventricles flows through the lungs and heart and is pumped to the whole body. There it passes through pores in the flesh into the veins through which it returns from the periphery everywhere to the centre, from the smaller veins into the larger ones, finally coming to the vena cava and right atrium. This occurs in such an amount, with such an outflow through the arteries and such a reflux through the veins, that it cannot be supplied by the food consumed. It is also much more than is needed for nutrition. It must therefore be concluded that the blood in the animal body moves around in a circle continuously and that the action or function of the heart is to accomplish this by pumping. This is only reason for the motion and beat of the heart."