6 2 THE BLOOD SYSTEM UNDERSTANDINGS Arteries convey

6. 2 THE BLOOD SYSTEM

UNDERSTANDINGS • Arteries convey blood at high pressure from the ventricles to the tissues of the body. • Arteries have muscle and elastic fibers in their walls. • The muscle and elastic fibers assist in maintaining blood pressure between pump cycles. • Blood flows through tissues in capillaries with permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillaries. • Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.

UNDERSTANDINGS CONT. • Valves in veins and the heart ensure circulation of blood by preventing backflow. • There is a separate circulation for the lungs. • The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node. • The sinoatrial node acts as a pacemaker. • The sinoatrial node sends an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles. • The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain. • Epinephrine increases the heart rate to prepare for vigorous physical activity.

APPLICATIONS • William Harvey’s discovery of the circulation of the blood with the heart acting as the pump. NATURE OF SCIENCE: Theories are regarded as uncertain- William Harvey overturned theories developed by the ancient Greek philosopher Galen on movement of blood in the body. • Causes and consequences of occlusions of the coronary arteries. • Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle.

SKILLS • Identification of blood vessels as arteries, capillaries or veins from the structure of their walls. • Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of the heart structure.

ARTERIES CONVEY BLOOD AT HIGH PRESSURE FROM THE VENTRICLES TO THE TISSUES OF THE BODY. • Arteries are blood vessels that take blood Away from the heart and takes it to the other tissues of the body under high pressure from the pumping of the heart. • The arteries work with the thick strong muscles of the heart to facilitate and control blood flow. • The artery walls are thick with elastic and muscle tissue. • Elastic tissue: • Contains elastin fibers that store energy and stretch at the peak of each pumping cycle. • The tissue recoils and help to propel the blood down the artery. • Muscle tissue: • Contraction of smooth muscle determines the diameter of the lumen helping to control the flow. • Both the elastic tissue and smooth muscle make the walls strong to withstand the constantly changing and intermittently high pressure in the artery without bulging or bursting.

ARTERIES HAVE MUSCLE AND ELASTIC FIBERS IN THEIR WALLS. • Tunica externa- tough outer layer of connective tissue • Tunica media- a thick layer containing smooth muscle and elastic fibers made of the protein elastin • Tunica intima- a smooth endothelium forming the lining of the artery.

THE MUSCLE AND ELASTIC FIBERS ASSIST IN MAINTAINING BLOOD PRESSURE BETWEEN PUMP CYCLES. • Arterial Blood Pressure • Blood enters an artery from the heartbeat at high pressure. • The peak pressure reached in an artery is called systolic pressure. • • It pushes the wall of the artery outward. Widens the lumen. Stretches the elastic walls. All of these factors store potential energy • At the end of each heartbeat the pressure in the artery falls sufficiently for the stretched elastic fibers to recoil and squeeze the blood in the lumen. • This minimum pressure in the artery is called diastolic pressure. • This recoil saves energy and prevents the pressure from being too low. • It keeps the blood flow steady and continuous driven by the beating heart.

How is blood pressure measured? Systolic is the pressure of the ventricles contracting (closing off of artery) Diastolic is the pressure during the relaxation or ventricles refilling. (resuming of blood flow) Pressure cuff is called a sphygmomanometer. Blood Pressure Measurement: Systolic Pressure Diastolic Pressure 120/80 mm. Hg

• Circular muscles in walls of arteries form a ring. • When they contract they narrow the lumen. • This process is called vasoconstriction. • This increases blood pressure in the arteries. • Arterioles (smaller branches of arteries) have a large amount of muscle cells. • Constriction in arterioles in response to hormones or nerve impulses can restrict all blood flow to a specific part of the body. • Vasodilation can widen the lumen and increase blood flow to a specific part of the body.

CAPILLARIES BLOOD FLOWS THROUGH TISSUES IN CAPILLARIES WITH PERMEABLE WALLS THAT ALLOW EXCHANGE OF MATERIALS BETWEEN CELLS IN THE TISSUE AND THE BLOOD IN THE CAPILLARIES. • Capillaries transport blood to almost all tissues of the body. *except lens and cornea of eye. • Capillaries are the narrowest blood vessel with a diameter of about 10 µm. • They branch and rejoin repeatedly to form a capillary network with an immense length and surface area.

• Capillary wall is only one endothelial cell thick and coated with a filter-like protein gel. • The wall is very permeable. • There also pores between the cells which allows plasma from the blood to leak out and form tissue fluid around the cells the capillaries are in contact with. • This fluid that leaks out contains oxygen, glucose and other small molecules carried in the blood. • The tissue fluid allows cells to absorb useful substances and excrete waste. • This fluid can then re-enter the capillary network and be moved through the circulatory system.

VEINS COLLECT BLOOD AT LOW PRESSURE FROM THE TISSUES OF THE BODY AND RETURN IT TO THE ATRIA OF THE HEART . • Veins are blood vessels that transport blood from the capillary networks in the body BACK to the heart. • The blood is transported at a much lower pressure than it was in the arteries. • Since the pressure is much lower their walls are much thinner and contain fewer muscle and elastic fibers. • This allows the lumen to be much wider and hold more blood than arteries. (80% of a sedentary person’s blood is in veins- this lowers as activity increases. )

• Blood flow in Veins • Blood flow is assisted by gravity and by the pressure exerted by skeletal muscle and other body tissues. • When a muscle contracts it gets shorter and wider squeezing it like a pump. • VALVES assist in making sure blood only flows in a one way direction.

VALVES IN VEINS AND THE HEART ENSURE CIRCULATION OF BLOOD BY PREVENTING BACKFLOW. • Valves in Veins • Valves prevent backflow. • Pressure can be so low in the veins that there is a danger of backflow towards the capillary networks and not move toward the heart. • To maintain circulation the veins contain pocket valves which have three cup- shaped flaps of tissue. • If blood flows backwards it gets caught in the flaps. • When blood flows towards the heart, it pushes the flaps to the sides and opens to allow the blood to flow freely.

IDENTIFICATION OF BLOOD VESSELS AS ARTERIES, CAPILLARIES OR VEINS FROM THE STRUCTURE OF THEIR WALLS.

THE HUMAN CARDIOVASCULAR SYSTEM • The circulatory system provides an effective internal transport system that brings necessary resources to the cells and removes unnecessary wastes in the blood.

The Heart There is a separate circulation for the lungs. The mammalian heart is a four chambered, double pump that allows for the double circulation of blood by two separate systems at the same time. • Pulmonary Circulationpumps blood to and from the lungs. • Systemic Circulationpumps blood to and from all other organs, including the heart itself.

• Parts of the Heart: • a. Atria: thin-walled upper chambers which collect blood returning to the heart. • b. Ventricles: thick, muscular lower chambers which pump blood to the lungs and other body tissue. • c. Septum (wall): separate the right and left sides of heart to prevent mixing of oxygenated and deoxygenated blood.

Valves- flaps of connective tissue which prevent the back flow of blood and keeps blood flowing in one direction. • Between each chamber is an atrioventricular valve (AV) to prevent blood from the atrium and ventricle from mixing. • Semilunar valves (SV) are at the 2 exits of the heart to prevent backflow as well.

RECOGNITION OF THE CHAMBERS AND VALVES OF THE HEART AND THE BLOOD VESSELS CONNECTED TO IT IN DISSECTED HEARTS OR IN DIAGRAMS OF THE HEART STRUCTURE.

Pulmonary Loop - Oxygen-poor blood returns from the body under low pressure and fills the RIGHT ATRIUM. - The blood passes through the (tricuspid) AV valve and fills RIGHT ventricle. - The RIGHT VENTRICLE then pumps oxygen-poor blood through the pulmonary semilunar valves into two pulmonary arteries to the capillary beds in the lungs under low pressure. -Blood takes up OXYGEN and unloads carbon dioxide in the lungs.

• - Oxygen-rich blood returns to the heart through two pulmonary veins to the LEFT atrium where it will pass through the (mitral) AV valve and into the LEFT ventricle.

Systemic Loop -The walls of the LEFT ventricle are much thicker then the walls of the right ventricle in order to pump blood to all of the body under higher pressure. - Oxygen – rich blood leaves the left ventricle thought the (aortic) semilunar valve and into the AORTA (artery-away). -The AORTA is the largest blood vessel (2. 5 cm diameter) - From the aorta- arteries branch off to supply coronary arteries with blood for the heart and other branches from the aorta go to the rest of the body.

• Coronary arteries supply heart muscles with oxygen and nutrients

Oxygen-poor blood from the body returns back to the RIGHT atrium through the large veins called the SUPERIOR VENA CAVA (upper body) and the INFERIOR VENA CAVA (lower body).

ATHEROSCLEROSIS CAUSES AND CONSEQUENCES OF OCCLUSIONS OF THE CORONARY ARTERIES.

• Atherosclerosis is the build up and hardening of fatty tissue or plaque in the artery walls. • High blood pressure, smoking, or high cholesterol damages the endothelium of the artery walls. • Low Density Lipoproteins(LDL) containing fats and cholesterol accumulate in the damaged tissue forming the fatty tissue called atheroma. • Phagocytic white blood cells engulf the fats and cholesterol and grow large. • Smooth muscle from the walls of the arteries form a tough fibrous cap over the atheroma. • The artery wall bulges and narrows the lumen of the artery. • Blood flow is hindered.

• Coronary Occlusions • The narrowing of the coronary arteries that supply blood that provides the heart tissue with oxygen and nutrients. • Lack of oxygen (anoxia) causes pain called angina and decreases the muscles ability to pump. • The heart beats faster to try to maintain the blood flow of the impaired heart. • The fibrous cap can rupture which causes the formation of blood clots in the damaged arteries. • These clots can completely block off the arteries leading to a heart attack. • Within a short time, death of heart muscle cells occurs, causing permanent damage.

• Factors associated with Atherosclerosis • High LDL concentrations in the blood. • High glucose concentrations in blood. • Obesity • Diabetes • High Blood Pressure • Smoking • Stress • Consuming trans fats. • Raises the levels of LDL and reduces HDL • Intestinal Microbes- http: //www. huffingtonpost. com/2013/04/24/gut-bacteria-heart-attack-stroke-tmao-lecithin_n_3149663. html *Trans fat is found in many processed foods, such as cookies, crackers, snack foods, and other processed foods made withshortening, partially hydrogenated vegetable oils, including some margarines and salad dressings or *HDL cholesterol acts as a maintenance crew for the inner walls (endothelium) of blood vessels. Damage to the inner walls is the first step in the process ofatherosclerosis, causes heart attacks and strokes. HDL scrubs the wall clean and keeps it healthy which

PRESSURE CHANGES IN THE LEFT ATRIUM, LEFT VENTRICLE AND AORTA DURING THE CARDIAC CYCLE.

THE CARDIAC CYCLE

• Atrial Systole 0. 0 -0. 1 seconds • Atria contract. • • • Rapid but small pressure increase. Pumps blood from atria to ventricles. AV valves are already open. Semilunar valves are closed. Pressure in arteries drops to its minimum as blood flows but is NOT pumped.

• Early Ventricular Systole 0. 1 -0. 15 sec. (Atrial diastole) • The ventricles contract. • A rapid pressure build up causes the AV valves to close. • The semilunar valves remain closed.

• Late Ventricular Systole 0. 15 -0. 4 sec. (Atrial diastole) • The pressure in the ventricles rises above the pressure in the arteries. • Semilunar valves OPEN. • Blood is pumped from the ventricles into the arteries. • Maximizing the arterial blood pressure. • Pressure slowly rises in the atria as the veins fill them with blood.

• Early Ventricular Diastole 0. 4 -0. 45 secs. (Atrial diastole) • The contraction of the ventricles lessens and pressure in the ventricles rapidly drops below the pressure in the arteries causing the semilunar valve to CLOSE.

• Late Ventricular Diastole 0. 45 -0. 8 secs. (Atrial diastole) • The pressure in the ventricles drops below the pressure in the atria so the AV valves OPEN. • Blood from the veins drains into the atria and into the ventricles slowly increasing the pressure in the ventricles.

THE HEART BEAT IS INITIATED BY A GROUP OF SPECIALIZED MUSCLE CELLS IN THE RIGHT ATRIUM CALLED THE SINOATRIAL NODE. • The heart is MYOGENIC- the muscles stimulate its self. • It’s muscles can contract with out stimulation from a motor neuron. • The muscle cell that contracts stimulates the other cells it is in contact with to also contract. • This allows a group of cells to contract almost simultaneously at a fast rate.

THE SINOATRIAL NODE ACTS AS A PACEMAKER. • Sinoatrial node (SA Node) • The sinoatrial node is the region of the heart in the wall of the right atrium that contains specialized cells with the fastest rate of spontaneous beating. • The SA node initiates each heart beat because the membranes of these cells are the first to depolarize in the cardiac cycle. • It maintains the heart pumping rhythm by setting the pace for the beating of the heart- PACEMAKER. • If the SA node becomes defective an artificial pacemaker is implanted which takes over stimulating the heart to beat.

• If the SA node becomes defective an artificial pacemaker is implanted which has electrodes that take over stimulating the heart to beat.

THE SINOATRIAL NODE SENDS AN ELECTRICAL SIGNAL THAT STIMULATES CONTRACTION AS IT IS PROPAGATED THROUGH THE WALLS OF THE ATRIA AND THEN THE WALLS OF THE VENTRICLES. • The Heart Beat • The SA node generates an electrical signal that spreads quickly through both atria. (0. 1 second) • The cardiac muscle fibers are branched and there are interconnections between adjacent muscle fibers which allows the impulse to be propagated in many cells. • This causes both atria to contract together.

• There is a 1/10 th of a second delay at the AV node which allows the atria empty completely into the ventricles. • Specialized muscle fibers then relay the signals to the tips of the ventricles and up through their walls. • This stimulates the ventricles to contract together and pump blood out into the major arteries of the heart.

THE HEART RATE CAN BE INCREASED OR DECREASED BY IMPULSES BROUGHT TO THE HEART THROUGH TWO NERVES FROM THE MEDULLA OF THE BRAIN. Control of Heart Rate • The rate of the heart beat can be modified by cardiovascular control centers in the medulla of the brain. • Input is received from receptors that monitor blood pressure, oxygen content and p. H. • p. H of blood indicates carbon dioxide concentration. • The more carbon dioxide the lower the p. H- more acidic.

• The Vagus nerves act as part of the parasympathetic (resting and digesting) nervous system to slow down the heart rate. • High blood pressure, high oxygen concentration, and high p. H are all indictors that the heart rate may need to slow down.

• The Accelerans nerves act as part of the sympathetic (fight or flight) autonomic nervous system to speed up the heart rate. • Low blood pressure, low oxygen concentration, and low p. H indicate that the heart rate needs to speed up to increase blood flow to the tissues. • Delivers more oxygen and removes more waste.

EPINEPHRINE INCREASES THE HEART RATE TO PREPARE FOR VIGOROUS PHYSICAL ACTIVITY. • Epinephrine is a hormone that is also called adrenalin. • It acts on SA node and increases the heart rate • Epinephrine is secreted by the adrenal glands and its secretion is controlled by the brain. • The body has a “fight or flight” response to epinephrine. • Adrenaline helps the body prepare for physical activity, excitation, stress, perceived harm, and survival.