Unit 5 Cardiovascular System: Heart and Blood Vessels Components of the Cardiovascular System Heart pumps blood Blood vessels the tubes through which the blood flows Functions of Blood Blood removes wastes from cells brings oxygen and nutrients to cells becomes oxygenated in the lungs receives nutrients at the intestines is filtered in the kidneys getting rid of wastes and keeping needed water and salts Has amino acids and toxins removed by the liver Functions of the Cardiovascular System The contractions of the heart generate blood pressure, which moves blood through the blood vessels Blood vessels transport blood from the heart into arteries, capillaries, and veins; blood then returns to the heart to complete the circuit Gas exchange (pick-up of CO 2 and drop-off of oxygen) occurs at the smallest vessels in diameter the capillaries The heart and blood vessels regulate blood flow as needed Lymphatic System Assists the cardiovascular system by collecting excess fluid and returning it to the cardiovascular system Excess fluid builds up as material exchange takes place Once the fluid is in the lymphatic vessels, it is called lymph (a fluid tissue like blood) Blood Vessels Arteries from the heart Capillaries - exchange Veins to the heart 1
Arteries The thick walls of the arteries have three layers Endothelium the inner most layer made up of thin cells Thick middle layer made up of smooth muscle and elastic tissue Outer layer connective tissue The strong walls of the arteries give it support when blood enters under pressure The elastic tissue allows for expansion to absorb the pressure Arterioles small arteries composed mostly of smooth muscle that control blood pressure Capillaries Arterioles branch into capillaries Capillaries are very narrow and are composed of a single layer of epithelial cells Networks of capillaries, called capillary beds, are present in all parts of the body, so no cell is ever too far from a capillary so that material exchange can occur Precapillary sphincters control the flow of blood through a capillary Atriovenous shunt when the sphincter is closed, blood goes directly from arterioles to venules to an area where exchange is needed. Veins Blood Vessels Venules - small veins that branch from capillaries and then join to form veins The walls of venules and veins have the same three layers as arteries, but there is less smooth muscle and less connective tissue, making the walls of veins thinner than the walls of arteries Valves allow blood to flow toward the heart only; present in most veins, especially those in the lower parts of the body where blood flow must work against gravity The heart is a cone-shaped muscular organ located between the lungs and behind the sternum (breastbone) The heart is tilted so that the apex (the pointed end) is oriented to the left The approximate size of your heart is the size of a fist covered with your other hand Myocardium makes up the major portion of the heart; the interior wall of cardiac muscle The muscles fibers of the myocardium are branched and connect to neighboring fibers by intercalated disks Gap junctions aid in contraction of the cardiac fibers Desmosomes contain protein fibers that prevent overstretching Pericardium the thick sac that surrounds and protects the heart Secretes a fluid that allows the pericardium to slide over the heart as it pumps 2
Septum the wall that separates the heart into the right and left sides There are 4 chambers in the heart Atria (singular atrium) the 2 upper, thinwalled chambers Left atrium and right atrium Each has a wrinkled, ear-like flap on the outer surface called a auricle Ventricles the 2 lower, thick-walled chambers Left ventricle and right ventricle Valves keep blood flowing in the right direction Atrioventricular (AV) valves lie between the atria and ventricles Chordae tendineae support and protect the valves Tricuspid valve right side Bicuspid (mitral) valve left side Semilunar valves lie between the ventricles and the blood vessels leading out of the heart Pulmonary valve right ventricle and pulmonary arteries Aortic valve left ventricles and aorta Superior Vena Cava and Inferior Vena Cava bring oxygen-poor blood into the right atrium from the cells in the body Superior Vena Cava from the cells above the heart Inferior Vena Cava - from the cells below the heart Right Atrium contracts and the blood is sent through the tricuspid valve into the right ventricle The right ventricle contracts sending the blood through the pulmonary valve into the 2 pulmonary arteries which lead to the lungs Capillaries within the lungs allow for gas exchange carbon dioxide leaves the blood and oxygen enters the blood is now oxygen-rich The blood returns to the left atrium through the pulmonary veins Left Atrium contracts and the blood is sent through the bicuspid valve into the left ventricle The left ventricle contracts sending the blood through the aortic valve into the aorta Arteries branch into arterioles, connect with capillaries where exchange takes place The capillaries connect with venules, which form veins that connect to the Superior and Inferior Vena Cava The whole process starts again Oxygen-poor (right side) and oxygen-rich blood (left side) never mix Blood must first go to the lungs to get from the right side to the left side The heart is a double pump the right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the rest of the body The muscles of the left ventricle are thicker because its job is harder and it must pump with greater force, making the blood pressure highest in the aorta and decreasing as the arteries branch out 3
Heartbeat Cardiac cycle occurs for each heartbeat When the heart beats, both atria contract at the same time, and then both ventricles contract at the same time Then all four chambers relax Systole refers to the contraction phase Diastole refers to the relaxation phase Average 60-80 times per minute with each heartbeat lasting about 0.85 seconds Heartbeat 2 audible heartbeat sounds lub-dup lub the increasing pressure of the blood causes the AV valves to slam shut and the pressure of blood in the ventricles causes the semilunar valves to open dup when the ventricles relax and the the semilunar valves close Heart murmur a slight swishing sound after the lub often due to leaky valves causing the blood to flow back into the atria after the AV valves have closed Internal Control of Heartbeat The rhythmic contractions of the heart are controlled by a unique type of cardiac muscle called nodal tissue which has both muscular and nervous characteristics SA (sinoatrial) node upper wall of the right atrium Initiates heartbeat and automatically sends out a signal every 0.85 seconds, which cause the atria to contract Called the pacemaker because it regulates the heartbeat If the SA node is not functioning properly, the heartbeat will be slower, and an artificial pacemaker can be implanted AV (atrioventricular) node base of the right atrium near the septum The signal initiated at the SA node allows the ventricles to contract External Control of Heartbeat Medulla oblongata controls the heartbeat externally When we are inactive decreases SA and AV nodal activity When we are active or excited - increases SA and AV nodal activity Hormones Epinephrine and norepinephrine stimulate the heart to beat faster during exercise Electrocardiograms Electrocardiogram (ECG) a recording of the electrical changes that occur during the cardiac cycle Body fluids that contain ions conduct electricity This is why the electrical changes in the heart can be felt at the surface of the skin electrodes are placed on the skin and are connected to a instrument in which a pen rises or falls on a moving strip of paper When the SA node triggers an impulse an electrical change called a P Wave is produced this shows the atria are about to contract The QRS Complex shows that the ventricles are about to contract T Wave the current produced when the muscles relax 4
Electrocardiograms There are many abnormalities that an ECG can detect Ventricular fibrillation uncoordinated, irregular activity of the ventricles Can be caused by an injury, heart attack, or drug overdose Tissues become deprived of oxygen Normal electrical activity must be established or the person will die Defibrillation when an electrical current is applied to the chest Causes all heart cells to discharge their energy at once The SA node may be able to establish a regular beat Pulse Rate Pulse the rhythmic expansion and recoil of the arteries as blood enters and causes their walls to stretch Felt in arteries that are close to the surface of the skin Radial artery (wrist) Carotid (neck) Average pulse rate in a healthy adult is between 60 and 80 beats per minute Regulation of Blood Flow Blood Pressure the pressure of blood against the wall of a blood vessel Systolic (top #) the highest arterial pressure that is reached when blood is leaving the heart Diastolic (bottom #) - the lowest arterial pressure that is reached when the ventricles relax The average normal resting blood pressure is 120 mm Hg over 80 mm of Hg Hypertension high blood pressure Hypotension low blood pressure As blood leaves the less ventricle, the pressure decreases and this causes the blood velocity to slow as it reaches the capillaries Regulation of Blood Flow The slow movement of blood through the capillaries is important because it allows for the exchange of materials between the capillaries and the surrounding tissues The precapillary sphincters will open and close to allow for adjustments in speed As blood makes it way back to the heart through the veins, its velocity increases this is due to the larger diameter of the veins Regulation of Blood Flow The flow of blood in veins back to the heart is dependent on 3 factors The skeletal muscular pump The movement of the skeletal muscles forces the blood to move through a valve The respiratory pump Inhalation reduces pressure in the thoracic cavity and forces the blood to flow from a higher pressure in the abdominal cavity to the lower pressure in the thoracic cavity The valves present in veins Prevent blood from flowing backwards Pulmonary Circuit Deoxygenated blood from all parts of the body enters the heart through the right atrium It passes down into the right ventricle and is then pumped out into the pulmonary trunk The pulmonary trunk splits into the right and left pulmonary arteries (the only arteries in the body that carry deoxygenated blood) which branch off into smaller arterioles and lead into each lung In the lungs the arterioles branch into capillaries and gas exchange takes place oxygen is put into the blood and CO 2 is released Blood then returns to the heart through venules, which lead to the pulmonary veins (the only veins in the body that carry oxygenated blood) The blood renters the heart through the left atrium 5
Systemic Circuit The heart pumps blood through 60,000 miles of blood vessels to deliver oxygen and nutrients to all the cells of the body Oxygenated blood leaves the heart from the left ventricle through the largest artery in the body, the aorta The aorta branches into smaller arteries, and then arterioles, which will reach all the cells of the body After exchange of materials (oxygen, nutrients, CO 2, wastes) has occurred through the capillaries of body cells, the blood starts to make its ways back to the heart through venules, then larger veins Eventually the veins will form the Superior (from the upper body) and Inferior (from the lower body) Vena Cava and the deoxygenated blood will reenter the heart through the right atrium Hepatic Portal System Specialized for the filtration of blood Hepatic portal vein drains blood from the capillaries of the digestive tract to the capillaries in the liver The blood going to the liver is deoxygenated, but high in glucose, amino acids and other nutrients The liver will store the glucose and glycogen and will either store the amino acids or use them to synthesize proteins The liver also removes toxins and pathogens from the blood After being filtered by the liver, the blood enters the hepatic vein and then the inferior vena cava to return to the heart Exchange at the Capillaries Two forces control the movement of blood through the capillaries Blood pressure causes movement of blood from capillaries to tissue spaces Osmotic pressure causes movement of water from tissue spaces to capillaries At the arterial end of a capillary, blood pressure is higher than the osmotic (water) pressure The osmotic pressure is caused by the proteins dissolved in the plasma This difference in pressure causes water to exit a capillary at the arterial end Exchange at the Capillaries Midway along the capillary, blood pressure is lower, and blood pressure and osmotic pressure will cancel each other out and there is no net movement of fluid This is where diffusion occurs for the exchange of materials Oxygen and nutrients diffuse out of the capillary CO 2 and wastes diffuse into the capillary Exchange at the Capillaries At the venule end of a capillary, osmotic pressure is greater than blood pressure causing fluids to move back into the capillary About the same amount of fluid enters the capillaries as had left them, but some of the fluid is collected by the lymphatic vessels and is called lymph The leading cause of death in the United States Types of cardiovascular disease Aneurysms a burst blood vessel that make be caused by high blood pressure or blocked blood vessels Can be detected by an MRI and can be prevented by replacing the blood vessel that is about to burst with an artificial one Hypertension high blood pressure; 140 or higher over 90 or higher Called the silent killer because it may not be detected until a heart attack or stroke occurs Can be treated with prescription drugs 6
Atherosclerosis buildup of plaque on the inside of blood vessels The plaque narrows the diameter of the blood vessels making it harder for the blood to flow through Can prevented through diets low in saturated fats and cholesterol Blood clots Thrombus stationary clot Embolism when the clot dislodges and moves along with the blood Thromboembolism a clot carried in the blood but then becomes stationary in a small blood vessel Stroke when a small arteriole in the brain bursts or is blocked by a clot Lack of oxygen causes death of the nerve cells in that area of the brain and may lead to paralysis or death Warning signs numbness in the hands or face, difficulty in speaking, temporary blindness Heart Attack also called a myocardial infarction when a portion of heart muscle dies due to lack of oxygen Angina Pectoris when a coronary artery becomes blocked Feelings of pressure or squeezing in the chest, with pain possible extending to the left arm Heart failure the heart no longer pumps as it should Many times after a heart attack, the heart is so damaged that it can no longer function correctly Treatment of cardiovascular disease Aspirin lowers the probability of clot formation Coronary bypass surgery when a blood vessel (usually from the leg) is attached to the aorta and a coronary artery bypassing the clogged artery Stent - a small mesh cylinder the holds an artery open after a blockage has been cleared Angioplasty when a tube containing a balloon is inserted into an clogged artery and when inflated, the balloon keeps the blocked artery open Implantable cardioverter-defibrillator (ICD) can detect an abnormal heartbeat and will automatically send a sock like an external defibrillator does Heart transplants Left ventricular device (LVAD) a tube pumps the blood into the aorta Total artificial heart (TAH) 7