Circulatory (Cardiovascular) System Structure and Function of Blood

Transcription

1 Circulatory (Cardiovascular) System Structure and Function of Blood Circulatory Systems Open Fluid is circulated through an open body chamber. Arthropods and most mollusks have an open circulatory system. Hemolymph is contained in a body cavity, the hemocoel. A series of hearts circulates the fluid. Ex. Insects, mollusks Closed Fluid is circulated through blood vessels. Vertebrates, annelid worms, and a few mollusks have a closed circulatory system. Blood is moved through blood vessels by the heart s action. It does not come in direct contact with body organs. EX. Worms, fish, humans Cardiovascular system Heart and blood vessels The heart pumps blood through blood vessels It brings nutrients to cells and helps get rid of wastes Exchange of substances occurs through interstitial fluid Functions of the cardiovascular system Transport: oxygen, carbon dioxide, and other waste products, nutrients, and hormones Protection: cells of the immune system are transported to help protect the body from infection Regulation: maintains homeostasis of a variety of the body s conditions That is, ph balance, electrolyte levels Page 1 of 23

2 Lymphatic system Assists the cardiovascular system by collecting excess tissue fluid and returning it to the blood When fluid enters the lymphatic vessels, it is called lymph Page 2 of 23

3 Vertebrate Cardiovascular Systems Two Chambered Heart Three Chambered Heart Four Chambered Heart simplest vertebrate heart fish A single atrium receives blood from the body cells. A ventricle sends blood to the gills to collect oxygen. Separate atria allow some separation of oxygenated and deoxygenated blood, which was an advantage for land organisms (reptiles, amphibians). Though blood can mix in the ventricle, mixing is minimal. Some reptiles have partial separation of the ventricle. birds and mammals, allows complete separation of oxygenated and deoxygenated blood. Complete separation is necessary to support a fast metabolism found in homeotherms. Page 3 of 23

4 Types of Blood Vessels Artery carries blood away from the heart Their walls have 3 layers: Endothelium the thin, inner epithelium Middle layer smooth muscle and elastic tissue Allows arteries to expand and recoil Outer layer connective tissue Arterioles-Small arteries Middle layer has mostly smooth muscle It contracts to constrict the vessel, reducing blood flow and raising blood pressure When relaxed, the vessel dilates, increasing blood flow and reducing blood pressure Capillaries -Microscopic vessels between arterioles and venules Walls of capillaries are made only of endothelium Form capillary beds where gas, nutrient, and waste exchange occurs Have precapillary sphincters, which control blood flow through the capillary bed. When closed, blood instead flows through an arteriovenous shunt Venules and Veins Venules small veins that receive blood from the capillaries Veins carry blood toward the heart Venule and vein walls have the same 3 layers as arteries, but less smooth muscle in the middle layer Veins that carry blood against gravity have valves to keep blood flowing toward the heart Walls of veins are thinner than arteries so they can expand to hold more blood At any one time, they store 70% of the blood If blood is lost (that is, hemorrhage), the nervous system causes the veins to constrict to increase blood volume Page 4 of 23

5 The heart Located between the lungs Points toward the left hip Consists mostly of the myocardium, which is made of cardiac muscle tissue Muscle fibers are branched and connected by intercalated disks, which contain gap junctions These allow cells to contract in unison Also connected by desmosomes, a type of cell junction that prevents overstretching by holding adjacent cells together Surrounded by a sac called the pericardium, which secretes pericardial fluid for lubrication Internally, the septum divides the heart into right and left sides Consists of 4 chambers: 2 upper atria and 2 lower ventricles 2 types of valves: semilunar valves and atrioventricular (AV) valves The AV valves are reinforced by chordae tendineae Left AV valve bicuspid, or mitral valve Right AV valve tricuspid valve Semilunar valves: pulmonary valve and aortic valve Page 5 of 23

6 Myocardium (cardiac muscle tissue) The myocardium needs its own blood supply Coronary arteries supply it They are the first branches off the aorta Coronary veins drain it Empty into the right atrium Coronary artery disease blockage in the coronary arteries causes a myocardial infarction (heart attack) Blood flow through the heart Oxygen-Poor and Carbon Dioxide-Rich Blood Flow The superior vena cava and inferior vena cava carry oxygen-poor, carbon dioxide-rich blood from the body to the right atrium Blood then flows through the right AV (tricuspid) valve into the right ventricle. The right ventricle pumps blood through the pulmonary valve into the pulmonary trunk, which branches into right and left pulmonary arteries. They lead to the lungs Oxygen-Rich and Carbon Dioxide-Poor Blood Flow The pulmonary veins carry oxygen-rich, carbon dioxide-poor blood from the lungs to the left atrium. Blood then flows through the left AV (bicuspid) valve into the left ventricle. The left ventricle pumps blood through the aortic valve into the aorta. The aorta branches into smaller arteries, which lead to arterioles, then capillaries, venules, veins and back to the vena cava Page 6 of 23

7 The walls of the left ventricle are thicker than the right ventricle because it must pump blood to the entire body, not just to the lungs The walls of atria are thinner than ventricles The cardiac cycle First the atria contract together, then the ventricles, then the heart relaxes Systole heart contraction Diastole heart relaxation Occurs 70 times per minute on average There are two audible sounds: lubdub Lub: from the closure of the AV valves Dub: from the closure of the semilunar valves Murmur: a swishing sound between lub and dub from regurgitation of blood (leaky valves) **Auricle is another name for Atrium Page 7 of 23

8 Internal (intrinsic) conduction system The SA node in the right atrium initiates the heartbeat by sending out an electrical signal; this causes the atria to contract SA node is called the pacemaker This impulse reaches the AV node, also in the right atrium AV node sends a signal down the AV bundle and Purkinje fibers; this causes ventricular contraction These impulses travel through gap junctions in the intercalated disks External (extrinsic) control of heartbeat The cardiac control center in the brain increases or decreases the heart rate depending on the body s needs Some hormones increase heart rate Page 8 of 23

9 Electrocardiogram (ECG) A recording of the electrical changes in the heart muscle during a cardiac cycle The atria produce an electrical current, called the P wave, when stimulated by the SA node QRS complex wave of electrical current traveling through the ventricles Signals that the ventricles are about to contract The recovery of the ventricles is represented as the T wave Detects abnormalities That is, ventricular fibrillation caused by uncoordinated, irregular electrical signals in the ventricles The heart can t pump blood; tissues become starved of oxygen Defibrillation applying a strong electrical signal to reset the heart; hopefully, the SA node will start firing again Blood Pressure Pressure that blood exerts against a blood vessel wall Is highest in the aorta, right next to the heart; it gradually decreases as it flows through the vessels in the body Pulse surge of blood into an artery causes the walls to stretch, and then recoil Usually measured in the radial artery at the wrist or carotid artery in the neck A measurement of the heart rate; averages beats per minute Contraction of ventricles creates blood pressure, which propels blood through the arteries Measured with a sphygmomanometer, in the brachial artery of the arm Page 9 of 23

10 Measuring Blood Pressure Systolic pressure the highest pressure; when blood is ejected from the heart Diastolic pressure the lowest pressure; when the ventricles relax Average is 120/80 mmhg (systolic/diastolic) Hypertension Hypotension high blood pressure low blood pressure Blood flow Blood pressure decreases as it flows away from the heart Is slowest in the capillaries to increase the exchange of gases, nutrients, and wastes Is adjusted by the precapillary sphincters Venous Return Blood pressure is very low in the veins, so doesn t contribute much to the movement of blood Venous return is dependent on three additional factors: Skeletal muscle pump (dependent on skeletal muscle contraction) Respiratory pump (dependent on breathing) Valves present in veins Page 10 of 23

11 Blood flows in two circuits: Pulmonary circuit circulates blood through the lungs Right atrium pumps deoxygenated blood into the right ventricle, which pumps it into the pulmonary trunk. The pulmonary trunk splits into right and left pulmonary arteries, which go to the lungs. In the lungs, the pulmonary arteries branch into arterioles, which lead to capillaries. This is where gas exchange occurs. The pulmonary capillaries lead to venules, which merge into the pulmonary veins. The four pulmonary veins empty into the left atrium. The pulmonary arteries carry oxygen-poor blood; the pulmonary veins carry oxygen-rich blood Systemic circuit circulates blood through the body tissues The left ventricle pumps blood into the aorta, which gives off branches to all the tissues of the body. Arteries branch into (eventually) arterioles, which lead to capillaries Capillaries lead to venules, which drain into veins, which lead to the superior and inferior vena cava. The vena cava empty into the right atrium Page 11 of 23

12 Usually, blood flows from the aorta into an artery that supplies an organ, then through veins back to one of the vena cava That is, aorta > renal artery > kidney > renal vein > inferior vena cava However, there are special routes that don t follow this pathway That is, the hepatic portal system Hepatic portal vein: Brings nutrient-rich blood from the digestive tract to the liver The liver synthesizes blood proteins from the amino acids in the hepatic portal vein and stores the glucose as glycogen The liver also removes toxins and pathogens that enter the blood through the digestive system Blood is drained from the liver into the hepatic veins, which drain into the inferior vena cava Two forces drive fluid in and out of capillaries: Blood pressure drives fluid out of the capillary, mainly at the arterial end of the capillary bed This fluid contains everything that blood contains except cells and plasma proteins Osmotic pressure draws water into the capillary by osmosis, mostly at the venule end Some tissue fluid enters lymphatic capillaries and becomes lymph, which is eventually returned to the cardiovascular system Page 12 of 23

13 Cardiovascular disease (CVD) Leading cause of early death in Western countries Disorders of the blood vessels Hypertension (high blood pressure) and atherosclerosis often lead to a stroke, heart attack, or aneurysm Hypertension (high blood pressure) Atherosclerosis A systolic pressure of 140 or greater or a diastolic pressure of 90 or greater A silent killer because there are few symptoms until it causes kidney failure, a heart attack, or stroke Treated with diuretics, which increase the production of urine, and other drugs A buildup of atherosclerotic plaque in the walls of blood vessels Plaques narrow blood vessel diameter, decreasing blood supply to tissues Can cause clots to form in the roughened walls of arteries Thrombus a clot that is stationary Embolus a clot that detaches and moves to distant sites Thromboembolism an embolus that has become lodged in a blood vessel Stroke (cerebrovascular accident, or CVA) Myocardial infarction (MI, or heart attack) Occurs when a cranial artery is blocked or bursts Part of the brain dies dues to lack of oxygen Symptoms may include numbness of hands or face, difficulty speaking, and inability to see in one eye Part of the heart dies due to lack of oxygen Caused by a blocked coronary artery It can begin with angina pectoris, pain in the chest from a partially blocked coronary artery Can be treated with drugs that dilate blood vessels Aneurysm A ballooning of a blood vessel, most often the abdominal aorta or blood vessels in the brain Atherosclerosis and hypertension can weaken a vessel and cause ballooning If a major artery ruptures, death can result Page 13 of 23

14 Treating clogged arteries Coronary bypass operation -a vein from the leg is taken and used to bypass a clogged artery Gene therapy -injection of the gene for vascular endothelial growth factor (VEGF) induces the growth of new vessels Then there is no need for bypass surgery Angioplasty -a tube is inserted into the clogged artery to insert a stent a mesh cylinder to hold it open Stents are usually coated in drugs to dissolve blockages Heart failure The heart no longer pumps properly Treatments: Wrapping the heart to prevent enlargement Implantable cardioverterdefibrillator (ICD) corrects an irregular rhythm Heart transplant Injection of stem cells to repair damaged heart Left ventricular assist device (LVAD) batterypowered pump to assist the heart Total artificial heart (TAH) temporary solution Blood The heart pumps 75 ml of blood with each contraction On average, the heart beats 70 times/minute Therefore the heart pumps roughly 5,250 ml per minute (75ml/beat 70beats/minute) the entire blood supply is circulated each minute Page 14 of 23

15 MAJOR FUNCTIONS OF BLOOD Transport dissolved materials (O 2, CO 2, nutrients, wastes, hormones) to and from body cells Regulates ph and electrolyte (ion) composition of interstitial fluid Restriction of blood loss from blood vessels (blood clotting) Defense against pathogens Stabilizes body temperature Page 15 of 23

16 COMPOSITION OF BLOOD Plasma (46% to 63%) Water (92%) transports dissolved materials Plasma proteins (7%) albumins, globulins, fibrinogen, regulatory proteins Other solutes (1%) ions, nutrients, wastes Formed elements Red blood cells (RBCs) Erythrocytes Transport O2 and CO2 99.9% of formed elements White blood cells (WBCs) Leukocytes Defense against pathogens Less than 0.01% of formed elements Platelets Thrombocytes Cell fragments Involved in blood clotting Less than 0.01% of formed elements Page 16 of 23

17 Plasma Consists of 91% water and 9% salts and organic molecules Solutes help maintain the osmotic pressure of blood Salts act as buffers Other solutes: nutrients, wastes, hormones Plasma proteins are the most abundant organic molecules Most are produced by the liver Create osmotic pressure in the blood Albumins Most abundant of the plasma proteins Contribute to osmotic pressure more than others Transport molecules in the blood Globulins Some transport substances in the blood Others, gamma globulins, fight pathogens Fibrinogen Inactive; when activated, forms blood clots Red Blood Cells (Erythrocytes) Characteristics: Biconcave shape increases surface area Contain the protein hemoglobin (Hb) A pigment that binds oxygen The reason RBCs, and therefore blood, are red Production of RBC Occurs in the red bone marrow As RBCs are produced, they lose their nucleus and most organelles Without a nucleus, can t make proteins for cell repair Therefore, only live about 120 days Old, worn out cells are removed from circulation by macrophages in the liver and spleen The disc shape allows them to squeeze through small capillaries and allows for maximum surface area (for gas diffusion) Page 17 of 23

18 Erythropoietin A hormone produced by the kidneys when oxygen levels of the blood are low Stimulates the bone marrow to produce more red blood cells Blood Doping increasing the number of RBCs, sometimes by injecting EPO, to increase stamina and athletic performance Very dangerous; blood becomes too thick and can cause heart failure Disorders of the Blood Jaundice accumulation of heme in the blood if the liver can t excrete it Skin and whites of the eyes turn yellow Anemia too few RBCs or too little hemoglobin Iron-deficiency anemia the most common form Inadequate intake of dietary iron, so can t make Hb Pernicious anemia lack of vitamin B 12, which is needed to make RBCs Hemolytic anemia Sickle-cell disease Folic-acid-deficiency anemia need folic acid to make RBCs too much hemolysis (rupturing of the RBCs) genetic disease that causes RBCs to become sickle-shaped and prone to rupture Due to defective hemoglobin structure Platelets (thrombocytes) Result from fragmentation of large cells called megakaryocytes in the red bone marrow So are not true cells About 200 billion platelets are made per day Function in blood clotting (coagulation) Is important so that plasma and formed elements don t leak out of broken vessels 13 different clotting factors, calcium ions, and enzymes participate in clot formation When a vessel breaks, platelets clump to partially seal it Page 18 of 23

19 Disorders of Blood Clotting Thrombocytopenia too few platelets Due to not enough being made in the bone marrow or the increased breakdown outside the marrow Can be caused by leukemia or drugs Symptoms: excess bleeding Thromboembolism when a thrombus (stationary clot) forms, travels (it s then called an embolism), and plugs another vessel Hemophilia genetic deficiency of a clotting factor Unable to form clots Blood types Determined by proteins on the surface of RBCs Blood transfusion transfer of blood from one person to another Need to make sure blood types are compatible to prevent agglutination, or clumping, of red blood cells ABO Blood Groups Antigen a foreign substance, often a glycoprotein, that stimulates an immune response Blood types are determined by the presence and/or absence of two antigens, type A and type B s Page 19 of 23

20 BLOOD TYPING I A = allele for antigen A I B = allele for antigen B ABO B LOOD G ROUPS i = allele for no antigen BLOOD TYPE GENETICS BLOOD A IAIA or I A i Antigen A Anti-B antibodies B IBIB or I B i Antigen B Anti-A antibodies AB IAIB Antigen A Antigen B No antibodies O ii No antigens Anti-A antibodies Anti-B antibodies Page 20 of 23

21 R = allele for Rh antigen r = allele for no antigen Rh Factor The Rh factor is another blood type antigen; if it is present, the blood is Rh positive (+); if not, it s negative (-) Unlike anti-a and anti-b antibodies, anti-rh antibodies only develop in a person after they are exposed to the Rh factor BLOOD TYPE GENETICS BLOOD Rh antigen Rh+ RR or Rr Rh- rr no antigen RH-NEGATIVE BLOOD AFTER EXPOSURE TO RH-POSITIVE BLOOD TYPE GENETICS BLOOD Rh- rr No Rh antigen Anti-Rh antibodies Page 21 of 23

22 IMPORTANCE OF TYPING BLOOD Anti-A antibodies from patient attack antigen A RBCs in transfusion Type A blood given to Type B patient Result: clumping Blocked blood vessels Page 22 of 23

23 TYPING BLOOD BLOOD TYPE BLOOD IN ANTI-A SERUM IN ANTI-B SERUM A Clumping No clumping B No clumping Clumping AB Clumping Clumping O No clumping No clumping BLOOD TRANSFUSIONS GENERAL RULE: Match antigen of donor with antibodies of recipient BLOOD TYPE CAN GIVE BLOOD TO: CAN RECEIVE BLOOD FROM: A A, AB A, O B B, AB B, O AB AB AB, A, B, O O O, A, B, AB O Page 23 of 23