Human Biology BIOL 104 Talk Six The Heart

Human Biology (BIOL 104) Talk Six: The Heart and Blood Vessels The Circulatory System (Chapter 31)

• Homeostasis Review Three basic components: • Heart - serves as pump that establishes the pressure gradient needed for blood to flow to tissues • Blood - transport medium within which materials being transported are dissolved or suspended • Blood vessels passageways through which blood is distributed from heart to all parts of body and back to heart Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Homeostasis Review • The cardiovascular system delivers: – Oxygen, nutrients, hormones, and other substances to body cells • It carries away wastes and substances cell produce • Flowing blood also carries excess heat to the body surface Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Closed Circulatory System • Humans have a closed circulatory system, typical of all vertebrates, in which blood is confined to vessels and is distinct from the interstitial fluid. –The heart pumps blood into large vessels that branch into smaller ones leading into the organs. –Materials are exchanged by diffusion between the blood and the interstitial fluid bathing the cells. Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Heart • The largest part of the heart is usually slightly offset to the left (though occasionally it may be offset to the right). • The heart is usually felt to be on the left side because the left heart is stronger, since it pumps to all body parts. – The left lung in turn is smaller than the right lung because it has to accommodate the heart. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Heart • The heart is supplied by the coronary circulation and is enclosed in the pericardial sac. • Comprised of two parts: the fibrous pericardium, made of dense fibrous connective tissue, and the serous pericardium. • Between the outer parietal layer and the visceral serous layer is the pericardial cavity which contains the pericardial Copyright: Edited with permission from Open. Stax Biology fluid which protects and for AP Courses, Open. Stax, and Rice University lubricates the heart

Heart has four chambers • Two upper atria, – the receiving chambers • Two lower ventricles – the discharging chambers. • The right atrium – receives deoxygenated blood from the body • The left atrium – receives oxygenated blood from the lungs. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Heart has four chambers • When these contract the blood is pushed into the ventricles, which pump to propel the blood to the lungs and the rest of the body. • The right atrium and the right ventricle together are sometimes referred to as the right heart and this sometimes includes the pulmonary trunk. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Heart has four chambers • Similarly, the left atrium and the left ventricle together are sometimes referred to as the left heart. • The atrioventricular septum separates the left heart from the right heart, giving two functional units. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

How does a heart beat work? • The internal pacemaker starts at the sinoatrial (SA) node, which is located near the wall of the right atrium. • Electrical charges spontaneously pulse from the SA node causing the two atria to contract in unison. • The pulse reaches a second node, called the atrioventricular (AV) node, between the right atrium and right ventricle where it pauses for approximately 0. 1 second before spreading to the walls of the ventricles. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

How does a heart beat work? • From the AV node, the electrical impulse enters the bundle of His, then to the left and right bundle branches extending through the interventricular septum. • Finally, the Purkinje fibers conduct the impulse from the apex of the heart up the ventricular myocardium, and then the ventricles contract. • This pause allows the atria to empty completely into the ventricles before the ventricles pump out the blood. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

How does a heart beat work? • Transmission of a cardiac action potential through the heart's conduction system • • Heart cells must beat in unison. Intercalated Disks allow calcium to regulate united beating Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University From the wikimedia free licensed media file repository

Mazz’s quick ‘n’ easy guide to the working of a nerve firing • Remember the ion channels of plasma membranes? • Resting Potential – Same electrical ion charge inside and outside of cell – Said to be polarized • Action Potential • Depolarization occurs by the movement of K+ and Na+ ions – 3 Na+ ions are pumped out and 2 K+ ions are pumped in – This makes and change in the voltage of the cell of muscle tissue, causing contraction • Repolarization – Reverse ion flow – back to resting potential Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University (credit: modification of work by Mariana Ruiz Villareal)

How does a heart beat work? • P- SA node triggers Depolarization (contraction) of atria • [P-R interval – ventricles fill with blood] • QRS – Depolarization of ventricles – starts main pumping contractions • T – ventricular repolarization (relax) From the wikimedia free licensed media file repository

Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University From the wikimedia free licensed media file repository

Flow of blood to and from the heart • Superior vena cava and inferior vena cava carries O 2 -poor blood to the Right Atrium • Right atrium sends blood via tricuspid valve to R. Ventricle • Right Ventricle sends blood to pulmonary trunk – – Divides up into two pulmonary arteries - go to lungs • Four pulmonary veins carry O 2 -rich blood to Left Atrium • Left Atrium sends blood via Mitral valve to L. Ventricle • Left Ventricle sends blood via semilunar (Aortic) valve to the Aorta and then to body Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Heart Sounds • First heart sound or “lubb” – Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole • Second heart sound or “dupp” – Results from closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole, lasts longer • Third heart sound (occasional) – Caused by turbulent blood flow into ventricles and detected near end of first one-third of diastole From Wikimedia Commons, a freely licensed media file repository

The Heart • The heart pumps 7, 000 liters of blood through the body each day • The heart contracts 2. 5 billion times in an average lifetime • The heart and all blood vessels make up the cardiovascular system • The blood vessels make up two circuits – Pulmonary circuit – Systemic circuit Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The double pump – Pulmonary and systemic circulation • Blood is pumped from veins of the systemic circuit into the right atrium of the heart, then into the right ventricle. • Blood then enters the pulmonary circuit, and is oxygenated by the lungs. • From the pulmonary circuit, blood re-enters the heart through the left atrium. • From the left ventricle, blood re-enters the systemic circuit through the aorta and is distributed to the rest of the body. Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Cardiovascular System The Blood, a quick look A. Plasma • Liquid portion of the blood. • Contains: • clotting factors, • Hormones • Antibodies • dissolved gases • Nutrients • waste

The Cardiovascular System The Blood, a quick look B. Erythrocytes - Red Blood Cells • Carry hemoglobin and oxygen. • Do not have a nucleus and live only about 120 days. • Can not repair themselves • Contain antigens – see later! Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Cardiovascular System The Blood, a quick look C. Leukocytes – White Blood cells • Fight infection and are formed in the bone marrow • Five types –. Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Cardiovascular System The Blood, a quick look • D. Thrombocytes – Platelets. • These are cell fragment that are formed in the bone marrow from magakaryocytes. • Clot Blood by sticking together – via protein fibers called fibrin. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Cardiovascular System Blood Vessels -A network of tubes –Arteries arterioles move away from the heart • Elastic Fibers • Circular Smooth Muscle –Capillaries – where gas exchange takes place. • One cell thick • Serves the Respiratory System –Veins Venules moves towards the heart • Skeletal Muscles contract to force blood back from legs • One way values • When they break - varicose veins form

The Cardiovascular System • Arteries take blood away from the heart. The major arteries diverge into minor arteries, and then smaller vessels called arterioles, to reach more deeply into the muscles and organs of the body • Arterioles diverge into capillary beds. Capillary beds contain a large number (10 to 100) of capillaries that branch among the cells and tissues of the body. • Capillaries are narrow-diameter tubes that can fit red blood cells through in single file • Are the sites for the exchange of nutrients, waste, and oxygen with tissues at the cellular level. Fluid also crosses into the interstitial space from the capillaries. Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

The Cardiovascular System • The capillaries converge again into venules that connect to minor veins that finally connect to major veins that take blood high in carbon dioxide back to the heart. • Veins are blood vessels that bring blood back to the heart. • The major veins drain blood from the same organs and limbs that the major arteries supply. • Fluid is also brought back to the heart via the lymphatic system. • Veins contain one way valves to stop backflow of blood between heartbeats. When they break - varicose veins form Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Special features of veins • Valves – Prevent backflow – Most abundant in legs (where blood has to travel against gravity) • Muscular contraction – Aids the return of blood to heart in conjunction with valves From Wikimedia Commons, a freely licensed media file repository

Capillary Beds • The capillaries are the smallest unit of the circulatory system, • Connect the arterioles and the smaller veins (venules). • Arterioles bring blood from the heart which is rich with oxygen and nutrients, while • Venules carry blood which has become deoxygenated back to the heart. Copyright: Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Capillary Beds • A capillary bed is a concentration of capillaries which supply blood to a specific organ or area of the body. • The density of the capillaries in a given bed can vary, depending on the requirements of the area it supports. • Precapillary sphincters regulate the flow of blood to tissues Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Capillary Beds • These areas are an important part of the circulatory system • Marks the point where the circulation reaches its terminus • Circulation then loops back around to allow blood to pass through the heart • Blood is then reoxygenated so that it can return to circulation. Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Capillary Beds • In organs with heavy nutrient and oxygen requirements, such as the liver, the capillary bed may be quite extensive • Point to remember: • At any given time capillary beds usually holds up to around 25% of the total blood supply of a human Copyright: Edited with permission from Open. Stax Biology for AP Courses, Open. Stax, and Rice University

Capillary Beds - Summary • Forms a maize of capillaries which lies between Artery and vein system. • When sphincter is relaxed (OPEN) – Blood flows through capillaries • Allows capillary exchange to occur • When sphincter is contracted (SHUT) – Blood flows through a shunt that carries it directly from an Arteriole to a Venule. – Known as an arteriovenous shunt

Capillary Exchange • Remember Osmosis? • Arterial end of capillary – Blood pressure HIGHER than osmotic pressure • Water leaves the bloodstream From the wikimedia free licensed media file repository

Capillary Exchange • Remember Osmosis? • Midsection • Small molecules follow concentration gradient • O 2 & nutrients leave. Wastes and CO 2 enter From the wikimedia free licensed media file repository

Capillary Exchange • Remember Osmosis? • Venous end of capillary • Osmotic pressure HIGHER than blood pressure • Water enters the bloodstream About 85% water return form arterial end. From the wikimedia free licensed media file repository

Disorders of the Circulatory System • Anemia - lack of iron in the blood, low RBC count • Leukemia - white blood cells proliferate wildly, causing anemia • Hemophilia - bleeder’s disease, due to lack of fibrinogen in thrombocytes • Heart Murmur - abnormal heart beat, caused by valve problems • Heart attack - blood vessels around the heart become blocked with plaque, also called myocardial infarction

Cardiovascular Disease • Also called heart disease is a class of diseases that involve the heart, the blood vessels (arteries, capillaries, and veins) or both. • Any disease that affects the cardiovascular system, principally cardiac disease, vascular diseases of the brain and kidney, and peripheral arterial disease. • Leading cause of deaths worldwide, though, since the 1970 s, cardiovascular mortality rates have declined in many highincome countries • At the same time, cardiovascular deaths and disease have increased at a fast rate in low- and middle-income countries

Cardiovascular Disease • Atherosclerosis: – An artery wall thickens as a result of the invasion and the accumulation of white blood cells • This accumulation of the WBCs is termed "fatty streaks" early on because of appearance being similar to that of marbled steak. • These accumulations contain both living, active WBCs (producing inflammation) and remnants of dead cells, including cholesterol and triglycerides. From Wikimedia Commons, a freely licensed media file repository

Effects of Aging on the Heart • Gradual changes in heart function, minor under resting condition, more significant during exercise • Hypertrophy of left ventricle • Maximum heart rate decreases • Increased tendency for valves to function abnormally and arrhythmias to occur • Increased oxygen consumption required to pump same amount of blood