Human Biology: Circulation - Heart and Blood Vessels

Chapter 7 Circulation: The Heart and Blood Vessels Cecie Starr | Beverly McMillan © Cengage Learning 2016  7.1 The Cardiovascular System: Moving Blood Through the...

Chapter 7 Circulation: The Heart and Blood Vessels Cecie Starr | Beverly McMillan © Cengage Learning 2016  7.1 The Cardiovascular System: Moving Blood Through the Body The cardiovascular system is built to rapidly transport blood to every living cell in the body – Cardiovascular system consists of heart (Greek word kardia) and blood vessels (Latin word vasculum). Heart – Muscular pump that generates pressure for pumping blood Blood vessels – Blood transport tubes of varying diameter © Cengage Learning 2016  Blood Vessels Arteries receive blood from the heart – Large diameter vessels Arterioles – Smaller and narrower than arteries Capillaries – Very narrow blood vessels Venules – Receive blood from capillaries Veins transport blood back to the heart © Cengage Learning 2016  Carotid Arteries Jugular Veins Ascending Aorta Superior Vena Cava Pulmonary Arteries Pulmonary Veins Heart Coronary Arteries Hepatic Vein Brachial Artery Renal Vein Carries Renal Artery Delivers Inferior Vena Cava Abdominal Aorta Iliac Veins Iliac Arteries Femoral Vein Femoral Artery © Cengage Learning 2016  Capillaries Bed © Cengage Learning 2016  The Cardiovascular System is Linked to The Lymphatic System Heart’s pumping action puts pressure on blood causes small amounts of water and some proteins to move into extracellular fluid The lymphatic system is a network of drainage vessels – picks up excess extracellular fluid and usable substances and returns them to the cardiovascular system – It includes organs with major roles in body defenses © Cengage Learning 2016  Blood Circulation is Essential for Maintaining Homeostasis Blood circulation is essential to maintain homeostasis – Brings oxygen and nutrients to body cells – Carries away metabolic wastes Blood picks up and delivers a diverse array of substances – Digestive system – Urinary system – Respiratory © Cengage Learning 2016 system © Cengage Learning 2016  7.2 The Heart: A Muscular Double Pump Heart is located more or less in the center of chest (Thoracic cavity) Myocardium – Heart consists mostly of cardiac muscle tissue called Myocardium Pericardium (Epicardium) – Tough, fibrous sac that surrounds and protects the heart Endocardium – Smooth lining inside heart Endocardium is composed of chambers connective tissues and a layer epithelial cells. © Cengage Learning 2016  The heart has two halves and four chambers Heart has two halves – Right and left – Each half has two chambers Atrium and ventricle Atrioventricular (AV) valve – Flaps of membrane separate the chambers Serve as one-way valves Pulmonary valve “Semilunar valve” – Controls blood flow to the pulmonary artery Aortic valve “Semilunar valve” – controls blood flow to the aorta © Cengage Learning 2016  The heart has two halves and four chambers: The AV valve in the right half of the heart is called a tricuspid valve because its three flaps come together in pointed cusps. In the heart’s left half, the AV valve consists of just two flaps; it is called the bicuspid valve or mitral valve. Tough, collagen-reinforced strands (chordae tendineae, or “heartstrings”) connect the AV valve flaps to cone-shaped muscles that extend out from the ventricle wall. When a blood-filled ventricle contracts, this arrangement prevents the flaps from opening backward into the atrium. Each half of the heart also has a. valve between the ventricle and the arteries leading away from it © Cengage Learning 2016 © Cengage Learning 2016  The heart has two halves and four chambers: The pulmonary valve controls blood flow to the pulmonary artery, and the aortic valve controls blood flow to the aorta. Because both these valves are shaped like a half- moon, they are also known as “semilunar” valves. During a heartbeat, the valves open and close in ways that keep blood moving in one direction, out of the heart. © Cengage Learning 2016  superior vena cava (flow from head, arms) aorta trunk of pulmonary right left pulmonary valve arteries (to lungs) lung lung (closed) aortic valve (closed) left right pulmonary pulmonary veins (from lungs) veins (from lungs) Right atrium Left atrium left AV valve (open) right AV valve (open) Left ventricle Right ventricle pericardium pericardiu inferior vena cava cardiac muscle m diaphragm (from trunk, legs) (myocardium) B septum endocardium A A: From Frances Sienkiewicz Sizer; Eleanor Noss W hitney, Nutrition: Concepts and Controversies © 2002 Cengage Learning; B–C: © Cengage Learning Right AV Left AV Aortic and C valve valve pulmonary valves © Cengage Learning 2016  In a ‘’ heartbeat the heart’s chambers contract, then relax © Cengage Learning 2016  A physician’s stethoscope detects this “lub-dup” At each “lub,” the AV valves are closing simultaneously as the two ventricles contract. At each “dup,” the aortic and pulmonary valves are closing as the ventricles relax © Cengage Learning 2016  4 Fluid pressure in filling atria opens AV valves; blood flows 1 Atria contract, and into ventricles. fluid pressure in ventricles rises sharply. 3 Ventricles relax even as Heart the atria begin sounds to fill and start another cycle. 2 Ventricles contract; blood is pumped into the pulmonary artery and the aorta. © Cengage Learning 2016  4 Fluid pressure in filling atria opens AV 1 Atria contract, and valves; blood flows fluid pressure in into ventricles. ventricles rises sharply. 3Ventricles relax Heart sounds even as the atria begin to fill and start another cycle. 2Ventricles contract; blood is pumped into the pulmonary artery and the aorta. Stepped Art © Cengage Learning 2016 Figure 7.6 p125  7.3 The Two Circuits of Blood Flow Every day, blood travels about 12000 miles Each half of the heart pumps blood and makes basis for two cardiovascular circuits Each circuit has own set of arteries, arterioles, capillaries, venules, and veins © Cengage Learning 2016  Pulmonary Circuit The circuit begins as blood from tissues enter right atrium, then moves through AV valve into right ventricle, this blood is fairly low in oxygen or high in CO2 (deoxygenated blood). When the ventricles contracts, blood moves through right semilunar valve into pulmonary artery, then into right and left pulmonary arteries, which carries this blood to lungs. Blood picks up oxygen in the lungs and gives up carbon dioxide that will be exhaled. The freshly oxygenated blood returns through two sets of pulmonary veins to the heart’s left atrium, completing the circuit. © Cengage Learning 2016  Systemic Circuit Blood travels to and from tissues Oxygenated blood pumped by the left half of the heart moves through the body and returns to the right atrium Circuit begins when the left atrium receives blood from pulmonary veins, and this blood moves through an AV (bicuspid) valve to the left ventricle Subsets of system vessels (in systemic circuit) serve the heart and liver For example, in a resting person, each minute a fifth of the blood pumped into the systemic circulation enters the kidneys via renal arteries © Cengage Learning 2016  Deoxygenated blood returns to the right half of the heart, where it enters the pulmonary circuit Both the pulmonary and the systemic circuits, blood travels through arteries, arterioles, capillaries, and venules, finally returning to the heart in veins – Blood from the head, arms, and chest arrives through the superior vena cava – The inferior vena cava collects blood from the lower part of the body Heart pumps constantly, the volume of flow through the entire system each minute is equal to the volume of blood returned to the heart each minute © Cengage Learning 2016  right pulmonary left pulmonary artery artery capillary capillary bed capillary beds of head and bed of of left lung upper extremities pulmonary right (to systemic trunk (to pulmonary aorta lung circuit) Lungs circuit) (from (from pulmonary systemic circuit) B circuit) pulmonary A veins systemic pulmonary circuit circuit for hear for blood heart blood flow t flow (© Cengage Learning) 100% capillary beds of other lungs organs in thoracic cavity heart’s right half heart’s left half diaphragm (muscular partition 21% between thoracic and digestive tract 6% abdominal cavities) liver kidneys 20% skeletal muscle 15% capillary bed of liver 13% brain 9% skin 5% hepatic portal vein © Cengage bone Learning 3% cardiac muscle 8% C all other regions Jose Luis Pelaez, Inc./Bridge/Corbis capillary beds of intestines capillary beds of other abdominal organs (© Cengage Learning) and lower extremities © Cengage Learning 2016  Subsets of Systemic Vessels Serve the Heart and Liver Coronary circulation Arteries and veins that serve only the heart provide what is called the Coronary circulation Two coronary arteries service most of the cardiac muscle They branch off the aorta, the major artery carrying blood away from the heart Coronary veins empty blood into the right atrium © Cengage Learning 2016  Hepatic Portal System Blood leaving the liver’s capillary bed enters the general circulation through a hepatic vein © Cengage TheLearning liver receives 2016 oxygenated blood via the hepatic artery  7.4 How Cardiac Muscle Contracts Electric signals from “pacemaker” cells drive the heart’s contractions – Cardiac muscle cells branch, then link to one another at their endings. – Gap junctions called intercalated discs span both plasma membranes of neighboring cells. – With each heartbeat, signals for contraction spread so fast across the junctions that cardiac muscle cells contract together, as a single unit. © Cengage Learning 2016  Where do the signals for heart contractions come from? About 1 percent of cardiac muscle cells function as the cardiac conduction system. – These cells do not contract, Instead, some of them are self-exciting “pacemaker” cells, spontaneously generate and conduct electrical impulses – Those impulses are the signals that stimulate contractions in the heart’s contractile cells – Because the cardiac conduction system is independent of the nervous system, the heart will keep right on beating even if all nerves leading to it are cut! © Cengage Learning 2016  Excitation begins with a cluster of cells called Sinoatrial (SA) node in the upper wall of the right atrium. About 70 times per minute, SA node generates signals that stimulate waves of excitation, which spread swiftly over both atria and causes them to contract. It then reaches the atrioventricular (AV) node in the septum dividing the two atria. When a stimulus reaches the AV node, it slows but keeps moving along bundles of conducting fibers that extend to the ventricles. At places along each bundle, cells called Purkinje fibers pass the signal on to contractile muscle cells in each ventricle. The slow conduction in the AV node is an important part of this sequence. It gives the atria time to finish contracting before the wave of excitation spreads to the ventricles. © Cengage Learning 2016 © Cengage Learning 2016  Of all cells of the cardiac conduction system, the SA node fires off impulses at the fastest rate and is the first region to respond in each cardiac cycle. It is called the “intrinsic cardiac pacemaker” because its self-generated rhythmic firing is the basis for the normal rate of heartbeat. People whose SA node chronically malfunctions may have an artificial pacemaker implanted to provide a regular stimulus for their heart contractions. © Cengage Learning 2016  R T P Q S Sinoatrial Left atrium (SA) node Right atrium Atrioventricular (AV) node Bundle of conducting muscle fibers Right ventricle Left ventricle Purkinje fibers https://www.youtube.com/watch?v=FIeCPC7Hpf8&t=20s © Cengage Learning 2016  The Nervous System Adjusts Heart Activity The nervous system can adjust the rate and strength of cardiac muscle contraction. Stimulation by one set of nerves can increase heart activity, while stimulation by another set of nerves can slow it. The control centers for these adjustments are in the spinal cord and parts of the brain. © Cengage Learning 2016  7.5 Blood Pressure © Cengage Learning 2016  Values for systolic and diastolic pressure provide important health information. Chronically elevated blood pressure, or hypertension, can be associated with various ills, such as atherosclerosis. © Cengage Learning 2016  Hypertension & Hypotension Hypertension can lead to a stroke or heart attack. – Personal blood pressure monitors are marketed as tools for keeping tabs on blood pressure. Abnormally low blood pressure is called Hypotension. – This condition can develop when for some reason there is not enough water in blood plasma for instance, if there are too few proteins in the blood to “pull” water in by osmosis. – A large blood loss also can cause blood pressure to plummet. Such a drastic decrease is one sign of a dangerous © Cengagecondition Learning 2016 called circulatory shock.  7.6 Structure and Function of Blood Vessels © Cengage Learning 2016  Arteries are Large, Strong Blood Pipelines The wall of an artery has several tissue layers.  The outer layer is mainly collagen, which anchors the vessel to the tissue it runs through  A thick middle layer of smooth muscle is sandwiched between thinner layers containing elastin  The innermost layer is a thin sheet of endothelium  Together these layers form a thick, muscular, and elastic wall In a large artery the wall bulges slightly under the pressure surge caused when a ventricle contracts, you can feel blood surges as your pulse  The bulging of artery walls helps keep blood flowing on through the system In addition to having stretchable walls, arteries also have large diameters. For this reason, they present little resistance to blood flow, so blood pressure in large arteries is quite stable. © Cengage Learning 2016  Arterioles Function as Control Points for Blood Flow Arteries branch into narrower arterioles, which have a wall built of rings of smooth muscle over a single layer of elastic fibers Arterioles dilate (enlarge in diameter) when the smooth muscle relaxes, and they constrict (shrink in diameter) when the smooth muscle contracts Arterioles offer more resistance to blood flow than other vessels As the blood flow slows, it can be controlled in ways that adjust how much of the total volume goes to different body regions – For example, you may feel sleepy after a large meal in part because control signals divert blood away from your brain and into vessels serving your digestive system. © Cengage Learning 2016  Capillaries are Specialized for Diffusion Human body has about 2 miles of arteries and veins but have 62,000 miles of capillaries. These tiny vessels often interlace in capillary beds, and their structure allows substances to readily diffuse between blood and tissue fluid. Specifically, a capillary has the thinnest wall of any blood vessel—a single layer of flat endothelium. © Cengage Learning 2016  The body’s capacity for maintaining homeostasis depends heavily on the diffusion of gases (oxygen and carbon dioxide), nutrients, and wastes that occurs across the walls of capillaries. Blood can’t move fast in capillaries. However, because there are so many capillaries and capillary beds, they present less total resistance to flow than do the arterioles leading into them, so overall blood pressure drops more slowly in them. © Cengage Learning 2016  Venules and Veins Return Blood to the Heart Capillaries merge into venules, “little veins,” which in turn merge into large-diameter veins – Venules function a little like capillaries, some solutes diffuse across their relatively thin walls. Veins are large-diameter, low-resistance transport tubes to the heart – Their valves prevent backflow, when blood starts moving backward due to gravity, it pushes the valves closed. – Unlike an arterial wall, a vein wall can bulge quite a bit under pressure. Thus, veins are reservoirs for variable volumes of blood, in an adult can hold up to 50 to 60% of the total blood volume. © Cengage Learning 2016  Venules and Veins When a person’s blood must circulate faster (for instance, during exercise), the smooth muscle in veins contracts. – The wall stiffens, the vein bulges less, and venous pressure rises so more blood flows to the heart. – Venous pressure also rises when contracting skeletal muscle especially in the legs and abdomen bulges against adjacent veins. – Muscle activity helps return blood through the venous system. – Obesity, pregnancy, and other factors can weaken venous valves. – The walls of a varicose vein have become overstretched because, over time, weak valves have allowed blood to pool there. © Cengage Learning 2016 © Cengage Learning 2016  Blood Vessel Roles in Homeostasis Many vessels have roles in homeostatic mechanisms that help control blood pressure Some arteries, all arterioles, and even veins have roles in homeostatic mechanisms that help maintain adequate blood pressure over time. Mechanisms of maintaining blood pressure I. Vasodilation: enlargement of vessel diameter Centers in the brain monitor resting blood pressure. When the pressure rises abnormally, they order slower, less forceful heart contractions. They also order smooth muscle in arterioles to relax. The result is vasodilation an enlargement (dilation) of the vessel diameter. © Cengage Learning 2016  II. Vasoconstriction: narrowing of vessel diameter When the centers detect an abnormal decrease in blood pressure, they command the heart to beat faster and contract more forcefully. Neural signals also cause the smooth muscle of arterioles to contract. The result is vasoconstriction, a narrowing of the vessel diameter. Hormonal Control In some parts of the body arterioles have receptors for hormones that trigger vasoconstriction or vasodilation, thus helping to maintain blood pressure. © Cengage Learning 2016  Baroreceptor Reflex – Pressure sensors called baroreceptors monitor changes in arterial pressure Brain uses information to coordinate heartbeats with blood vessel diameter changes Mechanism – Carotid arteries in the neck, in the arch of the aorta, and elsewhere contain pressure sensors called baroreceptors. – The sensors monitor changes in mean arterial pressure and send signals to centers in the brain. – The brain centers use this information to coordinate the rate and strength of heartbeats with changes in the diameter of arterioles and veins. – The baroreceptor reflex helps keep blood pressure within normal limits in the face of sudden changes, such as when you jump up from a chair. © Cengage Learning 2016  7.7 Capillaries: Where Substances Move Between Blood and Tissues Capillaries deliver blood close to nearly all body cells – Blood travels slowly to allow diffusion to occur – Most solutes that enter and leave the bloodstream diffuse across capillary walls Some substances pass through pores in capillary walls – Pores filled with water – Allow passage for substances that cannot diffuse through lipid bilayer © Cengage Learning 2016  A vast network of capillaries brings blood close to nearly all body cells Human body comes equipped with 40 billion thin capillaries At least one of these tiny vessels is next to living cells in nearly all body tissues. In addition to forming a vast network of vessels, this branching system also affects the speed at which blood flows through it. – Flow is fastest in the aorta, quickly “loses steam” in the more numerous arterioles, and slows to a relative crawl in the narrow capillaries. – Flow of blood speeds up again as blood moves into veins for the return trip to the heart. © Cengage Learning 2016  Why have such an extensive system of capillaries in which blood slows to a snail’s pace? Many of these exchanges occur by diffusion but diffusion is a slow process that is not efficient over long distances. In a large, multicellular organism such as a human, having billions of narrow capillaries solves both these problems. There is a capillary close to nearly every cell, and in each one the blood is barely moving. – As blood “creeps” along in capillaries, there is time for the necessary exchanges of fluid and solutes to take place. In fact, most solutes that enter and leave the bloodstream diffuse across capillary walls. © Cengage Learning 2016  Some substances pass through pores in capillary walls Slit like “pores” are filled with water, are passages for substances that cannot diffuse through lipid bilayer of the cells that make up the capillary wall, but that can dissolve in water. © Cengage Learning 2016  Bulk Flow When the blood pressure inside a capillary is greater than pressure from the extracellular fluid outside, water and solutes may be forced out of the vessel a type of fluid movement called “bulk flow”. Various factors affect this process, but on balance, a little more water leaves capillaries than enters them. © Cengage Learning 2016  Role of Lymphatic System The lymphatic system, which consists of lymph vessels, lymph nodes, and some other organs, receives fluid that leaves capillaries and returns it to the blood. – This system also plays a major role in body defense. Overall, the movements of fluid and solutes into and out of capillaries help maintain blood pressure by adding water to, or subtracting it from, blood plasma. The fluid traffic also helps maintain the proper fluid balance between blood and surrounding tissues. © Cengage Learning 2016  Blood in capillary beds flows onward to venules Capillary beds are the “turn around points” for blood in the cardiovascular system. They receive blood from arterioles, and after the blood flows through the bed it enters channels that converge into venules the beginning of its return trip to the heart. At the point where a capillary branches into the capillary bed, a wispy ring of smooth muscle wraps around it, called a precapillary sphincter, and it regulates the flow of blood into the capillary. The smooth muscle is sensitive to chemical changes in the capillary bed. – It can contract and prevent blood from entering the capillary, or it can relax and let blood flow in. © Cengage Learning 2016 © Cengage Learning 2016 © Cengage Learning 2016  Capillary Action in the Body For example, if you sit quietly and listen to music, only about one tenth of the capillaries in your skeletal muscles are open. But if you decide to get up and dance, precapillary sphincters will sense the demand for more blood flow to your muscles to deliver oxygen and carry away carbon dioxide. Many more of the sphincters will relax, allowing a rush of blood into the muscle tissue. The same mechanism brings blood to the surface of your skin when you blush or become flushed with heat. © Cengage Learning 2016 © Cengage Learning 2016