Circulatory System PDF

Circulatory System Dr Emily Wong 1 System Overview The three principal components that make up the circulatory system are: – the heart (the pump) – the blood vessels (the pipes) – the blood (the fluid to be moved) The cardiovascular system function is impacted by the endocrine system, nervous system...

Circulatory System Dr Emily Wong 1 System Overview The three principal components that make up the circulatory system are: – the heart (the pump) – the blood vessels (the pipes) – the blood (the fluid to be moved) The cardiovascular system function is impacted by the endocrine system, nervous system and kidneys. 2 Blood - Blood is responsible for transporting oxygen to the cells and removing carbon dioxide for excretion by the lungs. - Blood carries nutrients, ions, water, hormones and enzymes to all body cells and carries away the waste products. - Blood regulates the pH and temperature of the body. - Blood is composed of the liquid proportion plasma and solids called the formed elements. Plasma made up 55% of the total blood volume, 91% is water. 3 System Overview There are 2 “loops” in the cardiovascular system: Systemic and pulmonary. The pulmonary loop carries oxygen-poor blood to the lungs and back to the heart. The systemic loop carries blood from the heart to the rest of the body. This is considered a “closed system,” i.e., leaks are bad. 4 Pulmonary and Systemic Circulation The circulatory system keeps approximately five liters (for the average adult human) of blood circulating constantly through the body. Its most important organ is the heart that double pump that forces the blood through the blood vessels. The body's circulatory system really has three distinct parts: – circulation through the lungs (pulmonary circulation), – the heart (coronary circulation), – and the rest of the system (systemic circulation). 5 www.pennmedicine.org Plasma proteins are albumin to maintain osmotic pressure and water balance. Globulin antibodies help the immune system and fibrinogen, an essential component for blood clotting. The formed elements are erythrocytes or red blood cells (RBC), leucocytes or white blood cells (WBC), and thrombocytes or platelets. RBC contains hemoglobin that carries oxygen to the rest of the body and then carries away carbon dioxide. www.tikirobot.net 6 Pulmonary circulation, in which blood goes from the heart to the lungs and back to the heart, is when the blood exchanges carbon dioxide, a waste product it has picked up from the rest of the body, for oxygen, which it will carry to the rest of the body. The de-oxygenated, carbon-dioxide-laden blood returning to the heart from the body enters the right side of the heart through two veins (one for blood coming from the lower half of the body, the other for blood from the upper half). The heart pumps it to the lungs, where it drops off carbon dioxide to be excreted (exhaled), and picks up oxygen. The blood then returns to the left side of the heart, which pumps it out to the rest of the body. 7 8 The Pulmonary and Systemic Circulation The flow of the blood from the heart to the rest of the body and back to the heart is systemic circulation. The heart pumps the now oxygen-rich blood out through the arteries, which are wide, thick-walled blood vessels. Then the blood moves into smaller vessels called capillaries, where it releases the oxygen and nutrients it carries to the body's cells. At the same time, it picks up waste products like carbon dioxide. The blood then flows into the veins, which carry it back to the heart. 9 The Pulmonary and Systemic Circulation Structure of the blood vessels The blood vessels consist of arteries, arterioles, capillaries, venules, and veins. All blood is carried in these connecting vessels. The arteries, having thicker vessel wall, carry blood away from the heart and www.accessexcellence.org bear the highest blood pressures. Because arteries are elastic, they narrow (recoil) passively when the heart is relaxing between beats and thus help maintain blood pressure. Due to the thicker smooth muscle layer, the lumen of artery is usually smaller than that of the vein. The arteries branch into smaller and smaller vessels, eventually becoming very small vessels called arterioles. Arteries and arterioles have muscular walls that can adjust their diameter to increase or decrease blood flow to a particular part of the body. 10 11 Structure of Blood Vessels Capillaries are tiny, extremely thin-walled vessels that act as a bridge between arteries (which carry blood away from the heart) and veins (which carry blood back to the heart). The thin walls of the capillaries allow oxygen and nutrients to pass from the blood into tissues and allow waste products to pass from tissues into the blood. Blood flows from the capillaries into very small veins called venules, then into the veins that lead back to the heart. Veins have much thinner walls than arteries, largely because the pressure in veins is so much lower. Veins can widen (dilate) as the amount of fluid in them increases. Valves are present in veins only to allow the blood returning to heart and prevent the backflow of blood. 12 Structure of Blood Vessels The Capillary Bed The capillary bed is an important component of the skin. "Capillary bed" is the term used to refer to the network of capillaries (small blood vessels). These capillary networks are supplied with blood by arterioles and drained of blood by venules. Each capillary is a tiny blood vessel with walls that are only one cell thick, and so enable the exchange of oxygen, carbon dioxide, water, and salts between the blood varied through the capillary vessels and the surrounding tissues. 13 Vasodilation Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When vessels dilate, the flow of blood is increased due to a decrease in vascular resistance. Therefore, dilation of arterial blood vessels (mainly arterioles) leads to a decrease in blood pressure. The response may be intrinsic (due to local processes in the surrounding tissue) or extrinsic (due to hormones or the nervous system). Additionally, the response may either be localized to a specific organ, or systemic seen throughout the entire systemic circulation. 14 The blood vessels system of skin The human skin is supplied with nutrients and oxygen via a blood vessel system. Blood supplies the skin layer where cell growth is the strongest with nutrients. The blood vessel system of the skin provides nutrients to the cells and tissues; helps regulate body temperature and supports blood pressure regulation. www.medterms.com 15 16 The Blood Vessels System of the Skin The dermis and subcutis are pervaded with a complex system of blood vessels, while the epidermis is free of vessels. The blood supply to the skin (cutaneous blood supply) is provided for by arteries and veins, which carry blood to and away from the heart and by a microvascular vessel network. A superficial network comprises the interface between papillary and reticular dermis, while a lower network is located on the border between dermis and subcutis. Vertical vessels connect both networks and thus make it complete. 17 The Blood Vessels System of the Skin In the adjoining cutis and subcutis, as well as in the papillary and the stratum reticulare of the cutis, arteries (which are shown in red in our diagram) and veins (in blue) form network-like structures. From here, capillary loops arise into the papillaries of the connective tissue. The dermis, which mainly consists of connective tissue fibres, shows closely intertwined structures with the epidermis (papillaries). In these subpapillary spaces, arteries and veins are very densely structured. This finely capillarized vessel system supplies the bordering zone and the epidermis, which is free of vessels. Besides the nerves, the subcutis contains the larger blood vessels for the upper skin layers. 18 The Blood Vessels System of the Skin The skin’s blood vessel system supplies the cells and tissue with nutrients and supports the blood pressure regulation. A complex interplay between blood vessel system, warmth receptors of the skin, central nervous system and sebaceous glands is in charge of regulating the body’s heat balance. Cutaneous Circulation Major function of skin is acting as a regulator of body temperature. The skin has a blood supply from many small arterioles - these are small blood vessels take blood at higher pressure into the capillary networks. The capillary networks are made up of a great many tiny vessels with very thin walls. From these networks the blood flows back into venules - these are small veins that take the blood back to the larger veins and then ultimately the heart. Blood flow in the capillary networks is controlled by the body using both hormones and nerves (the sympathetic nervous system). Body HOT COLD Capillary network Functions Skin color Dilate (Vasodilation) Blood flow Heat loss Pink or red Constrict (Vasoconstiction) Blood flow Heat loss White 19 Skin Thermoregulation Body temperature is normally maintained at 37℃ It is controlled by a feedback system, that is, information about the temperature of the body For example from the temperature sensitive receptors in the skin, is fed back to the hypothalamus, the temperature-regulating centre of the brain. The brain then sends messages to parts of the body, including the skin, to keep heat in or to lose excess heat. If the body is too cold, the hairs are raised by small muscles to trap a layer of air near the skin giving the appearance of goose bumps. Air is an insulator so this helps to keep heat in. Shivering, a trembling of the muscles produces more heat and, during shivering, there is usually an increase in the rate of respiration, which also warms the surrounding tissues. 20 www.utmedicalgroup.com 21 Skin Thermoregulation The rate of heat loss depends on the amount of blood flowing through the skin. When cold, blood is kept away from the surface by vasoconstriction that is, narrowing of the blood vessels leading to the skin capillaries. Very little blood then flows through these capillaries and this minimizes the loss of heat from the skin. Sweating If the body is too hot, the blood vessels leading to the skin capillaries dilate, known as vasodilation. This allows lots of blood to flow near Reddish skin the surface and heat is lost through the skin by convection and radiation. To further reduce the body temperature, sweating occurs. Here the water evaporates, which removes heat from the skin therefore cooling the skin down. COLD When you feeling hot, blood vessels dilates to increase heat loss and vice versa. 22 Skin Thermoregulation HOT 23 Skin Thermoregulation If the body is too cold… 24 Skin Thermoregulation If the body is too hot… Mitral valve = bicuspid valve = left atrioventricular (AV) valve Tricuspid valve = right atrioventricular (AV) valve 25 26 Atria Ventricle Thin walled The ventricle walls are thicker because they pump blood greater distances. Blood is pumped via vena cava in the right heart or via the pulmonary veins through the left heart The left ventricle walls are thicker because they pump blood through the body where the resistance to blood flow is greater. 27 Blood Pressure Hydrostatic pressure exerted by blood on the walls of a blood vessel Measured in mmHg Systolic pressure is when the maximum arterial pressure reached during peak ventricular ejection Diastolic pressure is when the minimum arterial pressure occurs just before ventricular ejection begins (ventricular relaxation). Either the systolic or diastolic pressure can be elevated independently of the other number. Hypertension is a disease that affects millions of people. 28 * Systolic Pressure Normal Adult 90 *Source: Harvard Medical School 29 Difference between systolic and diastolic bp is called pulse pressure Pulse pressure increases with age due to the hardening of arteries e.g. atherosclerosis 30 31 32 33 Measurement of Systemic Arterial Pressure 34 Blood Vessels Blood vessels can be divided into arteries (muscular and conduit), arterioles, capillaries, venules and veins. All arteries carry blood away from the heart. All veins carry blood to the heart. In general, arteries carry oxygenated blood and veins carry deoxygenated blood. The exception to this is the pulmonary arteries carry deoxygenated blood to the lungs to get oxygenated and the pulmonary veins carry oxygenated blood to the heart to get sent to the rest of the body. 35 The Heart Anatomy 36 Heart Layers Epicardium: This is the most superficial (outer) layer. It is the visceral layer of the serous pericardium. Myocardium: This is the middle layer of the heart muscle. It is composed of cardiac muscle and forms the bulk of the heart mass. This is the layer that contracts. Endocardium: This is the inner layer of the heart. It is of endothelium which rests on a thin layer of connective tissue. It is continuous with the lining of the blood vessels entering and leaving the heart. 37 Heart Valves 38 Cardiac Muscle The cardiac muscle cells of the myocardium are arranged in layers that are tightly bound together and completely encircle the blood-filled chambers. When the walls of a chamber contract, they come together like a squeezing fist and exert pressure on the blood they enclose. Every heart cell contracts with every beat of the heart, so these cells do not get much rest. The heart has only a limited ability to replace its muscle cells. Recent experiments suggest that only about 1% of heart muscle cells are replaced per year. This is why heart attacks that result in myocyte death are so hard to fix. 39 Cardiac Communication Approximately 1% of cardiac cells do not function in contraction, but have specialized features that are essential for normal heart excitation. These cells constitute a network known as the conducting system of the heart and are in electrical contact with the cardiac muscle cells via gap junctions. The conducting system initiates the heartbeat and helps spread the impulse rapidly throughout the heart. Certain cells in the atria secrete the peptide hormone called atrial natriuretic peptide (regulates the concentration of Na+ in the extracellular fluid). 40 Innervation of the Heart The heart is innervated by both sympathetic and parasympathetic nerve fibers. The SNS innervates the entire heart muscle and node cells and releases norepinephrine (NE), whereas the PSNS innervates the node cells and releases primarily acetylcholine (ACh). The receptors for NE on cardiac muscle are mainly betaadrenergic receptors (β receptors). The hormone epinephrine, from the adrenal medulla, binds to the same receptors as NE and exerts the same actions on the heart. The receptors for acetylcholine are of the muscarinic (M) type. 41 Innervation of the Heart 42 Blood Supply The blood being pumped through the heart chambers does not exchange nutrients and metabolic end products with the myocardial cells. They receive their blood supply via arteries that branch from the aorta. The arteries supplying the myocardium are the coronary arteries, and the blood flowing through them is the coronary blood flow. The coronary arteries exit from behind the aortic valve cusps in the very first part of the aorta and lead to a branching network of small arteries, arterioles, capillaries, venules, and veins similar to those in other organs. Most of the cardiac veins drain into a single large vein, the coronary sinus, which empties into the right atrium. 43