Blood Vessels Notes PDF

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. BLOOD VESSELS Carrying away from the Heart: Arteries will divide into smaller arteries called Arterioles. Arterioles will further divide into smaller vessels called capillaries. Capillaries will permit gas exchange...

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. BLOOD VESSELS Carrying away from the Heart: Arteries will divide into smaller arteries called Arterioles. Arterioles will further divide into smaller vessels called capillaries. Capillaries will permit gas exchange to the organ or muscle. Carrying toward the Heart: Capillaries will reunite to form a vessel called a venule. Venules will reunite to form a vessel called a vein. Veins will carry blood toward the heart. Arteries - Aorta = Largest artery in the body * 3 parts of the aorta: Refer to your 1. Ascending aorta diagram for 2. Arch of aortas branches of each 3. Descending aorta (thoracic and abdominal) part of the aorta - Walls of an Artery: The walls of the arteries are comprised of three tunics (layers) 1. Tunica intima - inner most layer - The layer in contact with the blood. - It consists of: 1) Simple squamous epithelium – surrounded by the CT basal lamina 2) CT basal lamina (basement membrane) – function is for structural reinforcement, filtration, and compartmentalization. 3) Elastic fibers – provides elasticity 2. Tunica media – middle, largest and most developed layer - This is the layer that provides: 1) Support to the vessel 2) Allows changes in vessel diameter to regulate blood flow and BP - It consists of mostly smooth muscle. * These smooth muscle cells and fibers are arranged in a circular or spiral fashion around the vessel. 1 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. * Smooth muscle of the tunica media is innervated by the ANS: In Sympathetic Stimulation - norepinephrine causes vasoconstriction, which increases blood pressure In Parasympathetic Stimulation - acetylcholine causes vasodilation, which decreases blood pressure 3. Tunica externa (adventitia) - outer most layer - It consists of: Proportions of these 1) Mostly collagenous connective tissue are dependent on the 2) Varying amounts of elastic fibers type of vessel - The outermost layer binds the vessels to surrounding tissue structures. - Lumen of an artery = hollow center through which blood flows - Two Major Properties of Arteries: 1. Elasticity of the Artery * When the ventricles contract, arteries expand to accommodate the extra blood. However, it cannot handle a large capacity. * This process of expansion and then recoiling serves to absorb the shock of ventricular contractility and assists the forward movement of blood flow called Pulsitile Flow. * Arteries = high pressure, low capacity/volume Veins = low pressure, high capacity/volume 2. Contractility of the Artery * The ability to contract comes from its smooth muscle tissue coiled around the tunica media layer of the artery. * When smooth muscle contracts, the wall around the lumen is squeezed; therefore, narrowed. * Vasoconstriction = decrease in the size of the lumen Vasodilation = increase in the size of the lumen - The only artery that carries poorly oxygenated blood in post-natal life is the pulmonary artery. 2 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. Arterioles - Are the smallest vessels with 3 distinguishable layers in the wall. These layers have the same names as the arterial walls: intima, media, and adventia. - When arterioles branch into capillaries, the tunica media and adventitia disappear, leaving only 1 layer of simple epithelium (tunica intima) with a basement membrane. - The thickness of the walls is similar to the diameter of the lumen. - Divert and direct blood flow – the contraction of certain arterioles can shunt blood from one region to another. - Contraction and relaxation of arterioles are primarily under autonomic control. Sympathetic control – norepinephrine (vasoconstriction/increased blood pressure) Parasympathetic control – acetylcholine (vasodilation/decreases blood pressure) - Other factors that control arteriole smooth muscle contraction and regulate blood pressure: 1. Epinephrine (sympathetic stimulation) 2. Angiotensin – details will be discussed later 3. Atrionatremic factor (ANF) – regulates the BP of the heart 4. Kinins – released at wound sites 5. Histamine – released during tissue injury or immune reaction Capillaries - Considered to be the smallest and most numerous of the blood vessels. - Contain only 1 layer of simple epithelium (tunica intima) with a basement membrane. - Their structure of thin walls permits exchange of nutrients and wastes between blood and cells in tissues. The thick walls of arteries and veins present too great a barrier for any exchanges. - The diameter of a capillary is so small that 1 RBC must pass through one at a time. - The distribution of capillaries varies with metabolic demand. Skeletal muscle, the liver and the kidney have the most extensive capillary distribution. - Movement from the arterioles into the capillaries is controlled by: 3 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. 1. Hydrostatic pressure Fluid movements (bulk flow) (simple diffusion) of water also takes place across the capillary walls. 2. Osmotic pressure 3. Precapillary Sphincters * At their sites of origin, these sphincters control the flow of blood entering a capillary * Sphincters consist of bands of smooth muscle cells, that, when contracted, blood through the capillaries is reduced. When the sphincter relaxes, blood flow in increased. - Movement from the arterial side to the venous side is controlled by: Arterio-Venous Shunts (AV shunts) or AKA Metarterioles - Contraction of smooth muscle cells allow bypassing of the tissue bed served by the capillaries and enables the blood to be directed elsewhere. - AV Shunts are responsive to: 1. Thermal stimuli 2. Mechanical stimuli All 3 regulate the opening and closing of these structures 3. Chemical stimuli - The average capillary is 1mm in length. - Types of Capillaries: Capillaries are classified according to the morphology of their endothelial cells 1. Fenestrated capillaries – have porous walls (AKA: Fenestrations) that allow nutrients, water, and water soluble molecules and waste products to exit the capillary lumen. 2. Vesicular capillaries – function in bulk transport and contain numerous micropinocytotic vesicles, which form by endocytosis at the cell membrane. * Pinocytotic vesicles are used to transport large molecules and proteins across the endothelial cells. Note: A few capillary endothelial cells contain both fenestrae and vesicles. Blood flow through the Capillaries 4 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - Nutrients, water, and waste cross the endothelial cells in several ways: 1. Pores (fenestrations) 2. Open lateral intercellular spaces 3. Endocytosis/exocytosis involving pinocytotic vesicles - Transcapillary movement involves: 1. Simple diffusion – involves movement of oxygen, carbon dioxide, and glucose * Moves from a higher to lower concentration 2. Filtration – involves hydrostatic pressure to force water molecules and certain substances through the capillary wall * Hydrostatic pressure is the blood pressure generated by the ventricular contractions. * The arteriole end has more pressure than the venous end so the arterial end has more filtration occurring. 3. Osmosis – diffusion of water through a selectively permeable membrane Venules - Receive blood from the capillaries - Similar in structure to the capillaries - No nutrient or waste exchange takes place in the venules Veins - The walls of the veins have the same 3 layers as the arteries. - However, there is less smooth muscle and CT so this makes the walls of the veins thinner than arteries. - Being that venous walls are thinner than arterial walls, this allows the veins to adapt to a higher volume and lower pressure. - AKAS = "Capacitance Vessels" or "Blood Reservoirs" because of their ability to hold a great amount of blood. - Because the hydrostatic pressure in the superior vena cava is low, other mechanisms are required to maintain the forward movement of blood: 5 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. 1. Contraction of nearby skeletal muscle fibers (walking, jogging) 2. Movement of organs in the thorax during respiration 3. Movement of abdominal organs (GI tract motility) 4. Valves - derived from endothelium and connective tissue of the vein wall - Varicose veins -With age, veins become twisted or venous valves breakdown lending to an accumulation of blood. * An accumulation of blood breaks the valves flaps so that they no longer overlap and they permit the backflow of blood. * Superficial veins (Great saphenous vein) are more susceptible because they receive less support from the surrounding tissue. - Largest vein of the body is the vena cava. A bypass to the inferior vena cava is the azygos vein. * Superior Refer to the table for a * Inferior description of each area they drain - Longest vein in the body is the saphenous vein. It is the most susceptible to vericosities. Circulatory Routes - 2 Kinds of Circulatory Routes: 1. Systemic Circulation (leaves the left side of the heart and goes to the system) * Includes all the blood vessels that carry oxygenated blood that leaves the left ventricle through the aorta and reaches all systemic capillaries. * It also includes the blood vessels that carry deoxygenated blood that returns to the right atrium after traveling to all the organs including the nutrient arteries to the lungs. * Blood is returned to the heart through the systemic veins. All the veins of the systemic circulation flow into either the superior vena cava, inferior vena cava, or the coronary sinus. They in turn empty into the right atrium. 2. Pulmonary Circulation * When blood returns to the heart from the systemic route, it is eventually pumped out of the right ventricle through the pulmonary circulation to the lungs. * In pulmonary capillaries of the air sacs of the lungs, it loses some of its carbon dioxide 6 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. and takes on oxygen. * It is now bright red again. It returns to the left atrium of the heart and reenters the systemic circulation as it is pumped out by the left ventricle. * Divides into 2 Branches: 1) Right Pulmonary Artery - Runs to the right lung 2) Left Pulmonary Artery - Runs to the left lung * On entering the lungs, the branches of the pulmonary arteries divide and subdivide until ultimately they form capillaries around the alveoli (air sacs) in the lungs and is passed from the alveoli into the blood. * The capillaries unite, venules and veins are formed, and eventually 2 pulmonary veins exit from each lung and transport the oxygenated blood to the left atrium. * The pulmonary veins are the only postnatal veins that carry oxygenated blood. * Contractions of the left ventricle then send the blood into the systemic circulation. Clinical Coronary Occlusion - Clinical coronary occlusion involves a partial or complete blockage of one or more of the coronary arteries and their branches. Don’t forget: Right Coronary Artery – branches into the posterior interventricular and marginal arteries Left Coronary Artery – branches into the circumflex and anterior interventricular. * Both are the only branches off the ascending aorta. 1. Thrombus – blockage by blood clot that impedes blood flow * Clots can be either: a. Digested by enzymes or b. Lead to a myocardial infarction (MI) Infarction means death; myocardium refers to the layer of the heart 2. Atherosclerotic plaques – consist of fatty deposits in blood vessels * Characterized by angina pectoris (chest pain), which often radiate from the left shoulder down the left arm into the fingers. Not always on the left side – sometimes the right side of the brachial region. 7 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. Fetal Circulation - Compared to the adult, fetal circulation have some notable differences because the lungs, GI tract, and kidneys are not developed before birth. - The fetus obtains its oxygen and nutrients from the mother and depends on maternal circulation to carry away wastes and carbon dioxide. - All nutrients, gases, and waste exchange takes place across the placenta. Oxygenation of fetal blood takes place in the placenta; thus the lungs can be bypassed during the cardiac cycle. - The placenta is attached to: 1. Mother’s uterine wall 2. Umbilical cord of the fetus - The umbilical cord has three major blood vessels: 1. One umbilical vein – transport oxygenated blood toward the fetus and away from the placenta 2. Two umbilical arteries - transport deoxygenated blood away from the fetus and to the placenta - Special structures are present that shunt blood through the heart and bypass the lungs since they are not functional: 1. Foramen Ovale (FO) – an opening in the interatrial septum * This opening allows blood to go directly from the right atrium to the left atrium and into the systemic circulation. * This opening closes shortly before or after birth and referred to as “fossa ovalis”. * Failure to close causes “formem ovale sysndrome” which results in hypoxia (lack of oxygen). 2. Ductus Arteriosus – a vessel located between the pulmonary trunk and aorta * Permits blood in the pulmonary trunk to go directly into the descending aorta and to bypass the pulmonary circulation. - After birth it becomes a fibrous cord referred to as “ligamentum arteriosum”. Blood Flow - Relationship of blood flow to pressure: Blood flows in the same direction as the decreasing pressure gradient: 8 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. arteries capillaries veins - Velocity of blood flow: Blood flow is the slowest in the capillaries to allow proper exchange of gases and nutrients. - Relationship of blood flow to resistance: When resistance increases, the blood flow decreases. - Venous blood flow: Venous blood flow depends on skeletal muscle action, respiratory movements and contraction of smooth muscle in venous walls. Pulse - Pulse is defined as the alternating expansion and recoil of an artery in response to the blood ejected from the left ventricle during contraction. - It can be felt in places where an artery is near the surface of the body and passes over something firm like a bone. - Pulse provides vital information: 1. HR 2. Strength of contraction 3. Rhythmicity - Common areas to take one’s pulse: 1. Temporal artery 6. Radial artery 2. Facial artery 7. Femoral artery 3. Common carotid artery 8. Popliteal artery 4. Axillary artery 9. Dorsalis Pedis artery 5. Brachial artery Blood Pressure - Blood pressure (BP) is defined as the force of the blood exerted on the walls of the blood vessels. - Blood pressure is characterized by: 1. Systolic pressure (SBP) – a measurement of the amount of force exerted onto the walls of the arteries during ventricular contraction (systole). 2. Diastolic pressure (DBP) – a measurement of the amount of force exerted onto the walls of the arteries during ventricular relaxation (diastole). 3. Pulse pressure (PP) – the difference between systolic and diastolic pressures (when you take 9 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. someone’s pulse, this is what you feel) 4. Mean arterial pressure (MAP) – the average blood pressure in the arteries of the circulatory system; the mean pressure that maintains forward movement of blood through the vessels MAP = DBP + 1/3 PP - Measuring of BP: * To measure BP one needs the following: 1. Sphygmomanometer containing a mercury column 2. Inflatable Cuff 3. Stethoscope * The brachial artery is usually used to measure BP in clinical settings. * The sounds (as a result of blood flow) heard through the stethoscope are called Korotkoff sounds. * The cuff is usually inflated above the systolic pressure and at that point no Korotkoff sounds are heard. * Pressure in the cuff is released slowly and the pressure at which the first sound is heard is referred to as the systolic pressure. * The pressure at which the last sound is heard is referred to as the diastolic pressure. * Normal BP is typically 120/80 mmHg (systolic/diastolic). Pulse pressure would be 40 mm/Hg. - The highest pressures are in the elastic arteries and the lowest pressures are in the large veins. 1. Blood pressure is greater in the arteries than veins 2. As blood moves away from the left ventricle, blood pressure decreases 3. Blood pressure is inversely related to the distance from the left ventricle - 4 Factors the Affect Blood Pressure: * Each one has a direct relationship to BP. 1. Peripheral Resistance – results from the friction that blood encounters when it comes in contact with the vessel wall; - Blood in contact with the vessel wall moves very slowly due to the resistance offered by the vessel wall. However, blood in the center of the vessel moves very rapidly due to the reduction in resistance. This characteristic movement is called laminar flow. - If resistance increases, blood pressure increases. 10 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - 3 Factors Affecting Vascular Resistance: 1. Blood vessel diameter – the greater the diameter, the less the pressure Vasoconstriction is regulated by the sympathetic nervous system release of norepinepherine. 2. Circulating factors and hormones - can also cause vasocontriction (angiotensin II, aldosterone) 3. Fatty deposits build up within the lumen causing narrowing 4. Elasticity of the vessel – a decrease in elasticity causes an increase in BP. - Elasticity decreases with age and vessels become more rigid. 2. Blood Viscosity – refers to the thickness of the blood 2 Factors concerning Blood Viscosity: 1. Plasma (90% water) - An increase in the watery make-up (plasma) in blood = a decrease in viscosity - Any factor the increases plasma volume, will decrease blood viscosity - A decrease in viscosity = a decrease in pressure needed to force blood through the vasculature 2. Formed elements (RBCs, WBCs, Platelets) – RBCs add to the viscosity of the blood; therefore any factor that increases the hematocrit will increase the viscosity of the blood - Hematocrit defined - % (not #) of RBCs in whole blood - Recall These Terms: Erythrocytosis – excess RBC production Erythropenia – opposite of Erythrocytosis, lack of RBCs 3. Volume of blood - Varies with age, body size and gender but the average for an adult is 5 liters - Volume may be reduced by hemorrhage, vomiting, diarrhea or dehydration. 11 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - If blood volume increases then BP increases, and vice versa. 4. Cardiac Output – the amount of blood pumped from the ventricles in 1 minute. * Q = HR x SV * If HR or SV increases then Q increases which causes an increase in BP HR can be increased or decreased by sympathetic or parasympathetic stimulation. SV can be increased or decreased by: 1. Amount of stretch of the ventricles (Preload) 2. Amount of venous return Regulation of Blood Pressure - Blood pressure can be regulated by short and long-term methods. - 2 Short Term Mechanisms: Baroreceptors and Chemoreceptors 1. Baroreceptors * Located in the walls of the aortic arch and carotid sinus (bifurcation of the common carotid arteries) * These receptors respond when the walls are stretched by an increase in pressure. * If BP increases – the receptors send an action potential to the medulla oblongata (vasomotor and cardiac centers in the brain). - The medulla sends out a signal that decreases HR (which decreases Q) and cause vasodilation (decrease in peripheral resistance) * If BP decreases – causes a decrease in frequency of the action potentials from the receptors to the medulla oblongata, which increases HR and causes vasoconstriction. 2. Chemoreceptors * Found in the same location as the baroreceptors * Responds to changes in partial pressure of CO2, H+ (pH), and oxygen * When CO2 or H+ (pH) increases or oxygen decreases, receptors send stimulus to medulla oblongata * Medulla oblongata sends impulses that increase HR and peripheral resistance to 12 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. increase BP. An increased BP will increase blood flow to the lungs and tissues. - Long-term Mechanisms: (Renin/Angiotensin/Aldosterone Mechanism): * When BP decreases (especially during blood loss), the kidneys secrete the enzyme renin into the blood. * Renin activates the conversion of a blood protein angiotensinogen (precursor) to angiotensin I. * Angiotensin I circulating in blood travels to the lungs where it is converted to angiotensin II. * Angiotensin II does 2 things: 1. Causes vasoconstriction which will then increase BP. 2. Stimulates the adrenal cortex to secrete aldosterone. - Aldosterone stimulates the kidneys to resorb sodium. Remember that water follows sodium so now there is an increase in water volume which increases BP. Key Medical Terms Associated with Blood Vessels Angioplasty – surgical repair of a blood vessel Angiography – A procedure in which a radiopaque substance is injected into the blood stream and then radiographs are taken; used to determine the condition of the blood vessel. Arteriosclerosis – A condition of hardening of an artery, the artery becomes less elastic and does not expand under pressure. Atherosclerosis – a form or arteriosclerosis characterized by the buildup of plaques in the all of the vessel. Arterectomy – surgical removal of an artery. Hypertension (high blood pressure) - the most common disease affecting the heart and blood vessels Aneurysm - a thin, weakened section of the wall of an artery or a vein that bulges outward, forming a balloon-like sac of the blood vessel. Coronary Artery Disease - a condition in which the heart muscle receives inadequate blood because of an interruption of blood supply. Arteritis - inflammation of an artery, probably due to an autoimmune disease. Claudication - pain and lameness or limping caused by defective circulation of the blood in the vessels of the limbs. Hypotension - low blood pressure; most commonly used to describe an acute drop in blood pressure, as 13 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. occurs during excessive blood loss. Normotensive - characterized by normal blood pressure Occlusion - the closure of obstruction of the lumen of a structure such as a blood vessel. Orthostatic Hypotension (Postural Hypotension)- An excessive lowering of systemic blood pressure with the assumption of an erect or semierect posture; it is usually a sign of a disease. Phlebitis ("Phleb" = vein) - inflammation of a vein, often in a leg. Phlebotomy – incision into a vein Reynaud's Disease - a vascular disorder, primarily of females, characterized by bilateral attacks of ischemia, usually of the fingers and toes, in which the skin becomes pale and exhibits burning and pain; it is brought on by cold or emotional pain. Thrombophlebitis - inflammation of a vein with clot formation. Superficial Thrombophlebitis occurs in veins under the skin, especially the calf. Anticoagulants “AKA blood thinners”– these decrease the coagulating ability of the blood. Even though they are called blood thinners, they do not thin the blood nor do they dissolve exiting clots. Examples include - heparin, citrate, Coumadin, Hirudin (released by leeches). Helps to prevent clots from forming in the vessels and may prevent clots from becoming larger. Antiplatelets – keeps blood clots from forming by preventing blood platelets from sticking together. Example: aspirin. Helps to prevent clotting in heart attack patients, TIA (transient ischemic attacks “Mini stroke”), prescribed when plaque buildup is evident but has not formed an obstruction. 14