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2015 NURS1004 Week 11 Blood vessels & Blood pressure Part I, II & III Lecture notes prepared by Didy Button Refer to Martini et al., 2015, Fundamentals of anatomy and physiology, 10th edn, PearsonBenjamin Cummings, San Francisco. p. 750-759, 760765, 770-775, 779-784, 789-793, 801. OR Martini 20102 9th ed. p 708-717, 718-723, 728-732, 736-740, 748-749, 758. Part III p. 639- 646,650-652, 653-657, 660-664. OR International 9th ed 2014 . p 788-797, 798-803, 808- 812, 816-820, 828-829, 838. Part III p 715-722, 726-728, 729-734, 736-741. Blood Vessels and Circulation Vasodilation The relaxation of arterial smooth muscle Enlarging the lumen & BP goes down Vasoconstriction and Vasodilation Affect: Afterload on heart Peripheral blood pressure Capillary blood flow Arteries From heart to capillaries, arteries change From elastic arteries To muscular arteries To arterioles Arteries Carry blood away from heart Arterioles Are smallest branches of arteries Capillaries Are smallest blood vessels & is the location of exchange between blood and interstitial fluid Venules Collect blood from capillaries Veins Return blood to heart Elastic Arteries Also called conducting arteries Large vessels (e.g., pulmonary trunk and aorta) The Largest Blood Vessels attach to heart Pulmonary trunk Carries blood from right ventricle To pulmonary circulation Aorta Carries blood from left ventricle to systemic circulation Arterioles Are small Have little or no tunica externa Have thin or incomplete tunica media Capillaries: The Smallest Blood Vessels Have small diameter and thin walls Chemicals and gases diffuse across walls Muscular Arteries Also called distribution arteries Are medium sized (most arteries) Tunica media has many muscle cells Artery Diameter Small muscular arteries and arterioles Change with sympathetic or endocrine stimulation Constricted arteries oppose blood flow Resistance (R) Resistance vessels - arterioles The Structure of Vessel Walls have three layers Tunica intima (Inner Layer) Tunica media (Middle Layer) Tunica externa (Outer Layer) Capillaries Are smallest vessels with thin walls Microscopic capillary networks permeate all active tissues Capillary function Location of all exchange functions of cardiovascular system Materials diffuse between blood and interstitial fluid Differences between Arteries and Veins Arteries and veins run side by side Arteries have thicker walls and higher blood pressure Collapsed artery has small, round lumen (internal space) Artery lining folds Arteries more elastic Capillary Structure Endothelial tube, inside thin basement membrane No tunica media No tunica externa Diameter is similar to red blood cell Vein has a large, flat lumen Vein lining contracts, artery lining does not Veins have valves Arteries Elasticity allows arteries to absorb pressure waves that come with each heartbeat Contractility Arteries change diameter Controlled by sympathetic division of ANS Vasoconstriction The contraction of arterial smooth muscle by the ANS & BP goes up Continuous Capillaries Have complete endothelial lining Are found in all tissues except epithelia and cartilage Functions of continuous capillaries Permit diffusion of water, small solutes, and lipidsoluble materials Block blood cells and plasma proteins Specialised Continuous Capillaries Are in CNS and thymus Have very restricted permeability 1 For example, the blood–brain barrier Fenestrated Capillaries Have pores in endothelial lining Permit rapid exchange of water and larger solutes between plasma and interstitial fluid Are found in: Choroid plexus Endocrine organs Kidneys Intestinal tract Sinusoids (Sinusoidal Capillaries) Have gaps between adjacent endothelial cells Liver, Spleen, Bone marrow, Endocrine organs Permit free exchange of water and large plasma proteins between blood and interstitial fluid Phagocytic cells monitor blood at sinusoids Capillary Beds (Capillary Plexus) Connect one arteriole and one venule Precapillary Sphincter guards entrance to each capillary Opens and closes, causing capillary blood to flow in pulses Thoroughfare Channels Direct capillary connections between arterioles and venules Controlled by smooth muscle segments (metarterioles) Veins Collect blood from capillaries in tissues and organs Return blood to heart Are larger in diameter than arteries have thinner walls than arteries have lower blood pressure Venules Very small veins Collect blood from capillaries Medium-sized veins Thin tunica media and few smooth muscle cells Tunica externa with longitudinal bundles of elastic fibers Large Veins Have all three tunica layers Thick tunica externa Thin tunica media Venous Valves Folds of tunica intima Prevent blood from flowing backward Compression pushes blood toward heart The Distribution of Blood Heart, arteries, and capillaries 30–35% of blood volume Venous system 60–65% 1/3 of venous blood is in the large venous networks of the liver, bone marrow, and skin Capacitance of a Blood Vessel The ability to stretch Relationship between blood volume and blood pressure Veins (capacitance vessels) stretch more than arteries Venous Response to Blood Loss Vasomotor centers stimulate sympathetic nerves Systemic veins constrict (venoconstriction) Veins in liver, skin, and lungs redistribute venous reserve Total Capillary Blood Flow Equals cardiac output is determined by: Pressure (P) and resistance (R) in the cardiovascular system Part II of Lecture starts here Pressure (P) The heart generates P to overcome resistance The Pressure Gradient (P) Circulatory pressure The difference between: Pressure at the heart And pressure at peripheral capillary beds Flow (F) Is proportional to the pressure difference (P) Divided by R Measuring Pressure Blood pressure (BP) Arterial pressure (mm Hg) Capillary hydrostatic pressure (CHP) Pressure within the capillary beds Venous pressure Pressure in the venous system Circulatory Pressure ∆P across the systemic circuit (about 100 mm Hg) Circulatory pressure must overcome total peripheral resistance R of entire cardiovascular system Vascular Resistance Due to friction between blood and vessel walls Depends on vessel length and vessel diameter Adult vessel length is constant Vessel diameter varies by vasodilation and vasoconstriction R increases exponentially as vessel diameter decreases Viscosity R caused by molecules and suspended materials in a liquid 2 Whole blood viscosity is about four times that of water Arterial Blood Pressure Systolic pressure Peak arterial pressure during ventricular systole Diastolic pressure Minimum arterial pressure during diastole Abnormal Blood Pressure Normal = 120/80 Hypertension Abnormally high blood pressure Greater than 140/90 Hypotension Abnormally low blood pressure Elastic Rebound Arterial walls Stretch during systole Rebound (recoil to original shape) during diastole Keep blood moving during diastole Venous Pressure and Venous Return Determines the amount of blood arriving at right atrium each minute Low effective pressure in venous system Venous Pressure and Venous Return Low venous resistance is assisted by: Muscular compression of peripheral veins Compression of skeletal muscles pushes blood toward heart (one-way valves) The respiratory pump Thoracic cavity action Inhaling decreases thoracic pressure Exhaling raises thoracic pressure Capillary Pressures and Capillary Exchange Vital to homeostasis Moves materials across capillary walls by: Diffusion Filtration Reabsorption Diffusion : Movement of ions or molecules From high concentration To lower concentration Along the concentration gradient Filtration ; Driven by hydrostatic pressure Water and small solutes forced through capillary wall Leaves larger solutes in bloodstream Reabsorption : The result of osmotic pressure (OP) Blood colloid osmotic pressure (BCOP) Equals pressure required to prevent osmosis Caused by suspended blood proteins that are too large to cross capillary walls Interplay between Filtration and Reabsorption Net hydrostatic pressure: Forces water out of solution Net osmotic pressure: Forces water into solution Both control filtration and reabsorption through capillaries Capillary Exchange At arterial end of capillary: Fluid moves out of capillary Into interstitial fluid At venous end of capillary: Fluid moves into capillary Out of interstitial fluid Tissue Perfusion Blood flow through the tissues Carries O2 and nutrients to tissues and organs Carries CO2 and wastes away Is affected by: Cardiac output Peripheral resistance Blood pressure Cardiovascular Regulation Changes Blood Flow to a Specific Area At an appropriate time In the right area Without changing blood pressure and blood flow to vital organs Controlling Cardiac Output and Blood Pressure Autoregulation Causes immediate, localized homeostatic adjustments Neural mechanisms Respond quickly to changes at specific sites Endocrine mechanisms Direct long-term changes Autoregulation of Blood Flow within Tissues Adjusted by peripheral resistance while cardiac output stays the same Local vasodilators accelerate blood flow at tissue level Low O2 or high CO2 levels Low pH (acids) Nitric oxide (NO) High K+ or H+ concentrations 3 Chemicals released by inflammation (histamine) Elevated local temperature Neural Mechanisms Cardiovascular (CV) centers of the medulla oblongata Cardiac centers Cardioacceleratory center increases cardiac output Cardioinhibitory center reduces cardiac output Vasomotor Center Control of vasoconstriction Reflex Control of Cardiovascular Function Cardiovascular centers monitor arterial blood Baroreceptor reflexes Respond to changes in blood pressure Chemoreceptor reflexes Respond to changes in chemical composition, particularly pH and dissolved gases Baroreceptor Reflexes Stretch receptors in walls of: Carotid sinuses (maintain blood flow to brain) Aortic sinuses (monitor start of systemic circuit) Right atrium (monitors end of systemic circuit) For example, Adrenaline and Noradrenaline from adrenal medullae stimulate cardiac output and peripheral vasoconstriction Antidiuretic Hormone (ADH) Released by neurohypophysis (posterior lobe of pituitary) Elevates blood pressure Reduces water loss at kidneys ADH responds to: Low blood volume High plasma osmotic concentration Circulating angiotensin II Lecture Part III starts here Blood components and Coagulation A fluid medium (blood) •Is specialized fluid of connective tissue •Contains cells suspended in a fluid matrix •Transports materials to and from cells •Oxygen and carbon dioxide •Nutrients •Hormones •Immune system components •Waste products Baroreceptor Reflexes When blood pressure rises, CV centers: decrease cardiac output Cause peripheral vasodilation When blood pressure falls, CV centers: Increase cardiac output Cause peripheral vasoconstriction Important Functions of Blood Transportation of dissolved substances Regulation of pH and ions Restriction of fluid losses at injury sites Defense against toxins and pathogens Stabilization of body temperature Chemoreceptor Reflexes Peripheral chemoreceptors in carotid bodies and aortic bodies monitor blood Central chemoreceptors below medulla oblongata: Monitor cerebrospinal fluid Control respiratory function Control blood flow to brain Whole Blood •Plasma •Fluid consisting of: •Water •Dissolved plasma proteins •Other solutes •Formed elements •All cells and solids Chemoreceptor Reflexes Changes in pH, O2, and CO2 concentrations Produced by coordinating cardiovascular and respiratory activities CNS Activities and the Cardiovascular Centers Thought processes and emotional states can elevate blood pressure by: Cardiac stimulation and vasoconstriction Hormones and Cardiovascular Regulation Hormones have short-term and long-term effects on cardiovascular regulation Three Types of Formed Elements 1. Red blood cells (RBCs) or erythrocytes •Transport oxygen 2. White blood cells (WBCs) or leukocytes •Part of the immune system 3. Platelets •Cell fragments involved in clotting Three General Characteristics of Blood 1. 38C (100.4F) is normal temperature 2. High viscosity 3. Slightly alkaline pH (7.35–7.45) 4 •Blood volume (liters) = 7% of body weight (kilograms) •Adult male 5 to 6 liters •Adult female 4 to 5 liters Plasma •Makes up 50–60% of blood volume •More than 90% of plasma is water •Extracellular fluids •Interstitial fluid (IF) and plasma •Materials plasma and IF exchange across capillary walls •Water •Ions •Small solutes Plasma Proteins Albumins (60%) Globulins (35%) Fibrinogen (4%) •Albumins (60%) •Transport substances such as fatty acids, thyroid hormones, and steroid hormones •Globulins (35%) •Antibodies, also called immunoglobulins •Transport globulins (small molecules): hormonebinding proteins, metalloproteins, apolipoproteins (lipoproteins), and steroid-binding proteins •Fibrinogen (4%) •Molecules that form clots and produce long, insoluble strands of fibrin SerumLiquid part of a blood sample In which dissolved fibrinogen has converted to solid fibrin Other Plasma Proteins •1% of plasma •Changing quantities of specialized plasma proteins •Peptide hormones normally present in circulating blood •Insulin, prolactin (PRL), and the glycoproteins thyroid-stimulating hormone (TSH), folliclestimulating hormone (FSH), and luteinizing hormone (LH) Origins of Plasma Proteins •More than 90% made in liver •Antibodies made by plasma cells •Peptide hormones made by endocrine organs Red blood cells (RBCs) •Make up 99.9% of blood’s formed elements Hemoglobin •The red pigment that gives whole blood its color •Binds and transports oxygen and carbon dioxide Red blood cell count - the number of RBCs in 1 microliter of whole blood •Male: 4.5–6.3 million •Female: 4.2–5.5 million Structure of RBCs •Small and highly specialized discs •Thin in middle and thicker at edge Life Span of RBCs •Lack nuclei, mitochondria, and ribosomes •Means no repair and anaerobic metabolism •Live about 120 days •Hemoglobin (Hb) •Protein molecule that transports respiratory gases •Normal hemoglobin (adult male) 14–18 g/dL whole blood (adult female)12–16 g/dL whole blood Hemoglobin Function •Carries oxygen •With low oxygen (peripheral capillaries) •Hemoglobin releases oxygen •Binds carbon dioxide and carries it to lungs •Forms carbaminohemoglobin RBC Formation and Turnover •1% of circulating RBCs wear out per day •About 3 million RBCs per second •Hemoglobin Conversion and Recycling •Macrophages of liver, spleen, and bone marrow •Monitor RBCs •Engulf RBCs before membranes rupture (hemolyze) Hemoglobin Conversion and Recycling •Phagocytes break hemoglobin into components •Globular proteins to amino acids •Heme to biliverdin •Iron Breakdown of Biliverdin •Biliverdin (green) is converted to bilirubin (yellow) •Bilirubin •Is excreted by liver (bile) •Jaundice is caused by bilirubin buildup •Converted by intestinal bacteria to urobilins and stercobilins RBC Production 5 •Erythropoiesis •Occurs only in myeloid tissue (red bone marrow) in adults •Stem cells mature to become RBCs 19-3 Red Blood Cells Blood Typing Surface Antigens •Are cell surface proteins that identify cells to immune system •Normal cells are ignored and foreign cells attacked •Blood Types •Are genetically determined •By presence or absence of RBC surface antigens A, B, Rh (or D) Four Basic Blood Types 1.A (surface antigen A) 2.B (surface antigen B) 3.AB (antigens A and B) 4.O (neither A nor B) •Agglutinogens •Antigens on surface of RBCs •Screened by immune system •Plasma antibodies attack and agglutinate (clump) foreign antigens Blood Plasma Antibodies •Type A •Type B antibodies •Type B •Type A antibodies •Type O •Both A and B antibodies •Type AB •Neither A nor B antibodies •The Rh Factor •Also called D antigen •Either Rh positive (Rh) or Rh negative (Rh) •Only sensitized Rh blood has anti-Rh antibodies Cross-Reactions in Transfusions •Also called transfusion reaction •Plasma antibody meets its specific surface antigen •Blood will agglutinate and hemolyze •Occur if donor and recipient blood types not compatible Testing for Transfusion Compatibility •Performed on donor and recipient blood for compatibility •Without cross-match, type O is universal donor White Blood Cells (WBCs) •Also called leukocytes •Do not have hemoglobin •Have nuclei and other organelles •WBC functions: •Defend against pathogens •Remove toxins and wastes •Attack abnormal cells •Most WBCs in: •Connective tissue proper •Lymphatic system organs •Small numbers in blood •5000 to 10,000 per microliter Four Characteristics of Circulating WBCs 1.Can migrate out of bloodstream 2.Have amoeboid movement 3.Attracted to chemical stimuli (positive chemotaxis) 4.Some are phagocytic •Neutrophils, eosinophils, and monocytes White Blood Cells •Neutrophils •Also called polymorphonuclear leukocytes •50–70% of circulating WBCs •Pale cytoplasm granules with: •Lysosomal enzymes •Bactericides (hydrogen peroxide and superoxide) Very active, first to attack bacteria •Engulf and digest pathogens •Degranulation •Removing granules from cytoplasm •Defensins (peptides from lysosomes) attack pathogen membranes •Release prostaglandins and leukotrienes •Form pus Eosinophils (Acidophils) •2–4% of circulating WBCs •Attack large parasites •Excrete toxic compounds •Nitric oxide •Cytotoxic enzymes •Are sensitive to allergens •Control inflammation with enzymes that counteract inflammatory effects of neutrophils and mast cells Basophils 6 •Are less than 1% of circulating WBCs •Accumulate in damaged tissue •Release histamine •A cut triggers vascular spasm that lasts 30 minutes •Three Steps of the Vascular Phase 1.Endothelial cells contract and expose basement •Dilates blood vessels •Release heparin •Prevents blood clotting membrane to bloodstream Monocytes •2–8% of circulating WBCs •Are large and spherical •Enter peripheral tissues and become macrophages •Engulf large particles and pathogens •Secrete substances that attract immune system cells and fibrocytes to injured area Lymphocytes •20–30% of circulating WBCs •Are larger than RBCs •Migrate in and out of blood •Mostly in connective tissues and lymphoid organs •Are part of the body’s specific defense system The Differential Count and Changes in WBC Profiles •Detects changes in WBC populations •Infections, inflammation, and allergic reactions Three Steps of the Vascular Phase 2. Endothelial cells •Release chemical factors ADP, tissue factor, and prostacyclin •Release local hormones, endothelins •Stimulate smooth muscle contraction and cell division 3. Endothelial plasma membranes become “sticky” •Seal off blood flow The Platelet Phase •Begins within 15 seconds after injury •Platelet adhesion (attachment) •To sticky endothelial surfaces •To basement membranes •To exposed collagen fibers •Platelet aggregation (stick together) •Forms platelet plug which closes small breaks •Platelet Phase •Activated platelets release clotting compounds Myeloid Stem Cells •Produce all WBCs except lymphocytes •Lymphoid Stem Cells •Lymphopoiesis - the production of lymphocytes 1.Adenosine diphosphate (ADP) 2.Thromboxane A2 and serotonin 3.Clotting factors 4.Platelet-derived growth factor (PDGF) 5.Calcium ions Platelets •Cell fragments involved in human clotting system •Nonmammalian vertebrates have thrombocytes (nucleated cells) •Circulate for 9–12 days •Are removed by spleen •2/3 are reserved for emergencies The Coagulation Phase •Begins 30 seconds or more after the injury •Blood clotting (coagulation) •Cascade reactions •Chain reactions of enzymes and proenzymes •Form three pathways •Convert circulating fibrinogen into insoluble fibrin Three Functions of Platelets 1.Release important clotting chemicals 2.Temporarily patch damaged vessel walls 3.Reduce size of a break in vessel wall Hemostasis •Is the cessation of bleeding •Consists of three phases 1.Vascular phase 2.Platelet phase 3.Coagulation phase The Vascular Phase 13 Clotting Factors •Also called procoagulants •Proteins or ions in plasma •Required for normal clotting Three Coagulation Pathways 1.Extrinsic pathway 2.Intrinsic pathway 3.Common pathway •The Extrinsic Pathway •Begins in the vessel wall •Outside bloodstream 7 •Damaged cells release tissue factor (TF) •TF + other compounds = enzyme complex •Activates Factor X •The Intrinsic Pathway •Begins with circulating proenzymes •Within bloodstream •Activation of enzymes by collagen •Platelets release factors (e.g., PF-3) •Series of reactions activates Factor X The Common Pathway •Where intrinsic and extrinsic pathways converge •Forms enzyme prothrombinase •Converts prothrombin to thrombin •Thrombin converts fibrinogen to fibrin Calcium Ions, Vitamin K, and Blood Clotting •Calcium ions (Ca2+) and vitamin K are both essential to the clotting process Clot Retraction 1.Pulls torn edges of vessel closer together •Reducing residual bleeding and stabilizing injury site 2.Reduces size of damaged area •Making it easier for fibrocytes, smooth muscle cells, and endothelial cells to complete repairs Fibrinolysis •Slow process of dissolving clot •Thrombin and tissue plasminogen activator (t-PA) •Activate plasminogen •Plasminogen produces plasmin •Digests fibrin strands D Button 2015 8