Cardiovascular Physiology 2025 PDF

CARDIOVASCULAR PHYSIOLOGY  Describe the structure & function of the cardiac tissues Identify the flow of blood through the heart & circulation of the body Describe the cardiac conduction system Objectives Id...

CARDIOVASCULAR PHYSIOLOGY  Describe the structure & function of the cardiac tissues Identify the flow of blood through the heart & circulation of the body Describe the cardiac conduction system Objectives Identify physiologic factors involved in cardiac output & blood pressure regulation Discuss the components of blood and their functions Describe the process of blood clotting & the factors involved Medical Terminology Meaning Meaning Angi/o Vessel Ven/o Vein Vas/o Vessel Phleb/o Vein Aort/o Aorta Thromb/o Clot (thrombus) Arteri/o Artery Valv/o Valve Ather/o Thick, fatty Valvul/o Valve Atri/o Atria Vascul/o Blood vessel Cardi/o Heart Ventricul/o Ventricle Hem/o Blood Scler/o Hardening Hemat/o Blood  Prefix Meaning Brady- Slow Ecto- Out, outside En- In, within, inner End- Medical Terminology Endo- Macro- Large Micro- Small Oligo- Deficiency, few Pre- Before Pro- Before, forward Re– Behind, back Retro- Tachy- Rapid  Suffix Meaning -ary Pertaining to -cyte Cell -dynia Pain -edema Edema Medical Terminology -emesis Vomiting -genesis Creating, producing -gram Record -lysis Destruction -megaly Enlargement -oid Resembling -sclerosis Abnormal hardening -stasis Stopping, cessation  Comprised of cardiac muscle cells Cardiac Muscle (myocytes) – Generate own action potentials DON’T require nerve impulses to contract – Intercalated discs form end to end junctions of cells Folds in membrane create large surface area b/w myocytes Allows rapid spread of electrical activity in heart tissue Cardiac Muscle Functions as endocrine tissue – Releases ANP (atrial natriuretic protein) Secreted in response to increased atrial pressure – Due to increased blood volume or increased BP Also secreted in response to exercise & exposure to cold temperatures – Effects of ANP Decreases reabsorption of Na+ by the kidneys – More sodium is excreted in urine, pulling more water with it – Net effect of increasing fluid excretion Relaxes smooth muscles of blood vessels  vasodilation Promotes conversion of white adipocytes to brown/beige adipocytes  reduces fat storage & increases fat metabolism – Cardioprotective Structure of the Heart Located in mediastinum b/w lungs – Base of heart is uppermost, behind the sternum – Apex (tip) of the heart is just above diaphragm to the left of midline Heart enclosed in pericardial membranes – Fibrous pericardium: outermost layer Loose-fitting sac; strong fibrous connective tissue Extends inferiorly over diaphragm & superiorly over bases of large vessels that enter & leave the heart – Serous pericardium: folded membrane that has 2 layers Parietal pericardium: lines the fibrous pericardium Visceral pericardium (epicardium): on surface of heart muscle – Serous fluid is b/w the parietal and visceral pericardial membranes Reduces friction as heart beats Structure of the Heart: Pericardial Membranes Structure of the Heart Myocardium: thickest part of the walls of the heart; made of cardiac muscle Endocardium: layer of simple squamous epithelium lining chambers of heart – Also covers heart valves & continues into vessels as their lining (endothelium) – Smoothness of this tissue prevents abnormal blood clotting Structure of the Heart Chambers of the heart – Atria (right & left) Relatively thin walls Right & left atria are separated by interatrial septum Atria receive blood from the body or lungs – Ventricles (right & left) Thicker walls than the atria Right & left are separated by interventricular septum Pump blood to the lungs or body Structure of the Heart Left atrium (LA) – Receives oxygenated blood from lungs via the 4 pulmonary veins – Produces atrial natriuretic peptide (ANP) Left ventricle (LV) – Pumps blood to the body via the aorta Right atrium (RA) – Receives deoxygenated blood from body via superior & inferior caval veins (vena cava) – Produces atrial natriuretic peptide (ANP) Right ventricle (RV) – Pumps blood to lungs via pulmonary artery Valves of the Heart Heart valves – Atrioventricular valves Tricuspid valve – Right AV valve – Prevents backflow of blood from RV to RA when the RV contracts Bicuspid/mitral valve – Left AV valve – Prevents backflow of blood from LV to LA when the LV contracts Valves of the Heart Heart valves – Semilunar valves Pulmonary valve – Prevents backflow of blood from pulmonary artery to RV when RV relaxes Aortic valve – Prevents backflow of blood from aorta to the LV when LV relaxes Structures & Function of the Heart Papillary muscles – Columns of myocardium projecting into lower part of ventricles Chordae tendineae – Strands of fibrous connective tissue extending from papillary muscles to flaps of AV valves – When ventricles contract, papillary muscles also contract and pull on chordae tendineae Papillary muscles & chordae tendineae prevent inversion of AV valves during ventricular contraction Fibrous skeleton of the heart: fibrous connective tissue – Anchors the 4 heart valves to prevent stretching/enlargement of valve openings – Separates myocardium of atria from that of ventricles Prevents the contraction of atria from reaching the ventricles except via the normal conduction pathway Coronary Circulation Coronary vessels – Circulate oxygenated blood t/o myocardium Right & left coronary arteries – Branch off aorta immediately beyond aortic valve Branch into smaller arteries & arterioles, then to capillaries Coronary capillaries merge to form coronary veins – Coronary veins empty blood into a large coronary sinus that returns blood to the right atrium  Anterior view Posterior view A) Pulmonary artery has been cut to show the left coronary artery emerging from the ascending aorta B) The coronary sinus empties blood into the right atrium CARDIAC CYCLE & HEART SOUNDS The Cardiac Cycle Refers to the sequence of events in 1 heartbeat – Simultaneous contraction of the atria followed by simultaneous contraction of the ventricles Systole: represents myocardial contraction – Provides increase in pressure to eject blood from chamber Diastole: represent myocardial relaxation – Allows chamber to fill  Cycle begins with atria relaxed & filling with blood AV valves open as pressure of blood in atria increases & ventricles are relaxed Blood flows into ventricles, almost emptying the atria Atrial muscles contract, forcing any remaining blood into ventricles The atria relax Ventricles begin to contract & pressure increases in the ventricles AV valves close Briefly, all valves are closed as ventricular myocardium continues to contract, building up pressure Increasing pressure opens semilunar valves & blood is forced into pulmonary artery & aorta At the end of the cycle, atria have begun to fill again, the ventricles relax, the aortic & pulmonary valves close to prevent backflow of blood, & cycle repeats Ventricular contraction must Pulmonary circulation is a low- be strong enough to pressure system. The right ventricle overcome the opposing does not have to exert as much pressure in the artery to pressure to pump blood into the force the valves open pulmonary circulation as compared to the left ventricle pumping into the systemic circulation Cardiac Cycle Heart sounds heard with stethoscope (lub-dub) – S1 1st sound caused by ventricular systole closing the AV valves – S2 2nd sound caused by closure of aortic & pulmonary valves Pathways of Circulation Pulmonary – Right ventricle pumps blood into pulmonary artery, which divides into right & left pulmonary arteries – W/in the lungs each artery branches into smaller arteries and then to capillaries – Pulmonary capillaries surround alveoli of lungs Site of gas exchange – Capillaries unite to form venules  merge into veins  2 pulmonary veins – Blood is returned to left atrium Pathways of Circulation Systemic – Left ventricle pumps blood into aorta – Branches of aorta take blood into arterioles & capillary networks t/o body – Capillaries merge to form venules & veins – Veins from lower body take blood to inferior vena cava – Veins from upper body take blood to superior vena cava – Caval veins return blood to right atrium 1. Oxygenated blood fills LV 2. Blood is ejected from the LV into the aorta 3. Cardiac output is distributed among various organs 4. Blood flow from the organs is collected in the veins 5. Venous return to RA 6. Mixed venous blood fills the RV 7. Blood is ejected from RV into pulmonary artery 8. Blood flow from the lungs is returned to LA via the pulmonary vein CARDIAC CONDUCTION SYSTEM Cardiac Conduction System Cardiac cycle regulated by electrical activity of the myocardium Nerve impulses are NOT required for cardiac muscle contraction – Cardiac muscle cells can contract spontaneously Cardiac myocytes generate their own electrical action potentials – Intercalated discs allow electrical activity to spread quickly to adjacent muscle cells Allows the 2 atria to contract as a unit, followed by simultaneous contraction of 2 ventricles Electrical impulses follow a very specific path t/o the myocardium Conduction Pathway Sinoatrial (SA) node – Natural pacemaker; initiates the heartbeat – Located in wall of RA just below the opening of superior vena cava – Comprised of specialized group of cardiac myocytes with the most rapid natural rate of contraction Depolarize more rapidly than other myocardial cells b/c SA node cells are more permeable to sodium than others – Depolarization occurs 60 - 80 times per minute Atrioventricular (AV) node – Located in the lower interatrial septum – Transmission of impulses from SA node to AV node and rest of the atrial myocardium causes atrial systole Conduction Pathway AV bundle (bundle of His) – Only pathway for impulses from atria to the ventricles – Located w/in upper interventricular septum – Receives impulses from AV node & transmits them to right & left bundle branches Bundle branches – Impulses travel from bundle branches to Purkinje fibers Purkinje fibers – Terminal fibers of the pathway – Transmit impulses to rest of ventricular myocardium & stimulate ventricular systole Sinoatrial (SA) node Atrioventricular (AV) node Atrioventricular bundle (AV bundle or bundle of His) Right & left bundle branches Purkinje fibers Electrocardiogram P wave: represents depolarization of atria QRS complex: represents depolarization of ventricles T wave: represents repolarization of ventricles Resting Heart Rate (HR) Resting HR (pulse) of healthy adult: 60 - 80 beats per minute (bpm) – Parasympathetic impulses (vagus nerves) decrease rate – Sympathetic impulses increase rate – < 60 bpm: bradycardia – > 100 bpm: tachycardia Well conditioned individuals may have resting HR as low as 35 bpm – Results from the heart being more efficient in these individuals  Heart Rate If the SA node does not function properly – AV node will initiate heartbeat, but at a slower rate (50 - 60 bpm) – AV bundle can also generate contraction of ventricles (15 - 40 bpm) Arrhythmias or dysrhythmias are irregular heartbeats – Severity ranges from harmless to life-threatening – Experiencing occasional heart palpitations is very common Generally harmless Can be caused by too much caffeine, nicotine, or alcohol Cardiac Physiology Cardiac output (CO) – Volume of blood ejected by a ventricle in 1 minute – CO = SV × HR – Average resting CO: 5 - 6 L/min Stroke volume (SV) – Volume of blood pumped out of a ventricle in 1 contraction – Average resting SV: 60 - 80 mL/beat Cardiac Physiology Ejection fraction – % of blood w/in a ventricle that is pumped out per beat – Average ejection fraction of healthy adult: 60 – 70% Preload – Force that stretches cardiac muscle prior to contraction Related to amount of blood in venous return Afterload – Force required to eject blood from ventricles Determined by peripheral resistance in arteries Cardiac Physiology Starling’s law of the heart – The more cardiac muscle fibers are stretched, the more forcefully they contract During exercise, more blood returns to the heart (venous return) – Increased venous return stretches the myocardium of ventricles  increases force of contraction  increasing stroke volume Cardiac reserve – Difference b/w resting CO & maximum CO during exercise – Average cardiac reserve: 15 L or > Regulation of Heart Rate Cardiac control center in medulla oblongata – Controls rate & force of contraction via ANS – Accelerator center Sympathetic stimulation – Increases HR & contractility – Inhibitory center Parasympathetic stimulation Decreases HR Regulation of Heart Rate Stimulation of cardiac control center is related to BP & blood oxygen level – Baroreceptors (pressoreceptors) Located in the aorta and internal carotid arteries Detect changes in blood pressure – Chemoreceptors Located in the carotid bodies and aortic body Detect changes in blood oxygen level Sensory nerves for carotid receptors are the glossopharyngeal (9th cranial) nerves Sensory nerves for aortic arch receptors are the vagus (10th cranial) nerves VASCULAR PHYSIOLOGY Arteries & Arterioles Carry blood from the heart to capillaries Structure: 3 layer walls – Tunica intima (inner layer) Simple squamous epithelial tissue (endothelium) Very smooth  prevents platelet adhesion and abnormal blood clotting Secretes the vasodilator nitric oxide and the vasoconstrictor endothelin – Tunica media (middle layer) Smooth muscle and elastic connective tissue Contributes to maintenance of diastolic BP – Tunica externa/adventitia (outer layer) Strong, fibrous connective tissue  prevents rupture Vasoconstriction & vasodilation regulated by endothelial chemicals and the ANS Veins & Venules Carry blood from capillaries to the heart; three layers in walls Structure: – Tunica intima Smooth endothelium intermittently folds into valves – Prevent the backflow of blood – Tunica media Thin smooth muscle – Veins are not as important in the maintenance of BP – Tunica externa/adventitia Thin fibrous connective tissue – Veins do not carry blood under high pressure Greater capacity than arteries  greater volume of blood Artery Vein Anastomoses Anastomosis: connection/joining of vessels – Artery to artery – Vein to vein Provide alternate pathways for blood flow if one vessel is obstructed Arterial anastomosis – Helps ensure blood gets to capillaries of an organ to deliver oxygen & nutrients Venous anastomosis – Helps ensure blood will be returned to the heart in order to be pumped again Capillaries Carry blood from arterioles to venules Structure – Walls are only 1 cell in thickness – Capillaries are extension of endothelial lining of arteries & veins Most tissues have extensive capillary networks – Quantity or volume of capillary networks in an organ reflects its metabolic activity Some tissues don’t have capillaries – Epidermis, cartilage, the lens & cornea of the eye Capillaries Precapillary sphincters (smooth muscle cells) regulate blood flow into capillary networks – Found at the beginning of each network – Precapillary sphincters are NOT regulated by nervous system Constrict or dilate depending upon needs of tissues – Usually slightly constricted & will dilate to allow more blood flow when tissue needs more oxygen Capillaries Sinusoids – Specialized capillary network – Larger and more permeable than other capillaries Allows large substances such as proteins & blood cells to enter or leave the blood – Found in red bone marrow, spleen, lymph nodes, liver, and some endocrine glands Capillary Exchange Capillaries are sites of material exchange b/w blood & interstitial fluid Gases move via diffusion – From area of greater concentration to area of lesser concentration – Oxygen diffuses from blood in systemic capillaries to interstitial fluid – Carbon dioxide diffuses from interstitial fluid to the blood Filtration of plasma & dissolved nutrients occurs at arterial end of capillaries – Blood pressure entering arterial end of capillary is 30 - 35 mm Hg – Pressure of surrounding interstitial fluid ~ 2 mm Hg – Greater hydrostatic pressure causes shift of plasma & dissolved nutrients out of capillary Glucose, amino acids, & vitamins are brought to cells this way Capillary Exchange Osmosis brings fluid & waste products back into capillary on venous side – Proteins such as albumin have remained in the blood Albumin contributes to colloid osmotic pressure (COP) of blood Pulls interstitial tissue fluid into the capillaries, bringing waste products produced by cells Amount of tissue fluid formed is slightly greater than the amount returned to the capillaries – Excess tissue fluid enters lymph capillaries Velocity of Blood Flow Speed of blood flows differs in various parts of vascular system Inversely related to cross-sectional area Capillaries in total have greatest cross-sectional area, and blood velocity there is slowest – Slow rate of blood flow allows enough time for nutrient, plasma, gas exchange to occur When capillaries unite to form venules, and then veins, the cross-sectional area decreases and blood flow speeds up Total circulation time is ~ 1 minute or < COMPONENTS OF BLOOD Blood Viscosity or thickness – Blood is thicker than water – Viscosity of blood contributes to BP 4 - 6 liters – 38 – 48% is formed elements (cells) – 52 – 62% is plasma Arterial blood  bright red Venous blood  darker, dull red color Normal pH range: 7.35 – 7.45 – Venous blood slightly lower than arterial due to greater amount of carbon dioxide  Blood Plasma Blood cells Water Proteins Other Erythrocytes Thrombocytes Leukocytes substances Fibrinogen Hormones Basophils Globulins Nutrients Eosinophils Albumins Nitrogenous Monocytes wastes Respiratory Lymphocytes gases Electrolytes Neutrophils Plasma ~91% water Transports several substances – Glucose, amino acids, vitamins, & minerals circulated to body tissues – Waste products urea & creatinine are circulated through kidneys and excreted in urine – Hormones are carried to their target organs – Antibodies – Plasma proteins – Carbon dioxide is carried in plasma in the form of bicarbonate ions (HCO3–) CO2 is re-formed when blood reaches the lungs for diffusion into alveoli and exhalation Plasma Plasma proteins – Albumin Most abundant plasma protein; synthesized by liver Contributes to osmotic pressure of blood, pulling fluid into capillaries – Essential to maintain normal blood volume & blood pressure – Globulins Alpha & beta globulins – Synthesized by liver & act as carriers for molecules such as fats Gamma globulins (aka immunoglobulins) – Antibodies produced by lymphocytes – Prothrombin & fibrinogen – Synthesized by the liver and circulate until activated to form a clot Plasma Plasma also carries body heat – Heat is a by-product of cell respiration – Blood becomes warmer as it flows through active organs (liver, muscles, etc) – The heat is distributed to cooler parts of the body as blood continues to circulate Blood Cells 3 types: – Erythrocytes (red blood cells) – Leukocytes (white blood cells) – Thrombocytes (platelets) Produced from hemopoietic stem cells – Predominantly in red bone marrow Erythrocytes Biconcave discs Mature RBCs lack a nucleus Most abundant type of blood cell Normal RBC count: 4.5 - 6.0 million cells per microliter (µL) of blood – Males trend toward the higher end of range, females toward the lower end Hematocrit – Percentage of total blood cells that are RBCs – Normal value: 38% - 48% Erythrocytes: Red Blood Cells Hemoglobin (Hb) – Protein that gives RBCs their ability to carry oxygen – Normal range of hemoglobin: 12 - 18 grams per 100 mL of blood – Each RBC contains ~300 million hemoglobin molecules Each molecule can bond to 4 oxygen molecules (O2 binds to the iron of hemoglobin) Erythrocytes: Red Blood Cells RBCs pick up oxygen in pulmonary capillaries & oxyhemoglobin is formed – Circulates from lungs back to heart & then pumped to the body In the systemic capillaries, hemoglobin gives up much of its oxygen & becomes reduced hemoglobin Hemoglobin can also bond to CO2 – Transports some CO2 from tissues to lungs – Only accounts for only ~10% of total CO2 transport Erythrocytes: Red Blood Cells Produced in red bone marrow of flat irregular bones – Derived from stem cells (hemocytoblasts) – Very rapid rate (several million per second) – Rate of production is regulated by presence of oxygen When body lacks oxygen (hypoxia), erythropoietin is produced by kidneys – Stimulates RBC production – Can occur at high altitudes, following hemorrhage, or as part of normal homeostasis Erythrocytes: Red Blood Cells Stem cells go through various developmental stages – Last 2 stages: normoblast and reticulocyte – Normoblast: last stage with a nucleus Hemoglobin has been produced and DNA code for it is no longer needed – Reticulocyte Has fragments of ER present  present with blood smearing Normoblasts & reticulocytes are predominantly in red bone marrow – Large numbers of these in circulating blood suggests insufficient mature RBCs w/in body Erythrocytes: Red Blood Cells Maturation of RBCs requires several nutrients – Protein & iron needed for hemoglobin – Copper necessary for hemoglobin synthesis – Folic acid & vit B12 needed for mitosis of stem cells in bone marrow Erythrocytes: Red Blood Cells Old & damaged cells removed via tissue macrophage system – Spleen, liver, red bone marrow Phagocytized & digested RBCs are broken down & iron is released into blood for synthesis of new hemoglobin – Excess iron stored in liver if not immediately needed Globin (protein) portion is also recycled – Digested into amino acids and used to synthesize new proteins “Heme” portion is a waste product – Converted to bilirubin by macrophages Liver removes bilirubin & excretes it into bile – Bile secreted into small intestine and excreted in feces Some bilirubin converts to urobilinogen in colon & is absorbed back into blood – Converts to urobilin and excreted by kidneys in urine Avg life span: 120 days Old RBCs become fragile & membranes start to break down Leukocytes: White Blood Cells (WBCs) Larger than RBCs and have nuclei when mature Normal WBC count: 5,000 - 10,000 cells per µL Type of leukocytes – Granulocytes Neutrophils Eosinophils Basophils – Agranulocytes Monocytes Lymphocytes Leukocytes: White Blood Cells (WBCs) Function – All WBCs serve to protect body from pathogens and are immune system components – Specific function varies by type of leukocyte To be continued! Differential WBC count: % of each kind of leukocyte – Abnormal values can be indicative of specific disease states Thrombocytes: Platelets Fragments or pieces of cells Some stem cells in red bone marrow differentiate into large cells called megakaryocytes – These break up into small pieces that enter circulation Small, membrane-bound sacs of chemicals May last for 5 - 9 days, if not used before that Platelet production is regulated by thrombopoietin Normal platelet count: – Hormone produced by liver 150,000 to 300,000 – 500,000/µL Increases rate of platelet production Thrombocytes: Platelets Function: hemostasis – process to prevent/reduce blood loss – Mechanisms involved in hemostasis: Vascular spasm Platelet plugs Chemical clotting Help maintain junctions b/w adjacent epithelial cells that form capillaries & line larger vessels – Prevents leakage of RBCs & excess plasma Thrombocytes: Platelets Vascular spasm – Smooth muscle in wall of large blood vessels contracts in response to damage (myogenic response) – Platelets in area of damage release serotonin  causes more vasoconstriction – Diameter of vessel becomes smaller Smaller opening may then be blocked by a blood clot – If vessel didn’t constrict first, the clot that formed would quickly be washed out by force of the BP Thrombocytes: Platelets Platelet plugs – When capillaries rupture, damage is too slight to trigger formation of a blood clot – Rough surface causes platelets to change shape (become spiky) & become sticky Activated platelets stick to edges of damaged tissue and to each other – Forms mechanical barrier or wall to close off the break in the capillary  Thrombocytes: Platelets Chemical clotting (the clotting cascade) – Rough surface of damaged vessel stimulates clotting Greater the damage, the faster clotting begins (w/in 15 - 120 sec) – Series of rxns involving chemicals normally circulate in blood & others released when vessel is damaged Platelet factors, chemicals released by damaged tissues, calcium ions, prothrombin, fibrinogen, etc. Vitamin K needed for liver to synthesize prothrombin and other clotting factors – Our vitamin K is primarily produced by intestinal microbiota  Stages of Chemical Clotting Stage 1 Stage 2 Stage 3 Formation of Prothrombin Thrombin prothrombin activator activator converts from rxns of: converts fibrinogen to Platelet and clotting prothrombin fibrin factors, tissue to thrombin thromboplastin, & calcium ions Thrombocytes: Platelets Stage 1 begins when a vessel is cut or damaged internally – Prothrombin activator is product of stage 1 Enzyme that functions to activate prothrombin Prothrombin activator brings about stage 2 rxn – Conversion of prothrombin to thrombin – Thrombin is the product of stage 2 Thrombin brings about stage 3 rxn – Converting fibrinogen to fibrin Clot is made of fibrin: threadlike protein – Multiple strands of fibrin form a mesh that traps RBCs & platelets – Creates a wall across the break in the vessel Prothrombin activator Blood clot or thrombus, showing blood cells trapped by fibrin strands Thrombocytes: Platelets After clot forms & bleeding stops, clot retraction & fibrinolysis occur – Clot retraction requires platelets, ATP, and factor 13 Involves folding of fibrin threads to pull edges of damaged vessel wall closer together  makes the area to be repaired smaller – Platelet-derived growth factor (PDGF) is released as platelets break down  stimulates mitosis for repair of blood vessels As repair begins, the clot is dissolved (fibrinolysis) B/c clot is rough surface, failure to dissolve could stimulate more unnecessary clotting, potentially obstructing blood flow  Fibrinolysis Enzymatic breakdown of fibrin/clots Plasmin: enzyme that causes degradation of fibrin Tissue plasminogen activator (tPA) is primary activator of plasmin Primarily produced & secreted by endothelial cells tPA release is triggered by multiple local stimuli Shear stress Thrombin activity Histamine Bradykinin Other Factors in Clot Dissolution Heparin, produced by basophils – Natural anticoagulant that inhibits the clotting process Antithrombin, produced by liver – Combines with & inactivates excess thrombin Fibrin itself, absorbs excess thrombin and renders it inactive Together these limit the fibrin formed to what is needed to create a useful clot but not an obstructive one MAINTENANCE OF BLOOD PRESSURE Blood Pressure Force the blood exerts against the walls of the blood vessels Systolic pressure – Represents the blood pressure when the left ventricle is contracting Diastolic pressure – Sustained pressure when left ventricle is relaxed Blood pressure (BP) is altered by: – Cardiac output – Blood volume – Peripheral resistance to blood flow Factors Involved in Maintenance of Systemic Blood Pressure Venous return HR Cardiac contractility Peripheral resistance: the resistance blood vessels give to blood flow – Arteries & veins are usually slightly constricted (helps maintains normal diastolic blood pressure) – Changes in diameter of vessel with vasoconstriction or dilation will increase & decrease peripheral resistance, respectively Factors Involved in Maintenance of Systemic Blood Pressure Elasticity of large arteries – Allows some absorption of arterial force when ventricle contracts & recoil of vessel during diastole – Normal elasticity Lowers systolic pressure, raises diastolic pressure, and maintains normal pulse pressure Pulse pressure = difference b/w systolic & diastolic pressure Normal ratio of systolic to diastolic to pulse pressure is approximately 3:2:1 – Example: BP of 120/80 mm Hg Ratio is 120:80:40, or 3:2:1 Factors Involved in Maintenance of Systemic Blood Pressure Viscosity of blood – Depends upon RBCs and plasma proteins Elevated RBCs increases viscosity & BP Decreased RBCs or decreased albumin decreases viscosity & BP Loss of blood – Small loss of blood causes temporary drop in BP followed by compensatory increase in HR & vasoconstriction – Severe hemorrhages may exceed capacity of body to compensate  Factors Involved in Maintenance of Systemic Blood Pressure Hormones – Norepinephrine stimulates vasoconstriction  ↑ BP – Epinephrine causes vasoconstriction,↑ HR and contractility of heart  ↑ BP – Antidiuretic hormone (↑ BP) – Aldosterone (↑ blood volume, ↑ BP) – Renin-angiotensin-aldosterone system (vasoconstriction; ↑ BP)  Renin-Angiotensin Mechanism 1. Decreased BP stimulates the kidneys to secrete renin 2. Renin splits plasma protein angiotensinogen (synthesized by the liver) to angiotensin I 3. Angiotensin I is converted to angiotensin II by converting enzyme (secreted by lung tissue & vascular endothelium) Angiotensin II will: Cause vasoconstriction Stimulate the adrenal cortex to secrete aldosterone SUMMARY OF HORMONES IN THE REGULATION OF BP Questions?