Chapter 19 the cardiovascular system the blood
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Chapter 19 The Cardiovascular System: The Blood. Fluids of the Body. Cells of the body are serviced by 2 fluids blood composed of plasma and a variety of cells transports nutrients and wastes interstitial fluid bathes the cells of the body

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Chapter 19 The Cardiovascular System: The Blood

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Chapter 19 the cardiovascular system the blood

Chapter 19The Cardiovascular System: The Blood

Fluids of the body

Fluids of the Body

  • Cells of the body are serviced by 2 fluids

    • blood

      • composed of plasma and a variety of cells

      • transports nutrients and wastes

    • interstitial fluid

      • bathes the cells of the body

  • Nutrients and oxygen diffuse from the blood into the interstitial fluid & then into the cells

  • Wastes move in the reverse direction

  • Hematology is study of blood and blood disorders

Functions of blood

Functions of Blood

  • Transportation

    • O2, CO2, metabolic wastes, nutrients, heat & hormones

  • Regulation

    • helps regulate pH through buffers

    • helps regulate body temperature

      • coolant properties of water

      • vasodilatation of surface vessels dump heat

    • helps regulate water content of cells by interactions with dissolved ions and proteins

  • Protection from disease & loss of blood

Physical characteristics of blood

Physical Characteristics of Blood

  • Thicker (more viscous) than water and flows more slowly than water

  • Temperature of 100.4 degrees F

  • pH 7.4 (7.35-7.45)

  • 8 % of total body weight

  • Blood volume

    • 5 to 6 liters in average male

    • 4 to 5 liters in average female

    • hormonal negative feedback systems maintain constant blood volume and osmotic pressure

Components of blood

Components of Blood

  • Hematocrit

    • 55% plasma

    • 45% cells

      • 99% RBCs

      • < 1% WBCs and platelets

Blood plasma

Blood Plasma

  • 0ver 90% water

  • 7% plasma proteins

    • created in liver

    • confined to bloodstream

  • albumin

    • maintain blood osmotic pressure

  • globulins (immunoglobulins)

    • antibodies bind to foreignsubstances called antigens

    • form antigen-antibody complexes

  • fibrinogen

    • for clotting

  • 2% other substances

    • electrolytes, nutrients, hormones, gases, waste products

  • Formed elements of blood

    Formed Elements of Blood

    • Red blood cells ( erythrocytes )

    • White blood cells ( leukocytes )

      • granular leukocytes

        • neutrophils

        • eosinophils

        • basophils

      • agranular leukocytes

        • lymphocytes = T cells, B cells, and natural killer cells

        • monocytes

    • Platelets (special cell fragments)



    • Percentage of blood occupied by cells

      • female normal range

        • 38 - 46% (average of 42%)

      • male normal range

        • 40 - 54% (average of 46%)

        • testosterone

    • Anemia

      • not enough RBCs or not enough hemoglobin

    • Polycythemia

      • too many RBCs (over 65%)

      • dehydration, tissue hypoxia, blood doping in athletes

    Red blood cells or erythrocytes

    Red Blood Cells or Erythrocytes

    • Contain oxygen-carrying protein hemoglobin that gives blood its red color

      • 1/3 of cell’s weight is hemoglobin

    • Biconcave disk 8 microns in diameter

      • increased surface area/volume ratio

      • flexible shape for narrow passages

      • no nucleus or other organelles

        • no cell division or mitochondrial ATP formation

    • Normal RBC count

      • male 5.4 million/drop ---- female 4.8 million/drop

      • new RBCs enter circulation at 2 million/second



    • Globin protein consisting of 4 polypeptide chains

    • One heme pigment attached to each polypeptide chain

      • each heme contains an iron ion (Fe+2) that can combine reversibly with one oxygen molecule

    Rbc life cycle

    RBC Life Cycle

    • RBCs live only 120 days

      • wear out from bending to fit through capillaries

      • no repair possible due to lack of organelles

    • Worn out cells removed by fixed macrophages in spleen & liver

    • Breakdown products are recycled

    Erythropoiesis production of rbcs

    Erythropoiesis: Production of RBCs

    • Proerythroblast starts to produce hemoglobin

    • Many steps later, nucleus is ejected & a reticulocyte is formed

      • orange in color with traces of visible rough ER

    • Reticulocytes escape from bone marrow into the blood

    • In 1-2 days, they eject the remaining organelles to become a mature RBC

    Wbc anatomy and types

    WBC Anatomy and Types

    • All WBCs (leukocytes) have a nucleus and no hemoglobin

    • Granular or agranular classification based on presence of cytoplasmic granules made visible by staining

      • granulocytes are neutrophils, eosinophils or basophils

      • agranulocytes are monocyes or lymphocytes

    Wbc physiology

    WBC Physiology

    • Less numerous than RBCs

      • 5000 to 10,000 cells per drop of blood

      • 1 WBC for every 700 RBC

    • Leukocytosis is a high white blood cell count

      • microbes, strenuous exercise, anesthesia or surgery

    • Leukopenia is low white blood cell count

      • radiation, shock or chemotherapy

    • Only 2% of total WBC population is in circulating blood at any given time

      • rest is in lymphatic fluid, skin, lungs, lymph nodes & spleen

    Differential wbc count

    Differential WBC Count

    • Detection of changes in numbers of circulating WBCs (percentages of each type)

      • indicates infection, poisoning, leukemia, chemotherapy, parasites or allergy reaction

    • Normal WBC counts

      • neutrophils 60-70% (up if bacterial infection)

      • lymphocyte 20-25% (up if viral infection)

      • monocytes 3 -- 8 % (up if fungal/viral infection)

      • eosinophil 2 -- 4 % (up if parasite or allergy reaction)

      • basophil <1% (up if allergy reaction or hypothyroid)

    Bone marrow transplant

    Bone Marrow Transplant

    • Intravenous transfer of healthy bone marrow

    • Procedure

      • destroy sick bone marrow with radiation & chemotherapy

      • donor matches surface antigens on WBC

      • put sample of donor marrow into patient's vein for reseeding of bone marrow

      • success depends on histocompatibility of donor & recipient

    • Treatment for leukemia, sickle-cell, breast, ovarian or testicular cancer, lymphoma or aplastic anemia

    Platelets life history

    Platelets--Life History

    • Platelets form in bone marrow by following steps:

      • myeloid stem cells to megakaryocyte-colony forming cells to megakaryoblast to megakaryocytes whose cell fragments form platelets

    • Short life span (5 to 9 days in bloodstream)

      • formed in bone marrow

      • few days in circulating blood

      • aged ones removed by fixed macrophages in liver and spleen

    Complete blood count

    Complete Blood Count

    • Screens for anemia and infection

    • Total RBC, WBC & platelet counts; differential WBC; hematocrit and hemoglobin measurements

    • Normal hemoglobin range

      • infants have 14 to 20 g/100mL of blood

      • adult females have 12 to 16 g/100mL of blood

      • adult males have 13.5 to 18g/100mL of blood



    • Stoppage of bleeding in a quick & localized fashion when blood vessels are damaged

    • Prevents hemorrhage (loss of a large amount of blood)

    • Methods utilized

      • vascular spasm

      • platelet plug formation

      • blood clotting (coagulation = formation of fibrin threads)

    Blood clotting

    Blood Clotting

    • Blood drawn from the body thickens into a gel

      • gel separates into liquid (serum) and a clot of insoluble fibers (fibrin) in which the cells are trapped

    • If clotting occurs in an unbroken vessel is called a thrombosis

    • Substances required for clotting are Ca+2, enzymes synthesized by liver cells and substances released by platelets or damaged tissues

    • Clotting is a cascade of reactions in which each clotting factor activates the next in a fixed sequence resulting in the formation of fibrin threads

      • prothrombinase & Ca+2 convert prothrombin into thrombin

      • thrombin converts fibrinogen into fibrin threads

    Overview of the clotting cascade

    Overview of the Clotting Cascade

    • Prothrombinase is formed by either the intrinsic or extrinsic pathway

    • Final common pathway produces fibrin threads

    Clot retraction blood vessel repair

    Clot Retraction & Blood Vessel Repair

    • Clot plugs ruptured area of blood vessel

    • Platelets pull on fibrin threads causing clot retraction

      • trapped platelets release factor XIII stabilizing the fibrin threads

    • Edges of damaged vessel are pulled together

    • Fibroblasts & endothelial cells repair the blood vessel

    Anemia not enough rbcs

    Anemia = Not Enough RBCs

    • Symptoms

      • oxygen-carrying capacity of blood is reduced

      • fatigue, cold intolerance & paleness

        • lack of O2 for ATP & heat production

    • Types of anemia

      • iron-deficiency =lack of absorption or loss of iron

      • pernicious = lack of intrinsic factor for B12 absorption

      • hemorrhagic = loss of RBCs due to bleeding (ulcer)

      • hemolytic = defects in cell membranes cause rupture

      • thalassemia = hereditary deficiency of hemoglobin

      • aplastic = destruction of bone marrow (radiation/toxins)

    Sickle cell anemia sca

    Sickle-cell Anemia (SCA)

    • Genetic defect in hemoglobin molecule (Hb-S) that changes 2 amino acids

      • at low very O2 levels, RBC is deformed by changes in hemoglobin molecule within the RBC

        • sickle-shaped cells rupture easily = causing anemia & clots

    • Found among populations in malaria belt

      • Mediterranean Europe, sub-Saharan Africa & Asia

    • Person with only one sickle cell gene

      • increased resistance to malaria because RBC membranes leak K+ & lowered levels of K+ kill the parasite infecting the red blood cells



    • Inherited deficiency of clotting factors

      • bleeding spontaneously or after minor trauma

      • subcutaneous & intramuscular hemorrhaging

      • nosebleeds, blood in urine, articular bleeding & pain

    • Hemophilia A lacks factor VIII (males only)

      • most common

    • Hemophilia B lacks factor IX (males only)

    • Hemophilia C (males & females)

      • less severe because alternate clotting activator exists

    • Treatment is transfusions of fresh plasma or concentrates of the missing clotting factor



    • Acute leukemia

      • uncontrolled production of immature leukocytes

      • crowding out of normal red bone marrow cells by production of immature WBC

      • prevents production of RBC & platelets

    • Chronic leukemia

      • accumulation of mature WBC in bloodstream because they do not die

      • classified by type of WBC that is predominant---monocytic, lymphocytic.

    Chapter 20 the cardiovascular system the heart

    Chapter 20The Cardiovascular System: The Heart

    • Heart pumps over 1 million gallons per year

    • Over 60,000 miles of blood vessels

    Heart location

    Heart Location

    Anterior surface

    of heart

    • Heart is located in the mediastinum

      • area from the sternum to the vertebral column and between the lungs

    Heart orientation

    Heart Orientation

    • Apex - directed anteriorly, inferiorly and to the left

    • Base - directed posteriorly, superiorly and to the right

    • Anterior surface - deep to the sternum and ribs

    • Inferior surface - rests on the diaphragm

    • Right border - faces right lung

    • Left border (pulmonary border) - faces left lung

    Heart orientation1

    Heart Orientation

    • Heart has 2 surfaces: anterior and inferior, and 2 borders: right and left

    Surface projection of the heart

    Surface Projection of the Heart

    • Superior right point at the superior border of the 3rd right costal cartilage

    • Superior left point at the inferior border of the 2nd left costal cartilage 3cm to the left of midline

    • Inferior left point at the 5th intercostal space, 9 cm from the midline

    • Inferior right point at superior border of the 6th right costal cartilage, 3 cm from the midline



    • Fibrous pericardium

      • dense irregular CT

      • protects and anchors the heart, prevents overstretching

    • Serous pericardium

      • thin delicate membrane

      • contains

        • parietal layer-outer layer

        • pericardial cavity with pericardial fluid

        • visceral layer (epicardium)

    Layers of heart wall

    Layers of Heart Wall

    • Epicardium

      • visceral layer of serous pericardium

    • Myocardium

      • cardiac muscle layer is the bulk of the heart

    • Endocardium

      • chamber lining & valves

    Chambers and sulci of the heart

    Chambers and Sulci of the Heart

    • Four chambers

      • 2 upper atria

      • 2 lower ventricles

    • Sulci - grooves on surface of heart containing coronary blood vessels and fat

      • coronary sulcus

        • encircles heart and marks the boundary between the atria and the ventricles

      • anterior interventricular sulcus

        • marks the boundary between the ventricles anteriorly

      • posterior interventricular sulcus

        • marks the boundary between the ventricles posteriorly

    Chambers and sulci

    Chambers and Sulci

    Anterior View

    Chambers and sulci1

    Chambers and Sulci

    Posterior View

    Right atrium

    Right Atrium

    • Receives blood from 3 sources

      • superior vena cava, inferior vena cava and coronary sinus

    • Interatrial septum partitions the atria

    • Fossa ovalis is a remnant of the fetal foramen ovale

    • Tricuspid valve

      • Blood flows through into right ventricle

      • has three cusps composed of dense CT covered by endocardium

    Right ventricle

    Right Ventricle

    • Forms most of anterior surface of heart

    • Papillary muscles are cone shaped trabeculae carneae (raised bundles of cardiac muscle)

    • Chordae tendineae: cords between valve cusps and papillary muscles

    • Interventricular septum: partitions ventricles

    • Pulmonary semilunar valve: blood flows into pulmonary trunk

    Left atrium

    Left Atrium

    • Forms most of the base of the heart

    • Receives blood from lungs - 4 pulmonary veins (2 right + 2 left)

    • Bicuspid valve: blood passes through into left ventricle

      • has two cusps

      • to remember names of this valve, try the pneumonic LAMB

        • Left Atrioventricular, Mitral, or Bicuspid valve

    Left ventricle

    Left Ventricle

    • Forms the apex of heart

    • Chordae tendineae anchor bicuspid valve to papillary muscles (also has trabeculae carneae like right ventricle)

    • Aortic semilunar valve:

      • blood passes through valve into the ascending aorta

      • just above valve are the openings to the coronary arteries

    Myocardial thickness and function

    Myocardial Thickness and Function

    • Thickness of myocardium varies according to the function of the chamber

    • Atria are thin walled, deliver blood to adjacent ventricles

    • Ventricle walls are much thicker and stronger

      • right ventricle supplies blood to the lungs (little flow resistance)

      • left ventricle wall is the thickest to supply systemic circulation

    Thickness of cardiac walls

    Thickness of Cardiac Walls

    Myocardium of left ventricle is much thicker than the right.

    Atrioventricular valves open

    Atrioventricular Valves Open

    • A-V valves open and allow blood to flow from atria into ventricles when ventricular pressure is lower than atrial pressure

      • occurs when ventricles are relaxed, chordae tendineae are slack and papillary muscles are relaxed

    Atrioventricular valves close

    Atrioventricular Valves Close

    • A-V valves close preventing backflow of blood into atria

      • occurs when ventricles contract, pushing valve cusps closed, chordae tendinae are pulled taut and papillary muscles contract to pull cords and prevent cusps from everting

    Semilunar valves

    Semilunar Valves

    • SL valves open with ventricular contraction

      • allow blood to flow into pulmonary trunk and aorta

    • SL valves close with ventricular relaxation

      • prevents blood from returning to ventricles, blood fills valve cusps, tightly closing the SL valves

    Valve function review

    Valve Function Review

    Which side is anterior surface?

    What are the ventricles doing?

    Valve function review1

    Valve Function Review

    Ventricles contract, blood pumped into aorta and pulmonary trunk through SL valves

    Atria contract, blood fills ventricles through A-V valves

    Blood circulation

    Blood Circulation

    • Two closed circuits, the systemic and pulmonic

    • Systemic circulation

      • left side of heart pumps blood through body

      • left ventricle pumps oxygenated blood into aorta

      • aorta branches into many arteries that travel to organs

      • arteries branch into many arterioles in tissue

      • arterioles branch into thin-walled capillaries for exchange of gases and nutrients

      • deoxygenated blood begins its return in venules

      • venules merge into veins and return to right atrium

    Blood circulation cont

    Blood Circulation (cont.)

    • Pulmonary circulation

      • right side of heart pumps deoxygenated blood to lungs

      • right ventricle pumps blood to pulmonary trunk

      • pulmonary trunk branches into pulmonary arteries

      • pulmonary arteries carry blood to lungs for exchange of gases

      • oxygenated blood returns to heart in pulmonary veins

    Blood circulation1

    Blood Circulation

    • Blood flow

      • blue = deoxygenated

      • red = oxygenated

    Coronary circulation

    Coronary Circulation

    • Coronary circulation is blood supply to the heart

    • Heart as a very active muscle needs lots of O2

    • When the heart relaxes high pressure of blood in aorta pushes blood into coronary vessels

    • Many anastomoses

      • connections between arteries supplying blood to the same region, provide alternate routes if one artery becomes occluded

    Coronary arteries

    Coronary Arteries

    • Branches off aorta above aortic semilunar valve

    • Left coronary artery

      • circumflex branch

        • in coronary sulcus, supplies left atrium and left ventricle

      • anterior interventricular art.

        • supplies both ventricles

    • Right coronary artery

      • marginal branch

        • in coronary sulcus, supplies right ventricle

      • posterior interventricular art.

        • supplies both ventricles

    Coronary veins

    Coronary Veins

    • Collects wastes from cardiac muscle

    • Drains into a large sinus on posterior surface of heart called the coronary sinus

    • Coronary sinus empties into right atrium

    Conduction system of heart

    Conduction System of Heart

    Coordinates contraction of heart muscle.

    Conduction system of heart1

    Autorhythmic Cells

    Cells fire spontaneously, act as pacemaker and form conduction system for the heart

    SA node

    cluster of cells in wall of Rt. Atria

    begins heart activity that spreads to both atria

    excitation spreads to AV node

    AV node

    in atrial septum, transmits signal to bundle of His

    AV bundle of His

    the connection between atria and ventricles

    divides into bundle branches & purkinje fibers, large diameter fibers that conduct signals quickly

    Conduction System of Heart

    Rhythm of conduction system

    Rhythm of Conduction System

    • SA node fires spontaneously 90-100 times per minute

    • AV node fires at 40-50 times per minute

    • If both nodes are suppressed fibers in ventricles by themselves fire only 20-40 times per minute

    • Artificial pacemaker needed if pace is too slow

    • Extra beats forming at other sites are called ectopic pacemakers

      • caffeine & nicotine increase activity

    Timing of atrial ventricular excitation

    Timing of Atrial & Ventricular Excitation

    • SA node setting pace since is the fastest

    • In 50 msec excitation spreads through both atria and down to AV node

    • 100 msec delay at AV node due to smaller diameter fibers- allows atria to fully contract filling ventricles before ventricles contract

    • In 50 msec excitation spreads through both ventricles simultaneously

    One cardiac cycle

    One Cardiac Cycle

    • At 75 beats/min, one cycle requires 0.8 sec.

      • systole (contraction) and diastole (relaxation) of both atria, plus the systole and diastole of both ventricles

    • End diastolic volume (EDV)

      • volume in ventricle at end of diastole, about 130ml

    • End systolic volume (ESV)

      • volume in ventricle at end of systole, about 60ml

    • Stroke volume (SV)

      • the volume ejected per beat from each ventricle, about 70ml

      • SV = EDV - ESV

    Phases of cardiac cycle

    Phases ofCardiac Cycle

    • Isovolumetric relaxation

      • brief period when volume in ventricles does not change--as ventricles relax, pressure drops and AV valves open

    • Ventricular filling

      • rapid ventricular filling:as blood flows from full atria

      • diastasis: as blood flows from atria in smaller volume

      • atrial systole pushes final 20-25 ml blood into ventricle

    • Ventricular systole

      • ventricular systole

      • isovolumetric contraction

        • brief period, AV valves close before SL valves open

      • ventricular ejection: as SL valves open and blood is ejected

    Cardiac cycle

    Cardiac Cycle



    • Stethoscope

    • Sounds of heartbeat are from turbulence in blood flow caused by valve closure

      • first heart sound (lubb) is created with the closing of the atrioventricular valves

      • second heart sound (dupp) is created with the closing of semilunar valves

    Heart sounds

    Heart Sounds

    Where to listen on chest wall for heart sounds.

    Cardiac output

    Cardiac Output

    • Amount of blood pushed into aorta or pulmonary trunk by ventricle

    • Determined by stroke volume and heart rate

    • CO = SV x HR

      • at 70ml stroke volume & 75 beat/min----5 and 1/4 liters/min

      • entire blood supply passes through circulatory system every minute

    • Cardiac reserve is maximum output/output at rest

      • average is 4-5 while athlete is 7-8

    Influences on stroke volume

    Influences on Stroke Volume

    • Preload (affect of stretching)

      • Frank-Starling Law of Heart

      • more muscle is stretched, greater force of contraction

      • more blood more force of contraction results

    • Contractility

      • autonomic nerves, hormones, Ca+2 or K+ levels

    • Afterload

      • amount of pressure created by the blood in the way

      • high blood pressure creates high afterload

    Stroke volume and heart rate

    Stroke Volume and Heart Rate

    Congestive heart failure

    Congestive Heart Failure

    • Causes of CHF

      • coronary artery disease, hypertension, MI, valve disorders, congenital defects

    • Left side heart failure

      • less effective pump so more blood remains in ventricle

      • heart is overstretched & even more blood remains

      • blood backs up into lungs as pulmonary edema

      • suffocation & lack of oxygen to the tissues

    • Right side failure

      • fluid builds up in tissues as peripheral edema

    Regulation of heart rate

    Regulation of Heart Rate

    • Nervous control from the cardiovascular center in the medulla

      • Sympathetic impulses increase heart rate and force of contraction

      • parasympathetic impulses decrease heart rate.

      • Baroreceptors (pressure receptors) detect change in BP and send info to the cardiovascular center

        • located in the arch of the aorta and carotid arteries

    • Heart rate is also affected by hormones

      • epinephrine, norepinephrine, thyroid hormones

      • ions (Na+, K+, Ca2+)

      • age, gender, physical fitness, and temperature

    Regulation of heart rate1

    Regulation of Heart Rate

    Risk factors for heart disease

    Risk Factors for Heart Disease

    • Risk factors in heart disease:

      • high blood cholesterol level

      • high blood pressure

      • cigarette smoking

      • obesity & lack of regular exercise.

    • Other factors include:

      • diabetes mellitus

      • genetic predisposition

      • male gender

      • high blood levels of fibrinogen

      • left ventricular hypertrophy

    Exercise and the heart

    Exercise and the Heart

    • Sustained exercise increases oxygen demand in muscles.

    • Benefits of aerobic exercise (any activity that works large body muscles for at least 20 minutes, preferably 3-5 times per week) are;

      • increased cardiac output

      • increased HDL and decreased triglycerides

      • improved lung function

      • decreased blood pressure

      • weight control.

    Coronary artery disease

    Coronary Artery Disease

    • Heart muscle receiving insufficient blood supply

      • narrowing of vessels---atherosclerosis, artery spasm or clot

      • atherosclerosis--smooth muscle & fatty deposits in walls of arteries

    • Treatment

      • drugs, bypass graft, angioplasty, stent

    Clinical problems

    Clinical Problems

    • MI = myocardial infarction

      • death of area of heart muscle from lack of O2

      • replaced with scar tissue

      • results depend on size & location of damage

    • Blood clot

      • use clot dissolving drugs streptokinase or t-PA & heparin

      • balloon angioplasty

    • Angina pectoris----heart pain from ischemia of cardiac muscle

    By pass graft

    By-pass Graft

    Percutaneous transluminal coronary angioplasty

    Percutaneous Transluminal Coronary Angioplasty

    Stent in an artery

    Stent in an Artery

    • Maintains patency of blood vessel

    Chapter 21 the cardiovascular system blood vessels and hemodynamics

    Chapter 21The Cardiovascular System: Blood Vessels and Hemodynamics

    • Structure and function of blood vessels

    • Hemodynamics

      • forces involved in circulating blood

    • Major circulatory routes

    Anatomy of blood vessels

    Anatomy of Blood Vessels

    • Closed system of tubes that carries blood

    • Arteries carry blood from heart to tissues

      • elastic arteries

      • muscular arteries

      • arterioles

    • Capillaries are thin enough to allow exchange

    • Venules merge to form veins that bring blood back to the heart

    • Vasa vasorum is vessels in walls of large vessel



    • Tunica interna (intima)

      • simple squamous epithelium known as endothelium

      • basement membrane

      • internal elastic lamina

    • Tunica media

      • circular smooth muscle & elastic fibers

    • Tunica externa

      • elastic & collagen fibers

    Elastic arteries

    Elastic Arteries

    • Largest-diameter arteries have lot of elastic fibers in tunica media

    • Help propel blood onward despite ventricular relaxation (stretch and recoil -- pressure reservoir)

    Muscular arteries

    Muscular Arteries

    • Medium-sized arteries with more muscle than elastic fibers in tunica media

    • Capable of greater vasoconstriction and vasodilation to adjust rate of flow

      • walls are relatively thick

      • called distributing arteries because they direct blood flow



    • Small arteries delivering blood to capillaries

      • tunica media containing few layers of muscle

    • Metarterioles form branches into capillary bed

      • to bypass capillary bed, precapillary sphincters close & blood flows out of bed in thoroughfare channel

      • vasomotion is intermittent contraction & relaxation of sphincters that allow filling of capillary bed 5-10 times/minute

    Capillaries form microcirculation

    Capillaries form Microcirculation

    • Microscopic vessels that connect arterioles to venules

    • Found near every cell in the body but more extensive in highly active tissue (muscles, liver, kidneys & brain)

      • entire capillary bed fills with blood when tissue is active

      • lacking in epithelia, cornea and lens of eye & cartilage

    • Function is exchange of nutrients & wastes between blood and tissue fluid

    • Structure is single layer of simple squamous epithelium and its basement membrane

    Types of capillaries

    Types of Capillaries

    • Continuous capillaries

      • intercellular clefts are gaps between neighboring cells

      • skeletal & smooth, connective tissue and lungs

    • Fenestrated capillaries

      • plasma membranes have many holes

      • kidneys, small intestine, choroid plexuses, ciliary process & endocrine glands

    • Sinusoids

      • very large fenestrations

      • incomplete basement membrane

      • liver, bone marrow, spleen, anterior pituitary, & parathyroid gland



    • Small veins collecting blood from capillaries

    • Tunica media contains only a few smooth muscle cells & scattered fibroblasts

      • very porous endothelium allows for escape of many phagocytic white blood cells

    • Venules that approach size of veins more closely resemble structure of vein



    • Proportionally thinner walls than same diameter artery

      • tunica media less muscle

      • lack external & internalelastic lamina

    • Still adaptable to variationsin volume & pressure

    • Valves are thin folds of tunica interna designed to prevent backflow

    • Venous sinus has no muscle at all

      • coronary sinus or dural venous sinuses

    Varicose veins

    Varicose Veins

    • Twisted, dilated superficial veins

      • caused by leaky venous valves

        • congenital or mechanically stressed from prolonged standing or pregnancy

      • allow backflow and pooling of blood

        • extra pressure forces fluids into surrounding tissues

        • nearby tissue is inflamed and tender

    • Deeper veins not susceptible because of support of surrounding muscles



    • Union of 2 or more arteries supplying the same body region

      • blockage of only one pathway has no effect

        • circle of willis underneath brain

        • coronary circulation of heart

    • Alternate route of blood flow through an anastomosis is known as collateral circulation

      • can occur in veins and venules as well

    • Alternate routes to a region can also be supplied by nonanastomosing vessels

    Blood distribution

    Blood Distribution

    • 60% of blood volume at rest is in systemic veins and venules

      • function as blood reservoir

        • veins of skin & abdominalorgans

      • blood is diverted from it intimes of need

        • increased muscular activityproduces venoconstriction

        • hemorrhage causes venoconstriction to help maintain blood pressure

    • 15% of blood volume in arteries & arterioles

    Capillary exchange

    Capillary Exchange

    • Movement of materials in & out of a capillary

      • diffusion (most important method)

        • substances move down concentration gradient

        • all plasma solutes except large proteins pass freely across

          • through lipid bilayer, fenestrations or intercellular clefts

          • blood brain barrier does not allow diffusion of water-soluble materials (nonfenestrated epithelium with tight junctions)

      • transcytosis

        • passage of material across endothelium in tiny vesicles by endocytosis and exocytosis

          • large, lipid-insoluble molecules such as insulin or maternal antibodies passing through placental circulation to fetus

      • bulk flow see next slide



    • An abnormal increase in interstitial fluid if filtration exceeds reabsorption

      • result of excess filtration

        • increased blood pressure (hypertension)

        • increased permeability of capillaries allows plasma proteins to escape

      • result of inadequate reabsorption

        • decreased concentration of plasma proteins lowers blood colloid osmotic pressure

          • inadequate synthesis or loss from liver disease, burns, malnutrition or kidney disease

    • Not noticeable until 30% above normal



    • Factors affecting circulation

      • pressure differences that drive the blood flow

        • velocity of blood flow

        • volume of blood flow

        • blood pressure

      • resistance to flow

      • venous return

    • An interplay of forces result in blood flow

    Velocity of blood flow

    Velocity of Blood Flow

    • Speed of blood flow in cm/sec is inversely related to cross-sectional area

      • blood flow is slower in thearterial branches

        • flow in aorta is 40 cm/sec whileflow in capillaries is .1 cm/sec

        • slow rate in capillaries allows forexchange

    • Blood flow becomes faster when vessels merge to form veins

    • Circulation time is time it takes a drop of blood to travel from right atrium back to right atrium

    Volume of blood flow

    Volume of Blood Flow

    • Cardiac output = stroke volume x heart rate

    • Other factors that influence cardiac output

      • blood pressure

      • resistance due to friction between blood cells and blood vessel walls

        • blood flows from areas of higher pressure to areas of lower pressure

    Blood pressure

    Blood Pressure

    • Pressure exerted by blood on walls of a vessel

      • caused by contraction of the ventricles

      • highest in aorta

        • 120 mm Hg during systole & 80during diastole

    • If heart rate increases cardiacoutput, BP rises

    • Pressure falls steadily insystemic circulation with distance from left ventricle

      • 35 mm Hg entering the capillaries

      • 0 mm Hg entering the right atrium

    • If decrease in blood volume is over 10%, BP drops

    • Water retention increases blood pressure



    • Friction between blood and the walls of vessels

      • average blood vessel radius

        • smaller vessels offer more resistance to blood flow

        • cause moment to moment fluctuations in pressure

      • blood viscosity (thickness)

        • ratio of red blood cells to plasma volume

        • increases in viscosity increase resistance

          • dehydration or polycythemia

      • total blood vessel length

        • the longer the vessel, the greater the resistance to flow

        • 200 miles of blood vessels for every pound of fat

          • obesity causes high blood pressure

    • Systemic vascular resistance is the total of above

      • arterioles control BP by changing diameter

    Factors that increase blood pressure

    Factors that Increase Blood Pressure

    Venous return

    Venous Return

    • Volume of blood flowing back to the heart from the systemic veins

      • depends on pressure difference from venules (16 mm Hg) to right atrium (0 mm Hg)

      • tricuspid valve leaky andbuildup of blood on venousside of circulation

    • Skeletal muscle pump

      • contraction of muscles & presence of valves

    • Respiratory pump

      • decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium



    • Fainting or a sudden, temporary loss of consciousness not due to trauma

      • due to cerebral ischemia or lack of blood flow to the brain

    • Causes

      • vasodepressor syncope = sudden emotional stress

      • situational syncope = pressure stress of coughing, defecation, or urination

      • drug-induced syncope = antihypertensives, diuretics, vasodilators and tranquilizers

      • orthostatic hypotension = decrease in BP upon standing

    Control of blood pressure flow

    Control of Blood Pressure & Flow

    • Role of cardiovascular center

      • help regulate heart rate & stroke volume

      • specific neurons regulate blood vessel diameter

    Output from the cardiovascular center

    Output from the Cardiovascular Center

    • Heart

      • parasympathetic (vagus nerve)

        • decrease heart rate

      • sympathetic (cardiac accelerator nerves)

        • cause increase or decrease in contractility & rate

    • Blood vessels

      • sympathetic vasomotor nerves

        • continual stimulation to arterioles in skin & abdominal viscera producing vasoconstriction (vasomotor tone)

        • increased stimulation produces constriction & increased BP

    Hormonal regulation of blood pressure

    Hormonal Regulation of Blood Pressure

    • Renin-angiotensin-aldosterone system

      • decrease in BP or decreased blood flow to kidney

      • release of renin / results in formation angiotensin II

        • systemic vasoconstriction

        • causes release aldosterone (H2O & Na+ reabsorption)

    • Epinephrine & norepinephrine

      • increases heart rate & force of contraction

      • causes vasoconstriction in skin & abdominal organs

      • vasodilation in cardiac & skeletal muscle

    • ADH causes vasoconstriction

    • ANP (atrial natriuretic peptide) lowers BP

      • causes vasodilation & loss of salt and water in the urine

    Local regulation of blood pressure

    Local Regulation of Blood Pressure

    • Local factors cause changes in each capillary bed

      • autoregulation is ability to make these changes as needed by demand for O2 & waste removal

      • important for tissues that have major increases in activity (brain, cardiac & skeletal muscle)

    • Local changes in response to physical changes

      • warming & decrease in vascular stretching promotes vasodilation

    • Vasoactive substances released from cells alter vessel diameter (K+, H+, lactic acid, nitric oxide)

      • systemic vessels dilate in response to low levels of O2

      • pulmonary vessels constrict in response to low levels of O2

    Shock and homeostasis

    Shock and Homeostasis

    • Shock is failure of cardiovascular system to deliver enough O2 and nutrients

      • inadequate perfusion

      • cells forced to switch to anaerobic respiration

      • lactic acid builds up

      • cells and tissues become damaged & die

    Types of shock

    Types of Shock

    • Hypovolemic shock due to loss of blood or body fluids (hemorrhage, sweating, diarrhea)

      • venous return to heart declines & output decreases

    • Cardiogenic shock caused by damage to pumping action of the heart (MI, ischemia, valve problems or arrhythmias)

    • Vascular shock causing drop inappropriate vasodilation -- anaphylatic shock, septic shock or neurogenic shock (head trauma)

    • Obstructive shock caused by blockage of circulation (pulmonary embolism)

    Homeostatic responses to shock

    Homeostatic Responses to Shock

    • Mechanisms of compensation in shock attempt to return cardiac output & BP to normal

      • activation of renin-angiotensin-aldosterone

      • secretion of antidiuretic hormone

      • activation of sympathetic nervous system

      • release of local vasodilators

    • If blood volume drops by 10-20% or if BP does not rise sufficiently, perfusion may be inadequate -- cells start to die

    Restoring bp during hypovolemic shock

    Restoring BP during Hypovolemic Shock

    Signs symptoms of shock

    Signs & Symptoms of Shock

    • Rapid resting heart rate (sympathetic stimulation)

    • Weak, rapid pulse due to reduced cardiac output & fast heart rate

    • Clammy, cool skin due to cutaneous vasoconstriction

    • Sweating -- sympathetic stimulation

    • Altered mental state due to cerebral ischemia

    • Reduced urine formation -- vasoconstriction to kidneys & increased aldosterone & antidiuretic hormone

    • Thirst -- loss of extracellular fluid

    • Acidosis -- buildup of lactic acid

    • Nausea -- impaired circulation to GI tract

    Evaluating circulation

    Evaluating Circulation

    • Pulse is a pressure wave

      • alternate expansion & recoil of elastic artery after each systole of the left ventricle

      • pulse rate is normally between 70-80 beats/min

        • tachycardia is rate over 100 beats/min/bradycardia under 60

    • Measuring blood pressure with sphygmomanometer

      • Korotkoff sounds are heard while taking pressure

      • systolic blood pressure from ventricular contraction

      • diastolic blood pressure during ventricular contraction

        • provides information about systemic vascular resistance

      • pulse pressure is difference between systolic & diastolic

      • normal ratio is 3:2:1 -- systolic/diastolic/pulse pressure

    Pulse points

    Pulse Points

    Systemic circulation

    Systemic Circulation

    • All systemic arteries branch from the aorta

    • All systemic veins drain into the superior or inferior vena cava or coronary sinus to return to the right-side of heart

    Arterial branches of systemic circulation

    Arterial Branches of Systemic Circulation

    • All are branches from aorta supplying arms, head, lower limbs and all viscera with O2 from the lungs

    • Aorta arises from left ventricle (thickest chamber)

      • 4 major divisions of aorta

        • ascending aorta

        • arch of aorta

        • thoracic aorta

        • abdominal aorta

    Aorta and its superior branches

    Aorta and Its Superior Branches

    • Aorta is largest artery of the body

      • ascending aorta

        • 2 coronary arteries supply myocardium

      • arch of aorta -- branches to the arms & head

        • brachiocephalic trunk branches into right common carotid and right subclavian

        • left subclavian & left carotid arise independently

      • thoracic aorta supplies branches to pericardium, esophagus, bronchi, diaphragm, intercostal & chest muscles, mammary gland, skin, vertebrae and spinal cord

    Coronary circulation1

    Coronary Circulation

    • Right & left coronary arteries branch to supply heart muscle

      • anterior & posterior interventricular aa.

    Subclavian branches

    Subclavian Branches

    • Subclavian aa. pass superior to the 1st rib

      • gives rise to vertebral a. that supplies blood to the Circle of Willis on the base of the brain

    • Become the axillary artery in the armpit

    • Become the brachial in the arm

    • Divide into radial and ulnar branches in the forearm

    Common carotid branches

    Common Carotid Branches

    Circle of Willis

    • External carotid arteries

      • supplies structures external to skull as branches of maxillary and superficial temporal branches

    • Internal carotid arteries (contribute to Circle of Willis)

      • supply eyeballs and parts of brain

    Arteries of the lower extremity

    Arteries of the Lower Extremity

    • External iliac artery become femoral artery when it passes under the inguinal ligament & into the thigh

      • femoral artery becomes popliteal artery behind the knee

    Veins of the systemic circulation

    Veins of the Systemic Circulation

    • Drain blood from entire body & return it to right side of heart

    • Deep veins parallel the arteries in the region

    • Superficial veins are found just beneath the skin

    • All venous blood drains to either superior or inferior vena cava or coronary sinus

    Major systemic veins

    Major Systemic Veins

    • All empty into the right atrium of the heart

      • superior vena cava drains the head and upper extremities

      • inferior vena cava drains the abdomen, pelvis & lower limbs

      • coronary sinus is large vein draining the heart muscle back into the heart

    Veins of the head and neck

    Veins of the Head and Neck

    • External and Internal jugular veins drain the head and neck into the superior vena cava

    • Dural venous sinuses empty into internal jugular vein

    Circulatory routes

    Circulatory Routes

    • Systemic circulation is left side heart to body & back to heart

    • Hepatic Portal circulation is capillaries of GI tract to capillaries in liver

    • Pulmonary circulation is right-side heart to lungs & back to heart

    • Fetal circulation is from fetal heart through umbilical cord to placenta & back

    Hepatic portal system

    Hepatic Portal System

    • Subdivision of systemic circulation

    • Detours venous blood from GI tract to liver on its way to the heart

      • liver stores or modifies nutrients

    • Formed by union of splenic, superior mesenteric & hepatic veins

    Arterial supply and venous drainage of liver

    Arterial Supply and Venous Drainage of Liver

    Pulmonary circulation

    Pulmonary Circulation

    • Carries deoxygenated blood from right ventricle to air sacs in the lungs and returns it to the left atria

    • Vessels include pulmonary trunk, arteries and veins

    • Differences from systemic circulation

      • pulmonary aa. are larger, thinner with less elastic tissue

      • resistance to is low & pulmonary blood pressure is reduced

    Aging and the cardiovascular system

    Aging and the Cardiovascular System

    • General changes associated with aging

      • decreased compliance of aorta

      • reduction in cardiac muscle fiber size

      • reduced cardiac output & maximum heart rate

      • increase in systolic pressure

    • Total cholesterol & LDL increases, HDL decreases

    • Congestive heart failure, coronary artery disease and atherosclerosis more likely

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