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HUMAN ANATOMY
LECTURE SIXTEEN
CARDIOVASCULAR
SYSTEM
CARDIOVASCULAR SYSTEM
Includes:
• heart
• blood vessels
• fluid connective tissue component
BLOOD
FUNCTION - maintain homeostasis by:
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Transportation of gases, nutrients, and waste products
Transport of regulatory molecules (hormones)
Regulation of pH and ion concentration of interstitial fluids
Maintenance of body temperature
Protection against foreign substances (toxins and pathogens)
Clot formation
CHARACTERISTICS
• Fluid connective tissue consisting of
cells (formed elements) and cell
fragments (formed elements)
surrounded by a liquid matrix
(plasma)
• Temperature ~38 °C
• pH 7.35 - 7.45
PLASMA
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91% water, 7% proteins (albumin, globulins, fibrinogen), 2% other
High capacity for holding heat - distributes heat generated from metabolic activity of
tissues
Albumin
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Most abundant (60%) of plasma proteins
Important in transport of materials in the blood - A.A. and some hormones
Globulins
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Function as antibodies and for transport of some ions and hormones
Fibrinogen
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Responsible for formation of blood clots
FORMED ELEMENTS
• Erythrocytes (RBC), leukocytes
(WBC), thrombocytes (platelets)
• Produced by a process called
HEMATOPOIESIS - in adults occurs
in red bone marrow
• Derive from STEM CELLS that
differentiate into specific cell types
ERYTHROCYTES - RED BLOOD CELLS
• Biconcave disc with thin central region and thicker edges
- increases surface area for movement of gases in and out of cell
- ability to form stacks within tiny blood vessels
- flexibility to bend or stretch
• Lack organelles (to make room for more gases) - not able to divide so are
replaced every ~120 days
• HEMOGLOBIN is the main component - composed of 4 globins (large
protein molecules) and a heme (pigment molecule that holds iron)
- heme with oxygen = oxyhemoglobin (bright red)
- heme without oxygen = deoxyhemoglobin (dark red)
- heme with carbon dioxide = carbaminohemoglobin
BLOOD TYPING
• Antigens (proteins) appear on the
surface of RBC’s
TYPE A blood has A ANTIGENS
TYPE B blood has B ANTIGENS
TYPE AB blood has AB ANTIGENS
TYPE O blood has NO ANTIGENS
• Antibodies in the plasma attack antigens
TYPE A blood has B ANTIBODIES
TYPE B blood has A ANTIBODIES
TYPE AB blood has NO ANTIBODIES
TYPE O blood has A and B ANTIBODIES
• Donors give blood and recipients receive
blood
LEUKOCYTES - WHITE BLOOD CELLS
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Spherical cells that lack white hemoglobin (clear/white)
Much larger than RBC’s, have nucleus and other organelles
Primary functions are:
- to protect the body against invading microorganisms
- to remove dead cells and debris from the tissues by phagocytosis
Move out of the blood and through the tissues by ameboid movement cytoplasmic streaming into projections of the cellular membrane
Migrate through body tissues to areas of infection or injury - able to
chemically detect signs of tissue damage
Many are capable of phagocytosis (engulfing) of pathogens, cell debris, etc.
TYPES OF LEUKOCYTES
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Named for appearance when stained
- large cytoplasmic granules = GRANULOCYTES
- very small granules = AGRANULOCYTES
GRANULOCYTES
(1) Neutrophils – most common
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Have a very dense segmented nucleus with 2 – 5 lobes attached by a string-like
structure - polymorphonuclear leukocytes
Highly mobile, first to the site of an injury
Phagocytize foreign substances, attack bacteria “marked” by antibodies
(2) Basophils – least common
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Have many granules that stain very dark
Migrate to injury site and discharge granules into interstitial fluid - histamine dilates
blood vessels and heparin to prevent blood clotting
(3) Eosinophils
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Granules stain red
Attack objects coated with antibodies and release chemicals that reduce
inflammation
AGRANULOCYTES
(1) Lymphocytes – smallest WBC
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Large, round nucleus surrounded by a thin layer of cytoplasm
Continuously migrate through bloodstream, through tissues, and back into the bloodstream
Production of antibodies and other chemicals that destroy microorganisms, produce
allergic reactions, control tumors, and regulate immune system
(2) Monocytes – largest WBC
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Large spherical cells
Leave bloodstream and become macrophages - phagocytize bacteria, dead cells, and other
cellular debris within tissues
Release chemicals that attract other WBC’s
THROMBOCYTES - PLATELETS
• Fragments of cells - bits of cytoplasm
surrounded by cell membrane
• Produced in bone marrow by
megakaryocytes (very large cells)
• Prevent blood loss by:
(1) formation of platelet plugs to seal holes
in small vessels
(2) formation of clots to seal larger wounds
in vessels
- platelet plug forms to close site
temporarily
- chemicals released causing
vasoconstriction, bring more platelets to
the injury site, promoting vessel repair
- plasma proteins form permanent clot
HEART
• Located in the thoracic cavity between
the lungs, within the mediastium
• The apex (pointed tip) is the most
inferior region - directed anteriorly
and to the left, deep to the 5th
intercostal space (between the ribs)
• The base (flat top) is directed
superiorly and slightly posteriorly deep to the 2nd intercostal space
• Functions:
- generating blood pressure
- routing blood through the systemic
(body) and pulmonary (lungs) circuits
- ensuring one-way blood flow
EXTERNAL ANATOMY
Pericardium - double-layered closed sac anchoring the heart and
vessels within the mediastium
• Consists of:
- fibrous pericardium = outer layer with dense network of
collagen fibers
- serous pericardium = thin layer of connective tissue
• Serous pericardium is divided into:
- visceral pericardium or epicardium covering the outer surface
of the heart
- parietal pericardium lining the fibrous pericaridium
Pericardial cavity (space) between the visceral and parietal
pericardium
- full of pericardial fluid produced by serous pericardium –
reduces friction as the heart moves within the pericardium
PERICARDIUM
Auricles extend from each atria - expandable extension of atria
Coronary sulcus - deep groove separating atria and ventricles
- anterior and posterior interventricular sulci mark the
separation between the left and right ventricles (fat builds up in
these depressions)
HEART WALL
Three layers of tissue:
Epicardium (visceral pericardium)
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thin, serous membrane forming the outer layer
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simple squamous epithelium over a layer of loose connective tissue and fat
Myocardium
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Middle layer of cardiac muscle, blood vessels, nerves
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Concentric layers of cardiac muscle tissue
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The atrial myocardium contains muscle bundles that wrap around the atria and
from figure eights encircling the large vessels
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Superficial muscles wrap around the ventricles with deeper layers spiraling
around and between the ventricles
Endocardium
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Smooth inner surface of heart chambers
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Simple squamous epithelium continuous with lining of the large vessels
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Form the heart valves by folding with connective tissue between the layers
MUSCLE LAYERS
INTERNAL ANATOMY
• Divided into four chambers: right and left atrium - right and left ventricles
• Interatrial septum separates the atria and thicker interventricular septum
separates the ventricles
ATRIA
• Smaller, thinner walled upper chambers - receive blood
right atrium - superior and inferior vena cava bring blood from upper
and lower body
- small coronary sinus enters from the wall of the heart
left atrium - pulmonary veins (4) bring blood from the lungs
VENTRICLES
• Major pumping chambers - push blood to heart and body
right ventricle - pulmonary trunk to pulmonary arteries to lungs
left ventricle – aorta carries blood to body
• Left ventricle wall is thicker than the right – pumps blood further
• Walls have muscular ridges called trabeculae carneae
INTERNAL STRUCTURE
HEART VALVES
One-way valves prevent the backflow of blood as chambers contract
Fibrous connective tissue rings (skeleton of the heart) around the valves provide
solid support for the valves
ATRIOVENTRICULAR VALVES
• Located between the atrium and ventricles
right AV valve - tricuspid valve with 3 cusps (folds)
left AV valve – bicuspid (mitral) valve with 2 cusps
• After blood flows from atria to ventricles the valves are pushed backward
toward atria forcing the opening shut
• Papillary muscles attach to valves by thin, strong connective tissue strings
called chordae tendinae - muscles contraction prevents valves from opening
SEMILUNAR VALVES
• Found in aorta and pulmonary trunk
• Consists of three pocketlike semilunar cusps
• When ventricles contract blood pushes valves open - during relaxation blood
flows back toward the ventricle, entering pockets of cusps causing them to
bulge inward and meet in the center, thus blocking the vessel
VALVES
BLOOD SUPPLY TO THE HEART
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Myocardium is thick and very active
metabolically
Coronary arteries supply blood to
the heart wall
Two c. arteries originate from base
of the aorta, just above the semilunar
valve
- the left c. artery supplies the left side
and the right c.artery supplies the right
side - both lie within the coronary
sulcus
Cardiac veins drain blood from the
myocardium
The great cardiac vein runs along
the interventricular sulcus - running
parallel to the c.arteries and carries
blood to the coronary sinus (a large
vein within the coronary sulcus on
posterior side of heart)
The coronary sinus drains into the
right atrium
HEARTBEAT
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Contraction of the atria and ventricles is coordinated by specialized cardiac muscle cells
(nodes) in the heart wall that form the conduction system of the heart
SINOARTERIAL NODE
• The impulse originates in the SA node which contain pacemaker cells that establish
heartbeat
• Embedded in the posterior wall of the right atrium near the entrance of the superior
vena cava
• Send electrical impulses across the atria causing them to contract
• Connected to the AV node by internodal pathways in the atrial walls
ATRIAVENTRICULAR NODE
• Found within the floor of the right atrium near the opening of the coronary sinus
• Impulse is conducted into a bundle of fibers - the atrioventricular bundle or bundle of
His down the septum and divide into left and right bundle branches
• At the tips of the bundle branches the conducting tissue forms many small bundles of
Purkinje fibers - extend to the apex of the heart and to the cardiac muscle of the
ventricle walls
- conduct action potentials very quickly
SA node  atria contract  AV node  bundle of His  Purkinje fibers
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ventricles contract
while atria relax
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entire heart relaxes
ELECTROCARDIOGRAM
• Electrodes are placed on the surface
of the body to measure electrical
current of the heartbeat
• P wave - contraction of the atria
• QRS complex - contraction of the
ventricles
• T wave - relaxation of atria
BLOOD VESSELS
Walls of blood vessels (arteries and veins) are made up of three layers:
(1) Tunica intima - inner endothelial lining with connective tissue layer
- arteries have thick layer of elastic fibers
(2) Tunica media - concentric rings of smooth muscle bound to other layers by
collagen fibers
- in arteries separated from tunica externa by a layer of elastic
fibers - larger arteries have very thick layer
(3) Tunica externa - outermost layer, a connective tissue sheath for anchoring
- in arteries collagen fibers with elastin
ARTERIES
Carry blood away from the heart
Have thick, muscular, elastic walls that allow changes in diameter in response to
changes in blood pressure - allow artery to expand and contract
ELASTIC ARTERIES
• Largest in diameter with thickest walls
• Greater portion of elastic tissue as compared to smooth muscle compared to
smaller arteries
MUSCULAR or DISTRIBUTING ARTERIES
• Medium-sized arteries distribute blood to skeletal muscles and organs
• Walls are thick as compared to their diameter - thick tunica media layer
• Blood flow is controlled by vasoconstriction and vasodilation
ARTERIOLES
• Tunica media is only one or two layers of smooth muscle in larger arterioles,
small arterioles only have smooth muscle scattered throughout
• Innervated by sympathetic nerve fibers - vasoconstriction
CAPILLARIES
• Very thin walls allow exchange between blood and surrounding fluids
• Diameter so narrow that red blood cells flow through in single file
• Origin of each branch has precapillary sphincters of smooth muscle that
regulate blood flow
• At arteriole end oxygen and nutrients leave and at venous end carbon dioxide
and waste products enter
VEINS
Collect blood from tissues and organs and returns it to the heart
Walls are thinner than arteries because blood pressure is much lower
VENULES
• Take blood from capillaries
• Lack tunica media layer
MEDIUM-SIZED VEINS
• Tunica media layer is thin with little smooth muscle
• Thickest layer is tunica externa
• Tunica intima folds inward forming one-way valves to prevent backflow of
blood - more in veins of lower limbs
LARGE VEINS
• Have all tunica layers with thin media and thicker externa layers
ARTERIES vs VEINS
• Artery walls are thicker - more muscle and elastic fibers in the tunica media
• Lumen of the artery often looks smaller than that of a vein because it recoils
when not being stretched - looks pleated
• Arteries retain cylindrical shape - veins often collapse
• Arteries are more resilient - keep their shaped stretched
• Arteries don’t have valves
CARDIOVASCULAR SYSTEM
SYSTEMIC SYSTEM - heart to body to heart
left ventricle aorta  arteries of tissue or organ  capillaries  veins
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right atrium  vena cava
PULMONARY SYSTEM - heart to lungs to heart
right ventricle  pulmonary trunk  pulmonary arteries  lungs
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left atrium  pulmonary veins