Download Cardiovascular System Heart General Shape Approximately the size

Cardiovascular System
Heart
General
 Shape
o Approximately the size of a person’s fist
o Hollow, cone-shaped
 Location
o Apex rests on the diaphragm; leans to the left
o Base is at the level of the second rib
o Located between lungs in the mediastinum
Structure
 Atria: receiving chambers
 Ventricles: discharging chambers
 Coronary sulcus: deep groove, furrow separating atria from ventricles
 Interventricular septum: divides the heart into right and left parts
 Valves
o Allow blood to flow only in one direction through ventricles and out arteries
o AV (atrioventricular valves): between atria and ventricles
 Bicuspid (mitral) valve
 Left AV valve
 Has two cusps (flaps)
 Tricuspid valve
 Right AV valve
 Has three cusps
o Semilunar valves: three cusps
 Pulmonary valve
 Between right ventricle and pulmonary
artery
 Aortic valve
 Between left ventricle and aortic arch
 Coronary arteries and veins: blood supply to the heart
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Coverings
o Enclosed by double sac of serous membrane called pericardium
o Serous fluid produced by pericardial membranes to decrease friction as heart contracts
Walls
o Epicardium: outer layer
o Myocardium: thick bundles of cardiac muscle
o Endocardium: sheet of endothelium that lines the chambers of the heart, continuous with linings of blood
vessels entering and leaving the heart
Cardiac Conduction System
 General process of blood circulation
o Superior and inferior vena cava empty blood into right atrium
o Blood moves from right atrium through tricuspid valve to the right ventricle
o Blood from the right ventricle moves through the pulmonary semilunar valve to the pulmonary trunk
o Pulmonary trunk splits into right and left pulmonary veins
o Blood travels to lungs
o From the lungs, blood comes back to the heart through right and left pulmonary arteries
o Right and left pulmonary arteries empty into the left atrium
o Blood moves from the left atrium through the bicuspid valve into the left ventricle
o The left ventricle contracts to send blood up through the aortic semilunar valve into the aorta
o Blood travels from the aorta into body tissues
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Pulmonary circulation
o Blood vessels carry blood to and from the lungs
o Arteries carry deoxygenated blood from right side of the heart to lungs for gas exchange
o Veins carry oxygenated blood from lungs to left side of the heart
System circulation
o Blood vessels carry blood to and from all body tissues
o Arteries carry oxygenated blood from left side of heart to body tissues
o Veins carry deoxygenated blood from body tissues to right side of heart
Blood vessels
 Layers of tissue
o Tunica intima (tunica interna)
 Innermost layer
 Includes endothelium
 Forms smooth, friction-reducing lining
o Tunica media
 Middle layer
 Mostly circularly-arranged smooth muscle cells and sheets of elastin
 Elastin allows vessels to stretch and recoil
 Muscles
 Contracting/relaxing allows vasoconstriction (narrowing vessels) or vasodilation
(enlargement of vessels)
o Tunica adventitia (tunica externa)
 Outermost layer
 Composed mainly of loosely woven collagen fibers
 Protect blood vessel and anchor it to surround structures
 Infiltrated with nerve fibers and lymphatic vessels
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Types of blood vessels
o Arteries
 Transport blood away from heart
 Have thickest tunica media
Elastic
 Closest to heart
 Experience greatest pressure
 Have greatest amount of
elastin enabling them to
expand
 Recoil of elastic arteries helps
propel blood forward
 Contain smooth muscle but
generally do not vasoconstrict
o
Muscular
 Tunica media composed
mainly of smooth muscle
 Vasomotor fibers of
sympathetic nervous system
regulate activity
 More active than elastic
arteries in vasoconstriction
 Less elastin than elastic
arteries
Arterioles
 Smallest arteries
 Range from all three layers to
single layer of smooth muscle
 Control blood flow into
capillary beds
Capillaries
 Smallest blood vessels
 Contain only tunica interna
 Average diameter is 8-10 micrometers
 (little larger than diameter of red blood cell)
 Exchange materials (gases, nutrients, hormones)
 Pre-capillary sphincter
 Cuff of smooth muscle that surrounds each true capillary
 Regulates blood flow into capillary
 Blood flow regulated by vasomotor nerves and local chemical conditions
 Can bypass or flood capillary bed
Continuous
 Abundant in skin and muscles
 Most common
 Continuous endothelial cells
with gaps called intercellular
clefts; allow passage of small
solutes and fluids in/out of
capillary
 Brain capillaries DO NOT
have intercellular clefts
o BLOOD-BRAIN
BARRIER
Fenestrated
 Some endothelial cells have
pores (fenestrations) in them
 More permeable to small
solutes and fluids
 Found where active absorption
or filtration occurs
o (small intestine,
endocrine organs,
kidneys)
Sinusoid
 Leaky capillaries only in liver,
bone marrow, lymphoid
tissues and some endocrine
organs
 Large, irregular shaped
lumens and usually fenestrated
 Larger intercellular clefts than
continuous
 Allow large molecules and
blood cells to pass between
blood and tissues
o
Veins
 Muscular pump
 Skeletal muscle contraction pushes on adjacent veins
 Propels blood upward toward heart
 Venous valves
 Folds of tunica interna
 Prevent blood from flowing backwards
 Respiratory pump
 Diaphragm contracts to decrease volume in abdominal cavity
o Increase in pressure
o Squeezing of local veins that force blood toward heart
 Diaphragm contracts to increase volume of thoracic cavity
o Pressure decreases
o Increase in diameter of veins in thoracic cavity
o Speeds blood entry into right atrium
Venules
 Smallest veins
 Formed when capillaries unite
 Extremely porous
 Allow fluid and white blood cells to
move through their walls
 Primarily endothelium
Veins
 Have all three tunics
 Thinner walls and larger lumens than
arteries
 Can accommodate large volume of blood
 Thin tunica media
 Little smooth muscle or elastin
 Tunica externa is heaviest layer
 Superior/inferior vena cava have
longitudinal bands of smooth muscle
around tunica externa
Blood Pressure
 Force per unit area exerted on the wall of a blood vessel by its contained blood
o Expressed in mmHg
o Measured in reference to system arterial blood pressure in large arteries near heart
 Taken using sphygmomanometer and stethoscope
 Recorded as fraction
o Systolic pressure over diastolic pressure
 Systolic pressure: blood pressure when heart contracts
 Diastolic pressure: blood pressure when heart relaxes
o Pulse pressure: difference between systolic and diastolic pressure
 Influences
o Peripheral resistance
o Vessel elasticity
o Blood volume
o Cardiac output
Peripheral resistance
 Blood cells and plasma encounter resistance when they come in contact with blood vessel walls
 Sources of peripheral resistance: blood vessel diameter, blood viscosity, total vessel length
 Blood vessel diameter
o Diameter becomes smaller, greater proportion of fluid in contact with wall, resistance to flow is
increased, pressure rises
 Larger diameter, same volume, less pressure
 Smaller diameter, same volume, more pressure
o Diameter regulated by vasomotor fibers
 Sympathetic nerve fibers that innervate vessel’s smooth muscle layer
 Release vasoconstrictors: substances that cause blood vessels to constrict
 Norepinephrine
 Epinephrine
 Angiotensin II
 Vasopressin
o Diameter can decrease due to buildup of fatty deposits (plaques)
 Arteriosclerosis
 Blood viscosity
o Related to thickness of a fluid
o Greater viscosity, less easily molecules slide past one another
o Greater viscosity; greater resistance to flow; greater pressure required to pump same volume of fluid
 Total vessel length
o Increased fatty tissue requires more blood vessels and adds to total vessel length in body
o Longer total vessel length, greater resistance encountered, greater blood pressure
Vessel elasticity
 Healthy elastic artery expands to absorb shock of systolic pressure
 In arteriosclerosis, arteries become calcified and rigid: cannot expand
 Arteries experience higher pressures
Blood volume
 Greater volume of fluid; more fluid presses against walls; greater pressure
 Less volume, less pressure
 Reduced blood volume could be due to sweating
 Increased blood volume could be due to excessive salt intake
Cardiac output
 CARDIAC OUTPUT = STROKE VOLUME X HEART RATE
o Cardiac output: volume of blood pumped by one ventricle per minute
o Stroke volume: amount of blood ejected from ventricles with each beat
 Normal resting heart
o Heart rate (pulse): 75 beats/min
o Stroke volume: 70 mL/min
o Average cardiac output: 5.25 L/min
o Ventricle can hold 120 mL of blood (EDV)
o 50 mL remains in ventricle after contraction (ESV)
 Cardiac reserve
o Heart exceeding normal cardiac output
o In aerobic exercise, cardiac reserve is four times normal cardiac output
 Stroke volume
o Difference between EDV and ESV
o Preload: degree of stretch of cardiac muscle before it contracts
o Stretching increases number of cross bridge interactions
 Increases force of heart contraction
 Achieved by increasing amount of venous blood return to heart
Heart Imbalances
 Ectopic focus: abnormal pacemaker
 Incompetent valve: allows backflow of blood
 Arrhythmia: abnormal heartbeat
o Bradycardia: slow heart beat (below 60 beats/min)
o Tachycardia: rapid heart rate (about 100 beats/min)
 Fibrillation: heart is uncoordinated and useless as a pump
 Angina pectoris: chest pain resulting from ischemia of myocardium
 Congestive heart failure: circulation is inadequate to meet tissue needs due to cardiac decompensation
 Heart block: damage to AV node, releasing ventricles from control of SA node
 Myocardial infarction: Results from prolonged coronary blockage
 Pulmonary congestion: result of initial failure of left side of heart