bio 238. heart and blood vessels are part of the cardiovascular system heart pumps blood arteries...
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Heart and blood vessels are part of the cardiovascular system
Heart pumps blood Arteries carry blood away
from the heart to capillaries
Veins carry blood from capillaries to heart
Heart Chambers◦ 2 atria
Receive blood from veins
◦ 2 ventricles Pump blood to arteries
◦Atrial septum◦ Interventricular
septum
◦Heart is a double pump Left atria and ventricle: left pump Right atria and ventricle: right pump
◦Differences in wall thickness depend upon work performed by the chamber Ventricles have more muscle then atria: atria pump
to ventricle, ventricles pump out to body areas Left ventricle is most muscular: pumps blood to
body Right ventricle has less muscle: pumps blood to
lungs only
Heart Valves: ◦Allows blood to flow in one directionAtrioventricular
valves Allows flow from atria to ventricles Tricuspid valve: between R atrium and ventricle Bicuspid (mitral) valve: between L atrium and ventricle
◦Semilunar valves Located at base of blood vessels attached to ventricles Pulmonary semilunar valve: between R ventricle and
pulmonary trunk Aortic semilunar valve: between L ventricle and aorta
Includes:◦Systole: contraction phase◦Diastole: relaxation phase
When atria and ventricles are relaxed, blood flows into atria, then through open AV valves into ventricles◦Semilunar valves closed due to greater pressure in
arteries than in ventricles
Ventricular systole (atrial diastole) increases blood pressure in ventricles ◦Closes AV valves, opens semilunar valves◦Blood moves from ventricles and into arteries
Ventricular diastole (atrial diastole) follows◦Allows AV valves to open and
semilunar valves close◦Cycle repeats
Heart Sounds◦Lub-dup (pause) lub-dup◦Lub: closing of AV valves during
ventricular diastole◦Dup: closing of semilunar valves
during ventricular systole
Flow of Blood Through the Heart◦Two basic circuits of blood flow Pulmonary circuit
Deoxygenated blood flows from R ventricle to lungs
Oxygenated blood flows from lungs to L atrium Systemic Circuit
Oxygenated blood flows L ventricle to body Deoxygenated blood flows from body to R
atrium
Steps of heart circulation◦Superior and inferior vena cava return blood from
body to R atrium◦Pulmonary veins return blood from lungs to L atrium◦Atria push blood into ventricles◦R ventricle pumps blood into pulmonary trunk
Blood moves into R and L pulmonary arteries, which head to lungs
◦ L ventricle pumps blood into the aorta, which carries blood out to body
Conduction system consists of specialized muscle tissue that acts as neural tissue◦Spontaneously form impulses
◦ Impulses cause myocardium to contract
Sinoatrial node◦ Pacemaker of the heart◦ Rhythmically forms impulses to initiate each heartbeat◦ Impulses cause simultaneous contraction of atria
Atrioventricular node◦ Receives impulse from SA node◦ Delay in passing through node allows time for ventricular
filling and the completion or atrial contraction
◦ Passes impulse to the AV bundle
AV bundle◦Divides into L and R branches ◦Carries impulse down ventricular septum and up
lateral ventricle walls◦ Forms Purkinje fibers
Purkinje fibers◦Carry impulse to myocardium of ventricles◦Contraction occurs from the apex upward
Electrocardiogram (ECG or EKG)◦Recording of the electrical current generated during
heart contraction◦Performed by an electrocardiograph
◦Electrocardiogram has three distinct waves P wave: atrial depolarization QRS wave: ventricular depolarization T wave: ventricular repolarization
Numerous factors can act on the SA node to increase or decrease heart rate
Autonomic Regulation◦Cardiac center in the medulla oblongata
Stimulated by excessive blood pressure and emotional factors, such as grief and depression
Sympathetic neurons in the cardiac center cause an increase in heart rate
Parasympathetic neurons in the cardiac center cause a decrease in heart rate
Other factors affecting heart rate◦Age: resting rate declines with age◦Sex: females slightly faster than males◦Physical condition: good condition means
lower heart rate◦Temperature: increase in temperature
increases rate◦Epinephrine: increases strengthens heart rate◦Thyroxine: produces a lesser but longer
lasting increase in heart rate
◦Blood calcium levels Low levels slow heart rate Increased levels increase heart rate and prolong
contraction◦Blood potassium levels
Increased levels decrease both heart rate and force of contraction
Low levels can cause abnormal heart rhythms
Arteries◦Carry blood away from the heart◦Branch into smaller arteries, eventually forming
arterioles Play an important role in controlling blood flow and blood
pressure
Capillaries◦Most numerous and smallest vessels◦RBCs pass through one at a time◦Thin walls allow exchange of materials between blood
and cells
Veins◦Blood flows from capillaries into venules◦Venules unite to form larger veins, which in turn
unite to form even larger veins◦Valves exist in large veins to prevent blood
backflow and aid in venous blood return◦Veins hold ~60% of blood volume at any instant
Reducing venous volume can compensate for blood loss or increase in muscle activity
Blood flows from high pressure areas to low pressure areas◦Greatest in ventricles and lowest in atria
Ventricles create the pressure
Pressure decreases with increased distance from the heart◦Due to increase in overall cross-sectional area of vessels
due to branching
◦Due to low pressure, veins require assistance to return blood to the heart Skeletal muscle
contractions Contraction compresses
veins, forcing blood from one valved segment to another
Important in arms and legs
Respiratory movements Downward contraction of diaphragm during
inspiration Decreases thoracic pressure and increases
abdominal pressure High pressure in abdominal veins forces
blood into low pressure thoracic veins
Arterial blood pressure in the systemic circuit◦Systolic blood pressure
Highest pressure during ventricular systole◦Diastolic blood pressure
Lowest pressure during ventricular diastole◦Pulse pressure is difference between systolic and
diastolic blood pressures Causes the pulse: expansion and contraction of arterial
walls
◦Cardiac output Volume of blood pumped by heart in one minute
Determined by heart rate and blood volume pumped in contraction
Increase cardiac output, increase blood pressure Decrease cardiac output, decrease blood pressure
◦Blood volume Decrease in blood volume, decrease in blood pressure Increase in blood volume, increase in blood pressure
◦Peripheral resistance Friction of blood against blood vessel walls Constriction of arterioles increase both resistance and
blood pressure Dilation of arterioles decreases both resistance and
blood pressure
◦Viscosity Thickness of blood
Determined by blood cell concentration and plasma proteins Increase viscosity increases blood pressure Decrease viscosity decreases blood pressure
Control of Peripheral Resistance◦Vasomotor center in the medulla
Increases frequency of sympathetic impulses to cause vasoconstriction Increases blood pressure and velocity
Accelerates oxygen and carbon dioxide transport rates Decreases frequency of sympathetic impulses to
cause vasodilation Lowers blood pressure and velocity
Activity of vasomotor area can be modified Affected by epinephrine, impulses from higher brain
area, impulses from pressure and chemoreceptors Decrease in pressure, pH, or oxygen causes
vasoconstriction
◦Autoregulation Blood vessels are affected by localized
changes in blood composition Oxygen, carbon dioxide, pH
Effects can override vasomotor control Increases rate of exchange of materials
between cells and capillaries Example: decrease in oxygen and increase in
carbon dioxide causes vasodilation to increase blood flow
Arrhythmia◦ Abnormal heart beat◦ Caused by factors such as damage to conduction system and
drugs Bradycardia
Heart rate less then 60 beats/min
Tachycardia Heart rate over 100 beats/min
Heart flutter Heart rate over 200-300 beats/min
Fibrillation Very rapid heart rate with uncoordinated contraction Blood is not pumped from ventricles
Congestive heart failure (CHF)◦ Acute or chronic inability of hear to pump out returned to it◦ Symptoms include fatigue, edema, accumulation of blood
in organs◦ Possible cause is atherosclerosis
Heart murmurs◦ Unusual heart sounds associated with defective heart
valves
Myocardial infarction◦ Death of myocardium due to coronary artery blockage◦ Heart attack
Pericarditis◦ Inflammation of pericardium due to viral or bacterial
infection
Aneurysm◦ Weakened vessel wall bulges, forming balloon-like sac
filled with blood◦ Rupture can be fatal
Arteriosclerosis◦ Hardening of the arteries◦ Due to calcium deposits accumulating in tunica media
Atherosclerosis◦ Formation of fatty deposits in the tunica interna of arteries◦ Plagues reduce lumen size and increase probability of
blood clot formation
Hypertension◦ Chronic high blood pressure◦ Pressure exceeds 140/90◦ Pre-hypertension
A systolic pressure between 120-139 and diastolic pressure between 80-89
Phlebitis◦ Inflammation of a vein◦ Most common in the legs◦ Thrombophlebitis involves the formation of blood clots at
the inflammation site
Varicose veins◦ Dilated, swollen veins due to malfunctioning valves◦ Causes include heredity, pregnancy, and lack of physical
activity◦ Hemorrhoids
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