BIO 238

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

Atrial systole forces more blood into relaxed 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

Components include◦Sinoatrial (SA) node◦Atrioventricular (AV) node◦AV bundle◦Purkinje fibers

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