Cardiovascular System:The Heart

FUNCTIONS OF THE CARDIOVASCULAR SYSTEM

• Transports O2, nutrients, CO2, cell wastes, etc. to and from body cells

• Maintaining body temperature• Homeostatic relationships with

all body systems–With the urinary system,

regulation of blood volume and pressure

LOCATION OF THE HEART

Thoracic cavity between two lungs• ~2/3 to left of midline

Surrounded by pericardium:• Fibrous pericardium -

– Inelastic; anchors heart in place

• Inside is serous pericardium - double layer around heart– Parietal layer fused to fibrous pericardium– Inner visceral layer adheres tightly to heart– Filled with pericardial fluid - reduces friction

during beat.

HEART ANATOMY

The Heart Wall

• Epicardium - outer layer• Myocardium - cardiac muscle

–Two separate networks via gap junctions in intercalated discs - atrial & ventricular

–Networks- contract as a unit• Endocardium - Squamous epithelium

– lines inside of myocardium

The Heart Wall

The Heart Wall

The Heart Wall

Heart Chambers4 chambers:• 2 upper chambers = Atria

– Between is inter-atrial septum– Contains fossa ovalis - remnant of foramen ovalis

• 2 lower chambers = ventricles– Between is interventricular septum

• Wall thickness depends on work load– Atria thinnest– Right ventricle pumps to lungs & thinner than left

External Anatomy

External Anatomy

Internal Anatomy

Great Vessels of the Heart

Superior & inferior Vena Cavae• Delivers O2 depleted blood to R. atrium

from body• Coronary sinus drains heart muscle veins• R. Atrium R. VentriclePumps through Pulmonary Trunk• R & L Pulmonary Arteries• lungs

Great Vessels of the Heart

Pulmonary Veins from lungs• O2 rich blood• L. atrium Left ventricle

ascending aorta bodyBetween pulmonary trunk & aortic arch is the

ligamentum arteriosum• fetal ductus arteriosum remnant

Heart ValvesDesigned to prevent back flow in response

to pressure changes• Atrio-ventricular (AV) valves are found

between the atria and ventricles• Right AV valve = tricuspid valve (has

three flaps, or cusps)• Prevent backflow of blood into the right

atrium

Heart Valves• Left AV valve = bicuspid, or mitral valve• Prevents backflow of blood into left

atriumSemilunar Valves are found at the base of

aorta and pulmonary trunk• Prevent backflow of blood into the

ventricles

Heart ValvesChordae Tendinae:• Tiny white cords that anchor the AV valve

cusps to the wall of the ventricle• Help to anchor the flaps to prevent a prolapse

Coronary CirculationBlood flow through vessels in myocardium =

coronary circulation• Left & right coronary arteries

– branch from aorta to carry blood throughout muscle

• O2 - depleted blood collected by coronary sinus (posterior)

• Empties into right atrium

Coronary Circulation

HEART PHYSIOLOGY

Conduction System1% of cardiac muscle generate action potentials

= Pacemaker & Conduction system• Normally begins at sinoatrial (SA) node • Atria & atria contractAV node – slows the signal, then travels along:AV bundle (Bundle of His) bundle branches Purkinje fibers apex and up- then ventricles contract

Frontal plane

SINOATRIAL (SA) NODE

ATRIOVENTRICULAR(AV) NODE

Left atrium

Left ventricle

Anterior view of frontal section

ATRIOVENTRICULAR (AV)BUNDLE (BUNDLE OF HIS)

RIGHT AND LEFTBUNDLE BRANCHES

PURKINJE FIBERS

1

2

3

4

5

Right atrium

Right ventricle

ElectrocardiogramRecording of currents from cardiac

conduction on skin = electrocardiogram (EKG or ECG)

• P wave = atrial depolarization– Contraction begins right after peak– Repolarization is masked in QRS

• QRS complex = Ventricular depolarization– Contraction of ventricle

• T-wave = ventricular repolarization– Just after ventricles relax

http://www.youtube.com/watch?v=nK0_28q6WoM

Cardiac CycleAfter T-wave ventricular diastole• Ventricular pressure drops below atrial

pressure & AV valves open ventricular filling occurs

After P-wave atrial systole• Finishes filling ventricle (about 25% of

total)

Cardiac CycleAfter QRS ventricular systole• Pressure pushes AV valves closed• Pushes semilunar valves open and ejection

occurs• Ejection until ventricle relaxes enough for

arterial pressure to close semilunar valves

Cardiac Cycle Animations

Cardiac Cycle: Flow Terms• Cardiac Output (CO) = liters/min pumped• Heart Rate (HR) = beats/minute (bpm)• Stroke volume (SV) = volume/beat• CO = HR x SV• Average:

Cardiac Cycle: Control of Stroke Volume

• Degree of stretch = Frank-Starling law– Increase diastolic volume (stretch) increases

strength of contraction increased S.V.– Increased venous return increased S.V.

• Increased sympathetic activity • High back pressure in artery decreased S.V.

– Slows semilunar valve opening• Slow heart rate increased S.V.

Cardiac Cycle: Control of Heart Rate

Pacemaker adjusted by nerves• Cardiovascular Center in Medulla

Parasympathetic - ACh slows HR via Vagus nerve

Sympathetic - norepinephrine speeds HRSensory input for control:• Baroreceptors (aortic arch & carotid sinus)- B.P.• Chemoreceptors- O2, CO2, pH

Cardiac Cycle: Other ControlsHormones: • Epinephrine & norepinephrine increase H.R.• Thyroid hormones stimulate H.R.• Called tachycardia (opposite: bradycardia)Ions• Increased Na+ or K+ decrease H.R. & contraction

force• Increased Ca2+ increases H.R. & contraction

force

Exercise• Aerobic exercise (longer than 20 min)

strengthens cardiovascular system• Well trained athlete doubles maximum

C.O.• Resting C.O. about the same but resting

H.R. decreased

BLOOD VESSELS AND CIRCULATION

Blood VesselsArteries: carry blood away from heart

1. Elastic

2. Muscular: Their smooth muscle helps regulate blood pressure, directs flow

3. Arterioles: branches of main arteries; distribution to capillaries

Blood VesselsCapillaries: thin-walled for diffusion

Veins: carry blood back to heart1. Venules: collect blood from capillaries

2. Veins from tissues vena cavae heart

Blood Vessel Structure: Arteries, Veins

Three Layers:• Tunica externa: connective tissue• Tunica media: smooth muscle• Tunica interna (intima): endothelial

tissue

Blood Vessel Structure: Arteries, Veins

• Arteries: thicker tunica media– Elastic tissue and/or muscle

• Arterioles– Arterioles: control blood pressure, blood

flow• Veins

– Larger lumen, thinner walls– Contain valves to prevent backflow

• Venules– Venules: very thin, no valves

Blood Vessel Structure: Arteries, Veins

Blood Vessel Functions• Muscular arteries, arterioles regulate flow

– Sympathetic activity to smooth muscle vasoconstriction (narrowing)

– Decreased sympathetic activity causes relaxation (dilation)

• Arterioles adjust flow into capillaries• Capillaries: sites of gas exchange• Systemic venules and veins serve as blood

reservoirs (hold ~64% total blood volume)

Venous ReturnBlood enters veins at very low pressure• Inadequate to overcome gravity and return

blood to heart • Skeletal muscle contractions

– Contracting skeletal muscles (especially in lower limbs) squeeze veins emptying them

– Because of venous valves, flow is heart

Venous Return• Respiratory pump has similar action

– Inhalation decreases thoracic pressure and increases abdominal pressure blood to heart

– Exhalation allows refilling of abdominal veins

Venous Return

Blood Flow Through Vessels

Blood flow follows a pressure gradient• Greater gradient greater flow

– BP is highest in aorta: 110/70 mm Hg – BP declines as flows through more

vessels• Capillary beds ~35-16 mm Hg• 16 mm Hg at venules 0 at right

atrium

Factors Regulating Blood Flow

1. Blood volume and ventricular contraction cardiac output

2. Vascular resistance: opposition to flow (depends on lumen diameter, vessel length, and blood viscosity) • Smaller lumen (vasoconstriction) greater

resistance• Greater vessel length (with weight gain)

greater resistance• Higher viscosity (as with high hematocrit)

greater resistance

Cardiovascular Center• Located in medulla• Helps regulate

– Heart rate– Stroke volume– Blood pressure– Blood flow to specific tissues

• Mechanisms– By neural mechanisms– By hormonal mechanisms

Cardiovascular Center InputTo inform brain that BP should be altered:• Input from different parts of brain

– Cerebral cortex: thoughts, decisions– Limbic system: emotions– Hypothalamus: changes in temperature or blood

volume

• Input from sensory receptors and nerves– Proprioceptors, baroreceptors, chemoreceptors

Cardiovascular Center Input• Proprioceptors: monitor movements of

joints and muscles– Cause heart rate as exercise begins cardiac

output (CO) BP

• Baroreceptors in aorta and carotid: if BP – sympathetic stimulation CO BP– parasympathetic CO BP

• Chemoreceptors in aorta and carotid bodies– If low O2, high CO2, or high H+ (acidity)

resistance by vasoconstriction BP

Cardiovascular Center Input

Output Effects• ANS nerves to heart

– Sympathetic HR and force of contraction cardiac output (CO) BP

– Parasympathetic HR CO BP

• Vasomotor (sympathetic nerves)– To arterioles contract smooth muscle

vascular resistance BP– To veins contract smooth muscle move blood

to heart BP

Circulatory Routes• Pulmonary Circulation: from the right side

of the heart to the lungs and back to the left side of the heart

• Systemic Circulation: from the left side of the heart to the tissues and cells of the body and back to the right side of the heart

• Cardiac Circulation: from the left side of the heart through the coronary arteries and back to the right side of the heart

Circulatory Routes