Heart, Blood Vessels, Blood

CARDIOVASCULAR SYSTEM

- Heart, blood vessels, blood

- Consists of 2 circuits:

- Pulmonary Circuit

- Systemic Circuit

ANATOMY OF THE HEART

Pumps 7,000 liters of blood per day

It takes about 1 minute for blood to circulate around the body

Contracts 2.5 billion times in a lefetime

Size of the heart: 14cm long and 9 cm. wide

2 muscular pumps in one:

- left heart pumps blood to the body tissues

- right heart pumps blood to the lungs

The heart circulates the blood through the circulatory system. Blood carries oxygen and nutrients to the cells

Tisssues Covering the Heart

Pericardium – serous membrane that surrounds the heart

- Fibrous Pericardium – outer layer

- Parietal Pericardium – inner lining of fibrous pericardium

- Visceral Pericardium – inner layer

- Pericardial Cavity – space between the parietal and visceral layers. Contains serous fluid

Walls of the Heart

Epicardium – visceral pericardium

Myocardium – middle layer, thick and consists mostly of cardiac muscle tissue

Endocardium – inner layer consisting of epithelium and connective tissue

Anatomy of the Heart

1. Consists of 4 chambers

- 2 atria – superior chambers, thin muscular walls

- 2 ventricles – inferior chambers, thicker muscular walls

2. Valves:

- Atrioventricular valves:

- Tricuspid: separates right atrium and right ventricle

- Bicuspid (mitral): separates left atrium and left ventricle

- Semilunar valves;

- Pulmonary Semilunar: found between right ventricle and pulmonary artery

- Aortic Semilunar: found between left ventricle and aorta

Valves direct the flow of blood and prevent backflow of blood

Heart Murmur: if a valve is damaged or does not close properly, blood leaks backwards causing a “noise”

Blood Supply to the Heart

Coronary Arteries – supply blood to tissues of the heart

- the first 2 branches of the aorta

Cardiac Veins – empty into the right atrium (coronary sinus)

Path of Blood through the heart:

Vena Cava  R atrium  tricuspid valve  R ventricle  Pulmonary semilunar valve 

Pulmonary artery  lungs  Pulmonary vein  L atrium  bicuspid valve  L ventricle 

Aortic semilunar valve  aorta  body  vena cava

Heart Attack

- A block or narrowing of a coronary artery or one of its branches deproves the myocardial cells of oxygen

- Angina Pectoris – may occur during activty or stress

- A complete blockage kills heart tissue – Myocardial Infarction (MI), a heart attack

THE CARDIAC CYCLE

The heart beats in a coordinated fashion

- Systole – contraction of the atria

- Diastole – relaxation

- Cardiac Cycle – contraction and relaxation of the heart

Sounds of the Heart

“lubb – dupp”

- Lubb = ventricular systole, AV valves closing

- Dupp = ventricular diastole, pulmonary and aortic valves closing

The Heart Conduction System

- Sinoatrial (SA) node – maintains rhythym

- pacemaker

- found in the wall of the right atrium where the superior vena cava enters

- Atrioventricular (AV) node – found in the wall between the right atrium and right ventricle in the interatrial septum

Functional Syncytium – a mass of merging cells that act as a unit.

- atrial syncytium

- ventricular syncytium

SA Node  Junctional Fibers  Atrtial Synctium  AV node  AV Bundle (Bundle of His)  Bundle Branches  Purkinje Fibers 

Blood Pressure

Systolic blood pressure (the upper number) — indicates how much pressure your blood is exerting against your artery walls when the heart beats.

Diastolic blood pressure (the lower number) — indicates how much pressure your blood is exerting against your artery walls while the heart is resting between beats.

Normal BP – 120/80

Hypertension: >140/90

Hypotension: <90/60

The EKG

Electrocardiogram (ECG or EKG from the German word Elektrokardiogram) is a test that records the electrical activity of the heart.

- Measures the rate and regularity of heartbeats, as well as information about the heart anatomy.

Interpreting an EKG

P wave – atrial depolarization (contraction)

QRS complex – depolarization of the right and left ventricles

T wave – repolarization of the ventricles

PR interval – time for the cardiac impulse to travel from SA node through the AV node

QT interval – beginning of QRS complex to end of T wave. Prolonged QT interval is a risk for ventricular tachyarrythmias and sudden death

ST segment – segment where the ventricles are depolarized

THE WIGGER DIAGRAM

End-diastolic volume - the amount of blood in each ventricle at the end of ventricular diastole (the start of ventricular systole) 130 ml

End-systolic volume - the amount of blood remaining in each ventricle at the end of ventricular systole (the start of ventricular diastole) 50 ml

Stroke volume (SV) - the amount of blood pumped out of each ventricle during a single beat, which can be expressed as EDV – ESV = SV 130ml – 50ml = 80 ml

Ejection fraction - the percentage of EDV represented by the SV

The stroke volume divided by the EDV or 80/130 = 62%

A simple model of Stroke Volume

Stroke volume of the heart can be compared to the amount of air pumped from an old-fashioned bicycle pump. The amount varies with the amount of handle movement. The extent of the upward movement corresponds to the EDV; extent of the downward movement corresponds to the ESV

Cardiac Output – the amount of blood pumped by each ventricle in 1 minute

CO = SV x HR

If the stroke volume is 80 ml/beat and the heart rate is 75 bpm

CO = 80ml/beat x 75 bpm

CO = 6000 ml/min (6 L/min)

The EDV is affected by:

1. Filling Time – the duration of ventricular diastole

2. Venous return – the rate of blood flow over this period

The ESV is affected by:

1. Preload – the degree of stretching experienced during ventricular diastole, which is directly proportional to the EDV

The Frank-Starling Principle (Straling’s Law of the Heart): increases in EDV results in a corresponding increase in stroke volume

- Relationship between fiber length and force of contraction

- increase blood in heart  inc. ventricular distention  inc. contraction  inc. SV  inc. CO

2. Contractility – the amount of force produced during a contraction at a given preload

3. Afterload – the amount of tension the contracting ventricle must produce to force open the semilunar valve and eject blood

- The greater the afterload, the longer the period of isovolumetric contraction, the shorter the duration of ventricular ejection, and the larger the ESV

Or

- As afterload increases, the stroke volume decreases

- increases in arterial pressure (HYPERTENSION) increases afterload