Cardiovascular System - Anatomy & Physiology

Perdicardium

2 layered sac that surrounds the heart

2 layers of pericardium

• Fibrous pericardium: Outer (superficial) layer made of dense connective tissue

• Serous pericardium: Inner (deep) layer

  • Has 2 layers

Serous pericardium

• Parietal pericardium: simple epithelium

• Visceral pericardium (aka epicardium): simple epithelium

  • Pericardial fluid: between the serous pericardial layers, reduces friction as heart beats inside the sac

3 layers of heart wall

• Epicardium (aka visceral pericardium)

• Myocardium: cardiac muscle

• Endocardium: loose connective tissue and simple squamous epithelium, lines all the chambers of heart

4 chambers of the heart

• 2 atria: superior, small

• 2 ventricles: inferior, large, are the PUMPS of the heart

  • Left ventricle is much thicker than right

What is the function of heart valves

Maintain unidirectional flow of blood

What are the 4 valves in the heart?

• 2 atrioventricular valves

  • Left AV valve: bicuspid/mitral valve

    • 2 cusps/flaps

  • Right AV valve: tricuspid valve

    • 3 cusps/flaps

• 2 semilunar valves between ventricles and arteries

  • Both semilunar valves have 3 cusps (flaps)

  • Pulmonary semilunar on right

  • Aortic semilunar on left

Circulatory path

1. Right atrium

2. Tricuspid valve

3. Right ventricle

4. Pulmonary semilunar valve

5. Pulmonary arteries

6. Pulmonary capillary beds

7. Pulmonary veins

8. Left atrium

9. Bicuspid valve

10. Left ventricle

11. Aortic semilunar valve

12. Aorta out into systemic circulation

13. Arterioles (smaller arteries)

14. Capillary beds of the body tissues

15. Venules (smaller veins)

16. Veins

17. Inferior and superior venae cavae and then back into Right Atrium (where we started!)

What is a systole and diastole

• Systole = contraction of a chamber

• Diastole = relaxation of a chamber

Atrial systole

• The 2 atria contract

• Pushed blood down into ventricles

• AV valves are open, semilunar valves closed

• Ventricles are in diastole (relaxed) at this time

Ventricular systole

• The 2 ventricles contract

• Forces blood out into arteries

• AV valves closed, semilunar valves are open

• Atria in diastole (relaxed) at this time

What do lub and dub mean

• “Lub”: sound of turbulent blood flow caused by closing of AV valves

• “Dub”: sound of turbulent blood flow caused by closing of semilunar valves

Heart murmur

incomplete valve closure, some blood whooshes backward through the valve creating prolonged turbulence

Coronary arteries

Branch from base or aorta and run on surface of heart

Cardiac vein

drains the heart muscle and dumps the blood into coronary sinus that returns blood to the right atrium

Angina

sporadic chest pain due to narrowing of artery and reduction of O₂ rich blood to myocardium, usually during exercise or stress

Myocardial infarction

• Aka heart attack

• Complete blockage of a coronary artery and death of part of myocardium due to lack of blood

Cardiac arrest

• When the heart suddenly stops beating because of a serious arrhythmia

  • People with heart disease are at higher risk of sudden cardiac arrest but not all people who experience sudden cardiac arrest (SCA) have heart disease

  • Heart attack can cause SCA because dead areas of myocardium can interrupt electrical signals through the heart and cause ventricular fibrillation

Arteries

• Carry blood away from the heart

• Generally carry oxygenated blood, except the pulmonary artery which carries deoxygenated blood to the lungs

• Arteries have high pressure

3 layers of arteries

• Tunica intima: innermost layer, made of simple squamous epithelium

• Tunica media: middle layer, made of smooth muscle and elastic fibers, thickest layer, and have low compliance (are pressure reservoirs)

• Tunica externa (aka adventitia): lots of collagen fibers

Veins

• Carry blood towards heart

• Generally carry deoxygenated blood except pulmonary veins, which carry oxygenated blood from the lungs towards the heart

• Same 3 layers as arteries but tunica media is much thinner and not as elastic because veins have high compliance (are volume reservoirs)

• Have valves to prevent backflow because they are low pressure vessels

3 factors that help keep blood moving toward heart

1. Skeletal muscle contraction

2. Respiratory “pump”

3. Venous valves

What is intrinsic conduction system made of?

• Made of specialized cardiac muscle cells that have few myofibrils

  • Their job is NOT to contract

  • Their job is to initiate and distribute impulses (depolarize) throughout the myocardium to initiate and coordinate contraction of atria and ventricles

4 parts of Intrinsic Conduction System

1. Sinoatrial (SA) node: pacemaker

2. Atrioventricular (AV) node

3. Atrioventricular bundle (Bundle of His)

4. Purkinje fibers

SA Node

• Pacemaker

• On posterior wall of right atrium

• Initiates (starts) each heartbeat

• Self-excitatory at a rate of 70-80 times per min

AV Node

• At the junction of right atrium and ventricle

• Also self-excitatory but at a much slower rate

AV bundle

• Bundle of His

• In interventricular septum, then branch into right and left ventricles

Purkinje Fibers

• Branches of conducting tissue that fan out into wall of ventricles

Electrocardiogram (ECG/EKG)

• Records electrical current of the intrinsic conduction system that passes through the heart as it depolarizes (contracts)

• Upward deflection of ECG: produced when electrical impulses travel towards positive electrode

• Downward deflection of ECG: produced hen electrical impulses travel towards negative electrode

What is P wave, QRS complex, and T wave?

• P wave: atrial depolarization

• QRS complex: ventricular depolarization (masks atrial repolarization)

• T wave: ventricular repolarization

Sinus rhythm

Normal rhythm

• HR between 60 and 100 bpm

Sinus bradycardia

• HR < 60

• Possible causes

  • Fit/athletic

  • Hypothermia

  • Hypothyroidism

  • Some drugs

Sinus tachycardia

• HR > 100

• Possible causes

  • During exercise

  • Anxiety/pain/fear

  • Hypotension

  • Hyperthyroidism

  • Some drugs (caffeine)

Atrial fibrillation

• Atria beat out of coordination with ventricles

  • Very fast atrial contraction rate (400-600/min) and ventricular rate is frequently fast (100-200) too

• May have no symptoms, but if symptoms appear they include palpitations, shortness of breath, and weakness

• ECG: NO visible P waves and QRS complex has normal contours

• Treatment: drugs to control HR (beta-blockers) and anticoagulants to prevent blood clots due to inefficient blood flow through the atria and increased risk of strokes

Complete heart block

• No communication between SA node and AV node

  • Atria and ventricles each contract at their own rate (ventricles contract slower)

• Causes: prior heart attack, lyme disease, aging

• Symptoms: fatigue, dizziness, fainting

• Treatment: pacemaker

Wolff-Parkinson-White Syndrome

• Cause: extra electrical route (bundle of Kent) that bypasses AV node → tells ventricles to contract early (aka pre-excitation)

• ECG: The QRS-complex initially exhibits an early upstroke called the delta wave

• Symptoms: fast pounding heartbeat, lightheaded, dizzy, shortness of breath

• Treatment: ablation, medication, or nothing

Ventricular fibrillation

• Completely disorganized electrical activity through the heart

• Heart quivers but is not pumping blood (no cardiac output → blood is not being pumped out to lungs and body)

• Loss of consciousness and no pulse

• Can be caused by heart attack, heart disease, drugs, trauma

• Need CPR and external defibrillation (AED) to possibly correct this, epinephrine can be given

• Irreversible brain damage after 4-6 minutes of Ventricular fibrillation due to lack of oxygen, death soon follows