Cardiovascular System Notes

Cardiovascular System

• Consists of the heart and blood vessels.

• Heart pumps blood, which carries nutrients, oxygen, and waste.

• Circulatory system includes cardiovascular and lymphatic systems.

Blood Vessels

• Two muscular pumps in series: pulmonary and systemic circulations.

• Pulmonary: Right heart pumps low-oxygen blood to lungs for gas exchange.

• Systemic: Left heart pumps oxygen-rich blood to the body.

• Arteries distribute blood to tissues (largest).

• Arterioles also distribute blood to tissues (3rd largest)

• Capillaries provide cells with blood (smallest).

• Veins collect blood and return it to the heart (2nd largest), contain one-way valves.

• Venules collect blood from capillaries (4th largest).

Vessel Structure: Tunics

1. Tunica intima: Inner endothelial lining.

2. Tunica media: Middle smooth muscle layer (varies).

3. Tunica adventitia: Outer connective tissue coat.

Arteries

• Different types based on size, elastic tissue/muscle ratio, wall thickness.

• Continuum of types:

  1. Large elastic arteries.

  2. Medium muscular arteries.

  3. Small arteries and arterioles.

Large Elastic Arteries

• "Conducting Arteries".

• Elastic walls for expansion and recoil.

• Examples: Aorta, brachiocephalic, left common carotid, left subclavian arteries.

Medium Muscular Arteries

• "Distributing Arteries".

• Smooth muscle walls.

• Example: Femoral artery.

• Vasoconstriction regulates blood flow.

Small Arteries and Arterioles

• Narrow lumen, thick muscular walls.

• Regulate arterial pressure via smooth muscle tonus.

• Hypertension results from increased tonus.

Veins

• Return poorly oxygenated blood to the heart.

• Pulmonary veins carry oxygenated blood from lungs.

• Thin walls.

• Low blood pressure.

• Valves to aid blood return.

• Venules form larger veins.

• Medium veins have valves where flow opposes gravity.

• Large veins have smooth muscle and a developed tunica adventitia (e.g., SVC, IVC).

• Accompany veins are stretched/flattened by artery expansion, aiding flow.

• Musculovenous pump: Skeletal muscle contraction aids venous return.

Clinical Application: Varicose Veins

• Swollen, twisted veins, often in legs.

• Incompetent valves lead to increased pressure and weakened walls.

• Caused by high blood pressure, age, pregnancy, obesity, prolonged sitting/standing, inactivity, genetics.

Capillaries

• Endothelial tubes connecting arterial and venous sides.

• Sequence: Arterioles → Capillaries → Venules.

• Arteriovenous anastomoses (AV shunts) bypass capillaries.

• Conserves body heat (e.g., in fingers).

Clinical Application: Arteriosclerosis

• Hardening of arteries.

• Thickening and loss of elasticity.

• Atherosclerosis: Fat buildup (cholesterol) leads to plaque formation, narrowing, and irregularity.

• Thrombus (blood clot) can cause ischemia and infarction.

• Examples:

  • Myocardial infarction: Heart attack.

  • Stroke: Disrupted brain blood flow.

  • Gangrene: Limb necrosis.

Knowledge Test: Blood Vessel Ordering

1. Largest to Smallest: Arteries, Veins, Arterioles, Venules, Capillaries.

2. Heart to Tissues Back to Heart: Arteries → Arterioles → Capillaries → Venules → Veins.

Knowledge Test: Musculovenous Pump

• Musculovenous pump in lower limb aids venous return.

• Skeletal muscles contract to squeeze veins, pushing blood to the heart.

Overview of the Heart

• Right Atrium: Receives blood from SVC, IVC, coronary sinus.

• Right Ventricle: Forms anterior surface, tapers into the conus arteriosus leading to the pulmonary trunk.

• Left Ventricle: Forms apex of the heart.

• Left Atrium: Forms base of heart and receives blood from pulmonary veins.

Pericardium

• Double-walled sac enclosing the heart.

  1. Fibrous Pericardium: Protects against overfilling.

  2. Serous Pericardium:

     • Parietal Pericardium: Inside fibrous layer.

     • Visceral Pericardium: (Epicardium) on the heart.

• Pericardial Cavity: Potential space with serous fluid for frictionless movement.

Heart Wall Layers

• Epicardium: Thin external layer (visceral serous pericardium).

• Myocardium: Thick middle cardiac muscle layer.

• Endocardium: Thin internal lining membrane.

Heart: Right Atrium

• Pectinate muscles, openings for SVC, IVC, coronary sinus.

• Right AV orifice to right ventricle.

• Fossa ovalis: Remnant of fetal foramen ovale to bypass lungs.

Heart: Right Ventricle

• Forms most of the anterior surface of the heart.

• Trabeculae carneae, tendinous cords attach to tricuspid valve cusps.

• Papillary muscles anchor cords (3).

• Septomarginal trabecula (moderator band).

• Pulmonary valve (semilunar valve).

Heart: Left Atrium

• Pulmonary veins (4) enter the left atrium.

• Smooth wall, slightly thicker than right atrium.

Heart: Left Ventricle

• Mitral valve (bicuspid valve).

• Walls 2-3x thicker than right ventricle.

• Finer, more trabeculae carneae.

• Larger papillary muscles.

• Aortic valve (semilunar).

Knowledge Test: Heart Layers

• Fibrous pericardium, parietal pericardium, pericardial cavity, visceral pericardium (epicardium), myocardium, endocardium.

Knowledge Test: Heart Valves and Chambers

1. Right atrium to right ventricle: Tricuspid valve.

2. Pulmonary veins to left atrium: No valve.

3. Fossa ovalis location: Right atrium.

4. Thickest wall chamber: Left ventricle.

Blood Flow Through the Heart

1. SVC, IVC → Right atrium.

2. Right atrium → Right ventricle (Tricuspid valve).

3. Right ventricle → Pulmonary arteries (Pulmonary valve).

4. Lungs → Left atrium (Pulmonary veins).

5. Left atrium → Left ventricle (Mitral/Bicuspid valve).

6. Left ventricle → Aorta (Aortic valve).

Conducting System of the Heart

• Coordinates cardiac cycle.

• Cardiac muscle cells, specialized conducting fibers (nodal tissue).

• Nodal tissue initiates heartbeat.

Components

• Sinoatrial (SA) Node:

  • Initiates impulses (70x/min) - atria.

  • "Pacemaker".

• Atrioventricular (AV) Node:

  • Receives signal from SA node.

  • Distributes signal to ventricles through AV bundle (Bundle of His).

  • Bundle branches supply Purkinje fibers.

• Sympathetic stimulation speeds conduction; parasympathetic slows it.

Cardiac Cycle

• Synchronous pumping action of heart's 2 AV pumps (left and right chambers)

• Diastole: Ventricular elongation and filling.

• Systole: Ventricular shortening and emptying.

• "Lub": Blood transferred from atria to ventricles; Atrioventricular valves (Tricuspid and Mitral/Bicuspid valves) closing.

• "Dub": Ventricles expel blood from the heart; semilunar valves (pulmonary and aortic valves) closing.

Knowledge Test: Conducting System and Cardiac Cycle

1. Pacemaker: Sinoatrial Node, initiates and regulates impulses.

2. Lub sound: Atrioventricular valves closing (Tricuspid and Mitral/Bicuspid valves).

Lymphoid (Lymphatic) System

• Functions:

  • Drainage for surplus tissue fluid.

  • Removal of cellular debris/infection.

• Lymph:

  • Surplus extracellular fluid.

  • Similar composition to blood plasma.

• System Components:

  • Lymphatic vessels (thin-walled).

  • Lymph nodes (filter lymph).

  • Lymphocytes (immune cells).

  • Lymphoid organs (produce lymphocytes; e.g., spleen, thymus, tonsils).

Lymphatic Drainage

• Lymph traverses lymph nodes.

• Enters lymphatic trunks.

• Drains into:

  • Right Lymphatic Duct: Upper right quadrant; right subclavian/internal jugular vein junction.

  • Thoracic Duct: Remainder of the body; left subclavian/internal jugular vein junction.

Additional Functions

• Absorption and Transport of Dietary Fat:

  • Lacteals receive absorbed fat (chyle) from the intestine.

  • Transport through thoracic duct to venous system.

• Formation of Defense Mechanism:

  • Antibodies produced in response to foreign proteins.

Knowledge Test: Lymphatic System Functions

• Drainage for surplus tissue fluid.

• Absorption and transport of dietary fat.

• Formation of a defense mechanism.