Chapter 15 Lecture Notes – Cardiovascular System

The cardiovascular system is a complex network that is essential for maintaining homeostasis within the body. It consists of various components, including the heart, arteries, capillaries, veins, and blood, which work together to circulate important substances throughout the body.

Major Functions:

• Circulation of Substances: The primary function is to transport oxygen and vital nutrients to the cells and tissues, facilitating their metabolic processes.

• Waste Removal: It plays a critical role in removing metabolic waste products such as carbon dioxide (CO₂) and urea, which are byproducts of cellular metabolism that need to be eliminated to maintain healthy cellular function.

Two Circuits of Blood Flow:

1. Pulmonary Circuit:

   • This circuit is responsible for transporting oxygen-poor blood from the right side of the heart to the lungs. Here, blood is oxygenated and carbon dioxide is expelled through the process of respiration. This circuit is vital for replenishing oxygen in the blood and serves as a filtration system to remove gaseous waste from circulation.

2. Systemic Circuit:

   • This circuit delivers oxygen-rich blood and essential nutrients from the left side of the heart to the body's cells. As the blood traverses various tissues, it supplies the necessary components for cellular activity and collects metabolic waste products for removal, thus ensuring optimal functioning of bodily systems.

Heart Anatomy:
The heart is a muscular organ that pumps approximately 7,000 liters of blood daily, contracting about 3-4 billion times over a typical human lifespan, demonstrating remarkable endurance and efficiency.

• Pericardium:

  • The heart is encased in the pericardium, a protective sac that also contains pericardial fluid, which provides lubrication to reduce friction during heartbeats and prevents displacement.

Layers of the Heart:

• Endocardium:

  • A thin layer lining the heart chambers that ensures smooth blood flow within the heart.

• Myocardium:

  • The thickest layer composed of cardiac muscle fibers that contract and relax to pump blood throughout the body.

• Epicardium (Visceral Pericardium):

  • The outermost layer that serves as a protective layer of the heart.

• Pericardial Cavity:

  • The space between the pericardial membranes that contains fluid to minimize friction during the heart's movement.

• Parietal Pericardium & Fibrous Pericardium:

  • These layers further protect the heart, anchoring it to surrounding structures.

Heart Structure:

• Chambers:

  • Right Atrium: Receives deoxygenated blood from the body via the superior and inferior vena cavae.

  • Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary arteries for oxygenation.

  • Left Atrium: Collects oxygenated blood from the lungs through the pulmonary veins.

  • Left Ventricle: Pumps oxygen-rich blood into the systemic circulation through the aorta, having the thickest myocardium to handle higher pressure.

• Valves:

  • The heart contains four valves: Tricuspid, Mitral (bicuspid), Pulmonary, and Aortic valves that regulate blood flow and prevent backflow.

Internal Structures:

• Interatrial Septum: Separates the right and left atria, preventing mixing of oxygenated and deoxygenated blood.

• Chordae Tendineae: Tendon-like structures connected to heart valves that prevent backflow during ventricular contraction.

• Papillary Muscles: These muscles work with the chordae tendineae to help open and close the heart valves, ensuring unidirectional blood flow.

Coronary Circulation:

• Coronary Arteries: The first branches off the aorta, they supply vital blood to the heart muscle itself, ensuring it receives the oxygen and nutrients necessary for its function.

  • Right Coronary Artery: Supplies blood to the right atrium and right ventricle; key branches include the Posterior Interventricular Artery and Right Marginal Branch.

  • Left Coronary Artery: Supplies blood to the left atrium and left ventricle; significant branches include the Circumflex Branch and Anterior Interventricular Artery.

• Cardiac Veins: Collect deoxygenated blood from the heart and drain it into the coronary sinus, which then empties into the right atrium, completing the circulatory loop.

Cardiac Conduction System:
The heart functions as a dual pump with rhythmic contractions crucial for effective circulation.

• Systole: Refers to the contraction phase, where the heart chambers contract to eject blood.

• Diastole: The relaxation phase where chambers fill with blood.

• Electrical Conduction Pathway: Includes the Sinoatrial (SA) Node, the heart’s primary pacemaker generating ~100 bpm; the Atrioventricular (AV) Node, which delays impulse to allow filling of ventricles, and the His-Purkinje System, which conducts impulses rapidly ensuring synchronized contraction of ventricular muscle.

Electrocardiogram (ECG/EKG):
An essential tool for monitoring heart activity. It records electrical changes during the cardiac cycle, with distinct waves representing different phases:

• P Wave: Indicates atrial depolarization before atrial contraction.

• QRS Complex: Reflects ventricular depolarization just before ventricular contraction.

• T Wave: Represents ventricular repolarization, occurring before ventricular relaxation, aiding in assessing the heart's electrical activity and rhythm.

Heart Rate Regulation:
The cardiac center in the medulla oblongata regulates heart rate, influenced by various signals:

• Parasympathetic Signals: Via the vagus nerve, these signals slow the heart rate during restful states.

• Sympathetic Signals: Utilize norepinephrine to increase both heart rate and the force of contraction, preparing the body for physical activity or stress.

Blood Vessels:
The cardiovascular system contains diverse blood vessel types:

• Arteries: Thick-walled vessels that carry oxygenated blood away from the heart (except for pulmonary arteries).

• Arterioles: Smaller branches that lead to capillaries, they regulate blood flow through vasoconstriction and vasodilation.

• Capillaries: Microscopic vessels that facilitate the exchange of gases, nutrients, and wastes between blood and tissues through their thin endothelial walls.

• Venules: Collect blood from capillaries, merging into larger veins.

• Veins: Return deoxygenated blood to the heart, characterized by thinner walls and often equipped with valves to prevent backflow and ensure proper venous return.

Capillary Exchange Mechanisms:

• Diffusion: The primary method of transport for gases and nutrients.

• Filtration: Driven by hydrostatic pressure, this mechanism pushes fluid and solutes out of capillaries into surrounding tissues.

• Osmosis: The movement of water through the capillary walls, influenced by concentration gradients and plasma proteins.

• Transcytosis: Involves the transport of large substances across endothelial cells using vesicles.

Factors Influencing Exchange:

• Hydrostatic Pressure: Blood pressure within capillaries affecting the filtration rate.

• Colloid Osmotic Pressure: Created by plasma proteins, it attracts water back into the bloodstream, balancing fluid exchange.

Blood Pressure Management:

• Blood Pressure: The force exerted by circulating blood on the walls of blood vessels, typically measured using a sphygmomanometer.

• Normal Reading: Considered to be around 120/80 mm Hg (systolic/diastolic).

• Influenced by multiple factors including:

  • Cardiac Output: The total volume of blood pumped by the heart per minute.

  • Peripheral Resistance: The resistance blood encounters as it flows through blood vessels, influenced by vessel diameter and length.

  • Blood Volume: The total volume of blood circulating the body, affecting pressure levels.

Blood Vessel Disorders:
A variety of conditions can affect the health of blood vessels, including:

• Atherosclerosis: A disease characterized by the build-up of plaques within arterial walls, leading to narrowed arteries and potential for cardiovascular events.

• Hypertension: A chronic condition marked by elevated blood pressure, leading to increased risk for heart disease, stroke and kidney damage.

• Varicose Veins: Engorged, twisted veins that often appear on the legs and can cause discomfort and health complications.

• Aneurysm: A localized bulge in a blood vessel wall that can potentially rupture, leading to life-threatening internal bleeding.