WEEK 4 CARDIOVASCULAR SYSTEM

Why the Cardiovascular System?

• Essential for life: Constant circulation of oxygen and nutrients is vital for cell survival. Without a functional cardiovascular system, cells would quickly deplete their resources and succumb to metabolic waste buildup.

• Supports various occupations: The understanding of the cardiovascular system is critical in healthcare, leading to careers such as Cardiac Technicians who specialize in ECG and stress testing, as well as Cardiovascular Surgeons who perform complex heart operations.

The Athlete’s Heart

• Is there a link between heart size and athletic performance?

  • Hypothesis: Do athletes have enlarged hearts due to their training, a phenomenon known as "athlete's heart," or does an inherently larger heart provide a competitive advantage in endurance sports? This explores questions of physiological adaptation versus genetic predisposition.

Functions of the Cardiovascular System

• Comprises two systems:

  • Cardiovascular System (vascular system)

  • Transports blood containing gases ($$O2$,$$$, $$CO2$$), hormones, nutrients (glucose, amino acids, fatty acids), and cells throughout the body.

  • Functions:

    • Blood transport for nutrient/gas exchange between tissues: Delivers oxygen and nutrients while removing carbon dioxide and metabolic wastes.

    • Transport of hormones, enzymes, and waste products: Facilitates cell-to-cell communication and waste elimination.

    • Regulation of blood pressure and homeostasis: Maintains fluid balance, pH levels, and body temperature.

    • Directs blood flow to tissues based on need: Shunts blood to active muscles during exercise or diverts it to the digestive system after a meal.

Types of Circulation

• Systemic Circulation: Oxygenated blood flows from the left ventricle to body tissues, delivering oxygen and nutrients, and then returns deoxygenated blood to the right atrium.

• Pulmonary Circulation: Deoxygenated blood is pumped from the right ventricle to the lungs, where it picks up oxygen and releases carbon dioxide, before returning to the left atrium.

• Coronary Circulation: A network of coronary arteries and veins supplies oxygen-rich blood to the myocardium (heart muscle) and removes waste products. Blockage of these vessels can lead to myocardial infarction (heart attack).

Components of the Cardiovascular System

• Heart: Central organ pumping blood, composed of cardiac muscle and connective tissue.

• Blood Vessels:

  • Arteries: Carry oxygenated blood away from the heart (except for the pulmonary artery, which carries deoxygenated blood to the lungs). They have thick, elastic walls that can withstand high pressure.

  • Capillaries: Microscopic vessels, typically one cell layer thick, facilitating rapid substance transfer between blood and tissues; connect arterial and venous systems.

  • Veins: Return deoxygenated blood back to the heart (except for the pulmonary vein, which carries oxygenated blood from the lungs). They have thinner walls and contain valves to prevent backflow.

• Functions of Blood:

  • Transportation of substances: Carries oxygen, carbon dioxide, nutrients, hormones, and waste products.

  • Immunity and defense against disease: Contains white blood cells that protect against pathogens and initiate immune responses.

  • Hemostasis (blood clotting): Platelets and clotting factors prevent excessive bleeding after injury.

  • Regulation of pH and body temperature: Buffers maintain pH balance, and blood flow helps dissipate heat.

  • Note: Total blood volume is approximately 4-6 L depending on body size, with variations due to age, sex, and body composition.

Components of Blood

• Plasma:

  • Composed primarily of water; contains proteins (albumin, globulins, fibrinogen), lipids, carbohydrates (glucose), hormones, electrolytes, and wastes (urea, creatinine).

• Platelets (Thrombocytes): Cell-like particles assisting in clotting, forming a plug at the site of injury to prevent blood loss.

• White Blood Cells (Leukocytes): Primary defense against infection; includes neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each with specialized immune functions.

• Red Blood Cells (Erythrocytes): Contains hemoglobin, responsible for oxygen transport:

  • Each hemoglobin can carry up to 4 O2 molecules.

  • 280 million hemoglobin per red blood cell.

  • Each red blood cell has a lifespan of approximately 120 days, after which they are broken down in the spleen and liver.

Anatomy of the Heart

• Composed of various structures:

  • Superior/Inferior Vena Cava: Large veins that return deoxygenated blood from the body to the right atrium.

  • Atria (Right & Left): Upper chambers that receive blood; the right atrium receives deoxygenated blood, and the left atrium receives oxygenated blood.

  • Valves (Tricuspid, Bicuspid (Mitral), Pulmonary Semilunar, Aortic Semilunar): Ensure unidirectional blood flow through the heart.

  • Tricuspid Valve: Between the right atrium and right ventricle.

  • Bicuspid (Mitral) Valve: Between the left atrium and left ventricle.

  • Pulmonary Semilunar Valve: Between the right ventricle and pulmonary artery.

  • Aortic Semilunar Valve: Between the left ventricle and aorta.

  • Ventricles (Right & Left): Lower chambers that pump blood; the right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the body.

Heart Function and Cardiac Cycle

• Two Pumps: The heart functions as two separate pumps. The right side pumps deoxygenated blood to the lungs for oxygenation, while the left side pumps oxygenated blood to the body to supply tissues.

• Cardiac Cycle:

  • Diastole: Heart relaxes, and chambers fill with blood. Atrial contraction occurs at the end of diastole to ensure complete ventricular filling.

  • Systole: Heart contracts, and ejects blood into circulation. Ventricular contraction begins, increasing pressure, which closes the AV valves and opens the semilunar valves for ejection.

Electrical Activity of the Heart

• Pacemaker (SA node) controls heart rate. The sinoatrial (SA) node, located in the right atrium, initiates electrical impulses that spread through the heart, triggering contractions.

  • Normal intrinsic firing rate is ~100 bpm, influenced by the autonomic nervous system, which modulates heart rate based on physiological needs.

  • Resting heart rate is influenced primarily by parasympathetic stimulation (vagal tone), which slows the heart rate down from its intrinsic rate.

• Hormonal influences via catecholamines (epinephrine and norepinephrine) increase heart rate during exercise or stress, preparing the body for activity.

Electrocardiogram (ECG)

• Diagnostic tool measuring electrical activity of the heart using electrodes placed on the body surface. It provides a graphical representation of the heart's electrical activity over time.

  • P wave: Atrial depolarization, representing the electrical activity associated with atrial contraction.

  • QRS complex: Ventricular depolarization, representing the electrical activity associated with ventricular contraction. Atrial repolarization is masked by the QRS complex.

  • T wave: Ventricular repolarization, representing the electrical activity associated with the ventricles returning to their resting state.

Circulatory Systems Overview

• Capillaries: One cell layer thick, facilitating rapid substance transfer; link arterial and venous systems. Their small diameter and thin walls allow for efficient exchange of oxygen, carbon dioxide, nutrients, and waste products between blood and tissues.

• Venous System Functions:

  • Prevents backflow via one-way valves, especially important in the veins of the legs, where gravity opposes blood flow.

  • Assists with blood flow against gravity using skeletal muscle pumps, where muscle contractions compress veins and propel blood toward the heart.

Cardiovascular Terminology

• Heart Rate (HR): Number of heartbeats per minute, typically measured in beats per minute (bpm).

• Stroke Volume (SV): Blood volume ejected with each heartbeat, typically measured in milliliters (mL).

• Cardiac Output (CO): Total blood volume pumped per minute, calculated as $CO = HR \times SV$$$ CO = HR \times SV $$, typically measured in liters per minute (L/min).

• Ejection Fraction: Fraction of blood pumped out of the left ventricle per contraction, expressed as a percentage. A normal ejection fraction is between 55% and 70%.

• Blood Pressure:

  • Systolic Pressure (~120 mm Hg): Pressure during heart contraction (systole), representing the highest pressure in the arteries.

  • Diastolic Pressure (~70-80 mm Hg): Pressure during heart relaxation (diastole),