Cardiovascular System Overview

Cardiovascular System (Part I)

• The cardiovascular system's primary function is transporting blood, regulating various bodily functions, and protecting against diseases.

Blood Composition

• Blood is a connective tissue composed of:
  • Plasma (55%): Primarily water with proteins (albumins, globulins, fibrinogen), nutrients, wastes, and gases.
  • Formed elements (45%):
    • Red blood cells (erythrocytes): Biconcave discs containing hemoglobin, transporting oxygen; 4.2-6.2 million per cubic mm.
    • White blood cells (leukocytes): Protecting against disease-causing agents (pathogens). Different types with varying functions: neutrophils, lymphocytes, monocytes, eosinophils, basophils; 5,000-9,000 per cubic mm.
    • Platelets (thrombocytes): Essential for blood clotting; 130,000-360,000 per cubic mm.

Blood Functions

• Transportation: Carries oxygen, nutrients, hormones, and waste products.
• Regulation: Maintains homeostasis, balancing acids/bases and bodily fluids.
• Protection: Combats disease-causing agents and prevents excessive blood loss.

Red Blood Cells (RBCs)

• Transport oxygen throughout the body
• Biconcave-shaped, small enough for capillary passage
• Contain hemoglobin:
  • Oxyhemoglobin (bright red) carries oxygen
  • Deoxyhemoglobin (dark red) lacks oxygen.

White Blood Cells (WBCs)

• Granulocytes: Neutrophils (55%) - destroy bacteria, viruses, and toxins. Eosinophils (3%) - combat parasitic infections like worms. Basophils (1%) - control inflammation and allergic reactions.
• Agranulocytes: Monocytes (8%) - Destroy bacteria, viruses, and toxins. Lymphocytes (33%) - play a crucial role in the body's immunity.

Blood Platelets

• Fragments of cells that are crucial for blood clotting.
• About 130,000-360,000 per cubic millimeter of blood.
• Essential for hemostasis (stopping bleeding).

Controlling Bleeding (Hemostasis)

• A complex of three processes:
  • Blood vessel spasm
  • Platelet plug formation
  • Blood coagulation (formation of a clot.)

Blood Vessels

• Arteries & Arterioles: Strongest blood vessels, carry blood away from the heart under high pressure, possessing thick walls.
• Veins & Venules: Blood moves slowly in veins due to low pressure. Valves prevent backflow.
• Capillaries: Tiny blood vessels connecting arterioles to venules; sites of gas, nutrient, and waste exchange between the blood and body cells.

Lymphatic System

• Network of vessels collecting fluids between cells and returning them to the bloodstream, crucial for fluid balance and absorbing lipids.
• Also critical for defending the body against disease-causing agents (pathogens).
• Lymph nodes, thymus, and spleen are part of this system.

Lymph Fluid

• Tissue fluid that enters lymphatic capillaries
• Contains Valves preventing backflow of lymph

Circulation of Blood

• Blood circulates via two major circuits:
  • Pulmonary circulation: Blood travels from the heart to the lungs for oxygen uptake and release of carbon dioxide.
  • Systemic circulation: Blood travels from the heart to the rest of the body, delivering oxygen and nutrients and removing waste products.

Systemic and Pulmonary Circulation

• Systems using separate circuits allowing efficient oxygen and nutrient delivery, accompanied by waste elimination.

Coronary Circulation

• Coronary arteries supply the heart muscle with blood, providing oxygen and nutrients.
• Coronary veins collect used blood, transporting it to the right atrium.

Heart: A special muscle

• Specialized muscle with the job of pumping blood throughout the body.

Cardiac Muscle Characteristics

• Shorter, less circular than skeletal muscle fibers
• Branching structure giving a "stair-step" appearance.
• Typically one nucleus centrally located
• Ends of fibers connected by intercalated discs (desmosomes and gap junctions)
• Contains numerous mitochondria (40%).
• Actin and myosin arrangement is the same as in other muscle tissues.

Autorhythmic Fibers

• Specialized heart muscle fibers that self-excite, generating action potentials to trigger heart contractions.
• Serve as pacemakers regulating rhythmic heartbeats, forming the heart's conduction system.

Cardiac Conduction System

• Specialized conductive tissue (SA node, AV node, bundles of His, Purkinje fibers) directs electrical signals rapidly across the heart muscle, coordinating controlled and effective contractions for efficient blood pumping.

Action Potentials and Contraction

• Action potentials initiate contraction; depolarization initiates a contraction through the activation of contractile proteins.
• Depolarization occurs when there is a change in charge across the membrane, and contractile proteins are activated

ECG (Electrocardiogram)

• Composite record of action potentials generated by all heart muscle fibers.
• Wave forms (P, QRS, and T) visually represent the electrical activity during each stage of the cardiac cycle.

Cardiac Cycle

• The sequence of events where the heart alternately contracts and relaxes during blood flow; blood flows through each chamber in a rhythmic pattern.
• Atrial systole: atria contracts, blood enters relaxed ventricles.
• Ventricular systole: ventricles contract, blood is pumped into arteries.

Heart Sounds (Auscultation)

• Sounds caused by blood turbulence when heart valves close ( "lub" - atrioventricular valves, and "dup" - semilunar valves).

Cardiac Output (CO)

• Volume of blood pumped by the left ventricle per minute; calculated as heart rate multiplied by stroke volume.

Stroke Volume (SV)

• Amount of blood pumped by the left ventricle with each contraction. Regulated by factors in preload, contractility and afterload.

Factors Affecting Preload

• How much the heart chamber is stretched before it contracts; directly related to the end-diastolic volume and venous return, impacting the force of contraction.
• Frank-Starling law of the heart.

Factors Affecting Contractility

• The strength of heart contraction relating to a given volume of blood.
• Influenced by positive and negative inotropic agents (e.g., epinephrine) affecting calcium inflow.

Factors Affecting Afterload

• The pressure the ventricles must overcome to pump blood.
• Increasing afterload lowers stroke volume.

Exercise and the Heart

• Exercise significantly impacts cardiac output, Increasing heart rate and stroke volume.

Regulation of Heart Beat

• Autonomic nervous system regulates heart rate: sympathetic accelerates and parasympathetic slows it down which is regulated by the cardiovascular center in the medulla oblongata.
• Hormones (epinephrine/norepinephrine) and blood ionic levels also impact heart rate and contractility.

Questions addressed.

• How would increased sympathetic stimulation of the heart affect stroke volume?: Increased sympathetic stimulation leads to increased heart rate and contractility, subsequently increasing stroke volume.