Anatomy and Function of the Cardiovascular System and Blood

Anatomy of the Cardiovascular System

Learning Outcomes

  • List the main features of the cardiovascular system.

  • Describe the location of the heart in the body and identify its major anatomical areas.

  • Trace the pathway of blood through the heart.

  • Compare the pulmonary and systemic circuits.

  • Explain the operation of the heart valves.

  • Name the functional blood supply of the heart.

  • Compare and contrast the structure and function of arteries, veins, and capillaries.

Components of the Cardiovascular System (CV System)

  • Heart: Pumps the blood.

  • Blood and Blood Vessels:   - Arteries: Transport blood away from the heart.   - Veins: Carry blood back to the heart.   - Capillaries: Permit nutrient, waste, and gas exchange.

Anatomy of the Heart

  • Located near the front (anterior) of the chest wall, behind the sternum.

  • Sits slightly to the left, surrounded by the lungs.

  • Encased in the Pericardium: A double-walled sac containing serous fluid.

Exterior Heart Anatomy

  • Anterior View:   - Brachiocephalic trunk   - Left common carotid artery   - Left subclavian artery

  • Posterior View:   - Brachiocephalic trunk   - Superior vena cava   - Ascending aorta   - Right pulmonary artery   - Fibrous pericardium (cut)   - Right pulmonary veins   - Auricle of the right atrium   - Right coronary artery   - Right atrium   - Coronary sulcus (deep to fat)   - Right ventricle   - Inferior vena cava   - Arch of aorta   - Ligamentum arteriosum   - Left pulmonary artery and veins   - Auricle of left atrium   - Left ventricle   - Anterior interventricular sulcus (deep to fat)   - Descending aorta   - Posterior interventricular sulcus (deep to fat).

Heart Wall

  • Epicardium: The outer layer, also called visceral pericardium.

  • Myocardium: Muscular wall of the heart containing cardiac muscle tissue, vasculature, and nerves.

  • Endocardium: Inner layer composed of lining of epithelial cells.

Key Internal Heart Structures

  • Four Internal Chambers:   - Left and right atria.   - Left and right ventricles.

  • Two Types of Valves:   - Atrioventricular (AV) Valves: Separate each side’s atrium from its ventricle.   - Semilunar Valves: Aortic and pulmonary valves.

Heart Chambers

Atria

  1. Right Atrium:    - Receives oxygen-poor blood from:      - Superior vena cava      - Inferior vena cava      - Coronary sinus (from heart wall).

  2. Left Atrium:    - Receives oxygen-rich blood from the lungs via pulmonary veins.

Ventricles

  • Right Ventricle:   - Thick myocardium but thinner than left ventricle.   - Pumps blood to lungs (pulmonary circulation) for oxygenation.

  • Left Ventricle:   - Thickest myocardium.   - Pumps blood to systemic and coronary circulations.

  • Interventricular Septum: Separates ventricles providing structural support.

Internal Heart Anatomy

  • Right Ventricle: Thin, crescent-shaped wall.

  • Left Ventricle: Thick, circular wall.

  • Interventricular Septum: Divides the two ventricles.

Heart Valves

  • Blood must flow through the heart in one direction:   - From atria into ventricles.   - From ventricles into either pulmonary or systemic circulatory systems.

  • Four Valves ensure this one-way passage:   - Two Atrioventricular Valves (Right AV / Tricuspid valve and Left AV / Bicuspid or Mitral valve).   - Two Semilunar Valves (Prevent backflow of blood from arteries into ventricles, located at the base of the aorta and pulmonary artery, each with 3 cusps).

Heart Valves in Action

  • High pressure in the ventricle causes blood flow that pushes the aortic valve open.

  • High pressure in the ventricle pushes the blood upward to the mitral valve, closing it.

  • Pressure from the blood flowing backward in the aorta closes the aortic valve.

  • Pressure from blood in the left atrium pushes the mitral valve open, allowing blood in the left atrium to drain into the relaxed ventricle.

Coronary Arteries

  • The heart pumps large volumes of blood but needs its own supply.

  • Right and Left Coronary Arteries: Feed from the base of the ascending aorta.

Coronary Veins

  • Oxygen-poor blood from heart tissue drains to the coronary sinus via:   - Great cardiac vein   - Middle cardiac vein   - Small cardiac vein   - Anterior cardiac vein.

  • The coronary sinus empties blood into the right atrium near the base of the vena cava.

Blood Vessels

  • Blood vessels are divided into 5 classes:   - Arteries: Divided into elastic and muscular types.   - Arterioles: Smaller branches of arteries.   - Capillaries: Sites of exchange.   - Venules: Small veins collecting blood from capillaries.   - Veins: Return blood to the heart.

Structure of Blood Vessels

  • Artery and vein walls have 3 basic layers:   - Tunica Intima: Innermost layer, lined with endothelium and loose connective tissue.   - Tunica Media: Middle layer, consisting of smooth muscle and elastic fibers.   - Tunica Externa: Outermost layer, composed of connective tissue.

Blood Vessel Layers

  • Tunica Intima:   - Contains endothelium and loose connective tissue with internal elastic lamina.

  • Tunica Media:   - Comprised of smooth muscle and elastic fibers and external elastic lamina.

  • Tunica Externa:   - Contains collagen fibers with valvular structures.

Comparison of Artery and Vein Walls

  • Artery:   - Contains thick tunica media, smaller lumen.

  • Vein:   - Contains thinner tunica media, larger lumen, with valvular structures to aid blood flow and prevent backflow.

Summary of Cardiovascular System Function

  • The CV system comprises the heart and blood vessels:   - The heart contains left and right atria and ventricles.   - Arteries carry oxygen-rich blood around the body.   - Veins transport oxygen-poor blood back to the heart.   - Exceptions: Pulmonary artery (carries deoxygenated blood to lungs) and pulmonary veins (carry oxygenated blood to heart).   - Arteries and veins have the same three layers but differ in composition across vessel types.

Cardiac Physiology

  • The heart serves two specific functions:   - Receives oxygen-poor blood from the body to pump it through the lungs (Pulmonary Circulation).   - Receives oxygen-rich blood from lungs to pump through the body (Systemic Circulation).

Cardiac Contraction Cycle

  • The heart has a unique muscle contraction pattern:   - Atrial walls contract before the ventricles.   - Muscle cells in the heart function as a coordinated unit.   - Heart muscle is autorhythmic, meaning it can initiate its own contractions.

Pacemaker Cells and Contraction Control

  • Pacemaker cells initiate and propagate the action potential triggering contractions, primarily located in the sinoatrial (SA) node in the right atrium.

  • The cells in the SA node typically depolarize at a rate of 70-80 times/minute in a resting heart, with a potential increase to 100 times/minute in the absence of extrinsic factors.

  • Action potential spreads throughout both atria via gap junctions, leading to atrial contraction.

Conductive Pathway of the Heart

  • The electrical impulse from the SA node travels to the atrioventricular (AV) node, where a 100 msec delay occurs to prevent simultaneous contraction of the ventricles and atria.

  • The impulse continues down the AV bundle (Bundle of His), through bundle branches and spreads across Purkinje fibers, specialized cardiac muscle cells that conduct impulses rapidly.

  • Ventricles contract approximately 225 msecs after SA node activation.

Sequence of Cardiac Electrical Activity

  1. The SA node generates an action potential, which spreads to atrial cells and the AV node.

  2. After the delay at the AV node, the action potential continues to the AV bundle and travels down to the right and left bundle branches.

  3. The action potential spreads from the bundle branches along the Purkinje fibers to the contractile cells of the ventricles.

Cardiac Output

  • Defined as the amount of blood pumped out by each ventricle in 1 minute.

  • Calculated using the formula:
      Cardiac output=heart rate×stroke volume\text{Cardiac output} = \text{heart rate} \times \text{stroke volume}

Factors Affecting Cardiac Output

  • Affected by crisis stressors:   - Decreased blood volume (hemorrhage).   - Low blood pressure, physical/emotional trauma, increased body temperature, exercise.   - High blood pressure or blood volume increases sympathetic nervous system activity, leading to an increased contractile force of cardiac muscle.

  • Hormonal influences include:   - Increased hormone levels such as epinephrine and thyroxine.   - Achieved through vagus nerve control during parasympathetic nervous system response.

Blood Vessels & Circulation Overview

  • Arteries carry blood away from the heart, whereas veins return it.

  • Capillaries connect the arterial and venous systems, facilitating the exchange of materials in tissues.

  • Pulmonary Circulation refers to the movement of blood around the lungs; Systemic Circulation pertains to the flow of blood throughout the body.

Blood Vessel Structure & Function

  • Arterial System:   - Large diameter (2.5cm) arteries carry high volumes of blood, having a significant proportion of elastic fibers to withstand pressure fluctuations.   - Muscular arteries consider smooth muscle for vasoconstriction and dilation adjustments.

Capillaries

  • Measuring 5-10μm in diameter, allow red blood cells (8 μm wide) to squeeze through, facilitating substance exchange (gases, nutrients, wastes) depending on tissue needs.

Capillary Transport Mechanisms

  • Mechanisms include:   - Direct diffusion.   - Diffusion through intercellular clefts.   - Diffusion through pores in specialized capillaries.   - Transport via vesicles during absorption and filtration.

Venous System

  • Postcapillary Venules collect blood from capillary beds with loose intercellular junctions.

  • Veins have thinner tunica interna and media with a very thick tunica externa, larger lumen than arteries, and many contain valves to facilitate upward blood flow to the heart and prevent pooling.

Blood Pressure Dynamics

  • Varies during systole (contraction) and diastole (relaxation), with major changes occurring through the vascular system including decreasing pressures in capillaries and veins to aid blood return.

Venous Valves

  • Essential for low-pressure venous return, preventing backflow, particularly in limb areas to mitigate blood pooling; potential dysfunctions lead to conditions like varicose veins and hemorrhoids.

Blood Distribution in Circulatory System

  • Heart: 9%

  • Pulmonary vessels: 7%

  • Systemic arteries and arterioles: 13%

  • Systemic veins and venules: 64% (blood reservoirs)

  • Systemic capillaries: 7%

Summary of Cardiac and Vascular Function

  • Cardiac contraction is regulated by an intrinsic conduction system starting at the SA node, facilitating orderly electrical conduction and muscular contraction throughout the heart.

  • The vascular system circulates oxygen-rich and oxygen-poor blood, coordinating exchange processes at the capillary level.

Blood Overview

Learning Outcomes

  • List the main functions of blood.

  • Describe the composition and volume of whole blood.

  • Describe the composition of plasma and its importance.

  • List the cells making up the formed elements, describing each type.

  • Explain the role of the hemocytoblast.

  • Describe the ABO and Rh blood groups.

  • Explain the basis for blood transfusions.

Functions of Blood

  • Transportation of:   - O2, CO2, nutrients, waste, hormones.

  • Regulation of:   - Temperature through vasodilation and vasoconstriction.   - Acid-base balance.   - Fluid-electrolyte balance.   - Osmotic pressure impacts water content of cells.

  • Protection against infection:   - Via white blood cells, antibodies, and complement proteins.   - Clotting: Prevents fluid loss and generates pathogen barriers.

Blood Composition

  • Blood consists of:   - Plasma: 55% of blood volume.   - Buffy Coat: Comprising platelets and leukocytes (1%).   - Red Blood Cells (Erythrocytes): 44% (Hematocrit).

Centrifugation of Blood

  • Separation of components by centrifugation shows distinct layers: Plasma, Buffy coat, Erythrocytes.

Blood Volume

  • Approximate volume of blood in an average adult: 5 liters.

Hematopoiesis (Development of Blood Cells)

  • Hemocytoblast: A stem cell that differentiates into:   - Lymphoid Stem Cells: Produce lymphocytes.   - Myeloid Stem Cells: Lead to erythrocytes, platelets, and other leukocytes (basophils, eosinophils, monocytes, and neutrophils).

Blood Microscopy

  • Presence of blood components under microscopic evaluation:   - Includes RBCs, WBCs, and platelets.   - Erythrocytes: Biconcave shape increases surface area for gas transport.

Red Blood Cells

  • Shape: Biconcave, enhancing surface area by 30% compared to spherical shapes.

  • Diameter: Approximately 8μm, flexibly squeezing into capillaries.

  • Mature cells lack nucleus and mitochondria, enhancing oxygen carrying capacity due to hemoglobin.

  • Hemoglobin Details:   - Structure: Quaternary protein composed of heme (iron-containing) and globin (protein chains).   - Each RBC can carry up to 1.2 billion oxygen molecules.

Blood Groups and Types

  • Blood cells have genetic antigens on their surfaces, primarily categorized into:   - ABO system: Major blood types based on antigens.   - Rhesus (Rh) factors: Presence (Rh+) or absence (Rh-) of Rhesus antigens.

Antigens and Antibodies Interaction

  • Plasma usually contains antibodies that react with surface antigens, leading to agglutination.

Blood Typing Techniques

  • Blood typed through exposure to specific antibodies:   - Anti-A and Anti-B antibodies cause agglutination when encountering their respective antigens.

White Blood Cells - Leukocytes

  • Essential for defending the body against pathogens:   - Characteristics:     - Contain nuclei and organelles, unlike RBCs.     - Function without hemoglobin.

Classification of Leukocytes

  • Granulocytes:   - Neutrophils: Most abundant; Phagocytosis of pathogens.   - Eosinophils: Combat larger pathogens; involved in allergies.   - Basophils: Release histamine and heparin; promote localized inflammation.

  • Agranulocytes:   - Monocytes: Differentiate into macrophages, high phagocytic action.   - Lymphocytes: Key role in adaptive immunity; includes T-cells, B-cells, and NK cells.

Platelets

  • Cell fragments vital for clotting; lack a nucleus but have chemical vesicles for promoting blood clotting and stopping fluid loss.

Summary of Blood Functions

  • Blood is critical in transportation, regulation, and protection:   - RBCs carry oxygen via hemoglobin.   - Blood typing is defined by antigen presence and antibody interaction.   - WBCs are integral to immune response and homeostasis against infection.