A&P 115-117

Formed Elements and Blood Composition

  • Formed Elements Overview:

    • All formed elements of the blood are produced from stem cells located within red bone marrow.

    • Formed elements consist of three primary components: erythrocytes (red blood cells), leukocytes (white blood cells), and cell fragments termed thrombocytes (platelets).

  • Erythrocytes (Red Blood Cells):

    • Contain hemoglobin, which is synthesized from protein and iron.

    • Primary function is the transport of oxygen throughout the body.

    • Breakdown and Elimination Process:

      • When red blood cells die, the heme group of hemoglobin is broken down into a yellowish pigment called bilirubin.

      • Bilirubin is transported to the liver, where it is converted into bile.

      • Bile is subsequently excreted from the body.

  • Leukocytes (White Blood Cells):

    • Categorized based on distinct physical and biological characteristics: size, nuclear appearance, staining properties, and the presence or absence of visible cytoplasmic granules.

    • Granular Leukocytes:

      • Include neutrophils, basophils, and eosinophils.

      • Functions: Active in phagocytosis, defense against parasites, and mediating inflammatory responses.

    • Agranular Leukocytes:

      • Include lymphocytes and monocytes.

      • Functions: Active in antibody production, cellular immune responses, and phagocytosis.

  • Thrombocytes (Platelets):

    • Consist of specialized cell fragments.

    • Function: Active in the complex process of blood clotting.

Anatomy and Structure of the Heart

  • Pericardium:

    • A fluid-filled sac that surrounds the entire heart.

    • Composed of two structural layers:

      • Outer (parietal) layer.

      • Inner (visceral) layer.

  • Heart Wall Layers:

    • Epicardium:

      • Identical to the inner visceral layer of the pericardium.

      • Consists of a serous membrane that forms the outermost structural layer of the heart wall.

    • Myocardium:

      • The thick middle layer of the heart wall.

      • Composed entirely of specialized cardiac muscle tissue.

      • Vascular supply: Receives oxygenated blood directly from the coronary arteries. The coronary vascular system drains deoxygenated blood directly into the right atrium through the coronary sinus.

    • Endocardium:

      • The innermost layer of the heart.

      • Forms the thin inner lining of all four heart chambers and covers the physical structure of the heart valves.

Circulation of Blood and Heart Valves

  • Cardiovascular Dual-Pump System:

    • The heart operates as a double pump driving two distinct circuits:

      • Pulmonary Circuit: Pumps deoxygenated blood to the lungs for oxygenation.

      • Systemic Circuit: Pumps oxygenated blood to the rest of the body tissues.

  • Pathway of Blood Flow Through the Heart:

    1. Deoxygenated blood returning from systemic tissues is delivered via the superior vena cava and inferior vena cava into the right atrium.

    2. The right atrium sends deoxygenated blood into the right ventricle.

    3. The right ventricle pumps blood into the pulmonary arteries, which travel directly to the lungs.

    4. Gas exchange occurs within the lungs, converting deoxygenated blood into oxygenated blood.

    5. Oxygenated blood travels from the lungs through the pulmonary veins into the left atrium.

    6. The left atrium passes oxygenated blood into the left ventricle.

    7. The left ventricle pumps oxygenated blood into the aorta for distribution across systemic circulation.

  • Heart Valves:

    • The heart contains four valves designed to prevent retrograde (backward) blood flow into the preceding chamber upon exit.

    • Tricuspid Valve: Positioned between the right atrium and right ventricle.

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

    • Pulmonary Semilunar Valve: Positioned between the right ventricle and the pulmonary trunk (which branches into the right and left main pulmonary arteries).

    • Aortic Semilunar Valve: Positioned between the left ventricle and the aorta.

Heart Conduction System and Cardiac Cycle

  • Electrical Conduction System:

    • The heart possesses an intrinsic, self-generating beat initiated by the sinoatrial node.

    • Electrical impulses spread from the sinoatrial node along the specialized conduction system through the myocardium.

    • This spreading wave of electrical activity is measured and recorded externally using an electrocardiogram (ECG).

  • The Cardiac Cycle:

    • Defined as the exact time period measured from the end of one ventricular contraction to the end of the subsequent ventricular contraction.

    • Systole: The specific contraction phase of the cardiac cycle.

    • Diastole: The specific relaxation phase of the cardiac cycle.

  • ECG Interpretation and Myocardial Action:

    • ECG deflections do not directly represent the physical mechanical contractions (systole) or relaxations (diastole) of heart chambers.

    • ECG deflections capture the antecedent electrical activity (action potentials) that triggers the physical contraction and relaxation events of the myocardium.

    • Track Meet Analogy:

      • The firing of a starter's gun at a track meet precedes the physical running event; the gun's sound initiates the athletic action.

      • In cardiac physiology, the action potential functions like the starter's gun.

      • Physical cardiac muscle contraction begins immediately after the electrical action potential passes over the muscle cells.

Structure and Physiology of Blood Vessels

  • Vessels of the Cardiovascular System:

    • Arteries:

      • Carry oxygenated blood away from the heart toward systemic body tissues.

      • Possess thick, highly elastic walls engineered to withstand high blood pressure.

      • Systemic arterial flow originates at the aorta, which continuously branches throughout the body.

      • Arteries progressively narrow as distance from the heart increases; the smallest arterial vessels are termed arterioles.

    • Capillaries:

      • The smallest blood vessels in the human body.

      • Function as the precise functional site of exchange for water, essential nutrients, and metabolic waste products between blood plasma and surrounding tissues.

    • Veins:

      • Carry deoxygenated blood away from capillaries and back toward the heart.

      • Possess walls that are thinner and significantly less elastic than arterial walls, operating under lower pressure conditions.

      • Microscopic venules collect blood directly from capillaries and merge to form veins.

      • Veins generally run parallel to systemic arteries and typically share matching anatomical names.

      • Venous return culminates in the superior vena cava and inferior vena cava, which empty directly into the right atrium.

  • Vasomotor Control and Hemodynamics:

    • Smooth muscle embedded within arterial walls undergoes dynamic contraction and relaxation.

    • Vasoconstriction: Contraction of vascular smooth muscle, narrowing vessel lumens.

    • Vasodilation: Relaxation of vascular smooth muscle, widening vessel lumens.

    • These structural changes directly alter systemic blood pressure and precisely regulate regional blood distribution to target tissues.

Upper and Lower Respiratory System Anatomy

  • Upper Respiratory System:

    • Consists of the nasal passages, pharynx, and larynx.

    • Pharynx:

      • Functions dual-purpose as a component of both the respiratory tract and the digestive tract.

      • Serves as a common conduit for air, food, and drink.

    • Larynx:

      • Functions as a protective mechanical valve.

      • Prevents swallowed food and liquid from entering the lower respiratory tract from the pharynx.

  • Lower Respiratory System:

    • Consists of the lungs and the bronchial tree.

    • Gross Anatomy of the Lungs:

      • Apex: The superior tip/top portion of the lung.

      • Base: The broad inferior bottom portion of the lung.

      • Hilus: The structural medial indentation where primary bronchi and pulmonary vessels enter/exit the lung.

      • Right Lung Structural Division: Composed of three distinct lobes—Superior lobe, Middle lobe, and Inferior lobe.

      • Left Lung Structural Division: Composed of two distinct lobes—Superior lobe and Inferior lobe.

Bronchial Tree and Pulmonary Structures

  • Trachea and Main Airway Branching:

    • The bronchial tree originates at the trachea, which extends downward from the base of the larynx.

    • The trachea is structurally reinforced by cartilaginous rings to maintain airway patency.

    • The trachea terminates inferiorly at a specialized bifurcation site termed the caring (carina).

  • Hierarchical Airway Progression:

    1. Trachea divides at the caring (carina) into the Right Primary Bronchus and Left Primary Bronchus.

    2. Primary bronchi branch into Secondary Bronchi.

    3. Secondary bronchi branch into Tertiary Bronchi.

    4. Tertiary bronchi branch into smaller airways called Bronchioles.

    5. Bronchioles narrow into Terminal Bronchioles.

    6. Terminal bronchioles lead into microscopic Alveolar Ducts.

    7. Alveolar ducts open into Alveolar Sacs.

    8. Alveolar sacs consist of clusters of individual Alveoli.

    9. Alveoli are enveloped by dense networks of Capillaries, facilitating systemic gas exchange between pulmonary air spaces and blood.