Comprehensive Notes on the Cardiovascular System: Blood and Heart and Heart and the Cardiovascular System: Blood and Heart and the (Heart and Blood)

Anatomy vs. Physiology in Cardiovascular Studies

• Focus of Study: This course focuses on the anatomical structures of the cardiovascular system rather than complex physiological processes.

• Physiology Exclusions: Specific physiological topics such as Electrocardiogram ($EKG$) interpretation of electrical impulses, the conduction system components' verbatim explanations, and the step-by-step measurement of blood pressure are typically reserved for separate Human Physiology courses.

• Prerequisites: A background in chemistry is highly recommended before studying physiology, as human physiology is largely chemistry-based.

Chapter 21: The Composition and Function of Blood

• Matrix Classification: Blood is a liquid connective tissue consisting of protein fibers, cells, and ground substance (the matrix).

• Whole Blood Components:

  • Erythrocytes (Red Blood Cells): Comprise $44\%$ of a centrifuged blood sample. They give blood its red color.

  • Buffy Coat: A thin layer comprising less than $1\%$ of the blood sample, containing platelets and leukocytes (white blood cells).

  • Plasma: The liquid portion making up $55\%$ of whole blood.

Blood Plasma (55% of blood volume)

• Water Content: Approximately $92\%$ of plasma is water, though this varies based on hydration status.

• Proteins ($7\%$):

  • Albumin: The most abundant plasma protein, produced by the liver. It acts like salt by drawing water back into the vessels via osmotic pressure. A deficiency due to liver disease can lead to edema (swelling).

  • Fibrinogen: A precursor to fibrin, essential for blood clotting.

  • Globulins: Including immunoglobulins ($IgG$, $IgM$) which serve as antibodies in the immune system.

  • Regulatory Proteins: Various enzymes and hormones.

• Other Solutes: Dissolved substances including electrolytes (Sodium, Chloride, Potassium), nutrients (Glucose, Amino acids, Fatty acids), respiratory gases ($CO_2$ and bicarbonate ion $HCO_3^-$), hormones, and waste products. Oxygen ($O_2$) does not dissolve well in plasma.

• Blood pH Levels: The clinical range is $7.35 \text{ to } 7.45$, though physiological targets are strictly between $7.38 \text{ to } 7.42$.

  • Acidosis: pH lower than $7.35$.

  • Alkalosis: pH higher than $7.45$.

Formed Elements: Erythrocytes, Leukocytes, and Platelets

• Erythrocytes (Red Blood Cells):

  • Attributes: Not true cells (lock nucleus and organelles); biconcave shape; circulate for $120\,\text{days}$.

  • Hemoglobin: Each erythrocyte contains $280,000,000$ hemoglobin molecules. Each molecule has four subunits ($2 \text{ alpha}$, $2 \text{ beta}$), each containing a heme group with an iron atom ($Fe^{2+}$).

  • Oxygen Capacity: One hemoglobin molecule carries $4$ oxygen molecules, meaning one erythrocyte carries over $1,120,000,000$ oxygen molecules.

  • Terminology: Oxygenated (bound to oxygen) vs. Deoxygenated (oxygen dropped off).

  • Recycling: Occurs primarily in the spleen (sometimes the liver). Heme is converted to bilirubin (part of bile). Iron is transported by transferrin and stored by ferritin. The remaining erythrocyte is broken down into amino acids.

  • Rouleau: A single-file stack of red blood cells.

• Leukocytes (White Blood Cells):

  • Attributes: True cells with nuclei/organelles; larger than erythrocytes; perform glycolysis and the Krebs cycle.

  • Granulocytes: Neutrophils (abundant, first responders, explode to trap bacteria, form pus), Eosinophils (respond to parasites), Basophils (release histamine and heparin during allergic reactions).

  • Agranulocytes: Lymphocytes (T cells and B cells for memory/immunity), Monocytes (largest leukocytes, turn into macrophages/dendritic cells).

  • Behavior: Diapedesis (squeezing through vessel walls) and Chemotaxis (following chemical signals to infection sites).

  • Conditions: Leukopenia (low white blood cell count) and Leukocytosis (elevated count).

• Platelets (Thrombocytes):

  • Attributes: Cell fragments, not real cells; derived from megakaryocytes in the bone marrow. Lifespan is $8 \text{ to } 10\,\text{days}$.

  • Function: Responsible for blood clotting (hemostasis) upon contact with collagen.

  • Storage: Two-thirds are stored in the spleen.

  • Thrombocytopenia: A deficiency in platelets; can lead to spontaneous bruising (e.g., following viral infections).

Hematopoiesis (Blood Cell Production)

• Site: Red bone marrow.

• Stem Cells: Hematopoietic stem cells divide into two lineages:

  • Myeloid Lineage: Produces erythrocytes, platelets, granulocytes, and monocytes.

  • Lymphoid Lineage: Produces T cells, B cells, and Natural Killer ($NK$) cells.

• Significance: Myeloid leukemia affects RBC/platelet production, while lymphoid leukemia affects the immune system.

Chapter 22: Anatomy of the Heart

Blood Vessel Classification

• Arteries: Carry blood away from the heart (regardless of oxygenation).

• Veins: Carry blood back to the heart (regardless of oxygenation).

• Capillaries: Site of respiratory gas and nutrient exchange.

• Great Vessels: The aorta, inferior/superior vena cava, and pulmonary trunk.

Pulmonary and Systemic Circulation

• Pulmonary Circuit: The right side of the heart pumps deoxygenated blood to the lungs to drop off $CO_2$ and pick up $O_2$.

• Systemic Circuit: The left side of the heart pumps oxygenated blood to the body.

• Pumping Statistics: At rest, the heart pumps approximately $75\,\text{mL}$ per beat. At $70\,\text{bpm}$, this equals roughly $5\,\text{L/min}$, meaning the entire blood volume ($5\,\text{L}$) cycles through the body in approximately one minute.

• Pressure Generation: The left ventricle generates significantly higher pressure ($120\,\text{mmHg}$) compared to the right ventricle because it must pump blood to the entire body.

Heart Position and Layers

• Location: In the mediastinum, posterior to the sternum. The heart is deviated to the left and rotated posteriorly.

• Apex: The bottom point of the heart, pointing toward the left.

• Base: The top portion of the heart.

• Pericardial Sac:

  • Fibrous Pericardium: Outer structural layer.

  • Parietal Pericardium: Inner layer of the sac.

  • Visceral Pericardium (Epicardium): The layer directly on the heart surface.

  • Pericardial Cavity: Space between the parietal and visceral layers containing serous fluid to reduce friction.

• Pericardiacophrenic Ligament: Anchors the pericardial sac to the diaphragm. Taking deep breaths pulls the heart down and can slow the heart rate.

• Heart Wall Layers:

  • Epicardium: The visceral serous membrane.

  • Myocardium: Thick cardiac muscle layer responsible for contraction.

  • Endocardium: Inner lining composed of simple squamous epithelium.

External and Internal Anatomy

• Auricles (Appendages): Flaps on the atria that expand to increase blood capacity during activity. They are the primary site for blood clots in patients with Atrial Fibrillation ($A-fib$).

• Sulci: Grooves on the heart surface containing coronary vessels.

• Ligamentum Arteriosum: A remnant of the fetal ductus arteriosus.

• Internal Muscle Features:

  • Pectinate Muscles: Found in the atria.

  • Trabeculae Carneae: Fleshy branches of muscle in the ventricles.

• Heart Valves:

  • Atrioventricular ($AV$) Valves: Tricuspid (Right) and Bicuspid/Mitral (Left). These are anchored by Chordae Tendineae (strings) and Papillary Muscles (muscular anchors).

  • Semilunar Valves: Pulmonary (Right) and Aortic (Left). These are closed by the backflow of blood, not by strings.

  • Heart Sounds: "Lubb" (First sound - closing of $AV$ valves) and "Dubb" (Second sound - closing of Semilunar valves).

• Fibrous Skeleton: Provides structural framework for valves and acts as an electrical insulator between atria and ventricles.

Coronary Circulation

• Right Coronary Artery ($RCA$): Branches into the Right Marginal Artery and the Posterior Interventricular Artery ($PIA$).

• Left Coronary Artery ($LCA$): Branches into the Circumflex Artery and the Anterior Interventricular Artery ($LAD$).

  • LAD (Left Anterior Descending): Known as the "Widowmaker" because occlusion shuts off blood to the left ventricle.

• Aortic Branches: The coronary arteries are the very first branches off the aorta.

• Venous Drainage: The Great, Middle, and Small cardiac veins drain into the Coronary Sinus, which empties into the Right Atrium.

The Cardiac Conduction System

• Nodal Cells: Specialize in spontaneous depolarization (via sodium leak channels).

• Sequence of Conduction:

  1. Sinoatrial ($SA$) Node: The pacemaker ($120\,\text{bpm}$ intrinsic rate).

  2. Atrioventricular ($AV$) Node: Acts as a bottleneck; backup pacemaker ($80\,\text{bpm}$ intrinsic rate).

  3. AV Bundle (Bundle of His): Transfers impulse to the ventricles.

  4. Right and Left Bundle Branches.

  5. Purkinje Fibers: Trigger ventricular contraction.

• Innervation: The Vagus Nerve (Cranial Nerve $X$) provides parasympathetic tone to decrease the resting heart rate to $60 \text{ to } 70\,\text{bpm}$.

Questions & Discussion

• Q: Does the blood cycle through in two minutes?

  • A: No, it takes approximately one minute for all blood to cycle through the body.

• Q: What is a stent?

  • A: It is a metal mesh "straw" inserted into a vessel to keep it open and restore blood flow.

• Q: Can the heart beat outside the body?

  • A: Yes. Due to the sodium leak channels in nodal cells, the heart will continue to beat if placed in a saline solution with electrolytes, even without brain input.

• Q: Are blood types covered?

  • A: Not in this chapter; they fall under Physiology.

• Q: What happens in a "broken heart" death?

  • A: Extreme emotional distress can cause the papillary muscles to yank so hard on the chordae tendineae that they snap, resulting in heart failure.