The Blood

Formed Elements of Blood

The formed elements of blood are the cellular components suspended in plasma. They include:

• Erythrocytes (Red Blood Cells, RBCs): Responsible for oxygen transport via hemoglobin.

• Leukocytes (White Blood Cells, WBCs): Involved in immune defense.

• Thrombocytes (Platelets): Essential for blood clotting.

Types of White Blood Cells (WBCs)

WBCs are classified as granulocytes and agranulocytes:

• Granulocytes: Contain visible granules in their cytoplasm.

  • Neutrophils: Phagocytize bacteria; most abundant.

  • Eosinophils: Combat parasites and modulate allergic responses.

  • Basophils: Release histamine; involved in inflammation and allergic reactions.

• Agranulocytes: Lack visible granules.

  • Lymphocytes: B cells (produce antibodies), T cells (cell-mediated immunity), and NK cells (destroy abnormal cells).

  • Monocytes: Differentiate into macrophages; phagocytize pathogens and debris.

WBC Count and Terminology

• Leukocytosis: Increased WBC count, often due to infection or inflammation.

• Leukopenia: Decreased WBC count, may indicate bone marrow problems or certain infections.

Hematocrit

The hematocrit is the percentage of blood volume occupied by red blood cells. Normal values:

• Males: 40-54%

• Females: 36-48%

Difference Explanation: Males typically have higher hematocrit due to testosterone stimulating erythropoiesis.

Blood Separation by Centrifugation

When blood is centrifuged, it separates into three layers:

• Plasma: Top layer; contains water, proteins, nutrients, hormones.

• Buffy coat: Middle thin layer; contains WBCs and platelets.

• Red blood cells: Bottom layer; densest component.

Blood Types and Transfusion Compatibility

Blood types are classified by ABO and Rh antigens. Compatibility is crucial for safe transfusions.

• Type O negative: Universal donor for RBCs.

• Type AB positive: Universal recipient for RBCs.

Transfusion Scenarios:

• A person with type B negative blood can receive blood from: B- and O-

• A person with type O positive blood can donate to: O+, A+, B+, AB+

• A person with type AB negative blood can receive blood from: AB-, A-, B-, O-

• A person with type B positive blood can donate to: B+, AB+

The Heart

Cardiac Chambers

• Right atrium

• Right ventricle

• Left atrium

• Left ventricle

Cardiac Valves and Locations

• Tricuspid valve: Between right atrium and right ventricle

• Pulmonary valve: Between right ventricle and pulmonary artery

• Bicuspid (mitral) valve: Between left atrium and left ventricle

• Aortic valve: Between left ventricle and aorta

Cardiac Layers/Membranes

• Endocardium: Inner lining

• Myocardium: Muscular middle layer

• Epicardium: Outer layer (visceral pericardium)

• Pericardium: Double-walled sac surrounding the heart

Major Blood Vessels of the Heart

• Arteries: Carry blood away from the heart (e.g., aorta, pulmonary arteries)

• Veins: Carry blood to the heart (e.g., superior/inferior vena cava, pulmonary veins)

• Coronary circulation: Supplies blood to the heart muscle itself

Heart Conduction System

• Sinoatrial (SA) node: Pacemaker; initiates heartbeat

• Atrioventricular (AV) node: Delays impulse before passing to ventricles

• Bundle of His: Conducts impulse from AV node to ventricles

• Bundle branches and Purkinje fibers: Distribute impulse throughout ventricles

Heart Sounds and Valves

• First heart sound (S1): Closure of AV valves (tricuspid and mitral)

• Second heart sound (S2): Closure of semilunar valves (aortic and pulmonary)

The Vascular Tree

Arteries vs. Veins

• Arteries: Thick-walled, carry blood away from the heart, usually oxygenated (except pulmonary arteries)

• Veins: Thinner-walled, carry blood toward the heart, usually deoxygenated (except pulmonary veins)

Vessel Sidedness

• Use the ulnar (medial) and radial (lateral) arteries/veins to identify right vs. left sides.

Major Vessels and Blood Flow

• Vessels returning blood to the right atrium: Superior vena cava, inferior vena cava, coronary sinus (deoxygenated blood)

• Vessels carrying blood away from the heart: Aorta (oxygenated), pulmonary arteries (deoxygenated)

Abdominal Blood Supply

• Arterial supply: Abdominal aorta branches (e.g., celiac trunk, superior/inferior mesenteric arteries)

• Venous drainage: Hepatic portal system, inferior vena cava

Circle of Willis

The Circle of Willis is a ring of arteries at the base of the brain that provides collateral blood flow. Main arteries involved:

• Anterior cerebral arteries

• Anterior communicating artery

• Internal carotid arteries

• Posterior cerebral arteries

• Posterior communicating arteries

The Fetus (Fetal Circulation)

Arteries vs. Veins in Fetal Circulation

• Umbilical vein: Carries oxygenated blood from placenta to fetus

• Umbilical arteries: Carry deoxygenated blood from fetus to placenta

Fetal Shunts

• Foramen ovale: Opening between right and left atria; allows blood to bypass fetal lungs

• Fossa ovalis: Remnant of foramen ovale in adult heart

• Ductus venosus: Shunts blood from umbilical vein to inferior vena cava

• Ductus arteriosus: Connects pulmonary artery to aorta; bypasses fetal lungs

The ECG (Electrocardiogram)

ECG Waves and Their Significance

• P wave: Atrial depolarization (contraction)

• QRS complex: Ventricular depolarization (contraction)

• T wave: Ventricular repolarization (relaxation)

Key Points:

• The QRS complex shows ventricular depolarization.

• The P wave shows atrial depolarization.

• Ventricular repolarization is represented by the T wave.

Summary Table: Blood Types and Compatibility

Additional info: Some explanations and table entries were inferred and expanded for academic completeness.