Blood and Cardiovascular System: Structure, Function, and Physiology

Blood: Overview and Functions

Introduction to Blood

• Blood is a liquid connective tissue that interacts with all other body systems.

• It serves as a medium for the transport of substances and communication between organs.

Main Functions of Blood

• Transportation: Moves gases (O2, CO2), nutrients, wastes, and hormones throughout the body.

• Regulation: Maintains pH, temperature, and water content of tissues.

• Protection: Provides immune defense and enables clotting to prevent blood loss.

Characteristics and Components of Blood

• Blood is more viscous than water due to the presence of cells and proteins.

• Color varies with oxygen content: bright red (oxygen-rich), dark red (oxygen-poor).

• Normal blood temperature: 38°C (100.4°F).

• Blood volume: ~5-6 L in males, ~4-5 L in females (about 8% of body weight).

Components of Blood

• Red blood cells (RBCs): 44% of blood volume, responsible for oxygen transport.

• White blood cells (WBCs) and platelets: 1% (buffy coat), involved in immunity and clotting.

• Plasma: 55% of blood volume, the liquid matrix containing water, proteins, and solutes.

Plasma Composition

• Water: ~90% of plasma volume.

• Proteins: ~9% (albumin, antibodies, clotting factors).

• Solutes: ~1% (nutrients, wastes, gases, electrolytes).

Table: Main Components of Blood

Component	Percentage of Blood	Main Function
Plasma	~55%	Transport of nutrients, wastes, hormones
Red Blood Cells (RBCs)	~44%	Oxygen and carbon dioxide transport
Buffy Coat (WBCs & Platelets)	~1%	Immunity and blood clotting

Red Blood Cells (Erythrocytes)

Structure and Function

• Anucleate, biconcave discs (~5 million/μL).

• Lack organelles, maximizing space for hemoglobin (Hb).

• Each Hb molecule contains 4 polypeptide chains, each with a heme group that binds O2.

• RBCs live ~100-120 days; old cells are phagocytosed by WBCs.

Hemoglobin and Oxygen Transport

• Hemoglobin binds O2 in the lungs and releases it in tissues.

• CO2 is carried back to the lungs for exhalation.

Hematopoiesis

• Formation of blood cells occurs in red bone marrow.

• Stimulated by hormones: erythropoietin (RBCs), cytokines (WBCs), thrombopoietin (platelets).

Anemia

• Defined as decreased oxygen-carrying capacity of blood.

• Symptoms: pale skin, fatigue, shortness of breath.

• Causes: decreased hemoglobin, decreased hematocrit, abnormal hemoglobin.

• Examples: iron deficiency, vitamin B12 deficiency, sickle cell anemia.

White Blood Cells (Leukocytes)

Types and Functions

• Granulocytes: Neutrophils (phagocytic, first responders), eosinophils (parasitic defense), basophils (inflammatory response).

• Agranulocytes: Lymphocytes (B and T cells, immunity), monocytes (become macrophages).

Table: Types of White Blood Cells

Type	Main Function
Neutrophils	Phagocytosis, first response to infection
Eosinophils	Combat parasites, modulate allergies
Basophils	Release histamine, mediate inflammation
Lymphocytes	B cells (antibodies), T cells (cell-mediated immunity)
Monocytes	Become macrophages, phagocytose pathogens

Leukopoiesis

• Formation of WBCs from hematopoietic stem cells in bone marrow.

• Myeloid and lymphoid lineages produce different WBC types.

Leukocyte Disorders

• Leukocytosis: High WBC count, often due to infection.

• Leukemia: Cancer of WBCs; abnormal proliferation in bone marrow.

• Leukopenia: Low WBC count, increases infection risk.

Platelets and Hemostasis

Platelets (Thrombocytes)

• Cell fragments from megakaryocytes, involved in blood clotting.

• Lack nuclei, contain granules with clotting factors and enzymes.

• Life span: 5-9 days; removed by spleen and liver.

Hemostasis: Stopping Blood Loss

• Prevents blood loss from injured vessels via a series of steps:

  1. Vascular spasm: Vasoconstriction reduces blood flow.

  2. Platelet plug formation: Platelets adhere to exposed collagen and to each other.

  3. Coagulation: Clotting cascade forms a fibrin mesh to stabilize the plug.

  4. Clot retraction: Clot contracts to bring wound edges together.

  5. Thrombolysis: Clot is dissolved after healing.

Clotting Cascade

• Two pathways: extrinsic (triggered by external trauma) and intrinsic (triggered by internal vessel damage).

• Both lead to the formation of prothrombinase, which converts prothrombin to thrombin, and then fibrinogen to fibrin.

Key Equations:

• $\text{Prothrombin} \xrightarrow{\text{prothrombinase}} \text{Thrombin}$

• $\text{Fibrinogen} \xrightarrow{\text{thrombin}} \text{Fibrin}$

Blood Typing and Transfusion

Antigens and Antibodies

• Antigen: Molecule that stimulates an immune response.

• Antibody: Protein that binds to a specific antigen.

Blood Groups

• Type O: Universal donor (no antigens on RBCs).

• Type AB: Universal recipient (no antibodies in plasma).

• Rh factor: Rh+ (antigen present), Rh- (antigen absent).

Transfusion Reactions

• Clumping (agglutination) occurs if incompatible blood is transfused.

• Hemolytic disease of the newborn: Rh- mother, Rh+ fetus; maternal antibodies attack fetal RBCs in subsequent pregnancies.

The Heart: Structure and Function

Location and Anatomy

• Located within the mediastinum, between the lungs, posterior to the sternum, superior to the diaphragm.

• Pumps blood through ~75,000 miles of vessels.

Heart Wall Layers

• Pericardium: Fibrous and serous layers; encloses the heart.

• Myocardium: Cardiac muscle, 95% of heart mass.

• Endocardium: Lines chambers and valves, continuous with vessel lining.

Chambers and Valves

• 4 chambers: 2 atria (receive blood), 2 ventricles (pump blood).

• Valves prevent backflow: atrioventricular (tricuspid, bicuspid/mitral) and semilunar (pulmonary, aortic).

• Chordae tendineae and papillary muscles anchor AV valves.

Blood Flow Through the Heart

1. Oxygen-poor blood enters right atrium from venae cavae and coronary sinus.

2. Passes through tricuspid valve to right ventricle.

3. Pumped through pulmonary valve to pulmonary arteries and lungs.

4. Oxygen-rich blood returns via pulmonary veins to left atrium.

5. Passes through mitral valve to left ventricle.

6. Pumped through aortic valve to aorta and systemic circulation.

Coronary Circulation

• Supplies blood to the heart muscle itself via coronary arteries and veins.

• Blockage can lead to myocardial infarction (heart attack).

Cardiac Cycle and Physiology

Electrical Conduction System

• SA node (pacemaker) initiates heartbeat; impulse spreads through atria to AV node, bundle of His, bundle branches, and Purkinje fibers.

• Coordinates contraction and relaxation of heart chambers.

Electrocardiogram (ECG/EKG)

• Records electrical activity of the heart.

• P wave: atrial depolarization; QRS complex: ventricular depolarization; T wave: ventricular repolarization.

Cardiac Output

• Volume of blood pumped by each ventricle per minute.

• Calculated as:

$\text{Cardiac Output (CO)} = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}$

• Regulated by autonomic nervous system, hormones, and venous return.

Heart Sounds and Valve Function

• "Lub-dub" sounds correspond to closure of AV and semilunar valves.

• Heart murmurs indicate abnormal valve function.

Additional info:

• Some context and terminology were expanded for clarity and completeness.

• Tables and equations were formatted for study purposes.