Blood: Structure, Function, Disorders, and Hemostasis

Blood and the Cardiovascular System

Functions and Major Components

The cardiovascular system is responsible for transporting nutrients, gases, hormones, and waste products throughout the body. It consists of the heart, blood vessels, and blood.

• Transport: Oxygen, carbon dioxide, nutrients, hormones, and metabolic wastes.

• Regulation: Maintains body temperature, pH, and fluid balance.

• Protection: Defends against infection and blood loss.

Major components: Heart, arteries, veins, capillaries, and blood.

Blood Composition and Physical Characteristics

Whole Blood

Blood is a specialized connective tissue composed of plasma and formed elements. The average adult has about 5 liters of blood.

• Physical characteristics: Sticky, opaque fluid; color varies from scarlet (oxygen-rich) to dark red (oxygen-poor).

• pH: 7.35–7.45

• Viscosity: Higher than water due to cellular and protein content.

Plasma

Plasma is the liquid portion of blood, making up about 55% of its volume.

• Composition: 90% water, 8% proteins (albumin, globulins, fibrinogen), 2% solutes (electrolytes, nutrients, gases, hormones, waste products).

• Functions: Maintains osmotic pressure, transports substances, and provides a medium for cellular elements.

Erythrocytes (Red Blood Cells)

Structure, Function, and Normal Values

Erythrocytes are biconcave, anucleate cells specialized for oxygen transport.

• Structure: Biconcave shape increases surface area for gas exchange; lacks nucleus and organelles.

• Function: Transports oxygen (via hemoglobin) and carbon dioxide.

• Normal values: 4.7–6.1 million cells/μL (male), 4.2–5.4 million cells/μL (female).

Hemoglobin

Hemoglobin is the protein in erythrocytes responsible for binding oxygen.

• Structure: Four polypeptide chains (globin) and four heme groups, each containing iron.

• Function: Carries oxygen from lungs to tissues and carbon dioxide from tissues to lungs.

• Normal values: 13–18 g/dL (male), 12–16 g/dL (female).

Equation:

$\text{Hb} + \text{O}_2 \rightarrow \text{HbO}_2$

Erythropoiesis

Erythropoiesis is the process of red blood cell formation, regulated by erythropoietin (EPO) from the kidneys.

• Regulation: Stimulated by hypoxia (low oxygen levels).

• Dietary requirements: Iron, vitamin B12, folic acid, proteins.

Equation:

$\text{Stem cell} \rightarrow \text{Proerythroblast} \rightarrow \text{Erythroblast} \rightarrow \text{Reticulocyte} \rightarrow \text{Erythrocyte}$

Degradation of Erythrocytes

Old erythrocytes are removed by macrophages in the spleen, liver, and bone marrow.

• Hemoglobin breakdown: Heme is converted to bilirubin; globin is broken down to amino acids.

• Iron: Recycled for new erythrocyte production.

Red Blood Cell Disorders

Several disorders affect erythrocyte function and production.

• Hemorrhagic anemia: Caused by blood loss.

• Hemolytic anemia: RBCs destroyed prematurely.

• Aplastic anemia: Failure of bone marrow to produce RBCs.

• Iron deficiency anemia: Insufficient iron for hemoglobin synthesis.

• Pernicious anemia: Lack of vitamin B12 due to intrinsic factor deficiency.

• Thalassemia: Genetic disorder affecting globin chain production.

• Sickle cell anemia: Abnormal hemoglobin causes RBCs to sickle.

• Polycythemia vera: Excessive RBC production.

• Secondary polycythemia: Increased RBCs due to hypoxia or other factors.

Leukocytes (White Blood Cells)

Structure, Functions, and Normal Values

Leukocytes are immune cells that protect the body from infection.

• Normal values: 4,800–10,800 cells/μL

• Structure: Nucleated, larger than RBCs.

• Function: Defense against pathogens, removal of debris.

Classification: Granulocytes vs. Agranulocytes

Leukocytes are classified based on the presence of granules in their cytoplasm.

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Monocytes, lymphocytes

Comparison Table:

Type	Site of Formation	Life Span	Function	Normal Values
Neutrophils	Bone marrow	6 hours–few days	Phagocytosis of bacteria	50–70%
Eosinophils	Bone marrow	~5 days	Combat parasites, allergies	2–4%
Basophils	Bone marrow	~few hours–days	Release histamine	0.5–1%
Monocytes	Bone marrow	Months	Phagocytosis; become macrophages	3–8%
Lymphocytes	Bone marrow	Hours–years	Immune response (B and T cells)	20–40%

Leukocyte Disorders

• Leukopenia: Low WBC count.

• Leukocytosis: High WBC count.

• Leukemia: Cancer of WBCs; abnormal proliferation.

• Infectious mononucleosis: Viral infection causing increased lymphocytes.

Platelets

Structure, Function, Production, and Normal Values

Platelets are cell fragments essential for blood clotting.

• Structure: Small, anucleate fragments from megakaryocytes.

• Function: Initiate clotting by forming platelet plugs.

• Production: Thrombopoiesis in bone marrow.

• Normal values: 150,000–400,000/μL

Hemostasis

Mechanisms of Hemostasis

Hemostasis is the process that stops bleeding following vessel injury.

• Vascular spasm: Immediate vasoconstriction.

• Platelet plug formation: Platelets adhere to exposed collagen.

• Coagulation: Formation of a fibrin clot via intrinsic and extrinsic pathways.

• Clot retraction: Shrinking of the clot to bring wound edges together.

• Vessel repair: Growth factors stimulate healing.

• Fibrinolysis: Breakdown and removal of the clot.

Equation:

$\text{Prothrombin} \xrightarrow{\text{Prothrombinase}} \text{Thrombin}$

$\text{Thrombin} + \text{Fibrinogen} \rightarrow \text{Fibrin}$

Factors Limiting Clot Formation

• Endogenous factors: Antithrombin, protein C, heparin.

• Exogenous agents: Aspirin, warfarin, heparin (medications).

Hemostasis Disorders

• Thrombus: Clot in an unbroken vessel.

• Embolus: Traveling clot.

• Disseminated intravascular coagulation (DIC): Widespread clotting and bleeding.

• Thrombocytopenia: Low platelet count.

• Hemophilias: Genetic disorders affecting clotting factors.

Blood Groups and Compatibility

Agglutinogens and Agglutinins

Agglutinogens are antigens on RBC surfaces; agglutinins are antibodies in plasma.

• ABO system: Type A (A agglutinogen, anti-B agglutinin), Type B (B agglutinogen, anti-A agglutinin), Type AB (A and B agglutinogens, no agglutinins), Type O (no agglutinogens, anti-A and anti-B agglutinins).

• Rh system: Rh+ (D agglutinogen present), Rh– (D agglutinogen absent).

Compatibility Table:

Blood Type	Agglutinogens	Agglutinins	Can Receive From	Can Donate To
A	A	Anti-B	A, O	A, AB
B	B	Anti-A	B, O	B, AB
AB	A, B	None	A, B, AB, O	AB
O	None	Anti-A, Anti-B	O	A, B, AB, O

Rh compatibility: Rh– individuals can only receive Rh– blood; Rh+ can receive both.

Blood Group Incompatibility Disorders

• Erythroblastosis fetalis (hemolytic disease of the newborn): Occurs when Rh– mother carries Rh+ fetus; maternal antibodies attack fetal RBCs.

• Transfusion reactions: Occur when incompatible blood is transfused, leading to agglutination and hemolysis.

Example:

Type O– is the universal donor; Type AB+ is the universal recipient.

Additional info: These notes expand on the lecture objectives by providing definitions, normal values, and mechanisms for each blood component and disorder, as well as compatibility tables for ABO/Rh systems.