Blood Composition, Hematology, and Hemostasis: Study Guide for Anatomy & Physiology

Blood Composition and Centrifugation

Layers of Blood After Centrifugation

When whole blood is centrifuged, it separates into distinct layers based on density. Understanding these layers is essential for interpreting blood tests and assessing health.

• Plasma: The top, pale yellow layer, comprising about 55% of blood volume. It contains water, proteins, nutrients, hormones, and waste products.

• Buffy Coat: The thin, middle layer containing white blood cells (leukocytes) and platelets (thrombocytes).

• Red Blood Cells (RBCs): The bottom, red layer, making up about 45% of blood volume.

Hematocrit is the percentage of blood volume occupied by RBCs. It is a key indicator of oxygen-carrying capacity.

Plasma vs. Serum

Plasma is the liquid component of blood, containing clotting factors. Serum is plasma without clotting factors, obtained after blood has clotted.

• Plasma: Contains water, electrolytes, proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste.

• Serum: Lacks fibrinogen and other clotting proteins.

Formed Elements of Blood

Types and Characteristics

The formed elements of blood include erythrocytes, leukocytes, and platelets, each with distinct functions and properties.

• Erythrocytes (RBCs): Biconcave, anucleate cells specialized for oxygen transport via hemoglobin.

• Leukocytes (WBCs): Nucleated cells involved in immune defense. Classified into granulocytes and agranulocytes.

• Platelets (Thrombocytes): Small, anucleate cell fragments essential for blood clotting.

Leukocyte Classification

Leukocytes are divided into two main categories based on the presence of granules:

• Granulocytes: Neutrophils, eosinophils, basophils (contain visible cytoplasmic granules).

• Agranulocytes: Lymphocytes, monocytes (lack visible granules).

They can be identified on Wright's stained blood smear by their shape, size, and staining properties.

Functions of Leukocytes

• Neutrophils: Phagocytosis of bacteria; most abundant WBC.

• Eosinophils: Combat parasitic infections; modulate allergic responses.

• Basophils: Release histamine; involved in inflammatory responses.

• Lymphocytes: B cells (antibody production), T cells (cell-mediated immunity), NK cells (destroy abnormal cells).

• Monocytes: Differentiate into macrophages; phagocytosis of pathogens and debris.

Hemoglobin Structure and Function

Hemoglobin Composition

Hemoglobin (Hb) is the oxygen-carrying protein in RBCs. It consists of four polypeptide chains (globin subunits) and four heme groups.

• Each heme group contains an iron atom that binds oxygen.

• Two main types of globin chains: alpha and beta (in adult HbA).

There are two major subtypes of hemoglobin: adult (HbA) and fetal (HbF), which differ in their globin chains.

Oxygen and Carbon Dioxide Transport

• Oxygen binds reversibly to iron in the heme group.

• Carbon dioxide binds to the globin portion, not the heme.

• Hemoglobin can carry both O2 and CO2 simultaneously.

• Carboxyhemoglobin forms when CO binds to hemoglobin, reducing oxygen transport.

Hemoglobin Metabolism

• RBCs live about 120 days; destroyed mainly in the spleen.

• Hemoglobin is broken down into heme and globin.

• Heme is converted to biliverdin, then bilirubin (excreted in bile).

• Iron is recycled and transported by transferrin.

Red Blood Cell (RBC) Development and Regulation

Stages of RBC Development

RBCs develop through several stages in the bone marrow:

• Hemocytoblast (stem cell)

• Proerythroblast

• Basophilic erythroblast

• Polychromatic erythroblast

• Orthochromatic erythroblast

• Reticulocyte (immature RBC)

• Mature erythrocyte

These stages are named based on cell morphology and staining properties.

Hormonal Control of Erythropoiesis

• Erythropoietin (EPO): Hormone produced by the kidneys in response to hypoxia; stimulates RBC production in bone marrow.

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

• Deficiency in these leads to anemia.

Anemia and Polycythemia

Types and Causes of Anemia

Anemia is a condition characterized by reduced oxygen-carrying capacity of blood. Types include:

• Hemolytic anemia: RBC destruction exceeds production.

• Iron-deficiency anemia: Insufficient iron for hemoglobin synthesis.

• Pernicious anemia: Lack of vitamin B12.

• Aplastic anemia: Bone marrow failure.

Polycythemia

• Polycythemia: Increased RBC count; can be primary (polycythemia vera) or secondary (due to hypoxia).

• Distinguished from anemia by elevated hematocrit.

Leukocyte Development and Disorders

Leukopoiesis

Leukocytes develop from hematopoietic stem cells in bone marrow. Two major lineages:

• Myeloid lineage: Produces granulocytes and monocytes.

• Lymphoid lineage: Produces lymphocytes.

Leukocyte Disorders

• Leukopenia: Abnormally low WBC count.

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

• Leukemia: Cancer of WBCs; classified as acute or chronic, lymphocytic or myeloid.

Platelets and Hemostasis

Platelet Function and Formation

• Platelets are fragments of megakaryocytes; essential for clot formation.

• Platelets adhere to exposed collagen at injury sites, initiating clotting.

Hemostasis Steps

Hemostasis is the process of stopping bleeding, involving three main steps:

1. Vascular spasm: Vasoconstriction reduces blood flow.

2. Platelet plug formation: Platelets adhere and aggregate at injury site.

3. Coagulation: Cascade of clotting factors leads to fibrin clot formation.

Coagulation involves intrinsic and extrinsic pathways, both leading to activation of factor X and conversion of prothrombin to thrombin.

Clotting Factors and Coagulation Pathways

• There are 13 major clotting factors, most produced by the liver.

• Vitamin K is required for synthesis of several factors.

• Intrinsic pathway: Initiated by damage inside the vessel.

• Extrinsic pathway: Initiated by tissue factor from outside the vessel.

Fibrinolysis

• Fibrinolysis is the breakdown of clots by plasmin.

• Plasminogen is activated to plasmin, which digests fibrin.

Hemostatic Disorders

Types of Bleeding Disorders

• Thrombocytopenia: Low platelet count; causes excessive bleeding.

• Hemophilia: Genetic deficiency of clotting factors; types A, B, and C.

• Disseminated Intravascular Coagulation (DIC): Both excessive clotting and bleeding.

Blood Groups and Transfusion

ABO and Rh Blood Groups

Blood groups are determined by antigens on RBC membranes. The two major systems are ABO and Rh.

• ABO system: Four blood types (A, B, AB, O) based on presence of A and/or B antigens.

• Rh system: Rh-positive (antigen present) or Rh-negative (antigen absent).

Blood Type	Antigen(s) on RBC	Antibody in Plasma
A	A antigen	Anti-B
B	B antigen	Anti-A
AB	A and B antigens	None
O	None	Anti-A and Anti-B

Transfusion reactions occur if incompatible blood types are mixed, leading to agglutination and hemolysis.

Blood Typing and Transfusion Precautions

• Blood typing is performed by mixing blood with anti-A and anti-B sera and observing agglutination.

• Incorrect transfusions can cause serious complications.

• Precautions include matching donor and recipient blood types and screening for antibodies.

Key Equations and Concepts

• Hematocrit Calculation:

$\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100$

• Oxygen Transport by Hemoglobin:

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

• Coagulation Cascade (Simplified):

$\text{Prothrombin} \xrightarrow{\text{Thrombin}} \text{Fibrinogen} \xrightarrow{\text{Fibrin}} \text{Clot}$

Additional info: Some details, such as the exact names of developmental stages and the mechanisms of certain disorders, were inferred from standard Anatomy & Physiology curriculum.