HAP_12e_Lecture_Ch_17_Accessible (1)

Chapter 17: Blood

Overview

  • Author: Marieb Human Anatomy & Physiology 12th Edition

  • Prepared by: Justin A. Moore, American River College

  • Copyright: © 2025 Pearson Education, Inc.

Importance of Blood

  • Understanding blood anatomy and physiology helps in advising patients to prevent blood clots during hospital stays.

17.1 Functions of Blood

Main Functions

  • Transport

    • Delivers oxygen and nutrients to body cells.

    • Transports metabolic wastes to lungs and kidneys for elimination.

    • Carries hormones from endocrine organs to target organs.

  • Regulation

    • Maintains body temperature through heat absorption and distribution.

    • Maintains normal pH via buffers, providing "alkaline reserve" of bicarbonate ions.

    • Ensures adequate fluid volume in the circulatory system.

  • Protection

    • Prevents blood loss through clot formation initiated by plasma proteins and platelets.

    • Carries agents of immunity within blood: antibodies, complement proteins, and white blood cells.

17.2 Composition of Blood

Components

  • Plasma: Liquid component of blood, constitutes 55% of total blood volume.

  • Formed Elements:

    • Red Blood Cells (RBCs): Erythrocytes.

    • White Blood Cells (WBCs): Leukocytes.

    • Platelets: Cell fragments involved in clotting.

Blood Composition

  • Whole blood can be separated into three layers via centrifugation:

    • RBCs at the bottom (Hematocrit: 45% in males, 42% in females).

    • Buffy Coat: thin layer containing WBCs and platelets (less than 1%).

    • Plasma: upper layer (~55%).

Physical Characteristics and Volume

Physical Properties

  • Blood is a viscous, opaque fluid with a metallic taste.

  • Color varies based on oxygen content:

    • Bright red indicates oxygen-rich.

    • Dark red indicates oxygen-poor.

  • Normal blood pH ranges from 7.35–7.45.

  • Average blood volume:

    • 5–6 liters in males.

    • 4–5 liters in females.

Blood Plasma

Plasma Characteristics

  • Composition: Straw-colored, consists of 90% water and over 100 dissolved solutes including nutrients, hormones, gases, wastes, and proteins.

  • Plasma Proteins: Most abundant solutes (about 8% by weight) include:

    • Albumin: Regulates blood pH, carries various molecules, and maintains osmotic pressure.

    • Globulins: Include transport proteins and antibodies.

    • Fibrinogen: Responsible for blood clot formation.

Formed Elements

General Features

  • Formed elements consist of RBCs, WBCs, and platelets.

  • Unlike leukocytes, RBCs and platelets are not true cells:

    • RBCs: Lack nuclei and most organelles.

    • Platelets: Fragments of cells.

  • Most formed elements have a short lifespan and are replaced by stem cells in red bone marrow.

Erythrocytes (RBCs)

Role in Gas Transport

  • Structure: Small, lack nucleus, filled with hemoglobin (Hb).

  • Ideal for Gas Exchange:

    • Biconcave shape increases surface area.

    • No organelles ensure no consumption of oxygen being transported.

Functions of Erythrocytes

  • Transport oxygen and carbon dioxide, utilizing hemoglobin which binds reversibly.

  • Hemoglobin composition includes four heme groups, each can carry one molecule of oxygen.

Erythropoiesis: Production of Erythrocytes

Process Overview

  • Location: Red bone marrow.

  • Stem Cells: Hematopoietic stem cells differentiate into myeloid stem cells and then into erythroblasts.

  • Stages:

    • Commitment to erythrocyte pathway involves several transformations from proerythroblasts to reticulocytes.

Regulation of Erythropoiesis

Control Mechanisms

  • Hormonal control via Erythropoietin (EPO): Stimulates production based on oxygen levels in blood.

  • Nutritional Requirements: Amino acids, iron, folic acid, and vitamin B12 are essential.

Erythrocyte Disorders

Types of Anemia

  • Anemia: Reduced capacity to carry oxygen, classified into:

    • Blood Loss: Hemorrhagic anemia.

    • Not Enough RBCs: Iron-deficiency and pernicious anemia.

    • Too Many RBCs Destroyed: Hemolytic anemias such as sickle-cell anemia.

  • Polycythemia: Excess RBCs increase blood viscosity, potentially leading to thromboembolic events.

Leukocytes (WBCs)

Functions

  • Crucial for body's defense against diseases, including infections and tumors.

  • Typical ranges: 4,800–10,800 WBCs per microliter.

Types of WBCs

  • Granulocytes: Neutrophils, eosinophils, basophils.

  • Agranulocytes: Lymphocytes and monocytes.

Platelets

Characteristics

  • Cell fragments derived from megakaryocytes, essential for clotting and forming a platelet plug.

  • Regulated by thrombopoietin, with an average concentration of 150,000–400,000 platelets per microliter.

Hemostasis

Stages of Hemostasis

  • Step 1: Vascular spasm (contraction of blood vessels).

  • Step 2: Formation of a platelet plug.

  • Step 3: Coagulation (formation of a fibrin mesh to seal larger breaks).

Blood Tests and Clinical Implications

Blood Examination Insights

  • Levels of various components like hematocrit, leukocytes, and specific proteins indicate health status.

  • Blood typing and cross-matching are crucial for safe transfusions.

Developmental Aspects

Blood Formation in Fetus

  • Fetal blood formed initially in yolk sac, liver, and spleen; red bone marrow takes over by seventh month.

Aging Impact on Blood

  • Chronic conditions like leukemias and anemias due to aging can affect blood function.