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.