Comprehensive Study Notes on Blood: Structure, Function, and Components

BLOOD

Introduction

Blood is a specialized liquid connective tissue essential for the transportation of substances, regulation of physiological parameters, and protection against disease and blood loss. It is composed of plasma and formed elements, each with distinct roles in maintaining homeostasis.

OBJECTIVES FOR THIS TOPIC

• Understand the basics of hematopoiesis and the formed elements of blood

• Describe the structure, function, origin, and fate of erythrocytes, including the breakdown of heme

• Understand the significance of hematocrit and the basic types of anemia

• Describe the major components of plasma, including the major types of plasma proteins and their functions

• Describe the role of thrombocytes and platelet plugs in hemostasis

• Describe the overall function of the clotting cascade in producing a definitive blood clot

• Describe the basics of abnormal clot formation and endogenous anticoagulants

• Describe the basics of ABO and Rh blood groups

• Recognize the basic formed elements of blood under light microscopy

WHAT IS BLOOD?

Physical and Chemical Properties

• Liquid Connective Tissue: Blood is viscous, opaque, and has a metallic taste.

• Viscosity: About 5 times more viscous than water.

• Color: Ranges from bright red (oxygen-rich) to dark red (oxygen-poor).

• pH: Slightly alkaline, approximately 7.35–7.45.

• Temperature: About 1°C higher than body temperature.

• Volume: Accounts for ~8% of body weight (5–6 L in adult males, 4–5 L in adult females).

FUNCTIONS OF BLOOD

Key Functions

• Transportation:

  • Oxygen from lungs to tissues

  • Nutrients from GI tract to cells

  • Carbon dioxide and metabolic wastes to excretory organs

  • Hormones to target tissues

• Regulation:

  • Maintains body temperature and pH

  • Regulates fluid balance

• Protection:

  • Prevents blood loss via clotting

  • Defends against infection (antibodies, complement proteins, white blood cells)

HEMATOPOIESIS: BLOOD CELL FORMATION

Origin of Blood Cells

• In utero: Blood formed by liver and spleen

• After birth: Blood formed by red bone marrow

• ~100 billion new blood cells produced daily

• All blood cells originate from Hemopoietic Stem Cells (HSCs) (also called hemocytoblasts)

Types of Hemopoietic Stem Cells

• Lymphoid Cells: Give rise to lymphocytes (a type of white blood cell)

• Myeloid Cells: Give rise to erythrocytes, platelets, and other white blood cells

COMPONENTS OF BLOOD

Major Components

• Plasma:

  • Accounts for 55% of whole blood

  • Least dense component

• Formed Elements:

  • Accounts for 45% of whole blood

  • Includes erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets)

  • Leukocytes and platelets are found in the buffy coat of centrifuged blood

Table: Blood Components

Component	Percentage of Whole Blood	Main Constituents
Plasma	55%	Water, proteins, electrolytes, nutrients, hormones
Formed Elements	45%	RBCs, WBCs, Platelets

BLOOD PLASMA

Composition

• Water: 90% of plasma; acts as solvent and absorbs heat

• Plasma Proteins: 8% of plasma

• Electrolytes, Gases, Nutrients, Vitamins, Hormones: Remaining components

• Serum: Plasma with plasma proteins removed

Blood Plasma Proteins

• Albumin:

  • Most numerous and smallest (60%)

  • Regulates osmotic pressure; carrier for ions, hormones, lipids, medications

• Globulins:

  • Second most common (36%)

  • Transport materials; include antibodies

• Fibrinogen:

  • Third most common (4%)

  • Essential for blood clot formation

FORMED ELEMENTS

Types

• Erythrocytes (Red Blood Cells): Most common formed element

• Leukocytes (White Blood Cells): Immune function

• Thrombocytes (Platelets): Clotting function

ERYTHROCYTE ANATOMY & PHYSIOLOGY

Structure

• Biconcave discs, ~8 μm diameter

• No nucleus or organelles in mature RBCs

• Flexible, allowing passage through capillaries

• Contain hemoglobin (gives red color)

Hemoglobin Anatomy

• Composed of 4 globin chains, each with an iron-containing heme group

• Each hemoglobin binds up to 4 oxygen molecules

• ~280 million hemoglobin molecules per RBC

• Oxyhemoglobin: Hemoglobin with oxygen (bright red)

• Deoxyhemoglobin: Hemoglobin without oxygen (dark red)

Function

• Transport of respiratory gases (O2 and CO2)

• CO2 binds to globin, not heme

ERYTHROPOIESIS

Formation of Red Blood Cells

• RBCs live ~120 days; 2.5 million produced per second

• Regulated by erythropoietin (hormone from kidneys)

• Dietary factors: Vitamin B12, iron, folic acid, copper, vitamin C

Stages of Erythropoiesis

• Hemopoietic stem cell → Proerythroblast → Basophilic erythroblast → Polychromatic erythroblast → Orthochromatic erythroblast → Reticulocyte → Erythrocyte

ERYTHROCYTE DEATH & DISPOSAL

Process

• Old RBCs removed by macrophages in spleen and liver

• Hemoglobin broken down:

  • Iron stored in liver

  • Heme converted to bilirubin, excreted in bile

  • Globin broken down to amino acids

HEMATOCRIT

Definition & Significance

• Percentage of erythrocytes in blood

• Adult males: 42–56%; adult females: 38–46%

• Higher altitude increases hematocrit

ANEMIA

Types & Symptoms

• Low oxygen-carrying capacity

• Types:

  • Blood loss (hemorrhage)

  • Insufficient RBCs

  • Destruction of RBCs

  • Iron deficiency

  • B12 deficiency (pernicious anemia)

• Symptoms: Fatigue, pallor, shortness of breath, chest pain

POLYCYTHEMIA

Definition & Causes

• High RBC count, increased blood viscosity

• Causes: Dehydration, smoking, high altitude, air pollution, excessive exercise

• Blood doping: Artificially induced polycythemia for athletic performance (banned)

SICKLE-CELL DISEASE

Overview

• Hereditary disorder causing abnormally shaped RBCs

• Leads to inefficient movement and oxygen delivery

LEUKOCYTES (WHITE BLOOD CELLS)

Structure & Function

• Have nuclei and organelles

• 1–3x larger than RBCs

• Initiate immune response, defend against pathogens

• Can leave blood vessels (diapedesis)

• Classified into Granular and Agranular leukocytes

Granular Leukocytes

• Neutrophils: Most abundant, phagocytic, acute infections

• Eosinophils: Parasitic infections, allergies, asthma

• Basophils: Least abundant, release histamine and heparin (inflammation, allergic reactions)

Agranular Leukocytes

• Lymphocytes: Direct attacks on infected cells, produce antibodies

• Monocytes: Largest WBC, become macrophages, active in chronic infections

Table: Leukocyte Types and Functions

Type	Function
Neutrophil	Phagocytosis, acute infection
Eosinophil	Parasitic infection, allergy response
Basophil	Release histamine/heparin, inflammation
Lymphocyte	Immune response, antibody production
Monocyte	Phagocytosis, chronic infection

Additional info:

• Blood smears are used to identify formed elements under a microscope.

• Plasma proteins play critical roles in maintaining osmotic balance, immune defense, and clotting.

• Hematopoiesis is a tightly regulated process ensuring the constant renewal of blood cells.