Connective Tissue II: Blood, Cells, and ECM

• Connective Tissue II focuses on blood as a connective tissue

Levels of organization

• Cells are the basic unit of life
• Tissues are aggregates or groups of cells organized to perform specific functions
• Organs combine different tissues into structural and functional units
• Organ systems are groups of organs that cooperate to perform major bodily functions

Primary Tissue Types

• Epithelium covers body surfaces, lines cavities, and forms glands
• Connective tissue supports other tissues structurally and functionally
• Muscle tissue is responsible for movement via contractile cells
• Nerve tissue transmits nerve impulses

Connective Tissue Overview

• Connective tissue consists of cells and extracellular matrix (ECM)
• ECM is composed of fibers and ground substance
• Types of connective tissue include: connective tissue proper, bone and cartilage, and blood
• Cells include fibroblasts, adipocytes, macrophages, plasma cells, leukocytes, and mast cells

Blood Composition

• Blood consists of cells suspended in a fluid ECM called plasma
• Total blood volume in normal adults is about 6L
• Blood circulates through the cardiovascular system
• Blood's functions include transport of nutrients, O2, wastes, and CO2
• Blood delivers hormones and maintains homeostasis through coagulation and thermoregulation
• Blood also transports immune system agents and cells

Blood Components & Hematocrit

• Normal hematocrit levels in males are 39-50%
• Normal hematocrit levels in females are 35-45%
• Blood sample consists of plasma, white blood cells and platelets (1%), and red blood cells (hematocrit)
• Hematocrit is the packed erythrocytes' volume within a blood sample

Plasma Composition

• Plasma is a liquid, protein-rich ECM that gives blood its fluid properties
• Plasma components include water (90% as a solvent); proteins (7-8%) like albumin, globulins, and fibrinogen
• Plasma contains other solutes (1-2%), including electrolytes, waste materials (urea, uric acid, ammonium salts), nutrients (glucose, lipids, amino acids), blood gases (O2, CO2, nitrogen), and regulatory substances (hormones, enzymes)

Blood Smear Preparation

• Methylene blue is a basic dye
• Related azures are basic dyes
• Metachromatic imparts a violet to red color
• Eosin is an acidic dye

Blood Cell Formation (Hemopoiesis)

• Blood cell formation lineage goes from myeloblast to promyelocyte, neutrophilic myelocyte, neutrophilic metamyelocyte, band neutrophil, to neutrophil
• Blood cell formation lineage goes from myeloblast to promyelocyte, eosinophilic myelocyte, eosinophilic metamyelocyte, to eosinophil
• Blood cell formation lineage goes from myeloblast to promyelocyte, basophilic myelocyte, basophilic metamyelocyte, to basophil
• Proerythroblast produces basophilic erythroblast, which produces polychromatophilic erythroblast, which produces orthochromatophilic erythroblast (normoblast), which produces polychromatophilic erythrocyte (reticulocyte), which produces erythrocyte

Erythrocytes (Red Blood Cells)

• Erythrocytes are anucleate, biconcave discs with a 7.8µm diameter
• Erythrocytes lack organelles and function within the bloodstream
• Erythrocytes contain hemoglobin

Leukocytes (White Blood Cells)

• Leukocytes are white blood cells involved in immune responses
• Leukocytes are not permanent blood members and migrate to tissues
• Leukocytes are spherical but flatten while motile
• Leukocytes leave capillaries and enter connective tissue as transient cells

Leukocyte Migration

• In leukocyte migration, a macrophage gets activated
• Cytokines 1L-1 and TNF-alpha are released
• Selectins are released
• Interstitial space in connective tissue is active with integrin receptors ICAM-1
• 5 is Leukocyte extravasation to leave bloodstream and enter the infected tissue

Leukocyte Classification

• Leukocytes are classified into granulocytes and agranulocytes
• Granulocyte cytoplasm contains primary (azurophilic/lysosomes), secondary (specific), and tertiary granules
• Agranulocyte cytoplasm has non-specific granules (azurophilic/lysosomes)
• Granulocyte nuclei have 2+ lobes, while agranulocyte nuclei have no lobes

Granulocytes vs. Agranulocytes

• Granulocytes have specific and azurophilic granules

• Granulocyte nuclei have 2 or more lobes

• Granulocytes include neutrophils, eosinophils, and basophils

• Agranulocytes lack specific granules but have azurophilic granules

• Agranulocyte nuclei is round or indented

• Agranulocytes include lymphocytes and monocytes

Neutrophils

• Neutrophils are the most common leukocytes (50-70%) with a 10-12µm diameter
• Neutrophil nuclei have 2-5 lobes, including a Barr body in females (inactive X chromosome)
• Neutrophils contain specific, azurophilic, and tertiary granules
• Neutrophils are active phagocytes at inflammation sites

Eosinophils

• Eosinophils constitute about 1-3% of circulating leukocytes with 10-12µm diameter
• Eosinophils have bilobed nuclei and abundant cytoplasm with large, round, eosinophilic specific granules
• Eosinophils are found in connective tissue and are associated with allergic reactions, parasitic infections, and chronic inflammation.

Basophils

• Basophils are the least numerous leukocytes at less than 1%
• Basophils are 10-12µm in diameter
• Basophil nuclei have two irregular lobes, often obscured by granules
• Basophils' cytoplasm is filled with large basophilic specific granules and azurophilic granules
• Basophils release vasoactive agents involved in inflammation and hypersensitivity reactions

Lymphocytes

• Lymphocytes constitute about 30% of circulating leukocytes
• Lymphocytes are small, medium, and large sized with diameters 6-30µm
• Lymphocytes have slightly indented spherical nuclei with scant cytoplasm.
• Lymphocytes function as immune system effector and regulatory cells
• Lymphocytes are functionally divided by CD markers into T lymphocytes, B lymphocytes, and NK cells
• Lymphocytes are involved in the innate and adaptive immune response

Monocytes

• Monocytes are the largest leukocytes with a diameter of 18µm
• Monocytes have a distinct indented or kidney-shaped nucleus and azurophilic granules
• Monocytes are mononuclear phagocyte system precursors
• Monocytes differentiate into macrophages (phagocytes and antigen-presenting cells)

Platelets

• Platelets are anucleate cytoplasmic fragments
• Platelets are small, with diameters of 2-3µm
• Platelets originate from megakaryocytes in bone marrow
• Platelets appear in small clumps and function in clot formation