2.4 UNIT CELL PROCESSES 2. 4.1 Cell Activities Packaged"sequences(cascades)of cell activities/functions with an identifiable beginning and an 2.4.1.1 Mitosis(Proliferation) Mitosis is a complex of processes leading to the division of a cell such that the two daughter nuclei receive identical complements of the number of chromosomes characteristic of the cells of the species. All cells arise from the division of pre-existing cells. The process of mitosis is divided into four phases: a)prophases-formation of paired chromosomes disappearance of nuclear membrane, b)metaphase-chromosomes separate into exactly similar halves, c)anaphase- the two groups of daughter chromosomes separate and move along the fibers of a central"spindle", and d)telophase-the daughter chromosomes resolve themselve into a"reticulum"and the daughter nuclei are formed; the cytoplasm divides, forming tw complete daughter cells The term mitosis is used interchangeably with cell division, but strictly speaking it refers to nuclear division whereas cytokinesis refers to division of the cytoplasms 2.4.1.2 Synthesis(e.g, ECM structural proteins, enzymes) Synthesis refers to the putting together of a chemical compound by the cell through the union of the elements comprising the compound or from other suitable starting materials. The hemical compounds can be proteins that serve as structural elements(e.g, collagen), enzymes (e.g, collagenase ) regulators of other cells(e.g, hormones ), immunoglobulins, etc. The compounds can be carbohydrates, lipids, or other macromolecules required in cell,tissue,or organ function. The products of cell synthesis can be stored in the cytoplasm or excreted by the 2.4.1.3 Exocytosis (including degranulation) diffuse through the cell membrane. It is considered to be the opposite of endocytosi pr 2.4. 1.4 Endocytosis Endocytosis refers to the uptake by a cell of material too large to difuse through its membrane. In the process of ingesting the material the cell invaginates its membrane, collecting the material in the fold produced by the invagination. Particles of the material larger than approximately one micrometer are "phagocytosed. In this process the cell membrane binds to the particle through a membrane receptor. Particles less than one micrometer are collected in the folds of the invaginated membrane with or without receptor binding, referred to as receptor- mediated endocytosis and pinocytosis, respectively. Fluid is taken up by the cell through the process of pinocytosis 2. 4.1.5 Migration
2.4 UNIT CELL PROCESSES 2.4.1 Cell Activities "Packaged" sequences (cascades) of cell activities/functions with an identifiable beginning and an end. 2.4.1.1 Mitosis (Proliferation) Mitosis is a complex of processes leading to the division of a cell such that the two daughter nuclei receive identical complements of the number of chromosomes characteristic of the cells of the species. All cells arise from the division of pre-existing cells. The process of mitosis is divided into four phases: a) prophases-formation of paired chromosomes; disappearance of nuclear membrane, b) metaphase-chromosomes separate into exactly similar halves, c) anaphase-the two groups of daughter chromosomes separate and move along the fibers of a central "spindle", and d) telophase-the daughter chromosomes resolve themselves into a "reticulum" and the daughter nuclei are formed; the cytoplasm divides, forming two complete daughter cells. The term mitosis is used interchangeably with cell division, but strictly speaking it refers to nuclear division whereas cytokinesis refers to division of the cytoplasms. 2.4.1.2 Synthesis (e.g., ECM structural proteins, enzymes) Synthesis refers to the putting together of a chemical compound by the cell through the union of the elements comprising the compound or from other suitable starting materials. The chemical compounds can be proteins that serve as structural elements (e.g., collagen), enzymes (e.g., collagenase), regulators of other cells (e.g., hormones), immunoglobulins, etc. The compounds can be carbohydrates, lipids, or other macromolecules required in cell, tissue, or organ function. The products of cell synthesis can be stored in the cytoplasm or excreted by the cell. 2.4.1.3 Exocytosis (including degranulation) Exocytosis refers to the process by which a cell excretes particles that are too large to diffuse through the cell membrane. It is considered to be the opposite of endocytosis. 2.4.1.4 Endocytosis Endocytosis refers to the uptake by a cell of material too large to difuse through its membrane. In the process of ingesting the material the cell invaginates its membrane, collecting the material in the fold produced by the invagination. Particles of the material larger than approximately one micrometer are "phagocytosed." In this process the cell membrane binds to the particle through a membrane receptor. Particles less than one micrometer are collected in the folds of the invaginated membrane with or without receptor binding, referred to as receptormediated endocytosis and pinocytosis , respectively. Fluid is taken up by the cell through the process of pinocytosis. 2.4.1.5 Migration
Migration refers to the movement of cells as a result of the action of intracellular cytoskeletal and contractile proteins and the receptor-mediated adhesion of the cell to extracellular matrix components(by integrins) 2. 4.1.6 Contraction At the cell level. contraction refers to the shortening of a cell and the concomitant development of tension in the matrix, as a result of the action of intracellular contractile proteins The contractile proteins facilitating cell contraction are of the same family as facilitate cell migration 2. 4.2 Cell Protagonists became requires a specific differentiated cell protagonist(Table 2.1). The process begins when the cell es the protagonist when expresses a specific phenotype or engages in a specific activity 2.4.3 Chronology Can appear at different sites at different times in different physiological and pathological sequences(ie, modular; Table 2.2) 2.4.4 Matrix Requires an insoluble matrix component/substrate( Table 2.3) for the cell activity. Cell acts on a substrate(e.g, extracellular matrix) through a membrane receptor(e. g, integrin)and a series of stereospecific biochemical reactions initiated by a signal (i.e, soluble regulator; see sec. 2. 4.8). The matrix can serve as an insoluble regulator of cell function/activity 2.4.5 Products Results in a product that is a stable insoluble structure, soluble fragment, and/or mechanical force(Table 2. 4). The quality of the product is invariant but the quantity is not; the product is quantifiable with respect to amount and direction/orientation, thus making the product a vector quantity 2.4.5.1 Macromolecular Aggregates(Macromolecule)or Soluble Fragments An example is collagen. The structure of a macromolecule is its conformation In this case only one cell type is required(e.g, fibroblast) in the unit cell processes of synthesis and 2. 4.5.2 Acellular Multicomponent StructureMatri Examples are basement membrane and clot. The structure comprises two or more types of macromolecules and may include nonviable cells. The structure of a matrix is its architecture 2.4.5.3 Tissue(Cell Matrix) A system of multicomponent structures with viable cells. The structure of a tissue is its morphology 2.4.6 Examples Examples of unit cell processes are given in Tables 2.5 and 2.6
Migration refers to the movement of cells as a result of the action of intracellular cytoskeletal and contractile proteins and the receptor-mediated adhesion of the cell to extracellular matrix components (by integrins). 2.4.1.6 Contraction At the cell level, contraction refers to the shortening of a cell and the concomitant development of tension in the matrix, as a result of the action of intracellular contractile proteins. The contractile proteins facilitating cell contraction are of the same family as facilitate cell migration. 2.4.2 Cell Protagonists Requires a specific differentiated cell protagonist (Table 2.1). The process begins when the cell becomes the protagonist when expresses a specific phenotype or engages in a specific activity. 2.4.3 Chronology Can appear at different sites at different times in different physiological and pathological sequences (i.e., modular; Table 2.2). 2.4.4 Matrix Requires an insoluble matrix component/substrate (Table 2.3) for the cell activity. Cell acts on a substrate (e.g., extracellular matrix) through a membrane receptor (e.g., integrin) and a series of stereospecific biochemical reactions initiated by a signal (i.e., soluble regulator; see sec. 2.4.8). The matrix can serve as an insoluble regulator of cell function/activity. 2.4.5 Products Results in a product that is a stable insoluble structure, soluble fragment, and/or mechanical force (Table 2.4). The quality of the product is invariant but the quantity is not; the product is quantifiable with respect to amount and direction/orientation, thus making the product a vector quantity. 2.4.5.1 Macromolecular Aggregates (Macromolecule) or Soluble Fragments An example is collagen. The structure of a macromolecule is its conformation. In this case only one cell type is required (e.g., fibroblast) in the unit cell processes of synthesis and degradation. 2.4.5.2 Acellular Multicomponent Structure (Matrix) Examples are basement membrane and clot. The structure comprises two or more types of macromolecules and may include nonviable cells. The structure of a matrix is its architecture. 2.4.5.3 Tissue (Cell + Matrix) A system of multicomponent structures with viable cells. The structure of a tissue is its morphology. 2.4.6 Examples Examples of unit cell processes are given in Tables 2.5 and 2.6
2.4.7 Composite Processes Two or more unit processes can combine to form a composite process(Table 2.7) 2.4.8 Regulators Unit cell processes are regulated by diffusible soluble substances(Tables 2.8-2. 11)acting on the cell protagonist directly or by mechanical forces acting on the cell indirectly through the matrix(e.g. by deforming the matrix). The regulators signal the start and the termination of the process. They also serve as connecting links between processes that comprise a composite process(e.g, the"coupling factor"between bone resorption and bone formation). In addition, regulators can control the rate of the process by acting on the cell and the substrate 2. 4. 8 Rates of processes Conse if the time period over which the unit cell process acts is t, then the rate of the process could be ered to be the quantity of product divided by t (Continued on next page
2.4.7 Composite Processes Two or more unit processes can combine to form a composite process (Table 2.7). 2.4.8 Regulators Unit cell processes are regulated by diffusible soluble substances (Tables 2.8 - 2.11) acting on the cell protagonist directly or by mechanical forces acting on the cell indirectly through the matrix (e.g., by deforming the matrix). The regulators signal the start and the termination of the process. They also serve as connecting links between processes that comprise a composite process (e.g., the "coupling factor" between bone resorption and bone formation). In addition, regulators can control the rate of the process by acting on the cell and the substrate. 2.4.8 Rates of Processes If the time period over which the unit cell process acts is t, then the rate of the process could be considered to be the quantity of product divided by t. (Continued on next page.)
2. 4 UNIT CELL PROCESSES TABLE 2.1 Cell protagonists Cells of the same kind associate to form tissues. Tissues are divided into four types: connective tissue, epithelia, muscle, and nerve. Organs are formed by the combination of two or more tissues A. Connective Tissue(Matrix-Continuous) 1. Blood( Cells floating freely in a fluid matrix until clotting then a fibrillar matrix) atropa Basoph d. monocyte f plasma cell g Platelet h. Red blood cell 2. Reticular Tissue( Cells in semi-solid matrix comprising reticular fibers, ie, small diameter Type Ill collagen fibers. Examples include the framework of spleen, lymph nodes, bone marrow.) Fibroblast(synthesis of the Type Ill collagen) Reticular cell(macrophage-like) 3. Loose Fibrous Tissue( Cells in semi-solid matrix comprising reticular and thicker collagen fibers. An example is stroma, the supporting tissue or matrix of an organ, distinguisheded from its functional element, or parenchyma.) Fibroblast 4. Dense Fibrous Tissue(e.g, dermis, ligment, tendon) Fibroblast Adipose(Fat) Cell 6. Hyaline Cartilage and Fibrocartilag Chondrocyte a. osteoblast
2.4 UNIT CELL PROCESSES TABLE 2.1 Cell Protagonists Cells of the same kind associate to form tissues. Tissues are divided into four types: connective tissue, epithelia, muscle, and nerve. Organs are formed by the combination of two or more tissues. A. Connective Tissue (Matrix-Continuous) 1. Blood (Cells floating freely in a fluid matrix until clotting; then a fibrillar matrix) a. Neutrophil b. Eosinophil c. Basophil d. Monocyte e. Lymphocyte f. Plasma cell g. Platelet h. Red blood cell 2. Reticular Tissue (Cells in semi-solid matrix comprising reticular fibers, i.e., small diameter Type III collagen fibers. Examples include the framework of spleen, lymph nodes, bone marrow.) Fibroblast (synthesis of the Type III collagen) Reticular cell (macrophage-like) 3. Loose Fibrous Tissue (Cells in semi-solid matrix comprising reticular and thicker collagen fibers. An example is stroma, the supporting tissue or matrix of an organ, as distinguisheded from its functional element, or parenchyma.) Fibroblast 4. Dense Fibrous Tissue (e.g., dermis, ligiment, tendon) Fibroblast 3. Adipose (Fat) Cell 6. Hyaline Cartilage and Fibrocartilage Chondrocyte 7. Bone a. Osteoblast
b. Osteocyte C. Osteoclast 00 a. Odontoblast(synthesis of dentin b. Cementocyte(synthesis of cementum) (Continued on next page
b. Osteocyte c. Osteoclast 8. Tooth a. Odontoblast (synthesis of dentin) b. Cementocyte (synthesis of cementum) (Continued on next page.)