Cell and Tissue Characteristics

Cell and Tissue Characteristics
Functional Organization of the Cell
Smallest functional unit of the body
The nucleus is the control center
Organelles contained in the cytoplasm:
Mitochondria
Ribosomes
Lysosomes
The cell membrane encloses the cell

Three Major Components of the Cell
Nucleus
Cytoplasm
Cell membrane
Composition of Protoplasm
Water
Proteins
Lipids
Carbohydrates
Electrolytes
Nucleus as Control Center for the Cell
Contains deoxyribonucleic acid (DNA) essential to the cell
Its genes contain the information necessary for the synthesis of proteins to stay alive
Genes represent the individual units of inheritance that transmit information from one generation to another
Site of ribonucleic acid (RNA) synthesis

Organelles Imbedded in the Cytoplasm
Ribosomes
Endoplasmic reticulum
Golgi complex
mitochondria
Lyosomes and peroxisomes
Microtubules
Filaments
Centrioles

Structures of the Cytoskeleton
Microtubules
Develop and maintain cell form
Participate in intracellular transport mechanisms
Form basic structure for complex cytoplasmic organelles
Contain cilia and flagella
Contain centrioles and basal bodies
Structures of the Cytoskeleton (cont.)
Microfilaments
Produce muscle contraction
Support and maintain the asymmetric shape of cells
Are thin threadlike cytoplasmic structures
Categorized as thin, intermediate and thick myosin

Cell Membrane
Lipid bilayer surrounding the cells
Separates it from its surrounding external environment
Cell surface surrounded by the cell coat (glycocalyx)
Contains tissues antigens
Participates in cell-to-cell recognition and adhesion
Pathway for Cell Communication
Cells communicate with each other and internal and external environments via:
Electrical and chemical signaling systems controlling electrical potentials
The overall function of a cell
Gene activity needed for cell division and replication
Cell Receptors
Ion-Channel-Linked Receptors
Rapid synaptic signaling between electrically excitable cells
Transmission of impulses in nerve and muscle cells
G-Protein-Linked Receptors
The on-off switch for signal transduction
Enzyme-Linked Receptors
Receptors for certain protein hormones
Activate an intracellular domain with enzyme activity
Functions of the Cell Membrane
Provide for intracellular and intercellular communication
Transport materials into and out of the cell
Maintain the electrical activities that power cell function
Cell Cycle and Cell Division
Main stages of cell cycle (life cycle of a cell)
Mitosis: cell division stage
Interphase: non-dividing phase
Types of cell division
Mitotic cell division: occurs in somatic cells
Meiosis: occurs in gamete-producing organs
Two Phases of Metabolism
Catabolism
Stored nutrients and body tissues are broken down to produce energy
Anabolism
More complex molecules are formed from simpler ones in a constructive process
Movement of Substances Across the Cell Membrane
Passive movement: influenced by chemical or electrical gradients, does not require expenditure of energy
Diffusion: molecules and particles in a solution become widely dispersed and reach uniform concentration
Osmosis: water moves through semipermeable membrane along concentration gradient from an area of higher to one of lower concentration
Movement of Substances Across the Cell Membrane (cont.)
Active Transport: involves the expenditure of energy
Primary active transport: the source of energy is used directly in the transport of a substance
Secondary active transport: mechanisms harness the energy derived from the primary active transport of one substance for the cotransport of a second substance
Organization of Cells into Tissues
Cells with similar embryonic origin or function are often organized into larger functional units called tissues
These tissues associate with other, dissimilar tissues to form organs of the body
Connective or Supportive Tissue
Definition
The most abundant tissue of the body
Connects and binds or supports the various tissues
Types
Loose or areolar
Reticular
Adipose
Dense connective
Epithelial Tissue
Forms sheets that function to:
Cover the body’s outer surface
Line internal surfaces
Form glandular tissue

Muscle Tissue
Contains actin and myosin filaments
Contracts and provides:
Locomotion and movement of skeletal structures
Pumping blood through the heart
Contraction of blood vessels and visceral organs
Types of Epithelial Cells
Classification according to number of layers present:
Simple
Stratified
Pseudostratified
Classification according to shape:
Squamous
Cuboidal
Columnar
Nervous Tissue
Definition
Tissues that provides the means for controlling body function and sensing and moving about the environment
Types of cells
Neurons: function in communication
Neuroglial cells: support the neurons
Cell Junctions and Cell-to-Cell Adhesion
Tight junctions
Seal the surface membranes of adjacent cells together
Adhering junctions
Represent a site of strong adhesion between cells
Gap junctions
Involve the close adherence of adjoining cell membranes within the formation of channels linking the cytoplasm of the two cells
Extracellular Matrix
Composition
A variety of proteins and polysaccharides
Function
These are secreted locally and organized into a supporting meshwork in close association with cells that produced them
The amount and variety of matrix vary with different tissues and their function