cells and tissues

• Cells and Tissues:

  • Carry out all chemical activities needed to sustain life
  • Cells are the building blocks of all living things
• Cells are bathed in a dilute saltwater solution called interstitial fluid derived from the blood
• Tissues are groups of cells that are similar in structure and function, leading to organs, organ systems, and organisms
• Anatomy of the Cell:

  • Cells are not all the same in size, shape, and function
  • All cells share general structures
  • Cells are organized into three main regions: Nucleus, Cytoplasm, Plasma membrane
• Nucleus:

  • Control center of the cell
  • Contains genetic material (DNA)
  • Three regions: Nuclear membrane, Nucleolus, Chromatin
• Nuclear Membrane:

  • Barrier of the nucleus
  • Consists of a selectively permeable, double phospholipid membrane
  • Contains nuclear pores that allow for exchange of material with the rest of the cell
• Nucleoli:

  • Nucleus contains one or more nucleoli
  • Sites of ribosome production and partial assembly
• Chromatin:

  • Composed of unwound DNA and protein used for making proteins
  • Scattered throughout the nucleus
  • Chromatin condenses to form chromosomes when the cell divides
• Plasma Membrane:

  • Barrier for cell contents
  • Semi-permeable, Double phospholipid layer
  • Contains proteins, cholesterol, and glycoproteins
  • Specializations include microvilli, membrane junctions
• Cytoplasm:

  • Material outside the nucleus and inside the plasma membrane
  • Contains cytosol, organelles, and inclusions
• Cytoplasmic Organelles:

  • Mitochondria: "Powerhouses" of the cell, produce ATP for cellular energy
  • Ribosomes: Sites of protein synthesis, found free in the cytoplasm or attached to rough endoplasmic reticulum
  • Endoplasmic Reticulum: Rough ER studded with ribosomes, smooth ER functions in cholesterol synthesis and breakdown
  • Golgi apparatus: Modifies and packages proteins, produces secretory vesicles and lysosomes
• Cytoskeleton:

  • Network of protein structures that provide internal framework, determine cell shape, support organelles, and are involved in cell movement
  • Three types: Microfilaments, Intermediate filaments, Microtubules
• Centrioles:

  • Rod-shaped bodies made of microtubules near the nucleus
  • Direct formation of mitotic spindle during cell division
• Cellular Projections:

  • Cilia and Flagella used for movement, not found in all cells
• Solutions and Transport:

  • Solution is a homogeneous mixture of two or more components
  • Membranes are selectively permeable, allowing some materials to pass while excluding others
  • Transport occurs through passive transport (no energy required) and active transport (cell provides metabolic energy)
• Passive Transport Processes:

  • Diffusion: Movement of particles from high concentration to low concentration, affected by size and temperature
• Passive Transport Processes:

  • Movement from high concentration to low concentration, or down a concentration gradient
  • Movement is due to kinetic energy in the molecules and affected by size and temperature
  • Types of diffusion:
  • Simple diffusion (Passive diffusion):
  • Unassisted process
  • Solutes are lipid-soluble materials or small enough to pass through membrane pores
  • Osmosis:
  • Simple diffusion of water
  • Highly polar water easily crosses the plasma membrane
  • Occurs all the time
  • Facilitated diffusion:
• • Substances require a protein carrier for passive transport
  • Still moving down concentration gradient and so no energy is needed
• • Vesicle migrates to plasma membrane
  • Vesicle combines with plasma membrane
  • Material is emptied to the outside
  • Endocytosis:
  • Extracellular substances are engulfed by being enclosed in a membranous vesicle
  • Types of endocytosis:
  • Phagocytosis (cell eating)
  • Pinocytosis (cell drinking)
• Active Transport Processes:

  • Transport substances that are unable to pass by diffusion
  • Two common forms of active transport:
  • Solute pumping:
  • Amino acids, some sugars and ions are transported by solute pumps
  • ATP energizes protein carriers, and in most cases, moves substances against concentration gradients
  • Can transport different molecules different directions such as the sodium-potassium pump
  • Bulk transport:
  • Exocytosis:
  • Moves materials out of the cell
  • Material is carried in a membranous vesicle
• Cell Life Cycle:

  • Series of changes a cell goes through from the time it is formed until it divides
  • Cells have two major periods:
  • Interphase (metabolic phase):
  • Longest phase where the cell grows
  • Cell carries on metabolic processes
  • Cell division:
  • Cell replicates itself
  • Function is to produce more cells for growth and repair processes
  • DNA Replication:
  • Genetic material duplicated and readies a cell for division into two cells
  • Occurs toward the end of interphase
  • DNA uncoils and each side serves as a template
• • Spindle from centromeres are attached to chromosomes that are aligned in the center of the cell
  • Anaphase:
  • Daughter chromosomes are pulled toward the poles
  • The cell begins to elongate
  • Telophase:
  • Daughter nuclei begin forming
  • A cleavage furrow (for cell division) begins to form and finished dividing the cell into two by the end of cytokinesis
  • Everything from prophase is reversed
• Events of Cell Division:

  • Mitosis:
  • Division of the nucleus
  • Results in the formation of two daughter nuclei
  • Cytokinesis:
  • Division of the cytoplasm
  • Begins when mitosis is near completion
  • Results in the formation of two daughter cells
  • Stages of Mitosis:
  • Interphase:
  • No cell division occurs
  • The cell carries out normal metabolic activity and growth
  • Prophase:
  • First part of cell division
  • Centromeres migrate to the poles and direct the assembly of the mitotic spindle
  • Chromosomes form
  • Metaphase:
• Protein Synthesis:

  • Gene:
  • DNA segment that carries a blueprint for building one protein
  • Proteins have many functions:
  • Building materials for cells
  • Act as enzymes (biological catalysts)
  • Role of RNA:
  • Transfer RNA (tRNA):
  • Transfers appropriate amino acids to the ribosome for building the protein
  • Ribosomal RNA (rRNA):
  • Helps form the ribosomes along with proteins where proteins are built
  • Messenger RNA (mRNA):
  • Carries the instructions for building a protein from the nucleus to the ribosome
  • Transcription and Translation:
• • Transcription:
  • Transfer of information from DNA’s base sequence to the complimentary base sequence of mRNA – switching T for U
  • Translation:
  • Base sequence of mRNA is translated to an amino acid sequence based on codon/anticodon complements
  • Amino acids are the building blocks of proteins
• Body Tissues:

  • Cells are specialized for particular functions
  • Tissues:
  • Groups of cells with similar structure and function
  • Four primary types:
  • Epithelium (covering)
  • Connective tissue (support)
  • Nervous tissue (control)
  • Muscle (movement)
  • Epithelial Tissues:
  • Found in different areas:
  • Body coverings
  • Body linings
  • Glandular tissue
  • Functions:
  • Protection
  • Absorption
  • Filtration
  • Secretion
  • Epithelium Characteristics:
  • Cells fit closely together
• • Tissue layer always has one free surface – unattached, the apical surface
  • The lower surface is bound by a basement membrane – structureless material secreted by the cells
  • Avascular (have no blood supply) – depend on diffusion
  • Regenerate easily if well nourished
  • Classification of Epithelium:
  • Number of cell layers:
  • Simple (one layer)
  • Stratified (more than one layer)
  • Shape of cells:
  • Squamous (flattened)
  • Cuboidal (cube-shaped)
  • Columnar (column-like)
• Simple Epithelium:

  • Simple columnar epithelium is a single layer of tall cells that fit closely together
  • Often includes goblet cells
  • Found in the digestive tract
  • Goblet cells produce mucus
  • May function in absorption or secretion
• Pseudostratified columnar epithelium:

  • Single layer, but some cells are shorter than others
  • Often looks like a double cell layer
  • Sometimes ciliated, such as in the respiratory tract
  • May function in absorption or secretion
• Stratified Epithelium:

  • 2+ layers
  • Stratified squamous epithelium has flattened cells at the free edge and cuboidal or columnar cells close to the basement membrane
  • Found as a protective covering where friction is common in locations like skin, mouth, and esophagus
  • Stratified cuboidal and columnar epithelium is rare in the human body and mainly found in ducts of large glands
  • Transitional epithelium has cells whose shape depends on the amount of stretching and lines organs of the urinary system
• Glandular Epithelium:

  • Gland secretes a particular product, which contains protein molecules in an aqueous fluid
  • Two major gland types: Endocrine gland (ductless, secretes hormones that diffuse into blood) and Exocrine gland (empties through ducts to the epithelial surface, includes sweat and oil glands)
• Connective Tissue:

  • Found everywhere in the body
  • Functions include binding body tissues together, supporting the body, and providing protection
  • Variations in blood supply, some well vascularized and some avascular like tendons, ligaments, and cartilage
  • Extracellular matrix consists of ground substance (mostly water with adhesion proteins and polysaccharide molecules) and fibers (collagen, elastic, reticular)
• Connective Tissue Types:

  • Bone (osseous tissue) composed of bone cells in lacunae, hard matrix of calcium salts, and collagen fibers for protection and support
  • Hyaline cartilage composed of abundant collagen fibers and a rubbery matrix, found in the entire fetal skeleton
  • Fibrocartilage is highly compressible and forms cushion-like discs between vertebrae
  • Elastic cartilage provides elasticity and supports the external ear
  • Dense connective tissue has collagen fibers as the main matrix element, with rows of fibroblasts, found in tendons and ligaments
• • Loose connective tissue types include areolar connective tissue (soft, pliable tissue that functions as universal packing tissue and connective tissue glue) and adipose tissue (matrix is an areolar tissue with fat globules, functions in insulation, protection, and fuel storage)
  • Reticular connective tissue forms the stroma of lymphoid organs like lymph nodes, spleen, and bone marrow
  • Blood consists of blood cells surrounded by fluid matrix, functions as a transport vehicle for materials
• Muscle Tissue:

  • Function is to produce movement by contracting or shortening
  • Three types: Skeletal muscle (voluntarily controlled, striated, multinucleated), Cardiac muscle (involuntary, found only in the heart, striated, one nucleus per cell), Smooth muscle (involuntary, spindle-shaped, no visible striations, one nucleus per cell)
• Nervous Tissue:

  • Consists of neurons and nerve supporting cells
  • Function is to receive and send impulses to other areas of the body
  • Characteristics include irritability and conductivity
• Tissue Repair (Wound Healing):

  • Regeneration replaces destroyed tissue by the same kind of cells
  • Fibrosis is repair by dense fibrous connective tissue (scar tissue)
  • Events in tissue repair include capillaries becoming permeable, clotting proteins introduced to make a clot, walling off the injured area to prevent blood loss and infection, formation of granulation tissue containing capillaries and phagocytes, and regeneration of surface epithelium below the scab
• Regeneration of Tissues:

  • Tissues that regenerate easily include epithelial tissue, fibrous connective tissue, and bone
  • Tissues that regenerate poorly include skeletal muscle, replaced largely with scar tissue, cardiac muscle, and nervous tissue within the brain and spinal cord
• Developmental Aspects of Tissue:

  • Epithelial tissue arises from all three primary germ layers
  • Muscle and connective tissue arise from the mesoderm
  • Nervous tissue arises from the ectoderm
  • With old age, there is a decrease in mass and viability in most tissues