Tissues Cells Working Together Dr Anderson GCIT Tissues

Tissues – Cells Working Together Dr. Anderson GCIT

Tissues • Collections of similar cells that work together in an organ to perform a very specific function in that organ for the organism • Four basic tissue types – Epithelial – Connective – Movement – Control

Epithelial Tissue • Sheets of cells that cover the body or line body cavities – Covering – lining epithelium • Skin • Lines open cavities of digestive, respiratory, cardiovascular and reproductive systems – Glandular epithelium • Makes up the various glands (secretory organs) of the body

Functions of Epithelia • Protection – Protects stomach from digesting itself by secreting buffering compounds • Absorption – Cells can take in substances via endocytosis/diffusion/active transport • Filtration – Certain substances are preferentially removed/added to blood • Excretion – Wastes exit via exocytosis, diffusion • Secretion – Cells products (proteins) are exported via exocytosis, diffusion • Sensory Perception – Cells on the surface contain nerve endings that respond to stimulus (heat, pain, pressure, etc. )

Characteristics of Epithelia • Polarity – All epithelial cells have two distinct “ends” • Apical Surface – free surface exposed to exterior or lumen of a body cavity • Basal Surface – bordered by the basal lamina, a non-cellular adhesive sheet to which epithelial cells are attached that acts as a filter between the epithelia and underlying connective tissue

Polarity of Epithelial Cells Apical surface Basal lamina

Epithelial Connections • Tight Junctions – Prevent the movement of materials between cells • Desmosomes – Provide support and tensile strength to tissues

Epithelial Support • All epithelial cells are supported by a thin layer of connective tissue called the reticular lamina (just deep to the basal lamina) • The basal lamina and the reticular lamina form the basement membrane

Communication and Transport • Epithelial cells are innervated (nerves penetrate into the tissue) • However, epithelial cells are NOT perfused directly with blood vessels – Materials must be transported to and from blood in vessels lying under the basement membrane

Epithelial Cell Arrangement

Epithelial Regeneration • Cells are frequently lost due to abrasion, wounds, etc. • Epithelial cells have the capacity to regenerate the lost tissue via mitosis • How is this adaptive to the organism?

Classification of Epithelia • Morphology – Squamous – Cuboidal – Columnar • Arrangement – Simple – Stratified

Epithelial Morphology • Squamous – flat, much shorter than wide • Cuboidal – height and width are equidistant • Columnar – Height much greater than width

Simple Epithelium

Stratified Epithelium • Contain two or more cell layers • Major role: Protection • E. G - skin

Glandular Epithelia • Tissues that secrete substances (usually proteins) made by the cells in the tissue • Endocrine glands – no ducts – Produce hormones, proteins, steroids, etc. • Exocrine Glands – secrete onto body surfaces or into cavities – Mucus, sweat, oil, pancreas, salivary,

Endocrine Glands

Exocrine Glands • Unicellular – mucus glands and goblet cells • Multicellular - 3 parts – Duct - for export – Secretory unit – makes product to be secreted – Fibrous capsule – connective tissue, blood vessels and nerves; may divide the gland into lobes

Mode of Secretion • Cells metabolize the chemical to be released • Cells release this chemical into the duct via exocytosis (or cell lysis)

Tubular – if secretory cells are present in the duct Alveolar – if secretory cells are in the pocket of tissue

Connective Tissue • Function 1. 2. 3. 4. Binding and support (Bone, cartilage, fascia) Protection – Osteocytes (Bone) Insulation – Adipose Tissue (fat) Transportation ( Blood)

Common Characteristics • Common embryologic origin (mesenchyme) • Degrees of vascularity • Consists of living cells and an extracellular matrix – Non-living cell-derived substances – Made of ground substance and fibers

Ground Substance • Made of interstitial fluid, cell adhesion proteins, proteoglycans • Can range from very little to great viscosity – Serves to control diffusion rates into and out of adjoining cells (between blood vessels and epithelium)

Fibers • Collagen – provide tensile strength • Elastic Fibers - (elastin) can stretch, allowing flexibility • Reticular Fibers – collagen -based fibers that support small blood vessels and organs

Cells • Relative to what organ is being examined, each has a different job • Osteocytes • Chondrocyte • Hemocyte

Types of Connective Tissue • Loose Connective Tissue – Areolar – Adipose • Dense Connective Tissue – Regular – Irregular – Elastic

Areolar Connective Tissue • Very loosely arranged fibers in matrix – Provides a reservoir for water and salts for surrounding tissues – Very viscous – Damage to this area or nearby tissues results in water retention – an edema

Adipose Connective Tissue • Fat tissue – composed of adipocytes • Almost the entire volume of the cell is taken up by stored lipids • Stores energy, but subcutaneous fat (under the skin) acts as a – Shock absorber – Insulator

Dense Regular Connective Tissue • Contains closely packed collagen fibers that run parallel to the direction of pull providing great tensile strength – Fibroblasts are interspersed within this tissue to make new collagen fibers • Found in: – Tendons – connect muscle to bone – Aponeuroses – connect muscles to muscles – Fascia – covering that surrounds individual muscles

Dense Irregular Connective Tissue • Also contains bundles of collagen fibers, but are arranged irregularly • Forms fibrous coverings (capsules) that surround some organs and joints, e. g. kidneys, bones, cartilage, etc.

Cartilage • Combines flexibility and strength for support and shock absorption • Not vascular and not innervated • Hyline cartilage • Elastic Cartilage • Fibrous Cartilage

Hyaline Cartilage • Hyaline (glassy) cartilage – Provides firm support to the ends of long bones (cushioning) – Connects bones and provides structure • Bridge of nose • Connects ribs to sternum • Predecessor to bone in human embryos

Elastic Cartilage • More flexible and less rigid than hyaline cartilage • Examples – Ear – Epiglottis

Fibrocartilage • Able to resist heavy compressive forces in areas of the body under the most strain – Cartilage between the femur and tibia/fibula in the knee – Intervertebral discs

Bone • Primarily provides support to the body, but also houses tissues that produce fat and blood cells (marrow) • Bone is well supplied by blood vessels (bones are living tissue) • Great diversity of shapes and functions

Blood • Blood cells (WBC, RBC, platelets) surrounded by a liquid matrix (plasma) • Transports materials to all of the cells in the body – O 2, CO 2, food, wastes, hormones, etc. • Provides the second line of defense against pathogens

Nervous Tissue • Comprises the brain, spinal cord, and peripheral nerves • Major cell type – Neurons – respond to stimuli and transmit impulses

Muscle Tissue • Responsible for most types of movement – Internal movement as well as external • Three types – Skeletal – under voluntary control, moves skeleton – Smooth – under involuntary control, moves substances into, out of, or through the body – Cardiac – heart muscle, under involuntary control (largely)