Four Basic Tissue Types

• There are four basic tissue types: epithelial, connective, muscle, and nervous tissues.

Nervous Tissue

• Brain, spinal cord, and nerves facilitate internal communication

Muscle Tissue

• Muscle tissue contracts to cause movement and includes skeletal, cardiac, and smooth muscle types
• Skeletal muscle are attached to bones
• Cardiac muscle is the heart
• Smooth muscle is in the walls of hollow organs.

Epithelial Tissue

• Epithelial tissue forms boundaries between different environments and functions in protection, secretion, absorption, and filtration
• Epithelial tissue lines digestive tract organs and other hollow organs
• It also covers the skin surface (epidermis).

Connective Tissue

• Supports, protects, and binds other tissues together
• Connective Tissue includes bones, tendons, fat, and other soft padding tissue.

Classification of Epithelia

• Epithelia can be classified based on the number of cell layers or cell shape
• Classification by cell layer includes simple (single layer) and stratified (multiple layers)
• Classification by cell shape includes squamous, cuboidal, and columnar.

Simple Squamous Epithelium

• Consists of a single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm
• Allows materials to pass by diffusion and filtration in sites where protection is not important
• Secretes lubricating substances in serosae
• Located in kidney glomeruli, air sacs of lungs, lining of the heart, blood vessels, lymphatic vessels, and lining of the ventral body cavity (serosae).

Simple Cuboidal Epithelium

• Consists of a single layer of cubelike cells with large, spherical central nuclei
• Functions in secretion and absorption
• Located in kidney tubules, ducts and secretory portions of small glands, and the ovary surface.

Simple Columnar Epithelium

• Consists of a single layer of tall cells with round to oval nuclei
• Some cells bear cilia which may contain mucus-secreting unicellular glands (goblet cells)
• Functions: absorption, secretion of mucus, enzymes, and other substances
• Ciliated types propel mucus (or reproductive cells) by ciliary action.
• Nonciliated types line most of the digestive tract (stomach to rectum), gallbladder, and excretory ducts of some glands
• Ciliated varieties line small bronchi, uterine tubes, and some regions of the uterus.

Pseudostratified Columnar Epithelium

• Consists of a single layer of cells of differing heights; some not reaching the free surface
• Nuclei are seen at different levels and may contain mucus-secreting cells and bear cilia.
• They secrete substances, particularly mucus, and propel mucus by ciliary action.
• Nonciliated types are in the male's sperm-carrying ducts and ducts of large glands.
• Ciliated varieties line the trachea, most of the upper respiratory tract.

Stratified Squamous Epithelium

• Consists of a thick membrane composed of several cell layers.
• Basal cells are cuboidal or columnar while surface cells are flattened (squamous)
• In the keratinized type, the surface cells are full of keratin and dead.
• Basal cells are active in mitosis and produce the cells of the more superficial layers.
• Protects underlying tissues in areas subjected to abrasion.
• Nonkeratinized types form the moist linings of the esophagus, mouth, and vagina.
• Keratinized varieties form the epidermis of the skin, a dry membrane.

Transitional Epithelium

• Resembles both stratified squamous and stratified cuboidal
• Basal cells are cuboidal or columnar while surface cells are dome shaped or squamouslike, depending on the degree of organ stretch
• Stretches readily to permit stored urine to distend the urinary organ
• Lines the ureters, bladder, and part of the urethra.

Goblet Cells

• Goblet cells are unicellular exocrine glands
• They contain microvilli, secretory vesicles with mucin, golgi apparatus, rough ER, and a nucleus.

Types of Multicellular Exocrine Glands

• Simple Duct Structure (duct does not branch):
  • Simple Tubular: Intestinal glands
  • Simple Branched Tubular: Stomach (gastric) glands
  • Simple Alveolar
  • Simple Branched Alveolar: Sebaceous (oil) glands
• Compound Duct Structure (duct branches):
  • Compound Tubular: Duodenal glands of small intestine
  • Compound Alveolar: Mammary glands
  • Compound Tubuloalveolar: Salivary glands

Chief Modes of Secretion in Human Exocrine Glands

• Merocrine glands secrete their products by exocytosis
• Holocrine glands cause the entire secretory cell to rupture, releasing secretions and dead cell fragments.

Areolar Connective Tissue Cell Types

• A prototype (model) connective tissue
• Consists of Macrophages, Fibroblasts, Lymphocytes, Fat cells, Mast cells, Neutrophils, and Capillaries
• Extracellular matrix includes Ground substance, Collagen fiber, Elastic fiber, and Reticular fiber.

Comparison of Classes of Connective Tissues

• Connective Tissue Proper:
  • Loose Connective Tissue:
    • Areolar, Adipose, Reticular
    • Cells: Fibroblasts, Fibrocytes, Defense cells, Adipocytes
    • Matrix: Gel-like ground substance with all three fiber types: collagen, reticular, elastic
    • Features: Six different types; vary in density and types of fibers, Functions as a binding tissue, Provides reservoir for water and salts and Nutrient (fat) storage
  • Dense Connective Tissue:
    • Regular, Irregular, Elastic
• Cartilage:
  • Hyaline cartilage, Elastic cartilage, Fibrocartilage
    • Cells: Chondroblasts found in the growing cartilage and Chondrocytes
    • Matrix: Gel-like ground substance with fibers: collagen, elastic fibers in some
    • Features: Resists compression because of the large amounts of water held in the matrix. Functions to cushion and support body structures
• Bone Tissue:
  • Compact bone, Spongy bone
    • Cells: Osteoblasts, Osteocytes
    • Matrix: Gel-like ground substance calcified with inorganic salts and Fibers: collagen
    • Features: Hard tissue that resists both compression and tension; Functions in support
• Blood:
  • Cells: Erythrocytes (RBC), Leukocytes (WBC), Platelets
    • Matrix: Plasma and No fibers
    • Features: A fluid tissue; Functions to carry O2, CO2, nutrients, wastes, and other substances (hormones, for example)

Connective Tissue Proper: Loose Connective Tissue

• Areolar:
  • Contains a gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some white blood cells
  • Wraps and cushions organs; its macrophages Phagocytize bacteria; plays an important role in inflammation; holds and conveys tissue fluid
  • Widely distributed under epithelia of body (e.g., forms lamina propria of mucous membranes), packages organs and surrounds capillaries
• Adipose:
  • Contains a matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet
  • Provides reserve food fuel, insulates against heat loss and Supports and protects organs
  • Located under skin in subcutaneous tissue, around kidneys and eyeballs, within abdomen, and in breasts
• Reticular:
  • Contains a network of reticular fibers in a typical loose ground substance; reticular cells lie on the network
  • Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages
  • Is located in lymphoid organs (lymph nodes, bone marrow, and spleen).

Connective Tissue Proper: Dense Connective Tissue

• Dense Regular:
  • Contains primarily parallel collagen fibers; a few elastic fibers
  • The major cell type is the fibroblast
  • Attaches muscles to bones or to muscles, attaches bones to bones and withstands great tensile stress when pulling force is applied in one direction
  • Found in Tendons, most ligaments, and aponeuroses
• Dense Irregular:
  • Contains primarily irregularly arranged collagen fibers; some elastic fibers
  • The fibroblast is the major cell type
  • Withstands tension exerted in many directions and provides structural strength
  • Located in fibrous capsules of organs and joints, dermis of the skin, and submucosa of digestive tract
• Elastic:
  • A dense regular connective tissue containing a high proportion of elastic fibers
  • Allows tissue to recoil after stretching, maintains pulsatile flow of blood through arteries, and aids passive recoil of lungs following inspiration
  • Located in walls of large arteries, within certain ligaments associated with the vertebral column and in the walls of the bronchial tubes

Cartilage

• Hyaline:
  • Its matrix is amorphous but firm with collagen fibers forming an imperceptible network
  • Chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae.
  • Supports and reinforces, serves as resilient cushion and resists compressive stress.
  • Forms most of the embryonic skeleton, covers the ends of long bones in joint cavities, forms costal cartilages of the ribs and is in cartilage of the nose, trachea, and larynx.
• Elastic:
  • Similar to hyaline cartilage, but has more elastic fibers in the matrix
  • Maintains the shape of a structure while allowing great flexibility
  • Supports the external ear (pinna) and epiglottis
• Fibrocartilage:
  • Matrix similar to, but less firm than, that in hyaline cartilage, and thick collagen fibers predominate
  • Tensile strength allows it to absorb compressive shock
  • Located in intervertebral discs, pubic symphysis, and discs of the knee joint

Other Connective Tissues

• Bone (osseous tissue):
  • Hard, calcified matrix containing many collagen fibers with osteocytes lying in lacunae
  • Very well vascularized
  • Supports and protects (by enclosing), provides levers for the muscles to act on and stores calcium and other minerals and fat
  • Marrow inside bones is the site for blood cell formation (hematopoiesis)
• Blood:
  • Red and white blood cells in a fluid matrix (plasma)
  • Transports respiratory gases, nutrients, wastes, and other substances
  • Contained within blood vessels.

Muscle Tissue

• Skeletal Muscle
  • Description: Long, Cylindrical, Multinucleate cells with obvious striations (stripes)
  • Function: Initiates and controls Voluntary movement; locomotion; manipulation of the environment; facial expression; voluntary control
  • Location: In skeletal muscles attached to bones or occasionally to skin
• Cardiac Muscle
  • Description: Branching, striated, and generally uninucleate cells that interdigitate at specialized junctions (intercalated discs)
  • As it contracts, it Propels blood into the circulation; involuntary control.
  • Location: The walls of the heart.
• Smooth Muscle
  • Description: Spindle-shaped cells with central nuclei; no striations; cells arranged closely to form sheets
  • Propels substances or objects (foodstuffs, urine, a baby) along internal passageways and is subject to involuntary control.
  • Location: Mostly in the walls of hollow organs.

Nervous Tissue

• Description: Neurons are branching cells, cell processes that may be quite long extend from nucleus-containing cell body and also contribute to nervous tissue
• Functions: Transmit electrical signals from sensory receptors and to effectors (muscles and glands) which control their activity
• Supporting cells support and protect neurons.
• Location: In the brain, spinal cord, and nerves.

Classes of Membranes

• Cutaneous membrane:
  • A cutaneous membrane, or skin, covers the body surface
• Mucous membranes:
  • Mucous membranes lines body cavities that are open to the body exterior
• Serous membranes:
  • Serous membranes line body cavities that are closed to the exterior

Tissue Repair of a Nonextensive Skin Wound

• Regeneration and Fibrosis:
  • Inflammation sets the stage: Severed blood vessels bleed
  • Inflammatory chemicals are released. Local blood vessels become more permeable, allowing white blood cells, fluid, clotting proteins, and other plasma proteins to seep into the injured area
  • Clotting occurs and the surface dries and forms a scab.
  • The clot is replaced by granulation tissue, which restores the vascular supply
  • Inflammatory chemicals are released. Fibroblasts produce collagen fibers that bridge the gap. Macrophages phagocytize dead and dying cells and other debris. Surface epithelial cells multiply and migrate over the granulation tissue
  • The fibrosed area matures and contracts, and the epithelium thickens
  • A fully regenerated epithelium with an underlying area of scar tissue results.

Embryonic Germ Layers

• The primary tissue types they produce include epithelium (form from all three germ layers)
• Muscle and connective tissue (mostly from mesoderm)
• The inner lining of the digestive system (from endoderm)
• Nervous tissue (from ectoderm).