Animal and Plant Tissues

• Tissue refers to groups of similar cells performing specific functions
• Histology is the study of tissues
• Tissues organize into organs, facilitating complex functions within organ systems

Types of Tissue

• Four basic animal tissue types include: epithelial, connective, muscle, and nervous
• Plant tissue types include: meristematic, ground, dermal, and vascular

Animal Tissue

• Animal tissues are classified by cell type, structure, and function

Epithelial Tissue

• Covers body surfaces, lines cavities, and forms glands
• Functions: protection, absorption, secretion, excretion, and filtration
• Characterized by tightly packed cells and minimal extracellular matrix
• Exhibits polarity with apical (free) and basal (attached) surfaces
• Supported by a basement membrane
• Avascular, yet innervated, exhibiting high regeneration capacity

Types of Epithelial Tissue

• Classified by shape: squamous, cuboidal, columnar
• Classified by arrangement: simple, stratified, or pseudostratified
• Simple squamous epithelium: a single layer of flattened cells, facilitates diffusion and filtration, and is found in lung air sacs and blood vessel linings
• Simple cuboidal epithelium: a single layer of cube-shaped cells, involved in secretion and absorption, and found in kidney tubules and glands
• Simple columnar epithelium: a single layer of column-shaped cells, involved in absorption and secretion, lines the digestive tract, and may contain goblet cells or microvilli
• Pseudostratified columnar epithelium: a single layer of cells of varying heights, appears stratified, involved in secretion and propulsion of mucus, and lines the trachea
• Stratified squamous epithelium: multiple layers of flattened cells, protects against abrasion, and found in the epidermis of skin
• Stratified cuboidal epithelium: multiple layers of cube-shaped cells, involved in protection and secretion, and found in some sweat and mammary glands
• Stratified columnar epithelium: multiple layers of column-shaped cells, involved in protection and secretion, rare, and found in the male urethra and some gland ducts
• Transitional epithelium: can stretch and recoil; lines the urinary bladder

Connective Tissue

• Connects, supports, and protects other tissues and organs
• Characterized by an abundant extracellular matrix
• The extracellular matrix consists of ground substance and fibers
• The ground substance is an unstructured material filling spaces between cells
• Fibers include: collagen, elastic, and reticular fibers
• Highly vascular, besides cartilage and tendons

Types of Connective Tissue

• Connective tissue proper encompasses loose and dense connective tissues
• Cartilage types include: hyaline, elastic, and fibrocartilage
• Bone types include: compact and spongy bone
• Blood components include: erythrocytes, leukocytes, and platelets
• Loose connective tissue includes:
  • Areolar connective tissue: wraps and cushions organs, widely distributed under epithelia
  • Adipose tissue: stores fat, insulates, protects organs, and is found under the skin and around kidneys
  • Reticular connective tissue: forms supportive stroma for lymphatic organs, found in lymph nodes, spleen, and bone marrow
• Dense connective tissue includes:
  • Dense regular connective tissue: withstands tensile stress along one direction, found in tendons and ligaments
  • Dense irregular connective tissue: withstands tension exerted in many directions, found in the dermis of skin
  • Elastic connective tissue: allows recoil after stretching, found in walls of large arteries
• Cartilage includes:
  • Hyaline cartilage: supports and reinforces with resilient cushioning, found at the ends of long bones
  • Elastic cartilage: maintains shape while allowing flexibility, found in the external ear
  • Fibrocartilage: tensile strength allows it to absorb compressive shock, found in intervertebral discs
• Bone includes:
  • Compact bone: hard, calcified matrix with osteocytes, provides support and protection
  • Spongy bone: trabecular network containing red bone marrow
• Blood includes:
  • Red and white blood cells in a fluid matrix (plasma), transports gases, nutrients, wastes, and other substances

Muscle Tissue

• Responsible for movement
• Consists of elongated cells known as muscle fibers

Types of Muscle Tissue

• Skeletal muscle
  • Attached to bones, allowing voluntary movement
  • Striated
  • Multinucleated
• Cardiac muscle
  • Forms heart walls, responsible for involuntary blood pumping
  • Striated
  • Uninucleated
  • Intercalated discs: specialized junctions facilitating rapid electrical communication
• Smooth muscle
  • Located in hollow organ walls, responsible for involuntary movement
  • Non-striated
  • Uninucleated

Nervous Tissue

• Composed of neurons and glial cells
• Neurons: transmit electrical signals
• Glial cells: support and protect neurons
• Found in the brain, spinal cord, and nerves

Types of Nervous Tissue

• Neurons
  • Generate and conduct nerve impulses
  • Composed of a cell body, dendrites, and an axon
• Glial cells
  • Support, insulate, and protect neurons
  • Types include astrocytes, oligodendrocytes, microglia, and ependymal cells

Plant Tissue

• Classified by cell type, structure, and function

Meristematic Tissue

• Responsible for plant growth
• Contains undifferentiated cells that can divide rapidly

Types of Meristematic Tissue

• Apical meristems
  • Located at the tips of roots and shoots
  • Responsible for primary growth (increase in length)
• Lateral meristems
  • Located along the sides of stems and roots
  • Responsible for secondary growth (increase in width)
    • Vascular cambium: produces secondary xylem and phloem
    • Cork cambium: produces the periderm (bark)

Ground Tissue

• Fills the spaces between other tissues
• Functions include photosynthesis, storage, and support

Types of Ground Tissue

• Parenchyma
  • Thin-walled cells with large vacuoles
  • Involved in photosynthesis, storage, and secretion
• Collenchyma
  • Unevenly thickened cell walls
  • Provides flexible support
• Sclerenchyma
  • Thick, lignified cell walls
  • Provides rigid support
  • Includes sclereids and fibers

Dermal Tissue

• Forms the protective outer layer of the plant

Types of Dermal Tissue

• Epidermis
  • Single layer of cells covering the plant
  • Protects against water loss and pathogens
  • Cuticle: a waxy covering preventing water loss
  • Trichomes: hairlike structures protecting against herbivores and UV radiation
• Periderm
  • Replaces the epidermis in woody plants
  • Forms the bark

Vascular Tissue

• Transports water, minerals, and sugars throughout the plant

Types of Vascular Tissue

• Xylem
  • Transports water and minerals from roots to the rest of the plant
  • Includes tracheids and vessel elements
• Phloem
  • Transports sugars from leaves to the rest of the plant
  • Includes sieve-tube elements and companion cells