Histology, Tissues, and the Cell Cycle

Histology

The study of the microscopic structure of tissues, also known as "microscopic anatomy" or "microanatomy."

Tissue

Cells working together in functionally related groups via attachment and communication.

Hierarchical Organization of Living Matter

The structural levels of an organism arranged in order: Cells, Tissues, Organs, Organ systems, Organism.

Four Primary Tissue Types

The fundamental classes of animal tissues: Epithelial Tissue, Muscle Tissue, Nervous Tissue, and Connective Tissue.

Epithelial Tissue

A primary tissue type characterized by close cell contact, avascularity, innervation, high mitotic (regenerative) capacity, polarity, and attachment to connective tissue via a basement membrane.

Apical Surface

The "top" free region of an epithelial tissue layer that is modified for specific functions.

Basal Surface

The "bottom" region of epithelial tissue adjacent to the basement membrane that anchors it to connective tissue.

Squamous Epithelium

Epithelial tissue characterized by flat, scale-like cell shapes.

Cuboidal Epithelium

Epithelial tissue characterized by cube-shaped cells.

Columnar Epithelium

Epithelial tissue characterized by tall, column-shaped cells.

Simple Epithelium

Epithelium consisting of a single layer of cells.

Stratified Epithelium

Epithelium consisting of multiple layers of cells.

Muscle Tissue

Tissue composed of elongated cells called "muscle fibers" that are specialized to contract and produce movement.

Skeletal Muscle

Voluntary muscle tissue attached to and pulling on bones, characterized by striations and many nuclei.

Cardiac Muscle

Involuntary muscle tissue found only in the heart, characterized by striations, branching cells, a single nucleus, and intercalated discs.

Smooth Muscle

Involuntary muscle tissue located in the walls of hollow internal organs, characterized by non-striated, spindle-shaped cells with a single nucleus.

Nervous Tissue

Tissue found in the brain, spinal cord, and peripheral nerves, specialized for sensory reception and the conduction of nerve impulses.

Neurons

Amitotic "nerve cells" that coordinate, regulate, and integrate body functions through electrical and chemical signaling.

Neuroglia

"Glial cells" of nervous tissue that can divide, provide structural support, bind neurons together, and connect neurons to blood vessels.

Connective Tissue

A diverse and abundant tissue type consisting of cells and an extracellular matrix (ground substance and fibers) that binds structures, provides support, fills spaces, stores fat, and protects against infection.

Connective Tissue Proper

A category of connective tissue with a fibrous extracellular matrix, subdivided into dense types (regular, irregular, elastic) and loose types (areolar, reticular, adipose).

Cartilage Tissue

A rigid connective tissue with no direct blood supply that provides support and protection, housing chondrocytes within spaces called lacunae.

Bone Tissue (Osseous Tissue)

A rigid, highly vascular and active connective tissue containing osteocytes and mineralized calcium matrix, providing structural support, muscle attachment, blood cell formation, and rapid healing.

Compact Bone

Dense bone tissue organized into repeating concentric cylindrical units termed osteons.

Blood Tissue

A fluid connective tissue consisting of red blood cells (erythrocytes), white blood cells (leukocytes), platelets, and plasma, which functions in material transport.

Cell Cycle

A self-regulated sequence of events in a cell that controls its growth and leads to division, consisting of Interphase and M (mitotic)-phase.

Interphase

The period between two successive cell divisions in which cell growth, organelle production, and DNA replication take place.

$G_1$ Phase

The first gap phase of interphase characterized by cell growth, accumulation of nutrients, and synthesis of regulatory proteins controlling DNA replication.

S Phase

The synthesis phase of interphase during which DNA replication occurs, doubling the genetic material and forming new sister