Histology: Tissue Types

Location

Epithelial tissue, or epithelium, is found covering surfaces, lining body cavities, and forming glands. It constitutes the outer skin layer and lines various internal cavities.

Function

Its primary roles include protection from damage, absorption of substances, filtration for selective passage, and secretion of various compounds.

Structure

Epithelial tissue lacks direct blood supply (avascular), relying on diffusion from underlying connective tissue capillaries for nutrients. It features an apical surface exposed externally or to a cavity, and a basal surface attached to underlying connective tissue via a basement membrane.

Classification of Epithelial Tissue

Simple Epithelia

Simple epithelia consist of a single layer of cells, making them thin and ideal for absorption, secretion, and filtration. They offer limited protection.

Simple Squamous Epithelium

This tissue is a single layer of flattened, scale-like cells, crucial for rapid diffusion in areas like lung alveoli and capillary walls.

Simple Cuboidal Epithelium

Composed of a single layer of cube-shaped cells, it's involved in secretion and absorption in glands, ducts (e.g., salivary, pancreas), and kidney tubules.

Simple Columnar Epithelium

A single layer of tall, column-shaped cells, it lines the digestive tract, primarily facilitating absorption and secretion.

Pseudostratified Ciliated Columnar Epithelium

Appearing stratified due to varying nuclear levels, all cells attach to the basement membrane, though not all reach the surface. It often contains cilia and mucus-secreting goblet cells, lining the respiratory tract to trap and move particles.

Cartilage

Cartilage is a dense, resilient connective tissue providing flexible support and reducing friction in joints, ears, and nose. Avascular and aneural, it obtains nutrients via diffusion.

Types of Cartilage:

Hyaline Cartilage: The most common type, it has a glassy appearance with fine collagen fibers, providing flexible support and reducing friction in joints, nose, trachea, and larynx.

Elastic Cartilage: Contains elastic fibers for greater flexibility, allowing it to withstand bending, found in the external ear and epiglottis.

Fibrocartilage: The strongest type, with dense collagen bundles, offering high tensile strength and shock absorption. It's found in intervertebral discs, knee menisci, and the pubic symphysis.

Nervous Tissue

Nervous tissue forms the nervous system (brain, spinal cord, nerves), specializing in rapid communication by receiving stimuli and transmitting electrical signals to regulate body functions.

It consists of:

Neurons (Nerve Cells): Fundamental units transmitting electrical impulses, comprising a cell body, dendrites (signal reception), and an axon (signal transmission).

Neuroglia (Glial Cells): Support cells that protect neurons, providing structural, insulating, and metabolic assistance without transmitting impulses. Examples include astrocytes and Schwann cells, crucial for nervous system health.