HESI A2 - Histology - Key Terms and Concepts

Histology

The study of tissues and their structures at the microscopic level.

Epithelial tissue

A type of tissue that covers body surfaces and lines cavities, forming protective barriers.

Connective tissue

A category of tissue that links, supports, and shields organs and other tissues throughout the body.

Muscle tissue

A specialized tissue type that enables bodily movement through its ability to contract.

Nervous tissue

A type of tissue that transmits electrical signals and processes information.

Extracellular matrix

A complex network of chemicals and proteins that envelop cells, offering communication channels and mechanical support.

Basement membrane

A thin, fibrous layer that anchors epithelial tissue to underlying connective tissue.

Apical surface

The outermost surface of epithelial tissue that is exposed to the environment or an internal cavity.

Lumen

The hollow interior of a tubular structure, such as a blood vessel or intestine.

Goblet cell

A specialized epithelial cell that secretes mucus to lubricate and protect surfaces.

Simple squamous epithelium

A single flat cell layer that allows for rapid diffusion. It forms the lining of serous membranes (serosa).

Stratified squamous epithelium

Several layers of flat cells that protect against friction.

Simple cuboidal epithelium

Cube-shaped cells in a single layer that facilitate absorption and secretion.

Stratified cuboidal epithelium

Epithelial tissue composed of multiple layers of cube-like cells, primarily involved in reinforcement and protection. It is often found in sweat gland ducts.

Simple columnar epithelium

Tall columnar cells that release mucus and absorb nutrients, making up a single layer.

Stratified columnar epithelium

Multiple layers of column-shaped cells that provide protection and secretion (e.g., male urethra, mammary gland ducts).

Pseudostratified columnar epithelium

A single layer of irregularly shaped cells that appears multilayered and contains cilia (e.g., trachea, nasal cavity lining).

Transitional epithelium

A specialized epithelium that stretches and changes shape to accommodate volume changes (e.g., urinary bladder).

Keratinized epithelium

A type of stratified squamous epithelium containing keratin for extra protection (e.g., skin surface).

Non-keratinized epithelium

A type of stratified squamous epithelium that remains moist and flexible (e.g., esophagus lining).

Loose connective tissue

A connective tissue with a loosely arranged extracellular matrix that provides support and flexibility.

Dense connective tissue

A connective tissue with a tightly packed extracellular matrix that offers strength and resistance to stress. It also forms tendons and ligaments.

Areolar connective tissue

A type of loose connective tissue that allows mobility while supporting and cushioning organs.

Adipose tissue

A form of connective tissue that stores fat for energy, thermal insulation, and cushioning of organs.

Reticular tissue

A type of connective tissue made of a network of thin fibers, offering internal support for organs such as the spleen and lymph nodes.

Dense regular connective tissue

Connective tissue packed with parallel collagen fibers, providing high tensile strength in a single direction.

Dense irregular connective tissue

A connective tissue with irregularly arranged collagen fibers that withstand stress from multiple directions.

Elastic connective tissue

A connective tissue with abundant elastic fibers that allow for stretching and recoil.

Hyaline cartilage

A smooth, glassy cartilage that reduces friction and provides support. This cartilage is typically found on the nose, sternum, and trachea.

Fibrocartilage

A tough cartilage with densely packed collagen fibers that absorb shock. It can be found in intervertebral discs.

Elastic cartilage

A flexible cartilage with elastic fibers that maintains structure while allowing movement. It can be found in the ears and epiglottis.

Chondrocyte

A mature cartilage cell that maintains the extracellular matrix of cartilage.

Osteocyte

A mature bone cell that helps regulate bone tissue maintenance.

Osteoblast

A bone-forming cell that produces a new bone matrix.

Osteoclast

A bone-resorbing cell that breaks down bone tissue for remodeling and calcium release.

Collagen fiber

A strong protein fiber that provides tensile strength in connective tissues.

Elastic fiber

A stretchy protein strand that allows tissues to expand and then revert to their original shape.

Reticular fiber

A thin collagen fiber that forms a supportive framework in organs.

Erythrocyte

Oxygen-transporting red blood cells in the body.

Leukocyte

A white blood cell that helps defend the body against infections and foreign invaders.

Skeletal muscle tissue

A voluntary muscle tissue with striations that allows for body movement.

Cardiac muscle tissue

Involuntary muscle tissue found in the heart, characterized by rhythmic contractions and the presence of intercalated discs.

Smooth muscle tissue

Slow, continuous contractions are produced by this non-striated, involuntary muscle that is located in the walls of internal organs.

Sarcomere

The fundamental contractile unit of striated muscle, responsible for muscle contraction and relaxation.

Neuron

A nerve cell that transmits electrical impulses and communicates signals in the body.

Glial cell

A supportive cell in the nervous system that protects and nourishes neurons.

Myelin sheath

A fatty layer surrounding nerve fibers that increases the speed of electrical impulses.

Dendrite

A branching extension of a neuron that receives signals from other cells.

Axon

The long projection of a neuron that transmits electrical signals to other cells.

Synaptic cleft

The small gap between neurons which neurotransmitters are released for communication.

Cartilage connective tissue

A firm yet flexible connective tissue that cushions joints, absorbing shock and reducing friction between bones.

Glands

Specialized groups of epithelial cells that produce and release substances such as hormones, enzymes, or sweat.

Endocrine glands

Ductless glands that produce hormones that directly diffuse into the blood vessels. Examples are the pituitary gland and pancreas (islet of Langerhans).

Exocrine glands

Glands that release their secretions through ducts to a surface or cavity; examples are salivary glands, sweat glands, and pancreas (acinar tissue).