Epithelial Tissue Overview

Epithelial Tissue

Epithelial tissue is one of the four major tissue types; it is composed of closely packed cells with minimal extracellular matrix, forming sheet-like coverings and linings.
Muscle and Nervous tissue are the only types of tissues that are not considered Epithelial.
An organ is defined as a structure composed of multiple tissue types working together to perform a specific function.
The kidney tubule epithelium, composed of simple cuboidal epithelial cells, is involved in filtration and reabsorption of waste products.
Stratified squamous epithelium is a type of epithelium that is composed of multiple layers of cells. The outermost layer of these cells are flattened, which makes it more durable than simple squamous epithelium.
- This protective layer can be non-keratinized, as found in the mucosa of the vagina, or keratinized.
Pseudostratified columnar epithelium, which appears stratified but is actually a single layer of cells, is found in the respiratory tract where its cilia help move mucus and debris.
Transitional epithelium, found in the uterus, bladder, and urethra, is characterized by its ability to stretch and change shape; its cells are often binucleated.
Alveolar lining, the thin layer of epithelial cells that forms the air sacs in the lungs, allows for efficient gas exchange between the air and the bloodstream.

Gland Types

Goblet cells, which are found in simple columnar epithelium, secrete mucus to lubricate and protect surfaces.
Holocrine glands, which are secretory glands, store their product until the cell ruptures, releasing the product into the gland’s lumen.
Follicular glands are a type of exocrine gland where the entire cell contents constitute the product.
Endocrine glands secrete hormones directly into the bloodstream, where they travel to distant target cells.

Connective Tissue

Connective tissue (CT) is a diverse tissue type that supports, connects, and protects other tissues and organs.
- Commonly: bone, cartilage, fat, blood, lymphatic, adipose, dense.
The main components of CT are cells, protein fibers, and ground substance.
All connective tissues are derived from the mesoderm, one of the three primary germ layers in embryonic development.
Reticular fibers, a type of protein fiber found in CT, form a strong, supportive meshwork that provides a framework for cells and organs.
Hyaline cartilage, the most common type of cartilage, has glassy appearance and is found in many locations, such as the nose and trachea.
Bone, a strong yet lightweight tissue, is made up of collagen fibers, which give it its strength, and calcium phosphate, which gives it its rigidity.
Plasma, the liquid component of blood, is composed primarily of water, proteins, and electrolytes.

Muscle Tissue

Skeletal muscle is the only type of muscle that is under voluntary control, meaning it is controlled by conscious effort.
Intercalated discs, which are specialized junctions between cardiac muscle cells, allow for synchronized contraction of the heart.
Neurons, the primary cells of the nervous system, transmit signals throughout the body, enabling communication and coordination of bodily functions.
Metaplasia is a process where one mature cell type is replaced by another mature cell type.
Stratum corneum is the outermost layer of the epidermis, composed of dead, keratinized cells, which provides protection from abrasion and water loss.
Stratum corneum is rich in keratinocytes, the main type of cells found in the epidermis, which produce the protein keratin.
Stratified squamous epithelium is a type of epithelium that is composed of multiple layers of cells.
- This epithelial layer is found in skin and other locations.
Thick skin, found on the palms of the hands and soles of the feet, has additional layers compared to thin skin.
- This provides added protection and durability.
Melanocytes are pigment- producing cells that are found in the stratum basale of the epidermis and hair follicles.
- They produce melanin, which gives the skin its color and protects from UV damage.
The dermis, the layer of skin beneath the epidermis, is made up of a variety of structures, including blood vessels, hair follicles, sweat glands, and sebaceous glands.
This layer provides support and nourishment for the epidermis.
The reticular layer, the deeper layer of the dermis, is composed primarily of dense irregular connective tissue, which provides strength and elasticity to the skin.
Living cells in the hair are found in the hair bulb, located at the base of the hair follicle.
Goosebumps, caused by contraction of the arrector pili muscle, are a response to cold temperatures, emotions, or stimulation of the sympathetic nervous system.
Apocrine sweat glands, found in the armpits, groin, nipples, belly, ears, eyelids, and lips, secrete sweat into hair follicles.
Cerumen, or earwax, is produced by glands in the ear canal. It lubricates the ear canal and traps debris, preventing it from reaching the eardrum.
The greatest risk factors for skin cancer are excessive UV light exposure and sunburn.