Epithelial Tissue Vs Connective Tissue: Definition, 16+ Differences, Examples

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Definition of Epithelial Tissue

Epithelial tissue is a kind of animal tissue which is composed of highly aggregated polyhedral cells which are tightly attached to each other as cellular sheets which line the inside of hollow organs and cover the body surface.

Cells in epithelial tissue or epithelium (plural: epithelium) are organized in continuous sheets, in single or several layers.
The forms and sizes of cells in the epithelial tissue vary from tall columnar to cuboidal to low squamous, and the size and morphology of the cells are frequently determined by their function.
This tissue’s innermost layer of cells is attached to a basement membrane, which is a thin extracellular layer made up of proteins such as laminin and collagen.
Epithelial tissue has no blood flow and is avascular. Nutrient absorption and waste elimination happen through diffusion with the tissue beneath the epithelial tissue.
The cells also lack a nerve supply.
Because epithelial tissue has a rapid pace of cell division, dead or wounded cells are discarded and substituted by new ones, it is capable of ongoing repair and regeneration.
There are two forms of epithelial tissue based on their location: covering epithelium and glandular epithelium.
The covering epithelium is the tissue which forms the outside layer of the skin as well as the majority of internal organs such as blood vessels as well as body cavities. It is therefore subdivided into simple and stratified epithelium based on the complexity and number of cell layers.
Throughout the body, the glandular epithelium lines numerous glands and their ducts, which then proliferate to create various hormones and enzymes. The existence of ducts divides the glandular epithelium into exocrine and endocrine glands.
Initial line of defence against pathogenic bacteria is epithelial tissue, which also shields the underlying tissue from radiation, desiccation toxins, and physical stress.
Furthermore, glandular epithelial tissue is engaged in the release of a variety of important metabolites.
The intestinal epithelial tissue is engaged in absorption, and the cutaneous epithelial tissue is also involved in sensing and reception.

Definition of Connective Tissue

Connective tissue is an animal tissue composed of cells, fibres, and gel-like substances which sustains and structures the body.

Connective tissue, which is made up of cells and extracellular matrix, is the most prevalent tissue in the body.
Mesenchymal cells, which are embryonic cells, give rise to connective tissue cells.
All connective tissues are made up of immature cells termed blast cells which retain the ability to divide and secrete extracellular matrix.
Fibroblasts, macrophages, plasma cells, mast cells, adipose cells, chondrocytes, leukocytes, and other cells exist in various tissues.
The connective tissue’s ground substance or matrix, which can be fluid, semifluid, gelatinous, or calcified, supports cells, holds them together, stores water, and serves as a medium for the interchange of substances between the blood and cells.
Much of the tissue’s properties are determined by the structure of the extracellular matrix.
The extracellular matrix of cartilage, for example, is stiff yet flexible, while the extracellular matrix of bone is rigid and inflexible.
Except for cartilage and tendons, which are avascular and lack nerves, connective tissue is normally highly vascular and innervated; it has a plentiful blood and nerve supply.
Connective tissues are classified based on the diversity of their cells and extracellular matrix, as well as variances in their relative proportions. Liquid connective tissues, bones, cartilages, and adipose tissue are examples of these.
Connective tissue functions vary based on the kind and site of the tissue.
Connective tissues, such as bones, support and shape the body, whereas cartilage aids in movement.
Adipose tissue, which is found beneath the skin, functions as a heat insulator and also connects the epidermis to the tissue beneath.
Tendons and ligaments are located all over the body and serve as a connecting medium for bones, muscles, and cartilages.
Liquid connective tissue, such as blood and lymph, aids in the transmission of nutrients and waste, as well as the presence of immune cells that protect against external invaders.

Key Difference between Epithelial Tissue and Connective Tissue

(Epithelial Tissue Vs Connective Tissue)

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Epithelial tissue examples

Simple columnar epithelium

The simple columnar epithelium, like all other simple epithelium, is composed of a single layer of tall column-like cells.
These cells are linked to a basement membrane composed of two layers, the basal lamina and the reticular lamina.
The simple columnar epithelium is found as a lining epithelium in a lot of organs and is frequently modified to better suit a specific purpose.
The stomach’s columnar epithelium lacks surface features. The free surface of the cells lining the small intestine, on the other hand, is covered with microvilli, which improves the surface area for nutrient absorption from the small intestine.
The tracheal epithelium is likewise ciliated and has goblet cells which release mucus. Likewise, ciliary activity of the ciliated columnar epithelium in the uterine tubes propels eggs towards the uterus.
The columnar epithelium in many organs throughout the body provides a variety of tasks ranging from absorption to defence.

Endocrine organs

Endocrine glands are hormone-secreting glands that lack ducts. The glandular epithelium lines these glands.
The epithelium forms diverse sections of the glands, including the parenchyma in some and the ducts and surface of the gland in others.
Hormones, which are secretions of endocrine glands, diffuse into the bloodstream without passing via a duct.
Because the bloodstream distributes these fluids throughout the body, they have far-reaching consequences.
Endocrine glands include the pituitary gland at the base of the brain, the pineal gland in the brain, the thyroid and parathyroid glands near the larynx (voice box), the adrenal glands superior to the kidneys, the pancreas near the stomach, the ovaries in the pelvic cavity, the testes in the scrotum, and the thymus in the thoracic cavity.

Connective tissue examples

Bones

A bone is a connective tissue that contains live cells, tissues, and other constituents that are surrounded by non-living material.
The skeleton system in humans and other vertebrates is made up of bone tissues.
Internally, bone tissues in the hard structure create a honeycomb-like matrix made of two separate cells: osteoblasts and osteoclasts.
Bones are mineralized tissues that contain various kinds of tissues such as bone marrow, periosteum, endosteum, and blood vessels.
Such structures come in a variety of shapes and sizes, with varying degrees of complexity that are appropriate for various applications.
Since bone tissue is connective tissue, it’s indeed highly vascularized and surrounded by other connective tissues.
It is also innervated, therefore it receives several nerve supplies.

Blood

Blood is a fluid connective tissue that circulates throughout the body, allowing constant communication between tissues that are far apart.
Blood is made up of a transparent, straw-colored, watery fluid called plasma, as well as a variety of suspended blood cells.
Plasma is composed of approximately 90% water and dissolved and suspended components such as plasma proteins, inorganic salts, nutrients, waste products, hormones, and gases.
Blood cells include erythrocytes, leukocytes, and platelets, the majority of which are produced primarily in the red bone marrow. However, some lymphocytes are generated in lymphoid tissue.
Blood is a connective tissue that transports various things such as gases and nutrients. Furthermore, it delivers waste products to organs such as the kidney and liver.
Platelets in the blood contain cells called thrombocytes, which are responsible for blood clotting.

Epithelial Tissue Vs Connective Tissue Citations

Waugh A and Grant A (2004). Anatomy and Physiology. Ninth Edition. Churchill Livingstone.
Tortora GJ and Derrickson B (2017). Principles of Physiology and Anatomy. Fifteenth Edition. John Wiley & Sons, Inc.
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