Epithelial tissue in the context of "Epidermis"

In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a function. Tissues of different types combine to form an organ which has a specific function. The intestinal wall for example is formed by epithelial tissue and smooth muscle tissue. Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system.

An organ's tissues are broadly classified into parenchyma, the functional tissue, and stroma, the structural tissue with supportive, connective, or ancillary functions. For example, the gland tissue that produces hormones is the parenchyma, while the stroma includes the nerves that innervate the parenchyma, the blood vessels that oxygenate and nourish it and remove metabolic wastes, and the connective tissues that provide structure, placement, and anchoring. The primary tissues that form an organ generally have common embryologic origins, often arising from the same germ layer. Organs are present in most multicellular organisms. In single-celled organisms such as eukaryotes, the functional analogue of an organ is an organelle. In plants, there are three main organs.The number of organs in any organism depends on the definition used. There are approximately 79 organs in the human body; the exact number remains debated.

Connective tissue is biological tissue that is found in between other tissues in the body. Most types of connective tissue consists of three main components: elastic and collagen fibers, ground substance, and cells.

It is one of the four primary types of animal tissue along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesoderm, the middle embryonic germ layer.

The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma meaning "skin".

Generally speaking, the ectoderm differentiates to form epithelial and neural tissues (spinal cord, nerves and brain). This includes the skin, linings of the mouth, anus, nostrils, sweat glands, hair and nails, and tooth enamel. Other types of epithelium are derived from the endoderm.

The basement membrane, also known as the basal lamina, is a specialized form of extracellular matrix (ECM) common to all multicellular animals. It is a very thin, flexible, and strong sheet-like type of ECM that provides a supporting base for all types of epithelial tissue, separates it from another cell layer such as endothelium, and anchors it to the underlying connective tissue (stroma).

A basement membrane also surrounds some individual cells, including muscle cells, fat cells, and Schwann cells, separating them from surrounding connective tissue. Its composition can vary from tissue to tissue, and even in different regions of the same tissue. The other type of ECM is the interstitial matrix. The basement membrane may be described as having two layers or laminae, an external basal lamina, facing the epithelium, and an internal basal lamina that faces the connective tissue. These two laminae are also known as the basal lamina and the reticular lamina.