Epithelial Tissue (Part 2)

In simple columnar epithelium, the nucleus is elongated and located at the basal end of the cells. Most of the digestive tract's organs have simple columnar epithelium, including the stomach, small intestine, and large intestine. The uterus also has simple columnar epithelium.

Despite appearing stratified, pseudostratified columnar epithelium consists of irregularly shaped and differently sized cells arranged in a single layer. This pseudostratified columnar epithelium is located in the respiratory tract, where some of these cells are ciliated.

The goblet cells are columnar, goblet-shaped cells that secrete mucins that form a gel. The respiratory, reproductive, and gastrointestinal tracts typically contain columnar cells that surround the goblet cells.

In a stratified squamous epithelium, squamous (flattened) epithelial cells are arranged in layers atop a basal membrane. As a result, only one layer is in contact with the basement membrane; the others adhere to one another. This layer forms the outermost layer of the skin as well as the inner lining of the mouth, esophagus, and vaginal cavity.

Stratified cuboidal epithelium is a type of tissue found in sweat glands, mammary glands, circumanal glands, and salivary glands. Protecting areas like sweat glands, mammary glands, and salivary glands.

The transitional epithelium is a type of stratified epithelium. The epithelial cells in this tissue can contract and expand to adapt to the degree of distension required. The ureters and urinary bladder are the only parts of the urinary system where it is found.

It is a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- means "inside"). Endocrine gland secretions are called hormones. The anterior pituitary, thymus, adrenal cortex, and gonad are some examples of endocrine glands.

Secretions from exocrine glands leave through a duct that opens directly or indirectly to the external environment (exo- = "outside"). The exocrine gland releases its contents through a duct that leads to the epithelium. Secretions produced by exocrine glands include mucous, sweat, saliva, and breast milk.

The most common type of exocrine secretion is merocrine secretion. Vesicles that contain the secretions move to apical surfaces of the cells, where they are released by exocytosis. Watery mucus containing lubricants such as mucin, which offer some protection against pathogens, is a merocrine secretion.

Apocrine cells secrete secretions through their plasma membrane, producing vesicles bound to the extracellular membrane. As part of the gland's secretory cell, the apical portion pinches off and enters the lumen. The apocrine glands are mostly found in the breast areolae, anogenital region, and axillae.

The entire gland cell ruptures during holocrine secretion. Those lost by secretion are replaced by new gland cells differentiated from surrounding tissue. Holocrine glands and cells are responsible for producing oils on the skin and hair. Sebaceous glands are examples of holocrine glands.