Microvilli are tiny finger-like projections on cells, especially in the small intestine, aiding in nutrient absorption by increasing surface area.

They form structures like the brush border, found on both absorptive and secretory surfaces, and vary in length and composition. In the immune system, they are common on lymphocytes.

Stereocilia are non-motile cell modifications, similar to microvilli but longer and thicker.

They contain actin, lack an axoneme, and are found in the vas deferens, epididymis, and inner ear sensory cells.

Unlike cilia, stereocilia lack a basal body, may or may not have a glycocalyx coating, and have no fixed arrangement.

Cilia are small hair-like structures on mammalian cell surfaces, involved in both locomotion and mechanoreception.

They can be single or multiple, and organisms with cilia are called ciliates, using them for feeding and movement.

Numerous cilia on cell surfaces, particularly in the respiratory epithelium of the human respiratory tract, clear mucus and dust from the lungs.

Discovered in 1898, primary cilia were initially thought to be vestigial but now serve as non-motile sensory antennas coordinating cellular signaling pathways.

They play key roles in kidney cell signaling for urine flow, act as mechanoreceptors, and facilitate particle transfer in the retina.

Glandular epithelium, whether single cells or groups, produces and secretes specific products like mucin.

It typically invaginates into connective tissue but is separated by the basal lamina.

Glandular epithelium can be either endocrine (secreting into the bloodstream) or exocrine (secreting onto a surface).

They have a characteristic vacuole filled with mucus and function to secrete mucins.

Goblet cells are single intraepithelial glandular cells found in the small and large intestines, nasal mucosa, and respiratory tract.

Columnar epithelial cell conglomerates with bright cytoplasm (mucus-filled), lacking a vacuole.

Found in locations like the surface epithelium of the stomach and cervical canal, where they form entirely secretory epithelium.

Extraepithelial glands migrate during embryogenesis from surface epithelium into underlying connective tissue, resulting in an elaborate structure.

Closed gland connected to excretory ducts for secretion production, with various terminal ends.

Functions include the production and release of secretions into the lumen, draining into the excretory duct system.

Shape: tubular; wide, elongated lumen Examples: gastric glands (foveolas in the stomach),
colonic crypts

Epithelial-lined ducts connect glandular cells to the gland opening, facilitating secretion drainage and modifying its nature.

Duct shapes vary due to subdivision into lobules by connective tissue septa in extraepithelial glands.

In broad connective tissue septa, lead to excretory ducts, the thickest segment

Examples include bilayered columnar epithelium in terminal excretory ducts of various glands, such as apocrine and eccrine sweat glands and esophageal glands.

Release of ions and small molecules facilitated by transmembrane proteins through membrane protein transport. Found in almost all exocrine gland cells.

Secretion release rich in proteins occurs through cytosolic vesicle fusion with the cell membrane, utilizing the mechanism of exocytosis. Commonly found in exocrine glandular cells, such as salivary and sweat glands.

Lipid-rich secretions are released as a portion of the apical cytoplasm buds off, involving the cell membrane. This process, known as apocrine secretion, occurs exclusively in apocrine sweat glands and lactating mammary glands.

Entire cytoplasmic content is released through gland cell destruction via apoptosis. This mechanism, called holocrine secretion, is exclusive to sebaceous glands.

Low viscosity, protein, and enzyme-rich secretion, characterized by acinar glands, basal-rich rough endoplasmic reticulum, and apical granular secretions. Examples include the parotid gland and pancreas.

Viscous, mucin-rich secretion characterized by tubular glands with pale, bright cytoplasm. Examples include sublingual gland, esophageal glands, Brunner's glands, and all intraepithelial glands.

Low viscosity secretion containing both mucin and enzymes. Terminal end is mainly tubuloacinar with a serous demilune. Gland cells exhibit characteristics of both serous and mucous cells. Example: Submandibular gland.

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