GLANDULAR EPITHELIUM Membrane epithelium becomes glandular epithelium when
• Membrane epithelium becomes glandular epithelium when it invaginates / involutes into the tissue layer / layers below, forming a gland • There are two main types of gland. They are exocrine and endocrine.
FORMATION of Exocrine/Endocrine glands • Form the same way. • During prenatal development, some epithelial cells form a downward fold (invagination) into the connective tissue • These invaginations may be composed of one or more cells and they are called glands. • Glands usually in cuboidal and columnar epithelium.
• In exocrine glands, the original invagination develops into a duct. • The duct is a passageway that remains open to the free surface. • Products are secreted to surface via the duct
• Exocrine glands may be unicellular or they may be multicellular. • example : unicellular exocrine gland is the goblet cell. Produce mucus. Located throughout the body. • Typical exocrine glands include sweat glands, salivary glands, mammary glands, stomach, liver.
Multicellular exocrine glands are divided into two general categories according to structure • simple (exocrine) gland = connects to the free surface via an unbranched duct. • compound (exocrine) gland = connects to the free surface via branched ducts. • NOTE : There are several variations in each of the above categories.
• Both may be further classified according to: shape of the part of the gland that produces the secretions. These areas may be: • tubular = secretion area is shaped like a tube • alveolar / acinar = secretion area is shaped like a sac
ENDOCRINE GLANDS In endocrine glands, the connection to the free surface is lost.
Endocrine glands secrete products directly into the blood or lymph fluids because ducts are absent. EXAMPLE: Pituitary (hypophysis) 1. location 2. structure a. posterior lobe: hormone storage 1. oxytocin 2. antidiuretic hormone (ADH) b. anterior lobe: hormone production 1. abnormalities: hypersecretion and hyposecretion 2. regulation: hypothalamic factors
GLANDULAR SECRETIONS (see Handout – no need to copy) • 1). merocrine = The secretory cells (cells that produce the secretions) discharge only the secretions they produce. • 2). apocrine = The secretion is produced in the secretory cell. It accumulates in the end of the cell (apical portion). The end of the cell pinches off and the secretion is released along with the tip of the cell. • 3). holocrine = The secretion is produced and accumulates in the secretory cell. Then the cell dies, disintegrates and is discharged from the gland along with the secretion.
Complete “Name that Tissue” and hand in!