University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2021
Views:

305

Pages:

76
Author:

agatoary6zt

Glandular Epithelium Glands • Definition: • “Glandular epithelia are tissues formed by cells specialized to produce secretion.” or • “An aggregation of gland cells into a definite structure for the purpose of secretion. Glandular epithelial cells may synthesize, store, and secrete: • Proteins (e.g; pancreas), • Lipids (e.g; adrenal, sebaceous glands), • Complexes of carbohydrates and proteins (e.g; salivary glands). • The mammary glands secrete all 3 substances. Development of glands • Formation of glands from covering epithelia. • Epithelial cells proliferate and penetrate connective tissue followed by further differerntiation. • They may–or may not–maintain contact with the surface. • When contact is maintained, exocrine glands are formed; • Without contact, endocrine glands are formed. Classification of glands • Glands are generally classified into two major groups: • Exocrine glands (Gr. Exo, outside,+ krinein, to separate). • Release their products onto an epithelial surface, either directly or through a duct e.g; the salivary glands, sweat glands, mammary glands. • Endocrine glands (Gr, endon, within,+ krinein). • Release their products ( hormones) into the blood stream, e.g; thyroid gland, parathyroid glands, pituitary gland, Adrenal glands. • Mixed variety: Some glands possess both exocrine and endocrine function. e.g; pancreas, liver cells.  Exocrine glands secrete substances to specific organ via duct systems. Mammary glands Sweat glands • The cells of endocrine glands can be arranged in cords or in follicles. • The lumens of the follicles accumulate large quantities of secretions . Mixed gland: Pancreas Contains both endocrine and exocrine parts. Mixed gland: Pancreas Mixed gland: Pancreas Mixed gland: Liver Mixed gland: Liver General histological structure of gland General histological structure of gland • Externally a gland is surrounded by a dense layer of connective tissue which forms capsule of the gland. • From the capsule connective tissue septa extend into the gland, thereby dividing its substance into a number of lobes. • Thinner septa subdivide each lobe into smaller lobules. • Blood vessels and nerves pass along the connective tissue septa to reach the secretory elements. • The functional part of a gland, formed by its secretory cells, is known as parenchyma of the gland. • The supporting elements of the gland, which consists mainly of connective tissue, are referred to as stroma of the gland. Capsule Myoepithelial cells: Rich in actin and myosin, Help to propel secretory product into duct system Glands (Exocrine & Endocrine) Might be classified according to the number of cells : Unicellular glands: One Cell . Examples: • Exocrine: Goblet cells which are present in the lining epithelia of large intestine and the respiratory tract. • Endocrine: DNES (Diffuse Neuro-Endocrine Systems), or APUD (Amine Precursor Uptake and Decarboxylation) in small intestine. Multicellular glands : Number of cells. – They form most of the glands of the body. Examples: Exocrine: Salivary glands, lachrymal glands, sweat glands, … Endocrine: Thyroid gland, parathyroid glands, pituitary gland, ….. Unicellular gland -Goblet cell The goblet cell is highly polarized with the nucleus and other organelles concentrated at the base of the cell. The remainder of the cell's cytoplasm is occupied by membrane-bound secretory granules containing mucin. • Goblet cells produce mucus (Mucin) • Mucin + water  mucus • Protects and lubricates many internal body surfaces. Unicellular gland - DNES DNES (Diffuse Neuro-Endocrine Systems), or APUD Exocrine glands These can also be classified on the basis of: • Morphology of ducts and secreting portions. • Nature of secretory product. • Mode of secretion. Classified according to the duct system and the secretory part Duct Simple Compound Secretory part Tubular Acinar (alveolar) Tubuloacinar Morphology of ducts and secreting portions  Classified by structure of duct:  Simple : “if a gland consists of a single secretory passage”.  Compound: “ if a gland containing a branched duct system”.  Categorized by shape of secretory unit:  Tubular: Glands whose glandular cells form tubes, the tubes may be straight or coiled.  Acinar or alveolar: Glands whose glandular cells form sac-like pockets (called alveolus or acinus).  Tubulo- acinar: In some glands when the secreting portions are neither typically tubular nor acinar, but combine certain features of both. • A gland is branched if several secretory areas (tubular or acinar ) share a duct. • Note that “branched” refer to the glandular areas and not to the duct. Simple exocrine glands Simple tubular Simple branched tubular Simple Simple coiled tubular acinar (alveolar) Simple branched Acinar (alveolar) Compound exocrine glands Compound tubular Compound acinar (alveolar) Compound tubulo-acinar Simple exocrine glands Simple tubular A single, straight tubular lumen into which the secretory products are discharged eg. mucus-secreting gland of the colon; crypt of Lieberkühn Simple coiled tubular A single tube, tightly coiled in 3 dimensions eg. Sweat glands A single tube, tightly coiled in 3 dimensions eg. Sweat glands Simple branched tubular Several tubular secretory portions converge onto a single unbranched duct. eg. Mucus-secreting gland of the stomach and uterus Simple branched tubular Simple acinar Occur in the form of pockets in epithelial surfaces. Lined by secretory cells eg. Small mucous glands along the urethra. Simple acinar Simple branched acinar Each gland consists of several secretory acini (A) that empty into a single excretory Duct eg. Sebaceous glands, sebum secretion Simple branched acinar Simple branched acinar Compound exocrine glands Compound tubular Secretory portion is branched and coiled and the duct system is also Branched (difficult to visualise) eg. Brunner’s gland of the duodenum Compound acinar Secretory units are acinar and drain into a branched duct system eg. Exocrine pancreas, Parotid salivary gland. Compound tubulo - acinar 3 types of secretory units: Branched tubular, branched acinar and branched tubular with acinar endpieces called demilunes eg. Sublingual & Submandibular salivary gland. Classification on the basis of nature of secretory product Classification on the basis of nature of secretory product 1. Mucous glands: these glands produce a viscid, slimy, carbohydrate-rich secretion which is called mucus, e.g; Pyloric glands of stomach 2. Serous glands: these glands produce a thin, watery, proteinrich secretions, often high in enzymatic activity e.g; Exocrine pancreas, the parotid salivary gland. 3. Mixed glands: these glands produce both mucous and serous secretions e.g; the sublingual and submandibular salivary glands. Serous cell and Mucous cell Mucous Cells Mucous cells are larger than serous cells, with flattened basal nuclei. Most of the cytoplasm is filled with secretory granules containing mucinogen like that of goblet cells. The RER and Golgi complexes of mucous cells produce heavily glycosylated glycoproteins with waterbinding properties. Mucous tubules Serous Cells The lumens of mucous tubules are larger than those of serous acini. Much connective tissue surrounds the mucous tubules and ducts. Serous acini Serous demilune Serous demilune Mucous gland Esophagous gland Mucous gland Serous gland Parotid gland Mixed gland : Seromucous gland Submandibular gland Mixed gland : Mucoserous gland Sublingual gland Classification on the basis of the mode of secretion Classification on the basis of the mode of secretion: • Depending on their mode of secretion i.e; the manner in which the secretory product is elaborated. • The exocrine glands are classified into the following: 1. Merocrine (eccrine) glands 2. Apocrine glands 3. Holocrine glands Mode of Secretion Holocrine Merocrine glands Merocrine glands : The secretory product is delivered in membranebounded vesicles to the apical surface of the cell. Here, vesicles fuse with the plasma membrane and extrude their contents by exocytosis. Example: Sweat gland, Pancreas and salivary glands. Apocrine glands Apocrine glands : In these glands part of the apical cytoplasm is lost along with the secretory material. 1. Lactating mammary glands, 2. Special sweat glands located in axilla , perianal area & areola of nipples. 3. Ceruminous glands of the external auditory meatus (ear) Apocrine glands Mammary glands Holocrine glands Holocrine glands: In these glands entire cells laden with secretory material disintegrate and all of the cellular contents are discharged from the gland as secretions. e.g; the sebaceous glands of skin Holocrine glands Sebaceous glands Sebaceous gland Rounded cells filled with sebum. Basal undifferentiated cells Types of sweat glands Sweat glands Merocrine and apocrine sweat glands (a) Merocrine sweat glands (b) Apocrine sweat glands Apocrine sweat glands

Glandular Epithelium

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