Glandular Tissue

GLANDULAR EPITHELIUM

Glandular Epithelia A gland consists of one or more cells that make a secretion Many epithelial cells make secretions Secretions are usually water based fluids containing proteins Secretion is a process whereby gland cells obtain needed substances from the blood and transform them chemically into a product that is discharged from the cell

Types of Secretion Glandular Epithelia – Types of Secretions Serous glands – Watery secretions Mucous glands – Secrete mucins Mixed exocrine glands – Both serous and mucous

Glandular Epithelia Glands are classified on where they release their secretion: – endocrine(internal secretion) – exocrine(external secretion) Glands are classified by number of cells: – unicellular exocrine glands – multicellular exocrine glands Unicellular glands are scattered within epithelial sheets Multicellular glands develop by invaginating into an epithelial sheet and connective tissue

Classification of Epithelia Glandular Epithelia – Endocrine glands Release hormones – Into interstitial fluid – No ducts – Exocrine glands Produce secretions – Onto epithelial surfaces – Through ducts

Endocrine Glands All endocrine glands eventually lose their ducts and are considered to be ductless Endocrine glands produce hormones that regulate body functions These glands secrete directly into the extracellular space The hormones then enter the blood or lymphatic fluid – Pituitary, Thyroid, Parathyroid, Adrenal, Thymus,, and others

Exocrine Glands Exocrine glands are far more numerous than endocrine These glands secrete their products through a duct onto a body surface or into a body cavity These glands secrete mucous, sweat, oil, saliva, bile, digestive enzymes, and many other substances

Modes of Secretion Glandular Epithelia – Modes of Secretion 1.Merocrine secretion 2.Apocrine secretion 3.Holocrine secretion

Multicellular Exocrine Glands Modes of Secretion Merocrine glands (salivary, sweat, pancreas) – Secret their products by exocytosis and gland is not altered Holocrine glands (sebaceous oil glands) – The entire cell ruptures releasing the secretions Apocrine glands (mammary?) – The apex of the secretory cell pinches off and release its secretion

Figure 4-6 Modes of Glandular Secretion Salivary gland Mammary gland Hair Sebaceous gland Hair follicle Stem cell Cell division replaces lost cells Cells produce secretion, increasing in size Cells burst, releasing cytoplasmic contents Secretion Regrowth Golgi apparatus Breaks down Secretory vesicle Golgi apparatus Nucleus TEM  3039

Modes of Secretion – Merocrine Secretion Produced in Golgi apparatus Released by vesicles (exocytosis) For example, sweat glands

Chief Modes of Secretion Merocrine glands – Secrete products by exocytosis – Secretions do not alter gland – Secretions leave gland via duct

Figure 4-6a Modes of Glandular Secretion Salivary gland Mammary gland Hair Sebaceous gland Hair follicle Merocrine. In merocrine secretion, secretory vesicles are discharged at the apical surface of the gland cell by exocytosis. Secretory vesicle Golgi apparatus Nucleus TEM  3039

Modes of Secretion – Apocrine Secretion Produced in Golgi apparatus Released by shedding cytoplasm For example, mammary glands

Chief Modes of Secretion Apocrine glands – Accumulate products just beneath free surface – Apex of the cell pinches off releasing its contents – Cell repairs the damage and the process is repeated – Some controversy as to its presence in humans

Figure 4-6b Modes of Glandular Secretion Salivary gland Mammary gland Hair Sebaceous gland Hair follicle Apocrine. Apocrine secretion involves the loss of apical cytoplasm. Inclusions, secretory vesicles, and other cytoplasmic components are shed in the process. The gland cell then undergoes growth and repair before it releases additional secretions. Secretion Regrowth Golgi apparatus Breaks down

Chief Modes of Secretion Holocrine glands – Accumulate their products within the gland until they rupture – They are replaced by the division of underlying cells – Sebaceous oil glands are the only true example in humans

Modes of Secretion – Holocrine Secretion Released by cells bursting, killing gland cells Gland cells replaced by stem cells For example, sebaceous glands

Figure 4-6c Modes of Glandular Secretion Salivary gland Mammary gland Hair Sebaceous gland Hair follicle Stem cell Holocrine. Holocrine secretion occurs as superficial gland cells burst. Continued secretion involves the replacement of these cells through the mitotic division of underlying stem cells. Cell division replaces lost cells Cells produce secretion, increasing in size Cells burst, releasing cytoplasmic contents

Gland Structure Glandular Epithelia – Gland Structure Unicellular glands – Mucous (goblet) cells are the only unicellular exocrine glands » Scattered among epithelia » For example, in intestinal lining

Unicellular Exocrine Glands The only important example of a unicellular gland is the goblet cell Shaped liked a goblet Distributed in the epithelial linings of the intestinal and respiratory tract amid columnar cells with other functions Produces mucin which when dissolved in water forms mucus, a slimy coating that protects and lubricates surfaces

Goblet cells Found in columnar epithelium cells lining the intestinal and respiratory tract

Gland Structure Multicellular glands 1.Structure of the duct » Simple (undivided) » Compound (divided) 2.Shape of secretory portion of the gland » Tubular (tube shaped) » Alveolar or acinar (blind pockets) 3.Relationship between ducts and glandular areas » Branched (several secretory areas sharing one duct)

Multicellular Exocrine Glands Multicellular exocrince glands have two common structural elements – An epithelium derived duct – A secretory unit consisting of secreting cells In all but the simplest glands connective tissue surrounds the secretory unit supplying it with blood an nerve fibers Often the connective tissue forms a fibrous capsule and may subdivide the gland into lobes

Multicellular Exocrine Glands Structural Classification On the basis of their duct structures, multicellular exocrine glands are either simple or compound – Simple glands have a single unbranched duct – Compound glands have a branched duct The glands are further categorized by their secretory units – Tubular (forms tubes) – Alveolar (forms sacs) – Tubuloalveolar (contains both types)

Simple Duct Structure

Figure 4-7 A Structural Classification of Exocrine Glands SIMPLE GLANDS Gland cells SIMPLE TUBULAR SIMPLE COILED TUBULAR Examples: Intestinal glands Merocrine sweat stage in development of simple branched glands SIMPLE BRANCHED TUBULAR Examples: Gastric glands Mucous glands Not found in adult; a SIMPLE ALVEOLAR (ACINAR) SIMPLE BRANCHED ALVEOLAR Examples: Sebaceous (oil) glands of esophagus, tongue, duodenum glands Duct

Compound Duct Structure

Figure 4-7 A Structural Classification of Exocrine Glands COMPOUND GLANDS COMPOUND TUBULAR COMPOUND ALVEOLAR (ACINAR) COMPOUND TUBULOALVEOLAR Examples: Mucous glands (in mouth) Examples: Bulbo-urethral glands (in male reproductive system) tubules) Mammary glands Examples: Salivary glands Glands of respiratory passages Testes (seminiferous Pancreas