Unit VI- Exocrine Glands Flashcards
1
Q
How do exocrine glands develop
A
- induction by connective tissue
- exocrine glands develop as invaginations of surface epithelium
- exocrine glands retain a connection with the surface via ducts
2
Q
Structural organization of glands
A
- secretory portion: acinar or tubular
- acinus (plural: acini) - is a berry like cluster of cells with a central lumen
- conducting portion:ducts
- in some glands, ducts also have secretory function
3
Q
Classification of glands
A
- single-cell glands
- simple glands- single unbranched duct. Secretory portion can be branched or unbranced (sweat glands, sebaceous glands)
- compound glands- multiple branched ducts. Secretory portion can be acinar, tubular, or tubuloacinar (salivary glands and exocrine pancreas)
4
Q
Types of secretion
A
- holocrine
- apocrine
- merocrine (called eccrine in sweat glands)
5
Q
Holocrine
A
- lysis of cells filled with secretory product
- example: sebaceous glands of skin
6
Q
Apocrine
A
- shedding of apical cell segment filled with secretory product
- example: mammary glands
7
Q
Merocrine
A
- (called eccrine in sweat glands)
- exocytosis of proteins or glycoproteins
- examples: sweat glands, salivary glands, exocrine pancrease
8
Q
Glandular epithelium in merocrine glands
A
- serous cells
- mucous cells
- myoepithelial cells
9
Q
Serous cells
A
- stain well with H and E
- secrete proteins
- abundant RER and Golgi in the basal portion of the cell
- secretory granules in the apical cytoplasm
10
Q
Mucous cells
A
- secrete mucin, made of glycoproteins rich in complex carbohydrates
- mucins stain poorly with H and E but can be stained with periodic acid-Schiff (PAS) stain
- abundant RER and Golgi in the basal portion of the cell
- mucin filled secretory granules in the apical cytoplasm
- upon secretion, mucin becomes mucus, a vicous, jelly-like protective lubricant
11
Q
Myoepithelial cells
A
- located within the same basal lamina as secretory or duct cells
- possess long actomyosin-rich processes that surround the epithelial cells
- contraction helps expel secretory product from the gland lumen
- present in sweat, salivary, and mammary glands
12
Q
Ion and fluid transport across glandular epithelia
A
- ion channels and pumps. Example Na+/K+ ATPase
- mitochondria provide source of energy
- membrane specializations increase surface area
- tight junctions seal off the apical surface from the basal surface
13
Q
Unicellular glands
A
-goblet cells in the lining of the small intestine and in the respiratory epithelium of the trachea
14
Q
Multicellular simple glands
A
- sebaceous glands
- eccrine sweat glands
- apocrine sweat glands
15
Q
Sebaceous glands
A
-simple branched acinar glands
-holocrine secretion
-associated with hair follicles
-basal layer of cells that proliferate and differentiate into sebocytes
-sebum composition: triglycerides, cholesterol, squalene, wax esters
Clinical correlation: origin of acne
16
Q
Eccrine sweat glands
A
- simple (coiled) tubular glands
- stratified cuboidal epithelium in the duct and in the secretory portion
- cholingeric fibers of sympathetic nervous system stimulate sweat secretion
- pale (clear cells)- pyramidal to columnar in shape; located in periphery, resting on the basal lamina; produce watery component of sweat; contain abundant mitochondria; possess microvilli and intracellular canaliculli; have tight junctions
- dark cells- pyramidal in shape, near lumen, secrete glycoproteins and proteins, including bactericidal peptides
- myoepithelial cells: located within basal lamina; nucleus triangular or elongated; contain actomyosin-rich processes; contact to help expel the secretory product
- sweat ducts:
- epithelium stains darker than in secretory coli
- re-absorb sodium and chloride
- abundant Na+/K+ ATPase in the basal membrane
- abundant mitochondria
- tight junctions
17
Q
Apocrine sweat glands
A
- located in the axillary, areolar and perineal regions
- associated with hair shafts
- simple coiled glands
- the secretory coil is lined by simple cuboidal epithelium and has large lumen
- merocrine secretion
- secretory product may include pheromones
- stimulated by adrenergic fibers of the sympathetic nervous system
18
Q
Function of saliva
A
- moisture and lubrication
- initiation of the digestion of carbohydrates: alpha- amylase
- immune defense: lysozyme, lactoferrin and secretory IgA
- secretion of calcium and phosphate to make acquired pellicle
19
Q
Structure and organization of salivary glands
A
- connective tissue capsule
- septa-extensions of the capsule that divide parenchyma into lobules
- CT: capillary plexus that surrounds secretory and ductal components; nerves that control secretion: parasympathetic stimulation and sympathetic inhibition, lympocytes and plasma cells
- lobules contain salivons: a secretory unit consisting of acini, intercalated ducts, and interlobular excretory ducts
- acini drain into intercalated ducts
- intercalated ducts drain into intralobular ducts
- intralobular ducts drain into interlobular ducts located in the septa
20
Q
Acini in salivary glands
A
-types: mucous, serous, or mixed
Serous cells: pyramidal in shape, secrete proteins including sIgA
-Mucous cells:cuboidal to columnar in shape,secrete mucin
-myoepithelial cells (basket cells)- reside in basal lamina; possess long, branched contractile processes that prevent secretory protion distention and accelerate secretion; also present in ducts where they are spindle shaped and oriented along the duct length
21
Q
Intercalated ducts
A
- small, 4-6 cells in circumference
- cuboidal cells that lack secretory granules
- connect the secretory portion to the intralobular duct
22
Q
Intralobular ducts
A
- more that 6 cells in circumference
- lined by simple columnar epithelium
- basal striations: basal membrane infoldings that house mitochondria
- active transport of ions: saliva contains 7x potassium, 3x bicarbonate, 1/10 sodium compared to blood plasma
- mucous glands lack striated ducts
- also secrete sIgA
23
Q
Interlobular ducts
A
- large ducts located in septa
- lined with stratified cuboidal to columnar epithelium
24
Q
Mechanism of sIgA secretion
A
- plasma cells secrete dimeric IgA
- serous cells and intralobular duct cells produce IgA receptor
- IgA receptor mediates transcytosis of IgA into gland lumen
- proteolysis of receptor produces sIgA, the IgA in complex with receptor fragment called secretory components
25
Submandibular gland
- compound tubuloacinar gland
- serous and mucous acini
- mixed acini: serous demilunes
- serous cells secrete proteins including lysozyme
- some intralobular ducts are striated
26
Parotid gland
- compound acinar gland
- serous acini
- secretes alpha-amylase and other proteins
- intercalated ducts are long
- intralobular ducts are striated
- a diagnostic feature: the presence of abundant adipose tissue
27
Sublingual gland
- compound tubuloacinar gland
- primary mucous acini
- some mixed acini with serous demilunes
- intralobular ducts are not striated
28
Structure and function of exocrine pancreas
- compund acinar gland (similar to parotid)
- lobules separated by connective tissue septa
- septa contain blood vessels, lymphatics, nerves, and ducts
- secretory product contains: digestive proenzymes including proteases, lipases, nucleases, and amylolytic enzymes
- pancreatic enzymes are inactive and are activated by enterokinase cleavage in the duodenum. Pancreas also produces protease inhibitors
29
Serous acini of exocrine pancreas
- polarized serous cells surround small lumen
- abundant Golgi and RER
- zymogenic granules in the apical half of the cells (toward lumens)
- lack of myoepithelial cells
- secretion is stimulated by cholecystokinin, a hormone produced by enteroendocrine cells in duodenum
30
Intercalated ducts of exocrine pancreas
- protrude into acini as centroacinar cells
- lack secretory granules
- produce bicarbonate
- secretin, another hormone produced by enteroendocrine cells in duodenum, stimulates bicarbonate release
31
Intralobular ducts of exocrine pancreas
- lack striations
| - also secrete bicarbonate-rich fluid
32
Interlobular ducts of exocrine pancreas
- low columnar epithelium
| - also secrete bicarbonate rich fluid
33
Endocrine pancreas
- the endocrine portion of the pancreas is represented by the islets of Langerhands
- this is a diagnostic feature of the pancreas
34
Medical applications
- adenocarcinomas, the malignant tumors of glandular epithelia, are some of the most common tumors in adults
- reduced function of salivary glands due to disease or radiotherapy
- necrotizing pancreatitis
