Exocrine Glands Flashcards
1
Q
Development of exocrine glands
A
- Develop as invaginations of surface epithelium - Induction by connective tissue - Retain a connection with the surface via ducts
2
Q
Structural organization of glands
A
- Secretory portion: acinar (berry-like cluster of cells with central lumen) or tubular
- Conducting portion: ducts. Can be branched or unbranched, modifies secretory product by absorption
3
Q
Classification of glands
A
- Single-cell glands
- Simple glands: single unbranched duct, secretory portion can be branched or unbranched. Ex. sweat glands and sebaceous glands
- Compound glands: multiple branched ducts, secretiry portion can be acinar, tubular, or tubuloacinar. Ex. salivary glands and exocrine pancrease
4
Q
What is holocrine secretion?
Give and example
A
Lysis of cells filled with secretory product
Ex. sebaceous glands of skin
5
Q
What is apocrine secretion?
Give and example
A
Shedding of apical cell segment filled with secretory product
Ex. mammary glands
6
Q
What is merocrine (eccrine) secretion?
Give 3 examples
A
Exocytosis of proteins or glycoproteins
Ex. sweat glands, salivary glands, exocrine pancreas
7
Q
What are serous cells and where are they found?
A
Found in the glandular epithelium of merocrine glands
- Secrete proteins
- Secretory product stains well with H&E
- Abundant RER and Golgi at base
- Secretory granules in apical cytoplasm
Exocytosis
8
Q
What are mucous cells and where are they found?
A
Found in glandular epithelium in merocrine glands
- Secrete mucin - stains poorly with H&E, stains better with PAS
Upon secretion mucin becomes mucus (protective lubricant)
- Abundant RER and Golgi at base
- Mucin-filled secretory granules in apical cytoplasm
Exocytosis
9
Q
What are myoepthelial cells and where are they found?
A
Found in glandular epithelium in merocrine glands
- Locaated between basal lamina and secretory or duct cells
- Triangular or elongated nucleus
- Long contractile processes (actomyosin-rich)
- Contraction helps expel secretory product
Present in sweat, salivary, and mammary glands
10
Q
Ion and fluid transport across glandular epithelia
A
- Tight junctions seal off apical from basal surface
- Ion channels and pumps (ex. Na/K ATPase)
- Mitochondria provide energy
- Membrane specializations increase surface area
11
Q
What are goblet cells and where are they found?
A
- Mucin-secreting unicellular glands
Found in the lining of the small intesetine and in respirtatory epithelium of trachea
12
Q
Sebaceous glands
A
- Simple acinar glands
- Holocrine secretion: cells proliferate, differentiate into sebocytes, accumulate lipid droplets, and rupture
- Associated with hair follicles
- Sebum (waterproofs skin) composition: triglycerides, cholesterol, squalene, wax esters
Clinical correlation: origin of acne
13
Q
What causes acne?
A
- Increased sebaceous gland activity at puberty
- Hair follicle may get plugged
- Skin bacteria breaks sebum into free fatty acids–> cause irritation and inflammation –> attracts neutrophils –> more inflammation
14
Q
Eccrine Sweat Glands
A
- Simple coiled tubular glands
- Located in the dermis
- Functions: thermoregulation and excretory
- Secretion controlled by cholinergic fibers of SNS
15
Q
Histology of eccrine sweat glands
A
Stratified cuboidal epithelium
Secretory portion
- Pale cells: secrete fluid (watery component or sweat), located at periphery, intracellular canaliculli, membrane infoldings
- Dark cells: secrete proteins, located near lumen
- Myoepithelial cells: contract to expel product (actin-myosin bundles)
Conducting portion (sweat duct): reabsorbs NaCl and water
16
Q
Apocine Sweat Glands
A
- Located in the axillary, areolar, and perineal regions
- Simple cuboidal/columnar epithelium
- Simple coiled glands with large lumen
- Merocrine secretion
- Associated with hair shafts
Stimulated by adrenergic nerve fibers
17
Q
Functions and composition of saliva
A
- Moisture and lubrication in oral cavity
- Initiation of the digestion of carbs (alpha-amylase)
- Immune defense: lysozyme, lactoferrin and sIgA
- Secretion of calcium and phosphate to make acquired pellicle
18
Q
Structure and organization of salivary glands
A
- Connective tissue capsule
- Septa divides parenchyma into lobules
- CT stroma contains capillary plexus, nerves, lymphocytes, plasma cells
- Lobules contain salivons: secretory unit with acini, intercalacted ducts, intralobular excretory ducts
Drainage: acini -> intercalated ducts -> intralobular ducts -> interlobular ducts in septa
19
Q
Salivary glands clinical correlation
A
- Reduced fx due to radiotherapy or disease
- Dental caries
- Oral mucosa atrophy
- Speech difficulties - Salivary gland tumors
- 80% benign
- Pleiomorphic adenoma (65% of benign tumors, accumulation of cartilage-like material produced by myoepithelial cells)
20
Q
3 Types of acinar cells in salivary glands
A
- Serous acinar cells: pyramidal, secrete proteins (amylase, lysozyme, sIgA)
- Mucous acinar cells: cuboidal or columnar, secrete mucus
- Myoepithlial cells (basket cells):long contractile process that accelerate secretion, reside within basal lamina, also present in intralobular ducts
21
Q
Intercalated ducts in salivary glands
A
- Small, 4-6 cells in circumference
- Cuboidal cells, lack secretory granules
- Connect secretory portion to intralobular duct
22
Q
Intralobular ducts in salivary glands
A
- More than 6 cells in circumference
- Lined by simple columnar epithelium
- Basal striations: cell membrane infoldings that house mitochondria
- Apical surface: tight junctions
- Active transport of ions: saliva contains 7x K+, 3x bicarb, 1/10 Ha+ compared to blood plasma. Also secrete sIgA
- Mucous glands lack striated ducts
23
Q
Interlobular ducts of salivary glands
A
- Large ducts located in septa
- Lined with stratified cuboidal-to-columnar epithelium
24
Q
Steps of transcytosis (mechanism of sIgA secretion)
A
- Plasma cells secrete IgA dimer
- IgA binds receptor on acinar cell
- Endocytosis at the base of an acinar cell
- Proteolytic processing
- Exocytosis of sIgA at the apical surface (secretory component)
25
Identify and describe the gland
**Submandibular gland**
- Compound tubolacinar gland
- Mostly serous acini - secrete proteins (lysozyme)
- Some mucous and mixed acini (w/ serous demilunes - half moons)
- Shorter intercalated ducts
- Mostly striated intralobular ducts
26
Identify and describe the gland
**Parotid Gland**
- Compound acinar gland
- All serous acini, note adipocytes (diagnostic feature!)
- Secretes alpha amylase and other proteins
- Intercalated ducts are long
- Intralobular ducts are striated
27
Identify and describe the gland
**Sublingual gland**
**-** Compound tubuloacinar gland
- Primarily mucous acini
- Some mixed acini with serous demilunes (half moons)
- Intralobular ducts are not striated
28
What is the content of zygotmatic granules in the exocrine pancreas?
Secretory product: Digestive proenzymes
- Lipases
- Nucleases
- Amylases
29
Serous demilunes
- Half-moons on some salivary glands
- Considered fixation artifacts
- Found on distal end of secretory unit
30
Structure and function of the exocrine pancreas
- Compound acinar gland (similar to parotid)
- Lobules separated by connective tissue septa - contain bloodvessels, lymphatics, nerves, ducts
Secretory product contains:
1. Digestive proenzymes (lipases, nucleases, amylases; activated by enterokinase cleavage in duodenum)
2. Bicarbonate: neutralizes stomach acid, creating optimum pH for pancreatic enzymes
31
Regulation in the exocrine pancreas
Acidic chyme stimulate enteroendocrine cells in deuodenum -\> release cholescystokinin and secretin
Cholescystokini stimulates proenzyme secretion
Secretin stimulates bicarb. secretion
32
Special features of exocrine pancreas
1. Serous acini: polarized serous cells around lumen, zygomatic granules in apical half of cell, secretion stimulated by cholecystokinin
2. Lack of myoepithelial cells
3. Intercalated ducts: protrude into acini as centroacinar cells, produce bicard
4. Intralobular ducts: lack striations, secrete bicarb-rich fluid
5. Interlobular ducts: low columnar epithelium, also secrete bicarb
33
Diagnostic feature of endocrine pancreas
Islets of Langerhans
34
3 Medical Applications of Exocrine Glands
1. Adenocarcinomas (malignant tumors of glandular epithelium): some of the most common tumors in adults
2. Reduced fxn of salivary glands due to disease or radiotherapy
3. Necrotizing pancreatits
35
Sebaceous glands vs. Sweat Glands
Both are **cutaneous glands** (on skin) that are considered **exocrine** because their secretions do not circulate in blood
Sebaceous glands: holocrine glands, near side of hair follicles, produce and secrete sebum (waterproof)
Sweat glands: duct glands, secrete sweat
**Apocrine sweat glands:** viscous sweat, near hair follicles, fxn after puberty
**Eccrine sweat glands:** thin sweat, not associated with hairs, thermoregulation, found on soles and palms
36
Which cells are responsible for producing bicarconate in the pancreas?
Centroacinar cells
- Secrete is response to secretin
- Also secrete mucin
37
How can you differentiate the parotid gland from the pancreas on histological preps?
Parotid gland: all serous, has adipocytes
Pancreas: all serous, has Islets of Langerhans
38
What is the function of basal striations? Where are they found?
- Cell membrane infoldings that contain mitochondria
- Found in intralobular ducts of salivary glands with serous acini
- Absent in pancreas
39
Identification of compound glands
