11.3 - Branching Morphogenesis Flashcards
What are the 4 ways glands can be classified based on
1) location
2) mode of secretion (i.e. how they secrete)
3) Type of secretion (i.e. what they secrete)
4) Shape
Describe glandular classification based on location
- ex submucosal gland –> seen in extra pulmonary bronchus - in the submucosal layer
(can also be classified based on type of secretion - i.e. mucus/serous submucosa glands)
Describe glandular classifications based on mode of secretion –> what are the different modes of secretion possible that could be used for classification of glands
- Merocrine - product in granules
- apocrine - lipid product
- holocrine - cell lyse to secrete contents
- exocrine - produce released into lumen
- endocrine - product released into CT/blood through basal surface
- constitutive - product released as it is produced
- regulated - product released in controlled fashion
Describe merocrine secretion
- product contained in granules
- mostly protein products
- can be serous or muscus products
Describe apocrine secretion
- lipid product
- as product leaves it takes a portion of cell membrane with it
Describe holocrine secretion
- cells lyse to secrete contents
- for glands that rise from multilayered epithelium
- see piqnotic nuclei before product is released (apoptotic)
ex. sebaceous glands = stratified holocrine glands
Describe exocrine secretion
- product released into lumen - through apical surface
- how you most commonly see merocrine, apocrine, holocrine type secretions in this category
Describe endocrine secretion
- product released into CT or blood
- release through basal surface or basolateral surface
Describe constitutive secretion
- product is release as it is produced
Describe regulated secretion
- product released in controlled fashion
- many glands was see are this type
Describe glandular classification based on type of secretion
1) serous = watery secretion (i.e. most proteins are secreted this way
2) Mucus = glycoprotein secretion
- differences between 1 & 2 are often apparent in LM
3) Seromucus = mixed products, usually in adjacent cells –> serous cells in mixed seromucus cells tend to squeeze out and form half mood shape around gland - called serous demilune (during preparation)
Describe glandular classification based on Shape
of cells
1) Unicellular
2) Multicellular
Shape of Pathway from gland to lumen
1) Simple - straight forward connection to lumen
2) Branched - multiple diversions to path
3) Compound - (most of larger glands are this) complicated glands involving ducts (with have distinct epithelium from the glandular epithelium)
Gland Shape
1) Tubular = test-tube-like
2) Acinar = raspberry(grape-bunch)-like appearance - have exceedingly tiny lumens
3) Alveolar = large lumen but circular profile of gland (ex. = apocrine sweat glands)
What are the examples of gland shape given in the video
- Simple Tubular
- Simple coiled tubular (eccrine sweat glands)
- Simple branched tubular (gastric glands)
- Simple Acinar
- Compound tubular (Brunner’s Glands)
- Compound Acinar (Exocrine pancreas)
- Compound tubuloacinar (salivary glands)
Describe the digestive glands of the oral cavity
- All have discrete lobular organization
- all have acinar morphology
- all are paired
- differ in type of secretion
- formed by process of branching morphogenesis
- 3 salivary glands
1) Parotid glands
2) Submandibular glands
3) Sublingular Glands
Describe the parotid glands
- nuclei are basal
- zymogen granules
- located over temporal mandibular joint (TMJ)
- relatively long/large ducts
- paired glands
- pure serous secretion
Describe the submandibular glands
- located around/beneath/lateral to mandible bone
- relatively long/large ducts
- paired glands
- mixed seromucus secretion (90% serous/10% mucus)
- look for serous demilune here
Describe the sublingular glands
- under the tongue
- relatively short ducts
- paired glands
- mixed seromucus secretion (50/50)
- look for serous demilune here
Describe the organization of the salivary glands
A) Excretory Duct
B) interlobular duct
C) intralobular duct
D) striated ducts - have basal striations (see as fine lines) - are larger ducts with tall columnar cells
E) Intercalated ducts - very little cells more toward cuboidal shape - are farther out in branch
F) Secretory acini - predominate in the histological section
Describe the Exocrine pancreas
- Formed by branching morphogenesis
- pure serous secretion
Describe the organization of the Exocrine pancreas
A) Excretory duct (Wirsung, Santorini)
B) Interlobular ducts - 2 majro lobes of pancreas
C) Intralobular ducts
D) intercalated ducts (bicarbonate secretion) - distinct lumen - functionally important in pancreas
E) Centroacinar cells (bicarbonate secretion) - morphologically like a duct (intercalated ducts) - but sits in lumen of acinus
F) Secretory Acini (Zymogen secretion)
Describe the endocrine pancreas
- Pancreatic Islets (of langerhans)
- clumps of endocrine cells
- no duct
- no obvious lumen
- capillaries are important feature of this + all endocrine glands because they take product away
Serous gland
= gland that secretes a water-absed substance
mucous gland
= gland that secretes mucus (i.e. glycoprotein-based substance)
seromucous gland
= gland secretes both types of product (serous + mucous) - usually via different cells
Multicelllular gland
B) = may be simple tubular invaginations of epithelial surface
A) may be branched structures
A) branched glands
= considered compound if they have branched ducts = tubes specialized not to secrete but rather to convert product to the organ’s lumen
- unbrancehd duct might be present in a simple gland (e.x. eccrine sweat glands (simpler coiled tubular et have specialized ductal cells
Glands may classed by the shape of the secretory unit:
1) tubular
2) alveolar
= pit like, (like the bottom of a test tube)
3) tubulo-alveolar (mixture of both)
4) acinar
- like a raspberry or blackberry
- -> tubular and laveolar gland have visible lumen
- acinar glands usually do not
Serous demilunes
= in a mixed acinar gland
- serous cells form this structure around the outsid of the acinus –> artifact due to expansion of adjacent mucus cells
Excretory duct
= in large compound glands
- the largest proximal duct
Other ducts
a) striated ducts - with basal striations
b) intercalated ducts
Centroacinar cell
= ducts of the pancreas end is this specialized cell type
lactiferous ducts
= ducts in the breast
3) specialized regions of lactiferous ducts
1 - intralobular ducts
2 - interlobular ducts
3 - lactiferous sinus near the nipple
Overview of the lung formation via branching morphogenesis
1) airways of respiratory system arise form endodermal bud
- growth to form 17-18 branches in the adult
- among the branches respecification happens only once
- growing cells transition from a conducting (further respiratory epithelium) to a respiratory (future alveolar epithelium) morphology
- respiratory branches form late in embryonic life = 5th month - must happen for life outside the womb
Describe the 5 stages of trachea and lung development as an outgrowth of the esophageal portion of the endodermal gut tube
1) Embryonic
- lung bud arises from esophagus
- 1st several generations of bronchial branching occur
- tertiary bronchi (third branching) define the basic lobar outline of the adult lung:
- 3 lobes on right
- 2 lobes on the left
2) Pseudoglandular
- embryonic weeks 5-17
- bronchial branching up to 21 generations continues
- only one epithelial type i present
- bronchi fill the space afforded by pleural cavity –> which gives the lung a mesodermal lining (the future visceral peritoneum
- look similar to a gland at this stage
3) Canalicular Stage
- embryonic weeks 16-24
- epithelial cells of the distal ends of the bronchi (where contact capillaries) specialize into a flattened shape
- these cells continue to proliferate around the proliferating capillary bed –> forming alveolar sacs
- production of surfactant - begins during this stage
4) Saccular stage
- embryonic weeks 24-34
- alveolar sacs gain a mature lung-air interface
- are capable of high-efficiency gas exchange
5) alveolar stage
- beginning at week 34 of gestation –> end 2-4 years postnatal
- marked by increase in number of functional alveoli
Major glands developed from branching morphogenesis
- most major glands arise from an epithelial bud
- first one or several branches usually form ducts
- final branches from the secretory portions of the glands
- examples of these
1) three major salivary glands
2) pancreas
3) breast
Kidney branching morphogenesis development
- embryonic duct –> mesonephric duct forms retroperitoneally from fetal mesenchymal tissue
- this duct contributes to the structure of the uretrha, bladder, and ureter in the adult
- branches of the duct invade the mesenchymaltissue of the fetal kidney and become the calyces, collecting ducts, and collecting tubulaes of the kidney
- each adult kidney lobe arises foam distinct branch of the fetal mesonephric duct –> those these lobes grout together in the adult kidney
Uniqueness of the kidney from a branching morphogenesis standpoint:
- major epithelial structure in the kidney = the nephron
- -> does not arises from branching morphogenesis
- each nephron is induced to form at the terminus of branching mesonephric tissue
- nephrons are induced to form from fetal CT and elaborate long morphologically complex tubule that eventually connects its lumen wight eh mesonephrics lumen
- the fetal CT that surrounds the mesonephric buds in the kidney - the metanephros = the structure that gives rise to a nephron is a metanephric bud
