11.3 - Branching Morphogenesis

Question 1

What are the 4 ways glands can be classified based on

Answer 1

1) location
2) mode of secretion (i.e. how they secrete)
3) Type of secretion (i.e. what they secrete)
4) Shape

Question 2

Describe glandular classification based on location

Answer 2

• 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)

Question 3

Describe glandular classifications based on mode of secretion –> what are the different modes of secretion possible that could be used for classification of glands

Answer 3

• 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

Question 4

Describe merocrine secretion

Answer 4

• product contained in granules
• mostly protein products
• can be serous or muscus products

Question 5

Describe apocrine secretion

Answer 5

• lipid product

- as product leaves it takes a portion of cell membrane with it

Question 6

Describe holocrine secretion

Answer 6

• 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

Question 7

Describe exocrine secretion

Answer 7

• product released into lumen - through apical surface

- how you most commonly see merocrine, apocrine, holocrine type secretions in this category

Question 8

Describe endocrine secretion

Answer 8

• product released into CT or blood

- release through basal surface or basolateral surface

Question 9

Describe constitutive secretion

Answer 9

• product is release as it is produced

Question 10

Describe regulated secretion

Answer 10

• product released in controlled fashion

- many glands was see are this type

Question 11

Describe glandular classification based on type of secretion

Answer 11

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)

Question 12

Describe glandular classification based on Shape

Answer 12

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)

Question 13

What are the examples of gland shape given in the video

Answer 13

• 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)

Question 14

Describe the digestive glands of the oral cavity

Answer 14

• 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

Question 15

Describe the parotid glands

Answer 15

• nuclei are basal
• zymogen granules
• located over temporal mandibular joint (TMJ)
• relatively long/large ducts
• paired glands
• pure serous secretion

Question 16

Describe the submandibular glands

Answer 16

• 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

Question 17

Describe the sublingular glands

Answer 17

• under the tongue
• relatively short ducts
• paired glands
• mixed seromucus secretion (50/50)
• look for serous demilune here

Question 18

Describe the organization of the salivary glands

Answer 18

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

Question 19

Describe the Exocrine pancreas

Answer 19

• Formed by branching morphogenesis

- pure serous secretion

Question 20

Describe the organization of the Exocrine pancreas

Answer 20

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)

Question 21

Describe the endocrine pancreas

Answer 21

• 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

Question 22

Serous gland

Answer 22

= gland that secretes a water-absed substance

Question 23

mucous gland

Answer 23

= gland that secretes mucus (i.e. glycoprotein-based substance)

Question 24

seromucous gland

Answer 24

= gland secretes both types of product (serous + mucous) - usually via different cells

Question 25

Multicelllular gland

Answer 25

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

Question 26

Glands may classed by the shape of the secretory unit:

Answer 26

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

Question 27

Serous demilunes

Answer 27

= in a mixed acinar gland | - serous cells form this structure around the outsid of the acinus --> artifact due to expansion of adjacent mucus cells

Question 28

Excretory duct

Answer 28

= in large compound glands | - the largest proximal duct

Question 29

Other ducts

Answer 29

a) striated ducts - with basal striations | b) intercalated ducts

Question 30

Centroacinar cell

Answer 30

= ducts of the pancreas end is this specialized cell type

Question 31

lactiferous ducts

Answer 31

= ducts in the breast

Question 32

3) specialized regions of lactiferous ducts

Answer 32

1 - intralobular ducts 2 - interlobular ducts 3 - lactiferous sinus near the nipple

Question 33

Overview of the lung formation via branching morphogenesis

Answer 33

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

Question 34

Describe the 5 stages of trachea and lung development as an outgrowth of the esophageal portion of the endodermal gut tube

Answer 34

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

Question 35

Major glands developed from branching morphogenesis

Answer 35

- 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

Question 36

Kidney branching morphogenesis development

Answer 36

- 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

Question 37

Uniqueness of the kidney from a branching morphogenesis standpoint:

Answer 37

- 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