Oral Cavity and GI Track

Question 1

Parts of the Oral Cavity

Answer 1

• Oral cavity proper
  
  • hard and soft palates superiorly
  • tongue/floor of mouth inferiorly
  • entrance to oropharynx posteriorly
• Vestibule
  
  • space sperating lips and cheeks from alveolar ridges and teeth
• Tongue
• Salivary glands
• Tonsils
• Teeth, periodontal ligament, and gingiva

Question 2

Oral Cavity

Lining

Answer 2

• Lining mucosa is non-keratinized
  
  • Vestibule
  • Floor of the mouth
  • Underside of the tongue
  • Cheeks
• Masticatory mucosa either keratinized or parakeratinzied
  
  • gingiva
  • parts of the hard palate
• Parakeratinized epithelium
  
  • similar to keratinized
  • surface cells have visible pyknotic nuclei

Question 3

Tongue

Answer 3

Anterior portion is free.

• Inferior surface covered by minimally keratinized stratified squamous
• Superior surface has two seperate regions seperated by the sulcus terminalis
  
  • Anterior 2/3
    
    • covered by lingual papillae
      
      • ​Covered by varying stratified squamous epithelium
      • 4 types:
        
        • ​Filiform
        • Fungiform
        • Vallate
        • Foliate
  • Posterior 1/3
    
    • more irregular due to lingual tonsils

Posterior portion is anchored to the floor of the mouth and hyoid bone.

Bulk of the tongue is formed of interlaced bundles of skeletal muscles.

• Some arise outside of the tongue → extrinsic muscles
• Some completely contained within the tongue → intrinsic muscles
• Bundles of adipose tissues seperates muscle bundles
  
  • Allows greater mobility

Question 4

Lingual Papillae

Distribution

Answer 4

Question 5

Filiform Papillae

Answer 5

• Most numerous
• Thin, conical shape curved posteriorly
• Covered with maximally keratinized stratified squamous epithelium
• No taste buds

Question 6

Fungiform Papillae

Answer 6

• Narrow bases and slightly rounded top
• Covered with very thinly keratinized stratified squamous
• Less numerous and slightly taller than filiform papillae
  
  • Scattered among them
• Numerous underlying capillary loops gives redder tint
• Taste buds on dorsal surface

Question 7

Circumvallate Papillae

Answer 7

• Located in V-shaped line just anterior to sulcus terminalis
• Fewer in number (6-12)
• Covered in stratified squamous which may be keratinized
• Largest lingual papillae
• Surrounded by a deep sulcus or valley
• Ducts of serous von Ebner glands open into sulci
• Have ~ 250 taste buds located on the sides of each papilla

Question 8

Foliate Papillae

Answer 8

• Located on posterolateral aspect of tongue
• Covered in minimally keratinized stratified squamous
• Appears as vertical ridges seperated by furrows
• Few taste buds
• Serous glands open into sulci between the papillae

Question 9

Taste Buds

Answer 9

• Most located on fungiform or vallate papillae
• Clusters of 60-80 elogated cells
• Large at bases forming ovoid body
• Narrow superficial ends of cells converge around a taste pore
• Cell types:
  
  • basal cells → stem cells
  • neuroepithelial cells
  • supporting cells

Question 10

Salivary Glands

Answer 10

Major salivary glands:

Parotid, Sublingual, Submandibular

Minor salivary glands:

Lingual, Labial, Buccal, Molar, Palatine

• Compound tubuloacinar glands
• Secretory cells organized into acini → lobules → lobes
  
  • Serous, Mucous, or Mixed
• Intercalated duct → intralobular duct → striated duct → interlobular duct

Question 11

Parotid Glands

Answer 11

• Serous only
• Produces 30% salivary volume

Inset → Serous acinar at higher magnification.

Question 12

Submandibular Glands

Answer 12

• Mixed glands
  
  • Mostly serous acini
  • Some mucous acini with serous demilunes
• Producse 60% of salivary output
• Short intercalated ducts
• Long striated ducts

Left inset → mucous acini with serous demilune

Right inset → striated duct

Question 13

Sublingual Glands

Answer 13

• Mostly mucous
• May have some serous demilunes
• No pure serous acini
• Intercalated & striated ducts short

Inset → serous demilune

Question 14

Tonsils

General

Answer 14

• Aggregates of lymphoid tissues
• Encircles oral cavity and pharynx
• Forms the tonsillar (Waldeyer’s) ring
• Often has significant lymphocytic infiltration

Question 15

Lingual Tonsils

Answer 15

• Embedded in the dorsal surface of posterior 1/3 of tongue
• Numerous
• Luminal surface covered by minimally keratinized stratified squamous epithelium
• Each tonsil has a single shallow crypt
• Parenchyma composed of lymphoid tissue
  
  • Mostly secondary nodules with germinal centers
• Thin capule seperates deep surface of each tonsil from CT of tongue mucosa

Question 16

Palatine Tonsils

Answer 16

• Paired tonsils, one on each side of opening from oral cavity to oropharynx
• Minimally keratinized stratified squamous
• Each tonsil has 10-20 deep, branching crypts
• Parenchyma of mostly secondary nodules
• Seperated from underlying tissue by dense CT capsule

Question 17

Pharyngeal Tonsil

Answer 17

• Unpaired pharyngeal tonsil
• Located in roof of nasal pharynx
• Called adenoids when enlarged or inflammed
• Covered by pseudostratified columnar epithelium with patches of stratified squamous
• Surface with folds or pleats

Question 18

Dental Formula

Answer 18

The number and types of teeth in each quadrant of mouth.

(incisor, canine, premolar, molar)

Adult: 32 teeth with dental formula 2:1:2:3

Deciduous dentition: 20 teeth with dental formula 2:1:2

Question 19

Parts of a Tooth

Answer 19

• Crown
  
  • Projects above gum line
  • Dentin covered by enamel
  • Cusps - raised ridges at the occlusal surface
• Root
  
  • Part below gum line
  • Holds tooth in alveolus
  • Dentin covered by cementum
• Neck (Cervix)
  
  • Where crown and root meet at cemento-enamel junction (CEJ)
• Pulp
  
  • Internal part of tooth
  • CT with blood vessels, lymphatics, and nerves
    
    • Enter at apical foramen
  • Houses odontoblasts
    
    • Important in formation of dentin
• Periodontal Ligament
  
  • Extends from cementum to periosteum of alveolar bone
  • Holds tooth in body socket

Question 20

Enamel

Answer 20

• Dense calcified material
  
  • 95% inorganic material
  • NO collagen
  • Proteins involved in mineralization process
• Covers crown of tooth
• Avascular & acellular after eruption
  
  • Cannot be repaired
• Deposited as elongated rods
  
  • Extends thickness of enamel layer from dentin-enamel junction to external surface
• Formed by Ameloblasts

Question 21

Dentin

Answer 21

• Forms bulk of tooth
• Covered by:
  
  • enamel in the crown
  • cementum in the root
• Avascular
• Maintains nerve suppy inside dentinal tubule
• Similar composition to bone but more mineralized
• Secreted by Odontoblasts

Question 22

Cementum

Answer 22

• Calcified external covering of tooth root
• Derived from dental sac (dental follicle)
• Similar but less mineralized than bone
• Formed by cementoblasts → cementocytes
• Cellular cementum
  
  • cementocytes housed in lacunae
  • communicate through canaliculi
• Acellular cementum
  
  • found closest to junction with enamel or dentin
• Continuous production of cementum throughout life
• Reasorbed by odontoclasts
  
  • during exfoliation process
  • due to trauma

Question 23

Pulp

Answer 23

• Loose, mucoid CT
• Forms innermost tissue of tooth
• Supoortive function including continued formation of dentin
• Sensory and immune functions
• Lined by cell bodies of odentoblasts
• Contains:
  
  • fibroblast-like cells
  • reticular fibers
  • collagenous fibers
  • GAGS
• Highly innervated and vascularized
  
  • Nerve endings can enter dentinal tubules

Question 24

Periodontal Ligament

Answer 24

• Fibrous CT
• Collagen type I fibers arranged to exert tension on bone with chewing
• Anchors tooth in alveolar socket
  
  • Connects cementum to alveolar bones via Sharpey’s fibers
• Derived from dental sac

Question 25

Gingiva

Answer 25

• Dense irregular CT
• Covered by keratinized or parakeratinized stratified squamous epithelium
• Very thick basement membrane
• Surrounds teeth in alveoli
• Covers the alveolar processes

Question 26

Odontogenesis

Overview

Answer 26

Question 27

Odontogenesis

Stage 1: Initiation

Answer 27

1. Oral epithelium thickens through mitosis
   
   • Derived from ectoderm of stomodeum (primitive mouth)
2. Dividing cells invaginate into underlying ectomesenchyme
   
   • neural crest derived
3. Forms horseshoe shaped band of epithelial cells called dental lamina
   
   • Present in upper and lower jaw
   • Seperated from ectomesenchyme by basal lamina

Question 28

Odontogenesis

Stage 2: Bud Stage

Answer 28

• On each jaw:
  
  • 10 seperate areas of mitotic activity form knob like swellings called tooth buds
  • Each surrounded by ectomesenchyme
  • Develops asynchronously according to order of emergence

Question 29

Odontogenesis

Stage 3: Cap Stage

Answer 29

Deep surface of each tooth bud invaginates to form the tooth germ.

Consists of:

• Enamel organ (ectodermal origin)
  
  • Outer enamel epithelium (OEE)
    
    • Simple epithelium on convex surface
    • Provides protective barrier during amelogenesis
  • Inner enamel epithelium (IEE)
    
    • Simple epithelium on concave surface
    • Continueous with OEE at cervical loop
    • Cells differentiate into ameloblasts
  • Stellate Reticulum
    
    • Forms core of enamel organ
    • Lies between OEE and IEE
    • Loosely woven tissue with layers of star-shaped cells
    • Helps support enamel production
• Dental papilla
  
  • Formed by condensed ectomesenchymal cells in the indentation of the enamel organ
  • Responsible for the formation of the pulp and dentin
• Dental sac (dental follicle)
  
  • Formed by ectomesenchymal cells surrounding tooth germ
  • Gives rise to cementum, peridontal ligament, gingiva, and alveolus

Question 30

Odontogenesis

Stage 4: Bell Stage

Answer 30

1. Cells of tooth germ proliferate
   
   • Increased size
   • Development of bell shaped concavity
2. Stratum intermedium layer develops
   
   • Lies between stellate reticulum and IEE of enamel organ
   • Produces growth factors that regulate ameloblast and odontoblast differentiation
3. Cells of IEE differentiate first into ameloblasts
   
   • Apical Tome’s process will guide formation of enamel
4. This induces mesenchymal cells of dental papilla to differentiate into odontoblasts
   
   • Have extended odontoblastic processes that will extend through dentinal tubules as dentin forms

Question 31

Odontogenesis

Stage 5: Appositional Stage

Answer 31

1. Dentin production starts first
   
   • Odontoblasts secrete predentin
     
     • Includes organic components that will mineralize over time via matrix vesicles
2. This stimulates ameloblasts to secrete enamel
3. Dentin and enamel meet at the dentin-enamel junction (DEJ)
4. Dentin develops in layers moving odontoblasts away from DEJ
5. Odontoblastic process develops and elongates into the dentinal tubule
6. As enamel develops forming enamel rods, ameloblasts also move away from DEJ
7. Once full thickness of enamel matrix formed in a particular area, ameloblasts lose their Tome’s process → no longer actively secreting.
8. When tooth erupts, enamel can no longer regenerate because OEE and IEE (including ameloblasts) lost.

Question 32

Odontogenesis

Stage 6: Root Formation

Answer 32

• Root formation begins after completion of crown.
• Growth of tooth root stimulates tooth eruption.
• Cervical loop of Bell (formed of fused OEE and IEE) grows down to form Hertwig’s root sheath.
• Peripheral cells of root dental papilla differentiate into odontoblasts
  
  • Begin producing root dentin
• As Hertwig’s root sheath elongates, more root is produced.
• As dentin is formed, root sheath becomes perforated.
• Ectomesencymal cells from dental sac migrate through openings in root sheath.
• Cells differentiate into cementoblasts and begin forming cementum.

Question 33

Development

of

Permanent Dentition

Answer 33

• On lateral side of each deciduous dental germ, ectodermal cells form successional lamina
  
  • Forms precursors of 20 of the 32 permanent teeth
• Those without deciduous precursors form from posterior extensions of dental lamina

Question 34

Digestive Tube

General Structure

Answer 34

1. Mucosa: composed of 3 layers
   
   • Epithelial layer
     
     • Simple columnar except in esophagus and anus
     • Glands extend from epithelium into lamina propria or submucosa
   • Lamina Propria
     
     • Cellular loose CT
     • Houses lymphoid tissue
   • Muscularis mucosae
     
     • Smooth muscle
     • Thin and two layers in most locations
       
       • Inner circular layer
       • Outer longitudinal layer
2. Submucosa
   
   • Dense fibroelastic CT
   • Houses arteries which send branches into mucosa and muscularis externa
   • Houses Meissner’s submucosal plexus
   • Walls of gut may have folds with core of submucosa
     
     • Rugae in stomach
     • Plicae circularis in intestine
3. Muscularis externa
   
   • Smooth muscle except in upper esophagus
   • Two layers: Inner circular & outter longitudinal
   • Auerbach’s myenteric plexus located between layers
4. Serosa or Adventitia
   
   • Adventitia
     
     • CT surrounding an organ
     • Outermost layer of retroperitoneal parts
   • Serosa
     
     • Mesothelium (serous membrane) plus underlying CT coat
     • Outermost layer of intraperitoneal parts

Question 35

Enteric NS

Answer 35

• Innervates digestive tube, pancreas, and gallbladder
• Can control GI function with or without CNS input
• Includes both sensroy and motor neurons
• Two plexuses:
  
  1. Submucosal plexus (Meissner’s)
     
     • Controls secretory, absorptive, and vascular functions
  2. Myenteric plexus (Auerbach’s)
     
     • Controls peristalsis
• Parasympathetic input increases gut mobility and glandular secretions; relaxes sphincters.
• Sympathetic input decreases gut mobility and glandular secretions; activates sphincters.

Question 36

Esophagus

Structure

Answer 36

• Mucosa
  
  • Minimally keratinized stratified squamous
    
    • Langerhans cells
  • Muscularis mucosae
    
    • absent in upper part
    • becomes thicker going down
    • only one layer of longitudinal cells
  • Cardiac glands
    
    • ​Superior/inferior portions
    • Secrete neutral mucus
• Submucosa
  
  • Lots of elastic fibers
  • Esophageal glands proper
    
    • Compond tubuloalveolar glands
    • Produce acidic mucus
• Muscularis externa
  
  • Superior 1/3 → striated muscle
  • Middle 1/3 → mixed
  • Inferior 1/3 → mixed
• Thoracic portion covered by adventitia
• Short abdominal portion covered by serosa

Question 37

Stomach Regions

Answer 37

• Anatomical:
  
  • Cardia
  • Fundus
  • Body
  • Pyloris
• Histological: described based on types of glands
  
  • Cardiac
  • Fundic → fundus + body
  • Pyloric

Question 38

Stomach

Wall Structure

Answer 38

• Mucosa
  
  • Covered with simple columnar surface mucus cells
    
    • ​secrete mucus which is alkaline, viscous, PAS+
    • apices filled with secretory granules → apical cup
  • Invaginates forming gastric pits
  • 1-7 gastric glands open into base of gastric pit
    
    • Length of pits and type of glands varies by region
  • Lamina propria surrounds glands
• Submucosa
  
  • dense irregular CT
  • many elastic fibers
  • many blood and lymphatic vessels
• Muscularis externa
  
  • Contains additional innermost layer of smooth muscle → oblique layer
  • Circular layer complete
    
    • Forms pyloric sphincter at distal end
• Intraperitoneal → covered by serosa
• Non-distended stomach thrown into temporary folds → rugae
  
  • Includes mucosa and submucosa

Question 39

Fundic Glands

Answer 39

• Oxyntic glands are the most complicated
• Glands are long and straight
• Three regions in each gland:
  
  1. Isthmus
     
     • Opens into gastric pit
     • Lined mainly by surface mucous cells
  2. Neck
  3. Base/body
     
     • Deepest and longest part
• Five cell types:
  
  1. Mucous neck cells
     
     • In neck ⋙ body
     • Similar to surface lining cells without apical cup
     • Secretes soluble mucus
  2. Regenerative (stem) cells
  3. Parietal cells
     
     • Eosinophilic
     • Produce HCl and gastric intrinsic factor
     • Intracellular canaliculi at apical end lined with short microvilli
     • Tubulovesicular system in cytoplasm surround canaliculi in inactive cells
     • During HCl secretion, tubulovesicular system fuses with canaliculi
  4. Chief Cells
     
     • Most common at bases
     • Basophilic
     • Produces:
       
       • Pepsinogen
       • Rennin
       • Gastric lipase
  5. DNES cells
     
     • Scatters within glands
     • Called enteroendocrine cells in the gut
     • At least 15 types in the gut
       
       • A → glucagon
       • D → somatostatin
       • ECL → histamine
       • G → gastrin
     • Produce and secrete hormones into lamina propria

Question 40

Cardiac Glands

Answer 40

• Shallowest pits
• Short, coiled glands
• Most cells are mucous cells
  
  • Resemble those in the esophagus
  • Secrete neutral mucous
• There are some mucous neck cells, pareital cells, and DNES cells
  
  • DNES cells in this region mainly produce gastrin

Question 41

Pyloric Glands

Answer 41

• Gastric pits are the deepest
• Glands are short, branched, and twisted
• Similar cells to the cardiac glands
• Most common are mucous cells
  
  • Neutral mucus
  • Also produces lysozyme

Question 42

Small Intestine

Wall Structure

Answer 42

• Mucosa
  
  • Simple columnar epithelia
    
    • Forms outer surface of villus
  • Lamina Propria
    
    • Forms core of the villi
      • Dense network of capillaries
      • One or two lacteals
    • Surrounds intestinal glands
  • Muscularis mucosae
    
    • Inner circular layer extends into villi
      
      • Contracts rhythmically
• Submucosa
  
  • Dense irregular CT with many elastic fibers
  • Contains Meissner’s submucosal plexus
  • Site of Brunner’s glands in Duodenum
• Muscularis externa
  
  • Responsible for peristalsis
  • Auerbach’s myenteric plexus lies between two muscle layers
  • At the distal ileum, thickened to form the ileocecal sphincter
• Serosa in most places
• The retroperitoneal part of the duodenum with adventitia

Question 43

Small Intestine

Adaptations for Surface Area

Answer 43

1. Plicae circularis
   
   • circumferential folds of mucosa and submucosa
   • found in duodenum, jejunum, and proximal 1/2 of lieum
   • permanent
2. Villi
   
   • projections of the mucosa
   • finger-like to leaf-like
   • simple columnar epithelial
   • core of lamina propria
   • usually not found overlying aggregates of lymphoid tissue
3. Microvilli
   
   • surface projections on enterocytes
   • contain actin and myosin
   • coated with thick glycocalyx

Question 44

Enterocytes

Small Intestinal

Answer 44

• Intestinal absorptive cells
• Closely packed microvilli
• Thick glycocalyx
• Functions:
  
  • Absorb proteins and carbs
  • Absorb fats
  • Secretion of enzymes
    
    • Peptidases & disaccharidas
  • Transcytosis of IgA

Question 45

Goblet Cells

Small Intestine

Answer 45

• Produce mucinogens → mucins after absorbing water
• Density increases as you go along tract
• Acidic mucus

Question 46

DNES

Small Intestine

Answer 46

Question 47

M-Cells

Small Intestine

Answer 47

• Scattered among enterocytes overlying areas of lymphoid aggregation
  
  • Peyer’s patches
  • Appendix
• Broad cells
• Apical surface folded into interconnected ridges or microfolds
• Basal surface with deep invagination between cell and basement membrane
  
  • Filled with lymphocytes and APCs
• Transport Ag via transcytosis from lumen to APC in pockets

Question 48

Crypts of Lieberkühn

Answer 48

• Simple tubular glands
• Located in lamina propria & extends to muscularis mucosae
• Open into spaces between bases of villi
• Secrete isotonic fluid to lubricate digestive contents
• Contains:
  
  • Enterocytes
  • Goblet cells
  • DNES cells
  • Paneth cells
  • Regenerative cells

Question 49

Paneth Cells

Answer 49

• Found in crypts of Lieberkühn
  
  • Remain at the bottom of the crypt throughout 20 day life span
• Contain large strongly eosinophilic apical granules
• Structure of protein secreting cells
• Synthesize antibacterial substances:
  
  • lysozyme
  • 𝛼-defensins
• Some also transport IgA from lamina propria to lumen via transcytosis

Question 50

Brunner’s Glands

Answer 50

• Found in the submucosa of the duodenum
• Branched coiled tubular mucous glands
• Ducts pierce the muscularis mucosae
  
  • Usually open into the crypts of Lieberkuhn
• Produces clear alkaline mucus high in bicarb
• Also secretes human epidermal growth factor

Question 51

Peyer’s Patches

Answer 51

• Found in the ileum ⋙ jejunum
• 30-40 of them
• each has 10-200 lymphatic nodules that often extend into submucosa
• M-cells common in overlying epithelium → dome epithelium

Question 52

Cecum and Colon

Morphology

Answer 52

Cecum → Colon → Rectum → Anal Canal

• Mucosa
  
  • Simple columnar epithelium
    
    • No villi
    • Many intestinal glands → Crypts of Lieberkühn
      
      • No Paneth cells
      • More goblet cells than found in the small intestine
    • Numerous surface absorptive cells
    • DNES rare
  • Lamina propria
    
    • No lymphatics
• Submucosa
  
  • Form temporary folds which involve mucosa and submucosa
• Muscularis externa
  
  • Inner circular layer complete
  • Outer longitudinal layer thin or absent
    
    • Except for three thick evenly spaced longitudinal bands call taeniae coli
    • All layers of the intestinal wall bulge out between bands forming haustra
• Intraperitoneal parts have a serosa
  
  • cecum, transverse colon, sigmoid colon
  • small tags of fat called appendices epiploicae hang from serosa
• Retroperitoneal parts covered by adventitia
  
  • ascending and decending colon

Question 53

Rectum

Morphology

Answer 53

Similar to the rest of the large intestine except for special features below:

• Mucosa thrown into two or three transverse rectal folds
  
  • Located just distal to dilated region called the rectal ampulla
• Muscularis externa has two complete layers
  
  • No taeniae coli

Question 54

Anal Canal

Morphology

Answer 54

Similar to the rest of the large intestine except for special features below:

• Mucosa
• In upper portion:
  
  • Forms anal columns of Morgagni
  • Lower ends of columns joined by folds called anal valves
  • Valves and lower ends of columns form the pectinate line where:
    
    • Endodermally derived superior canal ⇒ ectodermally derived lower canal
    • Simple columnar ⇒ minimally keratinized stratified squamous ⇒ maximally keratinized in lower portion
    • Intermediate region of stratified cuboidal and/or stratified columnar often present
• In lower portion:
  
  • Minimally ⇒ maximally keratinized in lower portion
  • Contains hair follicles
  • Mucous anal glands extend into lamina propria
  • Large apocrine circumanal glands
• Submucosa:
  
  • Upper canal contains the internal rectal venous plexus
• Muscularis externa
  In the lower portion:
  
  • Circular layer ⇒ internal anal sphincter ⇒ involuntary
  • Longitudinal layer replaced by fibroelastic sheet
• _Skeletal muscles of pelvic floo_r ⇒ external anal sphincter ⇒ voluntary

Question 55

Anus

Answer 55

• Perianal skin contains
  
  • Eccrine sweat glands
  • Apocrine sweat glands
  • Hair follicles with sebaceous glands

Question 56

Vermiform

Appendix

Answer 56

• Extends from the cecum
• Often contains debris
• Epithelial surface contains:
  
  • goblet cells
  • intestinal absorptive cells
  • DNES cells
  • M cells replace goblet cells near lymph nodules
• Intestinal glands
  
  • short and distorted
  • Infrequent Paneth cells
• Lamina propria almost completely filled with lymph nodules distributed around entire periphery
• Has a serosa