Histology of the Oral Cavity

Question 1

What are the layers of the GI tract?

Answer 1

Lumen

Mucosa

Submucosa

Inner Circular Muscle

Outer Circular Muscle

Serosa (Adventitia replaces serosa in some areas)

Question 2

What are the layers of mucosa?

Answer 2

Epithelium lining villi

Lamina propria

Muscularis mucosa

Question 3

What are enteroendocrine cells?

Answer 3

Endocrine-paracrine cells of the gut

• sensitive to luminal contents
• Release hormones
• Can act locally (i.e. secrete Gastrin by G cells acting on parietal cells)
• Can act on more distance organs (i.e. Secretin secreted in duodenum acting on pancreatic duct cells)

Question 4

How does the parasympathetic nervous system affect the GI tract?

Answer 4

• Part of extrinsic innervation, it is usually excitatory on functions of the GI tract
• Carried by the vagus and pelvic nerves
• Preganglionic parasympathetic fibers synapse in myenteric and submucosal plexuses
• Cell bodies in the ganglia then send info to smooth muscle, secretory cells, and endocrine cells

Question 5

What does the vagus nerve innervate in the GI tract?

Answer 5

Esophagus

Stomach

Pancreas

Upper large intestine

Question 6

What does the pelvic nerve innervate in the GI tract?

Answer 6

Lower large intestine

Rectum

Anus

Question 7

How does the sympathetic nervous system affect the GI tract?

Answer 7

• Part of extrinsic innervation, it is usually inhibitory on functions of the GI tract
• Fibers originate in spinal cord between T8 and L2
• Preganglionic sympathetic cholinergic fibers synapse in prevertebral ganglia
• Postganglionic sympathetic adrenergic fibers leave the prevertebral ganglia and symapse in myenteric and submucosal plexuses. (direct innervation of blood vessels and some smooth muscle also occurs)

–> cell bodies of plexuses then innervate smooth muscle, secretory cells, and endocrine cells

Question 8

What is the enteric nervous system?

Answer 8

Intrinsic innervation
of the GI tract

• Coordinates and relays info from parasympathetic and sympathetic nervous systems to GI tract
• Uses local reflexes to relay info within the tract

Myenteric plexus: controls motility

• *Submucosal plexus:** controls secretion and blood flow
• receives info from chemoreceptors and mechanoreceptors

Question 9

What glands are found in the mucosal gland layer of the lip (mucosal surface)?

Answer 9

Labial salivary glands mostly secrete mucous

Question 10

What are the histological layers found on the mucosal layer of the lip?

Answer 10

Top –> Bottom:

Mucosal epithelium: non-keratinized simple squamous epithelium

Lamina propria

Mucosal glands

Orbicularis Oris: muscular layer

Question 11

What are ameloblasts?

Answer 11

Ameloblasts are the layer of a tooth that, during development, produce enamel.

Question 12

What are odontoblasts?

Answer 12

Neural crest-derived cells of tooth adjacent mesenchyme that produce dentin

Question 13

What is cementum?

Answer 13

A bonelike material that coverst he root of the tooth secreted by cementocytes

• Unlike bone, cementum is avascular

Question 14

What are the different types of tongue papillae?

Answer 14

• Filiform
• Fungiform
• Foliate
• Circumvallate

Question 15

What are filiform papilae?

Answer 15

• Smallest and most numerous papillae in humans
• Conical, elongated projections of connective tissue that are covered with highly keratinized stratified squamous epithelium
• NO taste buds
• Mechanical function only

Question 16

What are fungiform papillae?

Answer 16

• Mushroom shaped projections located on dorsal surface of tongue.
• Project above the filiform papillae and ar just visible to unaided eye
• More numerous near tip of tongue
• Taste buds are present on stratified squamous epithelium of papillae

Question 17

What are circumvallate papillae?

Answer 17

• **Large, dome shaped structures ** that reside in mucosa just anterior to sulcus terminalis
• Human tongue has 8-12 of these
• Each papillae is surrounded by moatlike invagination lined with stratified squamous epithelium that contains numerous taste buds
• Ducts of lingual salivary (von Ebner’s) glands empty serous secretion into base of moats (theoretically to flush taste buds)

Question 18

What are foliate papillae?

Answer 18

• Papillae that consist of parallell low ridges separated by deep mucosal clefts
• They are aligned at right angles to the long axis of the tongue
• Many taste buds are in the epithelium of the walls facing neighboring papillae and small serous glands empty into the clefts

Question 19

What is the structure of a taste bud?

Answer 19

• Taste pore: small opening onto the epithelial surface at the apex of the taste bud

3 principal cell types:

• Neuroepithelium
• Supporting cells
• Basal cells

Question 20

What are characteristics of the neuroepithelial cells of taste buds?

Answer 20

• They are the sensory cells and most numerous in the taste bud.
• Elongated cells that extend from the basal lamina of epithelium to the taste pore
• At base, form a synapse with the processes of afferent senory neurons of CN VII, IX, or X (depending on location on tongue)

Question 21

What are characteristics of the supporting cells of taste buds?

Answer 21

• Also elongated cells that extend from basal lamina to the taste pore
• Like neuroepithelial cells, contain microvilli on apical surface and possess tight junctions, but do not symapse with nerve

Question 22

What are characteristics of basal cells of taste buds?

Answer 22

• Small cells located in basal portion of taste bud
• They are stem cells for neuroepithelial (sensory) cells and supporting cells

Question 23

What are the five basic taste bud stimuli?

Answer 23

Sweet

Salty

Bitter

Sour

Umami

Question 24

Which tastes are detected by receptors and which by ion channels?

Answer 24

Receptors:
Bitter
Sweet
Umami

Channels:
Sour
Salty

Question 25

What is the mechanism of taste receptors?

Answer 25

Receptor activation --\> **G protein** stimulates **phospholiase C** --\> release of inositol 1,4,5-triphosphate (**IP₃**) --\> IP₃ **activates taste-specific Na⁺ Channels** --\> influx of Na⁺ into cell --\> **Depolarization of plasma membrane** and activation of **voltage -gated Ca²⁺ channels** --\> Ca2+ releases NTs which generates an AP on the post-synaptic afferent nerve

Question 26

What is the mechanism of sour taste?

Answer 26

- It is generated by H⁺ protons that are formed by hdrolysis of acidic compounds - H⁺ protons block K⁺ channels --\> Influx of H⁺ activates voltage-sensitive Ca²⁺ channels --\> Ca²⁺ triggers migration of synaptic vesicles, their fusion, and transmitter release, which results in generating AP in sensory nerve fiber

Question 27

What is the mechanism of Salty taste?

Answer 27

- Na⁺ enters the neuroepithelial cells through specific **amiloride-sensitive Na⁺ channels** - Na⁺ entering the cell depolarizes the membrane and activates **voltage-sensitive Na⁺ channels** and **voltange-sensitive Ca²⁺ channels** - As in Sour tatse, **Ca²⁺ triggers migration and release of synaptic vesicles**, resulting in AP activation of gustatory afferent nerve cell

Question 28

What does saliva contain?

Answer 28

Water Ions (K, Na, Bicarb, Cl) Enzymes and other glycoproteins Antibacterial agents Immunoglobulins Cells (including lymphocytes, 'shed' epithelia) ...more...