Histology: The Digestive System

• The Digestive System covered in Histology Lecture 1.1 includes both digestive organs and accessory organs.
• The lecture covered the histology of:
  • Oral Cavity
  • Gastrointestinal tract
  • Accessory digestive organs

Accessory Digestive Organs

• Salivary glands.
• Liver.
• Gallbladder.
• Pancreas.

Gastrointestinal (GI) Tract

• Begins at the oral cavity.
• Extends down to:
  • Pharynx
  • Esophagus
  • Stomach
  • Small and large intestine
  • Rectum

Oral Cavity

• The lining epithelium is stratified squamous non-cornified epithelium
• Organs such as the hard palate, the gingivae and filiform papillae have stratified squamous cornified epithelium

Oral Cavity Subdivisions

• Oral cavity proper: Large cavity behind the gums and teeth
• Oral vestibule: Cleft-like interval between gums/teeth internally plus lips/cheeks externally

Retromolar Space

• Only communication between oral vestibule and oral cavity proper
• Located between last two molars and the ramus of the mandible

Hard Palate

• Mucosa firmly bound to the periosteum without a submucosa
• The firmness is due to the adherence to the bone and is described as "hard palate"

Upper and Lower Lips (Outer)

• The Skin is lined with stratified squamous cornified epithelium (SSCE)
• Containing tubulo-alveolar, small salivary glands called labial glands that have mixed (mucous and serous) sections

Medical Term

• Labial is the medical term for lips

Lips (Mucosa)

• Stratified squamous non-cornified epithelium (SSNCE)
• Kapag sa skin (sa labas) – cornified epithelium
• Kapag sa mucosa (sa loob) – non-cornified epithelium

Muco-cutaneous Junction

• It can also be called the vermillion border
• The lining epithelium transitions abruptly from stratified squamous non-cornified epithelium

Lips External

• Do not have hair follicles, sweat glands, or sebaceous glands

Cheeks

• Skin lined with stratified squamous cornified epithelium (SSCE)
• The superficial fascia (inner layer of cheeks) is composed of buccal pad of fat
• The buccal pad of fat is described as "yung masarap kurutin na cheeks"

Bucco-pharyngeal Fascia

• Invests the buccinators muscle

Buccinator

• Muscle for chewing

Cheeks

• Submucosa containing tubulo-alveolar small salivary glands called buccal glands (mixed secretion)
• Mucosa lined by stratified squamous non-cornified epithelium SSNCE

Remember

• Skin (sa labas) – cornified epithelium
• Mucosa (sa loob) – non-cornified epithelium

Tongue (Inner)

• The upper surface contains lingual papillae
• The dorsum is divided by V-shaped groove called the sulcus terminalis
• Containing an anterior 2/3 (palatine portion) and posterior 1/3 (pharyngeal portion)

Tongue

• Composed of 4 different types of papillae:
  • Filiform: most numerous
  • Fungiform: constricted base, expanded surface
  • Folliate: leaf-like, rudimentary, common in animals, but not humans
  • Circumvallate: largest papillae that contain taste buds

Tongue (Undersurface)

• Contains salivary glands (called lingual glands)

Blandin and Nuhn Glands

• These are the anterior lingual glands
• Found: Anterior
• Type: Mucoserous - mixed type secretion

Von Ebners

• Posterior lingual glands
• Found: Posterior
• Type: Purely serous in secretion

Tongue

• The picture above shows: • Apex. • Body. • Roof

• The roof of the tongue is almost always nandon na siya sa tonsillopharyngeal area

• The structures encircled (yellow circles) are the commonly involved tonsils if you have tonsilitis

• It can be identified through oral cavity checks for patients

• When they show signs of namamaga ito (yung tonsils na nakaencircle)

Taste buds

• Loss of taste has been associated with COVID-19
• Loss of smell is among the most prominent symptoms of COVID-19

Gums

• Stratified squamous cornified epithelium

Gums

• Adherent to the mucoperichondrium or mucoperiosteum
• Either at the cartilage or at the bone

Take Note

• When the term perichondrium it contains cartilage
• Composed of Dense collagenous/connective tissue

Teeth

• The teeth in each animal are used for grinding
• With two types of teeth: temporary and permanent

Temporary Teeth

• These can also be called: deciduous or milk teeth
• 20 teeth
• Erupt from the 6th month up to the 6th year
• The temporary teeth will last until the 6th year

Permanent Teeth

• 32 teeth
• Erupt from the 6th year up to the 25th year

Teeth - Enamel

• It is the hardest structure of the body secreted by ameloblasts

Teeth - Dentin

• Formed by odontoblasts

Teeth - Cementum

• Covers the dentin of the root
• Secreted by cementocytes

Periodontal Membrane

• Serves to attach the root of the tooth to the alveolar socket
• Provides Dense connective tissue

Teeth - Pulp Cavity

• Contains BV's, N's, fibroblasts, histiocytes, and LV's
• If the tooth requires extraction or oral prophylaxis, it is very sensitive
• In the event the tooth requires extraction an anesthesia is needed because it is sensitive

Root Canal

• The whole stretch of a tooth ay meron talagang root canal
• If a dentist has performed a procedure but is unable reach the area indicated it can be very painful
• Kaya kailangan ng anesthesia na dapat papasok sa pulp cavity
• Pulp cavity contains so many blood vessels and nerves

Teeth Diagram (Upper)

• Central incisor (7-8 yrs.)
• Lateral incisor (8-9 yrs.)
• Canine (11-12 yrs.)
• 1st premolar (10-11 yrs.)
• 2nd premolar (10-12 yrs.)
• 1st molar (6-7 yrs.)
• 2nd molar (12-13 yrs.)
• 3rd molar (17-25 yrs.)

Teeth Diagram (Lower)

• 3rd molar (17-25 yrs.)
• 2nd molar (11-13 yrs.)
• 1st molar (6-7 yrs.)
• 2nd premolar (11-12 yrs.)
• 1st premolar (10-12 yrs.)
• Canine (9-10 yrs.)
• Lateral incisor (7-8 yrs.)
• Central incisor (6-7 yrs.)

Tooth Realignment

• If orthodontics are required to realign the teeth, the 3rd molar will be removed
• The reason is due to make room for the remaining teeth so they mag-adjust yung remaining teeth na i-bbraces

The Alimentary Tract Includes

• Mucosa
• Submucosa
• Tunica Muscularis
• Tunica Serosa

GI Tract

• It is important to remember the layers needed in the digestive tract: Mucosa, Subcumosa, Tunica Muscularis and Tunica Serosa
• Thrown into longitudinal folds giving the lumen an irregular or stellate shape

GI Tract - Mucosa

• Epithelium that varies depending on the region
• stratified squamous non-keratinized in most areas
• At the esophago-gastric junction epithelium is squamo-columnar
• Has Lamina propria: loose collagenous tissue and occasional containing lymphatic tissue
• Has Muscularis mucosae formed of a single layer of longitudinally arranged smooth muscle cells

Submucosa of the GI Tract is Made Up Of

• Dense irregular collagenous tissue that contains blood vessels, lymph vessels, and nerves, as well as Meissner's plexuses located in the layer
• There are submucosal glands and nerve plexuses located here

Glands in the GI Tract

• All GI Tract glands are only found at the lamina propria, except those in the esophagus that found the lamina propria and submucosa

Submucosa

• Most glands are superficial and deep and secrete mucus to lubricate mucosal surface to facilitate passage of food
• In the Duodenum: glands found in the:
  • lamina propria
  • submucosa: called Brunner's glands

Submucosal Nerve Plexuses

• Are for section
• Called Meissner’s Plexus

Tunica Muscularis

• Composed of smooth muscle
• Inner circular layer
• Outer longitudinal layer

Regions of the GI Tract

• Upper 1/3: composed of skeletal muscle only
• Middle 1/3: both smooth and skeletal muscles
• Lower 1/3: smooth muscle

Myenteric Nerve Plexus

• Found in between the inner circular layer and the outer longitudinal layer
• Is motor/peristalic and called Auerbach's plexus
• When this is stimulated, it can affect the movement of food within the GI Tract

Esophagus (Review)

• Stratified squamous non-keratinized/cornified lining of the epithelium
• Lamina propria: contains loose CT (connective tissue) and superficial esophageal glands
• Muscularis mucosa (MM): smooth muscle

The Submucosa

• Has dense irregular collagenous tissue, BV's, N's, and LV's
• Includes Meissner’s plexuses which are responsible for secretion in the GI tract
• Includes Deep esophageal glands/esophageal glands proper
• To summarize The glands at the esophagus in the submucosa are one of unique features

Upper Espohagus - Tunica Muscularis Organization

• UPPER 1/3: skeletal muscle

Middle Espohagus - Tunica Muscularis Organization

• MIDDLE 1/3: smooth and skeletal muscles

Lower Espohagus - Tunica Muscularis Organization

• LOWER 1/3: purely smooth muscle

Esophagus - Specific Tunica Muscularis

• Has Myenteric (Auerbach’s) plexuses which are responsible for peristalsis is found between the inner circular and outer longitudinal layer

The transition of the lining epithelium

• Changes in the areas between the esophagus and the the stomach with Stratified squamous (E)
• In the cardia of the stomach (C) – part of the stomach that is totally adherent to the esophagus
• Have a GP - gastric pits with a Diyan lumalabas ang secretion from these glands
• The area in between these structures: esophagogastric junction

Stomach

• Most dilated portion of the digestive tract
• Concerned with storage and digestion of food
• Composed of 4 layers including Mucosa, submucosa, tunica muscularis, and serosa
• Includes Rugae involusions
• Found on the surface are numerous minute depressions called Gastric pits or foveola gastrica
• Include a LE the lining of epithelium

Stomach Features The Following

• Simple columnar without goblet cells (GC)
• LP or LCT with dense LT, occasional nodules
• Gastric glands in entire thickness
• There are only found in the lamina propria We cannot find glands at the submucosa ICOL - inner circular and outer longitudinal

Pyloric Glands

• They include simple branched tubular glands Terminal end is extensively coiled Gastric pits are long and deep extending to about ½ the thickness of the mucosa Lumen is wider No parietal cells except in the pyloric sphincter Not much HCL and intrinsic factor secretion

Cardiac Glands

• More proxmial to the esophagus
• Simple tubular glands including Some compound tubular glands
• Terminal end is long and coiled
• Gastric pits are short and shallow Most mucous secreting cells include:
• Mucous neck cells are predominant in cardiac glands
• Parietal cells and argentaffin cells are few

The Stomach Includes Two Types Of Cells Gastric Pits

• Gastric Cells
• They include:
  • Mucous Neck Cells or columnnar cells with plae mucous
  • Chief or Principal/Zymogenic Cells Low Columnar/Cuboidal with Basophilic secretions
  • Pepsinogen and Gastric Lipases
  • Parietal or Oxyntic Cells including Spheroidal or PyramidalAcidophilic HCL and Intrinsic factor There are also Endocrine or Argentaffin cells that Include Pyramidal/Flattened with stains for seratonin, histamine and gastrin

Stomach Takeaways

• The parenchyma are parietal cells BUT…
• The most numerous cells are chief cells
• Argentaffin cells are only found with Silver and Chromium staining Cannot be visualized by simple Hematoxylin and Eosin (H&E) stain H&E can only visualize cells like Mucous Neck, Chief and Parietal Cells Endocrine cell secretion:
• Gastrin: promotes gastric secretion
• Serotonin: inhibits gastric secretion

Tunica Muscularis

• Consists of three layers:
• IOMCOL (inner oblique; middle circular; outer longitudinal)
• Also has Auerbach's plexus Also nerve plexus in the tunica muscularis

Stomach Important Points

• If that the mucosa has gastric pits
• That the gastric glands occupy the whole lamina propria The gastric glands is not found at the submucosa They are only found ONLY at the lamina propria

Stomach Functions

• Most important cells Peptic / Chief / Zymogenic Cells Most numerous cell Predominates at the Lower regions of the gastric glands Show abundant RER and secretory granules Secrete PEPSINOGEN
  • Pepsin: initiate the hydrolysis of ingested protein in the stomach
• Pepsinogen becomes pepsin once acted upon by stomach acid Produces GASTRIC LIPASES Digests lipids Lipases are responsible for breakdown of fats

Summary For The Small Intestine

• That it the part of the ailmentary tract between the stomach & the LI that has the main function for absortion
• That it has average length of 22ft and it’s luman is widened in widened in the the duodenam/narrowest next to ileocecal valve
• Divided into three parts: Duoedenum, jejumum and ileum

Lining of the Small Intestine

Simple columnar with goblet cells The amount of goblet cells can range from very to few goblet cells in the start of the duodenum

Lamina Propiria

LCT with loose connective tissue

Muscularis Mucosa

Thin smooth muscle layer Produces local movement and folding of mucosa

Muscularis Externa

• From the duodenum down to the large intestine, ICOL is the orientation of the muscle of the muscularis externa
• If is not in the in the duodenum and stomach you assume it in the IC and OL

Vili In the Small Intestine

Villi is not found within the appendix It is finger-like with projections at the lumen of the stomach Increases absorbsorbtive surface of small intestine

The Cells

• Enterocytes
• Goblet cells
• Paneth
• Enterochalffain cells
• Agerllfain
• Stem cells

Cells (Continued)

• Enterocytes -Tall colunner w/surphace microviilli -Ovoid nucleaus at lower part of cells-Most numerous *MAIn absoptive

• Goblet= Apux, distended w/mucagen drplets, base- secrrtany materials,nucleaus flat , cyrpaplasm

• L, Scattered amoung entercylls

Duodenum

• Includes Brunner glands
• Is connected to the dorsal wall of the abdomen And the main functionis on the lamina propriasee

Small Vs Large Intestine Goblet Count

• Punting papunta large intensine finakamaring -The para cheyna the the lar ge intensities ar e gobbler cells

Differences Duogenum, Jejunum, Illeum

• All in the upper region but the duodenum has the more villi than the ileum

Large Intestine

It is five to six feet long and subdivided into the ccumus, appendix transverse, segmen, and colon rectum

Colon Organization

• Complete ICOL in apple dix rectum and the angle canal

Large Intiestine Properties

• Comparelt Smooth Serfaced anar no il found in the
• Lrage intensides -mucosa flods are referred so plica, seruliaris
• Small plica semirlaris is bull no villi

Anal Canal

• Represents the terniral portiono of the
• Laige internines and a bout 11 i inches long , Runs don,nward am bac kward or right ande to the redum through

The large and small intestines

LP and LI have gall cells

The Gallbladder

• Temporary storage bile but does not produce If the the has fat you intake with signats and contracts the liver and excrete the

Hepatic Lobile

The anatomical unit if the