Cavidad bucal

Introduction to the Digestive System

Overview of the Presentation

• Fernando Pérez welcomes viewers to the channel, introducing himself as part of the Histology and Embryology Chair at the National University of Rosario, Argentina.

• He references a significant historical event: the Great Chicago Fire of 1871, which led to architectural innovations by Luis A. Sullivan, a pioneer in modern architecture.

The Digestive System

• The digestive system is described as a neuroendocrine coordinated system extending from the mouth to the anus, essential for nutrient acquisition through digestion.

• It includes accessory organs such as salivary glands, liver, and pancreas; its primary functions involve food degradation and absorption.

The Oral Cavity: Structure and Function

Anatomy of the Oral Cavity

• The oral cavity begins with lips that close off its opening; they are covered externally by skin and internally by non-keratinized stratified squamous epithelium.

• Histological sections reveal connective tissue papillae supporting this epithelium along with powerful salivary glands located deeper within.

Components of the Oral Cavity

• Key structures include lips, dental arches, hard palate, soft palate, tongue, salivary glands' ducts, and masticatory muscles.

• The oral cavity's lining consists of non-keratinized stratified squamous epithelium overlying connective tissue rich in salivary glands.

Teeth and Their Role in Digestion

Dental Structure

• Teeth are embedded in maxillary bones; they serve as mechanical tools for cutting and grinding food into smaller pieces.

• Each tooth comprises four tissues: enamel (outer layer), dentin (middle layer), cementum (root covering), and pulp (central soft tissue).

Types of Dentition

• Primary dentition consists of 20 teeth: two incisors, one canine, two molars per quadrant.

• Secondary dentition totals 32 teeth: two incisors, one canine, two premolars, three molars per quadrant.

Mucosal Structure and Tongue Functionality

Mucosal Composition

• The buccal mucosa features non-keratinized stratified squamous epithelium supported by loose connective tissue containing salivary glands.

Tongue Anatomy

• The tongue is divided into mobile anterior two-thirds and a fixed posterior third; it aids in food manipulation during mastication.

Anatomy of the Tongue and Its Structures

Overview of Tongue Anatomy

• The central area of the tongue features connective epithelial papillae, with a rich collection of lymphoid tissue in the posterior region forming the tonsils.

Dorsal Surface Structure

• The dorsal surface is divided into two-thirds anterior (mobile) and one-third posterior (root), with specific papillae types found in each section.

Types of Papillae

• Predominantly filiform papillae are interspersed with fungiform papillae on the anterior two-thirds; these structures vary in height due to their arrangement.

• The central part lacks both filiform and fungiform papillae, consisting solely of connective tissue, while skeletal muscle forms a significant portion beneath.

Microscopic Observations

• Optical microscopy reveals varying heights among filiform papillae, which have a triangular or shark fin shape; this contributes to their unique appearance.

• A detailed view shows stratified squamous epithelium on the dorsal side, primarily featuring filiform papillae along with underlying skeletal muscle.

Detailed Examination of Papillae

• Fungiform papillae appear mushroom-shaped with broad bases; they are more prominent at higher magnifications compared to triangular-shaped ones.

• Filiform and fungiform types cover the anterior two-thirds but lack taste buds; gustatory corpuscles are present only in certain types like circumvallate papillae.

Circumvallate Papillae Functionality

• Circumvallate papillae are larger and surrounded by a trench that drains saliva from glands, aiding in washing over taste buds located within them.

• These structures contain intraepithelial taste corpuscles that respond to stimuli, highlighting their role in gustation alongside surrounding glandular activity.

Glandular Structures

• Exocrine gland classification includes tubular types: simple tubules maintain consistent diameter throughout while branched or glomerular types exhibit variations based on cell height and lumen size.

Overview of Salivary Gland Histology

Types of Salivary Glands

• The salivary glands can be classified into three types: mucous, serous, and mixed. Mucous cells typically have flattened nuclei located at the periphery, while serous cells exhibit rounded nuclei that are not flattened.

Cellular Characteristics

• Mucous cells synthesize and secrete carbohydrate-rich products. Without specific histochemical techniques (e.g., Alcian blue), these cells may appear colorless or pale under staining.

• In contrast, serous cells produce enzymes, making them easier to stain due to their basophilic properties at the basal border and acidophilic characteristics at the apical border.

Mixed Glands Structure

• Mixed glands contain both mucous and serous components. The presence of a "serous demilune" indicates a combination of both cell types within the glandular structure.

Major Salivary Glands

• The major salivary glands include the parotid (exclusively serous), submandibular (mixed with predominance of serous), and sublingual (mixed with predominance of mucous).

• Histological sections reveal pink-stained ducts with larger diameters; darker structures represent serous acini while lighter ones indicate mucosal acini.

Histological Observations

• Observations show that mucosal acini have pale cytoplasm due to poor staining affinity, while nuclei are flattened towards the base. Serous acini display more pronounced basophilia in their cytoplasm.

Detailed Examination of Duct Structures

Ductal Epithelium Variations

• Higher magnification reveals duct structures lined by simple cuboidal or columnar epithelium. Mucosal acini present flattened nuclei at the periphery with pale cytoplasm.

• Mixed ducts show a combination of serosa on one side and mucus on another, indicating functional diversity within glandular tissues.

Structural Complexity in Duct Systems

• Larger ducts exhibit pseudo-stratified epithelium with multiple layers, indicating increased complexity as they transition from lobular to interlobular regions.

Parotid Gland Specificity

Parotid Gland Features

• The parotid gland is characterized by pure serosa; its histological features include reddish staining indicative of high enzyme content within its secretory units.

Submandibular and Sublingual Glands

• Both submandibular and sublingual glands contain all three cell types but predominantly feature serosa in their architecture.

Lymphoid Tissue in Pharyngeal Region

Tonsillar Structure

• Tonsils consist of lymphoid tissue associated with pharyngeal epithelium; they feature crypt-like invaginations supported by loose connective tissue rich in lymphatic nodules containing B lymphocytes.

Overview of Lymphatic Tissue and Tonsils

Structure and Function of Lymphatic Tissue

• The dense diffuse lymphatic tissue is characterized by a predominance of T lymphocytes, representing both cellular and humoral immunity. The epithelium, depicted in pink, forms crypts to increase surface contact for better interaction with substances.

• Underlying the epithelium are lymphatic tissues filled with lymphocytes. Activated nodules respond to antigens, leading to the production of antibodies through germinal centers.

• The third type of lymphatic tissue is the dense diffuse variety that fills nodules and follicles. Tonsils play a crucial role in interacting with environmental antigens via respiratory or digestive pathways.

Immune Response Activation

• Tonsils serve as immune organs that stimulate T and B lymphocytes upon contact with pathogens, enhancing their immunocompetence.

• This contact leads to differentiation in both T and B lymphocytes, resulting in a cellular immune response mediated by activated cells producing specific antibodies.

Types of Tonsils

• There are three types of tonsils:

• Pharyngeal tonsil (located at the back of the nasal cavity), which has pseudostratified respiratory epithelium.

• Palatine tonsils (in the oral cavity), featuring stratified squamous epithelium with deep crypts for increased contact area.

• Lingual tonsils (at the base of the tongue), showing deep crypts and significant nodular follicular tissue.

Histological Features

• The pharyngeal tonsil has shallow crypts lined with ciliated pseudostratified columnar epithelium. It contains follicles with large germinal centers amidst dense diffuse lymphatic tissue.

• Palatine tonsils exhibit multiple deep crypts that enhance interaction between incoming substances and underlying lymphatic tissue, showcasing well-developed germinal centers within follicles.

Cellular Changes During Immune Activation

• In histological sections, activated lymphocytes transform into larger blast cells characterized by looser chromatin and increased cytoplasm during immune responses.

• Lingual tonsils display numerous deep crypts filled with nodular follicular tissue containing clear germinal centers among dense diffuse lymphatic tissue.

Digestive Process Initiation

• After mastication, food is mixed with saliva to form a bolus which is pushed towards the esophagus for swallowing; this process begins voluntarily before becoming involuntary as it progresses through the digestive tract.