Study Notes on Oral and Pharyngeal Anatomy and Function, Esophagus and Stomach Anatomy and Regulation.

Overview of Oral and Pharyngeal Anatomy and Function

• Regular Dental Exams and Cleanings

  • Frequency is typically over six months.

  • Fluoride Treatments

  • Purpose: Strengthen enamel.

  • Sealants

  • Function: Prevent acids from remaining in crevices and damaging teeth.

  • Common dental practice.

Mouth Anatomy and Functions

• Cheeks

  • Function: Hold food in and aid in chewing.

  • Located on the lateral walls of the mouth.

• Lips

  • Function: Surround the mouth opening, contain sensory receptors for food characteristics.

• Tongue

  • Location: Floor of the mouth.

  • Functions:

  • Mixes food with saliva.

  • Moves food towards the pharynx.

  • Contains taste receptors, essential for tasting food.

• Palate

  • Forms the roof of the mouth.

  • Functions:

  • Holds food in the mouth.

  • Directs food toward the pharynx.

  • Divided into:

    • Hard Palate (anterior part)

    • Soft Palate (posterior part, ends at the uvula).

• Teeth

  • Located in sockets of the mandible and maxillae.

  • Functions:

  • Break down food particles (mechanical digestion).

  • Mix food with saliva during chewing.

• Saliva

  • Secreted by salivary glands.

  • Functions:

  • Moistens food particles and binds them together.

  • Dissolves food for tasting.

  • Begins chemical digestion of carbohydrates (starch) via enzymes.

  • Components:

  • Bicarbonate Ions: Maintain favorable pH for enzyme activity and protect teeth from acids.

  • Salivary Glands (major pairs):

    • Parotid Glands

    • Largest salivary glands.

    • Secrete serous saliva containing amylase (enzyme for starch breakdown).

    • Submandibular Glands

    • Located in the mandible.

    • Secrete serous saliva and mucus.

    • Sublingual Glands

    • Located under the tongue.

    • Secrete mainly mucus.

• Types of Secretory Cells in Salivary Glands

  • Serous Cells: Produce watery fluid with digestive enzymes (salivary amylase).

  • Mucus Cells: Secrete mucus for lubricating swallowed food.

Pharynx Anatomy and Function

• Pharynx

  • A cavity located posterior to the mouth.

  • Extends from the nasal cavity to the esophagus.

  • Divided into three parts:

  • Nasopharynx: Behind nasal cavity; no food passage.

  • Oropharynx: Behind oral cavity; air and food passage.

  • Laryngopharynx: Behind larynx; passageway to esophagus.

• Bolus

  • Definition: A mass of chewed food that is pushed towards the pharynx for swallowing.

• Swallowing Process

  • Begins voluntarily with food mixed with saliva forming a bolus.

  • Involuntary control begins after the bolus reaches the oropharynx.

  • Key Structures:

  • Epiglottis: Closes off the larynx to prevent food from entering the respiratory tract.

  • Peristalsis: Involuntary muscle contractions moving the bolus through the esophagus towards the stomach.

  • Swallowing mechanism stages:

    1. Voluntary Stage: Bolus formation.

    2. Pharyngeal Stage: Reflex triggers swallowing, closes soft palate and uvula to protect the nasal cavity.

    3. Esophageal Stage: Peristalsis transports food to stomach.

Esophagus Anatomy and Function

• Esophagus

  • Muscular tube connecting the pharynx to the stomach, approximately 25 cm long.

  • Penetrates the diaphragm at the esophageal hiatus.

  • Contains mucous glands in the submucosa to lubricate the inner walls.

  • Muscularis layer composition:

  • Superior 1/3: Skeletal muscle.

  • Middle 1/3: Combination of skeletal and smooth muscle.

  • Inferior 1/3: Smooth muscle.

  • Lower Esophageal Sphincter: Regulates food passage into the stomach and prevents regurgitation.

Stomach Anatomy and Function

• Stomach

  • Shape: J-shaped, approximately 25-30 cm long.

  • Location: Inferior to the diaphragm in the upper left portion of the abdominal cavity.

  • Rugae: Folds of mucosa and submucosa allowing stomach distension (stretching).

  • Functions: Receives food from the esophagus, mixes it with gastric juices, and initiates protein digestion.

  • Limited absorption capacity.

  • Divided into regions:

  • Cardia: Near the esophageal opening containing the lower esophageal sphincter.

  • Fundus: Rounded area above the cardia for temporary food storage, can trap swallowed air (belching).

  • Body: Main portion between fundus and pylorus.

  • Pylorus: Funnel-shaped distal portion closest to the small intestine, regulates gastric emptying via the pyloric sphincter.

• Gastric Secretions

  • Produced by tubular gastric glands in gastric pits.

  • Four types of secretory cells:

  • Mucous Neck Cells: Secrete mucus for lubrication, protecting stomach lining from acid.

  • Chief Cells: Secrete pepsinogen, which becomes pepsin in the presence of hydrochloric acid (HCl), breaking down proteins into polypeptides.

  • Parietal Cells: Produce HCl and intrinsic factor for vitamin B12 absorption.

  • Enteroendocrine Cells: Secrete hormones and local messengers regulating digestive activities.

  • Components of Gastric Juice: Mucus, pepsinogen, HCl, intrinsic factor.

Regulation of Gastric Secretion

• Nervous and Hormonal Control

  • Gastric secretion produced continuously but rate varies. Control is neural and hormonal:

  • Sympathetic Impulses: Decrease gastric activity.

  • Parasympathetic Impulses: Increase gastric activity and promote gastric secretion.

• Gastric Secretion Phases

  • Cephalic Phase: Triggered by the sight, taste, and smell of food leading to saliva secretion, preparing for digestion (involuntary).

  • Gastric Phase: Food presence in the stomach stimulates gastrin release, enhancing digestive activity.

  • Intestinal Phase: As food enters the small intestine, intestinal hormones (including CCK) temporarily inhibit gastric activity to allow for nutrient absorption.

• Absorption in the Stomach

  • Limited; primarily absorbs some water, salts, lipid-soluble drugs, and alcohol.