mouth to stomach

Anatomy & Physiology of Digestive System Organs

The Mouth

  • Mechanical Digestion

    • Accomplished by the teeth and tongue.

    • Functional Roles:

    • Teeth break food into smaller pieces through chewing (also known as mastication).

    • The tongue moves food to mix it with saliva and place it between teeth.

  • Salivary Glands: Produce enzymes that begin the process of chemical digestion.

Anatomy of the Mouth

  • Also referred to as the oral cavity.

  • Lining: Made up of mucous membrane.

  • Structural Components:

    • Lips: Protect the anterior opening of the mouth.

    • Cheeks: Form the lateral walls.

    • Hard and Soft Palate: Form the roof of the mouth.

    • Tongue: Occupies the floor of the mouth.

    • Tonsils: Located at the back of the mouth.

Mechanical Digestion

  • Process:

    • Physical breakdown of food into smaller pieces occurs when chewing.

    • The resulting mixture is referred to as a bolus.

    • Swallowing: Occurs when the bolus is pushed into the pharynx by the tongue.

  • Types of Teeth:

    • Molars

    • Pre-Molars

    • Canines

    • Incisors

Chemical Digestion

  • Saliva's Role:

    • Contains the enzyme salivary amylase, which initiates the digestion of carbohydrates.

    • Process: Polysaccharides (starch and glycogen) are broken down into smaller fragments, such as disaccharides.

Physiology of the Mouth

  • Accessory organs perform essential functions:

    • Initiation of swallowing.

    • Chewing.

    • Chemical digestion of starches.

  • Muscle Involved: The masseter muscle, which is a powerful chewing muscle.

Salivary Glands

  • Types of Salivary Glands: Three pairs produce saliva:

    • Parotid Gland

    • Submandibular Gland

    • Sublingual Gland

  • Composition of Saliva: Contains water, salivary amylase, mucus, antibacterial substances, and other components.

Swallowing (Deglutition)

  • Involves coordinated activities:

    • Tongue

    • Soft palate

    • Pharynx

    • Esophagus

    • Several muscles

  • Mechanism: Starts voluntarily and then moves to involuntary reflex actions as the food bolus is pushed to the back of the mouth.

Pharynx

  • Description: The area located behind the nose and mouth.

  • Sections: Consists of three parts:

    • Nasopharynx

    • Oropharynx

    • Laryngopharynx

  • Function: Serves as a common passageway for food, air, and liquids. The food bolus passes through the pharynx to enter the esophagus.

Esophagus

  • Structure:

    • Extends from the pharynx to the stomach, approximately 25 cm long.

    • Positioned posterior to the trachea and passes through the diaphragm.

  • Function: Conducts food bolus by means of peristalsis (the wave-like muscle contractions).

The Stomach

  • Description: J-shaped muscular organ, expands from the inferior end of the esophagus.

  • Function: Secretes enzymes that digest proteins and facilitates mechanical digestion through muscle contractions.

  • Gross Anatomy:

    • Approximately 25 cm long.

    • Food enters through the cardiac or cardioesophageal sphincter and exits through the pyloric sphincter at the duodenum.

    • Location: Upper left quadrant of the abdominal cavity.

    • Features:

    • Lesser curvature

    • Greater curvature

    • Rugae (folds in the stomach lining)

Muscle Layers of the Stomach

  • Stomach walls contain three layers of muscle:

    • Oblique Layer: Unique to the stomach, aids in churning.

    • Circular Layer

    • Longitudinal Layer

  • Function: These layers allow for effective churning and mixing of food.

Microscopic Anatomy of the Stomach

  • Lining: Composed of mucous membrane that secretes protective mucus.

  • Gastric pits: Small pores that contain cells responsible for secreting gastric juice.

Composition of Gastric Juice

  • Main Components:

    • Enzymes such as pepsinogen, which breaks down proteins (secreted by chief cells).

    • Intrinsic Factor: Allows for absorption of vitamin B12 in the small intestine (secreted by parietal cells).

    • Hydrochloric Acid (HCl): Activates pepsinogen, converting it into pepsin (also secreted by parietal cells).

    • Mucus: Protects the stomach lining from the effects of powerful enzymes.

    • Hormones (e.g., gastrin): Trigger increased secretion of gastric juice upon the presence of food and lower pH.

Physiology of the Stomach

  • Functions:

    • Stores food.

    • Initiates protein digestion.

    • Prepares food into a thick semi-liquid substance known as chyme.

    • Gradually releases chyme into the small intestine.