The Human Digestive System Part 1
Structure and Function of the Digestive System
Mouth: The mouth is a complex anatomical structure located in the anterior portion of the face. It
serves as the primary organ of the digestive system, allowing the intake of food and liquids. The
gross anatomy of the mouth includes the lips, cheeks, palate, tongue, teeth, and salivary
glands. The lips act as a barrier to the entrance of food and liquids, and the cheeks provide a
muscular structure for the mastication of food. The palate is the roof of the mouth, and it
separates the oral cavity from the nasal cavity. The tongue is a muscular organ located in the
floor of the mouth, and it is responsible for the manipulation of food during mastication and the
formation of speech. The teeth are embedded in the alveolar processes of the maxilla and
mandible, and they are essential for the breakdown of food into smaller particles. Lastly, the
salivary glands produce saliva, which helps to lubricate food and contains enzymes that aid in
digestion.
, Pharynx: The pharynx is a muscular tube located in the neck and is part of the digestive and
respiratory systems. Grossly, it can be divided into three sections: the nasopharynx, the
oropharynx, and the laryngopharynx. The nasopharynx is located at the back of the nasal cavity
and is responsible for filtering, warming, and moistening air that is inhaled. The oropharynx is
located between the soft palate and the epiglottis and is responsible for both the passage of
food and air. The laryngopharynx is located between the epiglottis and the larynx and is
responsible for the passage of food and air. Functionally, the pharynx acts as a passageway for
food, air, and saliva, and it also produces sound during speech.
Oesophagus: The oesophagus is a muscular tube that connects the throat to the stomach. It is
approximately 25 cm in length and has an average diameter of 2 cm. Anatomically, the
oesophagus is composed of four layers of tissue, including the mucosa, submucosa, muscular,
and adventitia. Functionally, the oesophagus serves as a conduit for food and liquids to pass
from the throat to the stomach. It is located in the thoracic cavity, posterior to the trachea and
anterior to the vertebral column. The oesophagus is also surrounded by the thoracic aorta, the
azygos vein, and the thoracic duct. The oesophagus also uses peristalsis which is a series of
wave-like muscle contractions that move food through the digestive tract. It starts in the
oesophagus where strong wave-like motions of the smooth muscle move balls of swallowed
food to the stomach.
The stomach: The stomach is a muscular organ located in the upper left quadrant of the
abdomen. It has a gross anatomy consisting of four main parts: the fundus, the body, the
antrum, and the pylorus. The fundus is the dome-shaped portion of the stomach and is located
near the esophagus. The body is the main portion of the stomach and is located between the
fundus and the antrum. The antrum is the lower portion of the stomach and connects to the
pylorus. The pylorus is the opening of the stomach that connects to the small intestine. The
primary function of the stomach is to store and break down food. It does this through the
production of digestive enzymes and acids, which help to break down the food into smaller
particles that the small intestine can absorb. The chyme in the stomach is a semi-liquid mixture
of partially digested food and gastric juice. It is produced by the mechanical and chemical
breakdown of food in the stomach. The pH of the chyme is highly acidic, typically ranging from
1.5 to 3.5, due to the presence of hydrochloric acid in gastric juice. The chyme moves from the
stomach to the small intestine where it is further digested and absorbed.
Duodenum: The duodenum is a part of the gastrointestinal tract located in the upper abdomen
and is the first section of the small intestine. It is approximately 25 cm in length and is
composed of four sections: superior, descending, horizontal, and ascending. Anatomically, the
duodenum comprises a mucosal lining, muscular layers, and an outer serosal layer. Its primary
function is to receive partially digested food from the stomach and to break down the food into
smaller particles further, allowing for the absorption of nutrients into the bloodstream.
Additionally, the duodenum secretes hormones and enzymes to aid in digestion.
Structure and Function of the Digestive System
Mouth: The mouth is a complex anatomical structure located in the anterior portion of the face. It
serves as the primary organ of the digestive system, allowing the intake of food and liquids. The
gross anatomy of the mouth includes the lips, cheeks, palate, tongue, teeth, and salivary
glands. The lips act as a barrier to the entrance of food and liquids, and the cheeks provide a
muscular structure for the mastication of food. The palate is the roof of the mouth, and it
separates the oral cavity from the nasal cavity. The tongue is a muscular organ located in the
floor of the mouth, and it is responsible for the manipulation of food during mastication and the
formation of speech. The teeth are embedded in the alveolar processes of the maxilla and
mandible, and they are essential for the breakdown of food into smaller particles. Lastly, the
salivary glands produce saliva, which helps to lubricate food and contains enzymes that aid in
digestion.
, Pharynx: The pharynx is a muscular tube located in the neck and is part of the digestive and
respiratory systems. Grossly, it can be divided into three sections: the nasopharynx, the
oropharynx, and the laryngopharynx. The nasopharynx is located at the back of the nasal cavity
and is responsible for filtering, warming, and moistening air that is inhaled. The oropharynx is
located between the soft palate and the epiglottis and is responsible for both the passage of
food and air. The laryngopharynx is located between the epiglottis and the larynx and is
responsible for the passage of food and air. Functionally, the pharynx acts as a passageway for
food, air, and saliva, and it also produces sound during speech.
Oesophagus: The oesophagus is a muscular tube that connects the throat to the stomach. It is
approximately 25 cm in length and has an average diameter of 2 cm. Anatomically, the
oesophagus is composed of four layers of tissue, including the mucosa, submucosa, muscular,
and adventitia. Functionally, the oesophagus serves as a conduit for food and liquids to pass
from the throat to the stomach. It is located in the thoracic cavity, posterior to the trachea and
anterior to the vertebral column. The oesophagus is also surrounded by the thoracic aorta, the
azygos vein, and the thoracic duct. The oesophagus also uses peristalsis which is a series of
wave-like muscle contractions that move food through the digestive tract. It starts in the
oesophagus where strong wave-like motions of the smooth muscle move balls of swallowed
food to the stomach.
The stomach: The stomach is a muscular organ located in the upper left quadrant of the
abdomen. It has a gross anatomy consisting of four main parts: the fundus, the body, the
antrum, and the pylorus. The fundus is the dome-shaped portion of the stomach and is located
near the esophagus. The body is the main portion of the stomach and is located between the
fundus and the antrum. The antrum is the lower portion of the stomach and connects to the
pylorus. The pylorus is the opening of the stomach that connects to the small intestine. The
primary function of the stomach is to store and break down food. It does this through the
production of digestive enzymes and acids, which help to break down the food into smaller
particles that the small intestine can absorb. The chyme in the stomach is a semi-liquid mixture
of partially digested food and gastric juice. It is produced by the mechanical and chemical
breakdown of food in the stomach. The pH of the chyme is highly acidic, typically ranging from
1.5 to 3.5, due to the presence of hydrochloric acid in gastric juice. The chyme moves from the
stomach to the small intestine where it is further digested and absorbed.
Duodenum: The duodenum is a part of the gastrointestinal tract located in the upper abdomen
and is the first section of the small intestine. It is approximately 25 cm in length and is
composed of four sections: superior, descending, horizontal, and ascending. Anatomically, the
duodenum comprises a mucosal lining, muscular layers, and an outer serosal layer. Its primary
function is to receive partially digested food from the stomach and to break down the food into
smaller particles further, allowing for the absorption of nutrients into the bloodstream.
Additionally, the duodenum secretes hormones and enzymes to aid in digestion.
