General and Sports Anatomy - L.V. Kapilevich, K.V. Davletyarova 2008

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Digestive System

It includes Organs responsible for the mechanical and chemical Processing of food, as well as nutrient absorption (Figure 25).

I. Oral Cavity:

1. Vestibule — located between the Lips, Cheeks, Teeth, and Gums.

It encompasses the oral fissure, which is bounded by the lips.

Teeth.

Deciduous teeth (20: 2 incisors, 1 canine, 2 molars on each side of the upper and lower jaws) and permanent teeth (32). 2 incisors, 1 canine, 2 premolars, 3 molars.

Teething transition occurs between 6 and 12–14 years of age; wisdom teeth appear after 18.

A tooth consists of a crown (the visible part of the tooth), a neck (the region encircled by the gum), and a ROOT (embedded in the dental alveolus). It is covered by layers: enamel, dentin, and pulp.

Surfaces: masticatory, lingual, vestibular, and contact.

2. Oral cavity proper.

Tongue: tip (apex), body, and root. The upper surface is the dorsum. The mucosa features papillae containing taste buds. The tongue consists of Striated Muscle tissue.

In the posterior region, the lingual Tonsils (glands) are located on the mucous membrane.

The soft palate is formed by muscular tissue.

Salivary Glands. Minor: palatine, labial, buccal, and lingual. Major: parotid, sublingual, and submandibular. Additionally, based on The Nature of their secretion, they can be serous (proteinaceous), mucous, or mixed.

II. Pharynx — the upper part of the digestive tract, consisting of three parts: nasopharynx, oropharynx, and laryngopharynx. Its wall has a fibrous membrane attached to the Base of the Skull. It features seven openings: two auditory tubes, two choanae leading to the Nasal cavity, the fauces (opening into the oral cavity), the laryngeal inlet (leading to the Trachea), and the opening into the Esophagus.

Longitudinal and circular Muscles propel food downward; during swallowing, the soft palate elevates to close off the entrance to the Larynx.

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Figure 25. Organs of the Digestive System.

III. Esophagus.

A hollow muscular tube. It connects the pharynx to The Stomach, with a length of 25–30 cm (extending from the level of the 6th–7th cervical vertebrae to the 11th thoracic vertebra).

Regions: cervical, thoracic (the longest), and abdominal (the shortest). It features three anatomical constrictions: superior, middle, and inferior. The muscular wall consists of striated muscle in the upper part and smooth muscle in the middle and lower parts. The mucosa is highly folded and capable of expansion.

IV. Stomach.

A hollow organ situated in the upper Abdominal cavity. Its regions include the cardia (where the esophagus opens), the body of the stomach, the pyloric part, and the fundus.

Layers: the mucosa is folded and contains glands that secrete gastric juice, with chief Cells producing Enzymes and parietal cells secreting Hydrochloric acid; the muscular layer comprises three layers: circular, longitudinal, and oblique. The serosa is formed by the peritoneal layer, which envelops the stomach and attaches to the omenta.

V. Small Intestine.

A hollow organ, 4.2–8.8 m in length, comprising three distinct parts.

1) Duodenum: 25–30 cm long, horseshoe-shaped, consisting of superior, descending, and horizontal parts. The ducts of The Liver and Pancreas open into it.

2) Jejunum: accounts for 2/5 of the length (at the level of the 2nd lumbar vertebra).

3) Ileum: accounts for 3/5 of the length.

It features numerous folds (which do not flatten upon stretching) and villi (which increase the surface area for absorption) containing nerves and Blood Vessels. The circular folds are formed by the mucosa and submucosa.

Villi: 30–40 per 1 mm², totaling 4–5 million. Crypts: epithelial depressions—up to 100 per 1 mm².

Function: absorption.

VI. Large Intestine.

A hollow organ comprising the cecum, colon, and rectum.

Its wall consists of three taeniae (free, mesenteric, and omental) and sacculations known as haustra. The mucosa lacks villi. The muscular layer comprises a longitudinal layer (forming the three taeniae) and a circular layer.

Rectum:

A hollow organ, the terminal segment of the digestive tract. Ampullary in shape, with a diameter of 7.5 cm and a length of 14–18 cm.

It has two sphincter rings: the internal sphincter (smooth muscle), which is involuntary, and the external sphincter (Skeletal Muscle), which is voluntary.

VII. Liver.

A parenchymatous organ located in the upper right quadrant of the abdominal cavity, weighing up to 1.5 kg.

Surfaces: superior (diaphragmatic), inferior (visceral), and the anterior margin.

The falciform ligament divides it into two parts, with the right lobe being larger than the left.

The inferior surface features three fissures that divide the organ into four lobes: right, left, quadrate, and caudate.

The anterior margin of the liver is sharp. The liver is covered by the Peritoneum and anchored to the Diaphragm by ligaments.

The structural unit of the liver is the hepatic lobule. It is prismatic in shape, approximately 1–2 mm in diameter, and consists of hepatic plates (trabeculae). A central vein runs through the middle of the lobule, while capillaries (sinusoids) are located at the periphery.

Cells: hepatocytes (epithelial cells).

Vessels entering the liver: hepatic artery (from The Heart) and portal vein (from the intestines); vessels exiting: hepatic vein (to the heart) and Bile duct (to the intestines).

Functions:

1. detoxification (hepatocytes absorb harmful substances from the blood);

2. bile production;

3. synthesizes Proteins

VIII. Gallbladder.

A hollow organ, pear-shaped, with a capacity of 0.4–0.6 L, a length of 8–12 cm, and a width of 3–5 cm. It has mucous and muscular membranes. It is covered by the peritoneum on the bottom and attached to the liver on the top. Cystic duct: bile flows from the liver to the gallbladder or from the gallbladder to the bile duct (into the duodenum).

IX. Pancreas.

A parenchymal organ. Weight 70–80 g, elongated shape, loose Structure; comprises a HEAD, body, and tail. Secretes fluid into the duodenum.

Functions:

1. Production of pancreatic juice containing digestive enzymes. The excretory duct leads to the duodenum and may merge with the bile duct.

2. Production of the hormone Insulin by the islets of Langerhans.