Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

The Study of Viscera (Splanchnologia)
Anatomy of Internal Organs
Digestive System

Lecture Plan:

1. Splanchnology

2. Structure OF THE human Digestive System.

3. Oral Cavity, Salivary Glands, Tongue, Teeth.

4. Pharynx.

5. Esophagus.

6. Stomach.

7. Small Intestine.

8. Liver, Pancreas.

9. Large Intestine.

Splanchnology (Latin Splanchnologia, from Greek splanchna meaning "viscera") is the branch of anatomy that studies the visceral Organs.

Viscera (Internal Organs) are defined as organs located within the Body Cavities: the oral cavity, neck, thoracic, abdominal, and pelvic cavities. They comprise the digestive, respiratory, urinary, and reproductive systems. Internal organs participate in METABOLISM and perform reproductive Functions. Since these processes are also inherent to plants, these organs are sometimes referred to as organs of vegetative life (vegetative organs). Internal organs are grouped into systems based on functional, topographic-anatomical, and genetic criteria. Within each organ system, despite structural variations, all organs cooperate to perform a single collective function. Furthermore, a single organ may belong to multiple Organ Systems.

Parenchymatous organs are internal organs composed of a continuous mass of tissue known as the parenchyma.

The parenchyma consists of the primary functional Cells specialized for the specific tasks of the organ, supported by a Connective Tissue framework called the stroma.

The stroma serves a structural, supportive role (acting as a soft Skeleton) as well as a trophic function.

It also houses the Blood Vessels, Lymphatic vessels, and nerves.

Examples of parenchymatous organs include the liver, pancreas, Lungs, and Kidneys.

Tubular, or hollow organs are internal organs that take the form of a cavity or a tube of varying diameter, separated from adjacent structures by distinct walls.

As a rule, hollow organs communicate with the external environment of the body.

The walls of all hollow organs consist of four distinct layers (tunics).

The innermost layer is the mucous membrane (mucosa).

External to it lies the submucosa, which forms the structural foundation of the organ wall.

This is followed by the muscular layer (muscularis) of the hollow organ's wall. Finally, the outermost layer is a connective tissue sheath known as the serous membrane (serosa) or adventitia.

Examples of hollow organs include the esophagus, stomach, intestines, Trachea, and Ureters.

The human digestive system (Latin Systema digestorium) is a group of organs responsible for Processing food (via Physical and Chemical breakdown), absorbing the digested nutrients through the mucosa into the BLOOD AND Lymph, and eliminating undigested waste.

The digestive organs include the oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, as well as digestive glands such as the salivary glands, liver, and pancreas. The shape and structure of the digestive organs are adapted for the intake, mechanical and chemical processing of food, absorption of its breakdown products, and elimination of indigestible residues.

- Digestion is the mechanical and chemical processing of food within the gastrointestinal (digestive) tract, a complex process that ensures food breakdown and its assimilation by cells.

- During digestion, food macromolecules are transformed into smaller molecules, specifically through the Cleavage of dietary Biopolymers into monomers.

- This process is carried out by digestive (hydrolytic) Enzymes. Following this processing phase, food is absorbed through the intestinal wall and enters the body's fluid media (blood and lymph).

- Thus, the digestive process consists of processing food and its subsequent assimilation by the Organism.

The Development of the digestive system begins in the Cytology/cytology/16.html">Early stages of Embryogenesis. On the 7th–8th day of fertilized egg development, the primitive gut begins to form from the endoderm in the shape of a tube, which by the 12th day differentiates into two parts: intraembryonic (the future digestive tract) and extraembryonic (the yolk sac). In the early stages of its formation, the primitive gut is isolated by the buccopharyngeal and cloacal membranes; however, by the 3rd week of intrauterine development, the buccopharyngeal membrane ruptures, followed by the cloacal membrane in the 3rd month. Disruption of membrane rupture leads to developmental anomalies. From the 4th week of embryonic development, the sections of the digestive tract are formed:

derivatives of the foregut — the pharynx, esophagus, stomach, and part of the duodenum, along with the primordia of the pancreas and liver;

derivatives of the midgut — the distal part of the duodenum (located further from the oral membrane), jejunum, and ileum;

derivatives of the hindgut — all sections of the large intestine.

- The pancreas develops from outgrowths of the foregut. In addition to the glandular parenchyma, pancreatic islets are formed from epithelial cords. By the 8th week of embryonic development, Glucagon can be detected immunochemically in alpha cells, and by the 12th week, Insulin is detected in beta cells. The activity of both types of pancreatic islet cells increases between the 18th and 20th weeks of gestation.

- After birth, the GROWTH AND DEVELOPMENT of the gastrointestinal tract continue. In children under 4 years of age, the ascending colon is longer than the descending colon.

The oral cavity begins with the oral fissure, bounded by the upper and lower Lips, and is divided into the vestibule and the oral cavity proper. The entire cavity is lined with a mucous membrane. The vestibule is the space bounded by the upper and lower lips and Cheeks (anteriorly), and by the teeth and Gums (posteriorly). The mucous membrane covering the alveolar processes of the upper and lower jaws in the region of the dental alveoli is called the gums. The oral cavity proper is bounded laterally by the cheeks, anteriorly by the teeth and gums, inferiorly by the tongue and the Muscles of the floor of the Mouth, superiorly by the Hard and Soft palates, and posteriorly by the soft palate. The posterior wall features an opening called the fauces, flanked by the Tonsils. The mucous membrane of the oral cavity contains numerous minor salivary glands and three pairs of major ones:

- parotid gland — paired, located near the auricle;

- submandibular gland — paired, located in the submandibular triangle;

- sublingual gland — paired, located in the sublingual fold.

The lips (lat. Labia oris) are musculocutaneous folds surrounding the entrance to the oral cavity — the upper lip (labium superius) and the lower lip (labium inferius).

The structure of each lip comprises three parts: cutaneous, intermediate, and mucosal:

- the cutaneous part, pars cutanea, has the structure of Skin. It is covered with Stratified squamous keratinized epithelium and contains sebaceous and Sweat Glands, as well as Hair;

- the intermediate part, pars intermedia, is a pinkish area that also has a skin covering, but the stratum corneum is retained only in the outer zone, where it becomes thin and transparent. The transition zone from skin to mucosa — the vermilion border — is rich in translucent blood vessels that give the lip margin its red color, and contains a high density of nerve endings, making it extremely sensitive.

the mucosal part, pars mucosa, which occupies the posterior surface of the lips, is covered with stratified squamous non-keratinized epithelium. The ducts of the labial salivary glands open here.

The bulk of the lips is formed primarily by the orbicularis oris Muscle, loose connective tissue, skin, and mucous membrane.

At the transition of the labial mucosa into the gums, two median vertical folds are formed, known as the superior labial frenulum and the inferior labial frenulum.

The inferior labial frenulum (lat. Frenulum labii inferioris) connects the midpoint of the lower lip to the gums, and the superior labial frenulum (lat. Frenulum labii superioris) connects the midpoint of the upper lip to the gums.

The upper lip is separated from the cheeks by the nasolabial sulcus. The lower lip is demarcated from the chin by the horizontally running mentolabial sulcus. At both corners of the mouth, the lips are joined together by labial commissures.

The submucosal tissue of the lips contains A large number of mucous labial glands, which can reach the size of a pea; the excretory ducts of these glands open onto The surface of the mucosal part of both lips.

The cheek (buccal region, Lat. Bucca) is a paired lateral part of the human face extending from the zygomatic arch to the lower margin of the Mandible. It is separated from the nasal and oral regions by the nasolabial sulcus and continues posteriorly into the parotid-masseteric region.

The skin of the cheek is thin, firmly fused with prominent subcutaneous adipose tissue, and contains the facial artery and vein. The cheek (buccal region, Lat. bucca) is a paired lateral part of the human face extending from the zygomatic arch to the lower margin of the mandible. It is separated from the nasal and oral regions by the nasolabial sulcus and continues posteriorly into the parotid-masseteric region.

The skin of the cheek is thin, firmly fused with pronounced subcutaneous tissue containing the facial artery and vein.

The gums (Lat. Gingiva) are the mucous membrane covering the alveolar process of the Maxilla and the alveolar part of the mandible, surrounding the teeth in the cervical region.

The tongue is an unpaired organ divided into the ROOT, body, apex, dorsum, and inferior surface; it consists of muscles covered by a mucous membrane.

The teeth are distributed equally across both jaws and evenly divided between the left and right halves of each jaw, totaling 32 in all: on each half of the jaw, starting from the midline, there are 2 incisors, 1 canine, 2 premolars, and 3 molars. Each tooth consists of a crown, a neck, and a root. The crowns vary in shape, which is related to the function performed by the tooth. The upper part of the tooth crown is covered with dense enamel, while the neck and root are covered with cementum, which connects to the dental alveoli via the periosteum. Dentin is located beneath the enamel and cementum, and inside the tooth lies a pulp cavity filled with pulp, through which blood Vessels and nerves pass, entering via the apical foramen at the root tip.

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The pharynx is a cone-shaped, unpaired organ that serves as part of the digestive tube and respiratory tract, located in the neck cavity from the Base of the Skull to the 6th cervical vertebra. Anteriorly, it is adjacent to the nasal and oral cavities and the Larynx; posteriorly, to the Deep Muscles of the Neck; and laterally, to the Middle ear. The pharynx has 7 openings: two with the Nasal cavity via the choanae, one with the oral cavity via the fauces, one with the larynx via the laryngeal inlet, two with the middle ear via the pharyngeal openings of the auditory tubes, and one with the esophagus (into which the pharynx continues). The pharynx is divided into three parts: nasal, oral, and laryngeal. The inner surface of the pharynx is covered by a mucous membrane, followed by a fibrous layer and pharyngeal muscles, and externally it is covered by a connective tissue layer. The mucous membrane in the nasal part is ciliated. During swallowing, the oral aperture closes, the soft palate elevates to close the choanae and prevent food from entering the nasal cavity, and the root of the tongue moves backward and downward, pressing on the epiglottis, which closes the laryngeal inlet.

The esophagus is a continuation of the pharynx and has a tubular shape. Its length is 25–30 cm (extending from the 6th cervical vertebra to the 11th thoracic vertebra); it is located in the neck, thoracic, and abdominal cavities, with the trachea anterior to it and the aorta posterior to it. It is divided into three parts: cervical, thoracic, and abdominal. It features an inner mucous membrane, a middle muscular layer, and an outer connective tissue layer.

The Stomach is the widest part of the digestive tract, and its shape and size are variable. It is located in the Abdominal cavity, within the epigastric and left hypochondriac regions, extending from the 11th thoracic to the 1st or 2nd lumbar vertebra. Its anterior surface is in contact with the Diaphragm and the visceral surface of the liver, while its posterior surface contacts the transverse colon, Spleen, pancreas, upper pole of the left Kidney, and left Adrenal gland. The stomach is positioned asymmetrically, with the greater part of it located to the left of the anterior median line of the body. The stomach has two curvatures (the greater curvature and the lesser curvature), two walls (anterior and posterior), and two orifices (the cardiac orifice at the entrance and the pyloric orifice at the exit). The stomach is divided into several parts: the cardiac part (near the esophageal opening), the fundus (the dome-shaped part lying to the left of the esophageal opening), the pyloric part (the junction between the stomach and the small intestine), and the body of the stomach (the middle, largest part). The stomach wall consists of three layers. The inner layer is the mucous membrane, which contains folds and gastric glands that produce gastric juice; the middle layer is the muscular coat, consisting of three strata (an inner oblique fiber layer, a middle circular fiber layer, and an outer longitudinal layer); and the outer layer is the connective tissue coat.

Functions of the stomach:

- storage of food mass, its mechanical processing, and propulsion into the intestine;

- chemical processing of food mass via gastric juice (1–2.5 L/day), which contains enzymes (Pepsin, chymosin, lipase) and Hydrochloric acid;

- secretion of Castle's intrinsic factor (it was noted in the mid-20th century that gastric resection leads to anemia), which promotes the absorption of Vitamin B12 from food;

- absorption of certain substances (Water, salts, sugars, etc.);

- excretory function (which increases in renal failure);

- protective (bactericidal) function—due to hydrochloric acid;

- endocrine function—production of various Hormones and BIOLOGICALLY ACTIVE SUBSTANCES (gastrin, motilin, Somatostatin, histamine, serotonin, substance P, etc.).

The small intestine is tubular in shape, though its first part, the duodenum, has a horseshoe shape. The length of the small intestine is 4.5–5 m; it lies in the abdominal cavity at the level of the 12th thoracic and 1st–3rd lumbar vertebrae and is divided into the duodenum, jejunum, and ileum. The wall of the small intestine has three layers, just like the stomach: a mucous membrane (containing intestinal glands that produce intestinal juice), a muscular coat (with two layers of muscle—an inner circular and an outer longitudinal layer), and an outer connective tissue layer. The HEAD of the pancreas is adjacent to the duodenum.

The large intestine is a continuation of the small intestine and has a tubular shape. It is 1.5 m long and occupies the abdominal and pelvic cavities. The large intestine is divided into three parts: the cecum, the colon, and the rectum; the vermiform Appendix extends from the cecum. The colon is subdivided into the ascending colon, transverse colon, descending colon, and sigmoid colon. The cecum lies in the right iliac fossa, the ascending colon in the right lateral abdominal region, the transverse colon in the umbilical region, the descending colon in the left lateral abdominal region, the sigmoid colon in the left iliac fossa, and the rectum in the pelvic cavity at the level of the sacrum. The rectum terminates at the anus. The wall of the large intestine has the same layers as the wall of the small intestine, but the mucous membrane lacks villi, and its cells secrete abundant mucus; the muscular coat consists of two layers—an outer longitudinal fiber layer and an inner circular layer. The Peritoneum is a serous membrane covering the organs and walls of the abdominal cavity. The portion of the peritoneum covering the organs is called the visceral peritoneum, while the portion lining the abdominal walls is called the parietal peritoneum; a slit-like space, the peritoneal cavity, is formed between them and filled with a small amount of serous fluid. As it transitions from the abdominal walls to the organs or from one organ to another, the peritoneum forms mesenteries, omenta, and ligaments.