HUMAN ANATOMY – VOLUME 1

5.When the food enters the oropharynx, the longitudinal muscles raise the pharynx, as if pulling it over the bolus.

6.Consecutive contraction of the constrictor muscles (from top to bottom) pushes the food bolus into the oesophagus.

OESOPHAGUS

The oesophagus (esophágus) is a hollow tubular organ connecting the pharynx and the stomach, which serves to conduct food masses (Fig. 127). The length of an adult esophagus is 25–27 cm. In its upper part it is somewhat flattened in the frontal plane, and in the lower part (beneath the level of the jugular notch) it is shaped like a flat cylinder. The esophagus begins at the level of C5–C7 vertebrae and enters the stomach at the level of T9–T12 vertebrae. Its lower boundary is usually 1–2 vertebrae higher in women than in men.

The c e r v i c a l p a r t of the oesophagus is 5–7 cm long. It is surrounded by loose connective tissue, which passes on the bottom into the adipose tissue of the posterior mediastinum. The front of the cervical part lies against the membranous wall of the trachea, with which it is tightly connected by loose fibrous connective tissue. The left laringeus recurrens nerve goes up along the front surface of the oesophagus, while the right laringeus recurrens nerve passes along its right side behind the trachea. In the back the oesophagus lies against the spine and the long muscles of the neck, which are covered by the vertebral lamina of the cervical fascia. On each side of the cervical part of the oesophagus are nerve and blood vessel bundles (the common carotid artery, internal jugular vein, vagus nerve).

The t h o r a c i c p a r t of the oesophagus is 16–18 cm long. In front of it lies the membranous wall of the trachea, lower down are the arch of aorta and the beginning of the main left bronchus. Between the posterior wall of the trachea, the left main bronchus and the oesophagus lie the muscle and connective tissue fascicles of the inconstant b r o n c h o e s o p h a g e a l m u s - c l e and l i g a m e n t. Below this point the oesophagus passes behind the pericardium in the region corresponding to the left ventricle.

Behind the thoracic part of the oesophagus is the spinal column (down to the level of T3–T4 vertebrae). Below this level the posterior surface of the oesophagus lies against the thoracic duct and, still lower, the azygos and hemiazygos veins.

The interaction between the oesophagus and aorta is complex. In the beginning the aorta lies against the left surface of the oesophagus, and then passes between it and the spine, while in the lower region the

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thoracic part of the oesophagus is situated in front of the aorta.

bra and then forms a slight curve in the

frontal plane to the left. At the level of T2–T3 vertebrae it shifts right toward the median line. The sagittal curve of the oesophagus is situated between C6 and T2 vertebrae (corresponding to the curve of the spine). Beneath the C2 vertebra it forms another curve to the front (due to its adjoining to the aorta). As it passes through the diaphragm the oesophagus leans to the front. The oesophagus has several narrow regions. These nar-

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rowings are found in the region of the pharygoesophageal transition, behind the aorta (at the level of the T4 vertebra) and in the region of the esophageal foramen of the diaphragm. There is sometimes a narrowing behind the left main bronchus.

The wall of the oesophagus is made up of four layers: the m u c o s a, s u b m u c o s a, m u s c l a r l a y e r and the a d v e n t i t i a. The wall is 3.5–5.6 mm thick.

On the inside the oesophagus is lined with non-keratinized stratified squamous epithelium (25–35 layers of epitheliocytes). In the upper third the epithelium is less thick than in the rest of the oesophagus. The basement membrane (0.9–1.1 ìm thick) is fenestrated. The lamina propria mucosa is well developed and forms many papillae, which protrude into the surface epithelium. The upper and, especially, lower parts of the oesophagus have cardiac glands, analogous to the homonymous glands in the stomach (these contain mucous cells and negligible amounts of parietal and endocrine cells). The thickness of the lamina propria notably increases in the zones where cardiac glands are located. The lamina muscularis mucosae gradually thickens from the pharynx to the stomach. The submucosa is well developed and promotes the formation of 4–7 well-expressed longitudinal folds of the mucosa. Along with vessels, nerves, various cells / immune, etc./ the submucosa contains 300–500 multicellular tubuloalveolar mucous glands; these contain solitary endocrine cells.

The muscular layer of the oesophagus in the upper third consists of the skeletal muscle, which gradually gets replaced with smooth myocytes in the middle third. In the lower part the muscularis fully consists of fascicles of the smooth myocytes. Muscle fibers and myocytes are situated in two layers: the internal layer is circular, the external—longitudinal one. In the cervical part of the oesophagus the circular layer is twice as thick as the longitudinal. In the thoracic part both layers are equal, while in the abdominal part the thickness of the longitudinal layer prevails. The muscle layer provides for peristalsis of the oesophagus, as well as the constant tone of its walls. On the outside the oesophagus is lined with adventitia, which is best expressed right above the diaphragm. At the level of the diaphragm the diaphragm is considerably thickened by fibers, which are connected to fascial fibers of the diaphragm. The abdominal part of the esophagus is completely or partially covered with the peritoneum.

STOMACH

The stomach (gáster) is a dilated portion of the digestive tract, located between the oesophagus and duodenum. Food remains in the stomach up to 4–6 hours. During this time it gets mixed and digested with

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gastric juices, which contain pepsin, lipase, hydrochloric acid and mucus. The stomach excretes urea and ammonia /its excretory function/. The stomach also performs absorption of sugar, alcohol, water and salt. In its mucosa formation of the antianemia factor /Castle’s intrinsic factor/ takes place, which is necessary for binding and absorbing vitamin B12. The shape of the stomach, its position and size constantly change depending on the amount of food consumed, position of the body and constitutional type.

In persons with a brachiomorphic constitution the stomach has the shape of a horn (cone) and is situated almost horizontally. In the dolichomorphic type the stomach is shaped like a stocking and is at first shaped almost vertically, then curving sharply to the right. In persons with a mesomorphic constitution it is shaped like a hook. Its long axis is directed from left to right and from back to front and lies almost in the frontal plane. The stomach is situated in the upper part of the abdominal cavity. Three quarters of the stomach lie in the left subcostal area, and one quarter in the epigastric region. The entrance into the stomach is located to the left of the spine at the level of T10-T11 /sometimes T12/ vertebrae. The exit t from the stomach lies to the right of the spine at the level of T12 or L1 vertebra. Sometimes, especially in heavy persons the stomach and its boundaries may be lowered (gastroptosis).

When it is empty, the stomach is 18–20 cm long and 7–8 cm wide. A moderately full stomach is 24–26 cm long and 10–12 cm wide. The volume of the stomach varies from 1.5 to 4 liters.

The stomach has an a n t e r i o r w a l l, which faces forward and somewhat up, and a posterior wall, which faces backwards and down. The place where the esophagus enters the stomach is called the cardiac orifice, next to which is the c a r d i a c p a r t (c a r d i a) of the stomach. To the left the stomach widens, forming the f u n d u s, which, on the bottom, passes into the b o d y of the stomach. Its left convex edge is called the g r e a t e r c u r v a t u r e, while the right concave edge — the l e s s e r c u r v a t u r e. The narrowing right part of the stomach, the p y l o r i c p a r t (p y l o r u s), is subdivided into two parts. It has a wide part — the pyloric cavity, and a narrow part — the p y l o r i c c a n a l, which passes into the duodenum. The border between the pylorus and the duodenum is marked on the outer surface of the organ by a circular sulcus — the p y l o r u s, which corresponds to the orifice of the pyloric canal and the circular muscle of the p y l o r i c s p h i n c t e r.

The lesser curvature has a small a n g u l a r i n c i s u r e at the border between the body on the stomach and the pylorus. On the greater curvature there is a notch between the cardiac part and the fundus.

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The front wall of the stomach (when it is hookshaped) touches the diaphragm with the cardiac part of its fundus and body, and in the area of the lesser curvature it contacts the visceral surface of the left liver lobe (Fig.128). A small triangular region of the stomach body is in direct contact with the front abdominal wall. Behind the stomach is the omental bursa, which is a narrow fissure-like space in the abdominal cavity, which separates the stomach from the organs that are located retroperitoneally. Behind the stomach and peritoneum lies the upper pole of the left kidney with the adrenal gland and the pancreas. The posterior sur-

face of the stomach adjoins the transverse colon with its greater curvature, while the upper part of this curvature contacts the spleen.

The stomach may shift during breathing and depending on the content of the neighboring hollow organs (transverse colon). The least mobile zones are the entrance into and exit from the stomach. The stomach is kept in position by fixating ligaments (folds of the peritoneum). The hepatogastric ligament starts at the porta hepatis and passes to the lesser curvature of the stomach. The gastrocolic ligament passes from the greater curvature and left part of the fundus to the hilus of the spleen. The stomach wall consists of the mucosa, submucosa, muscle layer and serosa (Fig. 129). The mucosa is 0.5–2.5 mm thick. It forms 4–5 longitudinal folds along the lesser curvature between the cardiac and pyloric orifices, which facilitated the movement of food masses (passage of the stomach). In the area of the fundus and body there are transverse, longitudinal and oblique folds, which constantly transform depending on physiological conditions. At the transition between the pyloric canal and duodenum the mucosa forms a circular fold — the pyloric screen.

The surface of the mucosa is made up of g a s t r i c a e r e a s (Fig. 130). These fields are of polygonal shape, vary in size from 1 to 6 mm,

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Fig. 129. Structure of stomach wall (acc. to V.Bargman).

1 — mucous membrane; 2 — gastric areas; 3 — gastric pits; 4 — muscularis mucosae; 5 — submucosa; 6 — muscular coat; 7 — solitary lymphoid nodule.

Fig. 130. Folds of mucous membrane of stomach (longitudinal section, internal surface of posterior paries).

1 — oesophagus; 2 — fundus of stomach; 3 — greater curvature; 4 — pyloric part; 5 — pyloric orifice; 6 — sphincter of pylorus; 7 — gastric folds; 8 — body of stomach; 9 — lesser curvature.

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and give the inside surface of the stomach a granular appearance. Deep furrows separate these fields from each other. On the surface of the gastric fields there are many indentations called g a s t r i c p i t s, into which the excretory ducts of glands open. Mm2 of mucosa has approximately 60 gastric pits. The m u c o s a is covered by simple columnar epithelium. The apical part of the cells is filled with granules. The basal part of epitheliocytes contains an ovoid nucleus and endoplasmic reticulum. The Golgi complex is located above the nucleus. The lamina propria mucosae contains vessels, nerves, lymphoid nodules, various cells (immunocytes, smooth myocytes, etc.), as well as gastric glands.

G a s t r i c g l a n d s are simple tubular unbranched glands. They are subdivided into proper (fundic), pyloric and cardiac glands. The fundi of the glands are situated deep in the lamina propria. The gland fundus (body) passes into the neck (excretory duct) followed by an isthmus. Isthmuses of 4–5 glands open into one gastric pit. The general number of gastric glands is approximately 35 million.

The f u n d a l (main, proper) g l a n d s are 0.65 mm long and 30–50 µm in diameter. The length of these glands is 2–3 times greater than the depth of the gastric pit. Their excretory duct makes up a third of the length. The fundic glands are fixed within the lamina propria mucosae, in the region of the excretory duct, by connective tissue. The fundic glands are subdivided into chief (peptic, enzyme-producing) cells, mucous cells, mucocytes and endocrine cells.

P r i n c i p a l c e l l s (granulocytes) have a cylindrical shape. They contain granules of protein secretion in the apical part of the cytoplasm. The plasma membrane in the apical region has many short microvilli. These cells have well-developed Golgi complex and rough endoplasmic reticulum, and a large number of ribosomes. Beneath the Golgi complex lies the nucleus.

P a r i e t a l c e l l s (granulocytes) are larger than chief cells. They have a round or ellipsoid nucleus and many mitochondria. It is characteristic of them to have branching intracellular secretory canaliculi, which open into the gland lumen. The canaliculi lumen contain an inactive hydrochloric acid and protein complex, which his synthesized by these cells. Once this complex is excreted onto the mucosa, it breaks down into a protein and hydrochloric acid.

M u c o u s c e l l s are smaller in size than chief and parietal granulocytes. They are of elongated shape, the nucleus located in their basal part with the organelles above. A relatively small amount of mucous granules is found in the apical region of the cytoplasm. The Golgi complex and endoplasmic reticulum are weakly developed and there are considerable numbers of mitochondria.

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Endocrine cells of gastric glands have certain morphological and biochemical peculiarities. More than 10 types of these cells are described. Enterochromaffin (EC-) cells produce serotonin. Enterochromaffin-like (EC-) cells secrete histamine. A-cells synthesize glucagons, D-cells — somatostatin, D.I-cells — vasoactive intestinal peptide, P-cells — bombesin, etc. A common characteristic for endocrine cells of different types is the presence of secretory granules in the basal part of the cell and the Golgi complex above the cell. The secretion of these cells is excreted through the basement and basolateral part of the cell membrane into the extracellular space.

P y l o r i c g l a n d s are found in the pyloric region on an area of 4.4– 5.5 cm2 at the lesser curvature and 4 cm2 at the greater curvature. Anatomical boundaries of the pyloric region and zones where these glands are located do not coincide. These glands may be found in the fundus in the shape of wide cords. The pyloric glands consist mostly of mucocytes, between which there are parietal and endocrine cells. These glands do not contain chief cells.

C a r d i a c g l a n d s are found in the cardiac region of the stomach. The extension of the area they occupy may vary in individuals. They contain mainly mucocytes, but contain also parietal and endocrine cells.

The l a m i n a m u s c u l a r i s m u c o s a e is formed by three layers of smooth myocytes: the internal and external layers have a circular orientation, while the middle layer is longitudinal. Solitary thin muscle fascicles may be found in the lamina propria mucosae. Contraction of smooth muscle elements promotes formation of folds on the mucosa and secretion by the glands.

The s u b m u c o s a is well developed. Its loose connective tissue is rich in elastic fibers and contains vessels, nerves, many lymphoid nodules and various cell elements.

The t u n i c a m u s c u l a r i s is formed my smooth muscle tissue and is made up of three layers (Fig. 131). The external layer is oriented longitudinally, the middle layer is circular, and the internal layer has an oblique orientation. Longitudinal muscle fascicles are located mainly close to the curvatures of the stomach, but some may also be found in the pyloric region. A thickening in the circular layer in the cardiac region forms the cardiac sphincter. Its thickness correlates to the shape of the stomach. The sphincter is thicker and narrow in a stalking-shaped stomach and thinner and wider in a horn shaped stomach. The circular layer is best developed in the pyloric region, where it forms the pyloric sphincter (3–5 mm thick). When it contracts, the passage between the stomach and duodenum becomes closed. Beneath the circular muscles there are oblique muscle fascicles. The obliquely oriented myocytes pass over the cardiac region to the left of

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the cardiac orifice and go downwards and to the right through the anterior and posterior walls of the stomach towards the greater curvature. Between the muscle layers there is a nervous plexus. The muscles of the stomach support its tone, create a constant pressure inside the stomach and mix food masses (peristalsis). The result of mixing of food with gastric juices is a thin mixture called chyme, which is passed into the duodenum in small portions.

On the outside the stomach is covered by the peritoneum (intraperitoneal position). The serous tegument is absent only on narrow strips along the lesser and greater curvatures. The serosa is separated from the muscularis by the subserosa.

I n n e r v a t i o n of the stomach: the gastric plexus is formed by the vagus nerve and sympathic nerve fibers from the celiac plexus.

B l o o d s u p p l y: left gastric artery /from the coeliac trunk; right gastric a./from the hepatic artery, right gastro-omental artery /from the gastroduodenal a./, left gastro-omental artery and short gastric arteries /from the splenic a./. The gastric and gastro-omental arteries anastomose, forming an arterial circle around the stomach.

Fig. 131. Muscular coat of stomach. Circular layer and oblique fibers (part of circular layer is removed).

1 — circular layer; 2 — oblique fibers; 3 — longitudinal layer; 4 — body of stomach; 5 — pyloric part; 6 — duodenum; 7 — lesser curvature; 8 — oesophagus.

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Ve n o u s o u t f l o w: left and right gastric vv., left and right gastroomental veins /enter the portal vein/.

Ly m p h o u t f l o w: right and left gastric, right and left gastro-omen- tal, pyloric lymph nodes.

SMALL INTESTINE

The small intestine (intéstinum ténue) is a part of the alimentary tract located between the stomach and the large intestine. Together with the large intestine it forms the longest part of the digestive system. The small intestine is divided into the d u o d e n u m, j e j u n u m and i l e u m. Inside the small intestine chyme (liquefied food mass), which has been partially digested by saliva and gastric juice, undergoes processing by bile, and intestinal and pancreatic juices. Within its lumen the process of digestion becomes completed and products of digestion are absorbed. Indigestible remnants of food move towards the large intestine. The small intestine also has an important endocrine function. Endocrinocytes, which are found in its epithelium and glands, produce bioactive substances (secretin, serotonin, motilin, etc.).

The small intestine begins at the level between the bodies of T12 and L1 vertebrae, and ends in the right iliac fossa. It is situated in the gastric region (middle section of the abdomen), and reaches the inlet into the minor pelvis. Its length in an adult is 5–6 meters. It is longer in men than in women. In a live person the small intestine is longer than in a cadaver, due to muscle tone. The duodenum is 25–30 cm long; the jejunum takes up 2.0–2.5 m (2/5 of the whole small intestine); and the ileum is approximately 2.5–3.5 m long. The diameter of the small intestine is 3–5 cm. It tends to decrease in the direction of the large intestine. Unlike the ileum and jejunum, which form the mesenteric part of the small intestine, the duodenum does not have a mesentery.

Duodenum

The duodenum is the beginning part of the small intestine. It is situated on the posterior wall of the abdominal cavity. The duodenum is a continuation of the pylorus. It ends in the duodenojejunal curvature, which lies near the left edge of the L2 vertebra. Usually, the duodenum has the shape of a horseshoe, which rounds the head of the pancreas. The duodenum consists of the superior, descending, horizontal and ascending parts.

The s u p e r i o r p a r t extends from the pylorus to the right and backwards, forming the s u p e r i o r d u o d e n a l f l e x u r e. If the stomach is full, the upper part of the duodenum lies almost in a sagittal position. When

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