HUMAN ANATOMY – VOLUME 1

men of the tubular organ. An example of this is the pyloric sphincter, situated at the border between the stomach and duodenum. By closing the lumen in this place it detains food inside the stomach for a certain period of digestion. The exit from the bladder has the internal smooth muscle sphincter, and the end section of the rectum has the internal anal sphincter.

The external layer of tubular organs (adventítia) is formed by loose fibrous connective tissue, which contains blood and lymph vessels and nerves. The adventitia not only covers and protects internal organs, but also attaches them to the walls of body cavities and to neighboring organs. Organs, which are situated in the abdominal cavity are covered on the outside by the serosa. The s e r o s a (peritoneum) lines the abdominal part of the esophagus, the stomach, the mesenteric part of the small intestie and parts of the large intestine. The serosa layer of the lungs is called pleura. The serosa is formed by a thin lamina of dense connective tissue (with elastic and collagen fibers), which is covered on the outside by simple squamous epithelium called mesothelium. Like adventitia, it contains blood and lymph vessels, and nerve fibers. The serosa also contains a large number of sensitive nerve endings.

TOPOGRAPHIC ORIENTATION POINTS OF INTERNAL ORGANS

Inside the body cavities the internal organs have a specific arrangement relative to each other, bones of the skeleton, muscles, nerves and vessels. In describing the location of organs several special anatomical concepts are used. The term «s k e l e t o t o p y» is used to define the position of an organ relative to the bones of the skeleton. The term «h o l o t o - p y» is used to determine the region of the body where the organ is located. The concept of «s y n t o p y» defines the position of organs relative to each other.

For more exact location of organs in the abdominal cavity and for defining their projection onto the surface, the abdomen is divided into several provisory regions. Two horizontal lines divide the anterior abdominal wall into tree stories. The intercostal line is drawn between the cartilages of the tenth ribs. The superior anterior spines of iliac bones are connected by the interspinous line. Above the intercostal line is the upper abdomen, or the e p i g a s t r i c r e g i o n. Between the intercostal and interspinous lines is the middle abdomen, or the m e s o g a s t r i c r e g i o n. The lower abdomen is called the h y p o g a s t r i c r e g i o n (hypogastrium).

Each of the three stories is divided into three sections by two vertical lines, drawn along the lateral edges of the rectus abdominis muscles (between the costal arch and the pubis). Thus, the epigastric region is divided

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into the e p i g a s t r i u m and the r i g h t and l e f t h y p o c h o n d r i a c (subcostal) r e g i o n s. The mesogastric region is divided into the r i g h t and l e f t l u m b a r r e g i o n s and the umbilical region between them. The hypogastric region is divided into the r i g h t and l e f t i l i a c (i n - g u i n a l) r e g i o n s and the p u b i c (hypogastric) r e g i o n.

Questions for revision and examination

1.What two groups are internal organs divided into? Describe the structure of these

organs.

2.What layers do walls of hollow organs consist of?

3.Describe the structure of the mucosa of internal organs.

4.What forms of glands can be found in internal organs? What structures promote discharge of secretion from glands?

5.Describe the structure of the muscularis layer of tubular organs.

6.What regions are defined on the front wall of the abdomen? What lines mark the borders between these regions?

THE DIGESTIVE SYSTEM

The digestive system (systéma digestórium) includes the oral cavity, the pharynx, the esophagus, the stomach and the small and large intestines (Fig. 117). The digestive system also includes the major salivary glands, the liver and the pancreas. Functions of the digestive system are mechanical and chemical break down of food, absorption of products of digestions, and elimination of unabsorbed or undigested substances.

The beginning of digestion takes place in the mouth, or oral cavity. In the mouth food is broken down by teeth, or chewed, and mixed together with saliva. Saliva is secreted by salivary glands, the excretory ducts of which open through the mucosa of the mouth. From the oral cavity food moves into the pharynx, then the oesophagus, and into the stomach. Food masses are retained in the stomach for a certain period, during which they become liquefied by gastric juices, are digested and begin to be absorbed. Partially digested food masses move into the small intestine, where they are mixed with bile from the liver and pancreatic juices. In the small intestine, which consists of the duodenum, jejunum and ileum, digestion by digestive enzymes (chemical break down) is completed, and nutrients (amino acids, simple sugars, emulsified fats) are absorbed into blood and lymph capillaries of the intestinal wall. The unabsorbed and undigested food mass passes into the large intestine, the functions of which are absorption of water, salts and vitamins, and formation of feces. Feces continue to move through the large intestine, towards the anal orifice. The large intestine is divided into the cecum, the ascending, transverse and descending colons, the sigmoid colon, and the rectum.

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Fig. 117. Structure of digestive system.

1 — parotid (salivary) gland; 2 — soft palate; 3 — pharynx; 4 — tongue; 5 — oesophagus; 6 — stomach; 7 — pancreas; 8 — pancreatic duct; 9 — jejunum; 10 — descending colon; 11 — transverse colon; 12 — sigmoid colon; 13 — external anal sphincter; 14 — rectum; 15 — ileum; 16 — vermiform process; 17 — caecum; 18 — ileocaecal valve; 19 — ascending colon; 20 — right colic flexure; 21 — duodenum; 22 — gallbladder; 23 — liver; 24 — bile duct; 25 — pyloric sphincter; 26 — submandibular (salivary) gland; 27 — sublingual (salivary) gland; 28 — lower lip; 29 — oral cavity;

30 — upper lip; 31 — teeth; 32 — hard palate.

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THE ORAL CAVITY

The oral cavity (cávum óris) is situated in the lower region of the face, and is the beginning of the digestive system. On the bottom it is limited by the mylohyoid muscles, which form the lower wall, or diaphragm, of the oral cavity. Its upper wall is formed by the hard and soft palates. At the sides the mouth is limited by the cheeks, and in the front— by the lips. In the back of the mouth is a large opening called the fauces, which communicates it with the pharynx. The oral cavity is divided into two sections. The smaller front section, or the v e s t i b u l e (vestíbulum óris), is situated between the lips and cheeks, and the teeth. Behind the teeth is the o r a l c a v i t y p r o p e r (cávitas óris própria).

The g i n g i v a e, or gums, are formed by the alveolar processes of the maxillae and the alveolar part of the mandible, which are covered by mucosa. The vestibule and the oral cavity proper communicated by a narrow fissure between the upper and lower teeth. The o r a l f i s s u r e (inlet into the vestibule) is located between the upper and lower lips, which are connected at the sides by labial c o m m i s s u r e (commissúra labiórum). The l i p s are formed by the orbicularis oris. The c h e e k s (búccae) are formed by the buccinator muscles. Between these muscles and the skin lies an accumulation, or lump, of adipose tissue (Bishe’s lump), which is usually best developed in infants. During this age the lump thickens the walls of the oral cavity, lowering the influence of atmospheric pressure, and, thus, easing the act of sucking.

Palate

The palate is divided into the hard and soft sections. The hard palate is formed by the palatine processes of the maxillae and the horizontal laminae of the palatine bones. The s o f t p a l a t e is attached to the posterior edge of the hard palate. It is formed by a connective tissue lamina, which is covered by mucosa. The anterior end of the soft palate lies horizontally, while its posterior end hangs down, and is called the p a l a t i n e v e l u m. From the middle of the posterior edge hangs a small rounded process called the uvula. Beginning at each lateral edge of the soft palate are two mucosal folds (arches). The p a l a t o g l o s s a l a r c h extends to lateral edge of the root of the tongue. The p a l a t o p h a r y n g e a l a r c h extends to the lateral wall of the pharynx. Between these arches, within the t o n s i l l a r f o s s a lies the palatine tonsil, which is an organ of the immune system.

Within the structure of the soft palate there are several paired striated muscles (Fig. 118).

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palatoglossus; 5 — musculus uvulae; 6 — tion it raises and shortens the uvula.

(m. p a l a t o g l ó s s u s) originates within the lateral part of the root of the tongue, stretches upward inside the homonymous arch, and inserts into the palatine aponeurosis. This muscle lowers the palatine velum, decreasing the size of the fauces. The p a l a t o p h a r y n g e u s m u s c l e (m. p a l a t o p h a r ý n g e u s) originates from the posterior wall of the pharynx and the posterior edge of the cricoid cartilage. It inserts into the p a l a t i n e a p o n e u r o s i s. During contraction it lowers the p a l a t i n e v e l u m, narrowing the f a u c e s.

The mucosa of the mouth is lined by striated squamous epithelium (its thickness ranging between 180–600 mm). In some places this mucosa lacks the muscular lamina. In the regions of the gums, tongue and hard palate there is no submucosal layer. On the hard palate the mucosa may form 1–6 transverse folds. There are small folds in the region of the tonsils. The mucosa of the mouth contains a large number of glands.

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Teeth

Teeth are vital anatomical formations situated in the dental alveoli of the jaws. They are grouped according to their structural characteristics,

m o l á r e s) (Fig. 119), and m o l a r s (d é n t e s m o l á r e s). Incisors are used mainly for seizing and biting food; canines are used for tearing; molars and premolars are for grinding food. The general structure of different types of teeth is similar. A tooth consists of the crown, the neck and the root (Fig. 120). The c r o w n, which is situated above the gingiva, is the largest part of the tooth. On it there are several surfaces. Its l i n g u a l s u r f a c e faces the tongue; the v e s t i b u l a r s u r f a c e faces the vestibule; and the c o n t a c t s u r f a c e s face the adjacent teeth. The o c c l u s - a l s u r f a c e s of analogous teeth of the maxilla and mandible are turned towards each other. On the inside of the tooth there is a c a v i t y, occupied by the p u l p. The r o o t of the tooth articulates with the dental alveolus by a gomphosis, which is a type of synarthrosis. Each tooth has 1–3 roots. The root ends with an apex, which is perforated by an opening. Between the crown and the root is the n e c k of the tooth, which is surrounded by

the root canal an artery and a nerve enter the pulp cavity, and a vein leaves it. The pulp is formed by loose fibrous connective tissue, which contains fibroblasts and other cells. The bulk of the tooth is formed by the dentine. In the region of the crown it is covered by the enamel, while its neck and root are surrounded by cellular cement. The enamel is an extremely durable substance. It is formed by enamel prisms 3–5 mm thick, which are separated from each other by an interprismatic component. This component has less electron density than the enamel prisms. On the surface the e n a m e l is covered by a thin cuticle. The composition of the enamel is mostly inorganic salts (96–97 percent), which include primarily calcium carbonate and calcium phosphate. The enamel also contains almost 4 percent calcium fluoride. The d e n t i n e contains approximately 28 percent organic substances (primarily collagen) and 72 percent inorganic material. The inorganic material consists mostly of calcium phosphate, magnesium phosphate and calcium fluoride. The structure of the cement resembles bone tissue. It is formed by calcified laminae, between which there are lacunae, containing multiprocessed cementocytes. The c e m e n t also contains collagen fibers, which tightly accrete the root with the periodontal ligament. Around the neck of the tooth the cement is thin and does not contain cells (acellular cement).

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Fig. 119. Teeth of maxilla.

A — permanent teeth; 1 — medial incisor; 2 — lateral incisor; 3 — canine; 4 — first premolar tooth; 5 — second premolar tooth; 6 — first molar tooth; 7 — second molar tooth; 8 — third molar tooth (Wisdom tooth). B — deciduous teeth of a 4 — year child: 1 — incisors; 2 — canine; 3 — molar teeth.

The composition of cement is 29.6 percent organic substances and 70.4 percent inorganic matter (primarily calcium phosphate and bicarbonate).

Teeth can also be classified as milk, or deciduous, and permanent. D e c i d u o u s t e e t h develop in children between the 5–7 months of age. Afterwards these teeth are shed and replaced by permanent teeth. Compared to permanent teeth, milk teeth have wider and shorter roots. The half of each jaw has 2 milk incisors, 1 canine and 2 milk canines (20 milk teeth altogether). There are no deciduous premolars.

Shortly before eruption of a permanent tooth the deciduous tooth falls out. P e r m a n e n t t e e t h begin to appear during the age of 6–7, and continue to erupt until ages 13–15. The first permanent teeth to erupt are the inferior molars; then the medial incisors and first superior molars. After them come the lateral incisors, followed by the first premolars, the canines, the second premolars, and then the second molars. The last to erupt (between ages 12–26) are the so-called wisdom teeth (third molars). The half of each jaw has 2 incisors, 1 canine, 2 premolars and 3 molars (Fig. 187 and 188). Altogether, there are 32 permanent teeth.

Different types of teeth are distinguished by their shape (Fig. 121). Incisors have a wide flattened crown with a sharp edge. The crowns of the

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Tongue

The tongue (língua) is a muscular organ, which participates in the mechanical processing of food, in the act of swallowing, taste perception and formation of speech. It is situated in the oral cavity and is elongated flattened in shape (Fig. 122). In the front it has a narrow a p e x (tip). The apex continues into a thick broad b o d y, behind which lies the r o o t of the tongue. The upper convex surface of the tongue is called the d o r s u m. The lower surface is present only in its front section. The m a r g i n s of the tongue are somewhat rounded. On the upper surface, along the median

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Fig. 121. Permanent teeth, right side; lingual facet.

1 — incisors; 2 — canines; 3 — premolar teeth; 4 — molar teeth.

line, passes the m e d i a n g r o o v e o f t h e t o n g u e. Beneath this groove is a fibrous plate, which divides the tongue into the right and left halves. In the back the median groove ends as the f o r a m e n c a e c u m. To the right and left of this foramen, towards the front, extends the V-shaped t e r m i n a l s u l c u s. This sulcus separates the body of the tongue from its root. In the region of the root lies the l i n g u a l t o n s i l, which is an important immune organ.

On the outside the muscles of the tongue are covered by mucosa. The surface of the dorsum has a velvety texture, because it is covered by papillae. Each papilla is a protrusion of the lamina propria of mucosa, which is covered by striated squamous epithelium. The connective tissue part of the papillae contains a large number of blood capillaries, while the epithelium contains gustatory nerve endings.

F i l i f o r m and c o n i c a l p a p i l l a e (p a p í l l a e f i l i f ó r m e s e t p a p í l l a e c o n i c a e) are the most numerous. They are spread diffusely over the entire dorsum region. They are approximately 0.3 mm in length. F u n g i f o r m p a p i l l a e (p a p í l l a e f u n g i f ó r m e s) are situated primarily on the apex and sides of the tongue. Their bases are narrower than the apexes. They are 0.7–1.8 mm long, and 0.4–1.0 mm in diameter. The epithelium of these papillae contains taste buds (3–4 on each papilla), which perceive taste. Va l l a t e p a p i l l a e (p a p í l l a e v a l l á t a e) are small papillae, embanked by a sort of torus (Fig.139). From 7 to 12 of these are situated along the border between the root and the body of the tongue, in

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front of the terminal sulcus. Vallate papillae are 1–1.5 mm long and 1–3 mm in diameter. They have a narrow base and a broad, flattened upper part. They are surrounded by a circular groove (flute), which separates the papilla from the surrounding torus. The epithelium of the sides of the papilla and the torus contains numerous taste buds. F o l i a t e p a p i l l a e (p a p í l l a e f o l i á t a e) are situated on the side edges of the tongue in the form of elongated plates 2–5 mm long. These papillae also contain taste buds.

of the tongue the mucosa is well developed, which promotes formation of folds. At the tip of the tongue there are two fringe folds. On the transition between the underside of the tongue and the mouth floor the mucosa forms a sagittal fold called t h e l i n g u a l f r e n u l u m. Situated at either side of the frenulum are two sublingual papillae. On each sublingual papilla are the excretory duct openings of the submandibular and the sublingual salivary glands. Behind each papilla is a sublingual fold, beneath which lies the homonymous salivary gland.

The paired striated muscles of the tongue are subdivided into proper muscles, and muscles which originate from the bones of the skeleton (skeletal muscles). The proper muscles originate and are inserted within the limits of the tongue.

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