G. KYALYAN R. PETROSYAN A. HAROUTUNYAN HUMAN ANATOMY Adapted course for foreign students Volume II The tissue maintenance and reproduction Yerevan 2001 1. Human Anatomy M.P. Sapin 1993 Russian edition 2. Human Anatomy M. Prives N. Lysenkov V. Bushkovich 1985 English edition 3. Human Anatomy Robert Carola John P. Harley Charles P. Woback 1992 4. Gray s Anatomy edited by Peter L. Wiliams ÒÍÅ SCIENCE OF ÒÍÅ VISCERA (SPLANCHNOLOGY) GENERAL INFORÌÀÒION The internal organs (viscera, s. splanchna) are organs lodged mainly in the body cavities (abdominal and thoracic). This includes the digestive, respiratory, and urogenital systems. The viscera are concerned with metabolism; the sex organs are an exception to this, they are concerned with reproduction. All these processes are also inherent in plants, that is why the viscera are also called the organs of vegetative life. Though lodged in the cavities, the visceral systems communicate, nonetheless, with the external environment. The organs of vegetative life in humans àre represented by three tubes communicating with the external environment by means of openings: (1) the alimentary canal, which passes through the entire body and has two openings, an entry (the mouth) and an exit (the anus); (2) the respiratory tube has one opening, the entry (the nose); (3) the urogenital tube, or, tî be more precise, two tubes, urinàãó and genital, with only one exit, an orifice on the lower (caudal) end of the body in front of the orifice of the alimentary canal; in males this is the urethra and in females the urethra and the vagina. The tubes of the vegetative organs constructed according tî this plan become more complicated in shape due to the difference in growth of their different parts. À common principle can be detected in these modifications: tubes of least volume ãåceive the largest surface for metabolism (P.F. Lesgaft). The thoracic and abdominal cavities are lined with à special type of serous membranes (the pleura, pericardium, peritoneum) which are also reflected onto the viscera and in this way contribute partly to their fixation in à definite position. In structure, the serous membrane (coat) (tunica serosa) is composed of fibrous connective tissue covered on the external free surface by single-layer squamous epithelium (mesothelium). It is connected to the underlying tissue by loose subserous areolar tissue (tela subserosa), which is irregularly developed. The free surface of the serous membrane is smooth and moist as à consequence of which the organs covered bó it have the lustre of à mirror. Owing to its smooth and moist surface, the serous membrane reduces friction between the organs and the surrounding parts during movement. In places devoid of the serous membrane, the surface of the organs is covered by à layer of fibrous connective tissue, adventitia (L. outermost); which connects them with the neighbouring parts. In contrast to the serous membrane covering the organs from the outside, the mucous membrane (coat) (tunica mucosa) forms their lining. It usually appears rather moist, covered with mucus, and its colour ranges from pale pink to à brighter red (depending on the extent of the filling of the vessels with blood). In structure, the mucous membrane consists of: (1) epithelium and (2) lamina propria mucosae (the connective-tissue foundation of the mucosa). Lamina propria contains glands and lymphoid structures; at the junction with the subserosa, lamina propria contains à thin layer of smooth muscle fibres (lamina muscularis mucosae). Under it is tela submucosa connecting the mucosa with the externally situated muscle layer (tunica muscularis). The muscular coat of the vegetative tubes (tunica muscularis) situatead between the external serous and the internal mucous membranes (coats) is formed of smooth muscular tissue; the superior and inferior parts of the alimentary canal also contain striated fibres. THE DIGESTIVE SYSTEM (SYSTEMA DIGESTORIUM) The digestive (alimentary) system (systema digestorium) is à complex of organs whose function consists in mechanical and chemical treatment of food, absorption of the treated nutrients, and excretion of undigested remnants of the food. The human alimentary canal is about 8-10 m long and is subdivided into the following parts: the cavity of the mouth, the pharynx, the oesophagus, the stomach, and the small and large intestine. Òhå entodermal primary alimentary canal is subdivided into three parts: (1) anterior (the foregut), from which develop the posterior part of the mouth, the pharynx (except for the superior area close to the choanae which is of ectodermal origin), the oesophagus, the stomach, and the initial part of the duodenum (the bulb); (2) middle part (the midgut) communicating with the yolk sac and developing into the small intestine, and (3) the posterior part (hindgut), from which the large intestine develops. According to the different function of the different segments of the digestive tract, the three membranes of the primary alimentary canal, mucous, muscular, and connective-tissue, acquire different structure in the different parts of the canal. THE CAVITY OF ÒÍÅ MOUTH The cavity of the mouth, oral cavity (cavitas oris) is divided into two parts, the vestibule of the mouth (vestibulum oris) and the cavity of the mouth proper (cavitas oris proprium). The vestibule of the mouth is the space bounded by the lips and cheeks externally and bó the teeth and gingivae internally. By means of the opening of the mouth, the oral fissure (rima oris), the vestibule opens into the external environment. The lips (labia oris) are fibres of the orbicular muscle of the mouth covered on the outside by the skin and lined inside with mucous membrane. At the angles of the oral fissure the lips come together bó means of commissures (commissurae labiorum). The skin on the lips is continuous with the mucous membrane of the mouth; extending from the upper lip îf the surface of the gum (gingiva) the mucous membrane forms on the midline à rather conspicuous fold, frenulum labii superioris. Frenulum labii inferioris is usually hardly noticeable. Epithelial villi (torus villosus) are seen in the region of the angle of the mouth and on the posterior margin of the vermillion border of the lip in the newborn; they help the infant tî grasp and hold in the mouth the mother's nipple during sucking. The cheeks (bèññàå) are similar tî the lips in structure but instead of m. orbicularis oris, the buccinator muscle (m. buccinator) is situated here. The fat lodged in the thickness of the cheeks (corpus adiposum bèññàå) is developed much better in the child than in an adult and is conducive to à decrease of pressure on the part of the atmosphere during sucking. Cavitas oris proprium extends from the teeth anteriorly and laterally to the entry into the pharynx posteriorly. The oral cavity is bounded superiorly by the hard palate and the anterior part of the soft palate; the floor is formed bó the diaphragm of the mouth (diaphrogma oris) (the paired mó1îhyoid muscles) and is occupied by the tongue. When the mouth is closed, the tongue comes in contact with the palate so that the oral cavity becomes narrow slit-like space between them. The mucous membrane extending to the inferior surface of the tip of the tongue forms on the midline the frenulum of the tongue (frenulum linguae). On each side of the frenulum is à noticeable eminence, caruncula sublingualis, with the opening of the ducts of the submandibular and sublingual salivary glands. The sublingual fold (plica sublingualis) stretches on each side laterally and posteriorly of the sublingual caruncle; it is formed by the sublingual salivary gland situated here. THE PALATE The palate (palatum) consists of two parts. Its anterior two thirds have a bony foundation, palatum osseum (the palatine process of the maxilla and the horizontal plate of the palatine bone); this is the hard palate (palatum durum). The posterior third, the soft palate (palatum molle) is a muscular structure with a fibrous foundation. During quiet breathing through the nose it hangs obliquely downward and separates the oral cavity from the pharynx. A seam, raphe palati, is seen on the midline of the palate. At the anterior end of the raphe is a row of transverse ridges (about six of ihem), plicae palatinae transversum (rudiments of palatine ridges contributtng in some animals to the mechanical treatment of the food). The mucous membrane covering the inferior surface of the hard palate adheres closely to the periosteum by means of dense fibrous tissue. The soft palate (palatum molle) is a duplication of the mucous membrane in which muscles are lodged together with a fibrous plate, the palatine aponeurosis, as well as glands. Its anterior margin is attached to the posterior edge of the hard palate, while the posterior part of the soft palate (velum palatinum) extends freely downward and to the back and has on the midline a tongue-like projection, the uvula. Laterally, the soft palate is continuous with folds, or arches. The anterior palatoglossal arch (arcus palatoglossus) passes to the lateral surface of the tongue, the posterior palatopharyngeal arch (arcus palatopharyngeus) stretches for some distance on the lateral wall of the pharynx. A depression forms between the anterior and posterior arches which lodges the palatine tonsil (tonsilla palatina). Each palatine tonsil is an oval-shaped mass of lymphoid tissue. The tonsil occupies the greater inferior part of a triangular depression between the arches (sinus tonsillaris s. fossa tonsillaris). The vertical dimension of the tonsil is 20 to 25 mm, the anteroposterior 15 to 20 mm, and the transverse dimension 12 to 15 mm. The nearest important blood vessel in the facial artery which sometimes (when it is tortuous) comes very close to the pharyngeal wall at this level. This must he borne in mind in operation for removal of the tonsils.