The digestive system is a complex of the organs which provide the mechanical and chemical treatment of the food, absorption of nutrients into the blood and lymph, the formation and excretion of faeces. Besides, it provides detoxification of different toxic substances getting with the food or substances which are produced by the splitting of food; and it provides the synthesis of biological active substances (hormones, vitamins, enzymes and so on).
The digestive system includes the following organs: the oral cavity, salivary glands, pharynx (having three parts: nasal, oral and laryngeal), oesophagus, stomach, small and large intestine, liver, pancreas. These organs are placed in the region of the head, neck, in the thoracic and abdominal cavities. In the oral cavity the food is crushed (masticated with the help of teeth), moistened by saliva produced by the salivary glands, and mixed by the tongue. Here the digestion begins. Then, through the pharynx and oesophagus the food passes into the stomach where it udergoes to the gastric juice activity. In the small intestine the bile, pancreatic and intestinal juice treat the chime; and here are the nutrients absorbed. Further, the food mass passes into the large intestine where the water is absorbed and faeces are formed. Faeces are excreted by the rectum.
Thus, the digestive system is like a tube 7-8 m in length, which begins by the mouth and ends by the anus.
Pay attention and memorize that the food makes the following way: through the mouth into the oral cavity, then into the oral part of the pharynx, then laryngeal part of the pharynx, then into the oesophagus, then stomach, then small (duodenum, jejunum, ileum) and large (caecum, ascending, transverse, descending, sigmoid colon and rectum) intestine, and through the anus outside (fig. 1).
You should be able to describe each of these organs. For the description we use the following indicative plan:
For the description of the organs it is important to know the right position of the digestive organs in the head and neck (relatively to the respiratory organs); to know the localization of the cervical cavity (which muscles and fasciae surround it); the walls of the thoracic and abdominal cavities (which bones, muscles, and fasciae form each of these walls).
Firstly look at this picture (fig. 2). Pay attention to the position of the respiratory organs (nasal cavity, nasal part of the pharynx, larynx, trachea) and the digestive organs (oral cavity, oral part of the pharynx, laryngeal part of the pharynx, oesophagus). You see that the nasopharynx is directly behind the nasal cavity, oropharynx is directly behind the oral cavity, the laryngopharynx is directly behind the larynx, oesophagus is directly behind the trachea. Thus, the organs of the digestive system are behind the organs of the respiratory system.
In the neck all the organs (larynx and trachea, laryngopharynx and oesophagus) are enclosed into the cervical cavity lined by the parietal layer of the endocervical fascia. The cervical cavity has the anterior, lateral and posterior walls. Downwards the cervical cavity opens into the thoracic cavity through the superior thoracic aperture. The anterior wall is formed by the sternohyoid, thyrohyoid and sternothyroid muscles and the parietal layer of the endocervical fascia. The lateral walls are formed by the scalenus muscles, partly by the sternocleidomastoideus and the parietal layer of the endocervical fascia. The posterior wall is formed by the prevertebral muscles and the parietal layer of the endocervical fascia. Don`t forget that all the organs of the neck are covered by the visceral layer of the endocervical fascia. Thus, between the visceral and parietal layers of the endocervical fascia the space is formed. This space is divided into the retrovisceral and paravisceral. In their turn, these are divided correspondently into the retropharyngeal and retrooesophageal (behind these organs), and parapharyngeal and paraoesophageal (on the sides of these organs). The spaces contain fat and communicate with the fatty spaces of the head and of the thoracic cavity, that has a clinical importance because the infection can spread through the spaces (from the head to the neck and to the thoracic cavity), involving in the inflammatory process several regions of the body.
The thoracic cavity is in the thorax and is lined by the endothoracic fascia. It has the anterior, lateral, posterior and inferior walls. Superiorly it has an opening, called the superior thoracic aperture, opened into the cervical cavity. The anterior wall is formed by the sternum, cartilaginous parts of true and false ribs, the proper muscles of the chest and by the endothoracic fascia. The lateral walls are formed by the ribs` bodies, by the proper muscles of the chest and by the endothoracic fascia. The posterior wall is formed by the thoracic part of the vertebral column, by the heads, necks and partly bodies of the ribs, by the proper muscles of the chest and by the endothoracic fascia. The inferior wall is formed by the diaphragm covered by the endothoracic fascia. The thoracic cavity is mostly occupied by the lungs covered by the visceral and parietal pleura. Between the parietal pleura of both lungs there is a complex of the organs, called mediastinum. It can be divided into anterior and posterior by means of the imaginary line passing through the anterior side of the trachea. Thus, the oesophagus passes through posterior mediastinum behind the trachea.
The abdominal cavity prolongates downwards into the pelvic cavity, and together they are like a cube having six walls: anterior, laterals, posterior, superior and inferior. It is lined by the endoabdominal fascia. The anterior wall is comprised of by both rectus anterior enclosed into the sheath formed by the aponeuroses of the external and internal oblique abdominins, transversus abdominis and by the endoabdominal fascia. The lateral walls are formed by the external and internal oblique abdominins, transversus abdominis and by the endoabdominal fascia. The posterior wall is formed by the lumbar part of the vertebral column, by the sacrum and coccyx, by the quadratus lumborum, psoas major and minor, by the iliacus and by the endoabdominal fascia. The superior wall is formed by the diaphragm lined by the endoabdominal fascia. The inferior wall is formed by the perineal muscles covered by the endoabdominal fascia (which is called here the pelvic fascia).
The abdominal cavity encloses the following organs of the digestive system: the stomach, small and large intestine, liver, pancreas.
The external borders of the anterior abdominal wall superiorly – the costal arches; inferiorly – the iliac crests, inguinal folds, anterior superior iliac spines and the superior border of the pubic symphysis.
For the description of the position of the internal organs (holotopy), the anterior abdominal wall is divided into the abdominal regions (fig. 3). For this we draw two horizontal conditional imaginary lines: the superior one (called linea bicostarum) connects the tenth ribs; the inferior one (called linea bispinarum) connects the anterior superior iliac spines. These lines divide the anterior abdominal wall into three areas: the epigastrium, mesogastrium, and hypogastrium. Besides, we draw two longitudinal conditional lines (called lineae pararecrales) passing along the outer borders of both rectus abdominis. Thus, each of three areas is divided into three more areas. Eventually, the anterior abdominal wall is divided into nine abdominal regions. The epigastrium includes the proper epigastric region, regio epigastrica propria, and the right and left hypohondriac regions, regio hypochondrica dextra et sinistra. The mesogastrium includes the umbilical region, regio umbilicalis, and the right and left lateral regions, regio lateralis dextra et sinistra. The hypogastrium includes the pubic region, regio pubica, and the right and left inguinal regions, regio inguinalis dextra et sinistra.
1- right hypochondriac region; 2 – proper epigastrium; 3- right hypochondriac region; 4 – right lateral region; 5 – umbilical region; 6 – left lateral region; 7 – right inguinal region; 8 – pubic region; 9 – left inguinal region
For the description of the skeletotopy of the lungs, heart and also liver, several topographical lines are distinguished on the thorax (fig. 4).
Topographical lines of thorax: 1- anterior median line; 2 – sternal line; 3 – parasternal line; 4 – midclavicular line; 5 – anterior axillary line; 6 — middle axillary line; 7 — posterior axillary line; 8 – scapular line; 9 – paravertebral line; 10 — posterior median line
All these lines are paired except the anterior and posterior median lines.
All the internal organs (including the digestive organs) are divided into tubular (hollow) and parenchymatous organs. They are different in structure.
The wall of the hollow organs is composed of three layers: mucous, muscular and adventitia (or serous).
The mucous membrane consists of the epithelium, underlying lamina propria, lamina muscularis and submucous layers.
The epithelium is organosilicate. It can be multi-layer (in the oral cavity) or single-layer (in the stomach and intestine).
The lamina propria is beneath the epithelium; it is comprised of loose connective-tissue and contains the blood and lymphatic vessels, nerves, glands and lymphatic follicles. The glandular cells secrete the mucus or secretion for the digestion of the food and also for protection of the mucous from the impact of enzymes. The lymphatic follicles can be solitary (0,5-3 mm in diameter) or aggregate (10-15 mm in diameter).
The lamina muscularis mucosae consists of 1-3 layers of smooth muscle cells. The mucous of the tongue, palate, gum, tonsils doesn`t has the lamina muscularis.
The submucous layer lies on the border between the mucous and muscular layers. It is formed by loose connective-tissue and provides firm fixation of the mucous membrane. Here is submucous vascular (arterial, venous, lymphatic) and nerve plexuses. The submucous layer possesses a high mechanical durability. It firmly linked with the lamina propria and muscularis and loosely linked with the muscular layer.
The mucous plays the multifarious role. First of all the epithelium protects the organ from the chemical and mechanical impacts. The contraction of the mucous and the mucus makes easier the transport of the content of the hollow organs. The lymphatic follicles play important role in the biological protection of the body. The secretions of the glands of the mucous are the components of the body metabolic processes. Also the mucous of the digestive system organs absorbs the nutrients and liquid. The mucous of such organs is increased due to the folds, villi and microvilli.
The muscular layer is a middle layer in the wall of a hollow organ. In most cases it is formed by two differently arranged layers of smooth muscle tissue. They are circular layer located inwardly, directly around the submucous layer, and longitudinal layer located outwardly. Some organs have only one muscular layer; in some organs the number of the muscular layers increases up to three layers. In this case besides the circular and longitudinal muscular layers, the oblique muscular layer is formed. In some places the smooth muscle fibers of circular layer concentrate to form sphincters which regulate the movement of the content from one to another organ.
Smooth muscle tissue, forming the muscular layer of hollow organs, contracts involuntarily and slowly. It is rich in blood supply and innervation. It should be noted that in the beginning and end parts of the digestive and urogenital systems, the smooth muscle tissue is replaced by striated muscle tissue. The latter allows to produce voluntary actions.
Thus, the functional role of the muscular layer in the wall of the hollow organs is to provide the tone of the wall, to move and mix the content, to provide the contraction and relaxation of the sphincters.
The adventitia (or serous membrane) is outer layer. The organs, the walls of which are fused with surrounding tissues, have the adventitia (for example, the pharynx, oesophagus, duodenum). These organs can not shift because their walls fix to the surrounding tissues. The adventitia is composed of fibrous connective tissue containing vessels and nerves. The mobile organs, which are able to change their position in the body, are covered by the serous membrane instead of the adventitia.
The serous membrane is a thin transparent membrane comprised of fibrous connective tissue and covered by the mesothelium from outside. The serous membrane is connected with the muscular layers by means of subserous layer. The latter is composed of by loose connective tissue and contains the vascular and nerve subserous plexuses. The free surface of the serous membrane is smooth and shiny; it is lubricated by the serous fluid formed by transudation from capillaries of vascular subserous plexus. The serous membrane divides the internal organs, provides the mobility of the organs and plays the regenerative role at damage. The kinds of the serous membrane are the peritoneum and pleura.
Most commonly the parenchymatous organs are large glands. The word “parenchyma” is from Greek word meaning “pulp”. It is glandular tissue of the organs, surrounding by connective tissue stroma where the vessels and nerves pass. The smallest parts of the parenchymatous organs, framed by connective tissue septa and having proper bloodstream, form the structural-functional units of the parenchymatous organs. For example, the structural-functional unit of the liver is a lobule; of the lung – acinus; of the kidney – nephron; of the thyroid gland – follicle, and so on. Besides the structural-functional units, the segments are distinguished in the parenchymatous organs. They are important in surgery. The segment is a macroscopically visible part of the organ, having relatively autonomic blood supply, innervation, lymph circulation, and bounded by the connective tissue layers.
The parenchymatous organs provide the most important processes of metabolism in the body (gas exchange, secretion of enzymes and hormones, detoxification, and so on).
The biliary system starts from the network of minute biliferous ductules; they do not have own walls and are formed by depressions on the surfaces hepatocytes, adjoining each other. The biliferous ductules merge to form larger lobular and segmental bile ducts and then right and left hepatic ducts. The latter ones merge to form the common bile duct which is joined by the cystic duct (from the gallbladder) to form the common bile duct. The common bile duct enters the descending part of the duodenum. All the bile ducts until righ and left hepatic are intrahepatic; the right and left hepatic ducts, cystic duct and common bile duct are extrahepatic. General length of all the bile ducts is more than 2 km.
The common bile duct, about 3 cm long, appears at the porta hepatis due to joining of the right and left hepatic ducts, the length of which is about 0,5-2 cm. The length of the common bile duct ranges from 4 to 12 cm, the diameter is about 8 mm. The common bile duct has four parts: 1) supraduodenal, 2) retroduodenal, 3) pancreatic, 4) duodenal (intramural).
The common bile duct joins the pancreatic duct to form the hepatopancreatic ampulla in the duodenal wall. The ampulla opens on the summit of the major duodenal papilla.
The sphinters of the biliary system regulating the passage of bile and preventing its back flow include the following ones: Lutkens` sphincter is formed by the circular muscle fibres at the place where the cystic duct enters the gallbladder; Mirizzi`s sphincter is formed by the circular muscle fibres at the place just after the joining of the cystic and common hepatic ducts; Oddi`s sphincter includes three sphincters: the sphincter of the pancreatic duct, the sphincter of the common bile duct and the sphincter of the hepatopancreatic ampulla.
The total square of the peritoneum is from 17000 to 20400 cm2 (approximately equal to the square of the skin). In normal the peritoneal surface is smooth, shine and moistened with serous fluid. The peritoneum contains mesothelial cells with microvilli, which form the mesothelium, a kind of covering epithelium; it produces and absorbs serous fluid (its normal volume is 20-25 ml). The mesothelium prevents adhesion between the abdominal organs. If the mesothelium is injured, intra-abdominal adhesions occur.
In females, the peritoneal cavity communicates with external environment through the abdominal orifices of the uterine tubes; in males the peritoneal cavity is completely closed.
The functions of the peritoneum:
1. Resorptive – the ability of the peritoneum to absorb the content of the peritoneal cavity (serous fluid; exudates and products of splitting and lysis of proteins; necrotic tissue; bacteria). The peritoneum of the diaphragm, greater omentum, ileum and caecum posseses the greatest resorptive ability.
2. Exudative — the ability of the peritoneum to secrete serous fluid and fibrin. The peritoneum covering the small intestine posseses the greatest exudative ability.
3. Barrier – mechanical protection of the viscera (the greater omentum plays the most important role; it can limit inflammation); protection with the help of humoral (antibodies) and cellular (macrophages) mechanisms.
Peritonitis is dangerous disease; it can occur because of the infective and chemical irritants (when gastric content, bile, blood, urine comes into the peritoneal cavity).
The most common cause of the peritonitis is perforation of hollow abdominal organ (perforation of the appendix; perforation of the gastric or duodenal ulcer; injury of the intestinal wall; necrosis of the intestinal wall in case of hernia; perforation of intestinal diverticulum; perforation of malignant tumor etc).
In peritonitis, the volume of serous fluid increases because the resorptive finction of the peritomeum is disturbed.
Peritonitis develops rapidly causing endogenous intoxication which determines the severity of the peritonitis and patient`s condition.
So, peritonitis requires immediate surgical intervention with sanitation of the peritoneal cavity (its recesses, bursae, sinuses etc).
The peritoneal cavity, bounded by the peritoneum, is within the abdominal cavity. The abdominal cavity is bounded by the abdominal and partly pelvic muscles and endoabdominal fascia lining those muscles. Thus, the peritoneal cavity is like inserted into the abdominal one, staying the spaces between the peritoneum and endoabdominal fascia: retroperitoneal, subperitoneal and anteperitoneal spaces containing the extraperitoneal organs.
The peritoneal cavity is divided into three levels (storeys): upper storey is between the peritoneum lining the diaphragm and transverse mesocolon; middle storey is between the transverse mesocolon and pelvi inlet; and the lower storey is below the pelvic inlet (pelvic cavity).
In the upper peritoneal storey there are hepatic, pregastric and omental bursae.
In the middle storey there are right and left mesenteric sinuses, right and left paracolic (lateral) canals, superior and inferior duodenal recesses, superior and inferior ileocaecal recesses, retrocaecal recess and intersigmoid recess.
In the lower storey there are rectovesical pouch (in males); rectouterine (of Douglas) and vesicouterine pouches in females.
All these peritoneal depressions must be examined and sanitized during the operation for perforation of a hollow abdominal organ or operation for peritonitis.
Of the bursae, the omental bursa is the deepest; it lies behind the lesser omentum and stomach and communicates with the peritoneal cavity through rather small epiploic foramen (picture 1). So, during the perforation of the posterior gastric wall, blood and stomach content can accumulate in this bursa or pass through the epiploic foramen into subhepatic space (included into hepatic bursa) and then into the right paracolic canal (picture 2). So, in any case, a surgeon must examine the omental bursa through the epiploic foramen to evacuate pathological fluid.
The hepatic and pregastric bursae are superficial, and widely communicate with the right paracolic canal and with peritoneal cavity in front of the greater omentum. The left paracolic canal is separated from the pregastric bursa by the phrenicocolic ligament (picture 3). Thus, in case of perforation of the anterior gastric wall or gallbladder, stomach content or bile will pass into the right paracolic canal and can reach the right inguinal fossa where the appendix usually lies. So, the noted diseases should be differentiated with appendicitis.
It should be noted that hepatic bursa includes subhepatic and right subphrenic recesses; the pregastric bursa includes the left subphrenic recess; they are deep and also can accumulate some pathological fluid.
The mesenteric recesses are in the middle storey (picture 3). The left one communicates with pelvic cavity; the right is separated from the pelvic cavity by the terminal ileum.
And in the lower storey (pelvic cavity) there are rectouterine (of Douglas) and vesicouterine pouches in females (picture 4) and rectovesical pouch in males (picture 5).
The sperm consists of the seminal fluid which is produced by the prostate (30%) and seminal vesicles (65%), and spermatozoa (5%).
The period of spermatozoon maturation lasts 64 days. And then spermatozoon may stay in the male body during about a month. In the body of a health man about 100 mln of spermatozoa is produced every day.
Spermatozoon is the smallest cell in a human body. They may contain Y- or X-chromosome. Ovum can be fertilized only by one spermatozoon, with equal probability Y and X.
Spermatozoon has a head, neck and tail. The head contains the nucleus with haploid number of chromosomes. After fertilization, zygote carrying diploid chromosome number is formed. The head of spermatozoon has a vesicle, a cap-like structure called the acrosome, containing lytic ferments which dissolve the coat of ovum.
The neck contain the mitochondria which synthesize ATP providing the motions of the tail.
So, spermatozoon moves with the help of the tail. Its speed may reach more than 30 cm per hour. After 1-2 hours after coitus, spermatozoa reach the ampullar part of the uterine tube (here fertilization occurs). In the male body spermatozoa stay in not active state; they are almost immobile. Their movements are passive, due to peristaltic contractions of the ducts` walls. Spermatozoa become active due to the influence of the prostatic ferments.
The movements of spermatozoa in the female body are active and occur against the flow of the fluid that is called rheotaxis. Spermatozoa have to overcome the way about 20 cm long (the cervical canal is about 2 cm, uterine cavity is about 5 cm, and uterine tube is about 12 cm). The medium in the vagina is destructive for spermatozoa but the seminal fluid neutralizes the vaginal acids and partially depresses the immune response of the female body against spermatozoa.
From the vagina, spermatozoa move towards the alkaline medium of the uterine cervix. So, they perceive pH of the medium surrounding them (pH in the vagina is about 6,0 , pH in the uterine cervix is about 7,2). Most spermatozoa can not reach the cervix and die in the vagina.
When spermatozoa come into the uterus, their mobility increases under the influence of the uterine medium that is called capacitation. Inside the uterus they can be active around 3 days.
For successful fertilization not less than 10 mln spermatozoa should come into the uterus. From the uterus they move into the uterine tubes. They find the direction, feeling the flow of the fluid and move against the flow. The fluid flow is directed by the peristalsis of the uterine tube and the movements of the epithelial cilia.
Most spermatozoa can not reach the ampulla of the uterine tube. Only several thousands can do this to fertilize ovum.
In the picture Perineal fasciae you can see the muscles of the urogenital diaphragm and fasciae covering them. I remind you, the urogenital diaphragm is a part of perineum between the pubic symphysis, ischiopubic rami and ishial tuberosities. And pelvic diaphragm is part of perineum between ishial tuberosities and coccyx.
Superficial perineal fascia (Colle`s fascia) is just beneath the skin of the anterior perineum. Anteriorly it is continuous with Scarpa`s fascia.
Deep perineal fascia overlies the superficial muscles of the urogenital diaphragm (superficial transverse perineal muscle, bulbospongiosus, ischiocavernosus and deep transverse perineal muscle). Anteriorly it fuses with suspensory ligament of penis or clitoridis and with rectus sheath.
Inferior fascia of urogenital diaphragm (or perineal membrane) is between superficial muscles of the urogenital diaphragm and deep transverse perineal muscle. Anteriorly it is fixed to the pubic bones.
Superior fascia of urogenital diaphragm is a part of pelvic fascia (continuation of endoabdominal fascia).
Between superficial and deep perineal fasciae there is subcutaneous perineal pouch connecting with subcutaneous tissue of abdomen.
Between deep perineal fascia and Inferior fascia of urogenital diaphragm (or perineal membrane) there is superficial perineal pouch. It contains superficial muscles of the urogenital diaphragm and does not communicate with subcutaneous or deep perineal pouches.
Between Inferior fascia of urogenital diaphragm (or perineal membrane) and Superior fascia of urogenital diaphragm there is deep perineal pouch. It communicates with the fat of the pelvic diaphragm.
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