• Situated in the superior mediastinum posterior to the sternum, and anterior to the pericardium and major vessels at the base of the heart

• Projection on the thorax is referred to as the thymic triangle.

• Lymphoepithelial organ, usually consists of two lobes (left and right lobes).

• Delicate connective tissue capsule, and trabeculae that extend into the parenchyma subdividing the thymus into lobules

• Each lobule is divided into a (darker) cortex and (lighter) medulla. Epithelial cells form a densely packed subcapsular layer around the fibrous trabeculae (blood–thymus barrier) and join together inside the thymus to form a three-dimensional network that encloses the lymphocytes. Epithelial cells in the medulla aggregate to form Hassall’s corpuscles.

• Other cell types: macrophages, myoid cells, dendritic cells

Mediastinal circulation. Owing to its location in the superior mediastinum, the thymus is supplied by the neurovascular structures of the mediastinum (entering and exiting the head).

• Arteries: thymic branches arising from the internal thoracic artery (proximity to sternum);

• Veins: thymic veins drain into the brachiocephalic veins.

• Lymphatic drainage: through the brachiocephalic lymph nodes into the bronchomediastinal trunks

• Autonomic innervation:

– parasympathetic through both vagus nerves, especially the recurrent laryngeal nerves

– sympathetic through branches of the cervical ganglia (cervical cardiac nerves)

• Maturation and differentiation (conferring immunological competence) of T-cells

• Induction of programmed cell death (apoptosis) in T-cells that respond to antigens: approximately 90 % of immature T-cells die in the thymus.

• Production of immune-modulating hormones (thymosin, thymopoietin, thymulin)

• Primary lymphatic organ

Note: The thymus is an organ “of childhood and adolescence.” It reaches its maximum size during puberty (approximately 30 grams). The degree of atrophy of thymic tissue in adults varies.

• The thymic epithelium is derived from the epithelium of the third pharyngeal pouch (endodermal origin).

• The epithelial primordium is populated with lymphocytes (mesodermal origin).

• Disorders of the thymus are very rare

• Absence of the thymus may be life-threatening (thymic aplasia), resulting in lack of cellular immunity

• Lymphatic diseases (e.g., certain types of leukemia) may affect the thymus

• Thymomas: tumors that originate from the epithelial cells of the thymus, and because of the immunologic function of the thymus are often accompanied by autoimmune diseases: myasthenia gravis (muscle weakness).

Situated in the thorax (middle mediastinum)

Fibrous sac that surrounds the heart consisting of

• Fibrous pericardium (outermost layer comprised of dense connective tissue; extends to the roots of the great vessels at the base of the heart);

• Serous pericardium (serous membrane) with

– parietal layer (adhered to the fibrous pericardium),

– visceral layer (epicardium, attached to the myocardium);

• Between parietal and visceral layer: pericardial cavity (narrow space);

• At the location where the visceral layer is folded back onto the parietal layer near the base of the heart, two sinuses are formed:

– transverse sinus (between the arteries and veins)

– oblique sinus (between the left and right pulmonary veins).

• One for the ascending aorta

• One for the pulmonary trunk

• Two for both caval veins

• Four for the four pulmonary veins.

• Mediastinal circulation

• Arteries: pericardiacophrenic artery (from the internal thoracic artery)

• Veins: pericardiacophrenic vein (to the internal thoracic vein)

• Lymphatic drainage: prepericardial lymph nodes, lateral pericardial lymph nodes (also superior phrenic lymph nodes and tracheobronchial lymph nodes into the bronchomediastinal trunk)

• Autonomic innervation: negligible

• Somatosensory innervation: phrenic nerve (from the cervical plexus)

Provides sliding-surface for the heart, however the pericardium is not essential for life.

Derived from lateral plate mesoderm:

• Visceral parts derived from splanchnopleure

• Parietal parts derived from somatopleure

• Pericarditis: inflammation usually caused by viral or bacterial infection.

• Tuberculous pericarditis, which is rare nowadays, can lead to pericardial calcium deposits. As a result, the heart can no longer expand; it is constricted (also known as constrictive pericarditis).

• Located in the thorax within the pericardium.

• The base of heart is directed upward, backward, and to the right. The base of the heart is the location of the venous entry and arterial exit points (inferior and superior venae cavae, pulmonary veins, ascending aorta and pulmonary trunk).

• The apex of heart is directed downward, forward and to the left.

• The longitudinal axis of the heart (from the base to the apex, the anatomical axis of the heart) is at a 45-degree angle to all body planes.

• Hollow organ, shaped like a cone: measures 12–14 cm in length, 9 cm in width at its broadest part.

• Weight: up to 300 g.

• Surfaces:

– sternocostal surface (anterior)

– right and left pulmonary surfaces

– diaphragmatic surface (inferior)

• Grooves on the outside of the heart:

– anterior/posterior interventricular sulci

– coronary sulcus

• Auricles: (left/right): protrusions attached to the atria (analogous to the primitive atria; potential site for thrombus formation) produce atrial natriuretic peptide (ANP) for regulation of blood pressure.

Chambers and openings of the heart

Cardiac valves

• Four contractile chambers:

– two atria: left and right atria separated by the interatrial septum (muscle);

– two ventricles: left and right ventricles, separated by the interventricular septum (muscular part and membranous part, thus part muscle and part connective tissue); both ventricles have an inflow tract (with trabeculae carneae) and an outflow tract (smooth-walled) following the direction of blood flow.

• Four openings that connect the atria and ventricles, the right ventricle and pulmonary trunk, and the left ventricle and ascending aorta:

– two openings in the right side of the heart: right atrioventricular orifice and pulmonary orifice;

– two openings in the left side of the heart: left atrioventricular orifice and aortic orifice.

• Additionally, openings for the two caval veins (in the right atrium) and the four pulmonary veins (in the left atrium, see flow of blood below) as well as the opening of the coronary sinus (in the right atrium: opening of coronary sinus with the valve of the coronary sinus).

Flow of blood through the heart chambers

• Generally: from the right heart to the lungs (oxygen absorption), from there to the left heart and then to the aorta (oxygen is released to serially connected organs)

• More specifically: from the superior and inferior venae cavae into the right atrium, from there through the right atrioventricular orifice to the right ventricle and through the pulmonary orifice to the pulmonary trunk, through both of the pulmonary arteries, and into the lungs; from there to the four pulmonary veins, then to the left atrium and through the left atrioventricular orifice to the left ventricle and finally through the aortic orifice to the aorta.

• By closing and opening (papillary muscles, see below) four valves ensure that blood flows in only one direction through the heart:

– two atrioventricular valves;

– two semilunar valves (pulmonary valve and aortic valve).

During ventricular contraction, the atrioventricular valves prevent backflow of blood from the ventricles into the atria; when the ventricles relax, the semilunar valves prevent the return of blood from the pulmonary trunk and ascending aorta back into the ventricles.

• Valves of the right side of the heart:

– right atrioventricular valve at the right atrioventricular orifice = cuspid valve with three cusps: septal/anterior/posterior cusps = tricuspid valve;

– pulmonary valve at the pulmonary orifice in the outflow tract of the right ventricle = semilunar valve with three cusps: anterior/left/right semilunar cusps;

• Valves of the left side of the heart:

– left atrioventricular valve at the left atrioventricular orifice = cuspid valve with two cusps = bicuspid valve: anterior/posterior cusps;

– aortic valve at the aortic orifice in the outflow tract of the left ventricle = semilunar valve also with three cusps: posterior/left/right semilunar cusps.

Grooves and crests on the inner walls of the chambers of the heart

Grooves (only in the atria):

• Right: fossa ovalis in the interatrial septum is the embryonic remnant of the foramen ovale.

• Left: valve of the foramen ovale is the counterpart of the fossa ovalis on the right side.

Crests (in atria and ventricles):

• Right and left atria: pectinate muscles: ridge-like muscle protrusions in the auricles, see above, correspond to the primitive atrium of the embryonic heart.

• Right and left ventricles:

– trabeculae carneae (muscular columns that line the ventricles; more prominent in the right than the left ventricle)

– papillary muscles: specialized extensions of the trabeculae carneae that project into the lumen of the ventricle; prevent the inversion or prolapse of valves during ventricular contraction

– in the right ventricle: three papillary muscles for the three cusps of the tricuspid valve, see above, (anterior, posterior, and septal papillary muscles)

– in the left ventricle: two papillary muscles for the two- cusps of the bicuspid valve, see above (anterior and posterior papillary muscles)

Skeleton of the heart

The heart valves all lie in one plane (valve plane) and are covered by endocardium. The valve rings are composed of dense connective tissue. All fibrous rings, together with the collagenous bands through which they are connected, form the cardiac skeleton.

Layers of the heart wall

The wall of the heart consists of three layers. From the inside to the outside they are

• endocardium (simple squamous epithelium): lines the cavities of the heart and covers the heart valves;

• myocardium (muscle, the fibers of which are arranged in different directions): muscle fibers roughly arranged in three layers;

• epicardium (serous membrane of the pericardium, simple squamous epithelium): strictly speaking, it is part of the pericardium, although it is often referred to as part of the heart.

• Mediastinal circulation

• Arteries: left coronary artery (with anterior interventricular branch and circumflex branch) and right coronary artery (with posterior interventricular branch), both arise from the ascending aorta where it exits the left ventricle.

• Veins: cardiac veins (great, middle, small), like the posterior vein of the left ventricle, the cardiac veins return blood to the right atrium through the coronary sinus.

• Lymphatic drainage: through the brachiocephalic lymph nodes and the tracheobronchial lymph nodes into the bronchomediastinal trunk

• Autonomic innervation: parasympathetic through the two vagus nerves (cervical and thoracic cardiac branches). The neuronal cell bodies are in the dorsal nuclei of the vagus nerves; sympathetic through branches of thoracic ganglia 2–5 (superior, middle and inferior cervical cardiac nerves) and thoracic cardiac nerves.

The heart functions as a suction-pressure pump to distribute blood around the body (heart volume approximately 780 ml, ventricular stroke volume 70ml).

• The heartbeat can be felt as pulse (resting heart rate ~ 1 Hz).

• Cardiac activity is divided into two phases: systole (contraction of the myocardium) and diastole (relaxation of the myocardium).

• Contraction of the ventricular myocardium (closure of the AV valves) and closure of the aortic and pulmonary valves are audible as the first and second heart sounds.

• Cardiac excitation conduction system composed of specialized myocardial cells: impulses are generated by the sinoatrial node (SA node) in the right atrium adjacent to the opening of the superior vena cava. Excitation is spread to the ventricles through the atrioventricular node (AV node), at the junction of right atrium and right ventricle, and then through the atrioventricular bundle (bundle of His) with its right and left branches, which terminate in the Purkinje fibers.

Note: Because of its autonomous excitation, the heart can trigger the impulse that generates the heartbeat. Even an isolated heart beats. The autonomic innervation (see above) modifies only the activities of the autonomous excitation and conduction system. The parasympathetic nervous system reduces the heart rate and atrioventricular conduction. The sympathetic nervous system increases both and as well as the stroke volume.

Of mesodermal origin, derived from the primitive heart tube and subsequently formed cardiac loop.

• Heart diseases are important and are the leading cause of death in the industrialized world: myocardial infarction = occluded coronary arteries that lead to inadequate blood flow to distinct parts of the myocardium, which results in myocardial necrosis

• Arrhythmia and dysfunction of the conduction system

• Valve defects (congenital or caused by inflammation of the endocardium) = incomplete opening of the valve (valve stenosis) or incomplete valve closure (valve insufficiency)

• With myocardial injuries without damage to the pericardium, the heart continues to pump blood into the pericardial cavity until cardiac arrest occurs (cardiac tamponade).

• Generally: formation of pathological blood clots (thromboses) in the heart, which may travel through the blood stream, for example, to the brain.

• Cervical part of the trachea situated in the neck

• Thoracic part of the trachea and main bronchi situated in the mediastinum

• Lobar bronchi and all segments inferior: intrapulmonary location

• Lungs: situated on either side of the mediastinum

• Surface of the lung covered by visceral pleura (pulmonary pleura). On the mediastinal surface at the pulmonary ligament the parietal pleura is folded back onto the visceral pleura.

• Apex of lung

• Base of lung

• Lobes of the lung. Three lobes in the right lung: superior lobe, middle lobe, and inferior lobe; two in the left lung: superior lobe and inferior lobe

• Fissures, two in the right lung: horizontal fissure below the superior lobe; oblique fissure between the middle lobe and inferior lobe. In the left lung one oblique fissure between the superior and inferior lobes

• Two margins: anterior and inferior margins

• Four surfaces: costal surface (adjacent to the ribs), diaphragmatic surface (at the base, adjacent to the diaphragm), mediastinal surface (adjacent to the mediastinum), interlobar surface (in the fissures between lobes)

Note: A term for the posterior margin of the lung (where the costal and mediastinal surfaces meet) is not listed in the official Terminologia Anatomica.

• Generally: tubes that divide by dichotomous branching with decreasing caliber

• The intrapulmonary airways, connective tissue, and neurovascular structures form a spongy organ—the paired lungs.

Structure of the trachea and bronchial tree:

• Trachea to terminal bronchioles = conducting (carrying air) portion.

• Terminal bronchioles to alveoli = respiratory (gas exchange) portion.

Components of the conducting portion:

• Cervical part of the trachea: first tracheal ring, see below, to superior thoracic aperture

• Thoracic part of the trachea: superior thoracic aperture to tracheal bifurcation

• At the tracheal bifurcation: division of the trachea into the right and left main bronchi

• Division of the right main bronchus into three lobar bronchi: superior, middle and inferior lobar bronchi

• Division of the left main bronchus into two lobar bronchi: superior and inferior lobar bronchi

• Division of the lobar bronchi into segmental bronchi: ten segmental bronchi in the right lung and 9 segmental bronchi in the left lung

• Division of the segmental bronchi into subsegmental bronchi

Components of the respiratory portion:

• Respiratory bronchioles: first to third order (where alveoli begin to appear)

• Alveolar ducts

• Alveolar sacs

Trachea:

• Hollow, tubular organ with 16–20 horseshoe-shaped cartilage rings

• Tracheal rings joined together by collagen and elastic fibers (annular ligaments)

• Mucosa of the trachea covered with respiratory epithelium, contains multiple glands (tracheal glands).

• Posterior tracheal wall: non-cartilaginous, composed of connective tissue (membranous wall of trachea), permeated by smooth-muscle cells (trachealis muscle).

Main, lobar, segmental and subsegmental bronchi:

• Generally similar in structure to the trachea.

• Concentric or spiral sheets of smooth-muscle cells in all bronchi (active changes in caliber)

• In segmental and subsegmental bronchi cartilaginous plates instead of cartilage rings

• Pseudostratified respiratory epithelium like tracheal mucosa

Starting from the respiratory bronchioles:

• Non-cartilaginous walls

• Ciliated epithelium with type I and type II pneumocytes (in the alveoli)

Structure of the airways determines the structure of the lungs:

• Both lungs aerated by trachea.

• Main bronchi (left and right, respectively) each aerate one lung (left and right, respectively).

• Lobar bronchi each aerate one lobe (pulmonary lobe).

• Segmental bronchi each aerate one lung segment (bronchopulmonary segment).

• Lobular bronchioles each aerate one lobule (pulmonary lobule).

• Terminal bronchioles each aerate one acinus; a group of acini forms a lobule.

Mediastinal circulation

• The intrapulmonary neurovascular structures in the lung either run along the divisions of the bronchial tree or within the connective tissue framework.

• Characteristic feature of the lungs: two circulation systems: bronchial arteries and veins to supply the lung itself, and pulmonary arteries and veins for gas exchange through the entire body.

Bronchial arteries and veins:

• Arteries: bronchial branches directly from the thoracic aorta or indirectly from posterior intercostal arteries

• Veins: on the right, bronchial veins to the azygos vein, on the left to the hemiazygos vein or accessory hemiazygos vein

Pulmonary arteries and veins:

• Arteries: the pulmonary arteries (left, right) carry deoxygenated blood from the pulmonary trunk. Segmental branches (segmental arteries) of the pulmonary arteries follow the segmental bronchi into the center of one of the 10 or 9 segments.

• Veins: drainage of oxygenated blood usually through four pulmonary veins into the left atrium of the heart

• Lymphatic drainage: through the intrapulmonary, bronchopulmonary, tracheobronchial, and paratracheal lymph nodes into the bronchomediastinal trunks

• Autonomic innervation:

– parasympathetic through the two vagus nerves to the pulmonary plexus,

– sympathetic through branches mainly from thoracic ganglia 2 or 3–4 (varies), also to the pulmonary plexus

Generally, the exchange of oxygen and carbon dioxide between the atmosphere and blood circulation, more specifically:

• Trachea and bronchi as well as their divisions (bronchial tree) except for the finest terminal portions: air conduction

• Final divisions of the bronchial tree (alveoli): gas exchange between atmosphere and blood; thus the important role of the lungs for

– energy production: oxygen is extracted from the atmosphere for oxidation processes.

– regulation of acid-base balance (release of carbon dioxide in the air when exhaling and thus influencing bicarbonate levels in the blood)

• Following changes in the thoracic volume through the pleural layers (capillary forces cause the visceral pleura, which is attached to the lungs, to adhere to the parietal pleura, which is attached to the inner surface of the thoracic wall); a change in lung volume leads to a change in intrapulmonary pressure resulting in drawing in or expelling air from the lungs.

Of endodermal origin, derived from the cranial foregut:

• Lung buds or respiratory diverticulum develops from a small outpouching on the ventral surface of the embryonic esophagus.

• Lung buds undergo repeated dichotomous branching (total of 22) to give rise to the trachea along with the bronchial tree including the alveoli.

Note: The lungs are fully matured at approximately the age of 10.

The bronchial tree and lungs are the parts of the body most commonly affected by diseases (entry points for infectious pathogens):

• Acute inflammation of the bronchial tree (bronchitis, bronchial catarrh, cold) is usually caused by viral infections and is generally harmless.

• Chronic inflammation (chronic bronchitis) is much more common in smokers.

• Bronchial asthma (often triggered by allergies) is a result of insufficient expansion of small bronchi and bronchioles during expiration.

• Lung overexpansion and rupture of the alveoli (pulmonary emphysema)

• Chronic obstructive pulmonary disease (COPD): endstage of the three previously mentioned diseases, with destruction of gas exchange tissue

• Malignant tumors (bronchial carcinoma) is among the leading causes of death for smokers.

• Pulmonary embolism: Acute occlusion of a pulmonary artery (or one of its branches) is caused by a blood clot that most commonly was formed in a vein and carried from the right heart to the lung. In that case it is crucial that the lungs possess a double circulation. Blood from the bronchial branches is sufficient to supply the tissue. Hence, blockage of the pulmonary artery does not result in tissue undersupply and subsequent destruction.

Situated in the neck and thorax (mediastinum) between the trachea and spinal column, as well as in the abdomen

• Tubular organ, measures about 23–27 cm in length from the entrance of the esophagus to its terminal portion.

• Measures about 20 mm in width (but see constrictions of the esophagus).

Divided into three parts corresponding to the regions of the body they are located in (see above)

• Cervical part (C 6–T 1): to the superior thoracic aperture

• Thoracic part (T 1–T 11): to the esophageal hiatus (site where the esophagus passes through the diaphragm)

• Abdominal part: to the cardiac orifice of the stomach (shortest segment, measures only 2–3 cm in length, lies intraperitoneally).

• Upper constriction: pharyngoesophageal constriction at the C6 level; 14–16 cm from the incisors

• Middle constriction: thoracic constriction at the T 4/T 5 level; 25–27 cm from the incisors, esophagus passes to the right of the thoracic aorta.

• Lower constriction: phrenic constriction at the T 10/T 11 level; 36–38 cm from the incisors, site where the esophagus pierces the diaphragm; functional closure of the esophagus by muscles and venous cushions of the esophageal wall, and muscles of the diaphragm

• Basically the same as in the gastrointestinal tract: mucosa, submucosa, muscularis, and adventitia, or in the lower part in proximity to the stomach: subserous membrane and serous membrane.

• Mucosa with stratified non-keratinized squamous epithelium (has no digestive function but provides mechanical protection against passing food, lubricated by esophageal glands)

• Musculature in the upper esophagus (variable degree of expansion), striated (like the pharyngeal muscles), in the middle and lower part smooth muscle (like the stomach), the lower part contains numerous veins.

• Muscles also contain fibers that wind obliquely around the esophagus.

• Combination of circular and longitudinal muscle fibers allows for the expansion and constriction of the esophageal inlet and outlet (swallowing).

• Primarily mediastinal circulation (thoracic part); to a lesser extent also cervical (cervical part) and upper abdominal circulation (abdominal part)

• Arteries: numerous esophageal branches of the inferior thyroid artery (cervical), thoracic aorta (thoracic), and left gastric artery (abdominal)

• Veins: numerous esophageal veins to the inferior thyroid vein (cervical), azygos veins and hemiazygos veins (thoracic), and left gastric vein (abdominal)

• Lymphatic drainage through the paraesophageal lymph nodes into the deep cervical lymph nodes (cervical), bronchomediastinal trunks (thoracic) and left gastric lymph nodes (abdominal)

• Autonomic innervation:

– parasympathetic through the two vagus nerves (vagal trunks), in the neck region specifically through the recurrent laryngeal nerves. Neurons for the smooth esophageal muscles in the dorsal nucleus of the vagus nerve, neurons for the striated muscles in nucleus ambiguus

– sympathetic through branches of thoracic ganglia 2–5. The autonomic fibers form the esophageal plexus on the esophagus.

During swallowing, active transport of solids and liquids from the pharynx to the stomach; when vomiting, transport of stomach contents from the stomach to the pharynx

• Derived from the endoderm of the cranial foregut.

• Lower part of the mesoesophagus may remain in the form of the hepatoesophageal ligament (connects liver to abdominal part of esophagus).

Note: As a result of the rotation of the stomach in the embryo, the esophagus also shifts slightly. Thus, the longitudinal layer of the smooth esophageal muscles is arranged in a rightward spiral pattern.

Diseases of the esophagus itself (rare except for esophageal reflux):

• Diverticulum (outpouchings of the wall), most common at the junction between the hypopharynx (laryngopharynx) and esophagus (also known as Zenker’s diverticulum, which is not an esophageal but a hypopharyngeal diverticulum).

• Malignant tumors (esophageal carcinoma; relatively rare)

• Inflammation of the esophageal mucosa as a result of chronic alcohol consumption

• Esophageal reflux: inflammation of the esophageal epithelium caused by reflux of stomach acid; caused by insufficient closing mechanisms at the junction of the esophagus and stomach.

• Barrett’s esophagus: as a result of chronic esophageal reflux, the columnar epithelium of the stomach may replace the squamous epithelium of the esophagus: increased risk of cancer.

In the case of liver cirrhosis, abnormally enlarged esophageal veins (esophageal varices: hemorrhagic risk) serve as a portacaval detour (drainage into the azygos system!).

Lies intraperitoneally in the left upper quadrant (=epigastrium).

• Sac-like hollow organ with anterior and posterior walls; different shapes may be encountered (hook-shaped stomach, bull-horn-shaped stomach, long stomach).

• Four parts of the stomach in cranial to caudal direction:

– top right: cardia = cardiac orifice = esophageal inlet

– fundus of stomach (base or dome of the stomach; appears on radiographs as an air-filled space above a fluid level)

– body of stomach

– bottom right: pyloric part of stomach = pylorus with pyloric antrum and pyloric canal; stomach terminates at the pylorus, which closes the pyloric orifice (exit from the stomach into the duodenum)

• The body of stomach has two curvatures:

– lesser curvature, faces right and upward, lesser omentum (connects the liver to the stomach) extends from it.

– greater curvature, faces left and downward, greater omentum extends from it.

• The stomach has two notches:

– the cardiac notch at the junction between the cardia and the body of stomach

– the angular notch at the junction between the body of the stomach and the pylorus

• Basically the same wall structure as the entire gastrointestinal tract: mucosa, submucosa, muscularis, and subserosa and serosa.

• Exception: muscularis consists of three layers: oblique fibers, circular layer and longitudinal layer (important for peristaltic motion).

• Mucosa contains specialized glandular cells that produce HCI and intrinsic factor (parietal cells), pepsinogen (chief cells; protein digestion) and mucus (surface epithelial cells and accessory cells, mucin-producing; protection against self-digestion).

Upper abdominal circulation.

• Arteries: owing to the location in the upper abdomen, all gastric arteries arise directly (left gastric artery) or indirectly (through the common hepatic or splenic artery) from the celiac trunk: left and right gastric arteries supply the lesser curvature, left and right gastro-omental arteries supply the greater curvature; variably a posterior gastric artery for the posterior wall of the stomach.

• Veins: left and right gastric veins, left and right gastro-omental veins, prepyloric vein and short gastric veins directly or indirectly (splenic or superior mesenteric vein) into the hepatic portal vein

• Lymphatic drainage: through groups of lymph nodes at the lesser curvature (left and right gastric lymph nodes), greater curvature (left and right gastro-omental lymph nodes), and at the pylorus (pyloric lymph nodes with prepyloric and retropyloric lymph nodes) into the celiac lymph nodes and from there into the cisterna chyli

• Autonomic innervation:

– parasympathetic through the two vagus nerves (vagal trunks)

– sympathetic, primarily through the greater splanchnic nerves and partially through the lesser splanchnic nerves (through the celiac ganglia)

• Temporary reservoir for food, hence its large volume (1.2–1.8 l) and high elasticity.

• Start of digestive process requirements:

– production of gastric juice containing HCl (approximately 2 l per day, responsible for protein denaturation and sterilizing food, HCl concentration 5 M/L) and protein-digesting enzymes (pepsin)

– liquefaction and mechanical grinding (through peristaltic motion of the stomach wall) of food into chyme which is passed in small amounts through the pylorus to the duodenum. Peristaltic transport of chime

– secretion of intrinsic factor for the intestinal resorption of vitamin B₁₂

• Of endodermal origin, derived from the foregut.

• The stomach has a dorsal and a ventral mesogastrium that develop into the greater and lesser omentum, respectively.

• As the stomach and the mesogastrium rotate, the liver and spleen shift to the right and left upper quadrants and the duodenum comes to lie retroperitoneally.

• Acute and chronic inflammation (gastritis)

• Ulcer (often caused by a type of bacteria called Helicobacter pylori)

• Malignant gastric tumor (gastric carcinoma)