Abdomen and abdominal cavity
The abdominal cavity (cavitas abdominis) is defined as an anatomical space, which is limited by the muscular diaphragm above (it separates the abdominal cavity from the thoracic cavity) and the pelvic inlet below.
Anteriorly the abdominal wall is formed above by the lower part of the thoracic cage and below by the fasciae and following four pairs of muscles:
- external oblique
- internal oblique
- transversus abdominis
- rectus abdominis
Posteriorly, the abdominal wall is formed by the fasciae and following muscles:
- psoas major and minor
- iliacus muscle
- quadratus lumborum
The upper part of the lateral abdominal wall is also protected by lower part of the thoracic cage.
For purposes of description, the abdomen is divided into nine compartments by the four planes: two horizontal and two saggital.
Nine abdominal regions are formed between two horizontal planes and two vertical lines. The transpyloric (TPP) and intertubercular (ITP) planes separate three horizontal abdominal areas:
- Epigastrial zone (epigastrium) above the transpyloric plane.
- Mesogastrial zone (mesogastrium) between TPP and ITP planes.
- Hypogastrial zone (hypogastrium) beneath ITP plane.
The left and right midclavicular lines and (as a continuation) midinguinal lines separate three horizontal abdominal areas:
- Two lateral abdominal
- Unpaired central abdominal zones
In the epigastrial zone two vertical lines separate:
- two hypochondriac regions on each side
- epigastric abdominal region – centrally
In the mesogastrial zone two vertical lines separate:
- Two lateral regions or flanks at the lateral abdominal areas on each side
- Umbilical region – centrally
In the hypogastrial zone lines -right vertical line and left vertical line separate:
- two inguinal regions on each side – some authors call it as left and right hypogastric region
- pubic region – centrally – some authors describe it as hypogastric region
Abdominal regions
Inside the rectus sheaths penetrate the superior (branch from the internal thoracic artery) and inferior (branch from the external iliac artery) epigastric arteries, adequate veins, terminal part of the inferior intercostal nerves, subcostal vessels. Also inside the sheaths may be situated two (each on each side) pyramidal muscles (musculi pyramidales) – pyramidal in shape with base down.
Fasciae of the anterolateral wall consist of a superficial and a deep layer. The superficial layer lies under the skin and contains a various amounts of adipose tissue. The deep layer covers the superficial muscles and it is very difficult to separate it from them.
Another fascia covers the internal surface of the anterolateral abdominal wall with the parietal peritoneum and is called the transversalis fascia.
The skin, muscles and parietal peritoneum are supplied by the ventral rami of the lower six thoracic nerves (intercostal nerves and subcostal nerve), and also by the iliohypogastricus and ilioinguinalis nerves (nervus iliohypogastricus et ilioingunalis) – branches of the lumbar plexus. They (except last two) pass forward between the internal oblique and transversus abdominis muscle, pierce the posterior wall of the rectus sheath and supply all of the muscles around. Next run through the anterior wall of the sheath and supply the skin too. The iliohypogastricus and ilioinguinalis nerves do not enter the rectus sheath. The first one passes through the aponeurosis of the external oblique and supplies the skin above the inguinal ligament. The second one emerges through the superficial ring and supplies skin below the inguinal ligament.
Branches of the external iliac artery and beginning of the femoral artery. The border between the iliac and femoral arteries is crossing under the inguinal ligament and passing through the vascular space (green ring on the picture).
The superficial network of veins radiates out from the umbilicus. It drains above into the lateral thoracic vein – into the axillary vein – and below into the femoral vein via the superficial epigastric vein.
Internal surface of the lower part of the anterior abdominal wall
Posterior view of the internal surface of abdominal wall.
The inguinal canal
The inguinal canal is an oblique passage through the lower part of the anterior abdominal wall and is present in the both sexes. It is about one and half inches (4 cm) long, runs inferomedially from the deep inguinal ring (hole in fascia transversalis) to the superficial inguinal ring (hole in a aponeurosis of the external oblique), just superiorly and parallelly to the medial half of the inguinal ligament.
The deep inguinal ring, oval shaped opening in the fascia transversalis, which lies about half inch above the midinguinal point. It is formed prenatally, when the processus vaginalis invaginates the transversalis fascia. It is related medially to the inferior epigastric vessels. Above and laterally, the arch fibres of the fascia transversalis bound it.
The superficial inguinal ring is a triangular shaped aperture in the aponeurosis of the external oblique muscle, which is palpable superiorly and laterally to the pubic tubercle. The pubic crest forms the base of this triangle. On the sides of the triangle are situated the medial and lateral crus which are formed by the aponeurosis of the external oblique muscle. The intercrural fibres from the inguinal ligament superomedially form an arch across the superficial ring.
- Anterior crus: intercrural fibres
- Posterior crus: reflected inguinal ligament
- Lateral crus: lateral fibres of the aponeurosis
- Medial crus: medial fibres of the aponeurosis
- The anterior wall: the aponeurosis of the external oblique muscle.
- The posterior wall: the transversalis fascia. It is reinforced in its medial third by the conjoint tendon (common tendon of the internal oblique and transversus abdominis muscles).
- The inferior wall: the inguinal ligament and also at the medial end the lacunar ligament.
- The superior wall: the arching lowest fibers of the internal oblique and transversus abdominis muscle.
Right superficial inguinal ring.
Walls of the inguinal canal.
In male the inguinal canal transmits:
- Spermatic cord
- Testicular arteries, each of them arises from aorta
- Pampiniform plexus of veins, which coalesces into the testicular veins
- Vas deferens, the efferent duct of the testes
- Arteries of the vas deferens, each arises from the iliac artery
- Genital branch of the genitofemoral nerve
- Branch of the ilioinguinal nerve
In female the inguinal canal transmits:
- Round ligament of the uterus
- Genital branch of the genitofemoral nerve
- Branch of the ilioinguinal nerve
Transverse section of the abdominal wall.
We distinguish two kinds of inguinal hernia: indirect (oblique) and direct (straight). The indirect hernia is located within the whole inguinal canal. The indirect hernia passes the deep and superficial inguinal ring of inguinal canal. It is most common type of hernia (80% of inguinal hernia). The direct hernia passes through the inguinal triangle. It passes only through the superficial inguinal ring.
The peritoneum and peritoneal cavity
The peritoneum is a thin, serosus membrane which consists of a layer of sqamosus epithelium and divides into two parts:
- Parietal peritoneum – lining the abdominal walls
- Visceral peritoneum – clothing the abdominal viscera.
A double-layer fold of peritoneum, which encloses an organ to the abdominal wall, is called a mesenterium. The mesenteries are continuations of the visceral and parietal peritoneum. The mesenteries are formed by back-to-back layers of reflected peritoneum. They provide nerves and blood vessels to the viscera. These nerves, blood and lymph vessels and sometimes secretory ducts of glands are placed between layers of mesenteric peritoneum, thus they have no direct contact with peritoneal cavity.
All viscera, which are covered around by peritoneum and fixed to the posterior abdominal wall by mesentery are situated intraperitoneally. Some viscera, which have not any mesentery, are situated extraperitoneally. Extraperitoneal viscera can be classified further as retroperitoneal and infraperitoneal.
- Retroperitoneal: are situated behind peritoneum
- Infraperitoneal: are situated under peritoneum
According to complicated development of relations within embryonic cavity of body all viscera of abdominal and pelvic cavities in adult can be divided as follows:
Development of secondarily intraperitoneal organ.
Development of secondarily extraperitoneal organ.
Peritoneum of the upper part of the abdominal cavity.
Peritoneum of the left abdominal wall.
Transverse sections through primitive abdominal cavity (celoma); left on a level of duodenum, right – beneath duodenum.
The peritoneal fold is a reflection of peritoneum, it covers for instance: the inferior epigastric vessels of the lateral abdominal wall.
The peritoneal recess. Is a tubular cavity, which is closed at one end and communicates freely with the rest of the peritoneal cavity on the other end.
The peritoneal ligament. Is a double layer of peritoneum which connects two organs or organ with abdominal wall. It can contain blood vessels or other structures (biliary duct).
The lesser omentum is attached to the stomach and part of the duodenum on the one end and to the liver on the other. It is a part of the ventral mesentery primarily placed behind the liver. Vide supra for parts of the lesser omentum.
The lesser omentum (actually the hepatoduodenal ligament) contains:
- Hepatic artery
- Portal vein
- Biliary duct
The lesser omentum seperates the omental bursa from the rest of the abdominal cavity.
The greater omentum hangs down like an apron between the intestines and the anterior abdominal wall and consists of various amount of adipose and lymphatic tissue. It connects the stomach with the transverse colon and is built of four layers of dorsal mesentery usually grown into one.
The potential space between the parietal and visceral peritoneum is called the peritoneal cavity. Capillary layer of the serous fluid can be found in the peritoneal cavity (peritoneal fluid as it is secreted by the peritoneum). It provides a lubricating film for parietal and visceral surfaces and facilitates free mobility of the viscera with minimal friction.
It is the largest cavity of the body and it has two sacs:
- Greater sac
- Lesser sac (omental bursa)
Omental bursa forming, and development of major omentum.
Anterior aspect of omental bursa situation
The lesser and greater sacs are subdivisions of the peritoneal cavity separated by folds of peritoneum. The greater sac is also referred to as the general peritoneal cavity and forms greater part of this potential space. The peritoneal cavity can be divided into supracolic, infracolic and pelvic departments.
The lesser sac represents the primitive right cavity of the coeloma.
The omental bursa is a diverticulum lying:
- Behind the stomach.
- In front of the posterior abdominal wall.
Peritoneal Relations of Organs of The Abdominal Cavity:
Development of the peritoneal cavity
The primitive gut is divided into three parts:
Starting point for the rotations of primitive gastrointestinal tract: lateral view and
coronary section.
The primitive alimentary tract is attached to the abdominal walls by the ventral mesentery (to the anterior wall) and dorsal mesentery (to the posterior wall). Ventrally there is the mesentery only in the foregut region and it is attached to the abdominal wall above the umbilicus.
The stomach undergoes accelerated growth in its dorsal part to produce the greater curvature. Differential growth pulls the mesogastrium to the left and produces the greater omentum.
The first stage of rotation of the primary intestinal loop (midgut) is connected with a physiological umbilical herniation ( 6th-9th week ). The abdominal cavity becomes temporarily too small for the developing gut because of the rapid hepatic and intestinal growth. The primary intestinal loop rotates 90 degrees counter clockwise around an axis provided by the superior mesenteric artery and the omphalomesenteric vitelline duct. In this stage the cranial limb of the primary intestinal loop comes to lie on the right and the caudal limb on the left side. Next primary intestinal loop rotates 90 degrees and at this stage produces “situs inversus” of the large intestine (the caecum develops in the superior part of the abdominal cavity).
Relations after 180° rotation around superior mesenteric artery.
The second stage of rotation of the primary intestinal loop is a result of the slower growth of the liver while the abdominal cavity becomes larger. Now, during the tenth week, the umbilical herniation is completely withdrawn. The jejunum is withdrawn first and the cranial limb of the primary intestinal loop develops intensively below its caudal limb. The caecum tends to lie to the right just below the liver. The caudal limb of the primary intestinal loop is withdrawn last. The primary intestinal loop lies now anteriorly.
Relations after 270° rotation around superior mesenteric artery.
The third stage is connected with the development of the caecal regions. In this stage the appendix develops. The ascending and descending mesocolon fuse with the parietal peritoneum and these parts become the secondarily retroperitoneal. The dorsal mesogastrium grows and fuses with itself forming the greater omentum. Now, the greater omentum fuses with the transverse mesocolon and forms the gastrocolic ligament.
Final effect of developmental changes in the abdominal cavity.
Descending colon as the secondarily retroperitoneal organ.
Abdominal organs
Gastrointensinal tract
The stomach is the J-shaped part of the alimentary tract that occupies the epigastric and umbilical regions of the abdomen. It has two openings: the cardiac orifice where the abdominal part of oesophagus enters and the pyloric orifice which is guarded by the pyloric sphincter controlling the rate of discharge of stomach contents into the duodenum.
The fundus is the rounded uppermost part above the level of the oesophageal junction, projects above and to the left of cardiac orifice, and is related to the diaphragm (in most radiograms of the stomach this region appears empty, but it is full of air).
The cardia – cardiac portion is located in the close vicinity of the oesophagus, around the orifice. This opening receives the oesophagus and is called the cardiac orifice of the stomach. The cardiac notch (incisura cardiaca) is the notch between the fundus and oesophagus.
The body of the stomach constitutes the major portion of the stomach, which is located below the fundus.
The pyloric part, the pylorus is the terminal part of the stomach and it forms the opening intto the duodenum – the pyloric orifice.
The pyloric part is further subdivided into:
- The pyloric antrum with its angular incisura
- The pyloric canal (narrow part, which separates the rest of the stomach from duodenum)
- The pyloric sphincter
Pyloric region.
- The greater curvature extends from the left of the oesophagus around the fundus to the pylorus. It forms the left border of the stomach and gives attachment to the gastrosplenic and gastrocolic ligaments.
- The lesser curvature is the right border and extends from the right oesophagus to the pylorus.
Anterior surface has three zones:
- zone of the liver left lobe
- zone of the diaphragm
- zone of the abdominal wall contact
Anterior surface of the stomach.
The posterior surface, wchich is separated by omental bursa from:
- zone of the diaphragm (bare area)
- zone of the pancreas
- zone of the spleen
- zone of the left kidney
- zone of the left suprarenal gland
- zone of the transverse mesocolon & colon
Posterior surface of the stomach.
The stomach has four ligaments:
- Hepatogastric ligament – ventral mesenterium
- Gastrophrenic ligament – dorsal mesenterium
- Gastrosplenic ligament – dorsal mesenterium
- Gastrocolic ligament – dorsal mesenterium
Ligaments of the stomach.
Relations of the stomach to vertebral column:
- The cardiac portion: on the level of the vertebra T10
- The pylorus: on the level of the vertebra L1
The stomach is related to other viscera in the following way:
- Anteriorly to the left costal margin, left pleura, lung, diaphram and left lobe of liver
- Posteriorly it is related to the lesser perineal sac, which is empty and thin, also trace relations to the diaphram, spleen, left renal, left adrenal and transverse mesocolon
- The pylorus also contacts the inferior region of the quadrate lobe and the neck of the gall blader
The outermost layer is formed by the visceral peritoneum, which completly covers the somach and leaves it’s curvatures as omenta (lesser and greater). The stomach is connected also with the spleen by the gastrosplenic ligament (it contains the left gastroepiploic vessels) and with the diaphragm.
The muscular wall of the stomach is composed of three muscular layers:
- The outer – longitudinal
- The middle – circular, this layer forms the pyloric sphincter
- The inner – oblique.
The innermost layer of the stomach wall is formed by mucous membrane, which is thrown into numerous folds.
Blood supply of the stomach. Splenic artery goes behind the stomach.
The gastric veins lie together with the adequate arteries and all of them, just like all veins which drain the abdominal viscera return blood into the portal vein circulation. The right and left gastric veins join exactly to the portal vein, but the short gastric veins and the left gastro-omental vein – gastroepiploic vein drain into the splenic vein. The right gastro-omental vein joins the superior mesenteric vein.
The parasympathetic fibres are derived from the anterior and posterior vagal trunks (formed by left and right vagus). The sympathetic fibres are derived from the celiac plexus (arise from T5-T8 segments).
The small intestine occupies the greater part of the abdominal cavity by extending about 6.4 m between the pylorus and ileocecal junction. Physiological processes of secretion, digestion and absorption take place within this structure. Among other functions it also plays important role in immunological response to foreign organisms, viruses and substances.
The small intestine has three parts:
The duodenum, C-shaped part of the alimentary tract, courses around head of the pancreas and is the first and shortest portion of the small intestine.
It is the widest and most fixed of three parts. It is divided into four segments and is located in the epigastric and umbilical regions of the abdomen on the posterior abdominal wall . The first three parts of the organ enclose the head of the pancreas while the fourth segment becomes continuous with the jejunum. Near the pylorus and duodenojejunal flexure, the surface is completely covered by the peritoneum; the remainder of the duodenum is retroperitoneal and relatively immobile. The organ measures about 24 cm.
For convenience of description the duodenum is divided into four parts:
The first duodenal segment (at level L1) about 5 cm (2 inches) long is called also ampulla or bulb. The 1st part of the duodenum begins at the pylorus, in the transpyloric (subcostal) plane. This part has mesentery, is situated interaperitonealy. It is the most mobile part of duodenum. The first 2 cm has similar peritoneal relations to the stomach. The lesser omentum passes from the upper border and the greater omentum from the lower. The hepato-duodenal ligament is attached to the bulb.
The first duodenal segment has following relations:
- frontally: quadrate lobe of the liver, gall bladder
- posteriorly: common bile duct, hepatic artery and portal vein
- below: head of pancreas
The second duodenal segment – descending part (pars descendens) descends from level L1 to L3) has no mesentery and just like the next two parts is located retroperitonealy. It is penetrated by the common bile and pancreatic ducts which pour their contents into the duodenum at the major duodenal papilla, which is guarded by the sphincter of hepatopancreatic ampulla. Sometimes the pancreatic duct ends as minor duodenal papilla.
The second duodenal segment has following relations:
- Anteriorly: transverse colon, liver and gall bladder
- Posteriorly: right kidney, it’s vessels, right suprarenal gland, IVC
Inner left surface of the descending part of duodenum.
Schematic drawing of ducts opening into the duodenum.
The third duodenal segment – horizontal part, (level L3) – lies horizontally from the right to the left across L3 vertebra. The 3rd part of the duodenum lies on the head and uncinate process of the pancreas.
It crosses posteriorly:
- The right ureter
- The right psoas major muscle
- The testicular (or ovarian) artery
- The inferior vena cava
- The aorta
- The inferior mesenteric artery
It is crossed anteriorly by:
- The superior mesenteric artery
- The superior mesenteric vein
- The root of the mesentery
The fourth duodenal segment – ascending part, runs upward from L3 to the left at the level of L2 and curves upwards along the left side of the aorta and the head of the pancreas on the left psoas major.
It crosses over:
- The psoas major muscles
- The gonadal vessels
- The sympathetic trunk
It joins the jejunum at the duodenojejunal flexure on the level of the second lumbar vertebra and superiorly to that is situated the body of the pancreas and medially is the head of the pancreas.
The duodenojejunal flexure is sometimes supported by a muscular slip – the suspensory muscle of the duodenum which comes from the right crus of the diaphragm. The suspensory ligament (of Treitz) is a surgical landmark, holds the ascending portion in place. Small peritoneal recesses are found on the left side of the 4th part of the duodenum and behind the adjacent part of the inferior mesenteric vein.
Arterial supply to the duodenum is from two sources. The upper half of the duodenum is supplied by the superior pancreaticoduodenal artery (from the gastroduodenal artery). The lower part is supplied by the inferior pancreaticoduodenal artery, which both arise from the superior mesenteric artery. These vessels anastomise and form anterior and posterior arcades, which are located between duodenum and pancreas.
The anterior and posterior superior pancreaticoduodenal arteries anastomise with anterior and posterior branches of the inferior pancreaticoduodenal artery and form anterior and posterior arterial arches around head of the pancreas. These arches are called the anterior and posterior pancreaticoduodenal arches.
All veins draining the duodenum are tributaries of the portal vein system, mostly through the superior mesenteric vein. All veins follow corresponding arteries except the prepyloric vein (of Mayo), which ascends anteriorly to the pylorus and drains into the right gastric vein. It exactly marks the gastroduodenal junction.
The anterior lymph vessels drain superiorly to the pancreaticoduodenal lymph nodes (nodi lymphatici pancreaticoduodenales) along the splenic artery and vein. From the lower part of the anterior surface, lymph is returned to the pyloric lymph nodes. Efferent vessels pass to the celiac lymph nodes.
The small bowel is supported by the mesentery proper and is situated below the transverse colon mainly in the central abdomen. The inferior part may extend into the pelvis. The peritoneal portion of the small bowel averages 7 m, varying 5 – 11 m. The jejunum is the upper two-fifths of the small intestine. We can’t identify clearly the border between jejunum and ileum. There is gradual change from one part to the other. The jejunum and ileum share blood supply, innervation, mesenteric support and functions. The small intestines are attached to the posterior abdominal wall by the mesentery and between two layers of peritoneum pass jejunal, illeal blood vessels, lymphatic vessels, nerves, also fatty tissue. Thanks to the mesentery, loops of jejunum and ileum are very mobile, except proximal and distal parts (shorter mesentery).
The space, where the visceral peritoneum is continuous with the parietal peritoneum is called the root of mesentery. The root of mesentery is 15 cm long and extends from left side L2 to the right sacroiliac joint.
It crosses posteriorly:
- Horizontal part of duodenum
- Abdominal aorta
- IVC
- Right psoas major muscle
- Right ureter
- Right testicular or ovarian vessels
Distinguishing characteristics of the jejunum and ileum.
| Jejunum | Ileum | |
|---|---|---|
| Localisation | the left lateral region | the pelvic cavity |
| Diameter | 2 – 4 cm | 2.5 – 3 cm |
| Linear measures | two-fifths | three-fifths |
| Wall | thick, heavy | thin, light |
| Vascularisation | greater | less |
| Arcades | large loops, few | short loops, many |
| Arteriae rectae | long | short |
| Fat in mesentery | less | more |
| Plicae circulares | well developed | rudimentary |
| Peyer’s patches | few | many |
Comparison of jejunum and ileum.
The celiac trunk is a short (about 1 cm), thick trunk which arises from the anterior surface of the aorta (level L1) and divides immediately into three branches.
The superior mesenteric artery (arteria mesenterica superior), next unpaired branch, arises also from the anterior surface of the aorta 1 cm below coeliac trunk at the level lower 1/3 of L1. It runs forwards between the pancreas and first part of duodenum (crosses in front of that), descends between layers of mesentery to the right iliac fossa.The superior mesenteric artery, next unpaired branch, arises also from the anterior surface of the aorta 1 cm below coeliac trunk at the level lower 1/3 of L1. It runs forwards between the pancreas and first part of duodenum (crosses in front of that), descends between layers of mesentery to the right iliac fossa.
From the superior mesenteric artery arise:
- Inferior pancreaticoduodenal artery
- Jejunal and ileac arteries
- Ileocolic artery
- Right colic artery
- Middle colic artery
Branches from the superior mesenteric artery supply: a part of the duodenum, all the small intestine, the large intestine until right two-thirds of the transverse colon.
Blood supply given by the superior mesenteric artery.
The length of the large intestine, from cecum to anus, can vary between 100 to 200 cm with a normal length of about 150 cm.
The large intestine is subdivided into:
The blind pouch of caecum measuring 6 cm in length and 8 cm in diameter lies superficially to the iliopsoas muscle within the right iliac fossa. The cecum is usually enveloped by the peritoneum, but mesentery is not present. The vermiform appendix projects from the dorsomedial aspect of the pouch while the ileocecal valve, the ileocecal orifice occurs on the medial side of the cranial portion of the cecum.
Localisation of the original point of the vermiform appendix in the projection on the abdominal wall.
- Mc Burney’s point – half of the diameter between the anterior superior iliac spine and umbilicus
- Lanza’s point – left 1/3 of the diameter between the right and left anterior superior iliac spine.
The ascending colon is located in the right lumbar region. This segment represents a specific region of the colon which projects superiorly for 15-20 cm between the cecum and the inferior surface of the liver and laterally to the gall bladder.
Right colic flexure is located at level of L2 and sixth right rib. Right colic flexure is connected sometimes with the liver by the hepato-colic ligament (ligamentum hepatocolicum). Impression of the right colic flexure is marked on the visceral surface of the liver.
The right colic flexure and features of the colon.
The anterior surface and partly sides of the tube are covered by:
- peritoneum
- midgut
The posterior aspect of the ascending colon is related to:
- the right kidney
- iliacus muscle
- quadratus lumborum muscle
The medial aspect is related to :
- partly to the psoas major muscle
- midgut
The posterior aspect of the ascending colon is related to the lateral wall of the abdominal cavity.
In distance of about 30 cm from the right colic flexure the transverse colon passes to the splenic or left colic flexure. The real lenght of that part of the clolon is bigger then the distance between the both flexures (40 to 50 cm), because the middle part of the transverse colon bends inferiorly with the apex of the curvature sometimes reaching the cavity of the true (lesser) pelvis. The left colic flexure is connected to the diaphragm by the phrenicocolic ligament (ligamentum phrenicocolicum) which supports the spleen at the level of the eleventh left rib. There is also the gastrocolic ligament between the stomach and the transverse colon. The diameter of the transverse colon is smaller than that of the ascending segment.
- Cranially, the transverse colon relates to, from right to left:
- Liver
- Gall bladder
- Stomach
- Spleen
- Posterior aspect of the ascending colon is related to:
- Descending part of the duodenum
- Head of the pancreas
- Left kidney
- Anterior surface of the tube is covered by:
- Major omentum
- Inferior aspect of the ascending colon is related to
- Midgut
The third part or descending segment of the colon passes inferiorly 28 cm along the left hypochondriac, lateral and inguinal regions between the left colic flexure and the pelvic brim.
- The anterior border, medial and lateral side of the organ are related as the ascending colon.
- The posterior aspect is free of peritoneum and relates to:
- The left kidney,
- The diaphragm,
- The three muscles of the posterior abdominal wall (quadratus lumborum, partly psoas major and iliacus).
The sigmoid colon is S-shaped. It begins at the point where the descending colon crosses the medial aspect of psoas major muscle and the external iliac vessels. This fourth part of the colon descends about 40 cm to the level of the vertebrae S3. The sigmoid descends along the left pelvic wall to reach the pelvic floor where it passes almost horizontally to the right. The junction of the two segments constitutes the narrowest part of the colon.
The sigmoid relates to:
- pelvic coils of ileum
- urinary bladder
- uterus (in women)
The sigmoid mesocolon encircles this specific portion of the colon and attaches it to the
pelvic wall.
The sigmoid colon and folds of its mucous membrain which can be observed in sigmoidoscopy.
The rectum is this segment of the large intestine which projects 12 to 14 cm between the sigmoid colon (at S3) and anus.
The rectum is divided into two parts: rectal ampulla and anal canal.
The large intensine (except the rectum, the anal canal, and the vermiform appendix) is characterized by:
- Fat-filled tags (appendices epiploicae) over its surface,
- Three bands of the teniae coli – the longitudinal layer of muscle layer,
- The haustra which are sacculated wall of the bowel.
The inferior mesenteric artery (arteria mesenterica inferior) projects from the aorta at the level of L3, passes downwards to the left iliac fossa and supplies: one-third part of the transverse colon, descending colon, sigmoid, superior part of the rectum.
It gives off following branches:
- Left colic artery anastomises with the middle colic artery to supply the transverse colon
- Two sigmoid arteries
- Superior rectal artery
The liver, the largest organ of the body, is the center of metabolic processes. It is supplied with blood from the portal vein (unoxygenated, sometimes nutrient – rich and toxic) and the hepatic artery (oxygenated). The blood drains to the hepatic vein, and then to the inferior vena cava. The liver secretes bile to the biliary tree. The bile is formed by the bile pigments (breakdown products of haemoglobin) and the bile salts, that aid in digestion by emulsification of the fats.
The normal adult organ weighs about 3 pounds (1.5 kg) in male and slightly less in female (1.3 kg).
The liver rests in the right hypochondriac and epigastric regions of the abdomen, extending frequently into the left hypochondrium. The greater part is situated under cover of the ribs and costal cartilages (level of T9 – L2) and is also in contact with the diaphragm. The upper surface is convex, modelled to undersurface of the domes of the diaphragm. The visceral surface (postero-inferior) is modelled by the adjacent viscera and is irregular in shape. It contacts with the oesophagus, stomach, duodenum, right colic flexure, right kidney, right suprarenal gland and gallbladder .
The liver is wedge-shaped and has two surfaces:
The right and the left lobe are separated by:
- Round ligament
- Groove of the inferior vena cava
- Fissure for the ligamentum venosum.
The liver is made up of liver lobules. The central vein of each lobule is tributary of the hepatic veins. In the spaces between the lobules are portal canals. These contain branches of the hepatic artery (which carries oxygenated blood) and portal vein (carries venous blood containing products of digestion absorbed from GI tract ).
Anterior surface of the liver.
Inferior s.urface of the liver.
The liver has two parts of the ventral mesenteric attachments.
Relations of the diaphragmatic surface
The liver is separated by the diaphragm from the heart, lungs and pleura. The bare area is related to the inferior vena cava and the right suprarenal gland.
Relations of the visceral surface
The left is in contact with the abdominal oesophagus and the stomach. The caudate lobe and gall bladder are related to the 1st part of the duodenum superiorly and to the transverse colon inferiorly. The caudate process forms the upper boundary of the epiloic foramen. The right lobe is related to the right colic flexure and the right kidney.
The gallbladder is a piriform sac (8 cm long, 3 cm wide) located in the gallbladder fossa on the inferior (visceral) surface of the right lobe of the liver (level Th12-L2). The gallbladder represents the major reservoir for bile storage (30 to 50 ml). The organ is divided into fundus (3 cm wide), body and the neck.
The inferior (ventral) and lateral surface of the organ are covered by peritoneum. The superior border of the organ comes in contact and attaches, via areolar connective tissue, to the fossa of the gallbladder which is located on the liver.
Parts of the gallblader are as follows:
The body forms the greatest part of the organ and comes in contact with duodenum (first and second part).
The fundus is normally located at the junction of the right ninth costal cartilage within the linea semilunaris (and lateral border of rectus abdominis m.) It projects slightly passing the anterior surface of the liver to touch the transverse colon.
The neck (about 1 cm) touches the superior region of the duodenum (first part) before it narrows to become the cystic duct (4 cm).
The gall bladder concentrates and stores bile and adds mucous to it. Overconcentration of the bile and changes in its contents may result in the precipitation of bile components, leading to concretions forming gallstone (cholelithus; state with presence of gallstones is termed cholelithiasis). Gallstones can be visible in an ordinary radiograph. Gallstones irritate the cystic mucosa (cholecistitis – inflammation of the gallbladder) and results in the erosion of the wall of the gallbladder. The gallstones are most often found in overweight, multiparous women over the age of 40 (4-F – fat, fertile, female, forty).
The biliary system.
The private system provides arterial, oxygenated, nutritious blood to the liver.
The hepatic artery (proper hepatic artery) is a continuation of the common hepatic artery (branch of the coeliac trunk) and runs between layers of the lesser omentum. Near the porta hepatis it is divided into right and left hepatic arteries.
The public system provides functional blood supply to the liver coming from intestines.
The portal vein also passes between layers of the lesser
omentum and at the right end of the porta hepatis it terminates by dividing into right and left branches.
Venous drainage for both systems (the private and public system): these vessels drain venous blood from the liver.
The hepatic veins (usually 3 in number) are formed by union of the central veins in its lobules and join IVC while it passes just behind or pierces the liver.
The portal circulation.
Lymphatic vessels drain the liver and enter the hepatic lymph nodes at the porta hepatis. The efferent vessels pass to the coeliac nodes. Some of the deep vessels follow the hepatic veins to the phrenic lymph nodes.
Liver receives sympathetic fibres via hepatic plexus, the largest derivative of the coeliac plexus, which receives fibres from the right vagal and phrenic nerves. Branches of the hepatic plexus lay between layers of the lesser omentum and enter the liver also at the porta hepatis.
The pancreas is an endocrine (secrets glucagon and insulin) and exocrine (produces pancreatic juice that enters the duodenum via pancreatic duct) gland. It is 12-14 cm long, and weighs about 80 g. The pancreas is a retroperitoneal organ which passes, from right to left, transversely across the posterior surface of the stomach. It lies within the epigastric and left hypochondriac regions of the abdomen at the level of L1 – L2.
It is subdivided into four parts:
The head of the pancreas is surrounded by the first three duodenal segments and is overlapped anteriorly by the pyloric region of the stomach. A part of the head extends to the left, behind the superior mesenteric vessels and is called uncinate process. The head is related posteriorly to the IVC and the aorta.
The superior mesenteric vessels pass behind the neck of the pancreas.
The body is triangularly shaped in cross section, crosses the midline and is related posteriorly to the vertebral column, aorta, splenic vessels, left kidney and left suprarenal gland.
The tail comes in contact with hilus of the spleen. Anteriorly the pancreas is related to the transverse colon, mesocolon, lesser sac and the stomach.
The pancreas, as an exocrine gland, produces pancreatic juice which enteres into the duodenum through the pancreatic duct. The internal secretions: glucagon and insulin enter the blood. The common bile duct passes posteriorly to the first duodenal segment and to the head of pancreas.
The main pancreatic duct begins in the tail and runs throughout the length of the gland and usually opens with common bile duct into hepatopancreatic ampulla. Sometimes the pancreatic duct opens alone into hepatopancreatic ampulla minor, which can be situated above the first one. The accessory pancreatic duct is variable, it drains part of the head and usually joins the main pancreatic duct.
The spleen is a lymphatic organ located in the left hypochondriac region of the abdomen. The organ participates in hemopoiesis during the fetal period. In the adult, the spleen filters blood, removes iron from fragmentation of red blood cells, produces lymphocytes and antibodies and stores blood.
The adult spleen weights 180 g and measures 12 x 8 x 4 cm. Its long axis lies along the 10th rib (level T11-L1) and crosses the midaxillary line. It is related to the ninth, tenth and eleventh ribs.
The spleen has a capsule surrounded by peritoneum, which passes from it at the hilum as the gastrosplenic ligament (carrying short gastric arteries and right gastroepiploic artery) to the greater curvature of the stomach and to the posterior body wall over the left side of the diaphragm as the phrenicosplenic ligament and to the left kidney as splenorenal ligament (the lower portion of the phrenicosplenic ligament).
Visceral surface of the spleen.
Localisation of the spleen in the abdominal cavity.
The spleen is related:
- anteriorly – to the stomach, the tail of the pancreas, and the left colic flexure.
- posteriorly – to the diaphragm.
- medially – to the left kidney.
Relation of the spleen to the rib cage.
The spleen is supplied by the splenic artery the largest branch of the celiac trunk. It divides into 5 or 6 branches, which enter the hilum of the spleen. It is interesting that each branch of the splenic artery supplies the individual element of the spleen and there are no anastomoses between them. Therefore any obstruction in one of these branches results in death of one region of the splenic tissue.
The splenic vein is formed by many tributaries which emerge from hilum of the spleen. The splenic vein is one of the three veins which form the portal vein.
All lymph from the spleen is transported along splenic vessels to the pancreaticosplenic lymph nodes.
Nerves of the spleen are derived from the celiac plexus and pass around branches of the splenic artery.
The abdominal aorta
The abdominal aorta is a continuation of the descending part of the thoracic aorta below the diaphragm and begins at level Th12.
It terminates on the body of the fourth lumbar vertebra, where it divides into two terminal branches, the common iliac arteries and small unpaired middle sacral artery.
The abdominal aorta descends from the aortic opening of the diaphragm (at level T12) on the front and to the left of vertebral column.
- On the right side: are situated IVC, azygos vein, thoracic duct.
- On the left side: the duodenojejunal flexure, left crus of the diaphragm,
- Anteriorly: the lesser omentum, stomach, duodenum, root of the mesentery, pancreas, left renal vein, celiac plexus.
- Posteriorly: bodies of the vertebrae and intervertebral discs, anterior longitudinal ligament.
For purposes of description branches of the aorta are divided into two groups: visceral branches – supply abdominal viscera and parietal branches – supply abdominal wall.
- The middle suprarenal arteries arise from lateral sides of aorta almost on the same level just like the coeliac trunk, pass to suprarenal glands and supply them.
- The renal arteries large trunks that arise from sides of the aorta just below the superior mesenteric artery and run horizontally to the kidneys. The right one and also longer one, crosses anteriorly to the vertebral column and behind IVC. It gives off inferior suprarenal arteries.
- Testicular (or ovarian) arteries arise from the aorta just below the renal arteries at the level L2. Each of them runs obliquely downwards in the front of the psoas muscle (right one anteriorly to IVC), crosses anteriorly the ureter, genitofemoralis nerve and inferiorly the external iliac artery.
All of parietal branches are paired. These branches of the abdominal aorta can be subdivided into:
- The inferior phrenic artery arises just below diaphragm and supplies inferior surface of the diaphragm. It gives off superior suprarenal artery.
- Lumbar arteries, four pairs arise from the abdominal aorta on the level L1- L4. They pass laterally behind quadratus and psoas major muscles. All these arteries supply posterior abdominal wall.
Branches of the abdominal aorta and their relation to the IVC.
The portal circulation
The portal circulation begins as a capillary plexus in the viscera and ends in the capillary circulation within the liver. There is only one blood vessel like that in all human body, which begins and ends as a capillary circulation.
The inferior vena cava
The inferior caval vein – IVC (vena cava inferior) is a main vein of the lower part of the body (under the diaphragm).
It begins on the level L5 as result of junction between two common iliac veins about 2.5 cm to the right of the median plane. The origin of the inferior vena cava is located inferiorly to the bifurcation of the abdominal aorta.
Right atrium of the heart
IVC ascends to the diaphragm and passes through with the right phrenic nerve on the level of T8 vertebra. IVC returns blood from the lower limbs, most of the abdominal wall and partly from the abdominopelvic viscera.
Abdominal tributaries of the IVC:
- Parietal branches:
- Inferior phrenic veins
- Ascending lumbar vein (partly)
- Visceral branches:
- Hepatic veins
- Suprarenal veins
- Renal veins
- Right testicular or ovarian vein
- Right and left common iliac vein
- Middle sacral vein (vena sacralis mediana) – IVC is a continuation of the middle sacral vein.
The IVC venous system communicates with the SVC venous system in several locations.
These communications are as follows:
- The lumbar veins return blood into IVC and partly via ascending lumbar veins into the azygos vein system and next into the SVC.
- The superior vena cava receives blood from superior epigastric vein through internal thoracic vein and brachiocephalic vein. IVC receives blood from the inferior epigastric vein through the external iliac vein and common iliac vein. Both superior and inferior epigastric veins anastomise in the umbilical region.
- The superficial epigastric vein drains into IVC via femoral, external iliac and common iliac veins. The superficial epigastric vein anastomises with the thoracoepigastric veins which return blood into the lateral thoracic vein and axillar, subclavian and brachiocephalic veins. All of them drain into SVC.
Lymphatic drainage of the intestinal tract and retroperitoneal space
The intestinal mucosa is richly supplied with lymphatics which drain via submucosal and subserous plexuses to nodes on the surface of the viscus. These drain into intermediate groups of nodes arranged along arteries (in the mesentery or on the abdominal wall) which in turn drain to one of three groups of the pre-aortic nodes arranged about the origins of the coeliac, superior and inferior mesenteric arteries.
Abdomen: the lymph vessels of the anterior abdominal pass to the axillary, anterior mediastinal and superficial inguinal nodes. The abdominal viscera and posterior abdominal wall drain to the aortic nodes which are subdivided into pre-aortic and para-aortic groups.
- Pre-aortic nodes – are arranged around the origins of the three arteries supplying the alimentary tract and its derivatives, and drain the corresponding structures. Their efferents unite to form the intestinal lymph trunk which enters the cisterna chyli.
- Para-aortic nodes – lay alongside the aorta around the origins of the paired lateral arteries. They drain the posterior abdominal wall, the kidneys, the suprarenals and the gonads and, through the common iliac nodes, the pelvic viscera and lower limbs. Their efferents unite to form the right and left lumbar lymph trunks.
Autonomic Nervous System in Abdomen and Pelvis
Like elsewhere it is composed of sympathetic and parasympathetic parts: