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Abdomen 

Abdomen
Chapter:
Abdomen
Author(s):

Dr Mark Harrison

DOI:
10.1093/med/9780199583836.003.0004
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Subscriber: null; date: 16 October 2017

Contents

  1. 4.1 Abdominal wall, [link]

  2. 4.2 Inguinal region, [link]

  3. 4.3 Testis, epididymis, and spermatic cord, [link]

  4. 4.4 Topography of the abdominal cavity, [link]

  5. 4.5 Peritoneum, [link]

  6. 4.6 Gastrointestinal tract, [link]

  7. 4.7 Liver and biliary tract, [link]

  8. 4.8 Pancreas, [link]

  9. 4.9 Spleen, [link]

  10. 4.10 Posterior abdominal wall, [link]

  11. 4.11 Kidneys, ureters, and bladder, [link]

  12. 4.12 Pelvis, [link]

  13. 4.13 Prostate, [link]

  14. 4.14 Female reproductive system, [link]

  15. 4.15 Male urogenital region, [link]

4.1 Abdominal wall

4.1.1 Regions of the abdominal wall

The abdominal wall is subdivided into regions as seen in Figure A.4.1.

Figure A.4.1 Regions of the abdominal wall

Figure A.4.1
Regions of the abdominal wall

4.1.2 Muscles of the anterior abdominal wall

  • External oblique

    • Origin: Lower 8 ribs

    • Insertion:

      • Xiphoid process

      • Linea alba

      • Pubic crest

      • Pubic tubercle

      • Iliac crest

      • (Is the origin of the inguinal ligament)

    • Innervation:

      • Lower 6 thoracic nerves

      • Iliohypogastric nerve

      • Ilioinguinal nerve

    • Action:

      • Supports abdominal contents

      • Assists in trunk flexion and rotation

      • Compresses abdominal contents

      • Assists in: Forced expiration, defecation, parturition, micturition, vomiting

  • Internal oblique

    • Origin:

      • Lumbar fascia

      • Iliac crest

      • Lateral two-thirds of inguinal ligament

    • Insertion:

      • Lower 3 ribs and costal cartilages

      • Xiphoid process

      • Linea alba

      • Symphysis pubis

    • Innervation:

      • Lower 6 thoracic nerves

      • Iliohypogastric nerve

      • Ilioinguinal nerve

    • Action: Same range of actions as external oblique

  • Transversus

    • Origin:

      • Lower 6 costal cartilages

      • Lumbar fascia

      • Iliac crest

      • Lateral third of inguinal ligament

    • Insertion:

      • Xiphoid process

      • Linea alba

      • Symphysis pubis

    • Innervation:

      • Lower 6 thoracic nerves

      • Ilioinguinal nerve

      • Iliohypogastric nerve

    • Action: Compresses abdominal contents

  • Rectus abdominis

    • Origin:

      • Symphysis pubis

      • Pubic crest

    • Insertion:

      • 5th-7th costal cartilages

      • Xiphoid process

    • Innervation: Lower 6 thoracic nerves

    • Action:

      • Compresses abdominal contents

      • Flexes vertebral column

      • Assists expiration

4.1.3 Rectus sheath

  • The rectus sheath is a fibrous sheath enclosing the rectus abdominis muscle.

  • It is formed mainly by the aponeurosis of the 3 main abdominal muscles described above (external oblique, internal oblique, and transversus).

  • It is best considered in 3 sections:

    • Above the level of the costal margin:

      • The anterior rectus sheath is formed by the external oblique aponeurosis only

      • There is no aponeurosis from internal oblique or transversus at this level

      • There is no posterior rectus sheath

      • Rectus femoris lies directly on 5th-7th costal cartilages

    • From the costal margin to the anterior superior iliac spine (ASIS) and arcuate line:

      • The anterior rectus sheath is formed by the external oblique aponeurosis and the anterior part of the split internal oblique aponeurosis

      • The posterior rectus sheath is formed by the posterior part of the split internal oblique aponeurosis and the transversus abdominis aponeurosis

    • From the ASIS and arcuate line to the pubis:

      • The anterior rectus sheath is formed by the combined aponeuroses of external oblique, internal oblique, and transversus

      • The posterior rectus sheath is absent and the rectus abdominis lies on transversalis fascia (which is thickened here to form the iliopubic tract)

4.1.4 Contents of the rectus sheath

  • The rectus sheath contains:

    • Pyramidalis muscle (if present)

    • Superior epigastric vessels

    • Inferior epigastric vessels

    • Nerves and vessels from T7-T12

    • Posterior intercostal nerves

4.2 Inguinal region

4.2.1 The inguinal canal

  • This is an oblique passage through the lower part of the abdominal wall. It allows passage of structures from the testis to the abdomen in males and the passage of the round ligament of the uterus from the uterus to the labium majus in females.

  • It is around 6cm long in the adult and lies parallel and above the inguinal ligament, from the deep inguinal ring to the superficial inguinal ring.

4.2.2 Boundaries of the inguinal canal

  • Roof

    • The arching lower fibres of internal oblique and transversus muscles

  • Anterior wall

    • Aponeurosis of external oblique along entire length

    • Reinforced by internal oblique in lateral third

  • Posterior wall

    • Fascia transversalis along entire length

    • Reinforced by conjoint tendon in medial third (this is the common tendon of insertion of internal oblique and transversus at the pubic crest)

  • Floor

    • The inguinal ligament (rolled under inferior edge of the aponeurosis of external oblique)

    • At the medial end the lacunar ligament contributes to the floor

4.2.3 Openings of the inguinal canal

  • Superficial inguinal ring

    • Triangular-shaped defect in the external oblique aponeurosis

    • Lies above and medial to the pubic tubercle

    • Margins of the superficial ring give rise to the external spermatic fascia

  • Deep inguinal ring

    • Oval opening in the transversalis fascia

    • Lies 1.3cm above the inguinal ligament, midway between ASIS and symphysis pubis

    • Margins of the deep ring give rise to the internal spermatic fascia

4.2.4 Contents of the inguinal canal (and spermatic cord)

  • Vas deferens

  • Arterial structures

    • Testicular artery

    • Artery to the vas deferens

    • Cremasteric artery

  • Venous structures

    • Pampiniform plexus

  • Lymphatic vessels

  • Nerves

    • Genital branch of the genitofemoral nerve

    • Sympathetic nerves (accompany arteries)

    • Ilioinguinal nerve

  • Processus vaginalis

4.3 Testis, epididymis, and spermatic cord

4.3.1 Spermatic cord

  • The covering of the spermatic cord consists of 3 concentric layers, acquired as the processus vaginalis descends through the layers of the abdominal wall:

    • Internal spermatic fascia: From transversalis fascia

    • Cremasteric fascia: From internal oblique and transversus

    • External spermatic fascia: From external oblique

4.3.2 The testes

  • Lie within the scrotum, with the left testis usually slightly higher than the right. See Figure A.4.2.

  • The testis is surrounded by a tough, fibrous capsule called the tunica albuginea.

  • Blood supply is from the testicular artery, which arises from the abdominal aorta and runs in the spermatic cord.

  • The testis is suspended in the scrotum on the spermatic cord. Twisting or torsion of the testis therefore leads to occlusion of the testicular artery and, if not treated, possible necrosis of the testis.

  • Lymph drainage of the testis is via the para-aortic lymph nodes. The coverings of the testis drain to the external iliac nodes. The scrotum drains to the superficial inguinal lymph nodes.

  • Innervation is via sympathetic fibres derived from T6-T10 and afferent fibres that accompany them. Testicular pain is therefore often referred to the abdomen.

Figure A.4.2 Outline diagram of testis

Figure A.4.2
Outline diagram of testis

4.3.3 Descent of the testes

  • The testes begin development in the abdomen from the mesodermal cells of the gonadal ridge covering the embryonic kidney, the mesonephros.

  • Each is embedded in the upper end of the gubernaculum, a thick gelatinous cord of mesenchyme.

  • The gubernaculum extends downwards through the region that will become the inguinal canal and on to the genital swelling that will become the scrotum or labium majus.

  • The gubernaculum swells and draws the testis down towards the developing scrotum, along with a diverticulum of peritoneum called the processus vaginalis.

  • The testis drags behind it the vas deferens, which develops from the mesonephric duct, along with its accompanying blood vessels and lymphatics.

  • The coverings of the cord form around these structures, resulting in the 3 concentric layers of fascia described above.

  • The gubernaculum ends up as a remnant in the scrotum and the vas passes down through the inguinal canal.

  • In the female the ovary only descends to the pelvis, so the inguinal canal contains only the remnants of the gubernaculum.

  • The processus vaginalis pinches off, forming the tunica vaginalis of the testis.

  • This embryological pathway explains the structure and content of the inguinal canal and spermatic cord.

4.3.4 Vas deferens

  • The vas deferens is a thick-walled tube, approximately 18cm long.

  • It allows the transport of mature sperm from the epididymis to the ejaculatory duct and urethra.

  • It arises from the tail of the epididymis and runs upwards through the inguinal canal. It leaves via the deep inguinal ring and passes around the inferior epigastric artery. It then passes along the lateral wall of the pelvis, downwards and backwards, and crosses the ureter at the level of the ischial spine.

  • It continues medially and downwards along the posterior surface of the bladder and opens out to form an ampulla, which then joins the duct of the seminal vesicle, forming the ejaculatory duct.

  • The ejaculatory ducts pierce the posterior surface of the prostate and open into the prostatic portion of the urethra, where the seminal fluid and sperm are drained.

4.4 Topography of the abdominal cavity

  • Structures within the abdomen can be divided up into intraperitoneal and retroperitoneal structures.

  • Retroperitoneal structures lie behind the peritoneum, whilst intraperitoneal structures lie within the peritoneum.

  • Intraperitoneal structures are suspended within the peritoneal cavity by 3 different types of tissues.

  • A mesentery is a 2-layered fold of peritoneum that connects parts of the intestine to the posterior abdominal wall. An example is the mesentery of the small intestine.

  • Omenta are 2-layered folds of peritoneum that connect the stomach to other viscera, for example the lesser omentum connects the lesser curvature of the stomach to the liver.

  • Peritoneal ligaments are 2-layered folds of peritoneum connecting solid viscera to the abdominal walls, for example the falciform ligament connects the liver to the diaphragm and anterior abdominal wall.

  • The position of an organ within the abdomen, whether it is retroperitoneal or intraperitoneal, whether it is suspended, and whether it is a solid or hollow viscus, all have an impact on that organ's susceptibility to different types of injury.

  • Compressive forces from direct blows or from external compression against a fixed object (e.g. seatbelt pressing against the spinal column) commonly cause tears and bleeding of solid organs. These forces may also cause deformity of hollow organs, resulting in raised intraluminal pressure and rupture of the viscus.

  • Deceleration forces cause stretching and linear shearing between relatively fixed and free objects. These longitudinal shearing forces tend to rupture supporting structures at the junction between free and fixed segments.

  • Common injuries resulting from this mechanism include liver injuries, where the liver is attached by the ligamentum teres, and bowel injuries at their mesenteric attachments.

  • Intraperitoneal organs

    • Stomach

    • Liver

    • Gallbladder

    • Spleen

    • Jejunum

    • Ileum

    • Transverse colon

    • Sigmoid colon

    • Uterus

    • Ovaries

  • Retroperitoneal organs

    • Kidneys

    • Adrenal glands

    • Aorta

    • Inferior vena cava

    • Urinary bladder

    • Prostate

    • Vagina

    • Rectum

    • Pancreas (except for tail)

    • Duodenum (2nd and 3rd portions)

    • Ascending colon

    • Descending colon

4.5 Peritoneum

  • The peritoneum is a thin, serous membrane lining the pelvic and abdominal cavities and covering the viscera of the abdomen and pelvis.

  • It has 2 layers:

    • Parietal peritoneum

      • Lines walls of abdominal and pelvic cavities

      • Sensitive to pain, temperature, touch, and pressure

      • Abdominal section supplied by lower 6 thoracic and 1st lumbar nerves

      • Diaphragmatic section supplied by phrenic nerves and lower 6 thoracic nerves

      • Pelvic section supplied by obturator nerve

    • Visceral peritoneum

      • Covers the organs

      • Sensitive only to stretch and tearing

      • Supplied by autonomic afferent nerves that supply viscera or travel in mesentery

    • Peritoneal fluid

      • Between layers of peritoneum

      • Lubricates and facilitates free movement

4.5.1 Functions of the peritoneum

  • Allows free movement of the viscera

  • Suspends the viscera within the abdominal cavity

  • Transmits nerves, blood vessel, and lymphatics to viscera

  • Leucocytes in peritoneal fluid absorb contaminants

  • Seals areas of infection

  • Stores fat

4.5.2 Peritoneal compartments

  • The peritoneum is divided into 3 sections:

    • Supracolic

    • Infracolic

    • Pelvic

  • The division between the supracolic and infracolic compartments is the transverse mesocolon. This attaches along the posterior abdominal wall from the lower border of the pancreas and extends to the right over the duodenum to the right kidney at the right colic (hepatic) flexure. On the left the attachment is over the lower part of the left kidney, at the left colic (splenic) flexure.

  • Infracolic compartment

    • The infracolic compartment is further divided into right and left infracolic compartments by the root of the mesentery, which begins on the left at the duodenojejunal junction and runs down and to the right at a 45° angle to the right iliac fossa.

    • The infracolic compartment contains small intestine and the ascending and descending colon.

  • The sigmoid mesocolon

    • An inverted V-shaped fold of peritoneum.

    • It begins on the medial side of the left psoas major and runs upwards and backwards to its apex, overlying the bifurcation of the left common iliac vessels and left ureter.

    • It then bends downwards to end at the level of the 3rd sacral vertebra in the median plane.

  • Supracolic compartment

    • This compartment contains the stomach, liver, and spleen.

  • Greater omentum

    • Connects the greater curvature of the stomach to the transverse colon.

    • It hangs down in front of the coils of small intestine, like an apron, and then folds back on itself to attach to the transverse colon.

4.6 Gastrointestinal tract

4.6.1Abdominal oesophagus

See Table A.4.1 for details relating to the oesophagus.

Table A.4.1 Oesophageal relations

Relations: Posterior

Pierces diaphragm at T10

Left crus of diaphragm

Right vagus nerve

Left lobe of liver

Anterior

Covered with peritoneum

Left vagus nerve

Points of constriction

Where oesophagus passes through diaphragm, 41cm from incisor teeth

Nerve supply

Vagus plexuses

Oesophageal plexus

Blood supply

Branches from left gastric artery

Venous drainage

Left gastric vein (tributary of portal vein)

4.6.2 Prevention of reflux

  • There is no anatomical sphincter at the lower end of the oesophagus. There is, however, a circular layer of muscle that acts as a physiological sphincter. Contraction of this sphincter under vagal control prevents regurgitation of stomach contents. Contraction is augmented by hormonal control by secretin, glucagons, and cholecystokinin.

  • Fibres of right crus of diaphragm help prevent reflux.

  • Muscularis mucosa has mucosal flaps that help to prevent reflux.

4.6.3 Stomach

  • The stomach is almost J-shaped with an anterior and posterior surface and a greater and lesser curvature.

  • The lesser curvature is attached to the lesser omentum.

  • The greater curvature is attached to the greater omentum (to the left this is continuous with the gastrosplenic ligament).

  • It has 2 openings, the cardiac and pyloric openings.

4.6.4 Structure of the stomach

See Figure A.4.3.

  • Cardia:

    • Lies to the left of the midline, at approximately T10

    • Cardiac opening between oesophagus and cardia

    • Most fixed portion of stomach

  • Fundus:

    • Dome shaped

    • Projects above the cardia and is in contact with the diaphragm

    • Usually full of gas

  • Body:

    • Largest section of stomach

    • Extends from cardiac orifice to the incisura angularis, a constant notch at the lower end of the lesser curvature

    • In the erect position may reach the level of the umbilicus at T10

  • Pylorus:

    • Tubular-like portion of the stomach

    • Pyloric antrum links pylorus and the body

    • Thick muscular wall called the pyloric sphincter - this is a true anatomical sphincter, unlike the cardiac sphincter

    • The pyloric opening lies to right of midline at level of L1 when in recumbent position

    • Pyloric sphincter controls rate of passage of stomach contents into duodenum

4.6.5 Relations of the stomach (from left to right)

  • Anterior:

    • Diaphragm

    • Anterior abdominal wall

    • Left lobe of the liver

  • Posterior:

    • Lesser sac

    • Diaphragm

    • Aorta

    • Pancreas

    • Spleen

    • Left kidney

    • Left adrenal gland

    • Transverse mesocolon

    • Transverse colon

4.6.6 Blood supply of the stomach

  • Left gastric artery:

    • Derived from the coeliac axis

    • Runs along lesser curvature

    • Anastomoses with right gastric artery

  • Right gastric artery:

    • Derived from hepatic artery

  • Right gastroepiploic artery:

    • Arises from gastroduodenal branch of hepatic artery

    • Runs along greater curvature

    • Anastomoses with left gastroepiploic artery

  • Left gastroepiploic artery:

    • Arises from splenic artery

    • Runs along greater curvature

    • Anastomoses with right gastroepiploic artery

  • Short gastric arteries:

    • Arise from splenic artery

    • Supply fundus

  • Venous drainage:

    • Veins are named in reflection of the arteries and drain into portal system

  • Lymphatics:

    • Area supplied by splenic artery drains to lymph nodes at hilum of spleen, then to those along the pancreas, and finally to the coeliac nodes

    • Cardia drains along left gastric artery to coeliac nodes

    • Remainder drains to coeliac nodes via hepatic artery and gastroepiploic vessels

    • Retrograde spread may occur into hepatic nodes at porta hepatis

4.6.7 Nerve supply

  • Vagus nerves supply the stomach.

  • Anterior and posterior vagi enter abdomen via oesophageal opening in diaphragm and supply parasympathetic fibres.

  • Anterior nerve (from left vagus) lies in contact with anterior oesophagus, is close to the wall of the stomach, and supplies the anterior aspect.

  • Branches:

    • Gastric branches

    • Hepatic branches

    • Branches to pyloric antrum

  • Posterior nerve (from right vagus) is further away in loose connective tissue and supplies the posterior aspect.

  • Branches:

    • Coeliac branch

    • Numerous branches to posterior stomach

  • Sympathetic nerve supply is via coeliac plexus.

4.6.8 Duodenum

  • The duodenum is the first part of the small intestine. It runs from the pylorus of the stomach to the jejunum.

  • It is situated in epigastric and umbilical region of the abdomen and divided into 4 parts.

  • It is a C-shaped tube, approximately 25cm long, and receives openings of bile ducts and pancreatic ducts. It is largely retroperitoneal.

4.6.9 First part of duodenum

  • First 5cm is intraperitoneal, the remainder is retroperitoneal

  • Begins at pylorus

  • Runs upwards and backwards on the right side of L1

  • Lies on transpyloric plane

  • Relations:

    • Anterior:

      • Right lobe of liver

      • Gallbladder

    • Posterior:

      • Lesser sac

      • Gastroduodenal artery

      • Bile duct

      • Portal vein

      • IVC

    • Superior:

      • Entrance to lesser sac

    • Inferior:

      • Head of pancreas

4.6.10 Second part of duodenum

  • 8cm long

  • Runs vertically downwards anterior to right kidney

  • Lies to right of L2 and L3

  • Halfway down medial border bile ducts and pancreatic ducts enter medial wall where they unite to form major duodenal papilla

  • Relations:

    • Anterior:

      • Fundus of gallbladder

      • Right lobe of liver

      • Transverse colon

      • Small intestine

    • Posterior:

      • Hilum of right kidney

      • Right ureter

    • Laterally:

      • Ascending colon

      • Right colic flexure

      • Right lobe of liver

    • Medially:

      • Head of pancreas

      • Bile duct

      • Main pancreatic ducts

4.6.11 Third part of duodenum

  • 8cm long

  • Runs horizontally to left

  • Crosses L3 and follows lower margin of head of pancreas

  • Relations:

    • Anterior:

      • Root of mesentery of small intestine

      • Coils of jejunum

    • Posterior:

      • Right ureter

      • Right psoas

      • IVC

      • Aorta

    • Superior:

      • Head of pancreas

    • Inferior:

      • Coils of jejunum

4.6.12 Fourth part of duodenum

  • 5cm long

  • Runs upwards and left to the duodenal flexure (held in place by ligament of Treitz)

  • Attached to right crus of diaphragm

  • Relations:

    • Anterior:

      • Beginning of root of mesentery

      • Coils of jejunum

    • Posterior:

      • Left margin of aorta

      • Medial border of left psoas

4.6.13 Blood supply of duodenum

  • Upper half supplied by superior pancreaticoduodenal artery (from gastroduodenal).

  • Lower half supplied by inferior pancreaticoduodenal artery (from superior mesenteric artery).

4.6.14 Jejunum and ileum

  • Together measure approximately 6 metres in length

  • Gradual change from one to the other

  • Jejunum begins at duodenojejunal flexure

  • Ileum ends at ileocaecal junction

  • Blood supply:

    • Supplied by branches from the superior mesenteric artery, which run in the mesentery to supply the gut

    • Anastomose to form a series of arcades

    • Lowest part of ileum supplied by ileocolic artery

  • Nerve supply:

    • Supplied by vagal sympathetic and parasympathetic nerves from the superior mesenteric plexus

    • Pain fibres pass to the spinal cord via the splanchnic nerves and pain from this region is referred to the dermatomes supplied by T9-T11. Pain is therefore felt in the umbilical region first and only later localizes to the inguinal region (as seen when a coil of small intestine incarcerates within a hernia and only localizes once it becomes inflamed)

4.6.15 Traumatic injury to jejunum and ileum

  • Jejunum and ileum are susceptible to trauma due to their being freely mobile but attached to the posterior abdominal wall by the mesentery of the small intestine.

  • They can also be compressed against the vertebral column and the sacral margin, again making them susceptible to blunt trauma.

4.6.16 Meckel's diverticulum

  • A diverticulum can occur in the ileum, which can be clinically significant. Classically said to occur in 2% of the population, 2 feet (60cm) from the caecum, and 2 inches (5cm) long.

  • True diverticulum and contains all 3 layers of intestinal wall. Most common congenital abnormality of small bowel.

  • May be attached to umbilicus by a fibrous cord, or be adherent to it. May contain ectopic gastric or pancreatic mucosa.

  • Can present clinically in a number of ways:

    • Haemorrhage or perforation (due to gastric mucosa)

    • Volvulus leading to obstruction

    • Intussusception with Meckel's as apex

    • Meckel's diverticulitis (mimics appendicitis)

4.6.17 Caecum

  • Part of large intestine in right iliac fossa.

  • It is guarded by ileocaecal valve to prevent reflux of material into ileum.

  • It is a blind-ended pouch, 6cm in length.

  • The appendix is attached to caecum.

  • Relations:

    • Anterior:

      • Coils of small intestine

      • Part of greater omentum

      • Anterior abdominal wall of RIF

    • Posterior:

      • Psoas and iliacus muscles

      • Lateral cutaneous nerve of thigh

      • (Due to these posterior relations localized infection may cause pain when psoas is stretched or on movement of the hip)

4.6.18 Appendix

  • The position of the appendix varies. Common sites are:

    • Retrocaecal

      • 62% of population

      • Poorly localizing signs

      • Proximity to ureter - white cells in urine

      • May lie between caecum and psoas (pain on psoas stretch)

    • Pelvic

      • 34% of population

      • Increased nausea and vomiting

      • May cause pain on hip rotation

    • Pre-ileal

      • 1%

    • Post-ileal

      • 0.5%

      • Poorly localized pain

    • Rare sites

      • RUQ appendix

      • Situs inversus LIF appendix

      • Long appendix - tip can be anywhere!

  • Classically pain of appendicitis felt at McBurney's point: Point one-third of the way from ASIS to the umbilicus.

4.6.19 Colon

  • Ascending colon

    • Lies in right lower quadrant and is approximately 15cm long

    • Extends upwards from caecum to inferior surface of right lobe of liver

    • Here it turns to the left, forming the right colic flexure (hepatic flexure), and becomes continuous with the transverse colon

    • Rarely has a mesentery

    • Usually retroperitoneal

  • Relations:

    • Anterior:

      • Coils of small intestine

      • Greater omentum

      • Anterior abdominal wall

    • Posterior:

      • Iliacus

      • Iliac crest

      • Quadratus lumborum

      • Origin of transversus abdominis

      • Lower pole of right kidney

      • Iliohypogastric and ilioinguinal nerves

  • Transverse colon

    • Extends across the abdomen in the umbilical region and is approximately 38cm long

    • Intraperitoneal

    • Begins at right colic flexure and hangs downwards, supported by transverse mesocolon, before ascending to the left colic flexure (splenic flexure)

    • Attached to pancreas via mesocolon

    • Left colic flexure is higher than the right and suspended from diaphragm by the phrenicocolic ligament

    • Position of the transverse colon is variable due to the length of the mesocolon

    • Mesentery attached to superior border, greater omentum attached to inferior border

  • Relations:

    • Anterior:

      • Greater omentum

      • Anterior abdominal wall

    • Posterior:

      • 2nd part of duodenum

      • Head of pancreas

      • Coils of small intestine

  • Descending colon

    • Approximately 25cm long, lies in left upper and lower quadrants

    • Extends from left colic flexure (splenic flexure) to pelvic brim, where it becomes continuous with the sigmoid colon

    • Rarely has a mesentery

    • Usually retroperitoneal

  • Relations:

    • Anterior:

      • Coils of small intestine

      • Greater omentum

      • Anterior abdominal wall

    • Posterior:

      • Lateral border of left kidney

      • Origin of transversus abdominis muscle

      • Quadratus lumborum

      • Iliac crest

      • Iliacus

      • Left psoas

      • Iliohypogastric nerve

      • Ilioinguinal nerve

      • Lateral cutaneous nerve of the thigh

      • Femoral nerve

  • Sigmoid colon

    • 25-40cm long, continuation of descending colon

    • Becomes continuous with rectum in front of S3

    • Attached to posterior abdominal wall by sigmoid mesocolon

    • Sigmoid mesocolon hangs down from an inverted V-shaped root overlying the bifurcation of the common iliac artery

  • Relations:

    • Anterior:

      • In male: Urinary bladder

      • In female: Posterior surface uterus; Upper part of vagina

    • Posterior:

      • Rectum

      • Sacrum

4.6.20 Blood supply of the large bowel

  • Superior mesenteric artery supplies:

    • Via ileocolic branch:

      • 1st part of ascending colon

      • Caecum

      • Appendix

    • Via right colic branch: Ascending colon

    • Via middle colic branch: Transverse colon

  • Inferior mesenteric artery supplies:

    • Via left colic branch: Descending colon

    • Via sigmoid branches: Sigmoid colon

    • Via superior rectal branch: Rectum

  • Branches of superior and inferior mesenteric arteries anastomose with their neighbours above and below, forming a continuous chain of anastomoses known as the marginal artery (of Drummond).

  • Mesenteric arteries may be occluded by disease of the aorta.

  • Inferior mesenteric artery susceptible to atherosclerotic disease and can result in infarction of the bowel.

  • Marginal artery provides anastomosis between superior and inferior mesenteric arteries, but is not always well developed and is often deficient just proximal to the splenic flexure where the 2 main artery territories meet.

  • Interruption of arterial supply can result in ischaemic colitis.

4.6.21 Nerve supply of the large bowel

  • Pain receptors transmit signals via sympathetic fibres that pass along arteries to the aortic plexus (T10-L2).

  • Main motor fibres for proximal colon, as far as distal transverse colon, come from vagus nerve.

  • Distal large bowel receives motor innervation from sacral nerves.

  • Intramural plexuses in the bowel wall connect with extrinsic nerves.

4.7 Liver and biliary tract

4.7.1 Surface markings of liver

  • Lies under the cover of the lower ribs on the right side.

  • Convex upper surface is moulded to shape of diaphragm and lies below it, rising to the approximate level of the xiphisternal joint.

  • Lower border roughly corresponds to the right costal margin (although at the midline it crosses the epigastrium below the margin).

  • In infants the liver may extend 1 or 2 finger-breadths below the costal margin.

  • In adults a hard, enlarged liver edge may be palpated below the costal margin, most easily on deep inspiration when the diaphragm pushes the liver down.

4.7.2 Lobes of the liver

  • 4 lobes:

    • Right lobe

    • Left lobe

    • Caudate lobe

    • Quadrate lobe

  • The liver is wedge shaped and has an upper diaphragmatic surface and a lower postero-inferior or visceral surface.

  • Diaphragmatic surface:

    • Convex and lies under diaphragm

    • Has superior, posterior, anterior, and right surfaces

    • Covered by peritoneum, which attaches it to the diaphragm

  • Postero-inferior surface:

    • Moulded to shape of adjacent viscera

    • Irregular

    • In contact with:

      • Abdominal oesophagus

      • Stomach

      • Duodenum

      • Right colic flexure

      • Right kidney

      • Right adrenal gland

      • Gallbladder

      • IVC

  • Anterior relations:

    • Diaphragm

    • Right and left costal margins

    • Right and left pleura and inferior lung margins

    • Xiphoid process

    • Anterior abdominal wall

4.7.3 Liver lobules

  • The liver is constructed from smaller building blocks, called liver lobules, and the liver as a whole is surrounded by a fibrous capsule.

  • These lobules each have a central vein (a tributary of the hepatic veins) and between the lobules are spaces called the portal canals.

  • These spaces contain branches of the hepatic artery and portal vein and a bile duct tributary. Together these 3 vessels are known as the portal triad.

  • Arterial and venous supply passes between the liver cells by means of sinusoids and then drains into the central vein.

4.7.4 Ligaments of the liver

  • The main stability of the liver comes from support by the attachment of the hepatic veins to the IVC.

  • The liver ligaments provide additional stability for the liver:

  • Falciform ligament:

    • Double fold of peritoneum

    • Ascends from umbilicus to liver

    • Contains the ligamentum teres in its free margin (remains of umbilical vein)

    • Divides into:

      • Coronary ligament: Formed by right layer

      • Left triangular ligament: Formed by left layer

      • Right triangular ligament: Extremity of coronary ligament

      • (Fibres of coronary ligament are widely spaced leaving a bare area on the liver, devoid of peritoneum)

  • Ligamentum teres:

    • Contains remains of umbilical vein

    • Passes into fissure on visceral surface of liver

    • Joins left branch of portal vein in porta hepatis

  • Ligamentum venosum:

    • Remains of ductus venosum

    • Attached to left branch of portal vein

    • Situated on visceral surface of liver

    • Attached to left branch of portal vein

4.7.5 Blood supply of liver

  • The liver is highly vascular and receives approximately 1.5 litres of blood per minute. 30% of this blood comes from the hepatic artery, a branch of the coeliac artery (oxygenated blood). 70% comes from the portal vein (deoxygenated blood, rich in products of digestion).

  • This blood travels to the central vein of each liver lobule, as described above.

  • Central veins drain into right and left hepatic veins, which open directly into the IVC. Right lobe of liver receives blood mainly from intestine. Left, caudate, and quadrate lobes receive blood mainly from stomach and spleen.

  • This distribution may explain the pattern of metastasis to the liver.

4.7.6 Lymph drainage

  • Liver produces around one-third of body lymph.

  • Lymph vessels leave liver via the porta hepatis.

  • Coeliac and posterior mediastinal lymph nodes are responsible for drainage.

4.7.7 Gallbladder

  • Pear-shaped sac on undersurface of liver.

  • Function is to store bile, and concentrate this by absorbing water.

  • Divided into a fundus, body, and neck.

  • Fundus:

    • Rounded and projects below the liver

  • Body:

    • In contact with visceral surface of liver

    • Directed upwards, backwards, and to the left

  • Neck:

    • Becomes continuous with cystic duct

  • Hartmann's pouch:

    • A dilated area of the gallbladder neck just before the point where it joins the cystic duct

    • Gallstones commonly lodge at this site

  • Relations:

    • Anterior:

      • Anterior abdominal wall

      • Inferior surface of liver

    • Posterior:

      • Transverse colon

      • 1st and 2nd parts of duodenum

  • The posterior relationship of the gallbladder to the duodenum and transverse colon means that gallstones can sometimes erode through into these structures, and may then lead to gallstone ileus.

  • Surface markings: Fundus of gallbladder lies opposite tip of right 9th costal cartilage, where lateral edge of right rectus abdominis crosses costal margin.

4.7.8 Biliary ducts

  • Bile is secreted by the liver, concentrated and stored in the gallbladder, and delivered into the duodenum to assist digestion.

  • Right and left hepatic ducts arise from the right and left lobes of the liver respectively, in the porta hepatis.

  • The right and left hepatic ducts run a short course and then unite to form the common hepatic duct.

  • Common hepatic duct then unites with the cystic duct from the gallbladder to form the common bile duct.

  • Common bile duct is approx 8cm long and is divided into 3 parts:

    • 1st part: Lies in the free margin of the lesser omentum, in front of the portal vein and to the right of the hepatic artery

    • 2nd part: Lies behind the 1st part of the duodenum, to the right of the gastroduodenal artery

    • 3rd part: Lies in a groove on the posterior surface of the head of the pancreas, and comes into contact with main pancreatic duct

  • Common bile duct ends by piercing the medial wall of the 2nd part of the duodenum, approximately halfway down its length.

  • Usually it is joined by the main pancreatic duct, and together they open into the duodenal wall at the ampulla of Vater.

  • The ampulla of Vater opens into the duodenal lumen via the major duodenal papilla and both these structures are surrounded by the sphincter of Oddi.

  • There are normal variants of this arrangement where the pancreatic and common bile ducts pierce the duodenum separately.

4.7.9 Nerve supply of bile ducts

  • Supply is sympathetic and parasympathetic vagal fibres from the coeliac plexus.

  • Biliary colic occurs when the smooth muscle of the gallbladder spasms to try and dislodge a gallstone. Afferent fibres ascend through the coeliac plexus and greater splanchnic nerves to the thoracic nerves, and referred pain is felt in the right upper quadrant or epigastrium (T7, T8, T9).

4.7.10 Portal vein

  • Porta hepatis is the hilum of the liver.

  • Contains:

    • Left and right hepatic duct, forming the common hepatic duct

    • Hepatic artery

    • Portal vein

  • Portal vein:

    • Formed by superior mesenteric and splenic veins

    • Normal portal pressure 5-10mmHg above IVC pressure

    • Portal hypertension can occur in cirrhotic and other disease processes of the liver, which cause obstruction in the portal tree

  • Portal hypertension causes:

    • Development of collateral portosystemic circulation

    • Splenomegaly

    • Hepatic failure

    • Ascites

  • There are 4 main areas of portosystemic anastomosis developed in portal obstruction:

    • Between left gastric vein and the oesophageal veins - leads to oesophageal varices

    • Between the obliterated umbilical vein and superior and inferior epigastric veins - leads to Caput Medusa

    • Between the superior and inferior rectal veins - leads to haemorrhoids

    • Retroperitoneal and diaphragmatic anastomoses - leads to potential intraoperative problems

4.8 Pancreas

  • The pancreas is a gland with both exocrine and endocrine functions.

  • Exocrine: Pancreatic juice excreted into the duodenum, containing:

    • Enzymes

      • Amylase

      • Lipase

      • Trypsinogen and chymotrypsinogen

      • Peptidases

    • Bicarbonate ions

    • Sodium ions

    • Water

  • Endocrine:

    • Insulin from ß-cells in islets of Langerhans

    • Glucagon from α‎-cells in islets of Langerhans

    • Somatostatin from δ‎-cells in islets of Langerhans

    • Pancreatic polypeptide from F cells

  • Anatomically the pancreas is divided into a head, neck, body, and tail.

    • Head:

      • Disc shaped

      • Lies in C-shaped concavity of duodenum

      • Has an uncinate process, which lies behind the superior mesenteric vessels

    • Neck:

      • Constricted section of pancreas

      • Lies in front of portal vein and origin of superior mesenteric artery

    • Body:

      • Passes left and upwards across the midline, forming part of stomach bed

    • Tail:

      • Lies within the lienorenal ligament and is in contact with the hilum of the spleen

4.8.1 Relations of the pancreas

  • Anterior (from R to L):

    • Transverse colon

    • Transverse mesocolon

    • Lesser sac

    • Stomach

  • Posterior (From R to L):

    • Bile duct

    • Portal vein

    • Splenic vein

    • IVC

    • Aorta

    • Superior mesenteric artery

    • Left psoas muscle

    • Left adrenal gland

    • Hilum of spleen

4.8.2 Surface marking of pancreas

  • Lies across the transpyloric plane, with the head below and to the right, the neck on the plane, and the body and tail above and to the left.

  • Transpyloric plane:

    • Horizontal plane through the tips of the 9th costal cartilages, at the point where the lateral margin of rectus abdominis crosses the costal margin

    • Lies at level of L1

    • Passes through:

      • Neck of pancreas

      • Pylorus of stomach

      • Duodenojejunal junction

      • Hila of kidneys

4.8.3 Blood supply of pancreas

  • Supply from the splenic and pancreaticoduodenal arteries.

  • Corresponding veins drain to the portal system.

4.8.4 Lymph drainage

  • Lymph drains to nodes situated along the arteries and then to coeliac and superior mesenteric lymph nodes.

4.8.5 Innervation

  • Innervation is from sympathetic and parasympathetic vagal nerve fibres.

  • Pain is referred to T6-T10 dermatomes.

4.9 Spleen

  • Largest lymphoid organ.

  • Various functions:

    • Filtering blood - Macrophages remove cellular and non-cellular material, e.g. bacteria, defective red cells, and platelets

    • Haemopoiesis - In foetus and if demand exceeds marrow capacity

    • Immune - Antigen recognition

    • Opsonization - Antibody synthesis

    • Protection from infection - Splenectomy leaves patients more prone to infection (from capsulated organisms)

    • Iron reutilization

4.9.1 Surface markings of the spleen

  • Situated in left upper quadrant, lying under cover of 9th-11th ribs.

  • Long axis corresponds to the 10th rib.

  • Does not normally project forwards in front of midaxillary line.

  • Lower pole may be palpated in children.

  • Splenic enlargement:

    • A pathologically enlarged spleen extends downwards and medially

    • As it projects below the left costal margin its anterior border can be palpated through the anterior abdominal wall

4.10 Posterior abdominal wall

4.10.1 Muscles of the posterior abdominal wall

  • Psoas

    • Origin: Transverse processes, bodies, and intervertebral discs of T12, L1-L5

    • Insertion: Lesser trochanter of femur

    • Innervation: Lumbar plexus

    • Action:

      • Flexes thigh on trunk

      • If thigh is fixed, flexes trunk on thigh (e.g. sitting up)

  • Quadratus lumborum

    • Origin:

      • Iliolumbar ligament

      • Iliac crest

      • Transverse processes of lower lumbar vertebrae

    • Insertion: 12th rib

    • Innervation: Lumbar plexus

    • Action:

      • Fixes 12th rib during inspiration

      • Depresses 12th rib during forced expiration

      • Laterally flexes vertebral column (same side)

  • Iliacus

    • Origin: Iliac fossa

    • Insertion: Lesser trochanter of femur

    • Innervation: Femoral nerve

    • Action:

      • Flexes thigh on trunk

      • If thigh is fixed, flexes trunk on thigh (e.g. sitting up)

  • NB Iliacus and psoas are often grouped together and referred to as iliopsoas.

  • Each of the 3 muscles is covered with a layer of thick fascia, derived from the lumbar fascia.

4.10.2 Vessels of posterior abdominal wall

  • Aorta

    • Surface markings:

      • Lies in the midline of the abdomen and bifurcates into the right and left common iliac arteries at the level of L4

      • Runs behind peritoneum on anterior surfaces of lumbar vertebrae

      • Enters abdomen through aortic opening in diaphragm at T12

    • Branches:

      • 3 anterior visceral branches: Coeliac; Superior mesenteric; Inferior mesenteric

      • 3 lateral branches: Suprarenal; Renal; Testicular/ovarian

      • 5 lateral abdominal wall branches: Inferior phrenic; 4 lumbar

      • 3 terminal branches: 2 common iliac; Median sacral

  • IVC

    • Surface markings:

      • Lies on the right side of the aorta, formed by the union of the common iliac veins behind the right common iliac artery at L5

      • Pierces central tendon of diaphragm at T8

    • Tributaries:

      • 2 anterior visceral tributaries: Hepatic veins

      • 3 lateral visceral tributaries: Right suprarenal vein; Renal vein; Right testicular/ovarian vein

      • 5 lateral abdominal wall tributaries: Inferior phrenic vein; 4 lumbar veins

      • 3 veins of origin: 2 common iliacs; 1 median sacral

4.10.3 Lumbar plexus

See Table A.4.2 and Figure A.4.4.

Table A.4.2 Nerves of the lumbar plexus

Branch

Nerve roots

Structures supplied

Iliohypogastric nerve

L1

External oblique

Internal oblique

Transversus abdominis

Skin of lower anterior abdominal wall and buttock

Ilioinguinal nerve

L1

External oblique

Internal oblique

Transversus abdominis

Skin of upper medial aspect of thigh

Root of penis/scrotum

Mons pubis/labia majorum

Lateral cutaneous nerve of the thigh

L2/L3

Skin of anterior and lateral thigh

Genitofemoral nerve

L1/L2

Cremaster muscle

Cremasteric reflex

Skin of anterior surface of thigh

Femoral nerve

L2/L3/L4

Iliacus

Pectineus

Sartorius

Quadriceps femoris

Skin of anterior surface of thigh

Skin of medial side of leg and foot

Branches to hip and knee joints

Obturator nerve

L2/L3/L4

Gracilis

Adductor brevis

Adductor longus

Obturator externus

Pectineus

Adductor portion of adductor magnus

Skin of medial surface of thigh

Branches to hip and knee joints

Segmental branches

Quadratus lumborum and psoas

4.10.4 Lumbar sympathetic trunk

  • Continuous with thoracic and pelvic sympathetic trunks.

  • Runs down along medial border of psoas on bodies of lumbar vertebrae.

  • Enters abdomen behind medial arcuate ligament and runs down to pelvis by passing behind common iliac vessels.

  • Right trunk lies behind right border of IVC.

  • Left trunk lies close to left border of aorta.

  • Possesses 4/5 segmentally arranged ganglia, with the first 2 often fused together.

4.10.5 Lymph vessels of the posterior abdominal wall

  • Lymph nodes are closely related to the aorta.

  • Preaortic lymph nodes:

    • Coeliac nodes

    • Superior mesenteric nodes

    • Inferior mesenteric nodes

  • Drain lymph from:

    • The gastrointestinal tract from lower third of oesophagus to halfway down anal canal

    • Spleen

    • Pancreas

    • Gallbladder

    • Greater part of liver

  • Para-aortic lymph nodes:

    • Drain lymph from:

      • Kidneys

      • Adrenals

      • Testes/ovaries

      • Uterine tubes

      • Fundus of uterus

      • Deep lymph of abdominal wall

      • Common iliac nodes

4.11 Kidneys, ureters, and bladder

  • Each kidney is approximately 11cm long, 6cm wide, and 3cm thick.

  • Each has:

    • An anterior and posterior surface

    • An upper and lower pole

    • A hilum (situated at the middle of the medial border)

  • The renal vein, renal artery, and renal pelvis enter and leave at the level of the hilum in that order, moving anterior to posterior (although the exact anatomy of the contents of the hilum is variable). See Figure A.4.5.

  • The kidneys are retroperitoneal and lie (from medial to lateral) on psoas, quadratus lumborum, and the origin of transversus abdominis.

  • The upper border of the kidney lies directly on the diaphragm. They are largely under the cover of the costal margin. The right kidney is slightly lower than the left, due to the large right lobe of the liver. With contraction of the diaphragm during normal respiration the kidneys move downwards in vertical direction by around 2.5cm.

  • In an individual with poorly developed abdominal musculature, the right kidney may be palpated in the right lumbar region at the end of deep inspiration. The left kidney is not normally palpable.

  • On the anterior abdominal wall the hilum of the kidney lies on the transpyloric plane (see above) approximately 3 finger-breadths from the midline.

  • On the back the kidneys extend from the spine of T12 to the spine of L3 and the hila are at L1.

4.11.1 Relations of the right kidney

  • Anterior:

    • Adrenal gland

    • Liver

    • 2nd part of duodenum

    • Right colic flexure

  • Posterior:

    • Diaphragm

    • Costodiaphragmatic recess of pleura

    • 12th rib

    • Psoas, quadratus lumborum, and transversus abdominis

    • Subcostal, iliohypogastric, and ilioinguinal nerves

4.11.2 Relations of the left kidney

  • Anterior:

    • Adrenal gland

    • Spleen

    • Stomach

    • Pancreas

    • Left colic flexure

    • Coils of jejunum

  • Posterior:

    • Diaphragm

    • Costodiaphragmatic recess of the pleura

    • 11th and 12th ribs

    • Psoas, quadratus lumborum, and transversus abdominis

    • Subcostal, iliohypogastric, and ilioinguinal nerves

4.11.3 Coverings of the kidney

  • Kidneys have 4 layers of coverings (from deep to superficial):

    • Fibrous capsule

    • Perirenal fat

    • Renal fascia

    • Pararenal fat

  • Renal fascia

    • Tough areolar membrane that splits to enclose the kidney and perinephric fat

    • Condensation of connective tissue, encloses kidneys and adrenals

    • Continuous laterally with transversalis fascia

    • Rupture of an abscess in the kidney into the perinephric tissue results in pus being trapped within the renal fascia

    • This perinephric abscess is contained within the fascia, and points posteriorly above the iliac crest. A large mass may form, with tenderness over the affected kidney. Onset is slow due to the containment of pus within the renal fascia.

4.11.4 Blood supply of kidney

  • The renal arteries arise from the aorta at the level of L2. Main arteries divide into posterior and anterior branches. May be a separate upper pole vessel in some patients.

  • Each renal artery divides into approximately 5 segmental arteries that enter the kidney at the hilum, which then supply different sections of the kidney.

  • These segmental arteries subdivide into lobar arteries and then divide again into interlobar arteries. The interlobar arteries then give off arcuate arteries, which are arranged like umbrella spokes between the cortex and the medulla.

  • Renal arteries are end arteries and occlusion results in infarction of the kidney.

4.11.5 Lymphatic drainage

  • The lymph vessels follow the renal artery and drain into the para-aortic and lumbar lymph nodes.

4.11.6 Renal colic

  • The nerve supply to the kidney is via coeliac plexus, sympathetic trunk, and spinal nerves.

  • The pain from renal calculi is colicky in nature and typically radiates from the ‘loin to groin’. The renal pelvis and ureter have afferent nerves that run to T11-L2.

  • The severe colicky pain occurs when strong peristaltic waves try to push the calculi along the ureter and the pain is referred to the areas supplied by T11-L2: the loin, groin, and flank. If the stone passes into the lower ureter, the pain may be felt in the scrotum or testis in the male, or in the labium majora in the female.

  • In addition, pain can sometimes be felt in the front of the thigh, as pain can be referred along the femoral branch of the genitofemoral nerve.

4.11.7 Structure of the kidney

  • The kidney is divided into the dark brown outer cortex and a lighter brown inner medulla.

  • The medulla is made up of approximately 12 renal pyramids, with the base facing the cortex and the apex (renal papilla) facing medially.

  • The pyramids indent approximately 12 minor calyces, which unite to form 2 or 3 major calyces, and in turn these join to form the renal pelvis.

  • The renal pelvis may be intra- or extra-renal and is continuous with the upper ureter, which usually lies behind the renal artery in the hilum.

4.11.8 The nephron

  • The glomerulus is formed by a group of capillaries, supplied by an afferent arteriole, which invaginates into the Bowman's capsule. It is drained by the efferent arteriole. See Figure A.4.6.

  • The glomerular membrane allows passage of small neutral substances into the Bowman's capsule.

  • The loop of Henle allows water, sodium, and chloride to be reabsorbed in the descending limb, whilst the ascending limb is impermeable to water but allows re-absorption of sodium and chloride ions.

  • This acts as a counter-current multiplier, with the cortex being isotonic and the medulla hypotonic, which allows the formation of dilute urine.

4.11.9 Ureters

  • The ureters are muscular tubes extending from the kidneys to the bladder. Urine is propelled along the ureters by peristaltic action.

  • The ureter emerges from the hilum of the kidney and runs retroperitoneally downwards on the psoas muscle, along the route of the tips of the transverse processes of the lumbar vertebrae.

    • Enters pelvis by crossing the bifurcation of the common iliac artery, in front of the sacroiliac joint.

    • Then runs down lateral wall of the pelvis to the level of the ischial spine, where it turns medially to enter the bladder at its lateral angle.

  • This path can be traced on x-rays, and calculi are sometimes visible along the route of the ureter in plain films. Contrast examination, e.g. IVU, can also be used to visualize the ureters.

  • Due to the proximity of the right ureter to the appendix, it can be involved in adhesions from a perforated appendix and is at risk during surgery for appendicitis.

4.11.10 Urinary bladder

  • The urinary bladder stores urine. It has a capacity of around 500ml in adults.

  • In adults it lies behind the symphysis pubis and is entirely within the pelvis when empty.

  • When full its superior border rises up to the hypogastric region, and in children the superior aspect also lies intrabdominally. This makes the bladder more prone to injury from abdominal trauma.

  • The empty bladder is pyramidal in shape. See Figure A.4.7.

  • Apex:

    • Points anteriorly and lies behind the upper margin of the symphysis pubis

    • Attached to the umbilicus via the urachus (median umbilical ligament)

  • Base:

    • Posterior surface

    • Faces posteriorly and is triangular in shape

    • Superolateral angles are joined by ureters and the inferior angle gives rise to the urethra

    • Upper part is covered with peritoneum, forming rectovesical pouch

  • Superior surface:

    • Completely covered with peritoneum

    • As bladder fills the superior surface becomes ovoid and bulges into abdomen

  • Inferolateral surface:

    • Lies behind the pubic bones

  • Neck:

    • Neck of the bladder lies inferiorly

  • Trigone:

    • The trigone of the bladder is an area of mucous membrane covering the internal surface of the base of the bladder

    • It lies between the two ureteral orifices superiorly and the urethral orifice inferiorly

  • Posterior relations of the bladder:

    • Male:

      • Seminal vesicles

      • Vas deferens

      • Ureters

      • Rectum

    • Female:

      • Uterus

      • Vagina

4.11.11 Nerve supply to bladder

  • From the hypogastric plexus.

  • Sympathetic postganglionic neurons (L1, L2) are vasomotor to the vessels of the bladder and motor to the trigone region and smooth muscle of the urethra at the internal urethral orifice.

  • Parasympathetic fibres arise as splanchnic nerves from S2-S4 and pass through hypogastric plexus to reach bladder wall.

  • Afferent sensory fibres reach the CNS via the splanchnic nerves, though some travel via the hypogastric plexus with the sympathetics to L1, L2.

  • Sympathetic nerves inhibit contraction of the detrusor muscle and stimulate contraction of the bladder sphincter.

  • Parasympathetic nerves stimulate contraction of the detrusor muscle and inhibit the action of the bladder sphincter.

4.11.12 Control of micturition

  • Reflex action - also under control of higher centres of brain (once toilet-trained).

  • Reflex initiated when stretch receptors detect bladder volume >300ml.

  • Afferent impulses pass up pelvic splanchnic nerves to S2-4 and also via hypogastric plexus to L1, L2 - conscious desire to micturate.

  • Efferent parasympathetic impulses leave cord at S2-4 and travel via pelvic splanchnic nerves and hypogastric plexuses to the bladder wall.

  • Smooth muscle of the bladder wall (detrusor) is made to contract and the bladder sphincter is made to relax.

  • The urethral sphincter also receives efferent impulses from S2-4 via the pudendal nerve and also relaxes.

  • Once urine enters the urethra, additional afferent impulses reinforce this reflex action, and contraction of abdominal muscles assists micturition.

  • In continent individuals this reflex is inhibited by the cerebral cortex until it is appropriate to micturate.

  • Inhibitory pathways in the corticospinal tracts pass to S2-4 and cause contraction of urinary sphincters, to allow voluntary control of micturition.

4.11.13 Spinal injury and bladder control

  • Initial ‘spinal shock phase’

    • Atonic bladder

      • Bladder wall relaxed

      • Bladder sphincter contracted

      • Urethral sphincter relaxed

      • Bladder becomes distended, then overflows

      • Lasts a few days to weeks

  • Cord lesion above S2-4

    • Automatic reflex

      • Bladder fills and empties as a reflex activity every 1-4 hours

  • Cord lesion destroying S2-4

    • Autonomous

      • No reflex control

      • Bladder fills to capacity and overflows

      • Constant dribbling

4.12 Pelvis

4.12.1 The pelvic cavity

  • The pelvis is made from a pair of inominate bones, forming the lateral and anterior walls, and the sacrum and coccyx, forming the posterior wall. See Figure A.4.8.

  • Inominate bones formed from 3 fused bones:

    • Ilium

    • Ischium

    • Pubis

  • Sacroiliac joints are part synovial, part fibrocartilaginous and are reinforced by the ligaments of the pelvis:

    • Sacrotuberous ligament

      • Extends from lateral part of sacrum and coccyx and posterior inferior iliac spine to the ischial tuberosity

      • Strong

    • Sacrospinous ligament

      • Triangular in shape

      • Base attached to lateral part of sacrum and coccyx

      • Apex attached to ischial spine

      • Strong

    • Iliolumbar ligament

      • Connects tip of L5 transverse process to the iliac crest

    • Posterior sacroiliac ligaments

      • Suspend sacrum between the iliac bones

      • Very strong

    • Anterior sacroiliac ligaments

      • Situated on anterior of joint

      • Thin structure

    • Sacrococcygeal joint

      • Cartilaginous joint between sacrum and coccyx, supported by ligaments

      • Mobile joint

  • The symphysis pubis is a cartilaginous joint, with a fibrocartilaginous disc interposed between cartilaginous articular surfaces.

  • Pelvis is lined with muscles and fascia, to support the pelvic organs. The pelvic floor is a layer of muscle that divides the pelvis into the main pelvic cavity (above the pelvic floor) and the perineum below.

4.12.2 Rectum and anus

  • The rectum is approximately 13cm long and begins anterior to S3, where the transverse mesocolon ends. It is a continuation of the sigmoid colon without structural differentiation.

  • The peritoneum covers the upper third of the rectum at the front and sides.

  • The peritoneum covers the middle third of the rectum at the front only.

  • It passes downwards in front of the sacrum and coccyx and ends by piercing the pelvic diaphragm to become the anus.

  • Puborectalis portion of the levator ani muscles forms a sling at the junction of the rectum and anus, and pulls this part of the bowel forwards, forming the anorectal angle.

  • The anal canal has 2 layers of circular muscle making up the wall, an internal anal sphincter of smooth muscle and an external anal sphincter of skeletal muscle. The puborectalis muscle is continuous with the external anal sphincter at this level.

4.12.3 Relations of the rectum and anus

  • Posterior relations (both sexes):

    • Sacrum

    • Coccyx

    • Levatores ani

    • Sacral plexus

    • Sympathetic trunks

  • Anterior relations (male):

    • Sigmoid colon

    • Posterior surface of bladder

    • Termination of vas deferens

    • Termination of seminal vesicles

    • Prostate

  • Anterior relations (female):

    • Rectouterine pouch

    • Posterior surface of vagina

    • Cervix

  • (On PR examination, only the prostate/cervix and the coccyx can be palpated in a ‘normal’ examination.)

  • The prostate and rectum are separated by the strong rectovesical fascia (of Denonvilliers), which helps prevent local spread of rectal carcinoma to the prostate and vice versa.

4.12.4 Innervation of rectum and anus

  • The sympathetic nerve supply is from branches from the hypogastric and coeliac plexuses.

  • The parasympathetic supply is from S2-4 via the pelvic splanchnic nerves.

4.12.5 Blood supply of the rectum and anus

  • Superior rectal artery - terminal branch of inferior mesenteric artery

  • Median sacral artery - from internal iliac artery

  • Middle rectal artery - from internal iliac artery

  • Inferior rectal arteries - from internal pudendal branch of internal iliac artery

4.12.6 Lymph drainage of rectum and anus

  • The lymph drainage of the rectum and anus is to the pararectal nodes and then along the branches of the arteries.

  • Lymph from the upper and middle sections accompanies the superior rectal artery to the inferior mesenteric nodes. Lymph from the lower part of the rectum and anus is drained accompanying the middle rectal artery to the internal iliac nodes.

4.12.7 Defecation

  • The rectum is empty until there is an increase in activity in the left side of the colon (e.g. after eating a meal). As faeces enter the rectum the person has the sensation of needing to pass stool. Sitting or crouching straightens the anorectal angle, and stool can enter the anal canal.

  • The person is able to distinguish gas from solids. Anal sphincter is under voluntary control.

  • The normal pressure of the anal sphincter (45-90mmHg) can be doubled by squeeze pressure. Diaphragm, levator ani, and abdominal wall muscles all contract to aid defecation. The rectum can accommodate up to 400ml of faeces.

4.12.8 Anal region in spinal pathology

  • Examination of the anus and rectum is important when patients present with spinal pathology. The skin around the anus is supplied by S5, S4, S3 in concentric circles and loss of sensation here can suggest spinal injury or cauda equine.

  • Loss of anal tone is also suggestive of serious spinal pathology as the anal sphincter is supplied by S2-4.

4.13 Prostate

  • The prostate is a glandular organ with a fibrous capsule, lying inferior to the bladder.

  • It surrounds the prostatic urethra and is approximately 3cm long.

  • The normal prostate weighs approximately 20g.

4.13.1 Relations

  • Superiorly: Neck of bladder

  • Inferiorly: Urogenital diaphragm

  • Anteriorly: Symphysis pubis (connected by puboprostatic ligaments)

  • Posteriorly: Rectum (separated by rectovesical fascia (of Denonvilliers))

  • The base of the prostate lies against the bladder neck and is pierced by the urethra at its centre.

  • The apex of the prostate lies against the urogenital diaphragm, and the urethra leaves the prostate just above the apex on the posterior surface.

  • The prostate is anatomically divided into 5 lobes:

    • Anterior

    • Middle

    • Posterior

    • Right lateral

    • Left lateral

  • The middle lobe contains a large amount of glandular tissue and so is often principally affected in benign prostatic hypertrophy (BPH).

  • This middle lobe enlarges upwards and encroaches on the bladder sphincter, causing the urinary symptoms associated with BPH (enlargement of lateral lobes contributes to this, often leading to urinary retention).

  • In BPH the enlarged prostate usually has a regular contour when palpated per rectum.

  • Malignant enlargement of the prostate tends to occur in the periphery of the prostate, and is limited by the prostatic capsule.

  • In malignant enlargement the prostate often feels hard and irregular when palpated per rectum.

  • Blood supply - Internal pudendal, inferior vesical, and middle rectal arteries.

  • Venous drainage - Peri-prostatic plexus.

  • Lymph drainage - Drains into the internal/external iliac, sacral, and vesical lymph nodes.

4.14 Female reproductive system

4.14.1 Uterus

  • Hollow pear-shaped organ with thick, muscular walls. See Figure A.4.9.

  • In a nulliparous adult it measures:

    • 8cm long

    • 5cm wide

    • 2.5cm thick

  • It is divided into the fundus, body, and cervix, as shown in Figure A.4.9.

  • The relations of the uterus are:

    • Anteriorly:

      • Superior surface of bladder

      • Uterovesical pouch

      • Anterior fornix of vagina (cervix)

    • Posteriorly: Rectouterine pouch (of Douglas)

    • Laterally:

      • Broad ligament/uterine vessels

      • Ureter

      • Lateral fornix of vagina

      • Round ligaments

      • Uterine (Fallopian) tubes

4.14.2 Uterine (Fallopian) tubes

  • The uterine tubes are 10-12cm long and run from the superolateral sides of the body of the uterus to the pelvic wall. Each uterine tube is contained within the broad ligament, a sheet of peritoneum draped over the tubes.

  • Each tube is divided into:

    • Indundibulum – trumpet-shaped opening into the peritoneal cavity, positioned over the ovary

    • Ampulla - wide, thin-walled, and tortuous

    • Isthmus - narrow, straight, and thick-walled

    • Intramural part - pierces uterine wall

  • Ectopic pregnancy occurs when a fertilized ovum implants outside the uterine cavity. The commonest site for implantation is the uterine tube (97%). Of these tubal pregnancies, 75% occur in the ampulla and 25% in the isthmus. The remaining 3% of ectopics occur intra-abdominally, in the ovary or the cervix.

4.14.3 Blood supply of the uterus and ovary

  • The uterus is supplied by the uterine artery (a branch of the internal iliac artery). It runs in the base of the broad ligament, and 2cm lateral to the cervix it passes anterior and superior to the ureter (‘water under the bridge’) to reach the uterus at the level of the internal os.

  • The artery ascends tortuously up the lateral side of the body of the uterus and then turns laterally and inferiorly, where it terminates by anastomosing with the terminal branches of the ovarian artery.

  • The uterine tubes receive blood supply from both the uterine and ovarian arteries. Erosion of the tube by an ectopic pregnancy results in effusion of a large quantity of blood into the peritoneal cavity, leading to peritonitis.

  • Innervation of uterus and uterine tubes - from the inferior hypogastric plexus.

4.14.4 Ovary

  • The ovary is an almond-shaped organ, measuring approximately 4cm × 2cm, lying against the lateral wall of the pelvis in the ovarian fossa.

  • It is attached to the posterior aspect of the broad ligament by the mesovarium. The suspensory ligament of the ovary is a fold of peritoneum, which merges with the peritoneum over psoas. The round ligament of the ovary is the remnant of the gubernaculum and links the medial edge of the ovary with the lateral wall of the uterus.

  • Blood supply of the ovary - Via the ovarian artery, a direct branch of the aorta.

  • Lymph drainage of the ovary follows the ovarian artery to the para-aortic nodes.

  • Innervation of the ovary is derived from the aortic plexus, and from T10, T11. There may also be fibres from the inferior hypogastric plexus, and ovarian pain may be felt paraumbilically or in the thigh, as in appendicitis.

  • The pathological ovary can cause local pressure on the lateral cutaneous nerve of the thigh, which will again lead to pain in the thigh.

4.14.5 Vagina

  • The vagina surrounds the cervix of the uterus and then passes forwards and downwards through the pelvic floor to open into the vestibule.

  • The vestibule is the area enclosed by the labia minora and contains the urethral orifice, which lies immediately behind the clitoris.

  • In the adult the vagina is usually 7-8cm long.

  • Its relations are:

    • Anterior:

      • Base of bladder

      • Urethra

    • Posterior:

      • Rectouterine pouch (of Douglas)

      • Anterior wall of rectum

      • Perineal body

      • Anal canal

    • Superior: Ureter

    • Lateral:

      • Levator ani muscles

      • Pelvic fascia

  • Structures palpable on digital vaginal examination:

    • Cervix

    • Uterus (bimanual palpation)

    • Adnexae (bimanual palpation)

    • Vaginal walls

4.15 Male urogenital region

4.15.1 Male urethra

  • The male urethra is approximately 20cm in length. It extends from the neck of the bladder to the external meatus on the glans penis.

  • It is divided into 3 parts:

    • Prostatic urethra:

      • Approximately 3cm long

      • Passes through prostate

      • Widest and most dilatable portion of urethra

    • Membranous urethra:

      • Approximately 1.5cm long

      • Lies within the urogenital diaphragm surrounded by the urethral sphincter muscle

      • Least dilatable part of the urethra

    • Penile urethra:

      • Approximately 15.5cm long

      • Enclosed in the bulb and corpus spongiosum of penis

      • External meatus is the narrowest part of the whole urethra

      • Urethra within the glans penis is dilated to form the fossa terminalis (navicular fossa)

      • Bulbourethral glands open into penile urethra below urogenital diaphragm

4.15.2 Scrotum

  • The scrotum is an out-pouching of the anterior abdominal wall and contains the testes, epididymis, and lower ends of the spermatic cords.

  • The innervation of the scrotal skin is from L1, S2, S3.

  • The anterior surface is supplied by the ilioinguinal nerves, and the genital branch of the genitofemoral nerves.

  • The posterior surface is supplied by branches of the peroneal nerves and the posterior cutaneous nerves of the thigh.

  • The lymph drainage of the scrotum is via the medial group of superficial inguinal lymph nodes.

4.15.3 Penis

  • The penis has a fixed root and a body, which is free.

  • The root of the penis is made up of 3 bodies of erectile tissue:

    • Bulb of penis

    • Right crus

    • Left crus

  • The bulb is situated in the midline and is attached to the undersurface of the urogenital diaphragm.

  • The bulb is traversed by the urethra and is covered by the bulbospongiosus muscles.

  • Each crus is attached to the side of the pubic arch and is covered by the ischiocavernosus muscle.

  • The bulb continues forward and becomes the corpus spongiosum.

  • The crura continue forward and merge, forming the corpora cavernosa.

  • The body of the penis is made up of 3 cylinders of erectile tissue, enclosed in a tubular sheath of fascia (Buck's fascia).

  • A cross-section through the body of the penis is shown in Figure A.4.10, demonstrating each of the different layers.

  • The penis is innervated by the pudendal nerves and the pelvic plexuses (S2-4).

Figure A.4.10 Cross-section of the penis

Figure A.4.10
Cross-section of the penis