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Planes and Regions of the Abdomen
The abdomen is divided into nine regions by two horizontal and two vertical planes:
Horizontal planes:
Transpyloric plane — passes through the lower border of the first lumbar vertebra and the tips of the ninth costal cartilages.
Transtubercular plane — passes through the tubercles of the iliac crests at the level of the fifth lumbar vertebra.
Vertical planes:
Right lateral plane and Left lateral plane — drawn vertically from the midpoints of the clavicles down to the mid-inguinal points.
These planes divide the abdomen into nine regions: right and left hypochondriac, epigastric, right and left lumbar, umbilical, right and left iliac, and hypogastric (pubic) regions.
Spleen
Lies along the long axis of the 10th rib.
Its upper border corresponds to the 9th rib, and the lower border to the 11th rib.
The medial end lies about 4–5 cm from the posterior midline, and the lateral end reaches the left midaxillary line.
Stomach
Cardiac orifice: Marked on the 7th costal cartilage, about 2.5 cm left of the median plane.
Pyloric orifice: On the transpyloric plane, approximately 1.2 cm right of the median plane.
Lesser curvature: A J-shaped line joining the cardiac and pyloric orifices.
Fundus: Lies beneath the left 5th intercostal space, corresponding to the left dome of the diaphragm.
Greater curvature: Extends from the fundus to the pylorus, crossing between the 9th and 10th costal cartilages and reaching down to the L3 vertebral level.
Duodenum
Located above the umbilicus and about 2.5 cm wide.
First part: 2.5 cm long, runs upward and to the right from the pylorus.
Second part: 7.5 cm long, descends vertically along the right lateral plane.
Third part: 10 cm long, crosses the midline horizontally just above the umbilicus at the subcostal plane.
Fourth part: 2.5 cm long, ascends to the duodenojejunal flexure, 1 cm below the transpyloric plane and 3 cm to the left of the median plane.
Caecum
Lies in the right iliac fossa, bounded by the inguinal ligament, right lateral plane, and intertubercular plane.
It measures about 6 cm in length and 7.5 cm in breadth, directed downward and medially.
The ileocaecal orifice (valve) lies at the junction of the right lateral and transtubercular planes.
Ileocaecal Orifice (Valve)
Lies at the junction of the right lateral and transtubercular planes.
Situated about 2.5 cm above the intertubercular plane and 5 cm medial to the right anterior superior iliac spine.
Represents the point where the ileum opens into the caecum.
Appendix
The base of the appendix corresponds to McBurney’s point, located one-third of the distance from the right anterior superior iliac spine to the umbilicus.
The tip may lie in various positions — most commonly retrocaecal, but also pelvic, subcaecal, preileal, or postileal.
Ascending Colon
Extends vertically in the right lumbar region from the caecum to the right colic (hepatic) flexure.
Lies along the right lateral plane, beginning at the level of the transtubercular plane and ending just below the transpyloric plane.
Transverse Colon
Extends across the upper abdomen from the right colic (hepatic) flexure to the left colic (splenic) flexure.
Crosses the umbilical and epigastric regions, with its midpoint usually near the umbilicus or slightly above it.
The left colic flexure is higher and more posterior than the right.
Descending Colon
Lies along the left lateral plane in the left lumbar region, extending from the left colic flexure down to the sigmoid colon.
It begins at the level of the 9th costal cartilage and descends to the iliac crest.
Rectum and Anal Canal
The rectum begins at the level of S3 vertebra, at the termination of the sigmoid colon.
The anal canal begins at the anorectal junction and extends downward and backward to the anus, situated in the midline, about 4 cm anterior to the tip of the coccyx.
Liver
The upper border of the liver follows a line from the right 5th rib in the midaxillary line to the left 5th intercostal space near the midclavicular line.
The lower border runs from the right 10th rib in the midaxillary line to a point just below the left costal margin near the 9th costal cartilage.
The inferior border crosses the midline midway between the xiphoid process and the umbilicus.
Gallbladder
The fundus lies at the tip of the right 9th costal cartilage, where it meets the lateral border of the rectus abdominis muscle.
The body extends upward, backward, and to the left, beneath the right lobe of the liver.
The neck lies at the level of the transpyloric plane, close to the junction of the right and left lobes of the liver.
Bile Duct
Represented by a 7.5 cm line that is vertical in the upper half and inclines to the right in the lower half.
It extends from a point 5 cm above the transpyloric plane and 2 cm to the right of the median plane, down to the medial border of the second part of the duodenum
Volume 2, BD Chaurasia’s Human …
.Pancreas
The head lies within the concavity of the duodenum.
The neck passes upward and to the left behind the pylorus, at the transpyloric plane.
The body runs upward and to the left for 10 cm, occupying the upper two-thirds of the space between the transpyloric and subcostal planes.
Kidney
Each kidney measures 11 × 5 cm.
On the back, it lies within Morrison’s parallelogram, between the 11th thoracic spine and the 3rd lumbar spine.
On the front, the hilum lies 5 cm from the median plane, slightly below the transpyloric plane on the right and above it on the left.
The upper pole is midway between the xiphisternum and transpyloric plane, about 4–5 cm from the midline.
The lower pole lies 6–7 cm from the midline, at the umbilical plane on the right and subcostal plane on the left
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.Ureter
On the front, it is marked by a line from the tip of the 9th costal cartilage to the pubic tubercle, running slightly medially downward.
The upper 5 cm of this line represents the renal pelvis.
On the back, it extends vertically from the posterior superior iliac spine to the second lumbar spine, at the level of the renal hilum
Volume 2, BD Chaurasia’s Human …
.Abdominal Aorta
Represented by two parallel lines 2 cm apart, beginning 2.5 cm above the transpyloric plane in the median plane, and ending 1.2 cm below and to the left of the umbilicus (at the level of L4 vertebra)
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.Common Iliac Artery
Occupies the upper one-third of a line drawn from the lower end of the abdominal aorta to the midinguinal point (midway between the anterior superior iliac spine and the pubic symphysis)
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.External Iliac Artery
Occupies the lower two-thirds of the same line from the aortic bifurcation to the midinguinal point, where it continues as the femoral artery after passing beneath the inguinal ligament
Coeliac Trunk and Its Branches
The coeliac trunk is marked as a point 1 cm below the origin of the abdominal aorta (just below the transpyloric plane).
Left gastric artery: A line drawn upward and to the left from the coeliac trunk toward the cardiac end of the stomach.
Splenic artery: A broad line extending leftward and slightly upward for about 10 cm from the coeliac trunk, following the course of the upper border of the pancreas.
Common hepatic artery: A line drawn rightward and slightly downward for about 2.5 cm, then turning upward for 3 cm as the proper hepatic artery, which ascends toward the liver hilum.
Superior Mesenteric Artery
Represented by a curved line convex to the left, extending from the abdominal aorta just above the transpyloric plane to the intersection of the transtubercular and right lateral planes.
It passes behind the pancreas and the splenic vein, then descends in front of the third part of the duodenum to supply the midgut.
Inferior Mesenteric Artery
Marked by a curved line slightly convex to the left, starting 4 cm below the transpyloric plane on the abdominal aorta.
The line extends downward to a point 4 cm below the umbilicus and the same distance to the left of the median plane, representing its course toward the left iliac fossa.
Inferior Vena Cava
Indicated by two vertical parallel lines 2.5 cm apart, slightly to the right of the median plane.
Extends from the sternal end of the right 6th costal cartilage downward to just below the transtubercular plane, corresponding to its origin at L5 vertebra.
Portal Vein
Represented by a broad line 8 cm long, beginning at a point on the transpyloric plane about 1.2 cm to the right of the median plane.
It ascends upward and to the right, behind the neck of the pancreas, where it is formed by the union of the splenic and superior mesenteric veins.
Inguinal Canal
Represented by two parallel lines 1 cm apart and 3.7 cm long, located above the medial half of the inguinal ligament.
Extends from the deep inguinal ring (1 cm above the midinguinal point) to the superficial inguinal ring, which lies above and lateral to the pubic crest.
The deep ring is marked as a vertical oval, while the superficial ring appears as a triangular opening just above the pubic crest.
Root of Mesentery
A 10 cm oblique line extending from the left side of the second lumbar vertebra (2.5 cm left of the midline) downward and to the right, ending at the right sacroiliac joint.
This line represents the attachment of the mesentery of the small intestine to the posterior abdominal wall, crossing over the third part of the duodenum, aorta, inferior vena cava, and right ureter.
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