Abdomen and Pelvis Anatomy

Learning Objectives

• Trunk 2 focuses on the abdomen and pelvis
• The learning objectives are:
• Osteology and Arthrology of Abdomen and Pelvis
• Walls of Abdominopelvic cavity
• Introduction to Inguinal Canal
• Revision

Regions of Trunk

• Regions of the trunk include:
• Thorax
• Abdomen
• Pelvis
• Perineum
• The Abdominopelvic region combines the abdomen and pelvic regions

Cavities of Trunk

• The thoracic cavity is bounded:
• Superiorly by the thoracic inlet
• Inferiorly by the diaphragm
• Laterally by the thoracic walls
• The abdominal cavity is bounded:
• Superiorly by the thoracic diaphragm
• Inferiorly by the pelvic inlet
• Anteriorly by the anterior abdominal wall
• Posteriorly by the posterior abdominal wall
• The true pelvic cavity is bounded:
• Superiorly by the pelvic inlet
• Inferiorly by the pelvic diaphragm
• Laterally by the pelvic walls
• The abdominopelvic cavity is bounded:
• Superiorly by the thoracic diaphragm
• Inferiorly by the pelvic diaphragm
• Laterally by the abdominal and pelvic walls

Trunk Osteology

• A lumbar vertebrae number is typically 5
• The lumbar vertebrae has a massive, kidney-shaped body
• The lumbar vertebrae has a small vertebral foramen
• Transverse process is long and slender on the lumbar vertebrae
• Articular processes are oriented in the sagittal plane
• Spinous processes are short, thick, and oriented horizontally
• The lumbar vertebrae have attachments for the:
• Psoas major muscle
• Psoas fascia
• Quadratus lumborum
• Thoraco-lumbar fascia
• Back Muscles
• Ligaments
• Crus of diaphragm
  • Right crus is at L1-3
  • Left crus is at L1-2

Sacrum and Coccyx

• The sacrum has N=5 fused segments
• The Coccyx has N= 3-5 segments
• Key features comprise the:
• Promontory
• Sacral Foraminae
• Ala
• Base
• Apex
• Articular surface for ilium (sacroiliac joint)
• Auricular Tuberosity Surface

Hip Bone

• The 3 sections comprising the hip bone:
• Ilium
• Ischium
• Pubis
• Key features include the:
• Acetabulum
• Articular surface for sacrum (sacroiliac joint)
• Tuberosity
• Auricular surface
• Iliac crest
• Iliac fossa
• Ala of ilium
• Anterior superior iliac spine
• Iliac spine
• Arcuate line
• Pecten pubis
• Body of ischium
• Greater sciatic notch
• Ischial spine
• Obturator foramen
• Ischial tuberosity
• Pelvic brim separates the true and false pelvis
• Pelvic brim includes the linea terminalis of the hip bone
• The linea terminalis comprises:
• arcuate line
• pecten pubis
• pubic crest
• False pelvis (part of abdominal cavity) is above the pelvic brim
• True pelvis (part of pelvic cavity) is below the pelvic brim

Bony Pelvis

• The two body pubis are united by fibrocartilage (secondary cartilaginous joint)
• The pubic ligaments support the pubic symphysis
• Sacroiliac joints consist of plane synovial and fibrous joints
• Sacroiliac joints exists between auricular surfaces of the sacrum and ilium
• The Sacrococcygeal joint is symphysis type but is considered highly variable
• Ligaments stabilizing bony pelvis run between the sacrum & ischium (Sacrotuberous & Sacrospinous)
• Ligaments together with hip bone create the greater and lesser sciatic foramina

True vs False Pelvis

• The pelvic brim, or pelvic inlet, includes:
• Sacral promontory
• Sacral ala
• Arcuate line
• Pecten pubis
• Pubic crest
• Pubic symphysis
• The pelvic inlet is outlined by the pelvic brim
• Pelvic outlet is the inferior opening of the bony pelvis
• The pelvic diaphragm (flat muscle) encloses the pelvic outlet
• The false pelvis is:
• Above the pelvic brim
• A component of the abdominal cavity
• The true pelvis is:
• Below the pelvic brim
• A component of the true pelvic cavity

Abdominal Walls

• The abdomen is a part of the trunk between the thorax and the true pelvis
• The abdomen lies in the plane between the thoracic diaphragm and the pelvic brim
• The abdominal cavity is supported by two bony rings
• Inferior margin & inferior part of the thoracic cage (lower ribs, costal cartilages)
• Bony false pelvis (bony pelvis above pelvic brim)
• The boundaries of the abdominal cavity are:
• Superiorly: Diaphragm
• Inferiorly: pelvic cavity at the pelvic inlet
• Anteriorly: Anterior abdominal wall, formed by muscles
• Posteriorly: Posterior abdominal wall, formed by lumbar vertebrae and muscles
• Laterally: Lower ribs and parts of muscles of the anterior abdominal wall
• The anterior/anterolateral wall is firm and elastic
• The posterior abdominal wall is osteo-muscular and rigid
• The Abdominopelvic cavity:
• Houses abdominal viscera, is flexible, dynamic & protective
• Contains most organs of the alimentary system
• Contains part of the urogenital system (kidney, ureters)
• Suprarenal glands
• Spleen, peritoneum
• Blood vessels, nerves & lymphatics
• Layers of the lateral abdominal wall from superficial to deep:
• Skin
• Superficial fascia
• 3 flat muscles
• Transverse Fascia
• Extraperitoneal fat
• Peritoneum
• Abdominal walls are innervated by somatic nerves
• Somatic nerves are derived from lower thoracic & upper lumbar spinal nerves

True Pelvis

• The boundaries of the true pelvis are:
• Superiorly: Pelvic inlet
• Inferiorly: Pelvic outlet enclosed by pelvic diaphragm
• Posteriorly: Sacrum and coccyx
• Anteriorly: Pubic body and symphysis
• Laterally: Hip bones
• The pelvic outlet is enclosed by pelvic diaphragm (pelvic floor)
• The Perineum is defined as the space below the pelvic diaphragm
• The Perineum contains the anus, openings of urethra and the opening of the vagina (for females)

Myology of Abdominal Wall

• The arrangement of abdominal wall muscles includes Intrinsic back muscles (erector spinae)
• It also includes linea alba, thoraco-lumbar Fascia etc.
• Posterior abdominal wall muscles:
• Iliopsoas
• Originates: T12-L5
• Inserts: lesser trochanter
• Function: prime flexor at hip joint & flexor of the trunk
• Quadratus Lumborum (QL)
  • Origin: Iliac crest
  • Inserts: The twelfth rib, the costal processes of the L1-L4 vertebrae
  • Function: bends the trunk to the same side or bearing down and expiration

Anterolateral Muscles

• Anterolateral abdominal wall muscles from superficial to deep:
• External Oblique (EAO)
• Internal Oblique (IAO)
• Transversus Abdominis (TA)
• Rectus Abdominis (RA)
• EAO:
• Origin: Outer aspects of the lower 8 ribs
• Inserts: Xiphoid process, linea alba, pubic crest and tubercle, anterior part of iliac crest
• IAO:
• Origin: Thoracolumbar fascia, anterior part of iliac crest, lateral 2/3rd of inguinal ligament
• Inserts: Lower 3 ribs, xiphoid process, linea alba, pubic crest, pectineal line
• TA:
• Origin: Inner aspect of the lower 6 costal cartilages, thoracolumbar fascia, iliac crest, 1/3rd of inguinal ligament
• Inserts: Xiphoid process, linea alba, pubic crest and pectineal line
• RA:
• Origin: Pubic symphysis and crest
• Inserts: Xiphoid process, 5th to 7th costal cartilages
• The ventral rami of lower thoracic (T6-12) & and L1 spinal nerves innervate the anteralateral muscles
• The muscles support the abdominal viscera against gravity and compress abdominal contents
• The muscles increase intra-abdominal pressure, help expulsive and expiratory acts, move trunk, and maintain posture
• The aponeurosis stretches between the ASIS and pubic tubercle, it forms the inguinal ligament
• It forms the superficial inguinal ring

Internal Oblique (IAO) and Transversus Abdominis (TA)

• Fibres arch, form the roof of the inguinal canal attached with the conjoint tendon to the pubic crest & pecten pubis
• Rectus Abdominis (RA) connective tissue is the rectus sheath that covers the muscle
• From superior to inferior:
• Above the level of costal margin, RA is placed directly against the intercostal muscles and costal cartilages
• Between costal margin & arcuate line, RA is surrounded by the anterior & posterior rectus sheath
• Below the level of arcuate line, RA has only an anterior rectus sheath and is covered by Transverse Fascia posteriorly
• Anterolateral abdominal wall include Aponeurosis of transversus abdominis muscle
• The Aponeurosis of external oblique is a key feature

Inguinal Canal

• The inguinal canal extends at 4cm between the pelvic regions
• Boundaries include:
• Anterior iliac spine
• Internal ring
• Inguinal ligament
• External ring
• Superficial lymph nodes
• Spermatic chord
• Canal walls include anterior, posterior, roof and floor
• Openings include a deep ring (into abdominopelvic cavity)
• A superficial ring, also enters to the groin region
• Boundaries of the inguinal canal:
• Anterior wall = aponeurosis of EAO
• Posterior wall = fascia of TA and conjoint tendon (IAO+TA)
• Roof = arching fibres of TA and IAO
• Floor = inguinal ligament
• Openings consist of a deep inguinal ring in transverse fascia midway between ASIS and pubic symphysis
• Also present is a superficial inguinal ring opening in aponeurosis of EAO, it is superior and lateral to the pubic tubercle
• The inguinal canal extends downward & medially just above and parallel to the inguinal ligament
• The content:
  • Spermatic cord in men
  • Round ligament in women

Revision

• Body membranes line the body and its cavities
• There are serous membranes, cutaneous membranes, and synovial membranes
• Mucous membranes line the digestive, respiratory, urinary, and reproductive tracts
• Serous membranes line body cavities closed to the exterior of the body:
• Peritoneal
• Pleural
• Pericardial
• The cutaneous membrane, or the skin, covers the body surface
• Synovial membranes line joint cavities and produce the fluid within the joint

Mediastinum

• The mediastinum contents of each compartment require knowing
• It divides the mediastinum into superior and inferior parts
• The superior part of the mediastinum includes the aortic arch and great vessels
• The inferior mediastinum is further divided into:
• Anterior
• Middle
• Posterior The mediastinum is an area between the lungs