Abdomen

Lesson 5: Abdomen

Course Information

  • Course Title: Human Anatomy and Embryology

  • Instructor: Prof. Jaime Marco

  • Program: Dentistry

  • Institution: UCAM (Universidad Católica de Murcia)

Index

  • Abdomen:

    • Abdominopelvic regions

    • Muscles

    • Peritoneum and peritoneal cavity

    • Inguinal canal

Abdomen Overview

  • Location and Boundaries:

    • The abdomen is defined as the part of the trunk located inferior to the thorax.

    • It is enclosed by musculomembranous walls surrounding a significant cavity known as the abdominal cavity.

    • The abdominal cavity is bounded superiorly by the diaphragm and inferiorly by the pelvic inlet.

    • It is continuous with the pelvic cavity and contains both the peritoneal cavity and various abdominal viscera.

    • Maximum superior extension may reach the fourth intercostal space.

Abdominopelvic Regions

  • Quadrant System:

    • The abdominopelvic region is often conceptualized using a system of four quadrants, defined by two imaginary lines—one horizontal and one vertical—intersecting at the umbilicus (navel).

    • This method aids in describing and diagnosing abdominal pain:

    • Right Lower Quadrant (RLQ): Indicates potential appendicitis.

    • Right Upper Quadrant (RUQ): May suggest gallbladder or liver issues.

  • Nine-Region Method:

    • A more detailed system divides the abdomen using two horizontal planes (subcostal and intertubercular) and two vertical planes (midclavicular).

    • Planes Defined:

    • Superior horizontal plane (Subcostal plane): Located below the costal margins, at the lower boundary of the costal cartilages of rib X.

    • Inferior horizontal plane (Intertubercular plane): Connects the iliac tubercles.

    • Vertical planes (Midclavicular planes): Extend from the midpoint of the clavicles down to a point between the anterior superior iliac spine and the pubic symphysis.

    • Regions:

    • Right hypochondrium

    • Epigastric region

    • Left hypochondrium

    • Right flank

    • Umbilical region

    • Left flank

    • Right groin

    • Pubic region

    • Left groin

Abdominal Wall

  • Anterolateral Muscles:

    • Muscle Groups:

    • There are five main muscles forming the anterolateral abdominal wall:

      • Flat Muscles:

      • External Oblique:

        • Most superficial abdominal muscle, directed inferomedially.

        • Has large aponeuroses covering the anterior abdominal wall up to the linea alba.

      • Internal Oblique:

        • Smaller and thinner than the external oblique.

        • Fibers run superomedially and blend into the linea alba.

      • Transversus Abdominis:

        • Deep to the internal oblique.

        • Fibers orient horizontally and blend into the anterior aponeurosis with the linea alba.

      • Vertical Muscles:

      • Rectus Abdominis:

        • Extends from the pubic symphysis to the costal margin.

        • Interrupted by 3-4 tendinous intersections.

      • Pyramidalis:

        • A small triangular muscle located anterior to the rectus abdominis; may be absent.

        • Located between the pubis and the linea alba.

  • Functions of Anterolateral Muscles:

    • Maintain the abdominal viscera within the cavity and provide protection.

    • Assist with quiet and forced expiration (internal oblique and transversus abdominis push viscera upward).

    • Play a role in increasing intra-abdominal pressure during actions like coughing, vomiting, childbirth, urination, and defecation.

  • Rectus Sheath:

    • Consists of the aponeuroses of external oblique, internal oblique, and transversus abdominis surrounding the rectus abdominis muscle forming a supportive structure.

  • Posterior Wall Muscles:

    • Medial:

    • Psoas Major and Minor: Cover the anterolateral surfaces of lumbar vertebrae, sometimes associated with minor muscle.

    • Lateral:

    • Quadratus Lumborum: Fills space between ribs XII and iliac crest; overlaps medially with psoas major and has lateral transversus abdominis borders.

    • Inferior:

    • Iliacus: Covers iliac fossa; fuses with psoas major to form iliopsoas muscle.

    • Superior:

    • Diaphragm:

      • Appears with right and left domes pushed up by abdominal contents: liver on the right, stomach and spleen on the left.

Diaphragm Structure

  • Structure:

    • Central muscular part with attached circumferential muscle fibers.

    • Anchored to lumbar vertebrae via musculotendinous crura, blending with anterior longitudinal ligament.

    • Right crus: longest and broadest, attached to L1-L3 vertebrae.

    • Left crus: attaches to L1 and L2.

  • Openings:

    • Aortic hiatus: accommodates aorta artery and azygos vein.

    • Oesophageal hiatus: for the oesophagus.

    • Caval opening: for inferior vena cava and includes right phrenic nerve.

Peritoneum and Peritoneal Cavity

  • Peritoneum:

    • Thin membrane lining abdominal cavity walls and covering many viscera.

    • Components:

    • Parietal Peritoneum: Lines cavity without covering organs.

    • Visceral Peritoneum: Covers abdominal organs.

    • Forms the peritoneal cavity which is defined by any organ suspended in the cavity (intraperitoneal) versus organs that are outside (retroperitoneal).

  • Organ Classification:

    • Intraperitoneal Organs:

    • Stomach, 1st part of duodenum, jejunum, ileum, cecum, appendix, transverse colon, sigmoid colon, rectum (1st third), liver, spleen, pancreatic tail.

    • Retroperitoneal Organs:

    • Includes 2nd & 3rd parts of duodenum, ascending and descending colon, kidney, suprarenal glands, ureters, renal and gonadal vessels, inferior vena cava, and aorta.

    • Subperitoneal Organs:

    • Rectum (2nd & 3rd parts), bladder, uterus, ovaries, oviducts.

Peritoneal Folds

  • Folds: These structures connect organs to each other or the abdominal wall, representing folds of peritoneum:

    • Omenta:

    • Greater Omentum:

      • A large, apron-like fold extending from the greater curvature of the stomach to the duodenum. It covers the intestines and contains fat and is vascularized.

    • Lesser Omentum:

      • Extends from the lesser curvature of the stomach and first part of the duodenum to the liver.

    • Mesenteries:

    • Attaches viscera to posterior wall, example includes mesentery for small intestine and mesocolon for large intestine.

    • Ligaments:

    • Connect two organs or an organ to body wall (e.g., splenorenal ligament connecting spleen to kidney, gastrophrenic ligament connecting stomach to diaphragm).

Inguinal Region

  • Area Characteristics:

    • Junction between anterior abdominal wall and thigh; area of possible hernia due to wall weakness.

  • Processus Vaginalis:

    • A peritoneal out-pouching covering structures in the inguinal canal.

    • Layers of covering:

    • Innermost: Transversalis fascia.

    • Middle: Internal oblique muscle.

    • Outer: Aponeurosis of external oblique.

Inguinal Canal

  • Structure:

    • Directed downward and medially, positioned above and parallel to inguinal ligament.

    • Defined by deep and superficial inguinal rings.

    • Contents:

    • In males: spermatic cord.

    • In females: round ligament of uterus and the genital branch of genitofemoral nerve.

Bibliography

  • Drake RL, Vogl AW, Mitchell AWM. Gray's Basic Anatomy, 4th Edition. Philadelphia, PA: Elsevier, 2019.

  • Drake RL, Vogl AW, Mitchell AWM, Tibbies R, Richardson P. Gray ́s Atlas of Anatomy, 3rd Edition. Philadelphia, PA: Elsevier, 2020.

  • MarQni FH, Tallitsch RB, Nath JL. Human Anatomy, 8th Edition. Pearson Education SA, 2018.

  • Soboea. Atlas of Human Anatomy, 15th Edition. Elsevier Gmbh, Munich.