Notes on Maternal Anatomy and Physiology
1. Overview of Anterior Abdominal Wall:
• The anterior abdominal wall serves multiple functions:
o Confines abdominal viscera.
o Stretches to accommodate the expanding uterus.
o Provides surgical access to internal reproductive organs.
• A comprehensive understanding of the layered structure is essential for surgical entry into
the peritoneal cavity.
2. Skin and Langer Lines:
• Langer lines describe the orientation of dermal fibers.
o In the anterior abdominal wall, they are arranged transversely.
o Vertical incisions: Greater lateral tension, leading to wider scars.
o Transverse incisions (e.g., Pfannenstiel incision): Align with Langer lines,
resulting in better cosmetic outcomes.
3. Subcutaneous Layer:
• The subcutaneous layer is divided into:
o Camper fascia: A superficial, fatty layer.
▪ Continues onto the perineum, providing fatty tissue to the mons pubis and
labia majora.
o Scarpa fascia: A deeper, membranous layer.
▪ Extends inferiorly onto the perineum as Colles fascia.
4. Muscles of the Anterior Abdominal Wall:
• Key muscles include:
o Rectus abdominis: Located at the midline.
o Pyramidalis: Small triangular muscles originating from the pubic crest.
o External oblique, internal oblique, and transversus abdominis: Span the entire
anterior abdominal wall.
• These muscles are enveloped by aponeuroses, which form the fascia and fuse at the
linea alba.
o The linea alba is normally 10 to 15 mm wide below the umbilicus.
o An abnormally wide separation may indicate diastasis recti or a hernia.
5. Rectus Sheath and Arcuate Line:
• Rectus sheath: Aponeuroses investing the rectus abdominis muscle.
o Above the arcuate line: The aponeuroses envelop both the dorsal and ventral
surfaces of the rectus abdominis.
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, o Below the arcuate line: All aponeuroses lie ventrally, with only thin transversalis
fascia and peritoneum beneath the rectus muscle.
• This transition is visible in the upper third of a vertical midline incision.
Superficial vessels:
• The superficial epigastric, superficial circumflex iliac, and superficial external
pudendal arteries originate from the femoral artery, just below the inguinal ligament.
• These vessels primarily supply the skin and subcutaneous layers of the anterior
abdominal wall and mons pubis.
Superficial epigastric vessels:
• Particularly important in surgery (e.g., obstetrics).
• Course diagonally from their origin toward the umbilicus.
• Located between the skin and anterior rectus sheath, above Scarpa fascia.
• Should be identified and surgically occluded during low transverse skin incisions.
Inferior epigastric vessels:
• Branch from the external iliac vessels.
• Supply the anterior abdominal wall muscles and fascia.
• Initially lateral, then posterior to the rectus abdominis muscle.
• May be lacerated during a Maylard incision for cesarean delivery; should be identified
and occluded.
• Can rupture following abdominal trauma, leading to a rectus sheath hematoma.
Hesselbach triangle:
• Defined by:
o Inferior epigastric vessels laterally.
o Inguinal ligament inferiorly.
o Lateral border of rectus abdominis muscle medially.
• Site of direct inguinal hernias.
• Indirect inguinal hernias pass through the deep inguinal ring, lateral to this triangle.
Innervation of the Anterior Abdominal Wall
• Key nerves:
o Intercostal nerves (T7-T11).
o Subcostal nerve (T12).
o Iliohypogastric and ilioinguinal nerves (L1).
• Path of intercostal and subcostal nerves:
o Anterior rami of thoracic spinal nerves.
o Run between the transversus abdominis and internal oblique muscles in the
transversus abdominis plane (TAP).
Copyright MAA MD 2025
, o TAP is a target for post-cesarean analgesia blockade.
• Anterior branches:
o Pierce the posterior sheath, rectus muscle, and anterior sheath to innervate the
skin.
o Can be severed during Pfannenstiel incisions.
• Iliohypogastric and ilioinguinal nerves:
o Originate from L1, travel retroperitoneally, pierce the transversus abdominis
and internal oblique muscles.
o Provide sensation:
▪ Iliohypogastric nerve: Supplies the skin over the suprapubic area.
▪ Ilioinguinal nerve: Supplies the mons pubis, upper labia majora, and
medial upper thigh.
• Risk during surgery:
o Both nerves may be severed or entrapped during low transverse incisions,
especially if extended beyond the rectus abdominis.
o This can result in loss of sensation or chronic pain in affected areas.
• Dermatomes:
o T10 corresponds to the umbilicus, suitable for labor and vaginal birth.
o For cesarean delivery, analgesia ideally extends to T4.
External Generative Organs
Vulva Anatomy
• Vulva includes all visible structures: mons pubis, labia majora/minora, clitoris, hymen,
vestibule, urethral opening, glands.
• Innervation & Blood Supply: Pudendal nerve.
Mons Pubis
• Fat cushion over symphysis pubis, covered by pubic hair post-puberty.
Labia Majora
• 7-8 cm long, 2-3 cm wide, rich in elastic fibers and fat, hair-covered.
• Prone to varicosities during pregnancy.
Labia Minora
• Thin, sensitive tissue folds, lack hair, with sebaceous glands.
• Divided into lamellae forming frenulum and prepuce.
Clitoris
• Main erogenous organ: 2 cm length, contains corpora cavernosa, highly innervated.
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, Vestibule
• Almond-shaped area, contains openings for urethra, vagina, Bartholin, and Skene glands.
Bartholin Glands
• Prone to cysts or abscesses after infection/trauma.
Paraurethral (Skene) Glands
• Ducts near the urethral meatus, inflammation can lead to diverticulum formation.
Vagina & Hymen
• Hymen surrounds vaginal opening, elastic tissue, changes after childbirth.
• Vagina: 6-10 cm length, muscular tube, lacks glands.
• Blood Supply: Uterine, vaginal, and pudendal arteries.
• Lymph Drainage: Inguinal and iliac nodes.
Perineum:
• The perineum is a diamond-shaped area located between the thighs. It has boundaries
that correspond to the bony pelvic outlet: the pubic symphysis, ischiopubic rami, ischial
tuberosities, sacrotuberous ligaments, and the coccyx.
• It is divided into two triangles by an arbitrary line between the ischial tuberosities:
o Anterior triangle (urogenital triangle)
o Posterior triangle (anal triangle)
Perineal Body:
• The perineal body, also called the central tendon of the perineum, is a fibromuscular
mass found at the junction between the two triangles.
• This structure is critical for perineal support, serving as the convergence point for several
muscles (e.g., bulbospongiosus, superficial transverse perineal, external anal sphincter)
and ligaments.
Anterior Triangle:
• The superficial space of the anterior triangle is bounded by the pubic rami, ischial
tuberosities, and the superficial transverse perineal muscles. It contains important
structures such as the Bartholin glands, vestibular bulbs, clitoral body, and pudendal
vessels and nerves.
• The deep space lies beneath the perineal membrane and contains the urethra, vagina, and
striated urogenital sphincter complex, essential for urinary continence.
Pelvic Diaphragm:
Copyright MAA MD 2025
1. Overview of Anterior Abdominal Wall:
• The anterior abdominal wall serves multiple functions:
o Confines abdominal viscera.
o Stretches to accommodate the expanding uterus.
o Provides surgical access to internal reproductive organs.
• A comprehensive understanding of the layered structure is essential for surgical entry into
the peritoneal cavity.
2. Skin and Langer Lines:
• Langer lines describe the orientation of dermal fibers.
o In the anterior abdominal wall, they are arranged transversely.
o Vertical incisions: Greater lateral tension, leading to wider scars.
o Transverse incisions (e.g., Pfannenstiel incision): Align with Langer lines,
resulting in better cosmetic outcomes.
3. Subcutaneous Layer:
• The subcutaneous layer is divided into:
o Camper fascia: A superficial, fatty layer.
▪ Continues onto the perineum, providing fatty tissue to the mons pubis and
labia majora.
o Scarpa fascia: A deeper, membranous layer.
▪ Extends inferiorly onto the perineum as Colles fascia.
4. Muscles of the Anterior Abdominal Wall:
• Key muscles include:
o Rectus abdominis: Located at the midline.
o Pyramidalis: Small triangular muscles originating from the pubic crest.
o External oblique, internal oblique, and transversus abdominis: Span the entire
anterior abdominal wall.
• These muscles are enveloped by aponeuroses, which form the fascia and fuse at the
linea alba.
o The linea alba is normally 10 to 15 mm wide below the umbilicus.
o An abnormally wide separation may indicate diastasis recti or a hernia.
5. Rectus Sheath and Arcuate Line:
• Rectus sheath: Aponeuroses investing the rectus abdominis muscle.
o Above the arcuate line: The aponeuroses envelop both the dorsal and ventral
surfaces of the rectus abdominis.
Copyright MAA MD 2025
, o Below the arcuate line: All aponeuroses lie ventrally, with only thin transversalis
fascia and peritoneum beneath the rectus muscle.
• This transition is visible in the upper third of a vertical midline incision.
Superficial vessels:
• The superficial epigastric, superficial circumflex iliac, and superficial external
pudendal arteries originate from the femoral artery, just below the inguinal ligament.
• These vessels primarily supply the skin and subcutaneous layers of the anterior
abdominal wall and mons pubis.
Superficial epigastric vessels:
• Particularly important in surgery (e.g., obstetrics).
• Course diagonally from their origin toward the umbilicus.
• Located between the skin and anterior rectus sheath, above Scarpa fascia.
• Should be identified and surgically occluded during low transverse skin incisions.
Inferior epigastric vessels:
• Branch from the external iliac vessels.
• Supply the anterior abdominal wall muscles and fascia.
• Initially lateral, then posterior to the rectus abdominis muscle.
• May be lacerated during a Maylard incision for cesarean delivery; should be identified
and occluded.
• Can rupture following abdominal trauma, leading to a rectus sheath hematoma.
Hesselbach triangle:
• Defined by:
o Inferior epigastric vessels laterally.
o Inguinal ligament inferiorly.
o Lateral border of rectus abdominis muscle medially.
• Site of direct inguinal hernias.
• Indirect inguinal hernias pass through the deep inguinal ring, lateral to this triangle.
Innervation of the Anterior Abdominal Wall
• Key nerves:
o Intercostal nerves (T7-T11).
o Subcostal nerve (T12).
o Iliohypogastric and ilioinguinal nerves (L1).
• Path of intercostal and subcostal nerves:
o Anterior rami of thoracic spinal nerves.
o Run between the transversus abdominis and internal oblique muscles in the
transversus abdominis plane (TAP).
Copyright MAA MD 2025
, o TAP is a target for post-cesarean analgesia blockade.
• Anterior branches:
o Pierce the posterior sheath, rectus muscle, and anterior sheath to innervate the
skin.
o Can be severed during Pfannenstiel incisions.
• Iliohypogastric and ilioinguinal nerves:
o Originate from L1, travel retroperitoneally, pierce the transversus abdominis
and internal oblique muscles.
o Provide sensation:
▪ Iliohypogastric nerve: Supplies the skin over the suprapubic area.
▪ Ilioinguinal nerve: Supplies the mons pubis, upper labia majora, and
medial upper thigh.
• Risk during surgery:
o Both nerves may be severed or entrapped during low transverse incisions,
especially if extended beyond the rectus abdominis.
o This can result in loss of sensation or chronic pain in affected areas.
• Dermatomes:
o T10 corresponds to the umbilicus, suitable for labor and vaginal birth.
o For cesarean delivery, analgesia ideally extends to T4.
External Generative Organs
Vulva Anatomy
• Vulva includes all visible structures: mons pubis, labia majora/minora, clitoris, hymen,
vestibule, urethral opening, glands.
• Innervation & Blood Supply: Pudendal nerve.
Mons Pubis
• Fat cushion over symphysis pubis, covered by pubic hair post-puberty.
Labia Majora
• 7-8 cm long, 2-3 cm wide, rich in elastic fibers and fat, hair-covered.
• Prone to varicosities during pregnancy.
Labia Minora
• Thin, sensitive tissue folds, lack hair, with sebaceous glands.
• Divided into lamellae forming frenulum and prepuce.
Clitoris
• Main erogenous organ: 2 cm length, contains corpora cavernosa, highly innervated.
Copyright MAA MD 2025
, Vestibule
• Almond-shaped area, contains openings for urethra, vagina, Bartholin, and Skene glands.
Bartholin Glands
• Prone to cysts or abscesses after infection/trauma.
Paraurethral (Skene) Glands
• Ducts near the urethral meatus, inflammation can lead to diverticulum formation.
Vagina & Hymen
• Hymen surrounds vaginal opening, elastic tissue, changes after childbirth.
• Vagina: 6-10 cm length, muscular tube, lacks glands.
• Blood Supply: Uterine, vaginal, and pudendal arteries.
• Lymph Drainage: Inguinal and iliac nodes.
Perineum:
• The perineum is a diamond-shaped area located between the thighs. It has boundaries
that correspond to the bony pelvic outlet: the pubic symphysis, ischiopubic rami, ischial
tuberosities, sacrotuberous ligaments, and the coccyx.
• It is divided into two triangles by an arbitrary line between the ischial tuberosities:
o Anterior triangle (urogenital triangle)
o Posterior triangle (anal triangle)
Perineal Body:
• The perineal body, also called the central tendon of the perineum, is a fibromuscular
mass found at the junction between the two triangles.
• This structure is critical for perineal support, serving as the convergence point for several
muscles (e.g., bulbospongiosus, superficial transverse perineal, external anal sphincter)
and ligaments.
Anterior Triangle:
• The superficial space of the anterior triangle is bounded by the pubic rami, ischial
tuberosities, and the superficial transverse perineal muscles. It contains important
structures such as the Bartholin glands, vestibular bulbs, clitoral body, and pudendal
vessels and nerves.
• The deep space lies beneath the perineal membrane and contains the urethra, vagina, and
striated urogenital sphincter complex, essential for urinary continence.
Pelvic Diaphragm:
Copyright MAA MD 2025
