The Male Pelvis & Internal Accessory Genitalia

Overview of the Male Pelvis

The male pelvis is a critical structure in human anatomy, situated as a transition zone between the trunk and lower limbs. It houses essential organs and provides structural support.

Definition of Pelvis: The area underneath the abdomen and above the thighs, medically defined as the region enclosed by the pelvic girdle, a basin-shaped ring of bones connecting the vertebral column to the femurs.
Subdivisions:
- False (Greater) Pelvis: Not part of the true pelvic cavity; it overlaps with the abdominal cavity and contains the appendix, sigmoid colon, and ileum.
- True (Lesser) Pelvis: The space inside the bony ring of the pelvis, superior to the pelvic brim. It forms the skeletal framework for the pelvic cavity and perineum.
Perineum: Located inferior to the pelvic cavity and separated from it by the pelvic diaphragm, it includes the anus and external genitalia.

Pelvic Girdle

The pelvic girdle is a bony ring formed by three key bones that serve multiple functions.

Components:
- Sacrum
- Two hip bones (ilium, ischium, pubis)
Functions:
- Protection and support for abdominopelvic organs.
- Attachment point for structures of the genital and urinary systems.
- Transfer of weight from the axial skeleton to lower limbs.

Bone Structure of the Pelvis

Bony Pelvis

The bony pelvis consists of several key features that contribute to its overall structure.

Sacrum: Composed of five fused sacral vertebrae.
Hip Bones: Formed from the fusion of ilium, ischium, and pubis at the acetabulum.
Articulations:
- Posterior articulation with sacrum at sacroiliac joints.
- Anterior articulation at the pubic symphysis.

Ilium

The ilium is the broadest bone part of the pelvis.

Characteristics:
- Ala: Lateral aspect shaped like a fan.
- Body: Forms acetabulum.
- Iliac Crest: The upper rim, bordered by the anterior and posterior superior iliac spines.

Ischium

The ischium forms the posterior part of the hip bone.

Components:
- Body: Part of the acetabulum.
- Ramus: Forms part of the obturator foramen.
- Ischial Tuberosity: The posterior protuberance.
- Ischial Spine: A bony spike important for nerve and blood vessel landmarks.

Pubis

The pubis is the anteroinferior portion of the hip bone.

Characteristics:
- Supports the bladder.
- Features include the superior ramus, inferior ramus, pecten pubis, pubic tubercle, and pubic crest.

Pelvic Inlet and Outlet

Pelvic Inlet

Defines the boundary between the false and true pelvis.

Defined by the pelvic brim consisting of the promontory and ala of the sacrum.

Pelvic Outlet

Boundaries consist of the pubic arch, ischial tuberosities, and the tip of the coccyx.

Anatomical and Functional Aspects

Anatomical Position

Understanding the anatomical position is essential for assessing pelvic anatomy.

Anterior superior iliac spines (ASIS) and pubic symphysis lie in the same vertical plane.

Biomechanics

The biomechanics of the pelvis involve significant adaptations for weight transfer and stability.

The sacrum receives body weight anterior to the rotary axis of sacroiliac joints, which could lead to forward rotation.
This is counterbalanced by sacrotuberous and sacrospinous ligaments.

Pelvic Cavity

Walls of the Pelvic Cavity

The walls of the pelvic cavity are formed by various structures.

Anteroinferior Wall: Supported by the pubic symphysis and rami of pubic bones.
Lateral Wall: Composed of the hip bones and obturator internus musculature.
Posterior Wall and Roof: Comprised of sacrum and coccyx plus associated ligaments.

Pelvic Floor

The pelvic floor plays a critical role in dividing the pelvic cavity from the perineum.

Components: Coccygeus and levator ani muscles.
Functions include supporting pelvic viscera and maintaining continence.

Pelvic Visceral Anatomy

Digestive System

The pelvic portion of the gastrointestinal tract includes the rectum.

Function: Temporary storage of feces, beginning at the rectosigmoid junction and extending to the anal canal.

Urinary System

Involves the urinary bladder and ureters.

Urinary Bladder:
- Characteristics include strong, distensible muscular walls for temporary urine storage.
- Located in the true pelvis.
Pelvic Ureters:
- Course entails crossing the pelvic brim and entering the bladder.

Reproductive System

Contains internal genitalia.

Pelvic Blood Supply

The pelvic region is rich in blood supply from numerous anastomosing arteries, primarily from the internal iliac arteries.

Main Arteries:
- Inferior vesical artery: Supplies the inferior bladder and prostate.
- Middle rectal artery: Supplies inferior rectum, prostate, and seminal glands.
- Internal pudendal artery: Supplies the perineum.

Pelvic Nerves

Formed mainly by the sacral plexus.

Key Nerves:
- Sciatic nerve: Supplies lower limb.
- Pudendal nerve: Supplies perineum and external genitalia.

Autonomic Control

The autonomic nervous system intricately regulates pelvic organ function.

Parasympathetics: Stimulate bladder and rectal emptying.
Sympathetics: Cause vasoconstriction and contractions of internal genital organs during orgasm.

Pelvic Lymphatics

Lymphatic drainage often follows venous pathways and includes several node groups.

Major Nodes:
- Sacral nodes
- Internal iliac nodes
- External iliac nodes

Conclusion

The male pelvis and associated structures are fundamental for understanding human anatomy, particularly regarding reproduction and urinary function. Proper knowledge of the anatomical features, blood supply, and innervation is essential for healthcare professionals.

Comprehensive Overview of the Male Pelvis and Internal Accessory Genitalia

Comprehensive Overview of the Male Pelvis and Internal Accessory Genitalia