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ANATOMY AND PHYSIOLOGY OF HUMAN REPRODUCTIVE SYSTEM AND THE FOETUS: MIDC: 201

LECTURER INFORMATION

  • Name: Alice Aluwah Blay
  • Department: Nursing & Midwifery
  • Faculty: Health & Applied Sciences
  • Institution: Christian Service University College, Kumasi

LEARNING OUTCOMES

  • By the end of the lecture, students will be able to:
      - Describe the structures of the female bony pelvis.
      - Describe the structures that form the joints and ligaments of the pelvis.

THE BONY PELVIS

  • Introduction:
      - The female pelvis is critical in midwifery as it is the pathway through which the baby is born.
      - Individual differences in the size and shape of the pelvis are important to note during examinations of pregnant women for any abnormalities.
  • Composition:
      - The pelvis is formed by:
        - Two innominate bones
        - One sacrum
        - One coccyx

STRUCTURES OF THE FEMALE BONY PELVIS

  • Key Components:
      - The bony pelvis consists of:
        - Two innominate bones (laterally positioned – left and right)
          1. Ilium
          2. Ischium
          3. Os Pubis
        - One sacrum
        - One coccyx
  • Pelvic Bones:
      - The sacrum comprises five fused parts and includes:
        - Anterior foramina
        - Coccyx (which has four parts)

DEFINITION OF THE PELVIS

  • The pelvis is defined as a basin-shaped organ or ring of bones joining the vertebral column above to the lower limb bones below.
      - These bones are connected by joints and covered inside and outside by ligaments and muscles.

PELVIC BONE CHARACTERISTICS

  • Situation:
      - Articulates with the fifth lumbar vertebra above and the head of each femur in the left and right acetabulum below.
  • Shape:
      - The shape resembles that of a bony basin, providing protection to pelvic organs.
  • Size:
      - Considered the largest bony formation in the human body.
  • Parts:
      - Composed of four bones: two innominate bones, one sacrum, and one coccyx.

INNOMINATE BONE (HIP BONE)

  • Forms the lateral and anterior wall of the pelvis.
  • Comprised of three fused bones:
      1. Ilium
      2. Ischium
      3. Os Pubis
  • Fuses before the age of 25 but is initially united by cartilages.
ILIUM CHARACTERISTICS
  • General:
      - Forms the upper, spread-out portion of the innominate bone.
  • Features:
      - The inner surface smooth and contains the iliac fossa, accommodating iliac muscles as a cushion for abdominal muscles.
      - The ilio-pectineal line forms a ridge of bone below the fossa and marks the junction of true and false pelvis.
      - Outer aspect bulges out for gluteal muscle attachment.
  • Landmarks:
      - Anterior Superior Iliac Spine (ASIS) - a projection at the anterior end of the iliac crest.
      - Anterior Inferior Iliac Spine (AIIS) - a small projection below the ASIS.
      - Posterior Inferior Iliac Spine marks the end of the posterior iliac crest, easily palpated on individuals.
      - Rhomboid of Michaelis - diamond-shaped area of the back marked by the posterior dimples and superior spinous process of the 5th lumbar vertebra.

ISCHIUM CHARACTERISTICS

  • Known as the "bone of the seat", it is the lowest part of the innominate bone.
  • Key Features:
      - Body and ramus with a tuberosity important as a seating landmark.
      - Ischial spine above the ischial tuberosity helps in assessment of fetal head position.
      - Separates the greater sciatic notch from the lesser sciatic notch.

OS PUBIS CHARACTERISTICS

  • The smallest component of the innominate bone, forming the remaining fifth of the acetabulum.
  • Joining Structure:
      - The right and left pubic bones unite at the front via the symphysis pubis (cartilaginous joint).
  • Anatomy:
      - Consists of a body and two rami: superior and inferior.
PUBIS DIMENSION
  • The body measures approximately 4 cm in depth and 2 cm in thickness, with the inner surface smooth and the upper surface rough and thick (pubic crest).
  • The upper margin featuring the pubic tubercle serves for inguinal ligament attachment.
  • The inferior ramus extends down to join the ascending ramus of the ischium, forming part of the pubic arch.

SACRUM CHARACTERISTICS

  • Forms the posterior aspect of the pelvis, triangular in shape with the base at the top.
  • Comprised of five fused vertebra and articulates superiorly with the 5th lumbar vertebra, and the lower part links with the coccyx to create the sacro-coccygeal joint.
SACRUM PROPERTIES
  • The inner surface is smooth and concave, while the back is rough for attachment of muscles and ligaments.
  • Contains four pairs of foramina allowing blood vessel and nerve passage and a central sacral canal for the spinal cord and spinal nerves, particularly at the 2nd and 3rd sacral vertebrae from which the cauda equina spreads to supply pelvic organs.

COCCYX DESCRIPTION

  • The smallest triangular section of the pelvis, articulating with the 5th sacral vertebra, found between the buttocks behind the anus.
  • Most mobility can sometimes be fixed at the sacro-coccygeal joint, affecting the normal descent during labor.

JOINTS OF THE PELVIS

  • Main Joints:
      - Sacro-coccygeal, Sacro-iliac (two), and Symphysis pubis (one).
      - Minimal movement in non-pregnant women; however, movement increases during pregnancy due to hormones (relaxin and progesterone).
SACRO-ILIAC JOINT
  • Formed by the articulation of the sacrum's alae with the ilium.
  • Reinforced by strong ligaments from the sacrum and 5th lumbar vertebra to the ilium.
  • During pregnancy, softening leads to increased joint mobility, contributing to backache.
SACRO-COCCYGEAL JOINT
  • Between the lower sacrum and upper coccyx, reinforced by ligaments and allowing slight movement during labor.
SYMPHYSIS PUBIS
  • Formed between the two pubic bones with a cartilage pad of about 4 cm.
  • Widens during pregnancy, which can lead to discomfort.
OTHER JOINTS
  • Include sacro-lumbar joints, connecting 1st sacral vertebrae with the 5th lumbar vertebrae, and the hip joint.

PELVIC LIGAMENTS

  • Definition:
      - Ligaments binding pelvic bones together.
  • Types:
      - Strengthening ligaments (sacro-iliac, sacro-coccygeal, interpubic) and filler ligaments (sacrospinous, sacrotuberous, inguinal, obturator).
STRENGTHENING LIGAMENTS
  1. Sacro-Iliac Ligament:
       - Binds sacrum and ilium at the sacroiliac joint.
  2. Sacro-Coccygeal Ligament:
       - Binds sacrum and coccyx at the sacro-coccygeal joint, extending both anteriorly and posteriorly.
  3. Interpubic Ligament:
       - Strengthens the symphysis pubis joint.
FILLER LIGAMENTS
  1. Sacrospinous Ligament:
       - Fills space between the sacrum and ischial spine.
  2. Sacrotuberous Ligament:
       - Runs from sacrum to ischial tuberosity, contributing to solidifying the pelvic wall.
  3. Inguinal Ligament:
       - Runs from the anterior superior iliac spine to the pubic bone's upper border.
  4. Obturator Ligament:
       - Closes the obturator foramen, allowing passage of nerves and blood vessels.

PELVIC RELAXATION

  • Hormones such as relaxin and progesterone cause softening and relaxation of pelvic muscles and ligaments, allowing mobility and enlargement of the birth canal during pregnancy, which can lead to back pain.
PELVIC DIVISIONS
  • The pelvis is divided regionally into:
      - False Pelvis - above the brim, not crucial in midwifery.
      - True Pelvis - below the iliopectineal line, significant in obstetrics due to forming the birth canal.

PELVIC BRIM & CAVITY

BRIM (INLET)
  • Upper boundary through which the fetus passes during birth.
CAVITY
  • Curved canal extending from the brim to the outlet, with varied diameters at differing points.

PELVIC OUTLET

  • Narrowest portion, diamond-shaped, defined by several anatomical landmarks, important during labor.

PLANE DIMENSIONS

  • Anterio-Posterior diameter is essential in assessing pelvic size for safe delivery.
      - Measured from sacrum to the pubic symphysis.
  • Oblique and transverse diameters also assessed.

PELVIC MEASUREMENTS

  • Key diameters measured via pelvimeter to assess delivery viability.
      - Internal and external measurements vary, particularly in the obstetric true conjugate and transverse diameters.

CLINICAL PELVIC ASSESSMENT

  • Confirmation of pelvic suitability for delivery through pelvic measurements and assessments of fetal positioning and maternal anatomy.

COMMON PELVIC TYPES

  1. Gynecoid:
       - Most common, 50% of women, round brim.
  2. Android:
       - Heart-shaped, male-type pelvis, reduces space for delivery.
  3. Anthropoid:
       - Oval-shaped, favorable for delivery.
  4. Platypelloid:
       - Broad and flat, complicates delivery.

ABNORMAL PELVIS TYPES

  • Other common conditions affecting pelvics:
      - Justo Minor, Nagele, Robert Pelvis, Contracted pelvis.

REFERENCES

  • Dildy, G. A. et al. (2003). Critical care obstetrics (4th ed.). Massachusetts: Blackwell Science.
  • Fox, S. I. (2011). Human Physiology, 12th ed. New York: McGraw-Hill.
  • Goldstein, A. H. (2011). Creative concepts in physiology. New York, NY: McArdle, W. D. and Katch, V. L. and Katch, F. I. (2006). Essentials of Exercise Physiology, 2nd ed. Philadelphia: Welters Klumer/Lippincott, William and Wilkins.
  • Myle’s (2020) Textbook for Midwives, 17th Edition Elsevier, UK.
  • Sylvia (1993) Anatomy and Physiology Applied to Obstetrics Author Sylvia 3rd Edition, Publisher Churchill Livingstone, 1993 UK.

CONCLUSION

  • Understanding the pelvic anatomy is crucial for midwives and healthcare providers to ensure safe delivery processes and manage any complications that may arise during labor.