15B21: Exam Report​

Outline the anatomy of the diaphragm (70% of marks). Describe the function of the diaphragm in respiration (30% of marks).

27% of candidates passed this question.

The diaphragm is the principal muscle of respiration. Important and unique features of its anatomy include a central tendon that blends with the pericardium above and the fibrous capsule of the liver below, arcuate ligaments and crura that are important points of muscle insertion. There are also three major and three minor openings that allow passage of structures between the thoracic and abdominal cavities. Candidates who had studied anatomy of the diaphragm were clearly distinguishable from those who had not.

Candidates who followed a traditional template for anatomy answers scored better, providing answers that covered the breath of the topic.

F1iii / 15B21: Outline the anatomy of the diaphragm + describe the function of the diaphragm in respiration

Definition

Diaphragm = Dome-shaped musculotendinous partition separating thoracic & abdominal cavities. The chief muscle of inspiration.

Insertions

Anterior

  • Xiphoid process
  • Costal cartilage 6 – 12

Posterior

  • Lateral arcuate lig. (overlies quadratus lumborum)
  • Medial arcuate lig. (overlying psoas major)
  • Median arcuate lig. (overlying aorta, b/w L) and R) crux)
  • R) & L) crux (blends with anterior longitudinal lig. from vertebral bodies)

Central tendon

  • Blends with PERICARDIUM superiorly
  • Blends with fibrous capsule of liver inferiorly

Openings

Caval Orifice

  • T8
  • Passage of IVC, R) phrenic, some lymph
  • IVC adheres to opening → therefore when diaphragm contracts in inspiration, widens & dilates IVC →  ↑VR

Oesophageal Hiatus

  • T10
  • Within sling of R) crura
  • Passage of oesophagus & vagus (X) nerve

Aortic Hiatus

  • T12
  • Posterior to median arcuate lig.
  • Passage of:
    • Aorta
    • Azygous v.
    • Thoracic duct

Blood Supply

Arterial

  • Superior: superior phrenic a.
  • Inferior: inferior phrenic a.

Venous

  • Superior: musculophrenic & pericardiophrenic v.
  • Inferior: inferior phrenic v.

Nerves

  • Motor – phrenic (C3 – 5)
  • Sensory – phrenic & inferior intercostal n.

Function

Inspiration

  • Diaphragm contracts
  • Dome flattens & descends
  • Pushes lower thoracic ribs outwards
  • Increases AP diameter & sup-inf. distance of thorax → ↑intrathoracic vol →  -ve intrathoracic P →  air inspiration
  • Caval orifice dilates → ↑VR
  • Oesophageal hiatus constricts → R) crus fibres merge to form a muscular sphincter →  prevents reflux