Download LECTURE 22 - THORACIC WALLS AND DIAPHRAM Function

LECTURE 22 - THORACIC WALLS AND DIAPHRAM
Function – protection and breathing
Ribcage – bony framework of the thorax supporting the thoracic
cage covered by tissues like muscles and skin. The breast is also
part of the thoracic wall
The ribcage is composed of the following bones–
• Sternum – made of three parts,
o Manubrium – the top section of the sternum where
sternoclavicular joints are found
o The body
o Xiphoid process – the bottom
• 12 thoracic vertebrae and intervertebral discs
• 12 pairs of ribs and costal cartilages
o true ribs – ribs 1 – 7 have their own cartilage that
directly articulates to the sternum
o false ribs – ribs 8 – 10 have cartilage that articulate
with the cartilage of the above rib, hence they
indirectly articulate with the sternum
o floating ribs – ribs 11 and 12 do not have cartilage
and do not articulate with the
sternum
The structure of typical ribs Ribs 3 – 9 are typical ribs, and 1,2, 10 – 12
are atypical ribs
Typical ribs –
• vertebral end – the head of the rib
is at the posterior and articulates
with the transverse processes of the
spine,
• the vertebral end has two smooth
impressions called facets, then the vertebral end narrows
into a neck
• articular facet - tubercle that is smooth for articulation
• the tubercle lateral to the articular facet is for muscle
attachment
• the body of the rib is curved
• the top of the body is called the
superior border, the bottom is the
inferior border.
• The costal groove runs along the
inferior border and it is for
neurovascular supply to muscles
between ribs
• sternal end – anterior, smooth
Thoracic vertebra –
Typically have 3 facets on each side.
There are 2 on the body of the vertebrae (superior and inferior
costal facets) that articulate with the vertebral head of the rib. This
is the costovertebral joint – 1 rib articulates with two vertebra, eg
the 7th rib will articulate with T6 and T7 vertebra.
There is one on the transverse processes called the transverse
costal facet which articulates with the tubercle. The costotransverse
joint is the joint between the smooth tubercle of the rib and the
transverse process of the above vertebrae
Thoracic apertures – the ribcage has 2 openings, the superior
aperture and the inferior aperture.
The superior aperture is at T1. It is partially closed by the
suprapleural membrane, but is centrally open
The inferior aperture is at T12 posteriorly and at the xiphoid process
anteriorly. It is completely closed off by the diaphragm
The diaphragm – muscle with a central
tendon / insertion and a circular origin around
the inferior aperture. The diaphragm has two
domes that attach to lumbar vertebrae via crus.
The right dome is higher because it is pushed
up by the liver, and the right crus is longer than
the left crus for a firmer attachment.
When the diaphragm contracts it increases the
volume in the rib cage, decreases the pressure
in the rib cage and leads to inspiration (breathe
in)
There are three holes in the diaphragm and
they have the following functions
• Allows the vena cava to pass through
• Allows the esophagus to pass trhough
• Allows the aorta to pass through
The aorta doesn’t really create a hole but it passes through the
space between the two crus – allowing the aortas blood pressure to
remain the same during contractions of the diaphragm
Nerve supply of the diaphragm comes from phrenic nerves (Cervical
supply)
Intercostal space
The space between ribs is called the intercostal space. It contains
intercostal muscles, intercostal nerves, intercostal arteries and
intercostal veins. Intercostal muscles are organized in three layers
• External – replaced by intercostal membrane anteriorly,
contraction of these muscles pulls ribs up and out to
increase volume during inspiration
• Internal – fibres in opposite direction of external muscles,
at the posterior of the ribcage replaced by intercostal
membrane, in theory contraction should lead to expiration
but expiration is actually passive.
• Innermost – discontinuous patchy layer
Nerve and vascular supply from the costal groove. The groove is
organized as vein, artery, then nerve (top to bottom). The
intercostal nerve comes from posterior rami of T1 – T11 spinal
nerves, runs between internal and innermost muscles, and supplies
the intercostal space and the thoracic wall.
Two types of intercostal arteries
• Posterior intercostal arteries – originate from the aorta
• Anterior intercostal arteries – originate from internal
thoracic arteries
The intercostal arteries supply to the intercostal space and the
cutaneous of the wall
Movements of the thoracic wall
The thorax can be changed at the vertical axis via the diaphragm,
contract longer, relax shorter
Anterposterior movements by movement of the upper ribs
The lateral dimension by movements of the lower ribs