The Notion Of The Body Wall Wk4

Question 1

What is the body wall?

Answer 1

• It is the continuous, layered, external surface of the human body consisting of derivatives from ectoderm and mesoderm and enclosing the body cavity
• The body wall creates a shell around the major cavities of the body
• Although functionally different, the wall of the thorax and that of the abdomino-pelvis are common both topographicallyand developmentally
• For this reason alone, it makes sense that we consider their general anatomy as derived from a common design template shared between vertebrates

Question 2

What is the general design of the body wall?

Answer 2

OUTSIDE TO INSIDE
- Skin
- Superficial fascia
With or without subcutaneous fat
- Deep fascia
Various layers at different levels
- Muscles of the body wall
- Endothoracic or transversalis fascia
This is a variant of deep fascia of the body
- Membranous linings
Pleural or peritoneal membranes
- Cavity of the region

Question 3

Overview of skin of the body wall

Answer 3

• It is common and continuous with skin from the rest of the body
• It varies in texture throughout the body wall
• Generally, it tends to be:
• Thin in front
• &
• Thick at the back
• Distribution of hair varies with sex, age and race
• Lines of cleavage run horizontally around the body wall
• Awareness of these has cosmetic value in guiding surgical incisions of skin

Question 4

What is the subcutaneous tissue of the body wall?

Answer 4

• It is through this tissue layer that our skin is:
• Tethered to the rest of the body
• Supple and flexible to move independently of deeper layers of the body
• This tissue layer is the same as that of the rest of the body
• Fat is contained in loculi whose fibrous walls connect the overlying dermis to the underlying deep fascia
• In the dilatable part of the abdominal wall, fibrous septa of subcutaneous tissues are condensed beneath the fat into a thin but strong membrane, the fascia of Scarpa

Question 5

What is cutaneous innervation of the body wall?

Answer 5

• Distribution of sensory innervation of the skin (i.e. cutaneous innervation) is complicated but can be simplified as follows:
  • Skin above the second rib is supplied by supraclavicular branches of the cervical plexus (spinal nerve root value C4)
  • Below the second rib, the skin is supplied by branches of segmental spinal nerves from neural levels of T2 to L1
  • Segmental nerves emerge in the mid-axillary line

Question 6

What is the muscle layer of the body wall made up of?

Answer 6

• This layer is divisible into 2 bilaterally symmetrical muscle groups
• Anterolateral muscle wall
• Also known as the ventrolateral wall
• Posterior muscle wall
• Also known as the dorsal muscle wall

Question 7

What are the 3 layers of muscles surrounding body cavities?

Answer 7

• It consists of 3 successive layers of muscles, irrespective of whether in front or back
• These muscles encircle the body cavity
• Fibres of muscles of the body wall run in 3 different slopes of obliquity
• The intermediate muscle layer is reinforced with bony condensations of ribs
• Ribs only insert within the intermediate layer the muscle wall
• Other muscle layers are arranged with one superficial to the ribs and the other deep
to the ribs
• Morphology of muscles of the posterior (or dorsal) abdominal wall have a different orientation to muscles of the anterolateral wall

Question 8

What are the anatomical spaces created by the body wall?

Answer 8

• As stated previously, the body wall creates the largest cavities of the boy
• Thoracic Cavity
• Abdominal Cavity
• These anatomical spaces of the body that are themselves continuations of
the embryonic fluid-filled cavity, the coelomic cavity
• A peculiarity of these cavities is that they are both lined with a double layer of mesothelium
• Also known as serous membranes
• Classified histologically as Simple Squamous Epithelium
• Also known as Pavement Epithelium
• The two layers of the mesothelium are continuous with one another
• One of the layers of mesothelium lines the inner surface of the body wall
• The other layer of mesothelium develops to enclose visceral organs of each the respective cavities

Question 9

What happens with embryology with anatomical spaces created by the body wall?

Answer 9

• During organogenesis, visceral organs form inside the embryonic cavities of the thorax and abdomen
  • As they form, these organs are able to move, grow, and develop separately and independently within confines created by the body wall
  • The manner in which visceral organs come to occupy thoracic and abdominal cavities is important because this also determines how these cavities are eventually divided into the various functional compartments
  • Compartments of thoracic and abdominal cavities are important in:
  • Anatomical organisation of the cavities
• Intrapleural & intraperitoneal cavities form the fist and balloon model (during organogenesis) - the balloon represents 2 layers of serous membranes that line the coelom and the fist represents developing visceral organ as it invades serous membranes
  • Clinical Setting

Question 10

What is a simplified overview of pleural or peritoneal cavity?

Answer 10

• Developing organs invade the thoracic or abdominal cavities by pushing against one side of the wall of the balloon whilst not having any contact with the other wall of the balloon
• The layer of the balloon that visceral organs of the thorax or abdomen push against becomes the visceral layer of pleura or peritoneum
• The layer of the balloon that most visceral organs of the thorax or abdomen do not have contact with becomes the parietal pleura or peritoneum
• The space within the balloon that lies between the 2 walls of the balloon represents the equivalent potential space found between the visceral and parietal layers of either pleura or peritoneum

Question 11

What is a simplified overview of intra-pleural or peritoneal cavity?

Answer 11

• The 2 innermost tissue layers that line the abdominal cavity are 2 closely apposed and continuous serous membranes
• Visceral Pleura or peritoneum
• Parietal Pleura or Peritoneum
• A ‘potential space’ between these peritoneal membranes is known as either the Pleural Cavity or Peritoneal Cavity

Question 12

A Simplified Overview of Pleural or Peritoneal Cavity

Answer 12

• The volume of the pleural cavity and peritoneal cavity are negligible to the point that they are almost non-existent due to closeness of the serous membranes
  • The pleural cavity or peritoneal cavity contains a thin film of fluid, the serous fluid
  • Serous fluid acts to reduce friction when the serous membranes rub against each other

Question 13

A Simplified Overview of The Intraperitoneal Cavity

Answer 13

• As developing organs invade the abdominal cavity, most of them push against the visceral layer of peritoneum until they are fully clothed in it
• Thus, most visceral organs are completely covered in the visceral layer of the peritoneum
• NB: Not all organs are covered as such
• Those visceral organs that are completely covered in the visceral layer of the peritoneum effectively create a compartment in which they are then contained within
• This is the intraperitoneal cavity

Question 14

Overview of the extraperitoneal space?

Answer 14

• In the adult, a select few abdominal organs are not covered by the visceral peritoneum
• There are 2 reasons to explain this
• 1) Some organs just do not develop within
the intraperiotoneal cavity
• 2) Other organs start off with cover of the visceral peritoneum which then degenerates during embryonic development, leaving such visceral organs devoid of the visceral layer of peritoneum
• Abdominal organs of the adult that are not covered by the visceral peritoneum are partially covered by the outer face of the parietal layer of the peritoneum instead
• These organs thus:
• Lie outside of both the intraperitoneal and
peritoneal cavities
• Are collectively known as extraperitoneal organs