Abdominal wall & Development

Question 1

What are the three basic layers of the abdominal wall?

Answer 1

Skin, subcutaneous fascia and muscles

Question 2

What four muscles comprise the abdominal wall?

Answer 2

Lateral (from outside to inside): external abdominal oblique, internal abdominal oblique, transverse abdominal
Ventrally: rectus abdominis (six pack)

Question 3

Define the functions of the abdominal wall muscles.

Answer 3

1. Encloses the abdominal cavity and its content
2. Motor functions e.g. contraction causes increase in intra-abdominal pressure (used in vomiting)

Question 4

What separates the left and right rectus abdominis muscle?

Answer 4

Linea alba

Question 5

Describe the external oblique muscles.

Answer 5

1. Outermost lateral abdominal wall muscle
2. Originates on lateral caudal surfaces of ribs 4+ and lumbodorsal fascia
3. Inserts on linea alba and prepubic tendon
4. Fibres run obliquely from cranio-dorsal to caudo-ventral

Question 6

Describe the internal oblique muscles.

Answer 6

1. Middle lateral abdominal wall muscle
2. Originates on coxal tuber and lumbodorsal fascia
3. Inserts on linea alba, last rib & cartilages of caudal ribs
4. Fibres run obliquely from caudo-dorsal to cranio-ventral

Question 7

Describe the transverse abdominal muscle.

Answer 7

1. Innermost lateral abdominal wall muscle
2. Originates on medial surfaces of ventral parts of caudal ribs and deep lumbodorsal fascia
3. Inserts on linea alba
4. Fibres run transversely

Question 8

Describe the sheath of rectus abdominis muscle.

Answer 8

1. Formed from the tendons of the lateral abdominal wall muscles
2. They pass above / below rectus abdominis m. to join in the midline
3. This join is referred to as an ‘aponeurosis’ and forms the linea alba

Question 9

Describe the innervation of the abdominal wall.

Answer 9

1. Innervated by spinal nerves of last thoracic vertebra & L1-L5
2. Dorsal roots innervate dorsal musculature
3. Ventral roots split into 3 branches
   Medial - Runs between TA & IAO down to RA
   Lateral - Runs between IAO & EAO down to midway
   Lateral cutaneous - Perforates EAO to innervate skin

Question 10

What is the inguinal canal?

Answer 10

• Internal oblique muscle has gap
• External oblique muscle has slit
• It is the potential space between these 2 slits

Question 11

Where do the abdominal organs develop from and what is this divided into?

Answer 11

Embryological gut tube - foregut, midgut and hindgut.

Question 12

What 3 arteries supply the divisions of the embryological gut tube?

Answer 12

Foregut - celiac trunk
Midgut - cranial mesenteric artery
Hindgut - caudal mesenteric artery

Question 13

What does the foregut differentiate into?

Answer 13

Pharynx, oesophagus, stomach and initial duodenum

Question 14

What does the midgut differentiate into?

Answer 14

Rest of duodenum, jejunum, ileum, caecum, ascending / transverse colon

Question 15

What does the hindgut differentiate into?

Answer 15

Descending colon and rectum