Anterior abdominal wall and GI tract

Recall the regions and quadrants of the abdomen.

Describe the bones of the abdomen (lumbar vertebrae)

5 lumbar vertebrae forming lumbar spine: large, kidney-shaped vertebral bodies, a triangular vertebral foramen, short and sturdy spinous processes for muscle attachment, and thick pedicles and laminae that create a strong vertebral arch

Describe the arrangement of the muscles that make up the anterior and lateral abdominal wall and describe their actions.

All muscles aim to stabilize the vertebral column, move the trunk, protect abdominal organs, and aid in forceful expiration and activities that increase intra-abdominal pressure

vertical rectus abdominis muscles and three flat, stacked muscles: the external oblique, internal oblique, and transversus abdominis

Distinguish the major segments of the gastrointestinal (GI) tract and recall the key features of each segment.

• mouth - ingestion

• pharynx/oesophagus - propulsion

• stomach - storage, mixing, digestion

• small intestine - digestion + nutrient absorption

• large intestine - water absorption + waste formation

• rectum/anus - elimination

Describe the pattern of blood supply and venous drainage of the GI tract.

blood supply: by branches of the abdominal aorta: coeliac trunk (foregut), superior mesenteric artery (SMA, midgut) and inferior mesenteric artery (IMA, hindgut).

venous drainage:

• SMV - midgut ie jejunum, ileum, cecum, appendix, ascending colon + first 2/3 of transverse colon

• splenic vein - foregut ie stomach spleen and pancreas

• IMV - hindgut, including the last 1/3 of transverse colon, descending colon, sigmoid colon, upper part of rectum

Which 2 main structures make up the abdomen?

abdominal wall and cavity 

What is the abdominal wall made up of?

muscles make up both the anterior and posterior abdominal wall

Which viscera are found within the abdominal cavity?

• GI tract (abdominal oesophagus, stomach, small intestine, large intestine, upper 1/3 rectum)

• Accessory organs of digestion, (liver, gallbladder, pancreas)

• Urinary system (kidneys, ureters)

Which vessels are found within the abdominal cavity?

arteries - abdominal aorta, veins - inferior vena cava, lymphatics etc

What qualifies an organ as being an “accessory“ organ of digestion?

no contact with food itself - will help store, secrete chime ie liquid food 

What is the abdomen’s position relative to the thorax?

inferior, just below the diaphragm and xiphoid process

Describe the morphology of abdominal wall muscles

flat muscles surrounding abdominal cavity

What are the functions of abdominal wall muscles?

• protect abdominal viscera (absence of bones means more protection is needed)

• maintain posture and move the trunk

What are the 2 functional groups of abdominal wall muscles?

• anterolateral muscles (lateral ie on left and right sides)

• posterior muscles 

What are the muscles of the abdominal wall from superficial to deep?

• anterolateral wall with anterior and lateral muscles

• external oblique muscles 

• rectus abdominis muscles

• internal oblique muscles 

• transversus abdominis muscle 

• rectus sheath

What is the function of muscles in the abdominal anterolateral wall?

increase intra-abdominal pressure for defecation and childbirth eg

How are fibres within the anterolateral wall organised?

different fibre orientation = stronger meshwork of fibres

What are the 2 groups of muscles making up the anterolateral wall of the abdomen? How many muscles make up the two groups?

• anterior muscles - 2 muscles on either side of the midline

• lateral muscles - 3 muscles on either side of the abdomen

What connects the 2 groups of muscles of the anterolateral wall of the abdomen?

rectus sheath

What is the most superficial muscle of the anterolateral wall? How does its fibres run?

external oblique muscle

medially and inferiorly towards the midline (like hands in a pocket)

What forms the anterior wall of the rectus sheath?

external oblique muscle aponeurosis

What is aponeurosis?

a sheet of pearly white fibrous tissue that acts as a tendon in flat muscles, having a wide area of attachment - attaches muscle to bone 

What do the muscles of the rectus abdominus run alongside?

the linea alba (white line)

What directions do the muscles of the rectus abdominus run?

long vertical muscles running superior to inferior

What are muscles of the rectus abdominus intersected by?

tendinous intersections

What two lines make up the “6 pack“ visible on some individuals? 

linea alba (vertical) and tendinous intersections (horizontal) forming the pockets known as a 6 pack

What does the rectus abdominus muscle lie within?

rectus sheath

Which structure’s fibres run perpendicular to those of the external oblique muscle?

internal oblique muscle 

Describe the orientation of the internal oblique muscle’s fibres

run medially and superiorly - perpendicular to those of the EOm

Where does the IOm aponeurosis divide? into which sections?

at rectus sheath

anterior ½ forms anterior wall, posterior ½ forms posterior wall

What is the deepest muscle?

transversus abdominis muscle

What separates the transversus abdominis muscle from the abdominal cavity?

transversalis fascia 

How are the fibres of the transversus abdominis muscle orientated?

horizontally

What does the TAm aponeurosis form?

posterior wall of rectus sheath

What forms the anterior and posterior walls of the rectus sheath? What does the latter contain?

formed by aponeurosis of the 3 lateral muscles:

• anterior made up of external oblique muscle aponeurosis + anterior ½ of the IOm

• posterior made up of aponeurosis of posterior ½ of IOm and t transversus abdominis muscle

contains the rectus abdominis muscle

Define fascia

thin casing of connective tissue that surrounds and holds structures

What defines the midline of the rectus sheath?

linea alba 

What is the goal of the gastrointestinal tract?

to process food and eliminate waste

What are secondary accessory organs of digestion?

salivary glands, liver, gallbladder, pancreas

What pathway does the GI tract follow?

continuous pathway from mouth to anus : Thoracic and abdominal oesophagus, stomach, small intestine, large intestine, upper 1/3 rectum

What does the blood supply for the GI tract come from?

from abdominal aorta: 3 branches coming anteriorly - coeliac trunk + superior mesenteric artery (SMA) + inferior mesenteric artery (IMA)

What are the 2 portions of the oesophagus?

• thoracic

• abdominal

What are the different parts of the stomach from superior to inferior?

from the oesophagus - cardia, fundus, body, pyloric region (antrum, canal and sphincter) + lesser and greater curvatures

What is the blood supply for the stomach?

coeliac trunk

Describe the anatomy of the thoracic portion of the oesophagus

superior and posterior mediastina, runs with vagal trunks, pierces diaphragm at oesophageal hiatus

Describe the anatomy of the abdominal portion of the oesophagus

very short, connects with stomach at cardiac sphincter

What is the blood supply to the small intestine ?

coeliac trunk + SMA

What are the 3 parts of the small intestine?

duodenum, jejunum, ileum

Which of the 3 parts of the small intestine is most distinct ? Why?

duodenum is very distinct with the major duodenal papilla

Which 2 parts of the small intestine are most similar ?

Jejunum and ileum share similarities but not the same! bc of different artery blood supply

What does the mesentery enclose? What does it attach these to?

small intestines and parts of colon (transverse/sigmoid)

posterior abdominal wall

What part of the small intestines is c shaped?

duodenum

What is the role of the major duodenal papilla?

nipple-like protrusion, external opening for the common bile duct and the pancreatic duct - aids in digestion, draining and controlling fluids from the bile and pancreatic ducts

Which structures are found within the mesentery?

blood vessels, nerves, lymphatic vessels, lymph nodes, and adipose (fatty) tissue

What is the blood supply to the small intestines?

coeliac trunk and superior mesenteric artery

What are different parts of the large intestines?

caecum, appendix, colon, rectum and anal canal

What is the colon divided into?

ascending, transverse, descending, and sigmoid colon

What are characteristic features of the large intestines?

epiploic appendices, taenae coli and haustrations

At what point does the small intestine become the big one?

at the ileocecal valve

What is the blood supply to the large intestines?

SMA + IMA

What do the embryological origins of the GI tract inform on? What are these 3 parts?

blood supply

foregut, midgut and hindgut

Which structures are found within the foregut?

From oesophagus to duodenum at the level of the major duodenal papilla (halfway along the duodenum)

What is the blood supply to the foregut?

coeliac trunk

Which structures are found within the midgut?

From major duodenal papilla to 2/3 of transverse colon

Which structures are found within the hindgut?

From last 1/3 of transverse colon to upper 1/3 rectum (+ anal canal)

What is the blood supply to the midgut?

SMA

What is the blood supply to the hindgut?

IMA

What are the 3 branches of the aorta supplying the GI tract?

first is celiac trunk, second is superior mesenteric artery, third is inferior mesenteric artery

At which level of the spine does the aorta bifurcate into L/R common iliac arteries?

L4 (lumbar 4)

At which level of the spine does the coeliac trunk come off the aorta?

thoracic 12, T12

At which level of the spine do SMA and IMA come off the aorta?

L1 and L3

At which level of the spine do renal and gonadal arteries come off the aorta?

renal off L1/L2, gonadal off L2

List the arteries that branch off the second branch of the abdominal aorta, the superior mesenteric artery

• inferior pancreaticoduodenal

• jejunal and ileal

• ileocolic

• right colic

• middle colic

What does the inferior pancreaticoduodenal artery of the SMA of the abdominal aorta supply?

pancreas and last part of duodenum

What do the jejunal and ileal arteries of the SMA of the abdominal aorta supply?

jejunum and ileum

What does the ileocolic artery of the SMA of the abdominal aorta supply?

ileocaecal artery 

What does the right colic artery of the SMA of the abdominal aorta supply?

ascending colon

What does the middle colic artery of the SMA of the abdominal aorta supply?

ascending colon and 2/3 of transverse colon

What is the junction below the liver of the large intestine called? What supplies it?

hepatic flexure

middle colic artery

At which lumbar vertebrae is the midgut supplied?

L1 over the duodenum

At which lumbar vertebrae is the hindgut supplied?

L3, under duodenum

What are the 3 branches coming off the inferior mesenteric artery of the abdominal aorta?

• left colic artery

• sigmoid arteries

• superior rectal artery

What does the left colic artery supply?

left side of colon ie last 1/3 transverse colon and descending colon

What do the sigmoid/sigmoidal arteries supply?

last part of descending colon and sigmoid colon

What does the superior rectal artery supply?

upper ⅓ of rectum

What separates the abdominal cavity from the thorax?

the diaphragm 

What are the 3 lateral muscles of the anterolateral abdominal wall? the 2 vertical ones?

EOm, IOm and TAm

RAm