Anatomy - Gastrointestinal Flashcards
Anatomy - Gastrointestinal
How is the abdominal cavity separated from the thorax?
By the diaphragm (it has apertures that allows structures to pass between the thorax and abdomen)
Pelvic cavity
- Inferior to abdominal cavity
- continuous with abdominal cavity
Which organs does the abdominal cavity contain?
Those in:
- gastrointestinal tract
- hepatobiliary system
- urinary system
- endocrine system
- also contains the spleen and the great vessels and their branches
Which organs are in the gastrointestinal tract?
- stomach
- small intestine
- large intestine
Which organs are in the hepatobiliary system?
- liver
- gallbladder
Which organs are involved in the urinary system?
- kidneys
- ureter
Which organs are involved in the endocrine system (in the abdomen)?
- pancreas
- adrenal glands
Spleen- what type of organ is it?
A haematopoietic and lymphoid organ
What are the anterior, lateral and posterior walls of the abdomen composed of?
- skin
- subcutaneous tissue
- muscles + their associated aponeuroses
Aponeuroses
Flat tendons
How many lumbar vertebrae contribute to the posterior wall of the abdominal cavity?
Five
What are the functions of the abdominal wall?
- protect the abdominal viscera
- increase the intro-abdominal pressure (e.g. for defamation and childbirth)
- maintain posture and move the trunk
What is the internal aspect of the abdominal wall lined with?
a serous membrane called parietal peritoneum
Boundaries of the abdominal cavity
- xiphisternum
- costal margin
- iliac crests
- anterior superior iliac spines (ASIS)
- pubic tubercles
- pubic symphysis (a fibrocartilaginous joint)
How can the anterior abdominal wall be described in clinical practice?
four quadrants - upper right and left and lower right and left
nine regions
Which two invisible lines outline the four quadrants?
- vertical line running down the midline through the lower sternum, umbilicus and pubic symphysis
- horizontal line running across the abdomen through the umbilicus
Why do the nine regions allow us to be more precise when describing pateint’s pain or location of tenderness, mass, swelling, or injury upon examination?
regions are smaller than the four quadrants
How is the abdomen divided into nine regions?
four imaginery lines:
- right and left midclavicular lines which extend vertically from the midclavicular point to the mid-inguinal point
- subcostal line
- intertubercular line
Subcostal line
horizontal line drawn through the inferior-most parts of the right and left costal margins (through the 10th costal cartilage)
Intertubercular line
horizontal line drawn through the tubercles of the right and left iliac crests and the body of L5
Three middle regions
superior: epigastric region
middle: umbilical region
inferior: hypogastric region
Three right side regions of anterior abdominal wall
superior: right hypochondriac region
middle: right lumbar region
inferior: right iliac region
Three left side regions
superior: left hypochondriac region
middle: left lumbar region
inferior: left iliac region
In clinical practice, what is the other term for left and right iliac region?
left and right iliac FOSSA
Other landmarks in the abdomen
- transpyloric plane
- transumbilical plane
- intercristal plane
- McBurney’s point
Transpyloric plane
- horizontal line passing through the tips of right and left 9th costal cartilages
- lies in between the superior border of manubrium and pubic symphysis
- transects the pylorus of stomach, gallbladder, pancreas and hila of kidneys
Transumbilical plane
- unreliable landmark
- position varies depending of the amount of subcutaneous fat present
- in slender individual it lies approximately at the level of L3
Intercristal plane
- horizontal line drawn between the highest points of right and left iliac crests
- cannot be palpated from anterior aspect of abdominal wall
- used to guide procedures on the back e.g. lumbar puncture
McBurney’s point
- surface marking of the base of the appendix
- lies two thirds of the way along a line drawn from the umbilicus to the right anterior superior iliac spine
What are the four pairs of muscles of the anterolateral abdominal wall?
- external oblique
- internal oblique
- transversus abdominis
- rectus abdominis
anteriorly, these muscles becomes aponeurotic - the aponeuroses fuse with each other and, in the midline, they fuse with the aponeuroses of the opposite side forming a tough midline raphe called LINEA ALBA.
Aponeuroses of these sheets also form the rectus sheath
External oblique (EO)
- diagonally orientated fibres
- most superficial
- fibres run medially and inferiorly, towards the midline
- lateral to rectus abdominis
Internal oblique (IO)
- diagonally orientated fibres
- lies deep to the EO
- fibres are orientated perpendicular to those of EO (they run medially and superiorly)
- lateral to rectus abdominis
Transversus abdominus
- horizontally orientated fibres
- deep to IO
- lateral to rectus abdominis
Rectus abdominus
- rectus = straight
- lie either side of the midline
- attached to sternum and costal margin superiorly and to pubis inferiorly
- surrounded by aponeurotic rectus sheath
Aponeurosis
a thin sheath of connective tissue that helps connect your muscles to your bones (flat tendon)
Midline Raphe
seam
Linea Alba
white line
What else does the rectus sheath do?
it encloses the rectus abdominis
Right and Left Rectus Abdominis muscles
- lie either side of the linea alba
- comprised of muscle segments interspersed with horizontal tendinous bands
- when muscle segments hypertrophy with exercise, they bulge either side of the tendinous bands and can be seen on anterior abdominal wall as bulges ‘six-pack’
True or false? The rectus abdominis lies within the rectus sheath
true
True or false? The anterior and posterior walls of the rectus sheath are formed by aponeuroses of EO, IO and transversus abdominis
true
What happens to the aponeurosis of IO as it approaches the midline?
it splits into anterior and posterior layers
What forms the anterior wall of the rectus sheath?
EO aponeurosis and anterior layer of IO aponeurosis
What forms the posterios wall of the rectus sheath?
posterior layer of IO aponeurosis and transversus abdominis aponeurosis
Transversalis fascia
lies deep to transversus abdominis
Where is the parietal peritoneum?
deep to the transversalis fascia
Inguinal ligament
formed from the attachment of the most inferior part of the external oblique aponeurosis to the anterior superior iliac spine laterally, and the pubic tubercle medially
Inhuinal canal
just above the inguinal ligament
Which arteries supply the anterolateral abdominal wall?
- musculophrenic artery (branch of internal thoracic artery)
- superior epigastric artery
- inferior epigastric artery
These vessels are accompanied by deep veins, an extensive network of superficial veins found in the anterolateral abdominal wall
Superior epigastric artery
- continuation of the internal thoracic artery
- descends in the rectus sheath
Inferior epigastric artery
- branch of external iliac artery
- ascends in the rectus sheath
- anastomoses with superior epigastric
What are the muscles and skin of the anterolateral abdominal wall innervated by?
- thoraco-abdominal nerves T7-T11
- the subcostal nerve
- iliohypogastric and ilioinguinal nerves
Thoraco-abdominal nerves T7-T11
- continuation of intercostal nerves T7-T11
- these somatic nerves contain sensory and motor fibres
Subcostal nerve
originates from T12 spinal nerve (runs along inferior border of 12th rib)
Iliohypogastric and Ilioinguinal nerves
bracnhes of the L1 spinal nerve
Hernias
- abnormal protrusion of tissues or organs from one region into another through an opening/defect
- hernia of anterior abdominal wall may occur if the muscles are weak or have been incised during surgery
- segment of the small intestine may protrude through a defect in the wall, forming a visible and palpable lumo under the skin
Laparotomy
- surgical opening of anterior abdominal wall
- used for when good access to the abdomen is needed
- midline sagittal incision of linea alba involves minimal risk to nerves and muscles
- ideally, muscles are split rather than cut
- keyhole surgery is performed where possible (laparoscopy) as it is associated with less post-operative pain, faster wound healing and a smaler risk of wound infection and post-operative hernia
Peritoneum
serous membrane that lines the abdominal wall and covers the viscera within it
Peritoneum
serous membrane that lines the abdominal wall and covers the viscera within it
Parietal Peritoneum
- Lines abdominal wall
- can be seen with naked eye
- innervated by somatic nerves that supply overlying muscles and skin of the abdominal wall
- pain from parietal peritoneum is usually sharp, severe, and well localised to abdominal wall
Visceral peritoneum
- covers the abdominal viscera
- adhered to surface of the viscera and cannot be seen with the naked eye
- innervated by visceral sensory nerves (these nerves convery ‘painful’ sensations back to CNS along the path of the sympathetic nerves that innervate the organ/structure it covers
- pain can be severe and is usually dull and diffuse
- ‘painful’ sensations may be percieved as nausea or distension
Peritoneal cavity
- lies between the parietal and visceral peritoneum
- in a healthy abdomen a thin film of peritoneal fluid lies here
What is the purpose of the peritoneal fluid?
allows the viscera to slide freely alongside each other
True or false? The two layers of peritoneum are continuous with each other
True - arrangement of the two layers mirrors the arrangement of the of the parietal and visceral pleura
How can the abdominal viscera be described as?
- Intraperitoneal: almost completely covered by peritoneum e.g. stomach
- Retroperitoneal: posterior to the peritoneum, hence only covered by peritoneum on their anterior surface e.g. pancreas and abdominal aorta
‘secondarily retroperitoneal’
- some retroperitoneal organs are described as this
- these organs were intrperitoneal in early development but came to be stuck down onto the posterior abdominal wall
Features of mesenteries, omenta, ligaments and folds
- composed of peritoneum and connect organs to each other and to the abdominal wall
- may carry blood vessels, nerves, nerves and lymphatics to the viscera
- they contain a variable amount of fat
Mesenteries
- folds of peritoneum that contain fat and suspend the small intestine and parts of the large intestine from the posterior abdominal wall
- arteries that supply the intestine (from abdominal aorta) and veins that drain the gut (tributaries of the portal venous system) are embedded into the mesenteries
Two Omenta
greater and lesser
Greater Omentum
- usually fatty and connect stomach to other organs
- hangs from the greater curvature of the stomach
- lies superficial to the small intestine
Lesser Omentum
- usually fatty and connect stomach to other organs
- connects stomach and duodenum to the liver
- hepatic artery, hepatic portal vein and bile duct are embedded within its free edge
The Portal Triad
- hepatic artery
- hepatic portal vein
- bile duct
Ligaments
- folds of peritoneum that connect organs to each other or to the abdominal wall
- falciform ligament
- coronary and triangular ligaments
Falciform ligament
connects the anterior surface of the liver to the anterior abdominal wall
Coronary and Triangular ligaments
connect the superior surface of the liver to the diaphragm
Peritoneal folds
- raised from the the internal aspect of the lower abdominal wall
- created by the structures they overlie
- somtimes they are difficult to see
- median umbilical fold
- medial unbilical fold
- lateral umbilical folds
Median umbilical fold
- lies in the midline and represents the remnant of the urachus
Urachus
an embryological structure that connected the bladder to the umbilicus
Medial umbilical folds
- lateral to the median umbilical fold
- these represent the remnants of the paired umbilical arteries, which returned venous blood to the placenta in foetal life
Lateral umbilical folds
- lateral to medial umbilical folds
- inferior epigastric arteries lie deep to these peritoneal folds
- they supply the anterior abdominal wall
Lateral umbilical folds
- lateral to medial umbilical folds
- inferior epigastric arteries lie deep to these peritoneal folds
- they supply the anterior abdominal wall
How is the peritoneal cavity divided into two regions of unequal size?
- smaller lesser sac (omental bursa)
- larger greater sac - the remaining part of the peritoneal cavity
The sacs communicate with each other via a passageway that lies posterior to the free edge of the lesser omentum - the epiploic foramen (also called the omental foramen)
Smaller lesser sac
a space that lies posterior to the stomach and anterior to the pancreas
True or false? The viscera of the abdominal cavity do not develop in the locations that we see them in the adult
true
Where does the gastrointestinal system develop from?
the embryonic gut tube which lies in the midline of the abdominal cavity, suspended from the posterior abdominal wall by the dorsal mesentery
True or false? Major branches of the abdominal aorta that supply the developing gut tube travel through the dorsal mesentery
true
Ventral mesentery
- connects the stomach to the anterior abdominal wall
- as the liver grows within it, the anterior part od the ventral mesentery becomes the falciform ligaments and the posterior becomes the lesser omentum
What happens to the organs after they grow, migrate and rotate towards their final position during development?
they ‘pull’ their peritoneal attachments with them
True or false? Growth, migration, and rotation of organs during development is responsible for the formation of the lesser sac and results in some organs being ‘pusched’ onto the posterior abdominal wall and becoming retroperitoneal
true
Peritonitis
- infection and inflammation of the peritoneum
- it may be localised or generalised
- may be caused by inflammation of an organ or rupture of a hollow viscus
- rupture of the intestine allows faecal matter and bacteria to contaminate the peritoneum
- because the peritoneum has a large surface area and is semi-permeable, peritonitis can lead to sepsis and is hence a life-threatening condition.
- extremely painful
Peritoneal Adhesions
- in healthy abdomen a thin layer of peritoneal fluid allows the abdominal viscera to slide freely alongside each other
- adhesions are pathological fibrous connections between the parietal and visceral peritoneum
- when the peritoneum is irritated it produces fibrin which causes the parietal and visceral peritoneum to adhere to each other.
- these connections may become fibrous
- can cause chronic abdominal pain and they increase the risk of volvulus (twisting) of the intestines, because it can no longer move freely
Ascites
An increased volume of peritoneal fluid.
An ascitic drain can be used to remove the fluid and relieve symptoms, but fluid will usually reaccumulate.
Oesophageal Hiatus
place at which oesophagus passes through the diaphragm at the level of T10
What does the muscle aroung the oesophogeal hiatus function as?
- sphincter
- prevents reflux of stomach contents into the oesophagus
The abdominal segment of the oesophagus is less than how many cm long?
The abdominal segment of the oesophagus is less than 2 centimetres long
What artery supplies the distal oesophagus?
bracnhes from the left gastric artery
What is the venous drainage of the distal oesophagus?
venous drainage is towards both the systemic system of veins (via oesophageal veisn that drain into the azygos vein) and to the portal venous system (via the left gastric veins)
- therefore the distal oesophagus is a site of PORTOSYSTEMIC ANASTOMOSES
What shape is the stomach
J shaped sac
What does the stomach chemically and mechanically break food down into?
chyme
What are the four parts of the stomach?
- cardia
- fundus
- body
- pyloric antrum
Cardia of the stomach
- the oesophagus travels through the diaphragm at the level of T10 and is continuous with the cardia of the stomach
Fundus of the stomach
- most superior part of the stomach
- llies superior to the level of entry of the oesophagus and is usually filled with gas
Body of the stomach
- largets part of the stomach
- inferior to cardia and fundus
Pyloric Antrum
- distal to the body
- wide and tapers towards the pyloric canal (which is narrow and contains the pyloric sphincter)
Pyloric sphincter
- formed of circular smooth muscle
- regulates the passageway of chyme into the duodenum
What is the right border of the stomach called?
lesser curvature
What is the left border of the stomach called?
greater curvature
Where does the stomach lie?
the left upper quadrant (but its size and position is variable)
What is the stomach covered with?
visceral peritoneum
What is the anterior surface of the stomach related to?
- The anterior abdominal wall
- diaphragm
- left lobe of the liver
What does the posterior surface of the stomach form?
The anterior wall of the lesser sac
True or false? The lesser sac and the structures that form it’s posterior wall lie posterior to the stomach
True
These include the pancreas, left kidney and spleen
What is the lesser omentum connected to?
The lesser curvature to the liver
What does the free edge of the lesser omentum contain?
- hepatic artery
- hepatic portal vein
- bile duct
What is posterior to the free edge of the lesser omentum?
The entrance to the lesser sac
Where does the greater omentum hang from?
The greater curvature
True or false? The stomach is supplied by arteries that branch from the coeliac trunk
True
What is the coeliac trunk?
One of the three large unpaired vessels that leave the anterior aspect of the abdominal aorta (level of T12) to supply abdominal viscera that are derived from the embryo logical foregut
What does the foregut comprise of?
- stomach
- first half of the duodenum
- liver
- gallbladder
- pancreas
Where does the spleen develop and what is it supplied by?
- develops in the dorsal messengers
- supplied by coeliac trunk
(Mesodermal in origin)
What are the branches of the coeliac trunk?
- left gastric artery
- common hepatic artery
- splenic artery
True or false? The left gastric is a much smaller calibre vessel than the common hepatic and splenic arteries
True
Where do the left and right gastric arteries run along?
The lesser curvature of the stomach (and anastomose with each other)
Where does the left gastric artery arise from?
The coeliac trunk
Where does the right gastric artery usually arise from?
The common hepatic artery
Where to the left and right gastrointestinal-omental (gastropiploic) arteries run along?
The greater curvature of the stomach and anastomose wit each other
Where does the left gastro-omental artery arise from?
The splenic artery
Where does the right gastro-omental artery arise from?
The gastroduodenal artery (a branch of the common hepatic artery)
What does the right and left gastric veins and the left gastric-omental veins drain into?
The hepatic portal vein
What is the hepatic portal vein?
A large vein that carries nutrient-rich venous blood from the GI tract to the liver
What nerve innervates the stomach?
- The vagus nerve (conveys parasympathetic fibres to the stomach)
- sympathetic fibres via the greater splanchnic nerve
What does parasympathetic stimulation of the stomach stimulate?
Promotes peristalsis and gastric secretion
What is the greater splanchnic nerve formed from?
Preganglionic sympathetic fibres that leave the spinal cord segments T5-T9
(Passes through the sympathetic trunk without synapsids)
Where do the sympathetic fibres from the greater splanchnic nerve synapse?
They synapse in the prevertebral ganglia around. The coeliac trunk.
The postganglioic fibres travel to the stomach and inhibit peristalsis and secretion
Hiatus hernia
- abdominal oesophageal and upper part of the stomach may herniate through the oesophageal hiatus into the thorax
- if contents of the stomach reflux in to the oesophageal the patient may experience heartburn and acid reflux
Gastric uLcer
- mucous lines the internal wall of the stomach and protects the mucosa from the acidic stomach contents
- a gastric (stomach) ulcer develops when the mucosal lining of the stomach breaks down
- this is normally due to infection with Helicobacter pylori, which erodes the mucosal lining, exposing the muscular wall to gastric acid and enzymes
- erosion through the wall and into nearby blood vessels can result in catastrophic intra-abdominal bleeding
Pyloric stenosis
- congenital malformation characterised by hypertrophy of the circular smooth muscle of the pyloric sphincter
- more common in baby boys than girls and typically presents at approximately six weeks after birth
- typical presentation is of vomiting (sometimes projectile) after feeds, but baby does not appear unwell and is hungry and willing to take more feeds
- with continued vomiting babies with pyloric stenosis becomes dehydrated and stop gaining weight
- can be treated surgically
Gastric cancer
- primary cancer of the stomach may present late as some of the symptoms are non-specific
- e.g. abdominal discomfort, early satiety, loss of appetite, nausea, weight loss, difficulty swallowing and indigestion
What are the three parts of the small intestine that are continuous with each other?
- duodenum
- jejunum
+ ileum
What is the duodenum?
- continuous with the pylorus of the stomach
- short and curved into a c-shape around the head of the pancreas
- most of the length of the duodenum is retroperitoneal
What is found approximately halfway along the internal wall of the duodenum?
The major duodena, papilla
What is the duodenal papilla?
Opening of the bile duct and the main pancreatic duct into the duodenum
Embryology of the duodenum
- first half develops from embryological foregut (supplied by arterial branches from coeliac trunk)
- second half develops from the embryological midgut (supplied by branches from the artery of the midgut SMA)
Jejunum
- continuous with the duodenum
- lies in the left upper region
- derived from embryological midgut
True or false? Both the jejunum and ileum are intraperitoneal and are ‘suspended’ from the posterior abdominal wall by the mesentery of the small intestine
True
Where are the blood vessels that supply the small intestine (from the SMA) embedded within?
The mesentery
Where does the small intestine lie in the abdomen?
Central
Where is the ileum in the abdomen?
Right lower region
What is the ileum derived from?
Embryological midgut (so is the jejunum)
True or false? The jejunum and ileum are the sites of nutrient absorption
True
Therefore have a vast surface area
The folds in the small intestine
- small intestine is long
- the mucosa is folded (pilcae circulates)
- the mucosal folds bear villi
- there are microvilli on the luminal surface of each epithelial cell
Where is the jejunum in the abdomen?
left upper region
Internal differences between the jejunum and ileum
- pilcae more pronouned in the jejunum
- internal ileum characterised by PEYER’S patches
Plicae
circular folds
Peyer’s patches
large submucosal lymph nodules
Meckel’s diverticulum
- a blind-ended diverticulum approximately one meter from termination in some people
- embryological remnant of the connection that was present between the midgut loop to the yolk sac
- if inflammed it may mimic appendicitis
True or false? The terminal ileum is continuous with the caecum
true - at the ileocaecal junction in the right iliac fossa
Caecum
- the first part of the large intestine
- distended blind-ended pouch
- covered by peritoneum but no mesentery
Role of the large intestine
reabsorbs water from faeca, meterial to form semi-solid faeces
Where is the large intestine?
lies peripherally in the abdomen