Anatomy Flashcards
How is the The abdominal cavity separated from the thorax?
By the diaphragm
Apertures
the diaphragm contains apertures that allow structures to pass between the thorax and abdomen.
The pelvic cavity lies inferior to the abdominal cavity and is continuous with it.
What organs does the abdominal cavity contain?
Organs of the
gastrointestinal tract (stomach, small and large intestine),
the hepatobiliary system (liver and gallbladder),
the urinary system (kidneys and ureters)
the endocrine system (pancreas and adrenal glands)
The abdomen also contains the spleen (a haematopoietic and lymphoid organ) and the great vessels (abdominal aorta and inferior vena cava) and their branches.
What are the anterior, lateral and posterior walls of the abdomen composed of?
skin, subcutaneous tissue and muscles and their associated aponeuroses (flat tendons).
Five lumbar vertebrae contribute to the posterior wall of the abdominal cavit
Functions of the abdominal wall
• protect the abdominal viscera
• increase intra-abdominal pressure (e.g. for defecation and childbirth)
• maintain posture and move the trunk
parietal peritoneum
Serous membrane lining the internal aspect of the abdominal walls
Several bony landmarks define the boundaries of the abdominal cavity. These are the:
• Xiphisternum
• Costal margin
• Iliac crests
• Anterior superior iliac spines (ASIS)
• Pubic tubercles
• Pubic symphysis (a fibrocartilaginous joint)
The 4 quadrants
a vertical line that runs down the midline through the lower sternum, umbilicus, and the pubic symphysis
• a horizontal line that runs across the abdomen through the umbilicus.
The 9 regions- The abdomen is divided into nine regions by four imaginary lines:
the right and left midclavicular lines, which extend vertically from the midclavicular point to the mid-inguinal point (halfway between the anterior superior iliac spine and the pubic tubercle)
• the subcostal line - a horizontal line drawn through the inferior-most parts of the right and left costal margins (through the 10th costal cartilage)
• the intertubercular line - a horizontal line drawn through the tubercles of the right and left iliac crests and the body of L5.
In addition to the subcostal and intertubercular planes described above, other landmarks and planes associated with the abdominal wall
Transpyloric plane
Transumbilical plane
Intercristal plane
McBurney’s point
Transpyloric plane
a horizontal line that passes through the tips of the right and left ninth costal cartilages.
It lies between the superior border of the manubrium and the pubic symphysis.
It transects the pylorus of the stomach, the gallbladder, the pancreas and the hila of the kidneys.
Transumbilical plane
this is an unreliable landmark as its position varies depending on the amount of subcutaneous fat present.
In a slender individual it lies approximately at the level of L3.
Intercristal plane
a horizontal line drawn between the highest points of the right and left iliac crests.
It cannot be palpated from the anterior aspect of the abdominal wall. It is used to guide procedures on the back (e.g. lumbar puncture).
McBurney’s point
the surface marking of the base of the appendix.
It lies two thirds of the way along a line drawn from the umbilicus to the right anterior superior iliac spine.
4 pairs of muscles comprise the anterolateral abdominal wall
External oblique
Internal oblique
Transversus abdominis (horizontally orientated fibres)
Recuts abdominis (rectus=straight)
Where can the rectus abdominis muscles be found?
The vertical right and left rectus abdominis muscles lie either side of the midline.
Rectus abdominis is attached to the sternum and costal margin superiorly and to the pubis inferiorly and is surrounded by an aponeurotic rectus sheath
Lateral to the rectus abdominis lie three sheets of muscle whose fibres run in different directions to each other:
• External oblique (EO) is most superficial. The fibres of EO run medially and inferiorly, towards the midline
• Internal oblique (IO) lies deep to EO. The fibres of IO are orientated perpendicular to those of EO (they run medially and superiorly).
• Transversus abdominis lies deep to internal oblique. Its fibres are orientated horizontally.
Anteriorly, these muscles become aponeurotic (an aponeurosis is a flat tendon)
The fibres of the aponeuroses fuse with each other and, in the midline, they fuse with the aponeuroses of the opposite side, forming a tough midline raphe (= seam) called the linea alba (‘white line’).
The aponeuroses of these muscles also form the rectus sheath, which encloses the rectus abdominis.
The right and left rectus abdominis muscles lie either side of the linea alba.
• It is comprised of muscle segments interspersed with horizontal tendinous bands
When the muscle segments hypertrophy with exercise, they bulge either side of the tendinous bands and can been seen on the anterior abdominal wall as bulges – the ‘six-pack’.
Rectus abdominis lies within the rectus sheath.
The anterior and posterior walls of the rectus sheath are formed by the aponeuroses of EO, IO and transversus abdominis
• As it approaches the midline, the aponeurosis of IO splits into anterior and posterior layers
• The EO aponeurosis and the anterior layer of the IO aponeurosis form the anterior wall of the rectus sheath
• The posterior layer of the IO aponeurosis and the transversus abdominis aponeurosis form the posterior wall of the rectus sheath.
The transversalis fascia lies deep to transversus abdominis
Deep to the fascia lies the parietal peritoneum
The most inferior part of the external oblique aponeurosis is attached to the anterior superior iliac spine laterally and the pubic tubercle medially, forming the inguinal ligament
Just above the inguinal ligament is the inguinal canal
Vessels of the Anterior Abdominal Wall- The anterolateral abdominal wall is supplied by the following arteries:
• musculophrenic artery, a branch of the internal thoracic
• superior epigastric artery, which is the continuation of the internal thoracic artery. It descends in the rectus sheath
• inferior epigastric artery, a branch of the external iliac artery. It ascends in the rectus sheath and anastomoses with the superior epigastric
These vessels are accompanied by deep veins.
An extensive network of superficial veins is found in the anterolateral abdominal wall
The muscles and skin of the anterolateral abdominal wall are innervated by:
• Thoraco-abdominal nerves T7 – T11. These are essentially the continuation of the intercostal nerves T7 – T11. These somatic nerves contain sensory and motor fibres
• The subcostal nerve – this originates from the T12 spinal nerve (so called because it runs along the inferior border of the 12th rib)
• Iliohypogastric and ilioinguinal nerves – both are branches of the L1 spinal nerve
Parietal peritoneum lines the abdominal wall
• It can be seen with naked eye and is innervated by the somatic nerves that supply the overlying muscles and skin of the abdominal wall
• Pain from the parietal peritoneum is usually sharp, severe, and well localised to the abdominal wall
Visceral peritoneum covers the abdominal viscera
• It is adhered to the surface of the viscera and cannot be seen with the naked eye
• The visceral peritoneum is innervated by visceral sensory nerves. These nerves convey ‘painful’ sensations back to the CNS along the path of the sympathetic nerves that innervate the organ / structure it covers
• Pain from the visceral peritoneum can be severe. It is usually dull and diffuse (i.e. it cannot be pinpointed to a specific location)
• ‘Painful’ sensations from the visceral peritoneum may be perceived as nausea or distension
Peritoneal cavity
Between the parietal and visceral peritoneum lies the peritoneal cavity
In a healthy abdomen, a thin film of peritoneal fluid lies in the peritoneal cavity
It allows the viscera to slide freely alongside each other
The two layers of peritoneum are continuous with each other. The arrangement of the two layers mirrors the arrangement of the parietal and visceral pleurae
Depending on the extent to which they are covered by peritoneum, the abdominal viscera are described as:
• Intraperitoneal: almost completely covered by peritoneum e.g. the stomach
• Retroperitoneal: posterior to the peritoneum, hence only covered by peritoneum on their anterior surface e.g. the pancreas and abdominal aorta.
Mesenteries, Omenta, Ligaments and Folds
• They are all composed of peritoneum and connect organs to each other and to the abdominal wall
• They may carry blood vessels, nerves, and lymphatics to the viscera
• They contain a variable amount of fat; some are usually very fatty (the omenta).
Mesenteries
are 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 the abdominal aorta) and veins that drain the gut (tributaries of the portal venous system) are embedded in the mesenteries.
The greater and lesser omertà
folds of peritoneum that are usually fatty and connect the stomach to other organs
The greater omentum
Hangs from the greater curvature of the stomach and lies superficial to the small intestine
The lesser omentum
connects the stomach and duodenum (the first part of the
small intestine) to the liver
The hepatic artery, the hepatic portal vein, and the bile duct (the ‘portal triad’) are embedded within its free edge.
Ligaments
Are folds of peritoneum that connect organs to each other or to the abdominal wall.
Peritoneal ligaments
falciform ligament, which connects the anterior surface of the liver to the anterior abdominal wall
the coronary and triangular ligaments, which connect the superior surface of the liver to the diaphragm
Where are peritoneal folds raised from?
Raised from the internal aspect of the lower abdominal wall and are created by the structures they overlie, like carpet running over a cable
Where does the median umbilical fold lie?
lies in the midline and represents the remnant of the urachus, an embryological structure that connected the bladder to the umbilicus.
Lateral to the median umbilical fold lie the medial umbilical folds
These represent the remnants of the paired umbilical arteries, which returned venous blood to the placenta in foetal life
Lateral to the medial umbilical folds are the lateral umbilical folds
The inferior epigastric arteries lie deep to these peritoneal folds. They supply the anterior abdominal wall
The peritoneal cavity is divided into two regions of unequal size
• The smaller lesser sac (also called the omental bursa) is a space that lies posterior to the stomach and anterior to the pancreas
• The larger greater sac is the remaining part of the peritoneal cavity.
How do the greater and lesser 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)
Where does the gastrointestinal system develop from
The gastrointestinal system develops from the embryonic gut tube which lies in the midline of the abdominal cavity, suspended from the posterior abdominal wall by the dorsal mesentery
Major branches of the abdominal aorta that supply the developing gut tube travel through the dorsal mesentery
The ventral mesentery connects the stomach to the anterior abdominal wall
As the liver grows within it, the anterior part of the ventral mesentery becomes the falciform ligament and the posterior part becomes the lesser omentum
During development, organs grow, migrate, and rotate towards their final positions
As they do so, they ‘pull’ their peritoneal attachments with them.
Growth, migration, and rotation of organs during development is responsible for the formation of the lesser sac and results in some organs being ‘pushed’ onto the posterior abdominal wall and becoming retroperitoneal
Distal oesophagus
The oesophagus passes through the oesophageal hiatus in the diaphragm at the level of T10.
The muscle around the hiatus functions as a sphincter that prevents reflux of stomach contents into the oesophagus.
The abdominal segment of the oesophagus is less than 2 centimetres long.
What is the distal oesophagus supplied by?
branches from the left gastric artery.
Its venous drainage is towards both the systemic system of veins (via oesophageal veins that drain into the azygos vein) and to the portal venous system (via the left gastric veins).
The distal oesophagus is thus a site of portosystemic anastomoses, which are clinically important.
Shape of the stomach
The stomach is a J-shaped sac that expands to accommodate food and fluid.
The stomach chemically and mechanically breaks down food into chyme
The stomach is described in 4 parts
• The oesophagus travels through the diaphragm at the level of T10 and is continuous with the cardia of the stomach
• The most superior part of the stomach is the fundus. It lies superior to the level of entry of the oesophagus and is usually filled with gas
• The largest part of the stomach is the body
• The pyloric part is distal to the body. The pyloric antrum is wide and tapers towards the pyloric canal, which is narrow and contains the pyloric sphincter The sphincter is a formed of circular smooth muscle. It regulates the passage of chyme into the duodenum
• The right border of the stomach is the lesser curvature. The longer left border is the greater curvature
Location and relations of the stomach and the lesser sac
The stomach lies in the left upper quadrant, but its size and position are variable. It is covered with visceral peritoneum
Its anterior surface is related to the anterior abdominal wall, diaphragm, and left
lobe of the liver
Its posterior surface forms the anterior wall of the lesser sac
The lesser sac and the structures that form its posterior wall lie posterior to the stomach: these include the pancreas, left kidney and spleen.
The lesser omentum connects the lesser curvature to the liver
The free edge of the lesser omentum contains the hepatic artery, hepatic portal
vein and the bile duct.
Posterior to the free edge is the entrance to the lesser sac.
The greater omentum hangs from the greater curvature
Blood supply of the stomach
The stomach is supplied by arteries that branch from the coeliac trunk.
The coeliac trunk is one of three large unpaired vessels that leave the anterior aspect of the abdominal aorta (at the level of T12) to supply the abdominal viscera that are derived from the embryological foregut.
The foregut comprises the stomach, the first half of the duodenum, the liver, gallbladder, and pancreas
The spleen develops in the dorsal mesentery, and is supplied by the coeliac trunk, but it is mesodermal in origin
The coeliac trunk is only a short stump; it divides into three branches close to the aorta
These are the left gastric artery, the common hepatic artery, and the splenic artery
The left gastric is a much smaller calibre vessel than the common hepatic and splenic arteries
The left and right gastric arteries run along the lesser curvature of the stomach and anastomose with each other.
• The left gastric artery arises from the coeliac trunk
• The right gastric artery usually arises from the common hepatic artery
The left and right gastro-omental (gastroepiploic) arteries run along the greater curvature of the stomach and anastomose with each other
• The left gastro-omental artery arises from the splenic artery
• The right gastro-omental artery arises from the gastroduodenal artery, a branch of the common hepatic artery
Right and left gastric veins and right and left gastro-omental veins accompany the arteries described above.
They ultimately drain into the hepatic portal vein (HPV).
The hepatic portal vein is a large vein that carries nutrient-rich venous blood from the GI tract to the liver
Innervation of the stomach
The vagus nerve conveys parasympathetic fibres to the stomach.
Parasympathetic stimulation promotes peristalsis and gastric secretion
Sympathetic fibres are conveyed to the stomach via the greater splanchnic nerve.
The greater splanchnic nerve is formed of preganglionic sympathetic fibres that leave spinal cord segments T5-T9 and pass through the sympathetic trunk without synapsing.
The fibres synapse in prevertebral ganglia around the coeliac trunk. The postganglionic fibres travel to the stomach and inhibit peristalsis and secretion.
Small intestine
The small intestine lies centrally in the abdomen and has three ‘parts’ that are continuous with each other; the duodenum, the jejunum, and the ileum
Duodenum
The duodenum is continuous with the pylorus of the stomach
It is short and curved into a C-shape around the head of the pancreas. Most of the length of the duodenum is retroperitoneal
Approximately halfway along the internal wall of the duodenum is the major duodenal papilla
This is the opening of the bile duct and the main pancreatic duct into the duodenum
Where does each part of the duodenum develop from?
The first half of the duodenum develops from the embryological foregut and is supplied by arterial branches from the coeliac trunk.
The second half of the duodenum develops from the embryological midgut and is supplied by branches from the artery of the midgut – the superior mesenteric artery.
Jejunum and Ileum
The jejunum is continuous with the duodenum
Both the jejunum and ileum are intraperitoneal and are ‘suspended’ from the posterior abdominal wall by the mesentery of the small intestine
Blood vessels that supply the small intestine (from the superior mesenteric artery) are embedded within the mesentery
The small intestine lies centrally in the abdomen; the jejunum lying in the left upper region and the ileum lying in the right lower region
Where are the jejunum and ileum derived from?
Both the jejunum and ileum are derived from the embryological midgut
Structure of the jejunum and ileum
The jejunum and ileum are the sites of nutrient absorption, so have a vast surface area: the small intestine is long, the mucosa is folded (plicae circulares), the mucosal folds bear villi and there are microvilli on the luminal surface of each epithelial cell.
Internal difference between the jejunum and the ileum
The plicae are more pronounced in the jejunum. The internal ileum is characterised by Peyer’s patches, which are large submucosal lymph nodules.
Meckel’s diverticulum
In some people, the ileum bears a blind-ended diverticulum approximately one meter from its termination; meckels diverticulum
It is the embryological remnant of the connection that was present between the midgut loop to the yolk sac. If it becomes inflamed, it may mimic an appendicitis (inflammation of the appendix)
The terminal ileum
The terminal ileum is continuous with the caecum - the first part of the large intestine – at the ileocaecal junction in the right iliac fossa.
The large intestine function
reabsorbs water from faecal material to form semi-solid faeces. It lies peripherally in the abdomen and is composed of the caecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal
Segments of the large intestine
Some segments are retroperitoneal, and some are intraperitoneal
Distinguishing between the large and small intestine
The large intestine is peripherally located, and larger calibre.
The outer longitudinal muscle layer is organised into three bands – the taeniae coli
The inner circular muscle layer forms ‘bulges’ called haustra (or haustrations).
The large intestine bears fatty tags called epiploic appendages (appendices epiploicae) that mark the point at which blood vessels penetrate the intestinal wall.
Caecum
The caecum is the first part of the large intestine. It is a distended (swollen), blind-ended ‘pouch’.
The caecum is covered by peritoneum but does not have a mesentery.
Appendix
The appendix is a small diverticulum that arises from the caecum and contains lymphoid tissue.
The surface marking of the base of the appendix is McBurney’s point.
The appendix varies in length and the position of its tip is variable. The appendix is connected to the caecum by a small mesentery, the mesoappendix.
Ascending colon
The ascending colon is continuous with the caecum. It runs vertically on the right side of the posterior abdominal wall in the right paracolic gutter. It is retroperitoneal (it is an example of a secondarily retroperitoneal organ).
The ascending colon makes a 90 degree turn left in the right upper quadrant, becoming continuous with the transverse colon.
The ‘bend’ in the colon here is the hepatic flexure (sometimes called the right colic flexure).
Transverse colon
The transverse colon is continuous with the ascending colon. It runs horizontally in the upper abdomen but often hangs inferiorly. It is intraperitoneal and is suspended from the posterior abdominal wall by the transverse mesocolon.
The transverse colon makes a 90 degree turn inferiorly in the left upper quadrant, becoming continuous with the descending colon. The ‘bend’ in the colon here is the splenic flexure (sometimes called the left colic flexure).
The splenic flexure is tethered to the diaphragm by the phrenicocolic ligament
The transverse colon marks the transition point between the embryological midgut and embryological hindgut
The proximal (first) two thirds develop from the embryological midgut, whilst the distal (last) third develops from the embryological hindgut.
This means that these two parts of the transverse colon are supplied by different blood vessels and nerve
Descending colon
The descending colon is continuous with the transverse colon superiorly and the sigmoid colon inferiorly.
It runs vertically on the left side of the posterior abdominal wall in the left paracolic gutter. It is retroperitoneal (also secondarily retroperitoneal).
Sigmoid colon
The sigmoid colon lies in the left lower quadrant and is named because of its sinuous shape.
It is continuous with the descending colon superiorly and the rectum inferiorly.
As the sigmoid approaches the midline, it makes a 90 degree turn inferiorly into the pelvis - this ‘bend’ is the rectosigmoid junction.
The sigmoid colon has a mesentery - the sigmoid mesocolon - and is therefore intraperitoneal.
Rectum and anal canal
The rectum descends inferiorly into the pelvis from the rectosigmoid junction and is retroperitoneal.
The rectum stores feaces until it is convenient to defecate.
The rectum is continuous inferiorly with the anal canal.
The gastrointestinal tract is supplied by three large unpaired arteries that leave the abdominal aorta. These are the:
• coeliac trunk
• superior mesenteric artery (SMA)
• inferior mesenteric artery (IMA)
Coeliac trunk
It leaves the aorta at the level of T12 and gives rise to branches that supply the foregut – the oesophagus, stomach, first half of the duodenum, liver, gallbladder, bile ducts, pancreas and spleen.
The superior mesenteric is the artery of the midgut
It leaves the aorta at the level of L1.
Its branches supply the midgut structures: the second half of the duodenum, the small intestine, and the large intestine as far as (and including) the first two thirds of the transverse colon.
Branches also supply parts of the pancreas.
The inferior mesenteric artery is the artery of the hindgut
It leaves the aorta at the level of L3. It is a smaller calibre vessel than the coeliac trunk and SMA.
Its branches supply the hindgut structures: the distal third of the transverse colon, the descending and sigmoid colon, the rectum, and the upper part of the anal canal.
The superior mesenteric artery
gives rise to several major branches that supply the midgut, but it is important to bear in mind that these vessels form extensive anastomoses with each other
Major branches are:
• Jejunal branches – several branches to the jejunum
• Ileal branches – several branches to the ileum
• Ileocolic artery – supplies the caecum, appendix, and ascending colon
• Right colic artery – supplies the ascending colon
• Middle colic artery – supplies the transverse colon.
The jejunal and ileal branches are embedded in the mesentery of the small intestine.
They anastomose with each other, forming ‘loops’ of arteries called arcades.
From these arcades run the vasa recta (‘straight’ vessels), which supply the intestinal wall.
The inferior mesenteries artery
gives rise to several major branches that supply the hindgut
Major branches are:
• Left colic artery – supplies the transverse colon and the descending colon
• Sigmoid branches – supply the sigmoid colon
• Superior rectal artery – the terminal branch of the IMA, which supplies the upper
rectum.
Branches of the middle colic artery (from the SMA) and left colic artery anastomose along the distal third of the transverse colon and the splenic flexure forming the marginal artery
Branches of the left colic and sigmoid arteries anastomose
The lower rectum is supplied by blood vessels that originate from the internal iliac arteries in the pelvis.
Venous blood from the gut ultimately reaches the inferior vena cava (IVC) and is returned to the heart.
However, venous blood from the gut contains absorbed nutrients, so it first enters the liver via the portal venous system before being returned to the heart via the IVC
The inferior mesenteric vein (IMV) accompanies the IMA and drains the hindgut.
The inferior mesenteric vein ascends on the left side of the abdomen and typically drains into the splenic vein from the spleen.
The superior mesenteric vein (SMV) accompanies the SMA and drains the midgut.
The SMV ascends and unites with the splenic vein close to the liver (posterior to the neck of the pancreas) to form the hepatic portal vein.
The hepatic portal vein enters the liver
After the nutrients are removed from the blood, it enters small hepatic veins, which unite within the liver to form two or three large hepatic veins that enter the IVC as it passes posterior the liver (hence the hepatic veins are within the liver and cannot be seen externally)
The midgut and hindgut are innervated by parasympathetic fibres that stimulate peristalsis and secretions
However, parasympathetic fibres travel to the midgut and hindgut via different nerves
The foregut and midgut (i.e. as far as two thirds of the way along the transverse colon)
are innervated with parasympathetic fibres via the vagus nerve
The hindgut (the last third of the transverse colon as far distally as the upper anal canal)
is innervated with parasympathetic fibres via the pelvic splanchnic nerves.
These nerves are formed by the axons of parasympathetic neurons that lie in the sacral spinal cord
The cell bodies of preganglionic parasympathetic neurons lie in sacral segments S2 – S4
The axons of these neurons leave the spinal cord and form the pelvic splanchnic nerves
The preganglionic axons synapse with a second neuron in a ganglion.
The parasympathetic ganglia are located very close to, or even within, the walls of the viscera
The pelvic splanchnic nerves also convey parasympathetic fibres to the pelvic viscera
Preganglionic sympathetic fibres from T5 – T12 pass through the sympathetic trunk (without synapsing) via the greater, lesser, and least splanchnic nerves.
• The greater splanchnic carries fibres from T5 – T9 and innervates the foregut.
• The lesser splanchnic carries fibres from T10 – T11 and innervates the midgut.
• The least splanchnic carries fibres from T12 and innervates the hindgut.
The preganglionic fibres in these nerves synapse within in ganglia that lie in the abdomen, clustered around the aorta and the coeliac trunk, SMA and IMA
The postganglionic sympathetic fibres form visceral nerves that innervate the gut
These fibres that inhibit peristalsis and secretions
The sympathetic fibres are visceral motor fibres
The gut is also innervated by visceral sensory fibres which convey visceral sensory information from the gut to the CNS
Such information usually does not reach consciousness, but painful sensations caused by ischaemia, distension or spasm do reach our conscious perception
Visceral sensory fibres from the foregut, midgut, and hindgut travel to the CNS alongside the sympathetic fibres that innervate that part of the gut, hence painful sensations from the:
• foregut enter spinal cord segments T5 - T9
• midgut enter spinal cord segments T10 – T11
• hindgut enter spinal cord segment T12
These regions of the spinal cord also receive somatic sensory information from the abdominal wall
• Segments T5 – T9 receive information from dermatomes T5 – T9 (upper abdomen and epigastrium)
• Segments T10 – T11 receive information from dermatomes T10 – T11 (the umbilical region)
• Segment T12 receives information from dermatome T12 (the suprapubic region)
Pain from the abdominal viscera is referred to the body wall:
• epigastric pain suggests foregut pathology
• central abdominal / umbilical pain suggests midgut pathology
• lower abdominal / suprapubic pain suggests hindgut pathology
The liver
The liver is a large organ that lies in the right upper quadrant and epigastrium of the abdomen
The liver is protected by the ribs and moves inferiorly with inspiration – the lowermost part of the liver may be palpable below the right costal margin in inspiration.
Function of liver
All the products of digestion, except lipids, are transported to the liver from the gut via the hepatic portal vein
The liver also produces bile, which is transported to the gallbladder for storage
Bile emulsifies lipids in the chyme entering the duodenum from the stomach
The liver has two surfaces:
• The diaphragmatic surface lies anterosuperior and is related to the inferior surface of the diaphragm
• The visceral surface lies posteroinferior and is related to other organs
The liver is mostly, but not entirely, covered by visceral peritoneum
The regions not covered by peritoneum are the:
• bare area of the liver – a region on the posterior surface that lies in contact with the diaphragm
• the region where the gallbladder lies in contact with the liver
• region of the porta hepatis – where hepatic blood vessels and ducts of the biliary system enter and exit the liver (the equivalent of the hilum of the lung)
The liver is composed of two anatomical lobes
a large right lobe and a small left lobe
They are separated by the falciform ligament, which connects the anterior surface of the liver to the internal aspect of the anterior abdominal wall
Two accessory lobes
the caudate and quadrate lobes, are located on the posteroinferior surface
These lobes do not represent the internal, functional organisation of the liver
Internally the liver is organised into eight functional segments
Each segment is served by its own branch of the hepatic artery and portal vein, and by its own hepatic duct
The liver is supplied by the right and left hepatic arteries
These branches ultimately derive from the coeliac trunk
• The coeliac trunk gives rise to the left gastric, splenic, and common hepatic arteries
• The common hepatic artery gives rise to the gastroduodenal artery; after this point, the common hepatic artery is called the hepatic artery proper (HAP)
• The hepatic artery proper bifurcates into right and left hepatic arteries, which enter the liver at the porta hepatis
Venous blood exits the liver via two or three large hepatic veins that lie within the liver
they are not visible external to the liver
They unite with the inferior vena cava as it passes posterior to the liver
It is a common mistake to confuse the hepatic veins with the hepatic portal vein. To be clear:
• Nutrient-rich venous blood that leaves the gut is transported to the liver via the hepatic portal vein, which receives blood from the superior and inferior mesenteric veins and the splenic vein
• Venous blood leaves the liver via the hepatic veins and enters the inferior vena cava
The liver is served by the hepatic plexus, which is formed of parasympathetic fibres from the vagus nerves and sympathetic fibres
These fibres follow the paths of the hepatic vessels and ducts of the biliary tree
Because the liver is a foregut derivative, pain arising from it is referred to the epigastric region
The liver is connected to the:
• diaphragm by the coronary and triangular ligaments
• anterior abdominal wall by the falciform ligament
• stomach and duodenum by the lesser omentum
The hepatic artery, hepatic portal vein and the bile duct run together
as the portal triad in the free edge of the lesser omentum
The portal triad and the free edge of the lesser omentum form the anterior boundary of the epiploic foramen;
the entrance into the lesser sac (which lies posterior to the stomach)
There are two recesses related to the liver:
• The hepatorenal recess lies between the right kidney and the posterior (visceral) surface of the right side of the liver
Fluid flows into this space in the supine position
• The left and right subphrenic recesses lie either side of the falciform ligament, between the anterosuperior surface of the liver and the diaphragm.
The liver develops from the embryological foregut
It grows from a tissue bud that develops in the ventral mesentery – a peritoneal fold in the upper abdomen that connects the stomach to the anterior abdominal wall
As the liver grows and migrates to the right side of the abdomen, its peritoneal attachments are pulled with it
The remains of the ventral mesentery form the lesser omentum and the falciform ligament
The peritoneal attachments of the liver anchor it to surrounding structures, including the diaphragm superior to it.
The free edge of the falciform ligament contains the round ligament of the liver (the ligamentum teres).
It is the remnant of the umbilical vein, which, in the foetus, carries oxygenated blood from the placenta to the foetus
Another embryological remnant, the ligamentum venosum, lies on the posterior surface of the liver, in the groove between the caudate lobe and the left lobe of the liver
It is the remains of the ductus venosus, which in foetal life diverts blood from the umbilical vein to the IVC, thus shunting oxygen-rich blood to the heart and bypassing the liver
The Gallbladder
The gallbladder stores and concentrates bile. It lies on the posteroinferior (visceral) surface of the liver and lies close to the duodenum
The gallbladder has three parts, the fundus, the body, and the neck
The body
forms the main part of the gallbladder which sits in the gallbladder fossa on the visceral surface of the liver
It tapers towards the neck, which communicates with the cystic duct
The fundus is the rounded end of the gallbladder, which typically extends to the inferior border of the liver
The surface marking of the fundus of the gallbladder
is at the tip of the 9th costal cartilage, at the point where the right midclavicular line intersects the right costal margin
Bile is continuously produced by hepatocytes in the liver and is first excreted into small channels called bile canaliculi
The canaliculi drain into bile ducts of increasing calibre, which ultimately converge to form right and left hepatic ducts that exit the liver at the porta hepatis
• The left and right hepatic ducts converge to form the common hepatic duct
• The common hepatic duct receives the cystic duct from the gallbladder. Distal to this point, the duct is called the bile duct (or common bile duct)
• The bile duct runs in the free edge of the lesser omentum
• It lies posterior to the superior part of the duodenum and posterior to the head of the pancreas
• The bile duct enters the duodenum
If bile leaving the liver is not needed for digestion, it enters the gallbladder via the cystic duct
When needed, bile flows from the gallbladder, via the cystic duct, to the bile duct and duodenum.
The spiral fold (spiral valve) lies at the junction between the gallbladder neck and the cystic duct
• Blood supply is via the cystic artery, which typically arises from the right hepatic artery (variation exists)
• The gallbladder is drained by cystic veins that pass directly into the liver or join the hepatic portal vein
• The gallbladder is innervated by parasympathetic and sympathetic fibres
• Visceral afferents from the gallbladder return to the CNS with the sympathetic fibres
Visceral pain from the gallbladder enters spinal cord levels T5 – T9 and is therefore referred to (i.e. felt in) the epigastrium.
• Gallbladder pain may also be referred to the right shoulder if gallbladder pathology (e.g. inflammation) irritates the diaphragm
The diaphragm is innervated by the phrenic nerve (C3-5)
Spinal cord segments C3-5 also receive somatic sensory information from the skin over the shoulder. Therefore gallbladder pathology involving the diaphragm may be felt in the right shoulder
• If gallbladder pathology irritates the parietal peritoneum, which is innervated by somatic nerves, pain is well localised to the right hypochondrium.
The left and right nasal cavities form the first part of the respiratory tract
Mucosa in the upper part of the nasal cavity contains olfactory receptors
The axons of these receptors form the olfactory nerves (CN I)
The left and right nasal cavities are separated from:
● each other by a thin midline septum, formed of cartilage and bone. When the head is bisected, the septum is seen on one half only
● the oral cavity inferiorly by the hard palate
● the brain superiorly by bone
The nasal cavity communicates with the nasopharynx posteriorly
The nasal cavity also communicates with the paranasal sinuses, which are cavities within the skull bones
The midline nasal septum is formed of cartilage anteriorly and two thin plates of bone posteriorly
The perpendicular plate of the ethmoid bone forms the superior part of the posterior septum, and the vomer forms the inferior part of the posterior septum.
The lateral wall of the nasal cavity bears three projections of bone, the superior, middle, and inferior conchae (Latin = shell), or turbinates
● The spaces inferior to them are the meatuses: the superior meatus lies inferior to the superior concha; the middle meatus lies inferior to the middle concha and the inferior meatus lies inferior to the inferior concha
● As inspired air travels through the meatuses it is warmed, humidified, and filtered
The nasal cavity is separated from the cranium and the brain by the cribriform plate
The cribriform plate is a delicate section of bone that is perforated with tiny holes (like a sieve)
The axons of olfactory neurons pass through these perforations to form the olfactory nerves, which travel to the brain
Olfactory receptors are located in the spheno-ethmoidal recess in the upper nasal cavity, between the superior concha and the cribriform plate
The paranasal sinuses are cavities within the skull bones and are named according to the bones within which they are located:
● frontal sinuses lie within the anterior part of the frontal bone
● ethmoid air cells lie within the ethmoid bone (superior to the nasal cavity and medial to the orbits)
● sphenoid sinuses lie within the sphenoid bone
● maxillary sinuses lie within the maxillae of the facial skeleton.
The frontal sinus and sphenoid sinus are usually clearly seen in the bisected head
The maxillary sinuses lie lateral to the lateral walls of the nasal cavity
The paranasal sinuses communicate with the nasal cavity via small ducts / channels as follows:
● the frontal sinus drains into the middle meatus
● the sphenoid sinus drains into the spheno-ethmoidal recess
● the ethmoid air cells drain into the superior and middle meatuses
● the maxillary sinus drains into the middle meatus.
The opening of the maxillary sinus into the middle meatus lies superomedially, therefore it cannot drain feely when the head is upright.
The nasal cavity also receives the nasolacrimal duct which drains the fluid (‘tears’) that lubricate the anterior surface of the eye
The duct opens into the inferior meatus.
When we cry, we get a runny nose because excess fluid runs down the nasolacrimal duct.
The nasal cavity also communicates with the middle ear
The middle ear is a small cavity within the temporal bone that is modified for hearing (it contains three tiny bones that transmit sound waves to the inner ear)
The auditory tube (Eustachian tube)
connects the middle ear to the nasopharynx.
The opening of the auditory tube can be seen on the lateral wall of the nasopharynx, surrounded by a slight bulge, which is formed of tonsillar tissue.
The auditory tube allows air to pass into the middle ear so that the pressure on either side of the tympanic membrane (eardrum), which lies between the middle and external ear, is equal
This is important for optimal conduction of soundwaves
The nasal cavity is supplied by several arteries
including branches of the maxillary artery, which is a terminal branch of the external carotid artery
An anastomotic network formed supplies the nasal septum and is often the site of bleeding in a nosebleed (epistaxis)
The sensory innervation of the nose is via branches of the trigeminal nerve (CN V).
Function of the Palate
The palate separates the nasal cavities from the oral cavity.
What is the palate composed of?
It is composed anteriorly of bone – the hard palate – and posteriorly of muscle – the soft palate.
The palate forms the roof of the oral cavity.
The Hard Palate
The hard palate is composed of two bones: the palatine bone of the maxilla and the horizontal plate of the palatine bone.
The hard palate is functionally important because:
● it prevents food or fluid entering the nasal cavity
● we push our tongue up against the hard palate during the first phase of
swallowing, which forces food and fluid backwards into the oropharynx
● we push our tongue up against the hard palate to articulate certain sounds
In some people the palate does not form properly during embryological development (a cleft palate), causing difficulty with eating, swallowing and speech if not repaired.
The Soft Palate
The soft palate lies posterior to the hard palate
uvula
A midline conical projection - the uvula - ‘hangs’ from the posterior border of the soft palate and can be seen at the back of the mouth
The soft palate is composed of several muscles,
the muscles of the soft palate contract during swallowing which elevates the soft palate
The nasopharynx is closed off from the oral cavity, preventing reflux of food and fluid into the nasal cavity
The muscles of the soft palate are innervated by the vagus nerve
The oral cavity is bounded:
● superiorly by the hard and soft palate (the roof of the mouth)
● inferiorly by soft tissues and muscles (the floor of the mouth)
● laterally by the cheeks (which contain the buccinator muscle)
The oral cavity is continuous posteriorly with the oropharynx
It contains the tongue, teeth and gums and the openings of the salivary ducts
The Teeth and Gums
● Adults have 32 teeth – 16 embedded in the maxilla (upper jaw) and 16 embedded in the mandible
In the upper and lower jaws
there are four incisors, two canines, four premolars
and six molars
The teeth are composed of:
● an inner pulp which contains blood vessels and nerves
● dentin which surrounds the pulp
● an outer, hard coating of enamel
Enamel and dentin can be eroded by bacteria or foodstuffs (e.g. sugar and acids).
This can lead to decay, inflammation, and infection of the pulp, which is painful
Infection may spread to the bone, leading to abscess formation
The Tongue
The tongue is essential for normal chewing, swallowing and speech
It bears papillae on its superior surface, some of which detect taste (‘taste buds’)
The anterior part of the tongue lies in the oral cavity, and the posterior part (the root) extends into the oropharynx
Vallecula
The space between the posterior tongue and the anterior aspect of the epiglottis
The tongue is composed of 2 types of muscles
Intrinsic
Extrinsic
Intrinsic muscles
lie entirely within the tongue. They are paired bilaterally and fuse in the midline. They change the shape of the tongue.
Extrinsic muscles
are attached to the tongue but originate from outside it (from the mandible and hyoid bone). They move the tongue
The muscles are innervated by the hypoglossal nerve (CN XII)
The sensory innervation of the tongue is via three cranial nerves:
● Taste in the anterior two thirds is served by the facial nerve (CN VII)
● General sensation (touch, pain, temperature) in the anterior two thirds is served by the trigeminal nerve (CN V)
● Taste and general sensation in the posterior third are served by the glossopharyngeal nerve (CN IX)
Vessels and Nerves of the Oral Cavity
● The oral cavity is supplied by the lingual, maxillary, and facial arteries, which are branches of the external carotid artery
● Innervation of the oral cavity is complex
The muscles of the soft palate are innervated by the vagus nerve
The tongue is innervated by four cranial nerves (CNs V, VII, IX and XII) as described above
Tonsillar tissue is found in several locations in the nasal and oral cavities
The pharyngea
The tubal
The palatine
The lingual
The pharyngeal tonsil
lies in the roof and posterior wall of the nasopharynx (sometimes called the ‘adenoid’)
The tubal tonsil
surrounds the opening of the auditory tube on the lateral wall of the nasopharynx
The palatine tonsil
lies on the lateral wall of the oropharynx.
Usually referred to as ‘the tonsils’, they are visible on either side of the oropharynx when the mouth is open.
The lingual tonsil
Is a collection of lymphoid tissue in the posterior tongue
The coeliac trunk leaves the anterior aspect of the aorta at the level of T12. It gives rise to three major branches:
• The left gastric artery – supplies the distal oesophagus and lesser curvature of the stomach
• The common hepatic artery – branches supply the liver, stomach, and duodenum
• The splenic artery – branches supply the stomach, pancreas, and spleen
The duodenum is the first and shortest part of the small intestine
It is continuous proximally with the pylorus of the stomach and distally with the jejunum
The pyloric sphincter regulates gastric emptying into the duodenum
• Most of the duodenum is retroperitoneal
• The duodenum forms a C-shape that cups the head of the pancreas
• The duodenum is described in four parts. These are the superior (first), descending (second), the inferior (third) and the ascending (fourth) parts
• The bile duct, gastroduodenal artery and the hepatic portal vein lie posterior to the first part of the duodenum
• The superior mesenteric artery lies anterior to the third part
• The fourth part meets the jejunum at the duodenojejunal flexure
• Approximately halfway along the internal wall of the duodenum is a small elevation called the major duodenal papilla (papilla = nipple-like)
This marks the point at which bile and digestive pancreatic secretions (‘pancreatic juice’) enter the duodenum
The first half of the duodenum is derived from the foregut and is supplied by branches of the coeliac trunk (the artery of the foregut)
The second half is derived from midgut and is supplied by branches of the superior mesenteric artery (the artery of the midgut)
Arterial branches that supply the duodenum are derived from the:
• gastroduodenal artery (from the common hepatic artery and hence the coeliac trunk)
• inferior pancreaticoduodenal arteries (from the superior mesenteric artery)
Veins follow the arteries and are tributaries of the hepatic portal vein.
The pancreas lies horizontally on the posterior abdominal wall at the level of L1 and is retroperitoneal
It does not have a capsule so in the cadaver its surface appears ‘bumpy’ rather than smooth
• It forms from dorsal and ventral pancreatic buds which fuse during development
• It is composed of four parts: the head, the neck, the body, and the tail
• The uncinate process is a hook-like projection of the head of the pancreas
• The head is cupped by the C-shaped duodenum and the tail extends to the hilum of the spleen
• The pancreas forms part of the posterior wall of the lesser sac
• The splenic artery runs towards the spleen embedded in the upper border of the pancreas. The splenic vein lies posterior to the pancreas
• The main pancreatic duct and the accessory pancreatic duct run within the substance of the pancreas
The pancreas has an endocrine and an exocrine function
It synthesizes and secretes insulin and glucagon
Insulin is released in response to high levels of glucose in the blood. The pancreas also produces pancreatic juice that contains digestive enzymes.
Pancreatic juice is transported through main pancreatic duct and the accessory pancreatic duct to the duodenum. The main and accessory pancreatic ducts usually communicate with each other.
The duodenum receives:
• bile from the liver and gallbladder via the bile duct
• pancreatic juice from the pancreas via the main and accessory pancreatic
ducts.
The bile duct and main pancreatic duct merge at the hepatopancreatic ampulla (ampulla = dilation)
The hepatopancreatic ampulla opens into the second part of the duodenum at the major duodenal papilla, which is located on the internal wall of the duodenum, about halfway along its length
The hepatopancreatic ampulla is surrounded by smooth muscle - the sphincter of Oddi
Contraction of the sphincter prevents reflux of duodenal contents into the bile and main pancreatic ducts
The accessory pancreatic duct empties pancreatic juice into the duodenum at the minor duodenal papilla, which lies just proximal to the major duodenal papilla
The pancreas is supplied by blood vessels derived from the coeliac trunk and blood vessels derived from the superior mesenteric artery:
• The splenic artery, a major branch from the coeliac trunk, runs along the upper border of the pancreas and gives rise to pancreatic arteries
• The gastroduodenal artery (from the common hepatic artery and hence the coeliac trunk) gives rise to the superior pancreaticoduodenal arteries that supply the pancreas
• The superior mesenteric artery gives rise to the inferior pancreaticoduodenal arteries that supply the pancreas
Veins follow the arteries
The splenic vein drains the pancreas and unites with the superior mesenteric vein to form the hepatic portal vein posterior to the neck of the pancreas
The spleen is a haematopoietic and lymphoid organ that lies in the left upper quadrant, protected by ribs 9 - 11
It is covered with visceral peritoneum
It has several functions that include the breakdown of old red blood cells, the storage of red blood cells and platelets, and various immune responses, including production of IgG
The spleen has two surfaces and four borders:
• the diaphragmatic surface lies adjacent to the diaphragm
• the visceral surface lies in contact with the stomach, left kidney and colon. The splenic vessels enter and exit the spleen at the hilum on the visceral surface
• the anterior and superior borders are typically notched
• the posterior and inferior borders are smooth
A normal sized spleen is not palpable below the costal margin
If it is palpable, it is enlarged by at least three times its normal size
The spleen is supplied by the splenic artery, a branch of the coeliac trunk
The splenic artery runs along the superior border of the pancreas, embedded within it
The artery divides into approximately five branches at the hilum
Venous drainage is via the splenic vein, which runs posterior to the pancreas
It unites with the superior mesenteric vein to form the hepatic portal vein
