Abdomen Flashcards
Anterolateral Adominal Wall Functions
Functions:
- forms a firm but flexible boundary that keeps the abdominal viscera within the cavity
- assists in maintaining viscera’s anatomical position against gravity
- protects the abdominal viscera from injury
- assists in forceful expiration by pushing the abdominal viscera upwards
- involved in any action (coughing, vomiting, defecation) that increases intra-abdominal pressure
Superficial Fascia
Superficial fascia is connective tissue. It’s composition depends on it’s location:
- above the umbilicus - single sheet of connective tissue, continuous with superficial fascia in other regions of body
- below the umbilicus - divided into two layers: fatty superficial layer (Camper-s fascia) & membranous deep layer (Scarpa-S fascia)
Superficial vessels & nerves run between the two layers of fascia
Types of Muscles in the Abdominal Wall
Flat Muscles
- three flat muscles
- situated laterally on either side of the abdomen & stacked upon one another
- fibres run in different directions and cross each other -strengthening the wall and decreasing risk of abdominal contents herniating
- in anteromedial aspect of abdominal wall, each flat muscle forms an aponeurosis (broad, flat tendon) that covers vertical rectus abdominis muscle
- linea alba - aponeuroses of all flat muscles become entwined in the midline, forming a fibrous structure from the xiphoid process of sternum to pubic symphysis)
Vertical Muscles
- two vertical muscles
- located in the midline of anterolateral abdominal wall
External Oblique
- Largest, most superificial flat muscle in abdominal wall
- Fibres run inferomedially
Attachments
originates: ribs 5-12
inserts: into iliac crest & pubic tubercle
Function
Contralateral rotation of the torso
Innervation
- thoracoabdominal nerves (T7-11)
- subcostal nerve (T12)
Internal Oblique
- Lies deep to external oblique
- Smaller & thinner structure
- Fibres running superomedially (perpendicular to external oblique fibres)
Attachments
originates: inguina ligament, iliac crest & lumbodorsal fascia
inserts: ribs 10-12
Function
- bilateral contraction compresses the abdomen
- unilateral contraction ipsilaterally rotates torso
Innervation
- thoracoabdominal nerves (T7-T11)
- subcostal nerves (T12)
- branches of lumbar plexus
Transversus Abdominis
- Deepest of flat muscles
- Transversely running fibres
- Well-formed fascia layer deep to muscle - transversalis fascia
Attachments
originates: inguinal ligament, costal cartilages 7-12, iliac rest & thoracolumbar fascia
inserts: conjoint tendon, xiphoid process, linea alba & pubic crest
Function
compression of abdominal contents
Innervation
- thoracoabdominal nerves (T7-T11)
- subcostal nerve (T12)
- branches of lumbar plexus
Rectus Abdominis
- Long, paired muscle found on either side of adominal wall midline
- Split into two by linea alba
- Borders create a surface marking - linea semilunaris
- Muscle is intersected by fibrous strips at several places - tendinous intersections
- tendinous intersections & linea alba give rise to ‘6-pack’
Attachments
originates: crest of pubis
inserts: xiphoid process of sternum & costal cartilages of ribs 5-7
Function
- assits flat muscles in compressing the abdomial viscera
- stabilises the pelvis during walking
- depresses ribs
Innervation
thoracoabdominal nerves (T7-T11)
Pyramidalis
- Small triangular muscle, found superficially to rectus abdominis
- Located inferiorly with base on pubis bone & apex attached to linea alba
Attachments
originates: pubic crest & pubic symphysis
inserts: linea alba
Function
tenses the lina alba
Innervation
subcostal nerve (T12)
Rectus Sheath
- Formed by aponeuroses of the three flat muscles
- Encloses the rectus abdominis & pyramidalis muscles
Has an anterior & posterior wall for most of it’s length:
Anterior wall: formed by aponeuroses of external oblique & half of the internal oblique
Posterior wall: formed by aponeuroses of half the internal oblique & transversus abdominis
- Midway between the umbilicus & pubic symphysis, all aponeuroses move to anterior wall of rectus sheath
- At this point, there is no posterior wall - rectus abdominis is in direct contact with the tranversalis fascia
- The demarcation point of the posterior layer to rectus sheath is the arcuate line
Surface Anatomy
- Umbilicus - attachment site of umbilical chord, midway between xiphoid process & pubic symphysis
- Linea semilunaris - lateral border of rectus abdominis, curved from 9th rib to pubic tubercle
- Linea alba - fibrous line that splits rectus abdominis in two, verticle groove extending inferiorly from xiphoid process
Horizontal Planes
- transpyloric plane - halfway between jugular notch & pubic symphysis, aproximately at L1 vertabre level
- intertubercular plane - horizontal line that runs between the superior aspect of right & left iliac crests
Vertical Planes
- left & right mid-clavicular lines - middle of the clavicle to mid-inguinal point (halfway between anterior superior iliac spine of pelvis & pubic symphysis)
The abdomen also has 4 quadrants & 9 reigons - useful for describing pain locaction, location of viscera & surgical procedures
Posterior Abdominal Wall
- Formed by lumbar vertabrae, pelvic girdle, posterior abdominal muscles & fascia
Five posterior abdominal muscles:
- iliacus
- psoas major
- psoas minir
- quadratus lumborum
- diaphragm
Quadratus Lumborum
- Located laterally in the posterior abdominal wall
- Thick muscular sheet - quadrilateral shape
- Muscle is positioned superficially to psoas major
Attachments
originates: iliac crest & iliolumbar ligament
attaches: fibres travel superomedially, inserting onto the transverse process of L1-L4 & inferior broder of 12th rib
Function
- extension and lateral flexion of vertebral column
- fixes 12th rib during inspiration so that diaphragm contraction is not wasted
Innervation
Anterior rami of T12-L4 nerves
Psoas Major
- Located near the midline of the posterior abdominal wall, immediately lateral to lumbar vertebrae
Attachment
originates: transverse processes & vertebral bodies of T12-L5
inserts: moves inferiorly & laterally, running deep to inguinal ligament, attaching to lesser trochanter of femur
Function
- flexion of the thigh at hip
- lateral flexion of vertebral column
Innervation
anterior rami of L1-L3 nerves
Psoas Minor
- Only present in 60% of population
- Located anterior to psoas major
Attachment
originates: vertebral bodies of T12 + L1
inserts: to ridge on the superior ramus of pubic bone, known as pectineal line
Function
flexion of vertebral column
Innervation
anterior rami of L1 spinal nerve
Iliacus
- fan-shaped muscle that is situated inferiorly on posterior abdominal wall
- combines with psoas major to form the ilipsoas - major flexor of thigh
Attachment
originates: surface of iliac fossa & anterior inferior iliac spine
inserts: fibres combine with tendon of psoas major, inserting into lesser trochanter of the femur
Function
- flexion of thigh at hip joint
- lateral rotation of the thigh at hip joint
Innervation
femoral nerve (L2-L4)
Clinical Relevance - Psoas Sign
- Medical sign that indicates irritation to the iliposoas group of muscles
- Elicited by flexion of the thigh at hip
- Postive test = lower abdominal pain
- Right-sided psoas sign is an indication of appendicitis
- As iliopsoas contracts, comes in contact with inflammed appendix, producing pain
Fascia of Posterior Abdominal Wall
- Layer of fascia lies between the parietal peritoneum & muscles of the posterior abdominal wall
- Continious with the transversalis fascia of the anteriolateral abdominal wall
One sheet but named according to the structure it overlies:
Psoas Fascia
- covers the psoas major muscle
- attached to the lumbar vertebrae medially
- continuous with the thoracolumbar fascia laterally
- continious with iliac fascia inferiorly
Thoracolumbar Fascia
- consists of three layers - posterior, middle & anterior (muscles lie between layers)
quadratus lumborum - between anterior & middle layers
deep back muscles - between middle & posterior layers
Peritoneum
- Continious membrane which lines the abdominal cavity & covers the abdominal viscera
- Acts to support & protect viscera
- Provides pathways for blood vessels & lymph to travel to/from viscera
Consists of two layers - continious with each other & made up of mesothelium (simple squamous cells)
Parietal Peritoneum
- lines internal surface of adominopelvic wall
- derived from somatic mesoderm in embryo
- recieves same somatic nerve supply as the abdominal wall reigion it lines - well localised pain
- sensitive to pressure, pain, laceration & temperature
Visceral Peritoneum
- covers the majority of the abdominal viscera
- derived from splanchnic mesoderm in embryo
- same autonomic nerve supply as viscera it covers
- poorly localised pain - only sensitive to stretch & chemical irritation
- pain refers to dermatomes - areas of skin supplied by same sensory ganglia & spinal chord segments as viscera’s nerve fibres
Peritoneal Cavity & Clinical Relevance
- potential space between the parietal & visceral peritoneum
- Only contains a small amount of lubricating fluid
Clinical Relevance - Peritoneal adhesions
- damage to the peritoneum can occur as a result of infection, surgery or injury
- resulting inflammation & repair may cause formation of fibrous scar tissue
- can result in abnormal attachments between visceral peritoneum of ajacent organs/between visceral & parietal peritoneum
- such adhesions can result in pain/complications such as volvulus, when intestine becomes twisted around an adhesion - resulting in bowel obstruction
Intraperitoneal & Retroperitoneal Organs
- Abdominal viscera can be divided anatomically by their relationship to the peritoneum
Two main groups, intraperitoneal & retroperitoneal organs:
Intraperitoneal
- organs enveloped by visceral peritoneum, covers them anteriorly & posteriorly
- examples: stomach, liver & spleen
Retroperitoneal
- only covered by parietal peritoneum on anterior surface
Can be further subdivided into:
primarily retroperitoneal: organs developed & remain outside of the peritoneum e.g oesophagus, rectum & kidneys
secondarily retroperitoneal: organs that were initially intraperitoneal, suspened by mesentery - during embryogenisis, mesentery fused to posterior abdominal wall so now only anterior surface is covered by peritoneum e.g colon
- SAD PUCKER mneumonic can be used to name the retroperitoneal viscera
Peritoneal Reflections
- Peritoneum covers nearly all viscera within gut & conveys neurovascular structures from the body wall to intraperitoneal viscera
- To fufil its functions, peritoneum develops into a highly-folded, complex structure
Terms used to describe the folds & spaces of peritoneum:
Mesentery
- double layer of visceral peritoneum
- connects an intraperitoneal organ to (usually) the posterior abdominal wall
- provides pathway for neurovascular bundles
Omentum
- sheets of visceral peritoneum that extend from stomach & proximal part of duodenum to other abdominal organs
Greater Omentum:
- consists of four layers of visceral peritoneum
- descends from greater curvature of stomach & proximal part, folds back up & attaches to anterior surface of transverse colon
- role in immunity, ‘abdominal policeman’ as it can migrate to infected viscera or site of surgical disturbance
Lesser Omentum:
- double layer of visceral peritoneum
- conisderably smaller than the greater
- descends from the greater curvature of the stomach & proximal part of duodenum to liver
- consists of the hepatogastric ligament (flat, broad sheet) & hepatduodenal ligament (free edge, containing portal triad)
Peritoneal Ligaments
- Double fold of peritoneum
- Connects viscera together or connects viscera to abdominal wall
- Example: hepatogastric ligament, a portion of the lesser omentum which connects the liver to stomach
Embryological Origins & Referred Pain
- Viscera pain is poorly localed - referred to as dermatomes of the skin that share the same sensory ganglia & spinal chord segments as visceral nerve fibres
- Pain is referred according to embryological origin of the organ
Foregut (epigastric reigion): oesophagus, stomach, pancreas, liver, gallbladder & duodenum (proximal to entrance of common bile duct)
Midgut (umbilical reigion): duodenum (distal to entrance of common bile duct) to junction of the proximal two thirds of transverse colon with the distal third
Hindgut (pubic reigion): distal one third of transverse colon to upper part of anal canal
- Pain in retroperitoneal organs (e.g kidney & pancreas) may present as back pain
- irritation of the diaphragm (e.g as result of inflammation of viscera) may result in shoulder tip pain
- Appendicitis - initially pain from midgut structure (umbilical reigion) that spreads to the parietal peritoneum, causing pain to localise to the lower right quadrant
Inguinal (Hesselbach’s) Triangle
- Reigion in the anterior abdomimal wall
- Alternatively known as the medial inguinal fossa
Borders
Located in the inferomedial aspect of the abdominal wall
- Medial - lateral border of rectus abdomimis muscle
- Lateral - inferior epigastric vessels
- Inferior - inguinal ligament
Contents
- other than abdominal wall, doesn’t contain any structures of clinical importance
- demarcates an area of potential weakness in the abdominal wall - herniation of contents can occur
Clinical Relevance - Inguinal Hernias
- Hernia = protrusion of an organ/fascia through the wall of the cavity that normally contains it
Direct Inguinal Hernia
- bowel herniates through a weakness in the inguinal triangle & enters the inguinal canal
- bowel can then exit the canal via the superficial inguinal ring & form a ‘lump’ in the scrotum or labia majora
- usually aquired in adulthood, due to weakening in the abdominal musculature
- occurs medially to inferior epigastric vessels (through inguinal triangle)
Indirect Inguinal Hernia
- more common than direct inguinal hernias
- bowel enters canal via deep inguinal ring
- occurs laterally to inferior epigastric vessels (through inguinal triangle)
- caused by the failure of the processus vaginalis (peritoneum) to regress
- degree to which the sac herniates depends on the amount of processus vagninalis present
Inguinal Canal
- Short passage that extends inferiorly & medially through inferior part of the abdominal wall
- Superior & parallel to inguinal ligament
- Serves as a pathway by which structures can pass from the abdominal wall to external genitalia (hence common site of herniation)
Has two openings, superficial & deep rings with boundaries:
Anterior - aponeurosis of external oblique, reinforced by internal oblique muscle laterally
Posterior wall - transversalis fascia
Roof - transversalis fascia, internal oblique & transversus abdominis
Floor - inguinal ligament (‘rolled up’ portion of external oblique aponeurosis), thickened medially by the lacunar ligament
Development of Inguinal Canal
- Tissues that become gonads establish in posterior adominal wall & descend through abdominal cavity
- A fibrous cord of tissue (gubernaculum) attaches inferior portion of gonad to future scrotum/labia & guides the descent
- Inguinal canal is the pathway by which the testes leave the abdominal cavity & enter scrotum
- In embryological stage, canal is flanked by an out-pocketing of the peritoneum (processus vaginalis) & abdominal musculature
- Processus vaginalis usually degenerates - failure to do so causes an indirect inguinal hernia
- Gubernaculum shortens during the descent & becomes a small scrotal ligament, anchoring testes
- Females also have a gubernaculum which attaches the ovaries to the uterus & future labia majora
- In females, because the ovaries are attached to the uterus by gubernaculum, they are prevented from descending as far so move into the pelvic cavity
- Gubernaculum then becomes two structres: ovarian ligament & round ligament of uterus
Inguinal Canal Contents
- Spermatic chord (males) - contains neurovascular & reproductive structures that supply/drain testes
- Round ligament (females) - originates from uterine horn & travels through inguinal canal to attach at labia majora
- Illioinguinal nerve - contributes towards the sensory innervation of genitalia
- only travels through part of the canal, exiting via the superficial inguinal ring (does not pass through deep inguinal ring)
- this is the nerve at most risk of damage during an inguinal hernia repair
- Genital branch of genitofermoral nerve - supplies cremaster muscle & anterior scrotal skin in males, skin of mons pubis & labia majora in females
Walls of the inguinal canal are usually collapsed around their contents, preventing other structures from potentially entering & becoming stuck
Inguinal Rings
Two openings to the inguinal canal, known as rings:
Deep (internal) ring
- found above midpoint of inguinal ligament, lateral to epigastric vessels
- created by the transversalis fascia, which invaginates to form a covering over the contents of the inguinal canal
Superficial (external) ring
- marks the end of the inguinal canal
- lies just superior to pubic tubercle
- triangle-shaped opening
- formed by the evagination of the external oblique, forms another covering of the inguinal canal contents
- opening contains intercrural fibres, which run perpendicular to aponeurosis of the external oblique & prevent the ring from widening
Calot’s Triangle
- AKA cystohepatic triangle - small anatomical space in abdomen
- Located at the porta hepatis of liver - where hepatic ducts & neurovascular structures enter/exit liver
Borders
medial - common hepatic duct
inferior - cystic duct
superior - inferior surface of liver
Contents
- right hepatic artery - formed by bifurcation of proper hepatic arteru into left/right branches
- cystic artery - typically arises from the right hepatic artery & transverses the triangle to supply gall bladder
- lymph node of Lund - first lymph node of gallbladder
- lymphatics
Clinical Relevance - Calot’s Triangle in Laparoscopic Chloecystectomy
- Clinical importance during laparoscopic chloecystectomy (removal of gallbladder)
- In procedure, triangle is carefully dissected by surgeon, contents & borders identified
- Allows surgeon to take in account of any anatomical variation & permits safe ligation/division of cystic duct & artery
- If Calot’s triangle cannot be delineated (e.g in cases of severe inflammation), surgeon may elect to perform a subtotal cholecystectomy or convert to open surgery
Spermatic Chord
- Collection of vessels, nerves & ducts that run to/from testes
- Surrounded by fascia, forming a chord-like structure
- Relatively short anatomical course - begins in inferior abdomen & ends in scrotum
- Formed at the opening of the inguinal canal (deep inguinal ring - inferior to epigastric vessels)
- Cord passes through inguinal canal, entering scrotum by superficial inguinal ring, continues into scrotum & ends at posterior border of testes
Spermatic Chord - Fascial Coverings
Contents of spermatic cord are mainly bound together by three fascial layers, derived from anterior abdominal wall:
- external spermatic fascia - derived from deep subcutaneous fascia (fascia innominata)
- cremaster muscle & fascia - derived from internal oblique muscle & it’s fascial coverings
- internal spermatic fascia - dervived from transversalis fascia
Three fascial layers themselves are covered by a layer of superficial fascia, which lies directly under scrotal skin
Cremaster muscle forms the middle layer of spermatic chord fascia - discontinious layer of striated muscle that is originated longitudinally
Clinical Relevance - Cremaster Reflex
- Can be stimulated by stroking the superior & medial part of the thigh
- Produces immediate contraction of the cremaster muscle, elevating testis on side that it has been stimulated
Spinal reflex consists of two parts:
- afferent (sensory) limb - ilioinguinal nerve (innervates skin of superomedial thigh), fibres from this nerve enter the spinal cord at L1
- efferent (motor) limb - genital branch of the genitofemoral nerve (innervates the cremaster muscle)
Spermatic Cord - Contents
Conveys several important structures that run to/from testis:
Blood vessels:
- testicular artery
- cermasteric artery & vein
- artery to the vas deferens
- pampiniform plexus of testicular veins
Nerves:
- genital branch of genitofemoral nerve - supplies cremaster muscle
- autonomic nerves
Other structures:
- vas deferens - duct that transports sperm from the epidiymis to the ampulla (dilated terminal part of the duct), ready for ejaculation
- processus vaginalis - projection of peritoneum that forms the pathway of descent for the testes during embryonic development (in adults, it is fused shut)
- lymph vessels - drain into para-aortic nodes, located in lumbar reigion
Lumbar Spine
- Third reigion of the vertebral column - located in lower back betwen thoracic & sacral vertebral segments
- Made up of 5 distinct vertebrae - largest in vertebral column, supports weight bearing structure
- Acessory processes - on posterior aspect of each transverse process base, act as sites of attachment for deep back muscles
- mammillary processes - on posterior surface of each superior articular process, sites of attachment for deep back muscles
- 5th lumbar vertabrae (L5) - distinctive characteristics, larger vertebral body & transverse process, carries the weight of the entire upper body
Lumbar Ligaments
Present throughout vertebral column:
- anterior & posterior longitudinal ligaments: long ligaments that cover the vertebral bodies & intervertebral discs
- ligament flavum - connects the laminae of adjacent vertebrae
- interspinous ligament - connects the spinous processes of adjacent vertebrae
- supraspinous ligament - connects tips of adjacent spinous processes
Unique to Lumar Spine
- iliolumbar ligaments - strengthens lumboscaral joint (L5-S1 vertebrae), fan-like ligaments radiating from transverse processes of L5 vertebra to ilia of pelvis
Liver
- Predominantly located in the right hypochondrium & epigastric areas
- Extends into left hypochondrium
- Aterial supply = hepatic artery proper (derived from coeliac trunk) & hepatic portal vein (supplies with partially deoxygenated blood & nutrients)
- Venous drainage = hepatic veins, open into inferior vena cava
- Nerve supply = hepatic plexus - contains sympathetic (coeliac plexus) & parasympathetic (vagus nerve) fibres
- Glisson’s capsule (fibrous covering of liver) is supplied by branches of the lower interocostal nerves - distention results in sharp, well-localised pain
- Lymphatic drainage = hepatic lymph nodes, drain into phrenic & mediastinal nodes, join with the right lymphatic & thoracic ducts
Hepatic Recesses
- Abdominal spaces between liver & surrounding structures
- Important clinical relevance as infection may collect & form abcesses
Subphrenic spaces - located between diaphragm & superior and anteiror aspects of the liver. Divided into a right/left by the falciform ligament
Subhepatic space - subdivision of the supracolic compartment, located between the inferior surface of liver & transverse colon
Morison’s pouch - potential space beyween visdceral surface of liver & right kidney. Deepest part of peritoneal cavity when supine, therefore fluid (blood/ascites) is most likely to collect in this reigion in a bed-ridden patient
Liver Lobules (Portal Triads)
- Cells of the liver (hepatocytes) are arranged into lobules
- lobules are hexagon-shaped, drained by a central vein
At the periphery, there are three structures collectively known as the portal triad:
Arteriole: branch of the hepatic artery entering the liver
Venule: branch of the hepatic portal vein entering the liver
Bile duct: branch of the bile duct leaving the liver
Portal triad also contains lymphatic vessels & vagus nerve (parasympthetic fibres)
Gallbladder
Divided into three parts:
- fundus - rounded distal portion
- body - largest part
- neck - tapers to become continious with cystic duct, leading to bilibary tree. Contains a mucosal fold (Hartmann’s pouch), common location for gallstones to become lodged, causing cholestasis
Vaculature: cystic artery - branch of the right hepatic artery (coeliac trunk) & cystic veins, drain into portal vein
Innervation: sympathetic & sensory fibres = coeliac plexus, parasympathetic = vagus nerve
Lymph drainage: cystic lymph nodes in gallbladder neck, empty into hepatic nodes then coeliac nodes
Biliary Tree
- Series of gastrointestinal ducts, allowing newly synthesised bile from liver to be concentrated & stored in gallbladder
- Bile is secreted from hepatocytes & drains from the left and right hepatic ducts
- Ducts amalgamate to form common hepatic duct, runs alongside hepatic vein
- Joined by the cystic duct - allows bile to flow in/out of gallbladder for storage & release
- Cystic duct & common hepatic duct form the common bile duct
- Common bile duct descends into first part of duodenum & head of pancreas (pancreatic duct)
- Joined by the main pancreatic duct, forming the hepatopancreatic ampulla, then empties into the duodenum via the major duodenal papilla
- Papilla is regulated by a muscular valve, sphincter of Oddi
Pancreas
- Exocrine & endocrine functions
- Supplied by pancreatic branches of splenic artery
- Head is additionally supplied by superior & inferior pancreaticoduodenal arties - branches of the coeliac trunk & superior mesenteric arteries
- Venous drainage of the head is into the superior mesenteric branches of the hepatic portal vein, rest is drained by splenic vein
- Lymph empties into the pancreaticosplenal nodes & plyoric nodes, drain into the superior mesenteric & coeliac lymph nodes
Clinical Relevance - Pancreatitis
- Refers to inflammation of the pancreas - acute or extended period (chronic)
- Causes of pancreatitis - GET SMASHED
- Pancreatitis causes severe epigastric pain which radiates to the back, nausea, vomiting & diarhoea
- Treatment involves supportive measures - IV fluids, analgesia etc
- Antibiotics are rarely required, as most cases are not due to infection - underlying cause will need to be treated
Lumbar Plexus
- Located in lumbar reigion within substance of psoas major & supplies the skin/musculature of lower limb
- Formed by the anterior rami (divisions) of lumbar spinal nerves L1-L4, with contributions from T12
- Remember: I, I Get Leftovers On Fridays
Iliohypogastric Nerve
- roots: L1, with contributions from T12
- motor functions: innverates internal oblique & transversus abdominis
- sensory: innverates posterolateral gluteal skin in pubic reigon
Illioinguinal Nerve
- roots: L1
- motor functions: innervates the internal oblique and transversus abdominis
- sensory: innervates skin on superior antero-medial thigh. Males - skin over root of penis & anterior scrotum. Females - skin over mons pubis & labia majora
Genitofemoral Nerve
- roots: L1, L2
- motor functions: genital branch innverates cremastic muscle
- sensory: The genital branch innervates the skin of the anterior scrotum (in males) or the skin over mons pubis and labia majora (in females). The femoral branch innervates the skin on the upper anterior thigh
Lateral Cutaneous Nerve of the Thigh
- roots: L2, L3
- motor functions: none
- sensory:
Innervates the anterior and lateral thigh down to the level of the knee
Obturator Nerve
- roots: L2, L3, L4
- motor functions: muscles of medial thigh - obturator externus, adductor longus, adductor brevis, adductor magnus & gracilis
- sensory: skin over medial thigh
Femoral Nerve
- roots: L2, L3, L4
- motor functions: muscles of anterior thigh - illiacus, pectineus, sartorius & quadriceps femoris
- sensory: anterior thigh & the medial leg
Spleen
- Filters blood - removing old red blood cells
- Cell-mediated & humoral immune responses
- Located in upper left quadrant (under diaphragm & ribcage) - cannot be palpatated unless enlarged
Attached to stomach & kidney by parts of the greater omentum - double fold of peritoneum that originates from the stomach:
Gastrosplenic ligament - connects the spleen to greater curvature of stomach
Splenorenal ligament - connects the hilum of the spleen to left kidney. Splenic vessels & tail of pancreas lie within ligament
- Both ligaments lie within the lesser sac
Structure of Spleen
- Slightly oval shape - covered by a weak capsule that protects the organ whilst allowing it to expand in size
Outer surface can be anatomically divided into:
Diaphragmatic Surface - in contact with diaphragm & ribcage
Visceral Surface - in contact with the other abdominal viscera
- Posteromedial & inferior borders are smooth
- Anterior & superior borders contain notches
- Enlargement of the spleen - superior border moves inferiormedially & notches can be palpated
Clinical Relevance - Rupture of the Spleen
- Organ with highest incidence of injury
- Splenic rupture occurs when there is a break in its fibroelastic capsule - disrupting underlying parenchyma
- Caused by blunt or penetrating trauma - associated with left rib fractures
- Leads to perfuse bleeding into the peritoneal cavity
- Splenectomy (sub-total or total) may be needed where haemorrhage & rupture are life-threatening
- Liver & bone marrow take over some splenic functions - person will still be more prone to some bacterial infections (may need life-long antibiotics_
Adrenal Glands
- Paired endocrine glands situated over medial aspect of the upper poles of each kidney
- Secrete steriod & catecholamine hormones directly into blood
- Retroperineal - parietal peritoneum covers anterior surface only
- Right gland - pyramidal shape, Left-gland - semi-lunar shape
- Perinephric (or renal) fascia encloses the glands & kidneys - attaches to crura of diaphragm
- Adrenal glands are seperated from kidneys by perineal fat
Anatomical Structure of Adrenal Glands
- Consist of outer connective tissue caspule, a cortex & medulla
Cortex & medulla are the functional portions - two seperate endrocine glands with different embryological origins:
- Cortex - derived from embryonic mesoderm
- Medulla - derived from ectodermal neural crest cells
Cortex
- yellowish in colour
- secretes two cholesterol derived horomones - corticosteriods & androgens
Zona gomerulosa - produces & secretes mineralocorticoids (e.g aldoesterone)
Zona fasciculuta - produces & secretes corticosteroids (e.g cortisol) & small amount of androgens
Zona reticularis - produces & secretes androgens (e.g dehydroepiandrosterone - DHES) & a small amount of corticosteroids
Medulla
- lies within centre of gland - dark brown in colour
- contains chromaffin cells - secrete catecholamines (e.g adrenaline) into bloodstream in response to stress
- produce a ‘fight or flight’ response
- also secrete enkephalins which function in pain control
Clinical Relevance - Pheochromcytoma
- Tumor of the adrenal medulla or preganglionic sympathetic neurones
- Secretes adrenaline & noradrenaline uncontrollably - blood pressure greatly increases
- Patients may present with palpatations, headaches & diaphoresis (profuse sweating)
- Phenoxybenzamine - competitive, irreversible agonist of adrenaline can be used in treatment to reduce blood pressure by binding to adrenaline receptors, making less available for adrenaline to act upon
Kidneys
- Main function - filter & excrete waste products from blood, water & electrolyte balance in body
- Waste secreted is transported to the bladder by ureters, leaves the body via the urethra
- Retroperineal, either side of vertebral column
- Extend from T12 to L3 but right kindey is slightly lower due to presence of the liver (each kidney is 3 vertabrae in length)
Kidney Layers
Kidney is incased in complex layers of fascia & fat:
- renal capsule - tough fibrous capsule
- perirenal fat - collection of extraperitoneal fat
- renal (perineal) fascia - encloses kidneys & suprareneal glands
- parenenal fat - located on posterolateral aspect of kidneys
Kidney Structure
- Can be divided into two main areas: outer cortex & inner medula
- Cortex extends into medulla, dividing it into triangular shapes - renal pyramids
- Apex of a renal pyramid - renal papilla, associated with a minor calyx that collects urine from them
- Urine passes into renal pelvis - flattened, funnel-shaped structure
- Renal hilum - deep fissure that marks the medial margin of each kidney, acts as a gateway (renal vessels & ureter enter/exit via structure)
Kidney Aterial Supply
Arterial Supply
- renal arteries that arise from abdominal aorta (right artery is slightly longer than the left & crosses vena cava posteriorly)
- at hilum level, renal artery forms an anterior & posterior division (75%:25%) blood flow
- 5 segmental arteries form from the two divisions
- avascular plane of the kidney (line of Brodel) - imaginary line that delineates segments
- segmental artery>interlobar arteries (either side of every renal pyramid) >arcuate arteries>interlobular arteries (90o to arcuate)>afferent arterioles (capillary network)
- outer 2/3 of the renal cortex, afferent arterioles form peritubular network - supplying nephron tubules with O2 & nutrients
- Inner 1/3 of cortex & medulla are supplied by long straight arteries called vasa recta
- Variation between patients - acessory arteries are common (supernumerary artery)
- If a supernumerary artery doesn’t enter through the hilum, it is called aberrant
Duodenum
- Most proximal part of small intestine
- Runs from plyorus of stomach to duodenojejunal junction
- Can be divided into four parts: superior, descending, inferior & ascending
- Forms a ‘C’ shape about 25cm long, wraps around the head of the pancreas
D1 - Superior (spinal level L1)
- known as the cap
- ascends upwards from pylorus of stomach, connected to liver by hepatoduodenal ligament
- common site of duodenal ulceration
- Initial 3cm is covered by visceral peritoneum (anteriorly & posteriorly) - remainder is retroperitoneal
D2 - Descending (L1-L3)
- curves inferiorly around head of the pancreas
- lies posteriorly to transverse colon & anterior to right kidney
- marked by the major duodenal papilla - opening for bile & pancreatic secretions
D3 - Inferior (L3)
- travels laterally to left
- crosses over inferior vena cava & aorta
- located inferiorly to pancreas, posterior to superior mesenteric artery & vein
D4 - Ascending (L3-L2)
- ascends & curves anteriorly to join jejunum at sharp turn - duodenojejunal flexure
- at junction, suspensory muscle of duodenum (slip of muscle) widens angle of flexure with contraction - aids movement of contents
Jejunum & Ileum
- Distal parts of the small intestine - intraperitoneal
- Attached to posterior abdominal wall by mesentery (double layer of peritoneum)
- Jejunum begins at the duodenojejunal flexure, ileum ends at ileocaecal junction
- No clear demarcation between jejunum & ileum but both are macroscopically different
- At ileocaecal junction, ileum invaginates into cecum to form ileocecal valve - can prevent reflux of material backwards
Jujunoileum Vasculature & Lymphatics
Arterial supply:
- superior mesenteric artery - arises from aorta at L1, inferior to coeliac trunk
- moves inbetween layers of mesentery, splitting into approximately 20 branches
- branches anastomose to form loops, arcades
- from arcades, long & straight arteries arise, vasa recta
Venous drainage:
- superior mesenteric vein - unites with splenic vein at neck of pancreas to form hepatic portal vein
Lymphatics:
- superior mesenteric nodes
Colon
Ascending Colon:
- retroperitoneal
- ascends superiorly from the cecum
- right colic (or hepatic) flexure - turns 90o to move horizontally when it meets the right lobe of liver
Transverse Colon:
- extends from right colic flexure to spleen
- turns another 90o to point inferiorly (left colic flexure)
- attached to diaphragm
- intraperitoneal, enclosed by transverse mesocolon
Descending Colon:
- moves inferiorly towards pelvis
- retroperitoneal but located anteriorly to left kidney, passing over lateral border
Sigmoid Colon:
- turns medially
- located in lower left quadrant, extends from left iliac fossa to level of S3 vertebra (gives ‘s’ shape)
- attached to posterior pelvic wall by a mesentry - sigmoid mesocolon
- long length (40cm) permits this part of colon to be particuarly mobile
Colon Anatomical Structure
Characteristic features, distinguishable from small intestine:
- omental appendices attached to surface - small pouches of peritoneum, filled with fat
- teniae coli run longitudinally along surface of large bowel - three strips of muscle: mesocolic, free & omental coli
- teniae coli contract to shorten wall of the bowel, producing sacculations known as haustra
- overall, much wider diameter than small intestine
Features cease at rectosigmoid junction, where smooth muscle of teniae coli broaden to form a complete layer within rectum
Colon Anatomical Relations
Colon Venous Drainage
- Ascending - ileocolic & right colic veins, empty into superior mesenteric vein
- Transverse - middle colic vein, empties into superior mesenteric vein
- Descending - left colic vein, drains into inferior mesenteric vein
- Sigmoid - drained by sigmoid veins into inferior mesenteric vein
- Superior & inferior mesenteric veins ultimately empty into hepatic portal vein - allows toxins absorbed in colon to be processed by liver for detoxication
Colon Arterial Supply
- Midgut-derived structures - superior mesenteric artery
- Hindgut-derived structures - inferior mesenteric artery
Ascending
- supply from two branches of superior mesenteric artery - ileocolic & right colic arteries
- ileocolic artery gives rise to colic, anterior & posterior cecal branches (all supply ascending colon)
Transverse
- derived from both mid & hindgut so is supplied by branches of superior & inferior mesenteric arteries
- right colic artery (superior mesenteric)
- middle colic artery (superior mesenteric)
- left colic artery (inferior mesenteric)
Descending
- single branch of inferior mesenteric artery - left colic artery
Sigmoid
- sigmoid arteries - branch of inferior mesenteric artery
Foregut, Midgut & Hindgut
