ABDOMEN CBD common bile duct by MikeJenny

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									                                      ABDOMEN V:
                         Abdominal Viscera II: Liver, Biliary System
Dr. Art Dalley                                                           September 30, 2004 (1:00 pm)

Moore & Dalley: Clinically-Oriented Anatomy, 4th ed.: pp. 258, 263-277, Clinical Cases 2.9, 2.20, 2.21
Sadler: Langman’s Medical Embryology, 9th ed.: 296-97, 298-304
Sauerland: Grant's Dissector, 12th ed.: pp. 65-68; 73-76
Agur & Dalley: Grant's Atlas of Anatomy (11th ed): pp. 2.1A, 2.19, 2.35-2.38, 2.49-2.61
Frank H. Netter, M.D., Atlas of Human Anatomy, 2nd ed. (book)/Interactive Atlas, ver. 2.0 (CD-ROM)/Clinical
Atlas, ver. 2.0 (CD-ROM): Plates: Plates 251, 257, 258A, 269-279A, 288, 293, 298, 309, 327, plus, in Clinical
Atlas, C128, C132-C133, C275-C277, C414-C416, C524-525, Visible Human – Abdomen; 3rd ed. (book): Plates
260, 266, 267A, 278-288A, 297, 302, 317, 336.
Clemente: Anatomy: A Regional Atlas, 4th ed.: 281-285, 292, 308-324
Rohen, Yokochi & Lütjen-Drecoll: Color Atlas of Anatomy, 5th ed.: 286-289, 299-307
Weir & Abrahams: Imaging Atlas of Human Anatomy, 3rd ed.: Identify liver, features of liver, and gallbladder in
abdominal CT & MRI; identify features of biliary system as demonstrated by US, cholangiogram, cholecystogram
As a result of attending the audiovisual presentations, reading/viewing the textbook, atlas and
notes, and participating in the laboratory experience, VUSM-1 students should understand and be
able to:

1.   Describe the surface projection, location and level, and surfaces of the liver as well as the
     attachments/reflections of the peritoneum related to the liver. Can any part of the normal liver be palpated
     during a physical examination? Be able to recognize the liver in CTs and MRIs which include the upper right
     quadrant of the abdomen.
2.   Compare and contrast the anatomical lobes of the liver and the surgical segments of the liver in terms of their
     anatomic, functional and clinical significance.
3.   Describe the vessels and nerves of the liver. Compare and contrast the two sources of blood to the liver in terms
     of their quantity and quality and role in nourishing hepatic structures. What are the most common sources of
     aberrant right and left hepatic arteries? Discuss the lymphatic drainage of the liver in terms of volume of
     lymph produced and the pattern of drainage.
4.   Describe the pathway followed by bile from the bile canaliculus to the duodenum, identifying the components
     of the biliary system. What controls its entry into the duodenum?
5.   Understand how the gall bladder and bile duct relate to the liver, anterior abdominal wall, duodenum and
     pancreas in the living, as may be demonstrated by means of ultrasound examination, or in the patient or cadaver
     as demonstrated by cross-sections and planar medical images.
6.   Describe the vessels and nerves of the biliary system. Understand and be able to explain why pain caused by an
     inflamed gallbladder may be perceived as coming from the right shoulder region.
7.   Describe the anatomical basis/significance of the following clinical phenomena:
             cholecystectomy (including identity/significance of “triangle of Calot”)
             role of cirrhosis in producing portal hypertension, and the anatomical consequences of the latter:
             portacaval (portasystemic) anatomoses/shunts
             caput medusae
             esophageal varices
8.   Discuss the embryological source of the liver and gallbladder, and the manner in which they develop.




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I.     The Liver:
           largest internal organ/gland (1200-1600g in adults), secretes up to 1 liter bile/day
           is also a blood reservoir and our greatest lymph-producing organ
            accounts for 1/4 to 1/2 of total vol. reaching thoracic duct
           initial „filter‟ through which all substances absorbed from the GI tract – except
            lipids – will pass to be broken down or detoxified.
           has a unique ability to regenerate from an approx. 10% remnant (exper. dogs).
       A. Location, shape and surfaces (GA11 2.1, 2.49; Netter 260, 278)
            1. occupies rt. hypochondriac & epigastric regions.
                  superiormost abdominal structure
                      plastered to underside of diaphragm, to which its superior surface
                          conforms exactly as it completely occupies right dome of the diaghragm;
                          thus it is . . .
                      almost entirely protected by the rib cage, and enjoys „pneumatic packing‟
                          from concavity of base of right lung above..
                      liver is attached to & moves w/ diaphragm during respiration.
            2. wedge-shaped when seen in an anterior view (GA11 2.49A; Netter 279A)
                  large round base on right, extending between 4th or 5th interspace (approx.
                     level of the male nipple) and costal margin in the midaxillary line.
                  apex reaches to zenith of left diaphragmatic dome (2 finger breadths below
                     left nipple).
                        Transcutaneous biopsy is performed 3 interspaces below upper limit of
                         liver dullness during full expiration (usually 9th intercostal space).
                    airfoil1 shaped in sagittal (and often in coronal) section
                  rounded, smooth, superior or diaphragmatic surface (Netter Pl. 270A/279A)
                  flat or even concave inferior or visceral surface (Netter Pl. 270B/279B )
                      faces inferiorly and posteriorly).
       B. Attachments and External Features (GA11 2.49-2.50; Netter 280A )
            mesenteric attachments -- discussed with peritoneum
                 falciform, round, coronary, and triangular ligaments


1
    Like a section of an airplane wing: round top, flat or concave bottom, round leading edge, sharp trailing edge


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       lesser omentum (= hepatogastric + hepatoduodenal ligs.)
           attachments tether liver in place, but are not weight-bearing
               weight is borne by subhepatic abdominal viscera, in turn supported by
                the tonus of the muscles of the anterolateral abdominal wall.
    H-shaped pattern of grooves on viscera surface
       left strut (umbilical or left sagittal fissure)
           fissure for the ligamentum venosum
           fissure for the round ligament (ligamentum teres hepatis)
       right strut (right sagittal fissure):
            fossa for the inferior vena cava (IVC)
            fossa for gall bladder
       cross-bar:
           porta hepatis – site of entry/exit of portal triad of structures
            (1) portal vein
            (2) hepatic artery
            (3) hepatic ducts
C. Lobation/Segmentation
    1. Classic (anatomical) lobes (GA11 Table 2.4, Fig. 2.53; Netter 279A, 281)
           Is divided very unevenly and superficially (externally) by peritoneal
            reflections and fissures (formed in relation to those reflections and the
            vessels serving the liver) into two main topographical (anatomical) lobes
            defined by the essentially midline plane of attachment of the falciform
            ligament to the diaphragmatic surface and the umbilical fissure in the
            visceral surface:
                 (1) right lobe
                         lies to right of falciform ligament/umbilical fissure (~ midline)
                         very large
                 (2) left lobe (much smaller)
             and two accessory lobes:
                 (1) caudate (Spigellian) lobe
                        is NOT most caudal -- so named because it often has a "tail" --
                         the papillary process of the caudate lobe.


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                   (2) quadrate lobe.
                            is essentially square
            outer surface is covered with Glisson's capsule deep to visc. peritoneum.
                  sensitive: pain with acute hepatomegaly, transient venous congestion
                       causing sudden distention ("runner's stitch").
  2.   Parts
            internally functionally and surgically), liver is more nearly equally divided
             into two parts – right and left:(or “right liver”, “left liver”)
                 parts separated by a plane (middle or main portal scissura) passing
                  through:
                  (a) Cantlie‟s line on the diaphragmatic surface
                         connects suprahepatic IVC and notch for fundus of gallbladder
                         deviates approximately 15° to rt. of sagittal plane
                  (b) right sagittal fissure
                 rt. & l. parts have separate biliary drainage & vascular supply.
                 quadrate lobe drains to l. hepatic duct & receives blood from l. hepatic
                  a.; thus, it is really part of l. part
                 caudate lobe is functionally part of both parts.
                 Even when divided this way, rt. liver is usually larger (50-70% of liver
                  mass)
           surgical (vascular/biliary) segmentation can be demonstrated by filling of
            vasculature
   3. Divisions and Segments (“Portal segments”): -- see under “Hepatic Veins” below
D. Blood Supply:
   1. Afferent blood flow -- like the lungs, the liver has a dual blood supply:
       a.    Hepatic artery (HA) (GA11 2.54, 2.55; Netter 281B, 282, 290, 292)
                  ~20-25% of blood entering liver comes via hep. a.
                  mainly concerned w/ supplying non-parenchymal structures (vasa
                   vasorum, hepatic nn., CT of capsule & portal areas, and the peribiliary
                   arterial plexus) (Netter Plate 274/283)
                        thus arterial injury may lead to ischemic strictures of ducts (esp.
                         post-transplant)


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            "typical" pattern of distribution is actually rather uncommon, 60-70%
             of individuals showing variations. (Netter Plate 288/297)
                most common source of aberrent (replaced or accessory) l.
                 hepatic a. = l. gastric a.
                most common source of aberrent (replaced or accessory) r.
                 hepatic a. = sup. mesenteric a.
    b.   Portal vein (PV) (GA11 2.60-2.61; Netter 300-302)
            80% of blood entering liver comes via the portal v.
            blood conveyed is less deoxygenated than most venous blood (40%
             more O2 than caval blood), and supplies the great majority (but not all)
             of oxygen and nutrients to the hepatic parenchyma (hepatocytes).
            valveless venous system; thus blood need not flow toward liver.
            formed posterior to neck of pancreas by merger of SMV & splenic v
            Least variable of the liver‟s vessels
                Length usually 11 cm (4 inches) in length, with superior 5 cm
                 having no branches
            portal v., hepatic a. & biliary ducts form "portal triads" beginning in
             hepatoduodenal lig, and through distribution in liver
                in hepatoduodenal lig., lies post. to hepatic a. and bile duct
            everything exc. lipids absorbed from G.I. tract pass via PV to liver.
            begins in (drains) capillary beds supplied by all three major (unpaired)
             brs. of abdominal aorta, ends as sinusoids of liver
            bifurcates into rt. & left branches before entering porta hepatis
                flow is quite laminar:
                  blood from sup. mesenteric v. mainly enters right branch
                  blood from splenic vein mainly enters left branch
                     obliterated umbilical v., lig. venosum assoc. with left branch.
2. Efferent blood flow:
    a.   Hepatic veins (HVs): (GA11 2.52, Table 2.4; Netter 282A, 283, 299A)
            originate as central veins surrounded by artifactual hepatic lobules.
            collecting veins interdigitate w/ portal triads.
            short, wide hepatic veins are entirely intrahepatic.


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                     are final (most superior) tributaries of inf. vena cava.
                     In the typical pattern, 3 major hepatic veins form:
                      (1) right
                      (2) middle
                      (3) left
                      with the middle and left uniting just before entering the IVC
                     the planes in which these veins course (portal scissurae) form the
                      basis for dividing the liver into four portal divisions or sectors
                         each receives a portal pedical (segmental br. of PV and HA)
                         each is drained by a segmental bile duct
                         three of the four portal divisions are further subdivided, based on
                          branching of the portal pedicle, creating 7 hepatic segments from
                          the main part of the liver (4 right, 3 left); the caudate lobe is an
                          autonomous segment, bringing the number of segments to eight
                          (Hepatic Segments I – VIII)
                         Hepatic segments are surgically resectable units of the liver
    D. Lymphatic Drainage (GA11 2.80D; Netter 298 2nd ed only))
            deep lymphatics join subperitoneal lymphatic vessels.
            most lymphatics from the diaphragmatic surface pass to & through the
             diaphragm to diaphragmatic and then lower parasternal (ant. mediastinal)
             nodes via either the falciform lig. (anteriorly) or the IVC (posteriorly).
            most lymphatics from the visceral surface pass to hepatic nodes at the porta
             hepatis (in the hepatic pedicle) and then to the celiac nodes.


II. The Biliary Apparatus:
    A. The Biliary Tract (Hepatic Tree) (GA11 2.37A-C, 2.54BC, 2.55A; Netter 285-287)
         1. R. & l. hepatic ducts ---> common hepatic duct.
                Hepatic ducts are extrahepatic (outside liver in region of porta hepatis)
         2. cystic duct
                duct allowing bidirectional flow between gallbladder and common
                 hepatic/bile duct
         3. common hepatic duct + cystic duct ---> (common) bile duct (CBD).


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           merging ducts (common hepatic & cystic) and inferior surface of liver form
            Calot‟s triangle – area where extreme care must be taken in identifying
            and dissecting cystic artery and aberrant hepatic arteries arising from SMA
           descends hepatoduodenal lig. as part of hepatic pedicle.
           passes post. to 1st pt. of duodenum & becomes embedded in head of
            pancreas (from which it can easily be dissected).
   3. near termination, CBD joins main pancreatic duct to form the . . .
           hepatopancreatic ampulla (Vater) which enters 2nd pt. duod.
               seen from duodenal lumen as the duodenal papilla
               sphincter of the hepatopancreatic ampulla (Oddi):
                    common ring of smooth muscle.
                    anatomically & functionally distinct from duodenal muscle
                    controlled by cholecystokinin (CCK)--& possibly vagi.
                    much variation; paradigm has 3 subdivisions:
                a.   Choledochal sphincter:
                        surrounds termination of common bile duct.
                        most consistent portion.
                        regulates flow of bile (emptying/filling of GB).
                b.   Pancreatic sphincter:
                        surrounds intraduodenal pancreatic duct.
                        present only in 20% of population.
                c.   Ampullary sphincter:
                        surrounds ampulla (common channel).
                        always considerably weaker than choledochal sphincter.
B. The Gallbladder (GB):      (GA11 2.37A, 2.54BC, 2.55A; Netter 285)
      surface projection: junction. of rt. semilunar line & costal marg.
      usually not palpable in the absence of stones.
      6-10 cm long, capacity = ~45 ml.
       1.   Morphology: fundus, body, neck, cystic duct.
               spiral fold ("valve"--not a true valve) maintains patency of cystic duct.
               normal variations: Hartman's pouch, phrygian cap.
       2. Blood vessels:


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                  a.    Cystic artery (GA11 2.54B, 2.55A, 2.57, Netter 285A, 290, 292, 297)
                           normally arises from rt. hepatic a.
                           normally found w/in Calot‟s triangle
                  b.    Venous drainage:         (GA11 2.54C)
                           vv. of attached (hepatic) surface  liver  hep. vv.
                           vv. of serous surface  cystic v.  liver (rarely does cystic v. enter
                            into portal vein).
            3. Function:
                       bile secreted continuously, needed only during digestion.
                       sphincter choledochus closed except during digestion -- thus bile
                        refluxes through cystic duct to GB.
                           GB stores & concentrates bile.
                       when CCK opens sphincter, it also causes GB contraction.


III. Embryology of Liver and Biliary System (Netter Clinical Atlas CD: C504-506, C525;
                                             Netter Embryo Atlas: 6.2-6.5; 6.7, 6.11)
       A. Development of septum transversum (previously covered w/ heart/diaphragm)
       B. Hepatic diverticulum (liver bud) appears in middle of 3rd week as an outgrowth
          of the endodermal epithelium at the distal end of the foregut
                rapidly proliferating cells of the cephalic portion of the diverticulum invade
                 the splanchnic mesoderm of septum transversum
                caudal portion or stalk of the diverticulum “narrows” into (remains
                 relatively small as) bile duct
                      small ventral outgrowth of bile duct gives rise to gallbladder/cystic duct
        C. Paired vitelline veins passing through the septum split up and branch out into
             a vascular plexus that becomes surrounded by the invading endodermal cells
                endodermal cells differentiate into the hepatocytes that comprise the
                 hepatic parenchyma
                vascular plexus becomes hepatic sinusoids & sinusoidal (Kupffer) cells
                portions of vitelline veins cranial & caudal to plexus become hepatic and
                 portal veins, respectively




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                 septum mesenchyme becomes connective tissue of capsule surrounding
                  liver, portal tracts penetrating the liver, and membranes connecting
                  capsule to ventral body wall (falciform lig.), diaphragm (coronary ligs.) &
                  stomach/duodenum (lesser omentum)


IV. Collateral Portal Circulation (Portacaval Anastomoses) (GA11 2.61; Netter 302)
   1. l. gastric v.  esophageal v. plexus  azyg./hemiazyg. vv.  SVC (esophageal
      varices).
   2. l. portal v.  paraumbilical vv.  sup./inf. epigastric vv.  SVC/IVC ("caput
      medusae").
   3. Inf. mesenteric v.  sup. rectal v.  middle/inf. rectal vv.  iliac vv.  IVC
      (hemorrhoids).
   4. veins of Retzius:
       numerous but typically very small veins which pass to body wall from the non-
          peritonealized surfaces of organs, e.g., asc. & desc. colon, duodenum/pancreas
          & liver, and from tributaries of the portal vein which lie retroperitoneally, such as
          the splenic and a portion of the SMV.
           permit diversion of portal blood into lumber, lower intercostal, and
             diaphragmatic brs. of the caval system.




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