THORAX - SAQ Topics

1. Thoraco-abdominal Diaphragm

• Diaphragm is a thin musculotendinous structure that fills the inferior thoracic aperture - this phrasing is uniquely Gray's
• Peripheral attachments: xiphoid process, costal margin, ends of ribs XI and XII, ligaments spanning posterior abdominal wall, and lumbar vertebrae
• Muscle fibers converge to the central tendon; the pericardium is attached to the middle part of the central tendon
• In the median sagittal plane, it slopes inferiorly from the xiphoid (vertebral level TVIII/IX) to the median arcuate ligament at vertebral level TXII
• IVC passes through the central tendon at TVIII (not the muscular part)
• Esophagus passes through the muscular part, just to the left of midline, at TX
• Aorta passes behind the posterior attachment at TXII (not through it - passes behind the median arcuate ligament)
• The thoracic duct passes behind the diaphragm with the aorta
• Azygos and hemiazygos veins may pass through the aortic hiatus or through the crura
• Sympathetic trunks pass outside the posterior attachments lateral to the aortic hiatus
• Greater, lesser, and least splanchnic nerves penetrate the crura
• Arterial supply from above: pericardiacophrenic and musculophrenic (branches of internal thoracic arteries) + superior phrenic arteries (from thoracic aorta)
• Largest supply is from below: inferior phrenic arteries (direct branches of abdominal aorta)

2. Internal Thoracic Artery

• Gives off pericardiacophrenic and musculophrenic branches that supply the diaphragm from above
• The musculophrenic artery supplies the diaphragm and the lower intercostal spaces
• The pericardiacophrenic artery accompanies the phrenic nerve through the thoracic cavity
• Terminates by dividing into the superior epigastric artery (anastomoses with the inferior epigastric) and the musculophrenic artery
• Located immediately lateral to the sternum, deep to the costal cartilages

3. Azygous System of Veins

• Consists of longitudinal vessels on each side draining the body wall, returning blood superiorly to the SVC
• Key functional point (Gray's emphasis): The azygos system serves as an important anastomotic pathway capable of returning venous blood from the lower body to the heart if the IVC is blocked
• There is significant variation in the origin, course, tributaries, anastomoses, and termination
• Azygos vein arises opposite vertebra LI or LII at the junction of the right ascending lumbar vein and right subcostal vein (or directly from IVC)
• Enters thorax through the aortic hiatus or through/posterior to the right crus
• Ascends to the right of the thoracic duct
• At vertebral level TIV, arches anteriorly over the root of the right lung to join the SVC before the SVC enters the pericardial sac
• Hemiazygos arises from left ascending lumbar + left subcostal veins, often has connection to left renal vein; enters through left crus or aortic hiatus
• Hemiazygos ascends to ~vertebral level TIX then crosses the midline posterior to the aorta, esophagus, and thoracic duct to enter the azygos vein

4. Thoracic Duct

• Is the principal channel through which lymph from MOST of the body is returned to the venous system
• Begins as a confluence of lymph trunks, sometimes forming the cisterna chyli (chyle cistern), which drains abdominal viscera, walls, pelvis, perineum, and lower limbs
• Extends from vertebra LII to the root of the neck
• Enters thorax through the aortic hiatus, posterior to the aorta
• In posterior mediastinum: ascends between the thoracic aorta on the left and the azygos vein on the right, posterior to the esophagus, anterior to vertebral bodies
• At vertebral level TV, moves to the left of midline and enters superior mediastinum
• Empties into the junction of the left subclavian and left internal jugular veins
• After joining: left jugular trunk (left head/neck) + left subclavian trunk (left upper limb)
• Drains: lower 6-7 intercostal spaces bilaterally, upper left 5-6 intercostal spaces, posterior mediastinal nodes, posterior diaphragmatic nodes

5. Pleura and its Divisions

• Parietal pleura lines the inner surface of the thoracic wall and reflects onto the mediastinum and diaphragm
• Visceral pleura adheres to and covers the lung surfaces, dips into the fissures
• The two layers are continuous at the root of the lung
• Below the root of the lung, the pleural layers form the pulmonary ligament, which helps support the lung
• Costodiaphragmatic recess: the lowest part of the pleural cavity where the costal and diaphragmatic pleurae meet - the lungs do NOT normally extend into this space; fills with fluid in pleural effusion
• Costomediastinal recess: where costal and mediastinal pleurae meet anteriorly - the anterior border of the lung does not fully occupy this space (especially on the left, creating the cardiac notch)
• Pain from the peripheral part of the diaphragmatic pleura is referred to the shoulder (via phrenic nerve C3-C5); pain from the costal pleura is referred to the chest wall and abdomen

6. Arch of Aorta

• Thoracic aorta = ascending aorta + arch of aorta + thoracic (descending) aorta
• Only the arch of the aorta is in the superior mediastinum
• Begins when the ascending aorta emerges from the pericardial sac; courses upward, backward, and to the left; ends on the left side at vertebral level TIV/V
• Extends as high as the midlevel of the manubrium
• Initially anterior to the trachea, then lateral to it
• Three branches from the superior border of the arch; all three are crossed anteriorly by the left brachiocephalic vein at their origins:
  1. Brachiocephalic trunk
  2. Left common carotid artery
  3. Left subclavian artery

7. Superior Mediastinum

• Posterior to the manubrium of the sternum, anterior to bodies of T1-T4
• Superior boundary: oblique plane from the jugular notch upward/posteriorly to the superior border of vertebra T1
• Inferior boundary: transverse plane at sternal angle to TIV/V disc - continuous below with the inferior mediastinum
• Lateral boundaries: mediastinal part of parietal pleura on either side
• Continuous with the neck above and inferior mediastinum below
• Contents include: thymus, right and left brachiocephalic veins, left superior intercostal vein, SVC, arch of aorta with three branches, trachea, esophagus, phrenic nerves, vagus nerves, left recurrent laryngeal branch of left vagus, thoracic duct

8. Middle Mediastinum

• Centrally located in the thoracic cavity
• Contains: pericardium, heart, origins of the great vessels, various nerves, and smaller vessels
• Lower half of the SVC is within the pericardial sac and is therefore in the middle mediastinum
• Fibrous pericardium is a cone-shaped bag with its base on the diaphragm and apex continuous with the adventitia of the great vessels
• Base attached to the central tendon of the diaphragm and small muscular area of diaphragm on the left
• Anteriorly attached to the posterior surface of sternum by sternopericardial ligaments (retains heart in position and limits cardiac distention)
• Phrenic nerves pass through the fibrous pericardium to reach the diaphragm

9. Posterior Mediastinum

• Posterior to the pericardial sac and diaphragm, anterior to mid and lower thoracic vertebral bodies
• Superior boundary: transverse plane from sternal angle to TIV/V disc
• Superiorly continuous with the superior mediastinum
• Contents: esophagus + nerve plexus, thoracic aorta + branches, azygos system of veins, thoracic duct + lymph nodes, sympathetic trunks, thoracic splanchnic nerves
• Esophageal relations (exclusive Gray's detail): Right side covered by mediastinal parietal pleura; thoracic duct is posterior/right inferiorly but crosses to the left more superiorly; passes immediately posterior to the left atrium (separated only by pericardium); below the tracheal bifurcation it is related to the right pulmonary artery and left main bronchus anteriorly

10. Coronary Sinus

• Located in the coronary sulcus on the POSTERIOR surface of the heart between the left atrium and left ventricle
• Empties into the right atrium between the opening of the IVC and the right atrioventricular orifice
• Most cardiac veins empty into the coronary sinus
• The right coronary artery gives an SA nodal branch that passes posteriorly around the superior vena cava to supply the SA node

11. Superior Vena Cava (SVC)

• Vertically oriented; begins posterior to the lower edge of the right first costal cartilage (where right and left brachiocephalic veins join)
• Terminates at the lower edge of the right third costal cartilage where it joins the right atrium
• Lower half of the SVC is within the pericardial sac (therefore in the middle mediastinum)
• Receives the azygos vein immediately before entering the pericardial sac; may also receive pericardial and mediastinal veins
• Easily visualized forming the right superolateral border of the mediastinum on a chest X-ray
• Because the SVC and IVC are on the same vertical axis, a guidewire can pass from the SVC through the right atrium into the IVC - used for: transjugular liver biopsy, TIPS, IVC filter insertion

12. Sternal Angle (Angle of Louis)

• Formed because the manubrium angles posteriorly on the body of the sternum, forming a raised palpable feature
• Marks the site of articulation of rib II with the sternum (rib I is not palpable, so rib II is used for counting)
• Lies on a horizontal plane passing through the intervertebral disc between TIV and TV
• This plane:
  • Separates the superior from the inferior mediastinum
  • Marks the superior border of the pericardium
  • Passes through the end of the ascending aorta and beginning of the arch of the aorta
  • Passes through the end of the arch and beginning of thoracic aorta
  • Passes through the bifurcation of the trachea
  • Passes just superior to the pulmonary trunk

13. Oesophagus

• Begins at the inferior border of the cricoid cartilage, opposite vertebra CVI
• Ends at the cardiac opening of the stomach opposite vertebra TXI
• Secured superiorly by attachment to the pharynx and inferiorly by attachment to the diaphragm
• Has a slight anterior-to-posterior curvature that parallels the thoracic vertebral column
• As it approaches the diaphragm, moves anteriorly and to the LEFT, crossing from the right side of the thoracic aorta to a position anterior to it
• Passes through the esophageal hiatus in the muscular part of the diaphragm at TX
• Passes immediately posterior to the left atrium (separated only by pericardium) - clinically important for trans-esophageal echocardiography

14. Pericardial Sinuses

• Two reflections of serous pericardium around roots of great vessels:
  1. Superiorly - around arteries (aorta + pulmonary trunk)
  2. Posteriorly - around veins (SVC, IVC, and pulmonary veins)
• The reflection around veins is J-shaped; the cul-de-sac within the J, posterior to the left atrium, is the oblique pericardial sinus
• The passage between the two reflection sites is the transverse pericardial sinus - lies posterior to ascending aorta + pulmonary trunk, anterior to SVC, superior to left atrium
• Surgical relevance (Gray's exclusive): When the pericardium is opened anteriorly, a finger in the transverse sinus separates arteries from veins; a hand under the apex moved superiorly slips into the oblique sinus
• Pain from the parietal pericardium is somatic (via phrenic nerves C3-C5) and may be referred to the supraclavicular region / lateral neck

15. Trachea

• Bifurcates at the level of the sternal angle plane (TIV/V)
• In the superior mediastinum, it is initially anterior then lateral to the arch of the aorta

ABDOMEN - LAQ Topics

1. Inguinal Canal

• A slit-like passage extending in a downward and medial direction, just above and parallel to the lower half of the inguinal ligament, approximately 4 cm long
• Begins at the deep inguinal ring, ends at the superficial inguinal ring
• Deep inguinal ring is at a point midway between ASIS and pubic symphysis, just above the inguinal ligament, immediately lateral to the inferior epigastric vessels - it is the beginning of the tubular evagination of transversalis fascia forming the internal spermatic fascia
• Superficial inguinal ring is a triangular opening in the aponeurosis of external oblique, superior to the pubic tubercle, with its apex pointing superolaterally and its base formed by the pubic crest; medial crus attached to pubic symphysis, lateral crus to pubic tubercle; intercrural fibers prevent widening
• Contents: genital branch of genitofemoral nerve + spermatic cord (men) or round ligament (women); ilio-inguinal nerve also passes through part of the canal and exits through the superficial ring
• Direct vs. Indirect hernias (key Gray's distinction):
  • Indirect hernias push into the deep inguinal ring (lateral to inferior epigastric vessels), through the entire canal, and potentially into the scrotum/labium
  • Direct hernias push through the posterior wall of the canal medial to the inferior epigastric vessels (through Hesselbach's/inguinal triangle)

2. Stomach

• Most dilated part of the GI tract, J-shaped, in the epigastric, umbilical, and left hypochondrium regions
• Four regions: cardia (surrounds esophageal opening), fundus (above level of cardial orifice), body (largest region), pyloric part (antrum + canal)
• The pylorus (most distal) contains the thickened pyloric sphincter and pyloric orifice; pyloric orifice is just to the RIGHT of midline in the transpyloric plane at lower border of LI
• Angular incisure: a bend on the lesser curvature (uniquely named in Gray's)
• Cardiac notch: superior angle where esophagus enters the stomach
• Arterial supply: left gastric (from celiac trunk), right gastric (from hepatic artery proper), right gastro-omental (from gastroduodenal), left gastro-omental + short gastric vessels (from splenic artery)
• Gastrosplenic ligament attaches to the greater curvature; lesser omentum attaches to the lesser curvature

3. Liver

• Largest visceral organ; primarily in right hypochondrium and epigastric region, extending into the left hypochondrium
• Two surfaces: diaphragmatic (anterior, superior, posterior - smooth and domed) and visceral (inferior)
• Associated recesses:
  • Subphrenic recess between liver diaphragmatic surface and diaphragm; divided into right and left by the falciform ligament (derived from the ventral mesentery)
  • Hepatorenal recess (Morrison's pouch): on the right between liver and right kidney/right suprarenal gland; subphrenic and hepatorenal recesses are continuous anteriorly - important in peritonitis/fluid collection
• The falciform ligament divides the subphrenic recess and is a remnant of the ventral mesentery
• Liver segments are defined by hepatic veins and portal triads (Gray's emphasis on functional anatomy)
• Bare area: the area of diaphragmatic surface not covered by peritoneum

4. Portal Vein

• "Final common pathway for transport of venous blood from spleen, pancreas, gallbladder, and abdominal GI tract"
• Forms by union of splenic vein and superior mesenteric vein posterior to the neck of the pancreas at LII
• Ascending toward liver: passes posterior to the superior part of the duodenum and enters the right margin of the lesser omentum
• In the lesser omentum: anterior to the omental foramen and posterior to both the bile duct (right) and hepatic artery proper (left)
• Tributaries:
  • Right and left gastric veins (drain lesser curvature + abdominal esophagus)
  • Cystic veins (from gallbladder)
  • Para-umbilical veins (associated with the obliterated umbilical vein, connect to veins on the anterior abdominal wall)
• Splenic vein is large and straight, contacts the body of the pancreas as it crosses the posterior abdominal wall

5. Pancreas

• Lies mostly posterior to the stomach; extends from the duodenum (right) to the spleen (left)
• Secondarily retroperitoneal except for a small part of its tail
• Parts: head, uncinate process, neck, body, tail
• The uncinate process projects from the lower part of the head and passes posterior to the superior mesenteric vessels
• Neck is anterior to the superior mesenteric vessels; portal vein forms posterior to the neck
• Tail passes between layers of the splenorenal ligament
• Pancreatic duct: begins in the tail, passes right through the body, turns inferiorly in the head; joins the bile duct to form the hepatopancreatic ampulla, which enters the descending (second) part of duodenum at the major duodenal papilla
• Sphincter of Oddi (sphincter of the ampulla) surrounds the ampulla
• Accessory pancreatic duct empties just above at the minor duodenal papilla
• Annular pancreas: embryological anomaly where a ring of pancreatic tissue encircles and may obstruct the duodenum

6. Kidney

• Each kidney has a smooth surface covered by a fibrous capsule (easily removable except during disease)
• Hilum: a deep vertical slit on the medial margin through which renal vessels, lymphatics, and nerves enter/leave; internally continuous with the renal sinus; perinephric fat continues into the hilum
• Renal cortex: continuous band of pale tissue that completely surrounds the medulla; extensions (renal columns) project into the medulla
• Renal pyramids: triangular, bases directed outward toward cortex, apex (renal papilla) projects inward into the sinus; papillary ducts open into the papilla, surrounded by a minor calyx
• Minor calices → major calices → renal pelvis (funnel-shaped, proximal ureter)
• Renal arteries arise just inferior to the origin of the superior mesenteric artery between LI and LII; left artery arises slightly higher than the right; right renal artery is longer and passes posterior to the IVC
• Left renal vein crosses the midline anterior to the abdominal aorta (important surgical landmark)
• Renal veins are anterior to the renal arteries
• Accessory renal arteries are common; they enter at the hilum or pass directly into the kidney (extrahilar arteries)

7. Urinary Bladder

• Most anterior element of the pelvic viscera; entirely pelvic when empty, expands superiorly into the abdominal cavity when full
• Empty bladder shaped like a three-sided pyramid tipped over on one of its margins - has apex, base, superior surface, and two inferolateral surfaces
• Apex directed toward the top of the pubic symphysis; continues as the median umbilical ligament (remnant of the embryological urachus) up the anterior abdominal wall to the umbilicus
• Base (trigone area) faces posteroinferiorly; two ureters enter the bladder at the superior angles of the base; the urethra exits at the inferior angle
• In women: related posteriorly to the vagina and cervix (uterovesical pouch separates)
• In men: related posteriorly to the seminal vesicles, ductus deferens, and rectum

8. Uterus

• Thick-walled muscular organ in the midline between the bladder and rectum
• Consists of body + cervix; superiorly, uterine tubes project laterally and open into the peritoneal cavity adjacent to the ovaries
• Body is flattened anteroposteriorly; cavity is a narrow slit laterally but inverted triangle anteriorly; superior corners continuous with uterine tube lumens; inferior corner continuous with the cervical canal
• Fundus of the uterus: rounded superior end, above the level of uterine tubes
• Implantation of the blastocyst normally occurs in the body of the uterus
• During pregnancy, uterus dramatically expands superiorly into the abdominal cavity
• Hysterectomy pearls (Gray's): tremendous care taken to identify the distal ureters and ligate nearby uterine arteries without damaging ureters (ureter is at risk because the uterine artery crosses over it - "water under the bridge")
• Uterine tubes: infundibulum (trumpet-shaped end), ampulla, isthmus; the infundibulum curves around the superolateral pole of the ovary

9. Testis

• Spermatic cord contains: testicular artery, pampiniform plexus of veins, vas deferens, testicular sympathetic nerves, lymphatics, genital branch of genitofemoral nerve, and ilioinguinal nerve passes with it
• The internal spermatic fascia is the tubular evagination of transversalis fascia at the deep ring
• External spermatic fascia is the continuation of the aponeurosis of external oblique at the superficial ring
• Cremasteric fascia is the middle layer (from internal oblique)
• Torsion of the testis occurs when the testis hangs in the tunica vaginalis like a clapper in a bell (Gray's emphasizes the "bell clapper deformity")
• Lymphatic drainage: para-aortic lymph nodes at LI (NOT inguinal nodes) - because the testis descended from the posterior abdominal wall

10. Rectum

• Continuous above with sigmoid colon at vertebra SIII and below with the anal canal
• Most posterior element of the pelvic viscera; immediately anterior to and follows the concave contour of the sacrum
• The anorectal junction is pulled forward (perineal flexure) by the action of the puborectalis part of the levator ani; the anal canal moves posteriorly as it passes inferiorly through the pelvic floor
• Three lateral curvatures: upper and lower curvature to the right, middle curvature to the left
• Lower part expanded to form the rectal ampulla
• Unlike the colon, rectum lacks taeniae coli, omental appendices, and haustra (sacculations)
• DRE (Gray's exclusive clinical): In men, the prostate is evaluated posteriorly; in persons who have undergone vaginoplasty, the prostate is more easily palpated transvaginally along the anterior wall of the neovagina rather than rectally

11. Anal Canal

• Begins at the terminal end of the rectal ampulla at the pelvic floor; terminates as the anus after passing through the perineum
• Surrounded along its entire length by internal and external anal sphincters (normally keep it closed)
• The lining reflects the position of the cloacal membrane in the fetus and marks the transition from GI mucosa to skin
• Structural features related to embryological origin - this is a uniquely Gray's emphasis distinguishing the upper and lower anal canal by their embryological origin
• The anal canal is angled posteriorly on the rectum - this flexure is maintained by the pelvic floor muscles and relaxed during defecation

All points above are sourced from Gray's Anatomy for Students (the edition in your medical library). Use these as add-on exam points to supplement standard textbook answers. The "In the Clinic" boxes from Gray's are particularly score-worthy in applied anatomy questions.