Anatomy overview

This article summarizes the most important anatomical concepts for exam and board purposes. For additional information, refer to the articles on specific topics.

Anatomy of the heart

Heart chambers

Heart valves

Coronary vessels

• The left and right coronary arteries arise from the root of the aorta and supply the heart muscle with arterial blood.
• Coronary arterial dominance
  • Right-dominant (∼ 85% of the population): posterior descending artery (PDA) supplied by the RCA
  • Left-dominant (∼ 8% of the population): PDA supplied by the left circumflex artery (LCX)
  • Codominant (balanced; ∼ 7% of the population): PDA supplied by both RCA and LCX
• Coronary blood flow peaks during early diastole at a point when the pressure differential between the aorta and the ventricle is the greatest (see the diagram for left ventricular pressure-volume).

The LAD is the most commonly occluded coronary artery and is often referred to as the “widow maker” because LAD infarction is associated with a high mortality rate.

The RCA usually supplies the heart's conduction system (sinus and AV node), so stenosis or occlusion of this vessel often leads to cardiac arrhythmias.

Pericardium

• Pericardial layers
  • Serous pericardium (innermost)
    • Visceral layer of the serous pericardium (epicardium)
    • Parietal layer of the serous pericardium
  • Fibrous pericardium (outermost)
• Innervation: phrenic nerve

Because of the sensory innervation of the pericardium by the phrenic nerve, pericarditis can result in referred pain to the neck, arms, or shoulders (more often to the left side).

Nasal cavity and paranasal sinuses

Blood supply

The blood supply to the nose and nasal cavity is provided by the ophthalmic, maxillary, and facial arteries.

Innervation

• Olfactory: olfactory nerve (CN I)
• General sensory: trigeminal nerve (ophthalmic and maxillary branches via pterygopalatine ganglion)

Paranasal sinuses

Larynx

Trachea

• Bifurcates at the level of T4 into the left and the right main bronchus (tracheal carina)
• Neighboring structures
  • Posterior: esophagus, descending aorta
  • Anterior: thyroid, ascending aorta, brachiocephalic trunk, superior vena cava

Bronchi and lungs

Only the right lung has a middle lobe. It can be auscultated in the fourth to sixth intercostal space anteriorly at the midclavicular line.

The right main bronchus is wider, shorter, and more vertical than the left main bronchus, so aspiration of foreign bodies and aspiration pneumonia are more likely in the right lung.

Each bronchopulmonary segment can be surgically removed without affecting the function of the others.

The Lingula is in the Left Lung.

Relation of lungs to ribs

Pulmonary circulation

“RALS” - Right: Anterior to the mainstem bronchus; Left: Superior to the mainstem bronchus (relationship of pulmonary arteries to the corresponding bronchi).

Derivatives of the foregut, midgut, and hindgut

Internal hemorrhoids lie above the pectinate line and are supplied by the superior rectal artery (branch of the inferior mesenteric artery), while external hemorrhoids lie below the pectinate line and are supplied by the inferior rectal artery (branch of the internal pudendal artery).

Gastrointestinal (GI) innervation

Liver and biliary tract

Liver

• Porta hepatis structures
  • Common hepatic duct (leaving)
  • Hepatic artery proper (entering)
  • Hepatic portal vein (entering)
  • Hepatic nerve plexus and lymphatic vessels

• Microscopic anatomy
  • Lobules
    • A central vein in the middle (drains into collecting veins that become hepatic veins, which leave the liver and empty into the vena cava)
    • Portal triads at the vertices, which consist of:
      • Branch of hepatic artery proper
      • Branch of portal vein
      • Bile ductule
    • Each portal triad is accompanied by the following structures:
      • Lymphatic vessels
      • Branch of the vagus nerve
      • Parenchyma
  • The basolateral surface of hepatocytes faces the sinusoids.
  • The apical surface of hepatocytes faces the lumen of the bile canaliculi.
  • Hepatic sinusoids are large capillaries lined with highly fenestrated endothelial cells: Blood flows through the sinusoids and empties into the central vein of each lobule.

Temporary occlusion of hepatoduodenal ligament (Pringle maneuver) can help to achieve hemostasis.

Gallbladder and bile ducts

• Gallbladder
  • Consists of the fundus, body, infundibulum, and neck (the narrowest part of the gallbladder)
  • Supplied by the cystic artery (branch of the right hepatic artery)
• Common bile duct
  • Formed by the common hepatic duct and cystic duct
  • Travels in the free edge of the lesser omentum, in the hepatoduodenal ligament
  • Posterior to the duodenum and the pancreas
  • Connects with the main pancreatic duct
  • Drains into the hepatopancreatic ampulla (ampulla of Vater)
• Hepatobiliary triangle (Calot triangle)
  • An anatomical space formed by the common hepatic duct, the cystic duct, and the lower border of the liver
  • The Calot triangle contains the cystic artery and the cystic lymph node (Lund's node).

During cholecystectomy, the Calot triangle must be carefully identified to prevent damage to the cystic artery and extrahepatic biliary system.

Pancreas

Structure

• Head
  • Located within the C-shaped duodenal curvature
  • Contains the pancreatic duct and distal common bile duct
  • Uncinate process of pancreas: an extension of the pancreatic head; located posterior to the superior mesenteric vessels (the remainder of the pancreas is not)
• Neck: lies anterior to the portal vein
• Body: lies anterior to the aorta and extends to the left kidney
• Tail
  • Lies in the splenorenal ligament and extends to the splenic hilum
  • The distal segment is intraperitoneal.

Blood supply

• Head and neck
  • Superior pancreaticoduodenal branches (from the gastroduodenal artery)
  • Inferior pancreaticoduodenal branches (from the superior mesenteric artery)
• Body and tail: branches of the splenic artery (itself a branch of the celiac trunk)

Tumors in the pancreatic head often cause bile duct obstruction and can manifest with painless jaundice (Courvoisier sign).

Kidney

Renal anatomy and topography

• Location: at the level of T12–L3
• Adjacent structures: superior pole is covered by ribs
  • Left kidney: 11^th and 12^th ribs
  • Right kidney: 12^th rib

Nearby structures

• At the superior pole: adrenal gland
• Anteriorly
  • Left kidney: spleen, stomach, pancreas, splenic flexure, jejunum
  • Right kidney: right lobe of the liver, descending duodenum, hepatic flexure of the colon
• Posteriorly
  • Muscles: diaphragm, psoas major, quadratus lumborum
  • Nerves: subcostal, iliohypogastric, ilioinguinal

Projections

• Anterior abdominal wall: RUQ and LUQ respectively
• Back: costovertebral angle

Renal structure

• Renal cortex: contains the glomeruli, proximal convoluted tubules, distal convoluted tubules, and cortical collecting ducts
• Renal medulla: contains the loops of Henle and collecting ducts, which merge to form the papillary ducts at the renal papillae
• Renal hilum structures (from anterior to posterior)
  • Renal vein (exits)
  • Renal artery (enters)
  • Renal pelvis (exits)

Renal blood flow

• Arterial supply
  • Renal artery → anterior and posterior branches → segmental arteries → lobar arteries → interlobar arteries → arcuate arteries → interlobular arteries → afferent arteriole → glomerulus → efferent arteriole → vasa recta
  • Renal arteries branch off the abdominal aorta at the level of L1–2
  • Blood flow in the renal medulla is relatively low compared to that in the renal cortex, so the renal medulla is more susceptible to ischemic damage.
• Venous outflow
  • Renal vein → inferior vena cava
  • The left renal vein is longer (and therefore the left kidney is more often used for kidney transplantation).
  • The left suprarenal and gonadal veins drain into the left renal vein.

Ureter

• Constrictions of the ureters (common sites of obstruction)
  • Ureteropelvic junction
  • Pelvic inlet
  • Ureterovesical junction
• Relations to other structures
  • Posterior to gonadal arteries
  • Anterior to common iliac artery
  • Posterior to uterine artery/vas deferens (retroperitoneal)
• Vascular supply
  • Proximal: renal arteries
  • Middle: gonadal arteries, branches of the aorta, common iliac arteries, internal iliac arteries
  • Distal: branches of common iliac and internal iliac arteries (e.g., superior and inferior vesical arteries)

Due to their close anatomical association with the female reproductive organs, the ureters are at risk of injury during gynecological procedures (e.g., ligation, dissection of the uterine/ovarian vessels).

Female reproductive system

Overview of female reproductive organs

Vessels

Male reproductive system

Cranial nerves

To remember the location of the cranial nerves, organize them into three groups of four: I–IV in the midbrain, V–VIII in the pons, and IX–XII in the medulla.

The nuclei located in the medial brainstem are factors of 12, except 1 and 2 (i.e., CN III, CN IV, CN VI, and CN XII).

“Standing Room Only”: CN V1 exits through the Superior orbital fissure; CN V2 exits through the foramen Rotundum; CN V3 exits through the foramen Ovale.

Most important brain anatomy

Cortex

Internal capsule

• Anterior limb: contains the thalamocortical tract
• Genu: contains the corticobulbar tract
• Posterior limb: contains the corticospinal tract and thalamocortical and somatosensory fibers

Brainstem

Cerebral blood supply

Important spinal cord anatomy

Spinal cord tracts ^[1][2]

Legs are represented Laterally in the Lateral spinothalamic and Lateral corticospinal tract.

Fasciculus graciLis carries sensory information from the Lower limbs; fasciculus cUneatus transmits information from the Upper limbs.

Dermatomes

Normal chest x-ray anatomy

• Cardiac shadow
  • Frontal view
    • Right border: right atrium
    • Left border: left ventricle and left atrial appendage
    • Inferior border: right ventricle
    • Superior border: atria and great vessels
  • Lateral view
    • Anterior border is formed by the right ventricle
    • Posterior border is formed by the left atrium and left ventricle
• Aortic knob: formed by the arch of the aorta

Pleura

• Definition: a thin double layer of tissue that surrounds the lungs and the thoracic wall; divided into a visceral and parietal layer

Breast

Ligaments and fascia

• Pectoral fascia: attachment point for the Cooper ligaments
• Suspensory ligaments of the breast (Cooper ligaments)
  • Run between the dermis and the pectoral fascia
  • In breast cancer, the ligaments can become fixated, resulting in skin dimpling.

Lymphatic outflow

• Axillary lymph nodes
  • Provide lymphatic drainage from the nipple and upper and lower lateral quadrant
  • Lateral and pectoral groups of axillary nodes are located close to the long thoracic nerve.
• Parasternal (internal thoracic) lymph nodes: drain upper and lower medial quadrant
• Posterior intercostal nodes: provide 5% of the lymphatic drainage of the breast

Resection of the nodes during mastectomy can result in damage to the nerve, leading to sensory loss to the medial arm and winged scapula.

Vessels of thoracic aorta

Veins

Diaphragm

• Function: main respiratory muscle
• Arterial supply
  • Branches of the thoracic aorta: superior and inferior phrenic arteries
  • Branches of the internal thoracic artery: musculophrenic arteries and pericardiacophrenic artery
• Venous drainage: superior and inferior phrenic veins
• Innervation
  • Phrenic nerve (C3–C5)
  • In pathologies that involve parietal peritoneum or pleura adjacent to diaphragm (e.g., peritonitis, cholecystitis), pain can be referred to the trapezius ridge (C3, C4) or the shoulder (C5).

C3, C4, C5 keeps the diaphragm alive.

Spine overview

Location and projections of epigastric organs

Aorta and its major branches

Portocaval anastomoses

• Distal esophagus: give rise to esophageal varices
  • Left gastric vein from portal vein and distal esophageal veins from azygos vein (right)/hemiazygos vein (left)
  • Left gastric vein from portal vein and left inferior phrenic vein from inferior vena cava
• Anterior abdominal wall: give rise to caput medusae
  • Paraumbilical veins from portal vein and superior epigastric vein from internal thoracic vein
  • Paraumbilical veins from portal vein and thoracoepigastric vein from axillary vein
  • Paraumbilical veins from portal vein and inferior epigastric vein from external iliac vein
• Rectum and anal canal: (gives rise to anorectal varices): inferior mesenteric vein from portal vein and superior, middle and inferior rectal veins from internal iliac vein

Peritoneal ligaments and omenta

Peritoneal sacs and foramina

Organs in relation to peritoneum

Scapular anastomosis

Shoulder muscles

Important upper limb spaces

Axillary spaces

Carpal tunnel

• Borders: flexor retinaculum and carpal bones
• Contents
  • Median nerve
  • Tendon of the flexor pollicis longus
  • Tendons of the flexor digitorum profundus
  • Tendons of the flexor digitorum superficialis

Brachial plexus

Nerves of the lower extremity

Important compartments of the lower extremity

Femoral triangle

• Boundaries
  • Superior: inguinal ligament
  • Lateral: medial border of the sartorius
  • Medial: medial border of the adductor longus
• Contents (lateral to medial)
  • Femoral nerve
  • Femoral branch of the genitofemoral nerve
  • Femoral artery
  • Femoral vein
  • Femoral canal
  • Lymphatics

Femoral artery catheterization above the inguinal ligament (outside of the femoral triangle) can lead to retroperitoneal hemorrhage.

Contents of the popliteal fossa

• Nerves: tibial nerve and common peroneal nerve (See “The leg, ankle, and foot” for more details.)
• Vein: popliteal vein
  • Origin: formed by the union of anterior tibial, posterior tibial, and the fibular veins at the inferior border of the popliteus
  • Becomes the femoral vein at the adductor hiatus
  • Main tributary: short saphenous vein
• Artery: popliteal artery

Inguinal canal

For more information about the features of different types of inguinal hernias, see “Inguinal hernia”.

• Boundaries
  • Roof (superior): internal oblique and transversus abdominis muscles
  • Floor (inferior): inguinal ligament (shelving edge of external oblique) and lacunar ligament (medially)
  • Posterior wall: transversalis fascia
  • Anterior wall: external oblique aponeurosis and internal oblique muscle laterally
• Inguinal hernias
  • Indirect hernia
    • Herniates through the external and internal ring
    • Outside of the Hesselbach triangle
    • Lateral to the inferior epigastric blood vessels
    • Surrounded by the external spermatic fascia, cremasteric muscle fibers, and internal spermatic fascia
  • Direct hernia
    • Only herniates through the external ring
    • Within the Hesselbach triangle
    • Medial to the inferior epigastric blood vessels and lateral to the rectus abdominis
    • Only surrounded by the external spermatic fascia

Femoral canal

• Boundaries of the femoral canal
  • Anterior: inguinal ligament (Poupart ligament)
  • Posterior: pubic ramus and pectineal ligament
  • Medial: lacunar ligament (Gimbernat ligament)
  • Lateral: femoral vein
• Femoral hernia: protrusion of intraperitoneal contents along with the transverse abdominal fascia through the femoral ring into the femoral canal

Soft tissue structures of the knee

Ligaments

Menisci

The unhappy triad: injury to the ACL, MCL, and medial meniscus caused by a lateral force to the knee

To remember the orientation of the cruciate ligaments, cross your middle finger over the index finger of the same hand and hold your hand over the ipsilateral knee. The middle finger represents the ACL (from lateral femoral condyle to anterior tibia) and the index finger represents the PCL (from medial femoral condyle to posterior tibia).

Arterial supply of the hip joint

• Superior gluteal artery
• Inferior gluteal arteries
• Deep femoral artery: Branches supply the head and the neck of the femur.
  • Medial femoral circumflex artery: Damage to this artery is most commonly associated with avascular necrosis of the femoral neck.
  • Lateral femoral circumflex artery
• Foveolar artery: supplies the head of the femur

Basic anatomy of the neck

• Two major fascial layers: superficial cervical and deep cervical fascia
• The deep cervical fascia is divided into 3 layers: investing, pretracheal and prevertebral layers.
  • Investing layer surrounds the sternocleidomastoid and trapezius muscles
  • Prevertebral layer surrounds the deep back and neck muscles
  • Pretracheal layer surrounds the infrahyoid muscles, thyroid and parathyroids, and trachea
  • The carotid sheath consists of fascia from all three deep layers and surrounds the common carotid artery, internal jugular vein, and vagus nerve.
• Deep neck spaces are spaces between these deep layers.
  • The retropharyngeal space communicates laterally with the parapharyngeal space and may drain into the prevertebral space.
  • The danger space extends from the skull base to the posterior mediastinum and is posterior to the retropharyngeal space.

Important compartments

• Retropharyngeal space
  • Boundaries
    • Lateral: carotid sheath
    • Posterior: prevertebral muscles
    • Anterior: esophagus
  • Clinical significance: site of infection (e.g., retropharyngeal abscess) and metastasis (e.g., from pharyngeal, laryngeal, oral malignancies) spread
• Carotid sheath: a part of the deep cervical fascia that covers the common carotid artery, the internal carotid artery, the internal jugular vein, and the vagus nerve
• Important triangles
  • Anterior triangle of the neck: contains the following important subcompartments
    • Carotid triangle
      • Bounded by the sternocleidomastoid muscle, posterior belly of digastric muscle, and superior belly of omohyoid muscle
      • Contains common and internal carotid artery, internal jugular vein, and vagus nerve
    • Submandibular triangle
      • Bounded by the mandible and the two bellies of the digastric muscle
      • Contains the submandibular salivary glands, hypoglossal nerve, and facial artery
  • Posterior triangle of the neck
    • Bounded by the trapezius and sternocleidomastoid muscles and the clavicle
    • Contains the brachial plexus, external jugular vein, and accessory nerve

Bony relations

• Hyoid bone: C3
• Bifurcation of the common carotid artery: C4
• Thyroid cartilage: C4–C5
• Cricoid cartilage: C6

Neck organs

• Thyroid gland
  • Extends from C5 to T1
  • Surrounded by pretracheal fascia (along with pharynx, trachea, esophagus)
  • Consists of a left lobe and a right lobe occasionally connected by an isthmus
  • Blood supply
    • Superior thyroid artery (external carotid artery)
    • Inferior thyroid artery (subclavian artery)
    • Thyroid ima artery (brachiocephalic trunk)
• Parathyroid glands
  • Four glands embedded in the posterior surface of the thyroid gland
  • Supplied via inferior thyroid arteries