Anatomy overview

Last updated: May 9, 2022

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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

Anatomy of heart chambers
Part Key features Clinical significance
Right atrium
Left atrium
Right ventricle
  • The part of the heart most commonly injured in thoracic trauma
Left ventricle
  • The most posterior part of the heart
  • Pumps oxygenated blood into the aorta

Heart valves

Anatomy of heart valves
Valve Key features Site of auscultation Clinical significance
Tricuspid valve
Pulmonary valve
Mitral valve
Aortic valve

Coronary vessels

Coronary arteries
Important branches Territory
Left coronary artery (LCA)
Right coronary artery (RCA)
  • Various branches

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

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.

Artery plexus of the nasal cavity
Kiesselbach plexus Woodruff plexus
Arteries
Location
  • Posteroinferior region of the lateral nasal cavity
Type of epistaxis

Innervation

Paranasal sinuses

Larynx

Trachea

Bronchi and lungs

Overview
Left lung Right lung
Lobes and bronchopulmonary segments
Bronchi

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

Overview of pulmonary circulation
Vessels Anatomy Characteristics
Pulmonary trunk
Left pulmonary artery
Right pulmonary artery
Pulmonary veins

“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

Overview of innervation of the GI tract
Innervation Foregut Midgut Hindgut Effect
Extrinsic innervation Parasympathetic innervation
  • ↑ Secretion
  • ↑ Motility
  • ↓ Sphincter tone

Sympathetic innervation (prevertebral ganglia)

  • ↓ Secretion
  • ↓ Motility
  • ↑ Sphincter tone
Site of referred pain
  • Epigastric region
  • Umbilical regions
  • Hypogastric region
  • N/A
Enteric nervous system
(intrinsic innervation)

Submucosal plexus (Meissner plexus)

  • Regulates local gastrointestinal secretion and nutrient absorption

Myenteric plexus (Auerbach plexus)

  • Regulates inherent myogenic motility of the GIT
  • The ICC act as pacemaker cells for the rhythmic phasic contractions of the gut (migratory motor complex) that occur in a fasting or interdigestive state.

Liver and biliary tract

Liver

Ligaments of liver
Ligament Function Contents
Falciform ligament
  • Connects liver to abdominal wall
  • Divides liver into right (larger) and left (smaller) lobes
Hepatoduodenal ligament
Gastrohepatic ligament
Vasculature of the liver
Type of vessel Vessels
Arteries
Veins
Lymphatics

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

Gallbladder and bile ducts

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

Pancreas

Structure

Blood supply

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

Nearby structures

Projections

Renal structure

Renal blood flow

Ureter

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

Blood vessels of the female reproductive organs
Vessel Description Area of supply

Ovarian artery

Ovarian vein
Uterine artery
Uterine vein

Male reproductive system

Vasculature, lymphatics, and innervation of male reproductive organs
Testes Scrotum Penis Prostate
Arteries
Veins
  • Drain to the external pudendal vein

Lymphatics

Autonomic Innervation

Motor innervation
  • None
  • None
  • None
Sensory innervation

Cranial nerves

Origin and pathways of the cranial nerves

Cranial nerve

Nerve origin Foramina/Structures Cranial nerve nuclei Destination
CN I
  • N/A
CN II
CN III
  • Ocular and orbital muscles
CN IV
CN V
CN VI
CN VII
CN VIII
CN IX
  • Medulla
CN X
CN XI
CN XII

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

Overview of the important cortical areas
Area Location Functions Effect of lesion

Primary motor cortex

  • Initiation of voluntary movement
  • Gives rise to axons that form the corticospinal tract
  • Functions are arranged medially to laterally as follows: toes, ankle, knee, hip, trunk, shoulder, elbow, wrist, hand, little finger to thumb, eye, facial expression, mouth, chin, tongue, muscles of swallowing.

Frontal eye field

  • Transient ipsilateral conjugate deviation of the eyes

Prefrontal cortex

  • Higher cognitive functions (e.g., goal-setting, decision-making)
  • Short term memory
  • Concentration
  • Contains Brodmann areas 8–14, 24, 25, 32, and 45–47

Broca area

Primary somatosensory cortex

Somatosensory association cortex
  • Superior parietal lobule and supramarginal gyrus
  • Integrates palpatory sensory information for pattern recognition

Primary auditory cortex

Wernicke area
Primary visual cortex

Internal capsule

Brainstem

Cerebral blood supply

Overview of cerebral blood supply
Artery Arterial territory Main branches Features of ischemia/hemorrhage

Anterior cerebral artery

(ACA)

Middle cerebral artery

(MCA)

Anterior choroidal artery

  • N/A

Posterior cerebral artery

(PCA)

Basilar artery
Vertebral artery

Important spinal cord anatomy

Spinal cord tracts [1][2]

Overview of the spinal cord pathways
Tract Function First-order neuron Second-order neuron Trajectory
Spinothalamic tract
Dorsal column
Spinocerebellar tract
Corticospinal tract

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

Important dermatomes
Dermatome Distribution
C6
  • Lateral aspect of forearms and thumbs
C7
  • Middle triceps and midpalm, including index and middle fingers
C8
T4
  • Level of the nipples
T10
L1
L4
  • Patella and large toe
L5
  • Dorsal web space between first and second toes
S2S4
  • Penile and anal regions

Normal chest x-ray anatomy

Pleura

  • Definition: a thin double layer of tissue that surrounds the lungs and the thoracic wall; divided into a visceral and parietal layer
Layers of pleura
Structure Parietal pleura Visceral pleura
Location
  • Lines the inner surface of the thoracic wall and the mediastinum
  • Divided into the following parts:
  • Lines the outer surface of the lungs and follows the contour of the lungs, including the fissures
Innervation
Clinical significance
  • Intrapulmonary pathologies (e.g., lung cancer) do not cause pain and remain unnoticed for a long time.

Breast

Ligaments and fascia

Lymphatic outflow

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

Branches of the aorta in the thoracic cavity
Structure Location Branches Supplies
Ascending aorta
Arch of the aorta
  • Head and intracranial structures
  • Upper extremities

Thoracic aorta

(part of the descending aorta)

Veins

Veins in the thoracic cavity
Structure Characteristics Tributaries
Superior vena cava (SVC)
Brachiocephalic veins
Azygos venous system

Azygos vein

Hemiazygos vein

Accessory hemiazygos vein

Diaphragm

C3, C4, C5 keeps the diaphragm alive.

Spine overview

Overview of spine segments
Spinal segment Number of vertebrae Short term Curvature
Cervical spine
  • 7
  • C1–C7
Thoracic spine
  • 12
  • T1–T12
Lumbar spine
  • 5
  • L1–L5
Sacrum
  • 5 (fused)
Coccyx
  • 3–5 (fused)
  • N/A

Location and projections of epigastric organs

Relations of epigastric organs
Organ Relations with bony structures Neighboring structures Projection Clinical significance
Liver
  • Protected by 7th–11th right ribs
Spleen
  • Protected by 9th and 10th left ribs
  • Left upper abdominal quadrant
Stomach
  • Fundus is protected by 8th to 12th left ribs
  • Left upper abdominal quadrant
  • Epigastric area
Duodenum Duodenal bulb
  • N/A
  • Epigastric area
Descending part
Horizontal part
Ascending part
  • Located on the left side of the L2 vertebra
  • N/A

Aorta and its major branches

Branches of the abdominal aorta [3]
Plane of origin Type Area of supply Branches Vertebral level
Anterior
  • T12
  • L1
  • L3
Lateral
  • L1
  • L1–L2
  • L2
Posterolateral
  • Paired parietal
  • Diaphragm
  • Body wall
  • T12
  • L1–L4

Portocaval anastomoses

Peritoneal ligaments and omenta

Overview of peritoneal ligaments
Ligaments Attachments Content(s) Clinical significance
Stomach and duodenal attachments
Greater omentum Gastrocolic ligament
Gastrosplenic ligament
  • Separates greater and lesser sacs on left side
Gastrophrenic ligament [5]
  • Anchors the stomach to the diaphragm
Lesser omentum Hepatogastric ligament
  • Separates greater and lesser sacs on the right side
  • Cut to access lesser sac during surgery
Hepatoduodenal ligament
Liver attachments
Falciform ligament
Triangular ligaments of the liver (paired)
  • Right: right lobe of liver and inferior surface of diaphragm
  • Left: left lobe of liver and inferior surface of diaphragm
Coronary ligament
  • Does not contain any structures
Ligamentum venosum
  • Does not contain any structures
Spleen attachments and supports
Splenorenal ligament
Phrenicocolic ligament
  • Does not contain any structures

Peritoneal sacs and foramina

Peritoneal sacs, foramina, and spaces
Spaces Description Boundaries Clinical significance
Greater sac
  • Surrounds the intraperitoneal organs
  • Divided into supracolic and infracolic compartments by the transverse mesocolon

Lesser sac (omental bursa) [3][8]

Epiploic foramen (foramen of Winslow)

Hepatorenal space (Morison pouch) [8]

  • Space between the inferior surface of the liver and the right kidney
Splenorenal recess (Koller pouch)

Subphrenic space [3]

Organs in relation to peritoneum

Overview of intraperitoneal and retroperitoneal organs
Type of organ Intraperitoneal organs Extraperitoneal organs
Retroperitoneal organs Secondary retroperitoneal organs Subperitoneal organs
Definition
Organs

Scapular anastomosis

Shoulder muscles

Important upper limb spaces

Axillary spaces

Carpal tunnel

Brachial plexus

Most important branches of the brachial plexus
Branches of the brachial plexus Spinal roots Motor innervation Sensory innervation Signs of injury Most common cause of injury
Lateral cord Musculocutaneous nerve
  • C5–C7
  • Trauma
  • Upper trunk compression (e.g., Erb palsy)
Lateral root of median nerve
  • C5–C7