MP

Thorax, Body Cavities & Cardiovascular Basics – Vocabulary Flashcards

Course & Unit Logistics

  • Final unit of the course (Unit 5)
    • Only 3 weeks remain in the term.
    • No cumulative final: written exam & lab practical cover today’s material onward only.
  • Content style
    • Less musculoskeletal detail than Units 2–3; resembles Unit 4.
    • Emphasis on flow concepts (sequential pathways):
    • Food through GI tract
    • Blood through heart & vessels
    • Urine through urinary tract
    • Air through respiratory system
  • Support
    • Flow-concept help available from instructor, GTAs, UTAs (office hours / appointments).

Body Cavities & Major Regions

  • Diaphragm = muscular landmark separating two large cavities.
    • Superior to diaphragm → Thoracic cavity.
    • Inferior to diaphragm → Abdominopelvic cavity.
  • Thoracic cavity (anterior view)
    • Pleural cavities (×2) – house lungs.
    • Pericardial cavity – houses heart; central subdivision = mediastinum.
    • Superior mediastinum (smaller upper portion) – not dissected in depth here.
  • Visualization tip: highlight diaphragm line when viewing anterior thorax images.

Serous Membranes & Layers

  • General structure
    • Parietal layer – lines inside wall of a cavity.
    • Visceral layer – adheres directly to organ surface ("viscera").
    • Serous fluid in microscopic potential space between layers → friction-free gliding.
  • Fist-into-balloon analogy
    • Outer balloon = parietal layer.
    • Balloon lining touching fist = visceral layer.
    • Air/water between = serous cavity (fluid).
  • Named serous membranes
    • Pleura (lungs)
    • Parietal pleura – lines pleural cavity walls.
    • Visceral pleura – on lung surface.
    • Pericardium (heart)
    • Parietal pericardium & visceral pericardium.
    • Peritoneum (abdominal organs below diaphragm)
    • Parietal peritoneum – abdominal wall lining.
    • Visceral peritoneum – covers GI organs, kidneys, etc.

Thoracic Wall – Bones, Joints, Muscles

  • Bony boundaries (thoracic cage)
    • Anterior: sternum.
    • Lateral: 12 pairs of ribs.
    • Posterior: T1–T12 vertebrae.
  • Intercostal spaces ("costal" = rib) – filled by 3 muscle layers
    1. External intercostals (superficial)
    • Fiber direction = "hands-in-pockets" (down & in).
    1. Internal intercostals (middle)
    • Fibers run ⟂ to externals (up & in, like thumbs out of pockets).
    1. Innermost intercostals (deepest)
    • Same fiber orientation as internals; visible from posterior thoracic view.
  • Function: assist diaphragm in inhalation (elevate ribs) & exhalation (depress ribs).
  • Neurovasculature in costal groove (order V A N – vein, artery, nerve) runs between internal & innermost layers.
    • Clinical: chest tube / needle placement safest at middle or lower part of space to avoid VAN bundle near upper rib margin.

Diaphragm – Anatomy & Key Openings

  • Primary muscle of respiration; separates thoracic & abdominal cavities.
  • Movement
    • Relaxed (exhale) → domed upward.
    • Contracted (inhale) → flattens downward, increasing thoracic volume (creates negative pressure).
  • Innervation: Phrenic nerves (paired) – originate from C3,4,5 spinal levels.
    • Mnemonic: "C3-4-5 keeps the diaphragm alive."
  • Three main hiatuses (memorize mnemonic "I 8 10 Eggs At 12")
    • T8 – Inferior Vena Cava.
    • T10 – Esophagus (& vagal trunks).
    • T12 – Aorta (with thoracic duct, azygos vein).

Thoracic Cavity – Contents & Roles

  • Contains
    • Lungs (right & left) in pleural cavities.
    • Heart in mediastinum within pericardial cavity.
    • Great vessels (aorta, pulmonary trunk, SVC/IVC, etc.).
  • Functions
    • Protection of heart & lungs.
    • Conduit for neurovascular structures between neck/upper limb & abdomen.
    • Attachment base for upper limb via clavicle–sternum articulation (sternoclavicular joint).

Mediastinum Overview

  • Region between pleural cavities; extends sternum → thoracic vertebral bodies.
  • Heart = dominant content.
  • Also contains: great vessels, trachea, esophagus, thymus, lymph nodes, etc.
  • NOT included: lungs (they occupy pleural cavities).
  • Test-style alerts
    • “Which of the following is NOT in the mediastinum?” → lungs or abdominal organs.

Arterial Supply of Thoracic Wall

  • Internal thoracic arteries (pair) – branches of subclavian; descend just lateral to sternum.
  • Anterior intercostal arteries – branch from internal thoracic; supply anterior 1⁄2 of each space.
  • Posterior intercostal arteries – branch from thoracic aorta; supply posterior 1⁄2 of space.
    • Anterior & posterior branches anastomose laterally.
  • Musculophrenic artery – terminal branch of internal thoracic; helps supply diaphragm (lab visibility limited).

Venous Drainage – Azygos System

  • Posterior intercostal veins → Azygos vein (on right side).
  • Left side drains via hemiazygos & accessory hemiazygos → cross midline → azygos.
  • Azygos empties into Superior Vena Cava.

Lymphatic System – Functions & Flow

  • Core functions
    • Fluid control – returns interstitial fluid, prevents edema.
    • Immunity – houses & transports lymphocytes (WBCs).
    • Transportation (dietary lipids, etc.).
  • Components
    • Lymphatic capillaries → small lymph vessels → larger trunks.
    • Lymph nodes – filtration stations clustered in axilla, cervical, inguinal, abdominal, etc.
    • Major ducts:
    • Right lymphatic duct – drains 25\% of body: right head & neck, right upper limb, right thorax → empties into right subclavian-internal-jugular junction.
    • Thoracic duct – drains remaining 75\% (both lower limbs, abdomen, left thorax, left head & neck, left upper limb) → empties into left venous angle.
      • Runs posterior mediastinum between aorta & esophagus; identifiable in lab.
  • Lymphoid organs
    • Tonsils (pharyngeal/adenoids, palatine, lingual).
    • Thymus – anterior to heart; T-cell maturation; involutes with age → fatty tissue.
    • Spleen – largest lymphoid organ; produces lymphocytes, removes aged RBCs.

Cardiovascular System Introduction – Heart Orientation

  • Located in mediastinum, tilted slightly left; apex points inferior-left; base faces posterior-superior.
  • Great vessels attach at base.
  • Chambers
    • Atria (receiving): right & left.
    • Ventricles (pumping): right & left.
  • External features
    • Auricles ("ear-like" outpouchings) extend each atrium.
    • Surface landmarks help judge anterior (apex left) vs posterior (apex right) views.

Circuits & Blood Flow Summary

  • Pulmonary circuit (right heart)
    • Deoxygenated blood enters right atrium via SVC, IVC, coronary sinus.
    • → Right ventricle → Pulmonary trunk → Pulmonary arteries → lungs for gas exchange.
  • Systemic circuit (left heart)
    • Oxygenated blood returns via 4 pulmonary veins → left atrium → left ventricle → aorta & branches → systemic tissues.
  • Key vessel naming rule: Arteries = away from heart; veins = toward heart (oxygen content may vary, e.g., pulmonary arteries/veins).

Internal Heart Landmarks (Atria-Focused)

  • Pectinate muscles – comb-like ridges in atrial walls (more prominent in right atrium).
  • Fossa ovalis – oval depression in right atrial septal wall, remnant of fetal foramen ovale (R→L atrial shunt before birth).
  • Coronary sinus orifice – posterior right atrium; drains venous blood from myocardium.

Mnemonics & Quick-Recall Aids

  • "C3-4-5 keeps the diaphragm alive." – phrenic nerve roots.
  • "I 8 10 Eggs At 12" – IVC T8, Esophagus T10, Aorta T12 pass through diaphragm.
  • "VAN" – order of neurovascular bundle in costal groove (Vein, Artery, Nerve).

Clinical & Practical Connections

  • Needle thoracostomy: target inferior half of intercostal space to avoid VAN bundle.
  • Enlarged tonsils (especially pharyngeal/adenoids) can obstruct pharynx → snoring, sleep apnea; tonsillectomy common.
  • Thymic involution may partly explain decreased immunity with aging.
  • Azygos system provides collateral pathway for venous return if IVC/SVC obstructed.
  • Fossa ovalis persistence (patent foramen ovale) can allow paradoxical emboli.

Next Steps in Course

  • Remaining heart lecture (ventricles, valves, coronary circulation, fetal shunts) & full respiratory system to be covered in subsequent sessions.