The thoracic cavity contains the lungs, heart, esophagus, and other structures. It is bounded by the thoracic wall anteriorly and the vertebral column posteriorly. The mediastinum divides the cavity into left and right pleural cavities which contain the lungs. The diaphragm separates the thoracic and abdominal cavities. Key structures in the thoracic cavity include the lungs, trachea, bronchi, blood vessels, esophagus, thymus gland, and diaphragm.

1. The Thoracic Cavity
Boundaries of and Structures Within

2. Remove frame
Body Cavities
• Dorsal body cavity
• Ventral body cavity
– Thoracic
• 2 Pleural
• Mediastinum
– Divided by Diaphragm
– Abdominopelvic
• Abdominal
• Pelvic
www.newworldencyclopedia.org/entry/Body_cavity

3. Serous membrane = Serosa
• Simple squamous epithelium + areolar connective tissue
• 2 Layers
– Outer layer = PARIETAL serosa
– Inner layer = VISCERAL serosa
• Between them = Serous Cavity containing Serous Fluid
– Serous fluid is blood filtrate + secretions by 2 layers of membrane
– Allows movement of organs with reduced friction
• Types of Serous Membranes
– Pleural = surrounds lungs
– Pericardium = surrounds heart, slightly modified
– Peritoneal = surrounds some abdominal organs

4. Pleural Cavities
• Surround the lungs
• Pleural fluid secreted by pleural
membranes
– Holds layers together
– Reduces friction of organs
• Benefit of Compartmentalization
pg 159

5. Pleural Cavities
• 2 Layers
– Visceral pleura (inner)
• root of lungs marks transition
• external surface of lungs
– Parietal pleura (outer)
• inner surface of thoracic wall
• superior surface of diaphragm
• lateral surface of mediastinum
pg 161

6. Pleural Abnormalities
• Pleural Effusion
– Excess fluid in the pleural cavity
– More than 20X
• Usually less than 1 ml of fluid
• Pneumothorax
– Air located in pleural space
Pg 238

7. Divisions of Mediastinum
•Superior (to heart)
•Contains: thymus, cranial vena cava, trachea,
esophagus, nerves
•Inferior
•Anterior (to heart)
•Contains: thymus
•Posterior (to heart)
•Contains: aorta, esophagus, trachea, bronchi,
nerves, caudal vena cava,
•Middle
•Contains: heart + pericardium
pg 177

8. Boundaries of Mediastinum
• Lateral
– parietal pleura of lungs
• Anterior
– ventral parietal pleura
• Posterior
– dorsal parietal pleura
• Superior
– dome of the neck
• Inferior
– diaphragmatic pleura pg 159

9. Respiratory Tract
• Upper Respiratory Tract
– Superior to Larynx
• Lower Respiratory Tract
– Larynx
– Trachea
– Primary Bronchi
– Secondary Bronchi
– Rest of Bronchial Tree pg 992
– Lungs
pg 168

10. Trachea = windpipe
• Starts at Larynx and travels through mediastinum
• Located Anterior to Esophagus
• Trachea terminates into 2 primary bronchi entering lungs
• Walls contain 16-20 “C” shaped rings Hyaline Cartilage
• Trachealis Muscle (smooth muscle and soft CT)
• Layers (deep to superficial)
– Mucosa = Ciliated Psuedostratified Epithelium
– Submucosa- contains seromucous glands
– Adventitia – made of connective tissue, contains cartilage rings
pg 966

11. Bronchial Tree
• Primary (main) Bronchi
– Bifurcation of trachea
– Basically the same structure
– Cartilage rings
– Posterior to pulmonary vessels
– Right is wider, vertical, shorter
• Secondary (lobar) Bronchi
– Each primary bronchi divides
– Same structure as primary bronchi
– Right lung has 3, Left has 2
• Tertiary (segmental) Bronchi
• Up to 23 divisions
pg 168

12. Bronchial Tree (continued)
• Bronchioles
– further divisions, < 1 mm diameter
• Terminal Bronchioles
– further divisions, 0.5 mm diameter
• Respiratory Zone
– Respiratory Bronchioles
– Alveolar Ducts
– Alveolar Sacs
• Terminal bunches of Alveoli
• Respiratory exchange chamber
• Among alveoli are blood vessels, nerves, lymphatics
www.nlm.nih.gov/.../ency/imagepages/1103.htm

13. Respiratory Zone (continued)
• Lining the Walls of Alveoli
– Respiratory Membrane
• Type I cells = simple squamous epithelial cells
• Basal lamina and fine areolar CT
• Covered with capillaries and elastic fibers
– Type II cells = cuboidal epithelial cells
• Secrete fluid containing surfactant
– Dust Cells (macrophages)
• Gas exchange
– Oxygen into blood
– Carbon Dioxide into alveoli

14. Throughout Bronchial Tree
• Psuedostratified columnar changes to simple columnar to
simple cuboidal
• Cartilage rings replaced by cartilage plates once bronchi
enter the lungs
• Smooth muscle and Elastic fibers remain important
• In Bronchioles
– Ciliated mucosa disappears, replaced by macrophages in alveoli
– Cartilage disappears
– Smooth muscle forms bands around smallest bronchi and
bronchioles (not found around alveoli)

15. LUNGS (continued)
• Located in Pleural Compartments
• Lateral to Mediastinum
• Location
– Apex posterior to clavicle
– Base lays on Diaphragm
– Costal Surface = Ant, Lat, Post surfaces contact ribs
• Left Lung = 2 lobes
– Upper
– Lower
– Oblique Fissure
– Cardiac Notch
• Right Lung = 3 lobes
– Upper
– Middle
– Lower
– Oblique fissure
– Horizontal fissure pg 168

16. LUNGS
• Hilus- medial indentation
• Root of Lung = structures enter each lung
– 2 Pulmonary Veins = carries O2-rich blood from each
lung to heart
– 1 Pulmonary Artery = carries O2-poor blood to each
lung
– Primary Bronchus
– Nerve plexus
– Lymph Vessels
pg 164

17. Lung Lobes
• Lobes are anatomically + functionally separate
• Lung lobes divided into Lobules
– Functionally separate
– Separated by dense CT
– Vary in size
• Stroma = lung tissue
– Areolar CT
– Many elastic fibers
pg 178

18. Esophagus
• Esophagus
– Pharynx to Stomach
– Passes thru diaphragm at esophageal hiatus
– Anterior to vertebrae, Posterior to trachea
• Layers of Esophagus (deep to superficial)
– Mucosa
• Stratified squamous epithelium
• Lamina propria (loose CT)
• Muscularis mucosae
– Submucosa
• Loose connective tissue
• Secretes mucus
– Muscularis Externa
• Circular/Longitudinal layers
• Skeletal m, Mix, then Smooth m
– Adventitia
• Fibrous CT
pg 212

19. The Diaphragm
• Skeletal Muscle
• Dome-shaped (relaxed)
• Flattens (contracts)
• Divides thoracic & abdominopelvic cavities
• Attachments
– O: Inferior Internal rib cage, Lumbar vertebrae (by
crura)
– I: Central tendon
pg 136 • Innervated by right + left PHRENIC Nerves

20. Action of the Diaphragm
• Primary muscle of respiration (involuntary)
– Contraction during inspiration
• Increases volume of thoracic cavity
• Decreases pressure of thoracic cavity
• Air moves into lungs (highlow pressure)
• Forced contraction (voluntary)
– Used for defecation, urination, labor
• Decreases volume of abdominal cavity
• Increases pressure in abdominal cavity
• Pushes on abdominal organs to move contents out
pg 136

21. Thoracic Cavity Capacity is Increased by:
• Contraction of diaphragm
• Intercostal muscles elevate ribs
• Rib elevation causes the sternum to move
anteriorly
pg 135

22. Openings of Diaphragm
• PosteriorAnterior
• Aortic Hiatus
– Aorta
– Azygos vein
– Thoracic duct
• Esophageal Hiatus
– Esophagus
– Vagus nerves
• Caval Opening
– Inferior Vena Cava
– Right Phrenic Nerve pg 157

23. Vena Cava
• Superior Vena Cava • Inferior Vena Cava
– in Superior mediastinum, – in Inferior mediastinum
right side (right side), runs through
abdomen
– Receives blood from regions
– Returns blood to heart from
above diaphragm regions below diaphragm
– Formed from Rt + Lft – Formed from Rt + Lft
Brachiocephalic Veins Common Iliac Veins
cranially – Empties into Right Atrium
– Azygos Vein empties into it – Widest blood vessel in body
just superior to heart
– Empties into Right Atrium

24. Veins of Thoracic Cavity
• Vena Cavae
• Azygos Vein
– “unpaired”
– right side of vertebral bodies (at level of T12)
– runs superiorly
– empties into Sup. Vena Cava
– drains right posterior intercostal veins
– Connects to hemiazygos and accessory hemiazygos
that drain left side
pg 153

25. Thymus Gland
• Lymphatic Organ
• 2-lobed w/lobules
• Sits on heart and great vessels
• Immature lymphocytes mature into T-lymphocytes
• Secretes Thymic Hormones: help T-lymphocytes gain
immunocompetence
• Decreases in size w/age
– Functional tissue is replaced with fatty tissue
• Contains lobes and lobules
pg 206 – Capsule
– Cortex
– Medulla