The Mediastinum and Lungs Flashcards
Mediastinum Borders
Anterior: sternum
Posterior: thoracic vertebral column
Inferior: diaphragm
Laterally: lungs and pleural cavities
2 Divisions of Mediastinum
- Superior mediastinum (sits on superior aspect of heart)
- Inferior mediastinum
Superior Mediastinumn
Viscera: superior portions of esophagus and trachea
Vessels: arch of aorta and branches, SVC and brachiocephalic veins
Inferior Mediastinum
Divided into:
1. Anterior Mediastinum
-between sternum and heart (pericardium)
-contains thymus gland
- Middle Mediastinum
-contains heart and roots of great vessels - Posterior Mediastinum
-between heart (pericardium) and vertebral column
-contains thoracic aorta, inferior esophagus and azygous system
Thymus Gland
-In anterior mediastinum
-Lymphoid organ (lymphatic system)
-Important site for white blood cell (T-cell) maturation; hormone production
Apertures of the Diaphragm
*superior view
- IVC (anterior and slightly right)
- Esophagus (middle of diaphragm)
- Aorta (along vertebral column)
Conducting Portion vs. Respiratory Portion of Respiratory System
Conducting portion: no gas exchange
Respiratory portion: gas exchange
Conducting Portion Pathway (9)
Passage of Air:
1. Nasal cavity
2. Pharynx
3. Larynx
4. Trachea
5. Primary bronchi
6. Secondary bronchi
7. Tertiary bronchi
8. Bronchioles
9. Terminal bronchioles
Conducting Portion Anatomy
-Trachea descends as C-shaped cartilage rings, contains trachealis muscle posteriorly (controls diameter of trachea)
-*Bifurcates at carina and splits into right and left primary bronchus
-3 secondary/lobar bronchi on right side, 2 secondary/lobar bronchi on left side
-9-10 tertiary/segmental bronchi in each lung
-Each supplies a bronchopulmonary segment
-continues as bronchioles and ends at terminal bronchioles to enter respiratory portion
Gross Anatomy of Lungs
Apex= superior
Base= inferior
Cardiac notch= medial and inferior on left
Right vs. Left Lung
Right:
-Superior lobe
-Middle lobe
-Inferior lobe
-Oblique fissure
-Horizontal fissure
*3 lobes, 2 fissures
Left:
-Superior lobe
-Inferior lobe
-Oblique fissure
-Cardiac notch
*2 lobes, 1 fissure, cardiac notch
Lung Hilum
Contains pulmonary artery, pulmonary vein and bronchus
*Pulmonary artery more superior in left lung
Pleural Membranes
Parietal pleura: covers inner surface of thoracic wall and extends over diaphragm and mediastinum
Visceral pleura: covers outer surface of lungs, extends into fissures between lobes
Pleural Cavity/Space
-Potential space between visceral and parietal pleura
-Contains small amount of pleural fluid (lubricates pleural surface to reduce friction during lung inflation/deflation)
Respiratory Portion
Gas exchange:
1. Respiratory bronchioles (continuous with terminal bronchioles)
2. Alveolar ducts
3. Alveoli and alveolar sacs
Alveoli and Alveolar Sacs
-Each alveolar duct ends in an expanded region known as an alveolar sac
-Alveolar sacs are made up of clusters of alveoli
*alveoli are main sites of gas exchange
-Each lung has approx. 150 million alveoli
-Gives lungs their spongy appearance
Alveoli Structure
-Primary sites of gas exchange: O2 into bloodstream, CO2 out of bloodstream
-Extensive capillary network surrounds each alveolus
-Elastic fibers surround alveoli which facilitate stretch and recoil during gas exchange
Pulmonary Blood Supply
-Pulmonary arteries and veins enter and exit the lungs via the respective hilum
-Branches of the pulmonary arteries and veins surround the alveoli of the lungs to facilitate gas exchange
-Bronchial arteries carry oxygenated blood to the lungs and bronchi, and bronchial veins carry deoxygenated blood from lungs and bronchi (and drain into azygous system)
Innervation of the Diaphragm
Phrenic nerve provide motor innervation to the diaphragm (right and left phrenic nerve)
Pressure and Volume
-Inversely related
Inspiration:
-As lung volume increases, pressure in lungs decreases relative to atmospheric pressure
-Air is drawn into lungs
Expiration:
-As lung volume decreases, pressure in the lungs increases relative to atmospheric pressure
-Air flows out of lungs
Mechanism of Breathing: Inspiration
Expansion of chest cavity in 3 dimensions
Primary muscle= diaphragm (contracts and flattens)
Secondary muscles= external intercostal muscles (elevate ribs)
-Decreased pressure pulls air into lungs
Mechanism of Breathing: Expiration
Primary muscle= diaphragm (relaxes and structures return to pre-inspiratory position)
Secondary muscle= internal intercostal muscles (depress ribs)
-Elastic recoil of alveoli, decreases thoracic and lung volume, increased pressure expels air from lungs
Gas Exchange and Respiratory Membrane
Exchange of O2 and CO2 between lungs and blood takes place by diffusion across the alveolar and capillary walls
-O2 and CO2 move between alveolar air and blood via a diffusion gradient
- O2 enters respiratory portion (inspiration), then diffuses from alveolus across the respiratory membrane into the capillary, where it can bind to RBCs and be transported throughout the body
- CO2 diffuses across the respiratory membrane into the alveolus and is expelled via expiration
