The Mediastinum and Lungs

Question 1

Mediastinum Borders

Answer 1

Anterior: sternum
Posterior: thoracic vertebral column
Inferior: diaphragm
Laterally: lungs and pleural cavities

Question 2

2 Divisions of Mediastinum

Answer 2

1. Superior mediastinum (sits on superior aspect of heart)
2. Inferior mediastinum

Question 3

Superior Mediastinumn

Answer 3

Viscera: superior portions of esophagus and trachea

Vessels: arch of aorta and branches, SVC and brachiocephalic veins

Question 4

Inferior Mediastinum

Answer 4

Divided into:
1. Anterior Mediastinum
-between sternum and heart (pericardium)
-contains thymus gland

2. Middle Mediastinum
   -contains heart and roots of great vessels
3. Posterior Mediastinum
   -between heart (pericardium) and vertebral column
   -contains thoracic aorta, inferior esophagus and azygous system

Question 5

Thymus Gland

Answer 5

-In anterior mediastinum
-Lymphoid organ (lymphatic system)
-Important site for white blood cell (T-cell) maturation; hormone production

Question 6

Apertures of the Diaphragm

Answer 6

*superior view

1. IVC (anterior and slightly right)
2. Esophagus (middle of diaphragm)
3. Aorta (along vertebral column)

Question 7

Conducting Portion vs. Respiratory Portion of Respiratory System

Answer 7

Conducting portion: no gas exchange

Respiratory portion: gas exchange

Question 8

Conducting Portion Pathway (9)

Answer 8

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

Question 9

Conducting Portion Anatomy

Answer 9

-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

Question 10

Gross Anatomy of Lungs

Answer 10

Apex= superior
Base= inferior
Cardiac notch= medial and inferior on left

Question 11

Right vs. Left Lung

Answer 11

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

Question 12

Lung Hilum

Answer 12

Contains pulmonary artery, pulmonary vein and bronchus

*Pulmonary artery more superior in left lung

Question 13

Pleural Membranes

Answer 13

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

Question 14

Pleural Cavity/Space

Answer 14

-Potential space between visceral and parietal pleura
-Contains small amount of pleural fluid (lubricates pleural surface to reduce friction during lung inflation/deflation)

Question 15

Respiratory Portion

Answer 15

Gas exchange:
1. Respiratory bronchioles (continuous with terminal bronchioles)
2. Alveolar ducts
3. Alveoli and alveolar sacs

Question 16

Alveoli and Alveolar Sacs

Answer 16

-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

Question 17

Alveoli Structure

Answer 17

-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

Question 18

Pulmonary Blood Supply

Answer 18

-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)

Question 19

Innervation of the Diaphragm

Answer 19

Phrenic nerve provide motor innervation to the diaphragm (right and left phrenic nerve)

Question 20

Pressure and Volume

Answer 20

-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

Question 21

Mechanism of Breathing: Inspiration

Answer 21

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

Question 22

Mechanism of Breathing: Expiration

Answer 22

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

Question 23

Gas Exchange and Respiratory Membrane

Answer 23

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

1. 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
2. CO2 diffuses across the respiratory membrane into the alveolus and is expelled via expiration