(4) Pleural Cavities & Lungs

Mediastinum

Centrally located space between the lungs

superior thoracic aperture

opening at the top of the thoracic cavity

pulmonary cavities

2 individual compartments containing lungs and pleurae. very little empty space.

Lobes

subdivisions of the lung, with two on the left (superior and inferior) and three on the right (superior, middle, inferior)

bronchopulmonary segments

Subdivisions of lung lobes. The right lung has 10, the left lung has 8-10 (due to different methods of partitioning)

horizontal/transverse fissure

separates the superior and middle lobes of the right lung

oblique fissure

separates the upper and lower lobes of the left lung and the middle and lower lobes of the right lung.

Trachea

a large membranous tube reinforced by rings of cartilage, extending from the larynx to the main bronchi at or below the level of the sternal angle (T4/T5 / (transverse thoracic plane). Brings air to and from the lungs.

tracheal cartilage

C shaped rings of cartilage that open posteriorly & give support to the trachea to help keep the airway open. Posterior wall formed by smooth muscle & lies against esophagus.

carina

wedge-shaped ridge of cartilage that projects upwards into

lumen of trachea at bifurcation

main (primary) bronchi

formed by the division of the trachea. 1 per lung.

lobar (secondary) bronchi

formed by the branching of the main bronchi. 1 per lobe; 3 in right lung, 2 in left lung.

segmental (tertiary) bronchi

formed by the branching of the secondary bronchi. 1 per bronchopulmonary segment. Give rise to smaller bronchioles.

pulmonary circulation

Circulation of blood between the heart and the lungs

pulmonary trunk

splits into right and left pulmonary arteries

pulmonary arteries

carry deoxygenated blood and CO2 from body tissues to the lungs. follow branching of bronchi. Segmental (single branch for a single pulmonary segment).

pulmonary veins

Carry oxygenated blood from lungs to heart for body tissues. Independent of bronchi & arteries. Intersegmental (single branch for multiple segments)

Distinction between arteries & veins is based on

directionality of blood flow (to or from the heart), NOT O2 content

systemic c

flow of blood from body tissue to the heart and then from the heart back to body tissues

bronchial arteries

Supply oxygenated blood to lung tissues. Arise from thoracic aorta or one of its branches.

bronchial veins

carry CO2 from lung tissue back towards heart. Drain to either hemiazygos system of veins (left) or azygos vein (right).

posterior border of lung

more smoothly sloping and blunt border of a lung

anterior border of lung

more flap-like border of a lung

apex of the lung

uppermost portion of the lung that projects upward.

cardiac notch

indentation in the left lung where the heart lies against it

Lingula

tongue-shaped process on left lung

hilum

The point of entry into each lung.

root of lung

Structures entering/exiting lung at hilum. Bronchi, pulmonary and bronchi vessels, lymphatics

Right pulmonary artery sits

anterior to right main bronchus

Left pulmonary artery sits

superior to left main bronchus

contact impressions

impressions left by adjacent structures. not as noticeable in living individuals

superior vena cava impression

groove anterior to hilum & superior to cardiac impression on right lung

arch of azygos impression

arch above hilum of right lung

cardiac impression

indent from heart on both lungs (larger on left)

arch of aorta impression

arch made by ascending aorta above hilum of left lung

thoracic aorta impression

groove passing posterior to hilum and cardiac impression of left lung

serous sac

closed sac that wraps around organs. contains a thin amount of serous fluid. Organs are NOT inside the sac.

types of serous sacs

pleura (lungs), serous pericardium (heart), peritoneum (GI)

pleura

serous membrane surrounding the lungs. adheres to the walls of the lungs. 2 sections: parietal and visceral.

parietal pleura

outer layer of the pleura that is adherent to the walls of the

pulmonary cavity

pleural cavity

space between visceral and parietal pleura

visceral pleu

inner layer of pleura that is adherent to lung tissue

pleural fluid

serous fluid of the pleura. Its surface tension (negative pressure) holds parietal and visceral pleura against each other and therefore holds surfaces of lungs against walls of pulmonary cavity, preventing the lungs from collapsing due to elastic recoil

surface tension

property of fluid that creates suction force between two surfaces

elastic recoil

the tendency for the lungs to recoil or reduce in volume after being stretched or expanded.

pulmonary collapse

Lung collapse due to break in surface tension of the pleural fluid

pneumothorax

air is pulled into pleural cavity by its negative pressure due to a breach in the pleural cavity

Mechanical Respiration

active movement of the ribs to get air into and out of the respiratory system

elevation of ribs

upward and outward motion of ribs that increases volume of thorax; used for inspiration

depression of ribs

downward and inward motion of ribs that decreases volume of thorax; used for expiration

2 types of rib movements in respiration (both of which occur simultaneously)

pump handle movement & bucket handle movement

pump handle movement

anterior ends of ribs (with sternum) swing upward to increase AP dimension or downward to decrease it

bucket handle movement

shaft of ribs swing upward and outward to increase transverse

dimension or downward and inward to decrease it

inspiration

breathing in (inhalation); muscular activity used to increase intrathoracic volume. Increase in volume causes decrease in intrathoracic pressure, allowing air to enter.

muscles of inspiration

diaphragm, sternocleidomastoid, scalenes, external intercostals

Diaphragm

major muscle of inspiration. Is pulled down & flattened to increase volume of thoracic cavity during inspiration so air can enter. Increases volume (vertical dimension) by pushing down on abdominal viscera.

sternocleidomastoid, scalenes, & external intercostals role in inspiration

increase volume by elevating ribs

quiet inspiration

inspiration that involves minimal muscular activity, primarily that of the diaphragm. somatic motor fibers in the phrenic nerve stimulate diaphragmatic contraction.

expiration

breathing out (exhalation). muscular activity used to decrease intrathoracic volume and push air out

muscles of expiration

internal intercostals, rectus abdominis, anterolateral abdominal wall muscles (transverse abdominis, internal obliques, external obliques)

internal intercostals role in expiration

decrease volume by depressing ribs

rectus abdominis role in expiration

decrease volume by depressing ribcage

anterolateral abdominal muscles role in expiration

increase intra-abdominal pressure to push abdominal viscera upward against diaphragm to decrease vertical dimension of thoracic cavity

quiet expiration

muscles of inspiration relax to permit elastic recoil of lungs and abdominal organs to decrease intrathoracic volume and squeeze air out

forceful expiration

muscular activity is used to forcefully decrease intrathoracic volume by depressing ribs or by squeezing abdominal organs against the diaphragm

Valsalva maneuver

attempting to forcefully exhale against a closed airway (usually larynx), such as when straining to defecate, performing heavy lifting, or pushing during childbirth. Increases abdominal pressure and intrathoracic pressure, impedes venous return to the heart (compresses weak-walled veins).

sympathetic innervation pathway for thoracic viscera

preganglionic cell bodies in T1-T5 -> T1-T5 ventral roots -> T1-T5 spinal nerves -> T1-T5 ventral rami -> T1-T5 white rami communicantes -> sympathetic chain -> *stay in place or ascend in chain -> postganglionic cell bodies in sympathetic chain ganglia at upper levels in chain (T5 & above) -> sympathetic "organ" nerves -> target

sympathetic "organ" (ex pulmonary) nerves

contribute to autonomic plexuses in the thorax; the postganglionic sympathetic axons that they carry will pass through these plexuses to reach their targets

2 pathways for parasympathetic innervation

1. Thoracic viscera and upper/middle abdominal viscera (foregut and midgut)

2. Lower abdominal visceral (hindgut) and pelvic viscera

*no parasympathetic innervation to visceral structures in the body wall

Parasympathetic pathway for thoracic viscera and upper/middle abdominal viscera

preganglionic cell bodies in the brainstem -> vagus nerve (CN X) -> postganglionic cell bodies in walls of target structure -> target

Preganglionic parasympathetic axons for thoracic organs pass through

autonomic plexuses in the thorax as they travel to targets

Preganglionic parasympathetic axons for upper and middle abdominal organs pass through

autonomic plexuses in the abdomen as they travel to targets

visceral pain pathway for thoracic viscera & abdominopelvic viscera above pelvic pain line

follows sympathetic innervation backwards until the spinal nerve, where it diverges to dorsal (bc sensory):

receptor -> sympathetic "organ" nerves -> sympathetic chain -> T1-T5 white rami communicantes -> T1-T5 ventral rami -> T1-T5 spinal nerves -> T1-T5 dorsal roots - cell bodies in T1-T5 dorsal root ganglia -> T1-T5 dorsal roots -> T1-T5 dorsal horns

visceral pain pathway for abdominopelvic viscera below pelvic pain line

follows parasympathetic innervation backwards until spinal nerve

referred pain

pain felt in a part of the body other than the actual source of stimulus. Thought to occur when sensory innervation from 2 different body regions converge at the same dorsal horn. Pain from viscera may be felt as somatic pain, from the dermatome that is innervated by the same spinal cord level as the visceral structure.

Function of sympathetic innervation of the lungs

In times of stress, to stimulate smooth muscle in walls of large pulmonary vessels to contract (vasoconstriction) and to adapt to increased pulmonary blood flow (as caused by sympathetic effects on the heart) as BP increases

Function of parasympathetic innervation of the lungs

In times of rest, to stimulate bronchosecretion and constrict bronchi, and promote vasodilation of large pulmonary vessels (relax the vascular smooth muscle)

Pain perception of lung tissue & visceral pleura

insensitive to visceral pain due to lack of innervation

Pain perception of parietal pleura

receives somatic sensory innervation via nerves that supply the tissue to which it is adhered; phrenic nerve for the parts on the mediastiunum & diaphragm (pain may be referred to shoulder or neck), intercostal nerves for the parts on the rib cage