ANATOMY Exam #2: The Lungs & Mediastinum

**The esophagus passes _____ to the left main bronchus before descending into the posterior mediastinum.

**BEHIND**

Parasympathetic Effects in Lungs

PNS stimulation causes: - *Bronchoconstriction* via Bronchial smooth muscle contraction - Inhibits/relaxes pulmonary vessels → Vasodilation

Lung Innervation

Parasympathetic: Vagus nerve (CNX) Sympathetic: T1-T5

Motor innervation of diaphragm

Phrenic nerve (C3-C5)

Thoracic Splanchnic Nerves

Preganglionic sympathetic axons destined to synapse in either the: - Prevertebral ganglia of the abdomen - Adrenal gland.

Alveolus (plural: alveoli)

Functional end unit in the lungs - Main site of gas exchange - Air sacs w/ thin walls containing many capillaries to facilitate diffusion.

Which nerves supplies the organs below the diaphragm?

Thoracic Splanchnic Nerves

Regions of Parietal Pleura:

*Costal*: Lines thoracic wall & includes: - Sternum - Ribs - Costal Cartilage - Intercostal muscles - Sides of thoracic vertebra *Mediastinal*: Medial surface; near mediastinum. *Diaphragmatic*: covers superior surface of diaphragm *Cervical*: Extends *2-3 cm above superior thoracic aperture* into the root of the neck.

Barrett's esophagus

*Glandular metaplasia of distal esophagus*: - Squamous → Glandular columnar cells - Adaption d/t chronic reflux of stomach acid into the esophagus. - ↑ risk of Adenocarcinoma

Which layer of the pleural sac is sensitive to pain and why?

*Parietal Pleura* because it is innervated by the intercostal nerves.

The _______ vagus nerve descends the superior mediastinum as the posterior vagal trunk (behind the esophagus). The _______ vagus nerve descends the superior mediastinum *IN FRONT of esophagus* as the anterior vagal trunk

*Right* Vagus Nerve → *Posterior* Vagal Trunk → Diaphragm @ Esophageal Hiatus *Left* Vagus Nerve → *Anterior* Vagal Trunk → Diaphragm @ Esophageal Hiatus

Esophageal Cancer

*Squamous cell carcinoma* - Poor prognosis - More common in males and older age groups Risks factors include: - Tobacco - Alcohol

The phrenic nerves are located within which divisions of the mediastinum

- *Superior* Mediastinum - *Middle* Mediastinum: Runs along with the pericardiophrenic vessels IN FRONT of *main bronchi*)

Costodiaphragmatic recess

- A potential space between the pleural layers which extends lateroinferiorly at the *junction of the costal & diaphragmatic pleura.* - Partially or completely occupied by lungs during inspiration. - Extends *2 ribs below inferior lung border* during quiet expiration

Pleural Cavity

- Airtight space between the visceral and parietal pleura. - Contains lubricating (serous) fluid that prevents friction & allows the two layers to slide against each other during respiration.

What structures enter the lungs at the Hilum?

- Bronchi - Pulmonary A. & V. - Bronchial A. & V. - Lymphatic Vessels - Nerves

Carina of trachea

- Cartilaginous ridge within trachea that runs between the two main bronchi bifurcation. - Located @ level of T6 Vertebra

Lower esophageal sphincter

- Circular ring of smooth muscles between the Esophagus and the stomach. - Common site of esophageal constriction

Thoracic sympathetic trunk

- Continuation of the cervical & lumbar sympathetic trunks. - Located bilaterally along the spine - Gives rise to the *thoracic splanchnic nerves*

**Pulmonary Ligament**

- Continuation of the pleural sleeve that hangs down from the lung root and extends medially to esophagus - Allows movement of pulmonary vessels & main bronchi during respiration

Thoracic Duct

- Drains lymph from the lower extremities & entire left side of the body. - Empties into the *left subclavian vein*

*Transthoracic Plane

- Horizontal plane that passes through the sternal angle & *T4/5* intervertebral disc. - Divides the Superior & Inferior mediastinum at the level of the *2nd rib*

Visceral pleura

- Inner layer of pleura adhering directly to the lung surface. - Lined with mesothelial cells

Pleural Sleeve

- Junction/area of continuity between the parietal & visceral pleura. - Located at the hilum.

Right & Left Phrenic Nerves

- Pass through the superior mediastinum alongside the pericardiophrenic vessels within the fibrous pericardium - Descend the middle mediastinum IN FRONT of the main bronchi & pulmonary vessels.

**Azygous venous system

- Passes through posterior mediastinum. - Drains posterior intercostal veins, thoracic viscera, thoracic vertebral column. - Empties into superior vena cava

Cisterna Chyli

- Saccular structure located within the abdominal cavity. - Most inferior portion of the thoracic duct - Functions as a storage area for purified lymph before this it returns to the venous bloodstream.

Why are esophageal varices dangerous?

- There is a higher risk of the veins rupturing. - Ruptured Esophageal veins can cause severe hemorrhage, hypovolemic shock & death.

Sub-divisions of inferior mediastinum

1. Anterior 2. Middle - Heart + Fibrous pericardium 3. Posterior - behind the pericardium

Esophageal Constrictions (3):

1. Junction with Laryngopharynx - *15 cm* below the incisor teeth. - Level of C6 2. Site where the esophagus is crossed by the *aortic arch & left main bronchus* - *23 cm* below incisors 3. *Lower esophageal sphincter* as it passes through the diaphragm @ esophageal hiatus - *40 cm* below incisors

Thymus

An immune organ that has both lymphoid and epithelial elements: - Located in the *Superior* & *Anterior Mediastinum*. - Atrophic remnants in adults can give rise to tumors called *Thymomas*. Critical role in developing immune system: - Site of T Lymphocyte maturation and is larger in early adolescents.

Level at which the trachea bifurcates into the right & left main bronchus

At the level of: - The *Sternal Angle* of Louis (T4/5 Intervertebral Disc) -*T6 Vertebra*

The left and right ventricles of the heart point left and lie within the _____________.

Cardiac Notch (depicted by the blue arrow)

Mediastinum

Central compartment within the thoracic cavity containing ALL the thoracic organs *except the lungs & pleurae*. Extends from: - *Superior thoracic aperture → diaphragm* - The sternum & costal cartilage → vertebral bodies Divided into superior & inferior mediastinum at level of the: - *Sternal Angle* (T4/5 Intervertebral Disc) - *Rib 2* - *Bifurcation of Trachea* into R/L Main Bronchi - "Where *SVC opens* into roof of the *RA*"

Esophageal Varices

Dilated *esophageal veins*, which *drain into the hepatic portal system*, due to increased pressure from portal hypertension.

Pleural Sac

Double-layered membrane (pleura) that envelopes each lung. It is composed of a flatted outer mesothelial layer overlaying an inner thin fibrous CT layer.

**Hemiazygos vein*

Drains inferior left half of body: - Ascends posterior mediastinum on the *left side from (T12-T9)* - Cross to the right (BEHIND the esophagus) & *joins Azygos vein @ T9*

Portal Hypertension

Elevated blood pressure within the portal venous system due to chronic liver disease.

Movement of the Costodiapragmatic recess during quiet respiration

Extends 2 ribs below the inferior lung border

True/False Beta-1 Agonists causes the smooth muscles of bronchioles to relax, resulting in bronchodilation

False. Beta 2 Agonists (Albuterol) causes bronchodilation

Caput medusae results from chronic shunting through what portal vein?

Hepatic portal vein d/t Portal HTN A potential complication of chronic alcoholism resulting in liver damage and obstruction of venous blood flow through the liver. The rising blood pressure in the veins between the gastrointestinal tract and liver causes engorgement of veins around the umbilicus (navel). The characteristic radiating pattern of veins is called a "caput medusae" (head of Medusa). Medusa was the "snake-haired lady" in Greek mythology.

What is the site where the roots of the lung enter the pleura?

Hilium

**Where does the thoracic duct drain into?

Junction of left subclavian and internal jugular veins

**Azygous Vein*

Large unpaired vein that ascends the posterior mediastinum on *right side from T12-T4* - Receives blood from *posterior intercostal veins* along the thoracic wall - Drains into the SVC*

The left lung has _______ lobes while the right lung has ______ lobes.

Left Lung has 2 Lobes Right Lung has 3 Lobes

What passes *anterior to aortic arch* and *posterior* to the *pulmonary hilum*?

Left Vagus Nerve

The *left vagus nerve* passes directly _____ to the arch of the aorta *before* entering the superior mediastinum

Left Vagus Nerve: 1. Passes IN FRONT of the *Aortic arch* 2. *Enters superior mediastinum* 3. Branches to form the: - Left Recurrent Laryngeal Nerves - Anterior Vagal Trunk 4. Anterior Vagal Truni

**What neuromuscular disorder is associated with thymomas?

Myasthenia Gravis

Right lymphatic duct

Receives lymph from the right upper part of the body and empties into the *right subclavian vein*

Hilum of the lung

Region where pleural sleeve encloses the air way and the *lung roots* (bronchi, pulmonary & lymphatic vessels and nerves) *enter the parietal pleura.*

Right Vagus Nerve (CNX)

Right Vagus: - *Passes OVER* (In front) *Right Subclavian* Artery → Posterior Vagal Trunk - Posterior Vagal continues descent along *posterior esophageal surface* R. Vagus → R. Recurrent Laryngeal Nerve: - Branches after crossing R. subclavian - *R. Recurrent Laryngeal* turns back & *loops superiorly* UNDERNEATH R. subclavian

Sensory Innervation for mediastinal/Diaphragmatic Pleura and pericardium

Sensory Innervation via two sources: - *T5-T12 Intercostal Nerves* - Phrenic Nerve

Bronchioles

Small airways branches within the lungs that lead from the bronchi to the alveoli. - *No cartilage* in their walls. - Smaller divisions have increasing amounts of smooth muscle

Reactive Airway Disease (RAD)

Spectrum of disorders characterized by: - Abnormal contractions of the smooth muscle inside the bronchioles. - Decreases air exchange in the lungs Examples Include: - Asthma - COPD - Viral Upper Respiratory Infections

**Describe the position of the esophagus within the superior and posterior mediastinum*

Superior Mediastinum: - Esophagus lies *BEHIND* *trachea* & in front of the spine - Passes *BEHIND* *Aortic Arch & Left Main Bronchi* as it descends into the posterior mediastinum. Posterior Mediastinum: - Esophagus descends to the *RIGHT of the Aorta* (posterior to the left atrium) - Crosses IN FRONT of *Abdominal Aorta* before passing through the diaphragm.

**Accessory hemiazygos vein*

Superior continuation of hemiazygos vein. - *Descends* left side of the posterior mediastinum (*T5 - T8*) - Crosses to the right & drains into the Azygos Vein at &T7/T8* intervertebral disc.

Which drug class causes relaxation of bronchiole smooth muscle?

Sympathomimetics (Sympathetic Agonists)

Parietal Pleura

The outer mesothelial layer of the pleural sac that lines the wall of the thoracic cavity.

The R/L recurrent laryngeal nerves ascend in the groove between the trachea & esophagus before passing _______ the thyroid lobes.

The recurrent Laryngeal nerves pass *BEHIND the thyroid* (# 3 & 4 in the picture)

Why are the esophageal constriction sites clinically significant?

They represent the site within the esophagus where swallowed objects are most likely to become lodged.

Endothoracic Fascia

Thin layer of loose areolar connective tissue separating costal parietal pleura & fibrous pericardium from the ribs & intercostal muscles of the thoracic wall.

Right Lung

Three Lobes: - Upper - Middle - Lower Two Fissures: - *Horizontal/Transverse Fissure*: Separates Right Upper & Middle lobes. - Oblique Fissure: Separates the Upper & Middle lobes from the Right Lower lobe.

Air pathway inside lungs

Trachea → (R/L) Main Bronchi → Lobular bronchioles → Segmental Bronchioles → Respiratory Bronchioles → Alveoli → Alveolar Ducts → Alveolar Sacs

True/False: The R/L Vagus Nerves pass *BEHIND* the *main bronchi*

True

The left recurrent laryngeal nerve

Turns superiorly & loops back *UNDERNEATH the aortic arch*

Left Lung

Two Lobes & 1 Fissure: - Upper and Lower lobe separated by a single, *oblique fissure*. - Majority of Posterior Surface = Lower Lobe Unique Features: - *Cardiac impression*: Indentation on medial aspect to accommodate the heart. - *Cardiac Notch*: Indentation along the anterior border of Upper lobe where the tips of the ventricles projects towards the left lung. - Lingula: Inferior tongue-like projection on the left lower lobe