Respiratory System

Respiratory system

Respiration
Taking oxygen and giving CO2
Types:

• External in the alveoli of the lungs
• Internal in the mitochondria

Organs

• Nose and paranasal sinuses
• Pharynx
• Larynx
• Trachea
• Bronchi and their branches
• Lungs and their coverings
• Muscles of respiration

Nasal cavity

• 1st organ of respiration
• Cavity divided into two by nasal septum

Boundaries:

• Anterior- nostrils
• Posterior- posterior choana
• Medial- septum
• Lateral- bony conchae
• Roof- cribriform plate of ethmoid bone
• Floor- palate

The septum has two parts:

• Bony part- made by nasal bone , ethmoid, maxilla, vomer  and palatine.
• Anterior cartilagenous part  made of septal cartilage and with anteriormost fibrofatty plate called columella

The anterior part of the nose is the commenest site of bleeding. This part of nose ismella called as kisselbach’s or little’s area. 

The bleeding from the nose is called as epistaxis.

• The nose is lined by cilliated columnar epithelium.
• The lateral wall has the three bones, superior, middle and inferior conchae.
• The superior and middle conchae are the projections from the maxilla, whereas the inferior conchae is an independent bone.
• The space below these conchae are called meatus. So we have three meatuses.
• Superior meatus- opening of posterior ethmoidal sinus
• Middle meatus- opening of maxillary, anterior ethmoidal and frontal sinus
• Inferior meatus- opening of nasolacrimal duct.
• Sphenoidal sinus opens in the roof of the nasal cavity near the posterior choana through sphenoethmoidal recess.

Functions:

• First part of respiratory passage.
• It filters the air, it traps the particles >10 microns.
• It humidifies the inhaled air.
• It warms the air.
• Smell perception.

Paranasal sinus 

• They are the air containing cavities in the cranial bones.
• They open in the lateral wall of the nose.
• They are also lined by the respiratory epithelium.

They are:
Frontal sinus- a pair in the frontal bone
Maxillary sinus- a pair in the maxilla, they are the largest ones.
Ethmoid sinus- multiple in the ethmoid bone, and are multiple.

Sphenoid sinus- they are single in the ethmoid bone.

Maxillary sinus 

• This is the first sinus to be devloped in the human being.
• This is a pyramidal-shaped sinus occupying the cavity of the maxilla. 
• Its medial wall forms part of the lateral face of the nasal cavity and bears on it the inferior concha.
• Above this concha is the opening, or ostium, of the maxillary sinus into the middle meatus in the hiatus semilunaris .
• This opening, unfortunately, is inefficiently placed as an adequate drainage point.
• The infra-orbital nerve lies in a groove which bulges down into the roof of the sinus.
• Its floor bears the impressions of the upper premolar and molar roots. 
• These roots are separated only by a thin layer of bone which may, in fact, be deficient so that uncovered dental roots project into the sinus.

Functions of sinus:

• They make the head light
• Vocal resonance

The infection of sinus is called as sinusitis.

Pharynx

Pharynx is a muscular tube like structure, that extends from the end of soft palate to the beginning of the esophagus.
It has three parts:

• Nasopharyx
• Oropharynx
• Laryngopharynx or hypopharynx

Nasopharynx;

• It lies behind the nasal cavity
• It has the openings of two eustachean tubes
• It has some lymphoid organ called as adenoid.
• It is lined by cilliated columnar epithelium.
• It serves as passage of air.

Oropharynx:

• It lies behind the oral cavity, behind the uvula.
• It is lined by the stratified squamos epithelium.
• It serves as the passage of both the food and the air.
• The palatine tonsils (tonsils) lie here in the oropharynx.
• Waldeyer’s ring.

Hypopharynx:

• It is the part of pharyns that lies in front of the larynx.
• It is lined by stratified squamos epithelium.
• It serves as passage of the food only.

Larynx 

• It is the part of the respiratory system that begins from the nasopharynx and ends in the trachea.
• It is also called as voicebox.
• It lies in front of cervical vertebrae, c3-c6.
• It is lined by cilliated columnar epithelium.

It has the following cartilages: (9 total)

• Thyriod
• Cricoid
• Epiglottis (elastic cartilage)
• Arytenoid (2)
• Corniculate 2 and 
• Cueniform. 2

Muscles of larynx 

Extrinsic laryngeal muscles

• Thyrohyoid muscles
• Sternothyroid muscles
• Omohyoid muscles
• Inferior constrictor muscles
• Digastric
• Stylohyoid
• Mylohyoid
• Geniohyoid
• Hyoglossus

Intrinsic Muscles

Cricothyroid muscles 

• lengthen and stretch the vocal folds.

Posterior cricoarytenoid muscles 

• abduct and externally rotate the arytenoid cartilages, resulting in abducted vocal folds.

Lateral cricoarytenoid muscles 

• adduct and internally rotate the arytenoid cartilages, which can result in adducted vocal folds.

Transverse arytenoid muscle 

• adducts the arytenoid cartilages, resulting in adducted vocal folds.

Oblique arytenoid muscles 

• narrow the laryngeal inlet by constricting the distance between the arytenoid cartilages.

Vocalis muscles 

• increase the thickness of the vocal folds, lowering the tone.

Thyroarytenoid muscles –

•  sphincter of vestibule, narrowing the laryngeal inlet, shortening the vocal folds, and lowering voice pitch.

Inner surface of larynx:

It has two vocal cords, they are

• False vocal cords (upper)
• True vocal cords (lower).
• The space between these folds is called as the ventricle of the larynx.

Blood supply

laryngeal branch of ascending pharyngeal artery

Nerve supply (from the branches of vagus nerve)- 

• Superior laryngeal nerve, that supplies the mucosa above vocal folds, and a muscle, cricothyroid.
• Recurrent laryngeal nerve, it supplies the mucosa below the vocal folds, and all muscles of the larynx except the cricothyroid.

Functions of larynx:

• Air passage
• Protection of airway
• Humidification and warming of air
• Voice production

Trachea

• Trachea begins from the lower part of larynx.
• It is made of 16-20 incomplete rings of hyaline cartilage.
• The posterior part has a muscle called trachealis muscle.
• It is lined by cilliated columnar epithelium.
• It bifurcates to become two bronchi, at the level of T4.

Function:

• Air passage
• Mucocilliary clearance
• Cough reflex
• Humidification of air

Bronchi 

• They are the branches from the trachea, and has the same tissue as the trachea.
• They divide 23 times to reach the alveoli.
• They are lined by cilliated columnar epithelium.
• The division goes as bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts and alveoli.
• The part after respiratory bronchioles is there for gas exchange.

Lungs 

• They are a pair of the lungs in the thoracic cavity, on either side of midline.
• They are enclosed in the thin sac like structure called as pleura.
• The pleura has two layers. The parietal pleura is the outer covering, which is tough and is pain sensitive, attached to the thorax wall.
• The inner layer is the visceral layer, it is attached to the the lungs, and is pain insensitive.
• The space between the two is called as the pleural space.
• The right lungs is the larger one and has three lobes.
• The left lung is the smaller one, with the two lobes only, due to relative position of the heart.
• The medial surface of the lung is called hilum, from where there enters the bronchi, pulmonary arteries, pulmonary veins and the lymphatics.
• Each lungs has small multiple respiratory units called as alveoli, where the gas exchange occurs.
• The total surface of the lungs is around 120 m2, the size of a tennis court.

Functions of lungs:

• Respiration
• Angiotensin converting enzyme production
• Protection
• Metabolism of certain chemicals and drugs
• Excretion of volatile chemicals like ethanol

Muscles of respiration 

Primary muscles:

• Diaphragm
• Intercoastal muscles

Secondary muscles:

• Sternomastoid
• Scalanei 
• Trapezius
• Abdominal muscles

Respiration 

It has two phases:

Inspiration

• Active process, needs energy.
• The pulling of diaphragm down to abdominal cavity increases the thoracic volume, and hence reducing the pressure in the lungs. This causes the air to move from the atmosphere into the lungs (pump handle movement).
• Similarly the pulling of the ribcage anterior by the intercoastal muscles also has the same effect (bucket handle movement).

Expiration:

• It is the passive process.
• The diaphragm recoils back into the thoracic cavity, and hence decreasing the thoracic volume, and increasing the pressure. And hence the air rushes out of the lungs into the air.
• Forced expiration is active process. The abdominal muscles are forced inside, and creating the increased intrathoracic  and intraabdominal pressure.

Lung volumes 

• Tidal volume- 500 ml
• Inspiratory reserve volume- 2.5 L
• Inspiratory capacity- 3 L
• Expiratory reserve volume- 1.5 L
• Residual volume- 1.2 L
• Vital capacity- 5 L
• Total lung capacity

• Minute ventillation
• Dead space
• Alvelar ventillation 

Forces and Pressures during respiration 

• Intrapleural pressure: it is always negaive pressure. It is around -5 cm H2O during equlibrium and it becomes more negative -7.5 during inspiration. This negative pressure is created by the two opposite forces, the chest recoil and the recoil of the lungs.
• Intra alveolar pressure: it is the pressure inside the alveoli. It is 0 (atmospheric) during equilibrium, -1 during inspiration and +1 during expiration. 

Compliance of lungs:

• The change is volume with change in pressure is called as lung compliance.
• It is calculated as dV/dP.
• It is around 0.02 L/cmH2O.

Gas transport in blood 
Oxygen:

• As oxyhemoglobin 99%
• Dissolved oxygen 

Carbon dioxide:

• As bicarbonate 70%
• Carbaminohemoglobin 23%
• Dissolved form 7%

Gas exchange and oxygen transport 

A. Partial pressure equals the total pressure times the fractional gas concentration.
B. Assuming that total pressure is atmospheric (760 mm Hg) and the fractional concentration of O2 is 0.21, then
Po2 = 0.21 × 760 = 160 mm Hg
C. The partial pressure of humidified inspired air is calculated as follows:
where
Patm = atmospheric pressure
PI gas = partial pressure of inspired gas
PH2O = partial pressure of H2O vapor
F gas = concentration of gas
The partial pressure of H2O at 37° is 47 mm Hg. Thus,

PI gas = F gas (Patm − PH2O

Saturation is the percentage of Hb-binding sites occupied by O2.

• 1. Each gram of Hb has an oxygen capacity of 1.34 mL O2, and because 100 mL of blood contains 15 g Hb, completely oxygenated blood contains approximately 20 mL O2 (1.34 mL O2 × 15 g Hb/100 mL).
• 2. Thus, the oxygen capacity of Hb in blood is approximately 20 mL O2/100 mL of blood or 20 vol%.
• 3. Each Hb molecule contains four subunits: two have α chains and two have β chains.

Concentration gradients of the gases. 

• The PO2 is about 104 mmHg in the alveolar air and 40 mmHg in the blood arriving at an alveolus.  
• Oxygen therefore diffuses from the air into the blood, where it reaches a PO2 of 104 mmHg. 
• Before the blood leaves the lung, however, this drops to about 95 mmHg because blood in the pulmonary veins receives some oxygen-poor blood from the bronchial veins by way of anastomoses.
• The PCO2 is about 46 mmHg in the blood arriving at the alveolus and 40 mmHg in the alveolar air. Carbon dioxide therefore diffuses from the blood to the alveoli

The Bohr effect. 

• Active tissues also generate extra CO2, which raises the H concentration and lowers the pH of the blood. Like elevated temperatures, a drop in pH shifts the oxygen-hemoglobin dissociation curve to the right and promotes oxygen unloading. 
• The increase in HbO2 dissociation in response to low pH is called the Bohr effect.

Haldane effect 

• Low level of HbO2 or O2 favors the systhesis of carbaminohemoglobin.
• This effect is called Haldane effect.

Control of respiration
Respiratory center:

• Primary: medulla
• Secondary: pons

Chemoreceptors:

• Central- medulla, they detect increased CO2 level
• Peripheral-
• Aortic arch and carotid bodies
• They detect decreased O2 level.

Regional anatomy of thorax

Regional Anatomy Of Thorax

Parts and regions of the thorax
Boundaries 

• Superior－jugular notch, sternoclavicular joint, superior border of clavicle, acromion, spinous processes of C7
• Inferior－xiphoid process, costal arch, 12th and 11th ribs, vertebra T12

Regions 

• Thoracic  wall
• Thoracic cavity 

Landmarks
Jugular notch corresponds with

• The 2th thoracic vertebra in male, the 3th thoracic vertebra in female 

Sternal angle connects 2nd costal cartilage laterally， corresponds with

• The lower border of 4th thoracic vertebra 
• The bifurcation of trachea in the adult
• The beginning of aortic arch which ends posteriorly at the same level 
• The esophagus is crossed by the left main bronchus  

Xiphoid process (xiphisternum) 

xiphisternal junction lies opposite the body of the 9th thoracic vertebra
Clavicle

• Inferior fossa of clavicle 
• Coracoid process

Ribs and intercostal spaces

Thoracic wall
Skin 
Superficial fascia 

• Thoracoepigastric v.
• Supraclavicular n.
• Anterior and lateral cutaneous  branches of intercostal n.

Deep fascia  

Internal thoracic vessels

• Internal thoracic a.&v
• Parasternal ln.                

Endothoracic fascia  

Intercostal space

Breast:

• The mammary gland (breast) secrete the milk, and are accessory glands of the reproductive system. 
• They exist in the male as well as in the female; but in the former only in the rudimentary state normally. 
• Enlarged male breast is called gynecomastia.
• Before puberty they are of small size, but enlarge as the generative organs become more completely developed. 
• They increase during pregnancy and especially after delivery, and become atrophied in old age.

Location:

• The female breast overlies the 2nd to the 6th rib.
• It extends from the mid-sternum to the midaxillary line.
• It is superficial organ which lie between the superficial and deep fascia of the thorax.
• It overlies the pectoralis major muscle.
• It is formed by the modification in the sweat gland, so it is ectodermal in origin.
• The deep fascia is attached with the skin by ligament of Cooper, which if pulled by any mass in the breast causes dimpling of the skin of the breast.

Structure: 

• The breast is made up of 15–20 lobules of glandular tissue embedded in fat; the latter accounts for its smooth contour and most of its bulk. 
• These lobules are separated by fibrous septa running from the subcutaneous tissues to the fascia of the chest wall (the ligaments of Cooper).
• Each lobule drains by its lactiferous duct on to the nipple, which is surrounded by the pigmented areola. This area is lubricated by the areolar glands of Montgomery

The areola is pinkish before puberty but gets pigmented later on.

The lactiferous duct  has a dilated portion near its opening, called as lactiferous sinus.
Lactiferous sinus helps storage of the milk.
Blood supply:
Arterial supply

• Axillary artery’s branch lateral thoracic artery
• Internal thoracic artery, branch of internal thoracic artery
• Pectoral branch of the thoracoacromial artery (axillary A)
• Intercoastal arteries

Venous drainage:

• Corresponding veins

Lymphatic drainage:

• Medial half excluding nipple: internal thoracic nodes
• Lateral half with nipples: axillary group of nodes.

The breast cancer spreads through the lymphatics early, so the cancer from the medial side may metastasize to the thorax as well as to the other breast, and from the lateral half will spread to the axillary group of lymph nodes.

Lymphatic drainage of breast

• Into pectoral ln. from lateral and central parts of breast
• Into apical and supraclavicular ln. from superior part of breast
• Into parasternal ln. from medial part of breast 
• Into interpectoral ln. from deep part of breast
• The lymphatic capillaries of breast form an anastomosing network which is continuous across the midline with that of the opposite side and with that of the abdominal wall

Rib
Typical Rib

• Head (two facets)
• Neck
• Tubercle (facet)
• Angle
• Proximal end – costal cartilage

Typical Rib

Rib Articulations (Anterior)
Rib 1 to sternum (manubrium)
Fibrous joint
No movement
Ribs 2 – 7 true ribs
Synovial (gliding) joints
Radiate sternocostal ligaments 
Ribs 8-10 = false, articulate with 7

Ribs 11-12 = floating

Sternum

Rib Articulations (Posterior)

Posterior Joints

• Superior costal facet with inferior articular facet of T vertebrae above
• Inferior costal facet with superior facet of rib with same number
• Facet on tubercle with transverse process of T vertebrae of same number
• Radiate ligaments (head)
• Costotransverse ligaments (tubercle with transverse process)

Muscles associate with the ribs
Intercostals
External
Internal
Innermost
Transversus thoracicis
Levatores costarum

• twelve in number on either side, which arise from the ends of the transverse processes of the seventh cervical and upper eleven thoracic vertebrae
• They pass obliquely like Intercostales externi, and each is inserted into the outer surface of the rib.
• Their role in normal inspiration, if any, is uncertain. They may play a role in vertebral movement and/or proprioception.

Muscles

Innervation/Blood Supply

Muscles/Nerves

Combined actions of muscles of respiration
Inspiration

• Diaphragm
• External intercostals
• Levatores costorum
• Accessory – SCM, Scalenes

Expiration

• Mostly passive
• Abdominals
• Internal intercostals

The muscles of thorax

Extrinsic muscles

• Pectoralis major 
• Pectoralis minor
• Serratus anterior

Intrinsic muscles

• Intercostales externi
• Intercostales interni
• Intercostales intimi

Pectoralis major:
Origin- 

• It arises from the anterior surface of the sternal half of the clavicle; 
• from breadth of the half of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib; 
• from the cartilages of all the true ribs, with the exception, frequently, of the first or seventh and 
• from the aponeurosis of the abdominal external oblique muscle.

Insertion:

• Lateral lip of the bicipital groove or intertubercular sulcus.

Nerve supply- 

• lateral and medial pectoral nerve 

Action-

• Arm flexion
• Medial rotation of humerus
• Arm adduction

Pectoralis minor:
Origin

• Third to fifth ribs, near their costal cartilages

Insertion   

• Medial border and superior surface of the coracoid process of the scapula

Artery

• Pectoral branch of the thoracoacromial trunk

Nerve

• Medial pectoral nerve (C8, T1)

Actions

• Stabilizes the scapula by drawing it inferiorly and anteriorly against the thoracic wall

Serratus anterior:

Origin

• fleshy slips from the outer surface of upper 8 or 9 ribs

Insertion   

• costal aspect of medial margin of the scapula

Artery

• lateral thoracic artery (upper part)
• thoracodorsal artery (lower part)

Nerve 

• long thoracic nerve (from roots of brachial plexus C5, 6, 7)

Actions

• protracts and stabilizes scapula, assists in upward rotation.

External intercostals 

• Origin: lower border of rib
• Insertion: upper border of rib below origin
• Action: elevate ribs adding in forced inspiration
• Replaced anteriorly by external intercostals membrane.

Internal intercostals

• Origin: upper border of rib
• Insertion: lower border of rib above origin
• Action: depress ribs for forced expiration
• Replaced posteriorly by internal intercostals membrane.

Diaphragm
Shape  and position:
 dome-shaped between thorax and abdomen, consists of a peripheral muscular part and a central tendon
Origin
Sternal part: the xiphoid process
Costal part: lower six and costal cartilages
Lumbar part: arises by two crura from upper 2-3 lumbar vertebrae
Insertion: central tendon
Weak areas: triangular spaces without muscular tissue
 Lumbocostal triangle: between costal and lumbar parts.

 Sternocostal triangle: between costal and sternal parts.

Openings in the diaphragm
Aortic hiatus
lies anterior to the body of the 12th thoracic vertebra between the crura. It transmits the aorta, thoracic duct
Esophageal hiatus 
for esophagus and vagus nerves at level of T10.

Vena cava foramen 
for inferior vena cava, through central tendon at T8 level

Action:
Contraction:

•  the dome moving downward, increases the volume of thoracic cavity   which results in inspiration, at the same time the intra-abdominal pressure is increased assists in defecation, vomiting or child birth.

Relaxation:

•  the dome returns to the former position, reduces the volume to the thoracic cavity, resulting in expiration.

Diaphragm

The Mediastinum
 Concept
All of organs between the left and right mediastinal pleurae is called mediastinum. It extends from the sternum in front to the vertebral column behind, and from the thoracic inlet above to the diaphragm below.

Subdivisions of mediastinu

Superior mediastinum

Inferior mediastinum

• Anterior mediastinum
• Middle mediastinum
• Posterior mediastinum

Left side of Mediastinum 

Right side of Mediastinum

Superior mediastinum

Locating

• from inlet of thorax to plane extending from level of sternal angle anteriorly to lower border of T4 vertebra posterioly

Contents
Superficial layer

• Thymus
• Three veins 
• Left brachiocephelic v.
• Right brachiocephelic v.
• Superior vena cava

Middle layer 

• Aotic arch and its three branches
• Phrenic n.
• Vagus n.

Posterior layer

• Trachea 
• Esophagus 
• Thoracic duct 

Relations of aortic arch

Anteriorly and to the left  

• pleura, lung，phrenic n., pericardiacophrenic vessels and vagus n.

Posteriorly and to the right

• trachea, esophagus, left recurrent n., thoracic duct, deep cardiac plexus

Superiorly

• its three branches, left brachiocephalic v. and thymus

Inferiorly

• pulmonary a., arterial ligament, left recurrent n., left principal bronchus and superficial cardiac plexus

Inferior mediastinum

Anterior mediastinum
Location

• posterior to body of sternum and attached costal cartilages, anterior to heart and pericardium

Contents

• fat,
• remnants of thymus gland, 
• anterior mediastinal lymph nodes

Middle mediastinum

Location

• between anterior mediastinum and posterior mediastinum

Contents: 

• heart and pericardium, 
• beginning or termination of great vessels, 
• phrenic nerves,  
• lymph nodes, 

Posterior mediastinum

Location

• posterior to heart and pericardium, anterior to vertebrae T5－T12

Contents: 

• esophagus 
• vagus n.
• thoracic aorta 
• azygos system of veins 
• thoracic duct, 
• thoracic sympathetic trunk, 
• posterior mediastinal lymph nodes

Relations of esophagus

Anteriorly

• trachea, 
• bifurcation of trachea, 
• left principal bronchus, 
• left recurrent n., 
• right pulmonary a., 
• anterior esophageal plexus, 
• pericardium, 
• left atrium, 
• diaphragm

Posteriorly

• posterior esophageal plexus.
• thoracic aorta.
• thoracic duct.
• azygos v. 
• hemiazygos v.
• accessory hemiazygos v. 
• right posterior intercostal v.

Left

• left common carotid a. 
• left subclavian a.
• aortic arch, 
• thoracic aorta, 
• uperior part of thoracic duct

Right

• arch of azygos v.

Relations of thoracic aorta

Anteriorly

• left root of lung, 
• pericardium and 
• esophagus

Posterior 

• hemiazygos v. 
• accessory hemiazygos v.

Right

• azygos v. and thoracic duct

Left

• mediastinal pleura

Mediastinal spaces

Retrosternal space

•  lies beween sternum and endothoracic fascia

Pretracheal space 

• lies within superior mediastinum, between trachea, bifurcation of trachea and aortic arch

Retroesophagus 

•  lies within superior mediastinum, beween esophagus and endothoracic fascia

Arteries of thorax

Pulmonary trunk 

• Arises from right ventricle 
• Runs up, back ,and to the left
• Bifurcates inferior to aortic arch into right and left pulmonary arteries, one for each lung 

Pulmonary arteries

• Right pulmonary artery－passes posterior to ascending aorta and superior vena cava to hilum of right lung 
• Left pulmonary artery－passes anterior to descending aorta and left main bronchus to hilum of left lung

Arterial ligament (ligamentum arteriosum)

•  remnant of ductus arteriosus, connects bifurcation of pulmonary trunk to inferior border of aortic arch

Ascending aorta

• Runs upward, forward and to the right,
• Extends to level of second right sternocostal joint (angle of louis)
• Branches: right and left coronary arteries

Aortic arch

• Continuation of ascending aorta
• Curves upward, to the left and posteriorly, then downward, arching over left principal bronchus and pulmonary trunk to lower border of T4 level, to become descending aorta
• Branches (from right to left )
• Brachiocephalic trunk－extends to right sternoclavicular joint, bifurcates into right subclavian and right common carotid arteries
• Left common carotid artery
• Left subclavian artery
• Arch of the aorta has:
• baroreceptor 
• chemoreceptor

Thoracic aorta

• Continuation of aortic arch at lower border of T4
• Courses downward on left side of, then in front of vertebral column 
• Passes through aortic hiatus of diaphragm at level of T12 vertebra to enter abdominal  cavity
• Main branches 
• Parietal branches
• Nine pairs posterior intercostals arteries
• One pair subcostal artery 
• For lower nine intercostals spaces and upper part of abdominal wall; superior phrenic arteries supply the superior surface of the diaphragm.
• Visceral branches
• Bronchial branches: one or two for each lung
• Esophageal branches
• Pericardial branches

Internal thoracic artery

• descends into thorax 1.2cm lateral to edge of sternum, and ends at the sixth costal cartilage by dividing musculophrenic and superior epigastric arteries

Veins of thorax

Brachiocephalic veins

• Formed by union of internal jugular and subclavian veins posterior to the sternoclavicular joint 
• Angle of union is termed venous angle 

Superior vena cava

• Formed by union of right and left brachiocephalic veins behind the right sternocostal junction of first rib
• Runs vertically down on right of ascending aorta 
• Joined by azygos vein at level of sternal angle
• Enters right atrium at lever of lower border of third right sternocostal joint
• Collects blood from veins of upper half of body 

Azygos vein

• Begins as continuation of right ascending lumbar vein
• Ascending along the right side of vertebral column
• Joins superior vena cava by aching above right lung root at level of T4 to T5
• Receives right posterior intercostals and subcostal veins plus some of bronchial, esophageal and pericardial veins, and hemiazygos vein
• Tributaries－hemiazygos v. and accessory hemiazygos v. which receive most left posterior intercostals vein and left bronchial veins 

The lymphatic drainage of thorax

The lymphatic drainage of thoracic wall

• To axillary lymph nodes
• To parasternal lymph nodes (along internal thoracic vessels)
•  To intercostals lymph nodes from deeper structures

lymph nodes of the thoracic contents

• lylymph nodes of trachea, bronchi and lungs
• Pulmonary lymph nodes_lie in the angles of bifurcation of branching lobar bronchi
• Bronchopulmonary hilar lymph nodes－lie in the hilus of the lung
• Tracheobronchial lymph nodes－situated above or below the bifurcation of trachea
• Paratracheal lymph nodes －along each side of the trachea

Anterior mediastinal lymph node

•  lies anterior to the large blood vessels of thoracic cavity and pericardium; the efferents unite with those of paratracheal lymph nodes, to form the right and left bronchomediastinal trunks. The left bronchomediastinal trunk terminates in thoracic duct, and right in the right lymphtic duct
• Posterior mediastinal lymph nodes 
• lie along the esophagus and thoracic aorta

Thoracic duct

• Begins in front of L1 as a dilated sac, the cisterna chyli, which formed by joining of left and right lumbar trunks and intestinal trunk
• Enter thoracic cavity by passing through the aortic hiatus of the diaphragm and ascends along on the front of the vertebral column, between thoracic aorta and azygos vein
• Travels upward, veering to the left at the level of T5
• At the roof of the neck, it turns laterally and arches forwards and descends to enter the left venous angle (junction of left subclavian and internal jugular veins)
• Drains lymph from lower limbs, pelvic cavity, abdominal cavity, left side of thorax, and left side of the head, neck and left upper limb

Right lymphatic duct

• Formed by union of right jugular, subclavian, and bronchomediastinal trunks
• Ends by entering the right venous angle
• Receives lymph from right half of head, neck, thorax and right upper limb

Anterior branches of thoracic nerves

Intercostal nerves (anterior rami of T1- T11):

• runs forward inferiorly to intercostals vessels in costal groove of corresponding rib, between intercostals externi and intercostals interni;
• first six nerves are distributed within their intercostals space,
• lower five intercostals nerves leave anterior ends of their intercostals spaces to enter abdominal wall

Subcostal nerve (anterior ramus of T12):

• follows inferior border of T12 rib and passes into abdominal wall
• 
  
• Distribution: distributed to intercostales and anterolateral abdominal muscles, skin of thoracic and abdominal wall, parietal pleura and peritoneum

The segmental innervation of anterior surface of trunk

 

T2－sternal angle
T4－ nipple
T6－xiphoid process
T8－costal arch
T10－umbilicus

T12－midpoint between umbilicus and symphysis pubis

Phrenic nerve

• Descends over scaleneus anterior to enter thorax
• Accompanied by pericardiophrenic vessels and passes anterior to lung roots between mediastinal pleura and pericardium to supply motor and sensory innervation to diaphragm
• Sensory fibers supply to pleurae, pericardium and peritoneum of diaphragm; usually right phrenic nerve may be distributed on liver, gallbladder and billiary system.

Left vagus nerve

• Enter thoracic inlet between left common carotid and left subclavian arteries, posterior to left brachiocephalic vein
• Crosses aortic arch where left recurrent laryngeal nerve branches off
• Passes posterior to left lung root (hilum)
• Forms anterior esophageal plexus
• Forms anterior vagal trunk at esophageal hiatus where it leaves thorax and passes into abdominal cavity , then divides into anterior gastric and hepatic branches

Right vagus nerve

• Enter thoracic inlet on right side of trachea
• Travels downward posterior to right brachiocephalic vein and superior vena cava
• Passes posterior to right lung root
• Forms posterior esophageal plexus
• Forms posterior vagal trunk at esophageal hiatus where it leaves thorax and passes into abdominal cavity, then divides into posterior gastric and celiac branches

Recurrent laryngeal nerves

• Right one hooks around right subclavian artery, left one hooks aortic arch
• Both ascend in tracheo-esophageal groove
• Nerves enter larynx posterior to cricothyroid joint, the nerve is now called inferior laryngeal nerve
• Innervations: laryngeal mucosa below fissure of glottis , all laryngeal laryngeal muscles except cricothyroid