Thorax – lab session

The thoracic cage contains some important organs such as: the lungs, trachea, oesophagus and the heart with the great vessels.

The following bony and cartilaginous elements form the thoracic cage:

• thoracic vertebrae
• ribs and costal cartilages
• sternum

The walls of the thoracic cage protect organs of two spaces:

• thoracic cavity (above diaphragm)
• abdominal cavity (beneath diaphragm)

The thoracic cage communicates with:

• neck by superior thoracic aperture (thoracic inlet)
• abdominal cavity by inferior thoracic aperture (thoracic outlet)

The superior thoracic aperture is limited by:

• jugular notch (suprasternal notch) of the sternum
• first rib
• body of the first thoracic vertebra.

The inferior thoracic aperture is limited by:

• xiphoid process of the sternum
• eleventh and twelfth rib
• costal arch (costal margin) formed by costal cartliges of false ribs (from 7th to 10th )
• body of the twelfth thoracic vertebra

Posterior wall of the thoracic cage contains pulmonary grooves located on both sides of the thoracic vertebrae.
In the front, lines of the costal arches form part of the inferior thoracic aperture. Between them there is the infrasternal angle (subcostal angle). Usually it is about 90^o.

Jugular notch

Clavicle

First rib

Sternum

Costal arch (margin)

Infrasternal angle

Skeleton of the thorax.

Mammilary line

Anterior axiliary line

Anterior median line

Parasternal line

Midclavicular line

Vertical lines of thorax.

Vertical lines and lines of the ribs are used to describe the location of anatomical structures within the thoracic cage. They are also used to describe the symptoms and results of a physical examinations.

• anterior median line in the midsagittal plane
• posterior median line = spinous line
• parasternal line on the lateral margin of the sternum
• midclavicular line is the parasagittal plane through the midpoint of the clavicle
• mammilary line is the parasagittal plane through the nipple of the breast (male & prepubertal female)
• midaxillary line is the coronal plane through the topmost point of the axilla
• scapular line is the parasagittal plane through the inferior angle of the scapula
• paravertebral line is the parasagittal plane through the transverse processes of the vertebrae.

The front of the chest is divided into pectoral regions. The pectoral regions are formed by:

• presternal region
• infraclavicular fossa
• pectoral region with:
  • lateral pectoral region
  • mammary region
  • inframammary region
• axillary region with axillary fossa

The clavipectoral triangle is located in the pectoral region. The clavipectoral triangle has three boundaries:

• Superior limit – Clavicle
• Lateral limit – Deltoid
• Medial limit – Pectoralis major

Clavipectoral triangle

Cephalic vein

Pectoralis major

Deltoid

The clavipectoral triangle

The clavipectoral triangle contains the following elements:

• thoraco-acromial artery
• cephalic vein
• thoraco-acromial vein
• deltopectoral lymph nodes
• infraclavicular fossa

Platysma

Deltoid

Serratus anterior

Latissimus dorsi

Clavicular part of pectoralis major

Sternocostal part of pectoralis major

Abdominal part of pectoralis major

The muscles of the thorax.

Muscles of the thorax are divided into two groups:

Superficial muscles

Superficial muscles of the anterior thoracic wall (the pectoral muscles). The pectoral muscles: 4 in number (superficial muscles of the anterior thoracic wall) are associated with movement of the upper limb.

Pectoralis major

Origin: medial 1/2 of the anterior surface of the clavicle, sternum, and costal cartilages from 1 to 6, aponeurosis of the external oblique; there are 3 parts of this muscle:

• Clavicular part
• Sternocostal part
• Abdominal part

Insertion: greater tubercule of the humerus

Action: adduction, flexion and medial rotation of the arm (accessory muscle of inspiration)

Nerve supply: both pectoral muscles – lateral and medial pectoral nerves; the short branches of brachial plexus

Pectoralis minor

Origin: outer surface of ribs 3-5 (between bone and cartilage)

Insertion: coracoid process of the scapula

Action: depression and protraction of the scapula (accessory muscle of respiration)

Nerve supply: both pectoral muscles – lateral and medial pectoral nerves; the short branches of brachial plexus

Subclavius

Origin: costal cartilage of the first rib

Insertion: lower surface of clavicle

Action: protection of the subclavian vessels

Nerve supply: subclavian nerve (short branch of the superior trunk of brachial plexus)

Serratus anterior

Origin: outer surface of ribs 1-8
Insertion: medial border of scapula
Action: fixation of scapula to the thoracic wall, protraction – accessory muscle of inspiration
Nerve supply: long thoracic nerve (C5-C7) – short branch of brachial plexus

Mnemonic for pectoral muscles:

A lady between two majors.

The pectoralis major attaches to the lateral lip of the bicipital groove, the teres major attaches to the medial lip of the bicipital groove, and the latissimus dorsi attaches to the floor of the bicipital groove. The “lati” is between two “majors.”

The arterial supplay & innervation of the superficial muscles of the thorax.

Deep thoracic muscles

Deep thoracic muscles are proper muscles of the thorax. Each of the 11 pairs of intercostal spaces contains the intercostal muscles, which form three layers.

First costal cartilage

1st rib

2nd rib

3rd rib

4rd rib

5th rib

6th rib

Anterior intercostal membrane

Internal intercostal muscle

External intercostal muscle

Relations of fibers of the intercostal muscles and intercostal membrane.

External intercostal muscles (the superficial)

The external intercostal muscles extend from the tubercle of the ribs posteriorly to the costochondral junctions anteriorly, where they terminate as an external (anterior) intercostal membrane – EIM (membrana intercostalis externa). They arise from the lower border of the rib and end on the upper border of the rib below. The intercostal fascia covers the outer surfaces of these muscles. Their fibres are directed obliquely downward and forward.

Direction of the fibers:

Vertebra \\\\\\\\\\ – EIM – Sternum – EIM – ////////// Vertebra

Mnemonic for the external oblique fiber direction

To remember the direction of the fibers of the external oblique, think of placing your hands in your pockets, ie. down and in.

Internal intercostal muscles (the middle)

The internal intercostal muscles occupy the intercostal spaces from the costal cartilages anteriorly to the angles of the ribs, where they terminate as an internal (posterior) intercostal membrane – IIM (membrana intercostalis interna). The intercostal fascia covers the inner surface of the internal intercostal muscles.

Their fibers run inferoposteriorly (in the direction opposite to the fibres of the external intercostal muscles) from the costal groove to the superior border of the rib below.

Direction of the fibers

Vertebra – IIM – ////////// Sternum \\\\\ – IIM – Vertebra

Innermost intercostal muscles (the deepest)

The innermost intercostal muscles form the deepest layer of the intercostal muscles and occupy the middle part of the intercostal spaces (from angle to cartilage). The vasonervous fascicle is situated between each pair of the internal and the innermost intercostal muscles. It contains: Vein, Artery and Nerve (VAN).

Function: All intercostal muscles keep the intercostal spaces rigid and prevent them from being bulged out during expiration and from being drawn in during inspiration. The external intercostal muscles belong to the muscles of inspiration. The internal intercostal muscles also partly (intercartilaginous part) belong to them. The rest of these muscles work as the muscles of expiration. The function of the innermost intercostal muscles is not fully understood.

• The subcostal muscles extend from the internal surface of the angle of the rib to the internal surface of the rib below. They cross one or two intercostal spaces. Their fibers run in the same direction as the fibers of the internal intercostal muscles.
• The transverse thoracic muscle is attached to the posterior surface of the inferior part of the body of the sternum and the posterior surface of the costal cartilages (from the second to the sixth). Its fibers pass superolaterally. The internal thoracic vessels (the internal thoracic artery and vein) separate them from the costal cartilages and the internal intercostal muscles. The transverse thoracic muscle is the muscle of expiration.

Fascia of the thoracic wall

Fascia of the anterior thoracic wall can be divided into two layers:

Superficial layer

Superficial layer covers the superficial muscles of the anterior thoracic wall as pectoral fascia, which is attached: superiorly – to the clavicle, medially – to the manubrium, inferiorly continuous as abdominal fascia and laterally – as axillary fascia (forms floor of the axilla).

Deep layer

Deep layer lies under the pectoral muscles.

Posterior primary branch

Anterior primary branch

Endothoracic fascia & pleura

Innermost intercostal muscle

Internal thoracic artery & veins

Sternocostalis muscle

Sternum

External intercostal membrane

Internal intercostal muscle

External intercostal muscle

Internal intercostal membrane

Relations of the muscles and membranes of the intercostal space.

The axillary fascia continues posteriorly as posterior thoracic fascia and distally as brachial fascia.

The clavicopectoral fascia is a strong fibrous sheet posterior to the clavicular part of the pectoralis major. It covers the axillary vessels and nerves.

The endothoracic fascia covers the internal surface of the ribs and intercostal muscles, and corresponds to the transverse fascia of the abdominal wall.

The internal thoracic artery or internal mammary artery is a branch of the subclavian artery. It arises from the inferior surface of the first part of this artery and descends on the posterior surface of the anterior thoracic wall, 1-2 cm lateral to the sternum. The internal thoracic artery lies between: the costal cartilages and the internal intercostal muscles anteriorly the transverse thoracic muscles, the endothoracic fascia and the parietal pleura posteriorly. The internal thoracic artery is crossed posteriorly by the phrenic nerve.

The internal thoracic artery gives off the following branches:

• Anterior intercostal arteries between the first and sixth intercostal spaces
• Mediastinal branches
• Thymic branches
• Pericardial branches
• Pericardiacophrenic artery
• Sternal branches
• Perforating arteries which supply the pectoral muscles (with the medial mammary branches)

The internal thoracic artery divides terminally at the level of the sixth intercostal space
into two branches: superior epigastric artery, and musculophrenic artery.

Superior epigastric artery descends in the original direction of the internal thoracic artery and passes through the diaphragm between the costal and sternal attachments of the diaphragm into the anterior thoracic wall. Below the diaphragm it supplies the muscles of the anterior abdominal wall and anastomoses with the inferior epigastric artery (from the external iliac artery).

Musculophrenic artery is directed inferolaterally and descends through the diaphragm at the level of the ninth rib and supplies the diaphragm. It gives off branches to the lower part of the pericardium and the anterior intercostal arteries between the sixth and ninth intercostal spaces.

The anterior intercostal arteries arise from the internal thoracic artery and from the musculophrenic artery.

The superior anterior intercostal arteries arise from the internal thoracic artery, and supplies the upper six intercostals spaces.

The inferior anterior intercostal arteries arise from the musculophrenic artery (a terminal branch of the internal thoracic artery), and supplies the intercostals spaces between 6th to 9th.

The lower two spaces contain only posterior intercostal arteries.

The posterior intercostal arteries arise from the posterolateral surface of the thoracic aorta, except the first two, which arise from the superior intercostal artery (branch of the costocervical trunk).

• The 1^st & 2^nd posterior intercostal arteries arise from the supreme intercostal artery (a branch of the costocervical trunk).
• The remainder of the posterior intercostal arteries arise from the posterolateral surface of the thoracic aorta (descending aorta).

All posterior intercostal arteries run together with the intercostal nerve and intercostal vein in the following order from top to bottom: vein, artery and nerve. Relations between vein, artery and nerve (VAN) are shown below:

• Vein is located superiorly
• Artery is situated between vein & nerve
• Nerve is located inferiorly

These structures form the vasonervous fascicle (VAN). VAN occupies the costal groove and is situated between the internal intercostal membrane externally, the parietal pleura internally, and after that, between the internal intercostal and innermost intercostal muscles.

Each posterior intercostal arteries gives off the posterior or dorsal branch, which lies with the dorsal branch of the spinal nerve and gives off:

• Medial cutaneous branch
• Lateral cutaneous branch
• Spinal branch

The dorsal branches supplies the spinal cord, vertebral column, and muscles of the back and skin. Next from each posterior intercostal artery arises the collateral branch of the lateral cutaneous branch (with the lateral mammary branches), which supplies muscles and skin of the lateral thoracic wall. The posterior intercostal artery anastomoses around the midclavicular line with the anterior intercostal artery.

Endothoracic fascia

Intercostal bundle (V. A. N.)

Parietal pleura

Internal intercostal membrane

External intercostal muscle

Rib

Parietal pleura

Innermost intercostal muscle

Intercostal bundle (V. A. N.)

Endothoracic fascia

Rib

Internal intercostal membrane

External intercostal muscle

Structures of the nervovascular bundle located: left — at the proximal aravetebral level, right — at the distal paravetebral level– lateral to the costal angle.

Rib

External intercostal muscle

Internal intercostal muscle

Endothoracic fascia

Intercostal bundle (V. A. N.)

Innermost intercostal muscle

Parietal pleura

Costal cartilage

Endothoracic fascia

Intercostal bundle (V. A. N.)

Colateral branch of anterior intercostal artery

Parietal pleura

Internal intercostal muscle

External intercostal membrane

Structures of the nervovascular bundle located left — at the axillary line, right — at the parasternal line – lateral to the sternum.

Dorsal primary branch, which turns posteriorly and passes through the muscles of the back and supplies the skin of the back.

Ventral primary branch, which passes in the costal groove under the intercostal vein and artery, almost in the same place as the posterior intercostal artery (which gives off the lateral cutaneous branch). The eleven pairs of ventral branches of the thoracic nerves are called the intercostal nerves. Each intercostal nerve gives off the muscular branches, the collateral branch and the lateral cutaneous branch, which divides into two branches (anterior and posterior) and supplies the skin on the lateral part of the thoracic wall. Not so far from the sternum, the intercostal nerves turn anteriorly, pass through the intercostal spaces and supply skin on the anterior thoracic wall as anterior cutaneous branches (rami cutanei anteriores), which are also divided into two branches (medial and lateral). The lateral cutaneous branches from Th4-6 of the intercostals nerves gives off the lateral mammary branches. The anterior cutaneous branches from Th2-4 of the intercostals nerves gives off the medial mammary branches.

Typical intercostal nerves are formed by the anterior (ventral) primary branches of the thoracic spinal nerves from 3rd to 6th.

It gives off the following branches:

• Lateral cutaneous nerve
  • anterior branch
  • posterior branch
• Anterior cutaneous nerve
  • medial branch
  • lateral branch
• Branches for the intercostal muscles
• Pleural branches

Atypical intercostal nerves are also formed by the anterior primary branches of the thoracic spinal nerves, but from the 1st , the 2nd , the 7th to the 11th and the 12th.

All of the intercostal nerves give off many unnamed muscular branches, which supply the
intercostal muscles and many sympathetic fibres (from a ganglion of the sympathetic trunk) to blood vessels and sweat glands.

The diaphragm is the principal muscle of respiration, which forms a musculo-fibrous septum between the thoracic and abdominal cavity. During respiration, it descends as it contracts and ascends as it relaxes. The diaphragm can be divided into two portions: periphereal and central.

Structures of the diaphragm.

The diaphragm is the principal muscle of inspiration. When the muscular fibers relax, it is dome-shaped. During inspiration the muscular fibers contract and the central tendon descends. The right and left domes are flattened. The diaphragm also elevates the ribs, to which it is attached. As a result, the vertical diameter of the chest is increased. As the diaphragm descends, it pushes on the abdominal viscera before it and decreases the intrathoracic pressure, allowing air to enter the lungs. At the end of inspiration the diaphragm relaxes and the thoracic wall returns to its natural position, causing the air to leave the lungs. The diaphragm assists the anterior abdominal muscles during micturition, defecation and parturition.

CT (transverse plane) right and left crus of the diaphragm.

• The superior surface of the diaphragm is supplied by:
  • musculophrenic artery.
  • pericardiacophrenic artery both branches from the internal thoracic artery.
  • superior phrenic artery – branch from the thoracic aorta.
• The inferior surface of the diaphragm is supplied by:
  • inferior phrenic artery – branch from the abdominal aorta which arises just above the celiac trunk.

The musculophrenic and pericardiacophrenic veins receive blood from the superior surface of the diaphragm and return it to the internal thoracic vein.

The inferior phrenic vein receives blood from the inferior surface of the diaphragm and returns it to the inferior vena cava.

The superior surface of the diaphragm is drained by lymphatic vessels, which return lymph to the phrenic lymph nodes, and next to the parasternal nodes and posterior mediastinal lymph nodes. From the inferior surface of the diaphragm lymph is returned to the lateral aortic lymph nodes.

The lymph vessels from the superior and inferior surfaces of the diaphragm communicate freely!!!

The diaphragm is supplied by motor and sensory fibers from the phrenic nerves – ventral branches of C3-C5 of the spinal cord (the longest nerve from the cervical plexus).

Cervical nerves supply the diaphragm, due to the caudal migration of this muscle during development. Only the peripheral portion of the diaphragm is supplied by sensory fibers from the intercostal nerves.

Mnemonic

C3, 4 and 5 keep the diaphragm alive.

A poetic way to remember the innervation of the diaphragm.

Clinical comments:

There are hernias in diaphragm area, which can be divided into hiatal hernias (90% of all diaphragmatic hernias) and paraoesophageal hernias 10 %). The hiatal hernia is usually connected with gastro–esophageal reflux disesase and can be treated by surgical procedure.

The diaphragmatic hernia are usually formed at:

• the sternocostal triangle
• the oesophageal hiatus

Its shape is that of a truncated pyramid with apex, base and four walls.

Walls of the axilla.

Posterior wall of the axilla.

In the axilla are located:

• axillary artery
• axillary vein
• cords and terminal branches of the brachial plexus
• coracobrachialis muscle
• biceps muscle
• axillary lymph nodes and lymph vessels
• fat

Apex of the axilla.

The axillary artery gives the following branches:

• Superior thoracic artery – to the anterior thoracic wall.
• Thoraco-acromial artery – pierces the clavipectoral fascia and supplies branches to the anterior axillary wall.
• Lateral thoracic artery – supplies lateral thoracic wall (in the female it contributes to the blood supply of the breast).
• Subscapular artery – the largest branch of the axillary artery. It gives off thoracodorsal artery and circumflex scapular artery. The circumflex scapular artery passes backwards around the lateral border of the scapula into the infraspinous fossa. The arteries take part in the anastomosis around the scapula.
• Anterior and posterior circumflex humeral arteries anastomose around the surgical neck of the humerus.

The axillary artery gives the following branches:

Lateral lymph nodes: they drain lymph from upper limb, except region which is supplied by lymph vessels accompaning cephalic vein.

Pectoral lymph nodes: they drain lymph from anterior thorax wall.

Subscapular lymph nodes: they drain lymph from upper part of back.

Central lymph nodes: they get lymph from 3 groups of lymph nodes mentioned above
and additionally directly from breast; they drain to apical lymph nodes.

apical or infraclavicular lymph nodes (they get lymph from central lymph nodes,
lymph vessels which pass together with cephalic vein and they drain to supraclavicular
lymph nodes).

• There are located on its left side:
  • left common carotid artery
  • left subclavian artery (branches from aortic arch)
  • aortic arch (below them)
• There are located on its right side:
  • right vagus nerve
  • azygos vein

Relations of the trachea.

The trachea bifurcates into main stem (primary) bronchi at the carina behind the sternal angle and at level T4.

Primary bronchi are located posteriorly in the hilus behind

• Pulmonary artery (intermediate)
• Pulmonary veins (anterior)

Relations of the bronchi.

The right main bronchus is larger then the left one and descends more vertically. It divides into three lobar bronchi. The right main bronchus is most probable a resting-place for aspirated objects because is closer to an imaginary continuation of the trachea.

The left main bronchus is longer, narrower and more horizontal then the right (because the heart is towards the left). It divides into two lobar (secondary) bronchi.

Division of the trachea.

The wall of the trachea and main bronchi are supported by C-shaped rings of cartilage; posteriorly, the tube is completed by the fibroses membrane. The cartilages are placed horizontally above each other and connected to each other by the annular ligament – intercartilaginous ligament.

Trachea and divisions of the main bronchi.

Two layers of the elastic fibroses membrane cover the outer and inner surfaces of the cartilages. The trachea and main bronchi are also formed by two layers of muscular fibres – longitudinal (outer) and transverse (inner between ends of the cartilages). The mucous membrane, which is located as the innermost layer contains ciliated epithelium and mucous – secreting cells.

The main bronchi divide into:

• Lobar bronchi and next subdivide into:
  • Segmental bronchi. The structure of the wall changes, as the bronchi divide into smaller parts, subsegmental bronchi. In the walls of segmental and subsegmental bronchi cartilages are present, mostly at points of branching. At their terminations subsegmental bronchi divide into ramifications called:
    • Terminal bronchioles which have no cartilages and split into:
      • Respiratory bronchioles the last generation with muscular tissue branching into:
        • Alveolar sacs
        • Pulmonary alveoli (aircells), which are connected with other alveoli by alveolar tissue. The muscular tissue disappears.

Terminal bronchioles, respiratory bronchioles, alveolar sacs and pulmonary alveoli make up structure called a lobule. All lobules are separated by septa which are formed by connective tissue.

Respiratory bronchioles, alveolar sacs and pulmonary alveoli make up a structure called an acinus.

Divisions of the segmental bronchus.

A segmental bronchus may branch 5 – 15 times to produce 50 – 70 respiratory bronchioles, which become alveolar sacs and terminate in the alveoli, constituting the lung parenchyma. The pulmonary parenchyma represents the expanded terminal portion of the bronchial tree.

General divisions of main bronchi

The pleura (pleura) is a serous membrane which surrounds the lung. The pleura has two layers. The inner layer of the pleura – visceral pleura- invests the external surface of the lung and the outer layer – parietal pleura – is attached to the internal surface of the thoracic cavity.

The thoracic cavity is divided into major spaces:

• Right pleural cavity
• Left pleural cavity
• Mediastinum – space between them (interpleural space)

The pleural cavities contain the lungs. All other visceral structures of the thorax are situated in the mediastinum.

The pleura is divided into two layers:

• Parietal pleura
• Visceral pleura

The parietal pleura covers the internal surface of the thoracic wall, superior surface of the diaphragm, separates the pleural cavity from the mediastinum and forms the external wall of the pleural sac.

The parietal pleura is subdivided into four parts:

• Costal pleura covers the internal surfaces of the sternum, costal cartilages, ribs and intercostal muscles. It is associated with the endothoracic fascia. Medially it continues as the mediastinal pleura, inferiorly it continues as the diaphragmatic pleura.
• Diaphragmatic pleura covers the superior surface of the diaphragm except, the space where the pericardium is associated with the diaphragm.
• Mediastinal pleura is adjacent to the mediastinum.
• Pleural cupula covers the apex of the lung and is formed by the junction of the costal and mediastinal pleura. It is located above the thoracic inlet, at the root of the neck, behind the clavicle and first rib.

The visceral pleura closely covers the lungs and forms the internal wall of the pleural sac. The visceral pleura invests the outer surfaces of the lung and invaginates into the fissures of lungs. The visceral pleura is continuous with the parietal pleura at the root of the lung.

Between the parietal and visceral pleura is formed the pulmonary ligament. The parietal pleura of the anterior and posterior walls of the thoracic cage is reflected off of the mediastinal wall towards the lungs.

Visceral pleura.

• The pleural sac is the space between the two the layers of the pleura, and contains normally only a capillary layer of serous fluid. Serous fluid is secreted by the pleura. Each pleural sac is a closed cavity.
• The pleural recess is empty space in the pleural cavities where the parietal pleura is in contact with visceral pleura which is not occupied by lungs during expiration. During deep inspiration, the lung parenchyma expands into recesses, but never completely fills these spaces.

Transverse section of the pleura.

The pleural recesses are as follows:

Sagittal section of the pleura.

• On the right side the following markings define the pleural cavity:
  • 3 cm above medial third of clavicle
  • to 2nd rib – in midline
  • to 6th rib – in sternal line
  • to 8th rib – anteriorly in midclavicular line
  • to 10th rib – in midaxillary line
  • to 12th rib – in paravertebral line
• On the left side following markings define the pleural cavity:
  • 3 cm above medial third of clavicle
  • to 4th rib – in midline
  • to 6th rib – in sternal line
  • to 8th rib – anteriorly in midclavicular line
  • to 10th rib – in midaxillary line
  • to 12th rib – in paravertebral line

Frontal section of the pleura.

The costal pleura is innervated by the 1st-12th intercostal nerves.
The central diaphragmatic pleura and mediastinal pleura is innervated by the phrenic nerve.

Innervation of the pleura:

The lungs are the paired essential organs of respiration, which are responsible for oxygenation of venous blood. In the thoracic cavity are situated two lungs; one placed on each side of the chest and separated from the other by the contents of the mediastinum. The right lung is larger than the left, mainly due to the cardiac notch of the left lung. The lung is spongy and elastic in texture and is a conically shaped organ. Each lung lies in the pleural sac and is attached to the mediastinum at a place called the hilum. The lung has an apex, base, two surfaces, three borders, a root and a hilum.

Each lung has:

• base rests on the convex surface of the diaphragm
• apex extends into the root of the neck about 1 cm above the level of the clavicle. The apex is covered by the cupula of the pleura. It is crossed by the subclavian artery, which makes a groove on the mediastinal surface of the lungs.

The hilum of the lung is the space where the lungs are attached to vessels and air passages; there are structures passing into the lung (main bronchi, arteries, nerves – efferent fibres) and structures leaving the lung (veins, lymphatic vessels, nerves – afferent fibres).

From anterior to posterior, main structures of the hilum of each lung are situated in the following order:From anterior to posterior, main structures of the hilum of each lung are situated in the following order:

1: the pulmonary veins, 2: pulmonary artery, 3: main bronchus and bronchial vessels

Mnemonic

VAB (anterior –> posterior) = Vein, Artery, Bronchus

Medial aspect of the root of the left and right lungs.

Lobes of the lungs.

The lungs are divided into lobes by the fissures.

• Sympathetic nerves are provided by short splanchnic branches from the left and right sympathetic chain to the anterior & posterior pulmonary plexuses.
• Parasympathetic nerves pass to the anterior & posterior pulmonary plexuses from the left and right vagus.

Sympathetic and parasympathetic regulations of the bronchial tree and pulmonary vessels:

The visceral pleura and subdivisions of the bronchi are innervated by the right and left pulmonary plexuses. Each plexus is divided into anterior and posterior parts. These plexuses are formed by fibres from CNX and the sympathetic trunk.The visceral pleura and subdivisions of the bronchi are innervated by the right and left pulmonary plexuses. Each plexus is divided into anterior and posterior parts. These plexuses are formed by fibres from CNX and the sympathetic trunk.

The visceral pleura and bronchial epithelium are supplied by afferent fibres of the CNX (touch and pain).

The costal and partly the diaphragmatic pleura are supplied (sensory fibre) by the intercostal nerves. The mediastinal and partly the diaphragmatic pleura are supplied by the phrenic nerves.

Lung tissue and the visceral pleura are devoided of pain-sensitive nerve endings, so pain in the chest is always the result of the conditions of the surrounding structures. In tuberculosis or pneumonia, for example, pain may never be experienced. If a lung disease crosses the visceral pleura and the pleural cavity to involve the parietal pleura, pain becomes a prominent feature.

The pulmonary veins (oxygenated blood!!!) begin forming after pulmonary capillaries, as small veins unite to form lager and ultimately form large vessels, which come into relation with arteries and bronchial tubes (see table 3-3), accompanying them to the hilum of the organ. The pulmonary veins are short wide vessels formed after transalveolar gas exchange, transporting oxygenated blood to the left atrium. In the hilum of the lung they (usually both upper and lower) lie below and in the front of the pulmonary artery. Venous capillaries combine to form intersegmental veins. The intersegmental veins unite to form the lobar veins. The right superior & middle lobar veins or left superior & lingular veins join to form the superior pulmonary veins. The inferior lobar veins continue as the inferior pulmonary veins.

The bronchial veins (deoxygenated blood) drain the large subdivisions of the bronchi. These veins do not receive all blood from the bronchial arteries (blood partly passes into the pulmonary veins). Usually the hemiazygous vein drains the left bronchial vein and the azygos vein the right.

Lymphatic vessels form two plexuses:

• The superficial lymphatic plexus of the lung is situated deep to the visceral pleura. Lymph vessels drain into the bronchopulmonary lymph nodes. These nodes are situated around the bifurcation of the trachea.
• The deep lymphatic plexus of the lung is located in the submucosa of the bronchi and in the peribronchial connective tissue and from it lymphatic vessels drain to the bronchopulmonary lymph nodes and to superior and inferior tracheobronchial lymph nodes.

Lymph is mainly returned from superior tracheobronchial lymph nodes by the right and left bronchomediastinal lymph trunks to the right lymphatic duct and thoracic duct.

The heart is a cone shape, double self-adjusting muscular pump. It is situated in the middle mediastinum between the lungs and is enclosed by the roots of the great vessels in the cavity of the pericardium. It propels the blood through the vessels to various parts of the body. The heart is subdivided by a muscular septum into two halves, left and right, and each half subdivides into two cavities. The upper cavity is called the atrium and the lower, the ventricle.

These parts normally work in union. The division of the heart into four chambers is indicated by grooves upon its surface. For example: the atria are separated from the ventricles by the atrioventricular groove or coronary groove (sulcus atrioventricularis). The ventricles are separated by the anterior and posterior interventricular groove (sulcus interventricularis anterior et posterior), which can be identified on the anterior and posterior surfaces.

Chambers of the heart.

The heart consists of the following three layers: the pericardium with epicardium, myocardium and endocardium.

Pericardium

The pericardium (pericardium) is the outer conical layer, a double-walled fibro-serous sac (two layers: external-fibrous pericardium and internal-serous pericardium), which contains the heart and roots of the great vessels and the pericardial cavity. It is located in the middle mediastinum.

The pericardium consist of two layers:

Fibrous pericardium

The fibrous pericardium is a strong, dense membrane and is composed of tough fibrous tissue. Its base is fused with the central tendon of the diaphragm. It is also fused anteriorly to the posterior surface of the sternum by the superior and inferior sterno-pericardial ligaments. Superiorly, the fibroses pericardium is also fused with the fibro-elastic coat of the great vessels.

Serous pericardium

The serous pericardium can be divided into two layers:

• The visceral pericardium covers the heart and forms the epicardium, the external layer of the heart wall. At the point where the aorta and pulmonary trunk leave the heart, the visceral pericardium is reflected from the heart and continues as parietal pericardium.
• The parietal pericardium is fused with the fibrous pericardium.

The pericardial cavity is a potential space between the parietal and visceral layers pericardium which contains a serous fluid. On the posterior surface of the heart, the reflection of the serous pericardium around the large veins forms a recess called the oblique pericardial sinus. Also on the posterior surface of the heart is the transverse pericardial sinus, which is a short passage that lies between the reflection of the serous pericardium around the aorta and the pulmonary arteries and the reflection around the large veins.

Clinical comments

Pericardial effusion is a condition in which fluid accumulate between visceral and parietal layers of serous pericardium. It can lead to cardiac tamponade, which has following symptoms: tachycardia, low blood pressure and quiet heart sounds.

Structure of the pericardium.

Myocardium

The myocardium is the middle layer of the heart. Muscular fibres are attached to the fibroses rings, which form the fibrous skeleton of the heart. The fibrous rings surround the atrio-ventricular (gives attachment for the mitral and tricuspid valves and also for muscular fibers of the atria and ventricles) and arterial orifices (gives attachment for the great vessels and semilunar valves). The atrioventricular rings and the aortic arterial ring are connected by the fibrous tissue.

Skeleton of the heart.

The myocardium is composed of three layers:

Cardiac muscular fibers with the atrial fibers

• The superficial fibers – fibers run in the transverse direction around two atria – common to both.
• The deep fibers, the inner layer -fibers proper to each atrium run in vertical directions, turn around the superior wall of each atrium and back on another wall to the fibroses rings

Ventricular fibers

The ventricular fibers consist of:

• Superficial layer – oblique – the outer layer is formed by fibers which run obliquely downwards around the two ventricles (only partly around one ventricle). Some of these fibers change directions to form a circle around the ventricles. Others turn around the ventricles and ascend, forming the vertical (inner) layer. At the apex of the heart, some fibers turn suddenly inward into the interior of the ventricle forming the vortex. It is common to both ventricles.
• Intermediate layer – circular – the middle layer (the strongest) is formed by fibers, which run transversely around each ventricle.
• Deep layer – longitudinal – with apex and vortex of ventricle.

Heart skeleton

The heart skeleton, which is made by dense connective tissue and consist of:

• The left & right A-V fibrous rings
• The aortic & pulmonary fibrous rings
• The left & right fibrous triangles
• Upper membranous portion of interventricular septum

The conducting system of the heart consists of the specialised cardiac muscle cells and conducting fibres. They initiate the normal heart beat and co-ordinate the contraction of the four heart chambers. They are present in the sinoatrial node, the atrioventricular node, atrioventricular bundle and its right and left terminal branches, also in the subendocardial plexus of Purkinje fibres.

The conducting system is comprised of the:

The sino-atrial node

The sino-atrial node (S-A) is situated at the upper part of the sulcus terminalis just to the superior vena cava into the right atrium. S-A node initiates atrial systole. It is the auto rhythmic pacemaker and initiates the contraction cycle with approximately 72 depolarizations a minute, which is spread over the atria and the atrioventricular node. From S-A, the cardiac impulse runs through the atrial myocardium to reach the atrioventricular node.

The atrioventricular node

The atrioventricular node (A-V), which is located in the lower part of the interatrial septum just above the attachment of the septal cusp of the tricuspid valve. A-V node is joined to the S-A node to initiate ventricular systole. It is located in the myocardium between the crista terminalis and the opening of the superior vena cava. It initiates the contraction cycle with approximately 40 depolarizations a minute. Next, the cardiac impulse is conducted to the ventricles by the atrioventricular bundle.

The atrioventricular bundle

The atrioventricular bundle (A-V) bundle (bundle of His) is the muscular connection between the myocardium of the atria and the myocardium of the ventricles. The atrioventricular bundle descends behind the septal cusps of the tricuspid valve to reach the inferior border of the membranous part of the ventricular septum and divides into right bundle branch and left bundle branch, one for each ventricle. Each branch usually subdivides into branches which become continuous with the fibers of the Purkinje plexus.

Clinical comments

When the conducting system doesn’t work in proper way, cardiac pacemaker, device, which generate electrical impulses,is inserted under skin and maintain physiological heart beat.

The septum of the heart consist of the interatrial and the interventricular septum. The interventricular septum consist of:

• muscular part
• membranous part

Endocardium

Endocardium is the innermost layer lining the cardiac chambers. It is a thin, smooth endothelium of the ventricles. It is a thin membrane which lines the interior surface of the heart (it also forms surfaces of the valves) and continues into the lining membrane of the great vessels.

The heart is situated obliquely, two-thirds to the left and one-third to the right of the median plane. In adults it measures 5 inches (about 12,5 cm) in length, 3,5 inches (7,5cm) in width, and 2,5 (5cm) in thickness.

The hearts weight varies from 280 to 340 g in men and from 230 to 280 g in women.

The heart has: a base, apex, three surfaces and four borders.

Left view

Position of the left surface of heart. Left view.

Right view

Position of the right surface of heart. Right view.

Right atrium

The right atrium receives deoxygenated blood from the following large vessels:

• The superior vena cava
• Inferior vena cava
• Coronary sinus

The right atrium has six walls:

Superior wall

On the superior wall is situated the opening of the superior vena cava, which returns deoxygenated blood from the upper part of the body.

Inferior wall

On the inferior wall is situated the right atrio-ventricular orifice.

Anterior wall

On the anterior wall is situated the right auricle, a conical muscular pouch that overlaps and covers the ascending aorta in the beginning and openings of smallest cardiac veins.

Posterior wall

On the posterior wall are located two orifices:

• the first one – the inferior vena cava orifice (returns deoxygenated blood from lower half of the body) with the nonfunctional after birth valve of the inferior vena cava. This valve directs oxygenated blood coming from the placenta into the left atrium through the foramen ovale, which is closed after birth.
• the second one – the coronary sinus orifice, wchich returns deoxygenated blood from the veins of the heart. This orifice contains the coronary valve, which is important during contraction of the atrium, because blood can’t return to the coronary sinus.

Medial wall

On the medial wall, the interatrial septum is located in the fossa ovalis in adults. This structure corresponds to the foramen ovale in the fetus, which normally closes after birth.

Lateral wall

On the lateral wall is located the crista terminalis, which represents the line of fusion of the sinus venosus of the embryonic with the primitive proper atrium.

Right ventricle

The right ventricle receives deoxygenated blood from the right atrium through the atrio-ventricular orifice during relaxation of the ventricle. After the contraction of the ventricle it moves blood through the pulmonary trunk (pulmonary orifice) to the lungs. Both of these orifices are separated from each other by the supraventricular crest.

Walls of the right ventricle.

The right atrio-ventricular orifice is surrounded by a fibrous ring, which is a part of the fibrous skeleton of the heart and gives attachment to the three cusps of the tricuspid valve – anterior, posterior and septal cusps. It lies behind the left half of the sternum opposite the fourth costal cartilage. The three edges of the cusps are attached to fibrous threads called the chordae tendinea or tendinous cords, which arise from the apices of the papillary muscles.

Three papillary muscles (conical shaped) are attached to the wall of the ventricle.

The anterior papillary muscle

The anterior papillary muscle is attached to the anterior wall of the right ventricle. Its chordae tendinea are connected with the anterior and posterior cusps. Base of the anterior papillary muscle is located on the septomarginal trabecula. It is connected from the one side with the right border and from the other with interventricular septum.

The posterior papillary muscle

The posterior papillary muscle is attached to the inferior wall of the right ventricle and its chordae tendinea are connected with the medial and posterior cusps.

The septal (medial) papillary muscle

The septal (medial) papillary muscle (musculus papillaris medialis s. septalis) is attached to the interventricular septum and its chordae tendinea are connected with anterior and medial (septal) cusps.

Position of the tricuspid valve.

The papillary muscles with the chordae tendinea prevent their inversion to the right atrium
during the right ventricle’s contraction.

Relations of papilary muscles and cusps.

The pulmonary valve lies at the apex of the conus arteriosus (lies behind the medial end of the left costal cartilage and the adjoining part of the sternum) and consists of three semilunar cusps (anterior, right and left). The cusps lie close to the walls of the vessel. When the right ventricle is contracts, the cusps are open and when the right ventricle relaxes, the cusps close to the pulmonary opening. There are nodules on the central part of the free margin of semilunar cusp and lunules which pass peripherally from the nodules.

The internal surface of the ventricular wall has irregular muscular elevations, called the trabeculae carneae, which gives a corsage like a sponge. Conus arteriosus is the only smooth area that the blood passes as it travels to the pulmonary orifice.

Left atrium

The left atrium receives oxygenated blood from the four pulmonary veins. We can identify four walls, but thicker then the walls of the right one. There are pectinate muscles on the wall of left atrium.

Anterior wall

On the anterior wall is situated the right auricle which covers the front of the pulmonary trunk.

Posterior wall

On the posterior wall are situated openings of the pulmonary veins (without valves).

Inferior wall

On the inferior wall is situated the left atrio-ventricular orifice with two cusps of the bicuspid valve.

Medial wall

The medial wall – the interatrial septum.

Relation of the walls and cusps of the ventricles of the heart.

Left ventricle

The left ventricle, is longer, more conically shaped, and three times more thicker then the right one. The left ventricle receives oxygenated blood from the left atrium, through the left atrioventricular orifice.

The aortic openings (guarded by the semilunar valves – anterior, right and left posterior) are located in front of the right side of the atrio-ventricle orifice (lies behind the left half of the sternum opposite to the third intercostal space). Part of the ventricle, just below the aorta is an opening called the aortic vestibulum and a wall surrounds this part which is mainly fibroses (not collapse during diastole). Trabecula carnae are smaller here, but there are more of them. The cusps contain nodules and lunules like cusps of pulmonary valve.

The left bicuspid valve or mitral valve contains two cusps: anterior (larger one) and posterior. The cusps are connected to the anterior (attached to the anterior wall) and posterior papillary muscles (attached to the posterior wall) by chordae tendinea.

Position of the cardiac valves.

Clinical comments

When listening to the heart with a stethoscope, two sounds can be heard: lub-dup. The first sound is produced by the contraction of the ventricles and the closure of the tricuspid and mitral valves. The second sound is produced by the sharp closure of the aortic and pulmonary valves. It is important for each physician to know where to place his/her stethoscope on the chest wall.

• The tricuspid valve is best heard over the right half of the lower end of the body of the sternum.
• The mitral valve is best heard over the apex of the heart.
• The pulmonary valve is heard over the medial end of the second left intercostal space.
• The aortic valve is the best heard over the medial end of the second right intercostal space.

Projection of the cardiac valves.

The heart is innervated by the sympathetic trunk and parasympathetic fibers of the autonomic nervous system via the cardiac plexuses. Should the blood supply to the myocardium become impaired, pain impulses reach consciousness via this pathway.

Motor fibers. The heart rate and ejection volume are controlled by the autonomic nervous system. It has:

• Parasympathetic division. The parasympathetic fibers come from the vagus nerves. The vagus sends fibers over the surface of the heart and to the nodal areas. These preganglionic fibers synapse with minute postganglionic fibers in the myocardium. Vagal activity slows the heart rate and reduces the stroke volume.
• Sympathetic division. The symphatetic fibers arise from the cervical and upper thoracic portions of the sympathetic trunks The cardiac accelerator nerves run down the neck to the heart from superior, middle, and inferior ganglia of the cervical sympathetic chain (trunk).

Thoracic splanchnic nerves run to the heart from ganglia T1 – T3. Sympathetic activity accelerates the heart rate and increases stroke volume.

Afferent sensation from the heart runs along the sympathetic pathways via both the cardiac accelerator nerves of the splanchnic thoracic nerves.

Efferent postganglionic fibers pass to the sino-atrial and atrio-ventricular nodes. These fibers are also distributed to the regions of the heart as nerve plexuses around the coronary arteries. Afferent fibers running with the vagus nerves take part in cardiovascular reflexes. Afferent fibers running with the sympathetic nerves carry nervosa’s impulses that normally do not reach consciousness.

Clinical comments

The pain of the angina pectoris and myocardial infarction radiates from the substernal region to the neck and along the medial aspect of the arm and forearm. The cardiac pain from the heart (result due to accumulation of the metabolic products and stimulates pain, but the heart is insensitive for touch and temperature) is transmitted by the sensory afferent fibers (the sympathetic cardiac nerves). The axons of the nerves enter spinal cord at the level T1-T5 on the left side. By the synaptic contact, cardiac pain is reflected to the left part of the chest, shoulder and arm.

Two branches of the ascending aorta, the left and right coronary arteries, which arise from the left and right aortic sinuses (it is located at the origin of the ascending aorta) and supplies the heart. These arteries pass anteriorly, on each side of the root of the pulmonary trunk.

Relations and branches of arteries of the heart.

Clinical comments

Angina pectoris is a result of heart ischaemia and it is caused by coronary insufficiency. Myocardial infarction is a necrosis of part of heart muscle and it is caused by acute coronary insufficiency too. These diseases can be treated in pharmacological way, by balloon angioplasty or by coronary bypass surgery.

Almost all veins of the heart returns the blood to the coronary sinus, which then drains into the right atrium. Just only the smallest cardiac veins open directly to the chambers of the heart.

• Anterior cardiac veins are situated on the anterior surface of the right ventricle and pass across the coronary groove and return blood directly into the right atrium.
• Venae cordis minimae begins in the myocardium and opens into the chambers of the heart.

The coronary sinus is the main vein of the heart, which is situated in the posterior part of the coronary groove and receives blood from the following veins:

• Great cardiac vein begins at the apex and ascends in the anterior interventricular groove, where it lies together with the anterior interventricular branch (left coronary artery) and then drains into the coronary sinus.
• Posterior left ventricular vein is located on the inferior surface and opens into the coronary sinus on the left side of the middle cardiac vein.
• Middle cardiac vein begins in a similar maner as mentioned above, at the apex, but then ascends on the other side in the posterior interventricular groove (with posterior interventricular branch from right coronary artery) and opens into the right side of the coronary sinus.
• The small cardiac vein is situated in the coronary groove (together with the marginal branch of the right coronary artery) and drains into the coronary sinus to the right of the middle cardiac vein. Besides there are following veins of heart:
  • Left coronary vein
  • Oblique vein of left atrium
  • Right marginal vein
  • Right coronary vein
  • Anterior vein of left ventricle
  • Right atrial veins
  • Left atrial veins
  • Atrioventricular veins
  • Ventricular veins

Veins of the heart. Relations of the coronary sinus.

The mediastinum is divided for purposes of description into two main parts:

Division of the mediastinum.

The brachiocephalic trunk called as the innominate artery arises posteriorly to the manubrium of the sternum (at the level T4 or T5) and ascends superolaterally to the right. It divides (at the level T2 or T3) into the right common carotid and right subclavian artery.

The left common carotid artery arises posteriorly to the manubrium (to the left of the brachiocephalic trunk – at the same level), ascends to the left and returns to the neck.

The left subclavian artery arises from the arch just behind the left common carotid artery, ascends laterally to the left and is located anteromedially to the left lung and pleura. It leaves the thorax and enters into the root of the neck.

The thoracic duct begins from the cysterna chyli at the level T12 or L1, ascends through the aortic hiatus in the diaphragm and lies on the left side of the bodies of the inferior seven thoracic vertebra between the azygos vein and aorta. It crosses to the left at level T4-T6, then ascends and empties into the left brachiocephalic vein.

It receives lymph from inferior lymphatic vessels below the diaphragm, posterior mediastinal lymph nodes, intercostal lymph nodes, and the left side of the: head and neck, upper limbs, lungs, side of the heart and pericardial sac, trachea and Oesophagus (3/4 of body). It returns lymph to left venous angle (point of connection of the left subclavian and the left internal jugular veins). Following trunks emptie to thoracic duct: left subclavian trunk, left jugular trunk and mediastinal trunks (anterior and posterior).

The right lymphatic duct receives lymph from the right upper (supradiaphragmatic) side of body (1/4 of body). It returns lymph to the right venous angle (point of connection of right subclavian and right internal jugular veins). Following trunks empties to right lymphatic duct: right subclavian trunk, right jugular trunk and mediastinal trunks (anterior and posterior).

Thoracic lymph nodes consist of:

• Paramammary lymph nodes
• Parasternal lymph nodes
• Intercostal lymph nodes
• Prevertebral lymph nodes
• Superior phrenic lymph nodes
• Prepericardial lymph nodes
• Lateral pericardial lymph nodes

• Anterior mediastinal lymph nodes
• Posterior mediastinal lymph nodes consist of:
  • Pulmonary lymph nodes
  • Tracheobronchial lymph nodes
  • Superior tracheobronchial lymph nodes
  • Inferior tracheobronchial lymph nodes
  • Bronchopulomonary lymph nodes
• Paratracheal lymph nodes