LUNG CANCER: BASIC MEDICAL SCIENCE

Our two lungs provide a large surface area for the exchange of gas with the air around us. The alveoli of the lung provide this exchange surface, where the air can come into close association with the circulation. The alveoli are joined by a series of bronchioles and bronchi to the trachea that communicates with the environment via the oral and nasal cavities. The gases exchanged; Oxygen and Carbon Dioxide are carried in the blood by various means around the body to or form the lungs.

The bronchioles are less than one millimetre in diameter, unlike the rigid bronchi, they have no cartilage support. The epithelium is of a simple columnar ciliated type with only a few goblet (mucus secreting) cells. Surrounding this is a smooth muscle layer that spirals around the bronchioles. The bronchioles split up into terminal bronchioles and then respiratory bronchioles that are connected to the alveolar sacs by alveolar ducts. Alveolar sacs each give rise to individual alveoli, this is where most gaseous exchange takes place. Alveoli consist of surface epithelium, supporting tissue and blood vessels (mainly capillaries [C]). The surface epithelium is made up of Type I pneumocytes [P₁] (lining cells) and Type II pneumocytes [P₂] which secrete surfactant. Surfactant reduces surface tension within the alveoli preventing alveolar collapse during expiration.

Each Lung has a blunt apex, which projects up into the neck for about 2.5cm above the clavicle; a concave base that sits on the diaphragm; a costal surface corresponding to the chest wall; and a concave mediastinal surface, which is moulded to the pericardium and other mediastinal structures. The hilum is where various structures (bronchi, vessels and nerves) forming the root of the lung, communicate with the lung. It is found at the middle of the mediastinal surface.

The lungs are separated into lobes by fissures, the left lung is separated by the oblique fissure, running from the base upward and backward across the medial and costal surfaces until it cuts the posterior border approximately 6cm below the apex. This gives the left lung two lobes (upper and lower). The right lung is separated by an additional horizontal fissure, giving it three lobes, the additional lobe is called the middle lobe.

The lungs are each divided into ten anatomical, functional and surgical bronchopulmonary segments. Each segment is the subdivision of lung that is supplied by a segmental bronchus, segmental artery, autonomic nerves and lymph vessels. Venous drainage to each segment is via the segmental vein, which runs in the connective tissue between adjacent segments. Individual segments can be removed surgically if diseased.

The lung connective tissue, bronchi and pleura receive their blood supply from the bronchial arteries which branch from the aorta, blood drains into the azygos and hemiazygos vein via the bronchial veins.

The lymph structure of the lungs is important, as it is a significant route of metastatic spread.

The lymph vessels originate in superficial and deep plexuses. The deep plexus drains the deeper lung structures, travelling along the bronchi and pulmonary vessels, it communicates with pulmonary nodes in the lung which in turn drain into the bronchopulmonary nodes in the hilum. The superficial plexus lies beneath the visceral pleura and drains the surface of the lung and then drains into the bronchopulmonary nodes. The bronchopulmonary nodes drain out of the hilum into the tracheobronchial nodes and then into the bronchomediastinal lymph trunks.

The lungs are surrounded by the ribcage. The ribcage and associated muscles facilitate expansion of the lungs for inspiration and the relaxation required for expiration. These two repeated actions serve to refresh the air in the lungs to permit efficient gaseous exchange. Inspiration is achieved by expansion of the ribcage and lowering of the diaphragm. Ribcage expansion is usually achieved by the action of the scaleni muscles of the neck and the intercostal muscles. Under heavier breathing and particularly when in respiratory distress, these muscles are assisted by other accessory muscles; sternocleidomastoid, trapezius, levator scapulae, rhomboid muscles, serratus anterior and pectoralis minor. Expiration is usually facilitated by elastic recoil, but under stressful situations forced expiration, involving the quadratus lumborum, serratus posterior and latissimus dorsi takes place.

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About Microscope Enhanced Dentistry

Technology is emerging in all fields and professions at a rapid pace. Dentistry is no exception. The changes are providing excitement and innovation for the dental professional and patient alike. Two challenges today are to be able to choose the advances that are most meaningful to your personal practice of dentistry and to progress rapidly through the necessary learning curves to make technology useful on a daily basis. An important trend is the incorporation of higher levels of magnification and illumination into the operatory and the dental laboratory. This is usually done with the help of operating microscopes.
Microscope Enhanced Dentistry is just starting to become available in India. It will soon become a standard feature in advanced dental clinics in the future here in India as well as around the world.
Teeth are normally small structures like the eyes, ear and nose. ENT surgeons, Ophthalmic surgeons and Neurosurgeons nowadays routinely use an Operating Microscope or magnifying loupes/spectacles to do surgeries of greater precision and accuracy. Cataract surgery is routinely done with a microscope now a days.
It is stunning treat to watch which teeth which are only 1 sq. cm in size magnified to fill a TV screen 14 or 21 inches cross!! And the joy of seeing a smile is all the more gorgeous to watch on a large TV screen. A big smile is made much bigger by the magnification provided by the Microscope. Highly improved quality of the fillings, Root Canal Treatments's, Crown and Bridge preparations and various other procedures which can be done with the microscope make the patient smile even more! The patient's confidence in his dentist is hugely increased as he can see the problems in his teeth very clearly under brilliant light and magnification. They co-operate better during the treatment as they are able to see on a TV screen the whole procedure being undertaken on their teeth, and it also ensures better compliance with advice given.
Back, neck, and shoulder damage are a leading source of physical disability for dentists. The majority of these disabilities are due to years of poor posture and positioning as dentists struggle to see what they are doing. When you see dentists who work without magnification, you notice that they typically work in a bent-over position. Their torsos are twisted, and the lower back and shoulders are strained as they struggle to see what they are doing. The dentist who uses the microscope is much more comfortable and avoids un-due strain on his neck and back. The up-right posture can be maintained during almost all procedures, which is otherwise impossible thus improving ergonomics.
The use of the operating microscope in the field of dentistry has just started recently in western Europe and parts of America. The American Dental Association has made it mandatory and compulsory for higher post-graduate training in Endo-dontics or the root canal treatment speciality to be trained in the use of the Operating Microscope.
Since microscopes have been used for endodontic Root Canal Treatment's, extra canals called MB2's and other minute accessory canals have been found and treated effectively which were not possible before. Thus, the chances of failure of Root Canal Treatment becomes much lesser. While performing complicated procedures like failed Root Canal Treatment's and removal of broken files deep inside the roots of teeth are challenges which demand the use of a microscope. Teeth will failed RCT's can be re-treated with a second RCT and successfully saved, when done very carefully, and the chances of success are much higher when done under the microscope.
Microscopes strongly aids in spotting the fine dividing line between healthy and non healthy. Some times when the tooth decay happens with the help of caries detector dye, only the decay is removed and RCT is avoided , which initially looked that almost require a RCT with the naked eye. But now we can spot the difference because it is possible with the help of microscope to see much better and clearer under magnification.
Scaling or cleaning of the teeth done under the Microscope affords better removal of tartar and stains and cleaner teeth at the end. Periodontal flap surgery when done under the Microscope, is able to remove much more damaged tissue, with much less damage to nearby healthy tissue, and hence give a better result. Suturing of wounds done under the microscope is much finer and delicate, hence better scars, faster healing, less post-operative pain and discomfort is possible.
Preparation of teeth to fit a metal or ceramic artificial crown is a routine procedure done in every dental clinic routinely. If a microscope is used for this while preparing the tooth, the margins of the teeth are much more neater and precise, thus allowing a much better fit of the artifical crown, better a esthetics and longer life with less problems like leakage and failure. The crown can also be checked before fitting on to the tooth under the microscope to check for defects in shape, size and irregularities as well. Less tooth structure is removed as well if possible, because we can see more clearly.
The fitting of crowns and bridges is made very precise and hence the longevity of these is hugely increased.
Needless to say Microscope enhanced dentistry is wonderful revolution and is the direction in which dentistry is moving higher magnification allows the dentist to see better! This is a win-win situation for both patient and the doctor.
(The author is former I/C HoD Opoative Endodontis)

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