Anatomy, Physiology and Pathophysiology of Tuberculosis

This case study explores the anatomy, physiology, and pathophysiology of tuberculosis. It discusses the normal anatomy of the respiratory system, the physiology of respiration, and the mechanism of pathophysiology in tuberculosis. It also covers prevention and treatment options for this infectious disease.

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ANATOMY, PHYSIOLOGY AND PATHOPHYSIOLOGY OF TUBERCULOSIS
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INTRODUCTION
Tuberculosis is a primarily respiratory infection which is caused by mycobacterium
tuberculosis. This may however spread to extrapulmonary sites such as the bones and the brain.
It affects the various body systems particularly the respiratory system. It is spread through air
droplets when one coughs, sneezes and prolonged contact with infected person. There are two
phases latent where one has the microorganism but noninfectious as the immune system has
controlled it. The infectious patient with tuberculosis when the immune system is unable to
control the organism. The macrophage phagocytoses the bacilli in a granuloma. When the
immune system weakens the granuloma now known as the Goon tubercle releases the bacilli and
the person is now infectious. Due to mutation of the microorganism or nonadherence to
medication there have been reported cases of multi drug resistant tuberculosis and extensively
drug resistant tuberculosis.
According to the World Health Organization (2018) tuberculosis is one of the leading
infectious causes of death in the world. In 2017,1.6 million of 10 million people infected with
tuberculosis succumbed. Tuberculosis has been associated with immune suppression such as
HIV/AIDs and people taking immunosuppressants due to different conditions. In the United
States there were 9105 new cases of tuberculosis in 2017(Center for Disease Control,2018). This
was reported in all the states across the country. The mortality rate however was also increased
from the year 2016.The diagnosis of tuberculosis is done through the Mantoux test also known as
tuberculin test.The definitive diagnosis is through chest xray,positive culture test by sputum and
molecular tests.Bacille Calmette Guertin is a vaccine given to provide immunity against
tuberculosis depending on different country policies.
NORMAL ANATOMY OF RESPIRATORY SYSTEM

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The respiratory system contains various parts which aid in the gaseous exchange. It is
divided into the upper and lower respiratory system; the upper respiratory is composed of the
nose,pharynx,larynx,epiglottis and the sinuses.The nose is well adapted for air entry through
small hairs which filter dust particles and warm air through the rich blood capillary supply.The
air moves to the pharynx and larynx which are the vocal cords.The epiglottis prevents food from
entering the lower respiratory tract.The lower tract consists of
trachea,bronchi,bronchioles,alveolar ducts,alveolar sacs and the alveoli.The trachea which is
cartilaginous bifurcates into two whereby the right bronchus is wider than the left
bronchus(Couture, 2017).The bronchus divides into lobar and segmental bronchus.The
bronchioles consist of smooth muscle which constrict and dilate during air entry and exit.The
right lung has three lobes while the left lung has two lobes;it is further divided into lobules and
segments.There are type I and type II types of alveoli.The alveoli are the primary site for gaseous
exchange and they are adapted by a high surface area,presence of moisture and rich blood
supply.
The system is adapted to protect against infections by presence of mucus produced by
goblet cells in the epithelium.The cilia also have a brush like activity which expel the trapped
paticles.Macrophages also phagocytose any microorganisms that may be present(Guilliams,
Lambrecht & Hammad, 2013)The pleural fluid reduces friction in the pleural cavity during
breathing.The primary muscles for respiration are diaphragm and intercostal muscles.The blood
supply to the lungs are the intercostal arteries while the nerve supply is through pulmonary
plexus from the sympathetic and parasympathetic fibers.
NORMAL PHYSIOLOGY OF RESPIRATORY SYSTEM

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Respiration is controlled by centers in the medulla and the pons; the chemoreceptors also
detect change in blood pH which also influence respiration. Respiration depends on these two
anatomical sites and the anatomical sites for effective gaseous exchange. The positive pressure in
the atmosphere force air rich in oxygen into the nose and the respiratory tract. The intrapleural
pressure is less than the intrathoracic and intrapulmonary pressure to prevent lung collapse.
Gaseous exchange occurs in the alveoli which has a single membrane to enhance oxygen
diffusion into the red blood cells while carbon (IV)oxide enters the alveoli for expiration.
The lungs compliance refers to the ability of the lungs to expand to a certain extent and
this is affected by various conditions. Ventilation perfusion ratio refers to the amount of air that
reaches the lungs versus the blood that is in the capillaries for gaseous exchange. This is
important as a decreased ratio means that the patient is not adequately oxygenated leading to
hyperventilation. There are various terms used to describe the lung volume; tidal volume refers
to the air inspired and expired during quiet breathing normally 500 mls.
MECHANISM OF PATHOPHYSIOLOGY
Mycobacterium tuberculosis is spread through air droplets which are inhaled through the
nose to the alveoli in the lungs. The immune response to the bacilli is phagocytosis by the
macrophages and inflammation in the alveoli. However, some bacilli remain in the alveoli in
tubercles which are calcified. This decreases the surface area for gaseous exchange although the
patient remains asymptomatic. The Ghon complex is diagnosed in an x-ray film. When the
immune system is lowered for example in HIV/AIDS the tubercle releases the bacilli causing
reactivation an infection.

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The tubercle breaks down the heavy bacterial load when the patient coughs spreads to
other bronchioles and may infect other people. The formation of the tubercle within the lung
tissue results in caseous necrosis whereby the alveolar wall changes to be fibrotic minimizing its
efficiency in gaseous exchange (Daffé,2015). The bacilli affect the pleural space causing
pleuritis and consequently pleural effusion. Due to the repeated inflammation and fibrosis the
patient may develop bronchiectasis where they are unable to clear the lung secretions
(Byrne,Marais, Mitnick, Lecca & Marks, 2015).
During the immune system response, the lung tissue undergoes inflammation which
results in fibrosis. This means there is restriction of the lung expansion during inspiration and
expiration decreasing the forced vital capacity(Ravimohan,Kornfeld,Weissman & Bisson,
2018).Airflow is restricted due to the tissue damage which may involve vascular structures
resulting in coughing and chest pain as the oxygen demand is higher than the supply. Ventilation
perfusion ration mismatch occurs in pulmonary tuberculosis due to the destruction of alveoli
which are the primary sites for gaseous exchange. The granuloma in the lung tissue causes
scarring of the tissue which consequently results in decreased sites for gaseous exchange.During
radiology there is visualization of fibrotic bands which are due to inflammation process of the
lung parenchyma which cause lung restriction and decreased airway flow into the lungs.Due to
the restriction of the lung tissue the forced expiratory volume/forced vital capacity is
decreased(Tarigan, Pandia,Eyanoer, Tina, Pratam & Fresia,2018)
PREVENTION
The most important step is to vaccinate infants against tuberculosis through the BCG
vaccine at nine months(Nguipdop-Djomo,Heldal, Rodrigues, Abubakar & Mangtani, 2016)
Ventilation is very important as it allows for air exchange in crowded spaces where there may be

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infected persons and airdroplets.This is important in crowded places such as prisons, buses and
meetings.Obseving good hygiene for example covering your mouth while sneezing ,the infected
person reduces contact with the uninfected persons. This may also necessitate the use of a mask
by the infected person. The health care workers also are involved in diagnosis and contact tracing
to ensure anyone around the infected person is healthy and takes the necessary precautions while
caring for the patient. In multiple drug resistant tuberculosis and extensive drug resistant
tuberculosis the patients are isolated during treatment to avoid further spread. Health care
workers involved in patients care should be protected by enhancing use of protective gear and
safe handling of specimens during collection.
TREATMENT
The treatment of tuberculosis consists of two phases; the intensive phase and the
continuous phase. The medications used are isoniazid, rifampicin,pyrazinamide,ethambutol over
a period of 6 to 9 months. During the intensive phase a combination of
isoniazid,rifampicin,,pyrazinamide and ethambutol is used lasting 2 months and the continuos
phase lasting four months a continuation of rifampicin and isoniazid is continued. Isoniazid
causes peripheral neuropathy, and this is treated by administering vitamin B6 to ease the
symptoms the patient is going through. In multi drug resistant tuberculosis and extensive
multidrug resistant tuberculosis second line generation anti-Tb drugs are used for example
ciprofloxacin,kanamycin,amikacin(World Health Organization,2016). .However this medications
have high toxicity levels,harsh side effects,less efficacious and they are expensive.Counselling
before drug regimen is began is important to ensure drug adherence.Patients on treatment are
prone to stop taking medications after the symptoms subside and due to increased undesired side

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effects. This increases drug resistance and spread of infection as they are still contagious in the
intensive phase.
CLINICAL RELEVANCE
Treatment of tuberculosis is important as it there are high mortality rates if left untreated.
This is also because the disease is a comorbidity of a lowered immune system and the body
defense mechanisms are low. The trends currently are increased cases of multidrug resistance
tuberculosis and extensive drug resistance tuberculosis due to poor drug adherence and
resistance. There is need for research in terms of improving undesired side effects of the drugs.
Drug susceptibility testing is conducted to ensure that the patients are susceptible to medications
and decrease the chances of resistance(Xie,Chakravorty,Armstrong, Hall, Via,Song &
Gao,2017).
CONCLUSION
Mycobacterium tuberculosis is causative organism of tuberculosis. These bacilli form a
tubercle and granuloma due to immune response by the macrophages. In lowered immunity the
bacilli are released causing reactivation of disease. The alveoli are the primary site of infection
and it can be extrapulmonary for example in the brain, joints, liver and peritoneum(Lee, 2015).
The treatment of tuberculosis is 6 to 9 months depending on the nature of infection. This can be
prevented by ventilation of crowded rooms, drug adherence until completion, avoid spread air
droplets by covering mouth while sneezing and when necessary isolation.

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Daffé, M. (2015). The cell envelope of tubercle bacilli. Tuberculosis, 95, S155-S158.
Guilliams, M., Lambrecht, B. N., & Hammad, H. (2013). Division of labor between lung
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Lee, J. Y. (2015). Diagnosis and treatment of extrapulmonary tuberculosis. Tuberculosis and
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Nguipdop-Djomo, P., Heldal, E., Rodrigues, L. C., Abubakar, I., & Mangtani, P. (2016).
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Ravimohan, S., Kornfeld, H., Weissman, D., & Bisson, G. P. (2018). Tuberculosis and lung
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