Introduction
The respiratory system can be termed as a biological system comprising of specific structures and organs that are used, by an organism, in the respiration process. It participates in the exchange together with intake of oxygen and carbon dioxide between an organism and its environment (Seeley, Stephens and Tate).
In vertebrates that breathe air, respiration occurs in the organs of respiration, lungs. The air passage to the lungs for supply of oxygen to the body is called inhalation, while the air passage away from the lungs to release carbon dioxide is called exhalation. In human beings, the anatomical characteristics of the system are bronchi, trachea, lungs, bronchioles, and diaphragm (Seeley, Stephens and Tate). There is passive exchange of oxygen and carbon dioxide molecules, through diffusion, between the blood and the external gaseous environment. This process of exchange takes place in the lungs’ alveoli air sacs (Maton, Jean and Susan).
The respiratory system consists of the nose, bronchi, mouth, nasopharynx, sinuses, trachea, larynx, lungs and alveoli. It contains upper, as well as lower respiratory tracts. The upper tract has the respiratory organs that are situated on the outside of the chest cavity. These include upper trachea, larynx, pharynx, nose and nasal cavities (Seeley, Stephens and Tate). The lower tract, on the other hand, is composed of organs that are situated within the chest cavity, and these include the bronchi, bronchioles, alveoli, lower trachea and the lungs. The lower bronchi parts, the alveoli and bronchioles, are all situated in the lungs. It is in the alveoli that gas exchange occurs. The pleura can be termed as a membrane, which covers the lungs. The muscles forming the chest cavity are as well component of the lower respiratory tract. The centre of respiration in the brain that is situated in the medulla oblongata is responsible for regulation of breathing.
Development of the respiratory system
During pregnancy, the respiratory system is normally dormant in the human fetus. At birth, it functions fully on exposure to air, even though a number of lung development and growth go on all through childhood. Premature birth may result in infants with lungs that are under-developed. These lungs indicate partial development of the alveolar type II cells. Fundamental scientific studies agree on the potential for utilizing steroids as a way of promoting type II alveolar cells development (Sullivan and Orgeig).
Physiology of the respiratory system
In the physiology of respiration, ventilation is the rate of entry or exit of gas into or from the lung. Ventilation takes places under the regulation of the autonomic nervous system from the brain stem parts, the pons and the medulla oblongata. This brain region makes the regulatory center of respiration (Seeley, Stephens and Tate). The sections are the apneustic center, the pneumotaxic center, and the ventral and dorsal respiratory groups. This section is particularly sensitive in infancy, and the neurons may be damaged if the infant is violently shaken (Van De and Kent). The rate of breathing rises with the carbon dioxide concentration in the blood that is detected by central chemoreceptors in the medulla, as well as peripheral chemoreceptors situated in the carotid artery and aorta. Exercise also raises the rate of respiration because of the proprioceptors action, the body temperature increase, the epinephrine release, and motor impulses arising from the brain. Additionally, it can rise because of raised inflation in the lungs that is detected by stretch receptors (Van De and Kent).
Inhalation is started by the diaphragm and backed by the intercostal muscles located externally. Resting respirations that are normal are 10 to 18 breaths each minute, with 2 seconds time period. In vigorous inhalation or in approaching failure of respiration, respiration accessory muscles are enrolled for back up (Seeley, Stephens and Tate). These comprise of platysma, sternocleidomastoid, and the neck scalene muscles. Latissimus dorsi and pectoral muscles are also accessory muscles (Van De and Kent). During normal conditions, the diaphragm acts as the key primary inhalation driver. When it contracts, it causes expansion of the ribcage, as well as the downward movements of the contents of the abdomen. This leads to a negative pressure and larger thoracic volume within the thorax. As the chest pressure falls, there is movement of air into the conducting zone where the air is warmed, humidified and filtered as it moves to the lungs. In forced inhalation, the accessory muscles and external intercostal muscles help in further expansion of the thoracic cavity (Van De and Kent).
Exhalation can be termed as a passive process, but active exhalation is attained by the internal intercostal and the abdominal muscles. In this process, air is breathed out. The lungs are naturally elastic such that as they recoil from the inhalation stretch air moves back out until the chest and the atmosphere pressures are at equilibrium. In forced exhalation, expiratory muscles create thoracic and abdominal pressure that forces air out of the lungs (Van De and Kent).
The key respiratory system’s role is gas exchange between the circulatory system of an organism and the external environment. In human beings, this exchange enhances blood oxygenation with a concomitant removal of gaseous metabolic wastes including carbon dioxide from the circulation (Jon). As gas exchange takes place, the body’s acid-base balance is maintained as part of homeostasis. If there is no proper maintenance of ventilation, there may occur two opposing conditions namely, respiratory alkalosis and respiratory acidosis (Jon).
On inhalation, gas exchange takes place at the alveoli, the lungs’ fundamental functional component. The walls of alveoli are exceedingly thin and comprise of a single epithelial cells layer near the pulmonary capillaries that comprise of a single endothelial cells layer. The two cell types proximity permit gases permeability, thus, gas exchange. This gas exchange mechanism is performed by the simple pressure difference phenomenon (Jon).
Functions of the respiratory system
The fundamental respiratory system organs are lungs that play a role in uptake of oxygen and expulsion of carbon dioxide in the process of breathing. Red blood cells carry out collection of oxygen to the body parts that require it from the lungs (Seeley, Stephens and Tate).
Immune functions
Epithelial cells of the airway can produce various molecules that help in the protecting the lungs. Secretory immunoglobulins, defensins, collectins and other proteases and peptides, reactive oxygen and nitrogen species are all created by epithelial cells of the airway. The secretions produced can directly act as antimicrobials to protect the airway from infection (Seeley, Stephens and Tate). The epithelial cells of the airway also produce various cytokines and chemokines that enroll the traditional immune cells infections site. Majority of the respiratory system has mucous membranes containing mucosal-associated lymphoid tissue that forms white blood cells (Jon).
Endocrine and metabolic functions of the lungs
The lungs also play several metabolic roles. They have a fibrinolytic system, which disintegrates clots within the pulmonary vessels. They produce various substances that get into the systemic blood in the arteries, and they get rid of other substances out of the systemic blood in the veins that get to them through the pulmonary artery (Jon). Prostaglandins are eliminated from the blood flow, though they are as well produced in the lungs and discharged into the blood upon stretching of the lung tissue. In the pulmonary circulation, the lungs as well trigger decapeptide angiotensin I to aldosterone-stimulating octapeptide angiotensin II. The reaction also takes place in other tissues, though it is outstanding in the lungs (Jon).
The gas movement through the mouth, pharynx and larynx permits phonation in humans. This occurs through the syrinx. The respiratory system is also involved in temperature control (Jon).
The respiratory system diseases
Respiratory diseases are commonly diagnosed by use of diagnostic tools, which include pulmonary function test, chest x-ray, as well as computerized tomography scan. A bronchoscopy can as well be done through insertion of a bronchoscope into the air passage, for examination of inflammation, tumors, bleeding or other abnormalities (Kim). Respiratory systems’ conditions and diseases can arise from the inhalation of foreign substances, for instance, chemicals, allergens, cigarette smoke, as well as other irritants. Environmental factors, however, do not produce respiratory diseases in everyone, and genetics as well plays a part in respiratory diseases development (Kim).
Asthma leads to breathing problems because of inflammation of bronchioles and bronchi, which results in a limitation, in the flow of air into the alveoli. Pollution of air, factory fumes, tobacco smoke, infections, cleaning solvents, foods, pollens, exercise, cold air, medications and chemicals are some common asthma activates (Kim). Cancer of the lung is often linked to smoking, but it can cause be present non-smokers, as well. Like all cancers, cancer of lung results from the uncontrolled abnormal cells’ growth. A number of other illnesses that involve the respiratory system are respiratory tract infections, which include pneumonia, influenza, and tuberculosis (Kim).
Works Cited
Herlihy, B. Anatomy & Physiology Online for The Human Body in Health and Illness (Text, User Guide and Access Code Package). 3rd. St. Louis. Mo: Elsevier, 2007.
Jon, Barron. The Anatomy of The Respiratory System. 2 February 2009. 5 March 2014. <http://jonbarron.org/article/anatomy-respiratory-system#. Uxdzs4WPuB4>.
Kim, Ann Zimmermann. Respiratory System: Facts, Function and Diseases. 22 August 2012. 6 March 2014. <http://www.livescience.com/22616-respiratory-system.html>.
Maton, Anthea, et al. Human Biology and Health. Prentice Hall: Englewood Cliffs, 2010.
Seeley, R., T. D. Stephens and P. Tate. Anatomy and Physiology. 6th. New York: The McGraw Hill Companies, 2004. Print.
Sullivan, L. C. and S. Orgeig. "Dexamethasone and epinephrine stimulate surfactant secretion in type II cells of embryonic chickens". American journal of physiology." Regulatory, integrative and comparative physiology 281 (2001): R770–7.
Van De, Graaff and M. Kent. Human Anatomy. Burr Ridge: McGraw Hill Publishing, 2002.
