Introduction to The Respiratory System

The respiratory system is responsible for providing oxygen required for body cells. It has the function of carrying carbon dioxide waste. The muscular and skeletal systems are tasked with movements that make breathing possible. This is an efficient structured organ system, yet it has its weaknesses. The air can contain various particles, microbes, or allergens that can be hazardous to health. The respiratory system has delicate structures that are susceptible to severe damage. Respiratory disorders are among the most common of illnesses. Air that is inhaled transports to the trachea through the bronchi reaching the lungs. There are a total of two lungs in the human body. Each lung contains bronchioles, which are tube like in structure. These pipe structures cluster in alveoli The gases migrate the alveolar walls both to and from blood vessels. The intercostal  muscles as well as the diaphragm beneath the lungs allow for air to be drawn in and out. This happens in a particular time interval. Air enters through the nostrils and thus begins the process of respiratory function.
    The respiratory system contains both a upper and lower tract. The upper tract contains the nose, nasal cavity, paranasal sinuses, and pharynx. These networks of passages warm, filter, and humidify outgoing air. The lower respiratory tract houses the larynx, trachea, bronchi, bronchioles, and alveoli. Breathing requires respiratory reflexes. The brain's respiratory centers.Receptors must process the sensory information arriving that are sensitive to oxygen, carbon dioxide, and acidity levels present in blood and cerebrospinal fluid. Receptors are also delivering information to blood pressure receptors and stretch receptors in the lungs. This either lets it be known their is pain or nasal irritation. Breathing pattern can change in rate depending on the behavior of receptors. This can prevent the lungs from over inflating or act as a defense mechanism against harmful matter in the air. Breathing is a subconscious action, but emotions can change it. Feeling nervous could cause a person to breath fast than when they were calm. The common respiratory reflexes include coughing, sneezing, yawning, and hiccups.

These reflexes are reactions to the environment.  Coughing forcefully releases air from the lungs in order to clear the airways. Cough receptors will become irritated by inhaled particles or large amounts of mucus. Once the trachea and bronchi are cleared, normal function resumes. The cough happens with a deep breath causing the glottis to close entrapping the air in  the lungs. The diaphragm including other muscles contract. The result is pressure causes the glottis to open once more forcing out the contaminants. Mucus droplets aid in the elimination of bacteria and other particles. Coughing acts as a defense against foreign air born material that could be harmful to the body. Sneezing also acts in a similar manner. When irritation occurs from inhaled particles, odors, or infection large amounts of inhalation happen. The glottis closes while a person's eyes will close as well.  Contraction then causes air to be expelled from the nose and mouth. Yawning is involuntary and is learned even during embryonic development. It is a common trait among all vertebrate animals. When blood levels are showing an increase in carbon dioxide more oxygen in dawn into the lungs. Blood oxygen levels increase. Yawning may also allow for blood to cool while passing through the brain. 

Another know respiratory reflex are hiccups. These are nothing more than involuntary contractions from diaphragm. Hiccups could be evidence of the human evolutionary past when our early amphibious ancestors went between land and water. The glottis closing would have stopped water from going into the lungs and push it out through gills. A human fetus even hiccups and contains gill like structures. Surrounded by amniotic fluid  this helps protect the lungs from fluid getting inside of them. Hiccups are primarily induced by nerve activity that controls the muscle in the diaphragm.  

      The respiratory system  has specific structures that have various functions. The larynx has the role of securing the entrance to the trachea and housing the vocal cords. The larynx consists of nine pieces of cartilage. This includes thyroid, cricoid, epiglottis, arytenoid, corniculate, and cuneiform cartilages. The larynx is situated between the pharynx and trachea. The thyroid cartilage forms a mound beneath the skin of the neck. This is known as the laryngeal prominence ( Adam's apple ). This structure is more pronounced in men than in women. The cartilage is secured by support from muscles and ligaments. The hyoid bone acts as an anchor for the muscles supporting the larynx.Internally the larynx is a hollow chamber and this enables air to enter during breathing. The cartilage will tilt moving vocal cords producing speech.  What appears to be a simple process relies on a network of various structures. Branchioles  and air sacs are also important to the respiratory system. There are two main bronchi which are subdivided in the lungs. The right bronchus forms three secondary bronchi. The left bronchus only forms two. Gas exchange happens at the terminal point. 

    The pleural sacs are found as enclosed shields  lungs. They have two layers which contain parietal wall and a visceral wall. The visceral wall is located  beneath the lung, while the parietal is attached to the chest of the wall. This explains why the lungs are able to slide over the chest wall during breathing. The thin layer of lubricated fluid  that divides pluera enables this process without harm to the lungs. The diaphragm dome like in shape is a muscle that separates the chest and the abdomen. Along with the intercostal muscles these are the primary muscles that contribute to breathing. This reduces pressure on the thoracic cavity. This means the lungs have the ability to expand downward. The lower respiratory system has a lining which is a moist mucus membrane. Bronchi lined with columar epithelium are contributors to moving particles out of the lungs. The cilia of the columar epithelium act as an remover of possibly hazardous substances. This is an example of internal protection, but the body's twelve ribs act as a shield for the lungs and heart. The lungs are the most recognizable structures of the respiratory system. The human body has a total of two, which are cone structured in appearance. There is a difference between the right and left lung. The right lung as three lobes, while the left has only two. This allows for room for the heart. The right lung is only a little bit larger in comparison and averages 60% of lung volume. The pharynx is a structure that allows moistened air to pass through the throat. There are also other auxiliary structures that  collaborate in air passage. The nasopharynx enables the passage of air. Both the oropharynx and laryngopharynx  permit safe passage for food and various fluids. The concha present in the nasal cavity from the etmoid bone. This forms three ledges, which capture air borne particles and can increase the surface area of the naval cavity. 

    The respiratory system also enables phonation. This is the process of  an individual to produce speech sounds form the vocal cords. The vocal cords are made from two folds of mucus membrane stretched horizontally across the larynx. It is connected to thyroid cartilage in the front. The arytenoid cartilages are the support in the back. When the vocal cords close when  air coming through during exhalation, this causes vibration . The result is sound produced. These are just a few of the basic structures of the respiratory system. 

     The lungs are on the largest organs in the body and central part of the respiratory system. The lungs contain alveoli, which are clump like structures. Elastic and thin walled they have the shape of grapes. Macrophages are present on the outer surfaces. Macrophages are white blood cells responsible for protecting against air borne irritants. The alveoli also have  networks of capillaries. When oxygen comes through it gets into the blood by diffusion. Then it travels through the alveolar and capillary walls. Carbon dioxide diffuses another way from the blood into the alveoli. There is a total of 300 million alveoli present in the lungs. They provide a huge surface area  for gas exchange. It is estimated to be forty times greater than the body's surface. The pulmonary venule will take fresh high  oxygen blood, while the pulmonary arteriole gives used low oxygen blood.  The apex of the lung is the upper point, which projects just above the clavicle. The left primary bronchus is narrower and longer compared to the lobar bronchus. The lobar bronchus has to form one of two air ways. The segmental bronchus has to aerate the broncopulmonary segment. The pulmonary arteries must bring deoxygenated blood from the heart. The pulmonary veins have to send oxygenated blood to the heart. There is a total 30,000 terminal bronchioles in each lung. They branch out into either two or more respiratory bronchioles. The lungs are hard at work being the area of  gas exchange. 

         Oxygen is drawn into the body through the lungs. The process of gas exchange in the lungs starts with oxygen from the air dissolving into fluid lining  in the alveolus. It will then disperse through the blood capillary wall and alveolar wall. Oxygen  then shall enter the blood plasma and will bond with hemoglobin. Carbon dioxide will then diffuse from blood plasma and goes in air in the alveolus. The red oxygenated blood makes the journey through the aorta by pathway of the arteries reaching the body's tissues. Thin capillaries then are required to transport oxygenated blood. The newly delivered red blood cells the bind to  the body of each cell. The oxygen will  leave hemoglobin in the red blood cells. The diffusion will result in hemoglobin in the blood capillary walls and into the tissue cells. Carbon dioxide diffuses into the tissues of the cells, wall of the blood capillary and ends with going into the blood plasma.  

Cellular respiration also occurs in the human body. Blood sugar known as glucose is the body's primary energy source. Cellular respiration happens in every body cell when oxygen interacts with glucose. The result becomes energy released in chemical form. The product made form this is carbon dioxide and water which is called metabolic water. There is a difference in aerobic capacity between the sexes. Men have on average larger lungs and hearts, which give them higher aerobic capacity. Besides that there is no difference in the respiratory system between men and women. 

       Breathing is essential to organisms with a respiratory system. Bodily respiration is tasked with taking in air capturing oxygen, while removing used air and waste product through carbon dioxide. The actual movement depends on pressure in the lungs and the atmospheric pressure of the environment. The pressure differences occur due to an expanding chest and muscular action. The sternocledomastoid is a muscle that has to pull the clavicle and sternum upwards to enlarge the chest cavity. The pectoralis minor pulls the third. fourth, and fifth ribs in the body. The scalenes must elevate the upper ribs. Other muscles such as the external intercostals also contribute. The need to breath is dictated by the function of the nervous system. The brain stem generates responses on how best to regulate breathing. Breathing can alter the volume of the thoracic cavity. The lungs can become larger depending on inhalation or exhalation. Inhalation requires the use diaphragm, ribs, external intercostals and the sternum. This can enable the chest to expand, while the lungs can be stretched. Exhalation seems more passive in labor and action. The lungs recoil when the diaphragm, intercostals, and other muscles come to a state of relaxation. Abdominal pressure moves the diaphragm upward in the process. The lungs are then compressed to a point beyond the usual resting volume. Pressure can either be classified as either positive or negative. Negative pressure involves lung volume increasing as air pressure decreases. This means atmospheric pressure which is external is higher resulting in air being sucked in . Condition for positive pressure involve lung volume decreasing when exhalation occurs. Pressure is built up in the lungs causing air to be pushed out. This explains why air come out through the mouth and nose. This is the basic function of the respiratory system. Like other organ system it collaborates with other to the biophysical machine known as the human body.  

References 

Brewer, Sarah. The Human Body A Visual Guide To Anatomy. London: Quercus, 2012.     

  

Parker, Steve. The Human Body Book. New York : DK Publishing, 2013.