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Sunday, May 26, 2019

The Respiratory System

         The Respiratory System






The Respiratory System





Since the cells of our body cannot be deprived of oxygen, during breathing we must constantly oxygenate our bodies. This generally involuntary action, governed by specialized brain stem neurons, is to transport the external air into the deeper lungs, thanks to the tree network of the lower respiratory tract. These innumerable ramifications make up most of the lung mass, the main organs of respiration




The Organs of the Respiratory System



The Respiratory System



The respiratory system consists of a series of ducts intended for the transport of external air. alveoli of the lungs, where gas exchange takes place. We distinguish the upper forms of breathing, including the nasal cavity and pharynx and lower passages (larynx, trachea, bronchi and lungs)



Functional Anatomy of the Respiratory System


The respiratory system can be divided into three main groups of structures: the airways, the muscles involved in breathing and the lungs. Discover these three sets of structures and organs of the respiratory system by dragging and dropping them into the box on the right



Nose and nasal cavity


It is a space behind the nose which is divided longitudinally by a thin wall. At the front,  the only visible part of the respiratory system  is the nasal cavity forms the nose. The human nose features in its anatomy and morphology between different racial and ethnic groups. Structurally, the nose can be divided into the external part which is actually called the nose and the internal portions are the nasal cavities (nostrils; cavum nasi). At the base of the nose there are two openings called nostrils (anterior nostrils, cant. Naris) and are separated from the cartilage of the nasal septum (vertebral column). The nostrils are a portal where air and particles enter the nasal cavity. Its shape can be very elliptical or circular, which varies between people of different ethnic backgrounds and races


Pharynx


It is a funnel-shaped tube about 13 cm long that connects the nasal cavity and mouth with the esophagus and larynx. It serves as a passageway for air and food and is generally known as a throat. Structurally, the pharynx can be divided into three anatomical parts based on their position, which are the nasopharynx (posterior to the nasal chambers), the oropharynx (posterior to the mouth) and the laryngopharynx (posterior to the pharynx). The pharynx serves to provide a passage to both the digestive and respiratory tracts, as food and air pass through it. Food or air is directed through the correct passage, either the esophagus or the trachea


Larynx


Or the "voicemail", has a maximum length of 5 cm. It forms the cross between the pharynx and the trachea and houses the vocal cords. The larynx conveys air and food into the appropriate tubes: the esophagus for food and the trachea for air. It is located in the anterior neck, connecting the hypopharynx with the trachea, which runs vertically from the tip of the epiglottis to the lower edge of the cricoid cartilage. The ciliated mucous lining of the larynx further contributes to the ability of the respiratory system to eliminate foreign particles and warm and moisten the inhaled air (the same physiological characteristic of the nasal cavity)

Pharynx or larynx? The larynx and pharynx (commonly called throat) are part of the upper respiratory tract together with the nasal cavity and the oral cavity. Enter each of the following organ names and features in the appropriate column of the table, depending on whether they are associated with the larynx or pharynx


The Trachea


It is a movable flexible tube approximately 12 cm long. Connect the larynx to the bronchi. This tube is made up of C-shaped stacked cartilage rings. The trachea is divided into the main bronchi (primary bronchi) in the hull, with the right bronchi wider, shorter and more vertical than the left bronchi (average lengths of ∼ 2.2 cm and ∼ 5 cm respectively). The main right bronchus forks posteriorly and inferiorly in the bronchus of the right upper lobe and in an intermediate bronchus. This bifurcation occurs earlier in the right lung than in the left lung in all models

The left bronchus passes inferolaterally at a greater angle than the vertical axis with respect to the right bronchus. It is located anterior to the esophagus and thoracic aorta and lower than the aortic arch. Each main bronchus leads to the lung from its respective side. The main right bronchus is divided into three (secondary) lobular bronchi (bronchus of the upper right lobe, bronchus of the right middle lobe and bronchus of the right lower lobe) while the main left bronchus is divided into two (bronchus and bronchus of the left upper lobe) . of the lower left lobe). Each lobar bronchus acts as an airway for a specific lung lobe. When the incoming air reaches the end of the trachea, it is warm, clean of most impurities and saturated with vapor


The bronchi and subdivisions


The air passages in the lungs branch out and branch out again, about 23 times in total. This branching airway pattern is often called the bronchial or respiratory tree. The bronchial tree is the site where the structures of the conductive area give way to the structures of the respiratory area


Conductive zone structures

The trachea forms through dividing the left and right main (primary) bronchi. Each bronchus runs obliquely into the mediastinum before diving into the medial (ilyl) depression of the lung on its side. The main right bronchus is wider, shorter and more vertical than the left one, therefore it is the most common place to lodge an inhaled foreign object. Once inside the lungs, each main bronchus is divided into lobular (secondary) bronchi, three on the right and two on the left, each of which provides a lung lobe

The lobular bronchi are divided into segmental bronchi (tertiary bronchi), which provide the bronchopulmonary segments. From each lobe Technically there are ten bronchopulmonary segments in each lung, however in the left lung some of these segments merge and there are only eight bronchopulmonary segments. The bronchi divide continuously into smaller and smaller bronchi up to about 23-24 generations of divisions of the main bronchi. As the bronchi shrink, their structure changes:

• Modification of support structures

The cartilaginous rings that support the branches become irregular cartilage plates and eventually disappear when the bronchioles (∼ 1 mm in diameter) are reached. When the bronchi eventually lose all support (usually between 12-15 generations), the airways are called bronchioles. However, elastic fibers are found on the walls of the tube along the bronchial tree

• Changes in the type of epithelium

The epithelium changes from columnar to columnar pseudostratification and therefore cuboidal in the terminal bronchioles. There are no cells that produce eyelashes or mucous membranes in the bronchioles and foreign particles are removed from the macrophages located in the alveoli instead of the mucociliary action. The amount of smooth muscle in the walls of the tube increases when the ducts become smaller

• Increase in the amount of smooth muscles

The passage from the trachea, which forks into the main left and right bronchi, which divide into the lobe bronchi, then segmental, and continues this process of bifurcation to the terminal bronchioles (which are the smallest airways without alveoli) conductive airways. In this area the exchange of gas does not take place because no alveoli are present and contributes to the anatomical dead space which occupies about 150 ml of volume


Tree The tracheobronchial tree is the structure of the trachea, bronchi and bronchioles that make up the upper part of the airways of the lung


Respiratory area structures:

Defined by the presence of thin-walled air pockets called alveoli (small alveolar cavity), the respiratory zone begins when the terminal bronchioles feed on the respiratory bronchioles inside the lung. The respiratory bronchioles lead to sinuous alveolar ducts, the walls of which are made up of diffuse rings of smooth muscle cells, connective tissue fibers and pocket alveoli. The alveolar ducts lead to terminal groups of alveoli called alveolar sacs


The lungs and pleura


Lung Anatomy




The Respiratory System



The lungs of children are pink and the lungs of adults are pinkish gray. At maturity, each lung has a volume of over 2 liters. The two lungs featur slightly in shape and size, due the apex of the heart is slightly to the left of the median plane. The left lung is smaller than the right one and the cardiac notch forms a concavity in its medial aspect and houses the heart. The thoracic cavity is covered by a body membrane called the parietal pleura, while the surface of the lungs is covered by a visceral pleura. The continuous branching of the bronchial tree causes the lung tissue that increasingly occupies the pleural cavity, covered by the visceral pleura. The endoderm-coated bronchial tree becomes a splanchnic mesoderm that forms cartilage, fascia, smooth muscle and pulmonary vessels

The lungs include bronchi, bronchioles, lobes, pulmonary vesicles and alveoli. Its function is to allow the exchange of gas between air and blood. There are no muscles in the lungs. The right lung is divided into three lobes and the left lung is divided into two lobes due to the location of the heart

The alveolar region of the lung includes respiratory bronchioles (divided by terminal bronchioles and with only occasional alveoli in their walls) and alveolar ducts (completely lined with alveoli). This area is called the respiratory zone and gas exchange occurs here. The distance from the terminal bronchiole to the distal bed is only a few mm, but the respiratory area constitutes most of the lung, its volume is approximately 2.5 to 3 L


Blood supply and lung innervation

The lungs are perfused by two circulations, the pulmonary and the bronchial ones, which differ in size, origin and function. Systematic venous blood that is oxygenated in the lungs is released from the pulmonary arteries


The pleuras

The pleura form a thin double layer serosa. The layer called parietal pleura covers the chest wall and the upper aspect of the diaphragm. Continue around the heart and between the lungs. The pleura spreads when the layer called the visceral pleura covers the outer surface of the lung, dips and aligns its crevices. The thin space between the two pleural membranes is called the pleural cavity, which is filled with a clear fluid called the plural fluid to minimize friction between the tissues and provide surface tension in the pleural cavity. The water molecules in the pleural fluid allow the two pleural membranes to adhere to each other, to prevent the collapse of the lungs

The diaphragm: it is one of the main muscles involved in breathing. It is located at the base of the lungs. The diaphragm contracts during inhalation and expands during exhalation. The diaphragm plays a more important role in men than in women during breathing

The heart is the major muscular organ of the circulatory system. Although not part of the respiratory system, the two systems work closely together. The heart is located between the lungs and the center of the thoracic cavity (thorax)



Breathing


                        (Exchange between air and blood)


Contractions of the diaphragm and intercostal muscles control inspiration, which carries air to the lungs. However, no muscle work is required for the expiration, which expels the carbon dioxide produced by the cells. At the ends of the bronchial tree there are small cavities, the pulmonary alveoli, in close contact with the blood capillaries. The alveoli are so numerous that their total area exceeds 100 m2. Along this surface is the exchange of gas between air and blood



Breathing Mechanisms


The Respiratory System




Lung breathing or ventilation consists of two phases: inspiration, the period in which air flows to the lungs and the expiration, the period in which gases leave the lungs. The gas law states that gas molecules always spread from an area of ​​higher pressure to an area of ​​lower pressure

Inspiration

It is the active part of the breathing process, which started from the respiratory control center in the medulla oblongata (brain stem). Activation of the marrow causes a contraction of the diaphragm and intercostal muscles which leads to an expansion of the thoracic cavity and a decrease in pressure in the pleural space. As the external intercostal muscles contract, the chest volume increases, which decreases the pressure inside the lung (intraalveolar pressure) due to Boyle's law. When intra-alveolar pressure drops below atmospheric pressure (758 mmHg versus 760 mmHg respectively), the gas law states that gases move from the environment to the lungs

Expiration 

It is a passive event due to the elastic recoil of the lungs. A passive process in which the elastic tissues of the lungs and diaphragm retract to their original position, while the diaphragm and external intercostal muscles relax and move away, the volume of the chest decreases, increasing the intra alveolar pressure (again due to Boyle's law), when intra-alveolar pressure is As it rises above atmospheric pressure (762 mmHg versus 760 mmHg, respectively), the gases move from the lungs into the environment (again due to the gas law)



The role of the nose in breathing


Inspired air enters the body through the nostrils and passes through the nostrils to get the pharynx. During this trip, it is filtered by the nose hairs, which hold more thick. The mucus that lines the nostrils also retains unwanted particles and helps moisten the air. At the end of the small blood vessels, be careful to warm the cold air before it enters the lungs



Pulmonary ventilation


It consists of inspiration and expiration, it is a mechanical process that depends on changes in volume in the thoracic cavity. It is the mechanism by which air is exchanged between the atmosphere and the alveoli. Air is exchanged due to the expansion and contraction of the lungs

Inspiration

Visualize the thoracic cavity as a box full of gas with a single inlet at the top, the tubular trachea. The volume of this table is variable and can be increased by expanding all its dimensions

• Diaphragm action:

When the dome diaphragm contracts, it moves downward and flattens. As a result, the upper-lower dimension (height) of the thoracic cavity increases

• Action of the intercostal muscles: 

The contraction of the external intercostal muscles raises the rib cage and raises the sternum. The contraction of the diaphragm is lowered, widening the intrapleural cavity, the elevation of the ribs also expands the intrapleural cavity, these factors decrease the pressure of the intrapleural cavity: therefore, air flows into the lungs (inspiration)


Expiration

During the expiration, the diaphragm relaxes, the ribs are lowered, this increases the pressure of the intrapleural cavity, this causes the movement of the air out of the lungs, normal silent breathing is obtained entirely by the movement of the diaphragm. About 6 liters of gas per minute enter and leave the lungs, ventilation can increase up to almost 100 liters per minute during peak exercise



Gas Exchange between Blood, Lungs and Tissues:


The respiratory membrane is made up of the walls of the alveoli and capillaries, where both are made of simple squamous epithelium, thin enough to allow the diffusion of gas called gas exchange. The exchange of gas during the breathing process takes place in the alveolus on its surface which separates the alveolus from the capillary. In addition, each alveolus is smaller than a grain of salt, in which there are about 300 million of them in the lungs



  • External breathing: occurs in the lungs to oxygenate the blood and remove CO2 from the deoxygenated blood. O2 diffuses from the alveoli to the capillaries, while CO2 diffuses from the alveoli to the alveoli
  • Internal breathing (tissue breathing). It occurs in the body's tissues to supply O2 to tissue cells and remove CO2 from the cells


Regulation and control of breathing

To maintain normal levels of partial pressure of oxygen and carbon dioxide, both the depth and the respiratory rate are precisely regulated. The basic elements of the respiratory control system are (1) strategically placed sensors (2) central controller (3) respiratory muscles



Breathing control:

Although our tidal-like breathing appears so wonderfully simple, its control is more complex than you think. The upper brain centers, chemoreceptors and other reflexes modify the basic respiratory rhythms generated in the brain stem. Control of respiration mainly involves neurons in the reticular formation of the medulla and bridge. Since the medulla lengthens the respiratory rate, we will start there


Central controller:


• Medullary respiratory centers: Neurons grouped into two areas of the medulla oblongata seem to be of fundamental importance in breathing. These are (1) the dorsal respiratory group (DRG), located dorsally near the root of the cranial nerve IX, and (2) the ventral respiratory group (VRG), a network of neurons that extends into the ventral brain stem from the spinal cord to the pons-medulla junction

• Pontine respiratory centers: Called a pneumotaxic center, although VRG generates the basic respiratory rhythm, the Pontine respiratory centers influence and modify the activity of spinal neurons


Respiratory muscles


The diaphragm, intercostal muscles and other accessory respiratory muscles work in coordination for normal breathing under the central controller. There is evidence to suggest that in preterm infants this coordination is not mature enough and this may be responsible for the sudden infant death syndrome


Sensors


• Mechanoreceptors: these receptors are located on the walls of the bronchi and pulmonary bronchioles and the main function of these receptors is to prevent excessive swelling of the lungs

• Chemoreceptors: the respiratory system maintains the concentrations of O2, CO2 and the pH of body fluids within the normal range of values. Any deviation from these values ​​has a marked influence on breathing. Chemoreceptors are specialized neurons activated by changes in O2 or CO2 levels in the blood and brain tissue


Central chemoreceptors are associated with respiratory centers. CO2 combines with water with carbonic acid, which in turn releases H + ions into the CSF. Stimulation of these areas increases alveolar ventilation. Existence of peripheral chemoreceptors in the carotid and aortic bodies. It indicates that,  these chemoreceptors detect a low concentration of O2. When the O2 concentration is low, alveolar ventilation increases



Homeostatic interrelationships between the Respiratory System and Other Body Systems



Nervous system: the medullary and pontine centers regulate respiratory rate and depth; Stretch receptors in the lungs and chemoreceptors provide feedback

Endocrine system: the angiotensin converting enzyme in the lungs converts angiotensin I to angiotensin II. Epinephrine dilates the bronchioles

• Cardiovascular system: blood is the means of transport of respiratory gases

• Lymphatic system / Immunity: the immune system protects the respiratory organs from bacteria, bacterial toxins, viruses, protozoa, fungi and tumors or cancer

• Integumentary system: the skin protects the organs of the respiratory system by forming surface barriers

Skeletal system: the bones protect the lungs and bronchi by enclosure

• Muscular system: activity of the diaphragm and intercostal muscles essential to produce volume changes that lead to pulmonary ventilation; Regular exercise increases respiratory efficiency

Digestive system: the digestive system supplies the necessary nutrients for the organs of the respiratory system

Urinary system: the kidneys eliminate metabolic waste from the organs of the respiratory system (other than carbon dioxide) and maintain long-term pH homeostasis

• Reproductive system: the respiratory system provides oxygen and disposes carbon dioxide



Chronic Obstructive Pulmonary Disease



• Emphysema: Stands out for the permanent expansion of the alveoli, accompanied by the destruction of the alveolar walls. Invariably, the lungs lose their elasticity

• Chronic bronchitis: inhalation irritants lead to excessive production of chronic mucus by the mucous membrane of the lower respiratory tract and inflammation and fibrosis of the mucous membrane. These responses block the respiratory tract and severely impair lung ventilation and gas exchange

Asthma: Asthma is characterized by episodes of coughing, wheezing, wheezing and chest tightness alone or in combination. Most acute attacks are accompanied by a panic asthma sensation characterized by acute exacerbations followed by periods without symptoms. the obstruction is reversible

• Tuberculosis: Tuberculosis (TB), the infectious disease caused by the Mycobacterium tuberculosis bacteria, is transmitted by coughing and enters the body mainly in the inhaled air. Tuberculosis mainly affects the lungs, but can spread through the lymphatic vessels to affect other organs

• Lung cancer: Lung cancer is the leading cause of cancer death for men and women in North America, resulting in multiple deaths from breast, prostate and colorectal cancers combined. This is tragic, because lung cancer is widely preventable: almost 90% of lung cancers are the result of smoking

• Pneumonia: Infectious inflammation of the lungs, in which fluid accumulates in the alveoli; The eighth most common cause of death in the United States. Most of the over 50 different varieties of pneumonia are viral or bacterial

• Pulmonary embolism: blockage of the pulmonary artery or one of its branches by an embolus,very often a blood clot that has been transported from the lower extremities and through the right side of the heart into the pulmonary circulation


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