Human Anatomy
The Respiratory System
The Respiratory Tract
Respiration and breathing are two vital functions of this system, which includes the pharynx, larynx, trachea, and lungs.
Breathing is only one of the many activities performed by the respiratory system, which also provide an extensive gaseous exchange surface between air and the blood. The respiratory tract also helps protect people from diseases by filtering and expelling airborne waste particles and irritants.
The respiratory system is involved in ventilation, which is the process of moving air into and out of the lung’s change surfaces. This system has mechanisms in place to protect respiratory surfaces from dehydration, environmental variations, and pathogens. The respiratory system also helps humans produce sounds and regulate their blood volume, blood pressure, and body fluid pH.
The respiratory tract can be divided into two sections. The first section is the upper respiratory tract, which comprises the nose, nasal passages, paranasal sinuses, pharynx, larynx (or voice box), and trachea (or windpipe). The lower section includes the bronchi and lungs, which are made up of the bronchioles, alveolar ducts, alveolar sacs, and alveoli.
The nostrils are the primary point of entry into the respiratory system, and the mouth serves as an alternate pathway when the nose is blocked. Behind the nostrils lies the nasal cavity, which is lined with mucous membranes and tiny cilia. The latter are little hairs inside the nasal cavity that filter air, which blocks dirt an dust from getting into the lungs. The paranasal sinuses surround the nasal cavity. These are air-filled spaces in the skull that are lined with mucosa. They humidify and warm air as it is inhaled.
The pharynx carries food and air down the respiratory tract. It is therefore part of both the digestive system and the respiratory system. It is situated behind the mouth and nasal cavity and has three sections: the nasopharynx, oropharynx, and laryngopharynx.
The nasopharynx is the upper section, which leads to the nasal passages. The oropharynx is the middle section and sits directly behind the oral cavity. The laryngopharynx is the bottom section. It is a flexible passageway for air between the oropharynx and trachea. The pharynx also contains lymphoid tissue: the adenoids in the nasopharynx and the palatine tonsils in the oropharynx.
The larynx is found between the pharynx and trachea and is divided in three parts: the supra glottis, glottis, and sub glottis. The epiglottis is found at the opening of the larynx. It closes over the glottis as food is swallowed to prevent it from entering the respiratory tract. It also closes when a person coughs, to prevent anything harmful from being inhaled into the lungs. The larynx houses the vocal cords, which are essential for phonation (i.e., speech sounds). It closes and rises when a person swallows, which moves the epiglottis over the trachea.
The trachea is a short, flexible tube that divides into brooch. In the lower respiratory tract, the primary bronchi - left and right - each take air into a lung. The bronchi then divide into secondary and tertiary bronchi, and eventually into minute bronchioles. Air next travels through the alveolar ducts, alveolar sacs, and alveoli.
Strengthening the lungs: The lungs are the chief organ of the respiratory system. As with many body parts, exercise helps to strengthen the lungs. However, a number of special breathing techniques can exercise the lungs as well as relive anxiety and stress.
Belly breathing involves lying flat on your back, placing a hand on your abdomen, and breathing in until you feel your belly rise. This will help you learn how to properly use your diaphragm. Another exercise is Lion’s breath. You start in a relaxed pose and then ope your mouth, stick your tongue out and down toward your chin, and exhale with a drawn out “Ha-a-a-a-a-a-a-a.” Equal breathing is a technique that starts in a relaxed pose and involves slowly matching your inhalations and exhalations for 3 to 5 seconds.
Organs of the respiratory system:
Pharynx: tube that connects the nasal cavity and larynx as well as the mouth and esophagus.
Larynx: involved in breathing and sound production. This organ, commonly known as the voice box, is located in the neck, forming the upper part of the trachea.
Trachea: tube that runs from larynx to bronchi; transport air to and from lungs.
Nasal cavity: air-filled space behind nose that is divided into two halves (fosse) by nasal septum.
Nostril: external openings that lead to the nasal cavity.
Lung: primary organs of the respiratory system.
Bronchus: these branch off into smaller bronchi and 30,000 bronchioles.
The trachea: this tube is about 4 inches (10 cm) long and less than 1 inch (2.5 cm) in diameter. It begins just under the larynx, runs down behind the breastbone, and then divides into two smaller tubes called bronchi one for each lung.
The Lungs
In large land mammals, including humans, the gas exchange mechanism that characterizes breathing has been internalized into a pair of lungs. The lungs are, therefore, the major organs of the respiratory system, providing the oxygen that is required by every cell in the human body to remain alive and healthy.
The lung are paired organs that are found in the thoracic cavity and are separated from each other by the heart and other structures in the mediastinum, which is the membrane between the lungs. The left lung consists of two lobes, whereas the right lung has three lobes. Since the heart tilts to the left, the left lung is smaller than the right. The left lung also has an indentation called the cardiac impression to accommodate the heart.
The lungs are enclosed in the Plura, which is a slippery membrane that covers the lungs and the inside of he chest wall. It allows the lungs to expand and contract smoothly during breathing and as a person moves around. The pleura has two layers: visceral and parietal. The space between these two layers is called the pleural cavity. The two pleural layers have small amount of lubricating fluid in between them. This allows the two layers to glide easily over each other as the lungs size and shape as a person breathes.
The respiratory passages from the trachea to the bronchioles are called the tracheobronchial tree. The trachea divides into the right and left lungs.
Each bronchus enters the lungs at a slit in the mediastinal surface called the hilum. Blood vessels, lymphatic vessels, and nerves also enter the lungs through the hilum. This region is sometimes called the root of the lungs.
Approximately 16 generations of branching occur from the trachea to the terminal bronchioles. This part of the lungs, which includes the respiratory bronchioles, alveolar ducts, and alveolar scas, is called the acinus.
The pulmonary artery supplies deoxygenated blood to the pulmonary capillaries, which form respiratory membranes together with the alveoli. The pulmonary veins return newly oxygenated blood to the heart so it can be transported throughout the body.
Lung protection: the soft, spongy lungs are well encased in the rib cage and its surrounding network of muscle. These structures flex and help move inhaled air into and out of the lungs.
Pleural membrane: this thin, moist, slippery tissue is composed of two layers: the outer (or parietal) layer lines the rib cage and diaphragm; the inner (or visceral) layer covers the lungs.
Dust cells: as alveolar macrophage is a type of phagocyte (immune cell) found inside pulmonary alveoli. They remove dust and microorganisms from respiratory surfaces. Dust cells can form dense populations and are highly active, playing a key role in homeostasis, immunity, and tissue remodeling. Alveolar macrophages are adaptive cells that release various secretions and interact with other cells and molecules.
Breathing and Respiration
Breathing ventilates the lungs, moving a volume of gas into and out of them. Humans require oxygen to burn the sugars, fatty acids, and other fuels from food that supply us with energy. Oxygen is, literally, the breath of life.
Breathing is the act of pulmonary ventilation, and it is characterized by movement of air between the atmosphere and the lungs’ alveoli. It can be broken down into two steps: Inspiration (or inhalation) involves moving air into the lungs, and expiration (or exhalation) involves moving air out the lungs.
During inspiration, the diaphragm contracts and pulls down, the intercostal muscles contract, and the rib cage expands, which draws air into the lungs. During expiration, the diaphragm relaxes and goes up, the intercostal muscles relax, and the rib cage collapses, which presses the lungs like a bellows and pushes air out. These two processes make up one breathing cycle.
The conducting airways for breathing include, in order, the nose, nasopharynx, larynx, trachea, bronchioles, and terminal bronchioles.
The accessory mechanical components for breathing include the rib cage, diaphragm, and intercostal muscles. The rib cage is composed of the sternum, 12 ribs, and 12 thoracic vertebrae. The diaphragm and intercostal muscles are involved in peaceful, regular breathing. Additional muscles are engaged during forced expiration, including the rectus abdominis and the transverse abdomens as well as the external and internal oblique muscles.
The respiratory center in the brain stem controls the nerve stimulation for breathing. Three neuronal groups of the medulla oblongata and pons in the brain stem are involved in breathing. The dorsal respiratory group is the inspiratory center, the ventral respiratory group controls forced expiration, and the pneumotaxic center controls the rate and depth of breathing.
Breathing, however, is not the same everywhere. While the concentration of oxygen is essentially constant all over theEarth’s terrestrial elevations, air is said to be thin at high altitudes. This caused by the lower pressure at higher elevations. In order to get the same amount of oxygen as at sea level, one needs to breathe in more air. This is achieved by breathing faster and more deeply (called hyperventilation).
Additionally, the heart pumps more blood to the brain and muscles at higher altitudes. This leads to a greater loss of carbon dioxide from the blood, leaving it slightly alkaline. The body, however, acclimatizes during the first few days at high altitude, as the kidneys remove the alkali from the blood (in the form of bicarbonate ions).
There is also a breathing process related to high-pressure conditions and the way the body’s gases react after leaving that environment. Known as decompression sickness (DCS), caisson disease, or the blends, it occurs when too-swift depressurization causes dissolved gases to come out of solution and form bubbles in the body. It most commonly arises after underwater dives. The effects can range from a rash and joint pain to paralysis and death. Decompression sickness is managed by decompression procedures, such as divers controlling their ascent speed. Treatment in a recompression chamber may be necessary.
The vocal cords and larynx: The vocal cords are located within the larynx (or voice box), which is found at the top of the trachea. These cords open during inhalation and move together and close during swallowing or phonation (i.e., making sounds). The vocal cords vibrate and modulate the expelled airflow from the lungs, which results in speech and singing. The false vocal cords (also called the superior vocal cords or ventricular folds) play no role in speech; the close off the larynx when a person swallows.
Healthy bronchi: Also called bronchial tubes or airways, they can be prone to disorders like asthma, which inflame the tube and produce mucus, constricting airflow and hindering breathing.
Epiglottis: A leaf-shaped flap in the throat that prevents food and liquids from entering the trachea and lungs. It remains open when breathing, allowing air into the larynx.
Coughing: This reflex action forcefully releases air from the lungs to clear the threat of mucus or irritants. It can be triggered by smoke, gas, allergies, colds, or improperly swallowed food or beverages.
Snoring: The hoarse ragged, harsh sounds a person makes while asleep occur when inhaled air flows past the relaxed throat tissues, making them vibrate - often quite noisily. Snoring is not uncommon, but for some people it can become chronic, disturbing the sleep of their partner. It can also indicate serious health issues, such as sleep apnea. Lifestyle changes, like losing weight, avoiding alcohol at night, or side sleeping can improve the condition.
Respiration and Gaseous Exchange
Respiration is the exchange of oxygen and carbon dioxide across a membrane. It occurs in two locations in the body, which determines whether it is external or internal. Gaseous exchange is the mechanism by which oxygen and carbon dioxide move between the external environment and the bloodstream.
There are three processes that are essential for the transfer of oxygen from the external environment into the blood that flows through the lungs: ventilation, diffusion, and perfusion. Ventilation is the process by which muscles move air in and out of the lungs. Diffusion, meanwhile, is the spontaneous movement of gases from an area of higher concentration to a lower concentration. This is an efficient mechanism that does not require any expenditure of energy. Diffusion happens in the lungs between the gas in the alveoli and the blood in the capillaries, and it also happens at the cellular level in tissues. Perfusion refers to the exchanges that happen via the cardiovascular system. External respiration occurs in the lungs, between the alveoli and a network of tiny blood vessels called capillaries. Alveoli are tiny, balloon-shaped air sacs that sit at the end of the bronchial tree and are arranged in clusters throughout the lungs. They are only one cell thick, which facilitates the exchange of oxygen and carbon dioxide between them and the capillaries. There are at least three different types of cells in the alveoli. Type I pneumocystis form part of the barrier across which gas exchanges occur. Type II pneumocystis are foamier than type I cells, and they contain phospholipid multilanellar bodies, which are the precursor to the lung’s surfactant. (A surfactant reduces the surface tension of a liquid.)
In external respiration, the concentration of oxygen is higher in the alveoli, so oxygen diffuses into the capillaries. Conversely, the carbon dioxide concentration higher in the capillaries, so it diffuses into the alveoli. Carbon dioxide molecules exit the body during the next expiration, while oxygen molecules attach to the hemoglobin in red blood cells, while oxygen molecules attach to the hemoglobin in red blood cells, which travel back to the heart and are then circulated throughout the rest of the body (i.e., perfusion). Internal respiration refers to the exchanges that happen at the cellular level via a fluid. It includes a organism obtains energy when oxygen reacts with glucose, producing water, carbon dioxide, and energy. Carbon dioxide is, therefore, a waste product of internal and cellular respiration; it comes from the oxygen and carbon in glucose. Through diffusion, the carbon dioxide moves across the capillary wall and into the blood, while the oxygen from the blood moves into the tissues.
The carbon dioxide molecules then attach to the hemoglobin in the red blood cells, which travel back to the heart. In this way, the circulatory system connects the external and internal respiration processes.
Oxygen-rich and carbon-dioxide-deficient blood travels from the lungs through the pulmonary veins and into the left side of the heart, from where it is pumped to the rest of the body. The oxygen molecules are then metabolized by the cells in the tissues to produce energy, which generates carbon dioxide.
Oxygen-deficient and carbon-dioxide-rich blood then travels from the tissues to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava. This blood is pumped through the pulmonary artery to the lungs, where the carbon dioxide diffuses out and oxygen diffuses in, and so the processes continue.
Gaseous Exchange: The structure of the alveoli; an important part of the lungs’ structure, the alveoli are tiny, cup-shaped air sacs that have very thin walls; roughly 480 million of them form bunches at the ends of bronchial tubes.
Alveolar ventilation: This is the exchange of gas between the alveoli and the external environment. Oxygen is drawn into the lungs, and carbon dioxide is carried to the lungs, in venous blood and is expelled.
Capillary diffusion: This allows small molecules, such as oxygen or glucose, to flow from blood to tissues. It also facilitates the movement of carbon dioxide from tissues into the blood.
Alveoli: This diagram traces the gaseous exchange that takes place inside the alveoli, including how indrawn air supplies oxygen to the blood.
Resuscitation: Immediately after an accident or injury in which a person has stopped breathing - for example, from a crushing blow or electrocution - cardiopulmonary resuscitation (CPR) needs to be performed to get the lungs and heart working in order for oxygenated blood to continue to reach the brain. CPR involves the compression of the chest in a rapid sequence along with providing rescue breaths every 30 compressions.
Capillary Exchange: Capillary exchange is the name given to the exchange of material, such as nutrients and waste, that happens between the blood and tissues via the capillaries. Capillaries are tiny, thin-walled blood vessels that connect arterioles and venues. There are three mechanisms that facilitate capillary exchange: diffusion, transcytosis, and bulk flow. Diffusion is the most prevalent of these.