What Body Cavity Is The Lungs In
There are several important cavities within the body. One of these is the thorax. It is a part of the torso that includes the chest, as well as the abdomen, below the rib cage (chest wall), and above the pelvis. The chest cavity is one of the most important parts of the body because it contains some of our vital structures. There are two major sections to this cavity – the upper and lower thorax. The upper section has three divisions: the throat, larynx, and trachea; the middle section has four divisions: the pleural space, pericardial sac, hemithorax, and peritoneal cavity; and the lower section has five divisions: the peritoneal cavity, pericardium, lower sternocostal region, diaphragm, and pelvis. The chest cavity also contains the heart and great vessels. The lung is contained within the thorax cavity, so we’ll discuss the anatomy of the lungs next.
The lungs are located on each side of the chest cavity. The right lung is larger than the left lung. Both have multiple lobes that branch off into smaller branches called bronchi. Each lobe is made up of millions of air sacs known as alveoli. These alveolar units form the basic unit of the lung structure. Alveoles are interconnected by small passageways called respiratory bronchioles. Within the alveolar walls are microscopic capillaries that allow oxygenated blood to flow in and carbon dioxide out of the alveolus. Oxygen diffuses across the thin membranes of the alveolus and carbon dioxide diffuses out through the thin membrane of type II pneumocytes. This process allows breathing to occur. When you inhale, your breath passes down through the respiratory bronchioles into the terminal bronchioles, then into the branching bronchioles, and finally into the airways where they connect with the alveolar ducts. From there airways lead directly into the alveolar spaces or indirectly into the pulmonary veins via the pulmonary arteries. The main purpose of the airways is to carry air from the environment through the parenchyma to the outside world. As mentioned earlier, the lungs contain both gas exchange tissue and fluid-filled compartments. The gas exchange compartment makes up about 80 percent of the total volume of the lungs. The remaining 20 percent is filled with fluid that helps maintain surface tension at the interface between the airway epithelia and the surrounding liquid. Surrounding the airways are smooth muscle bundles that control airflow and movement of mucous secretions. The airways terminate at the level of the alveolar duct entrance and exit. At this point the airways become covered with cilia. Cilia are tiny hair like projections that beat rhythmically to help move mucous along toward the mouth. Once in the airways, the mucous becomes trapped in the narrower portions of the airways until the person exhales when it is expelled from the mouth.
Diagram of the lungs:
The heart is enclosed in a double layered sleeve called the pericardium. The outer layer is composed of a tough fibrous tissue called epicardium while the inner layer is a meshwork of fibers called myocardium. The heart is suspended in a jelly substance known as chordae tendineae. Chordae provide attachment points for the muscles of the heart. Two sets of chambers are formed by muscular partitions called septa. The left side contains two chambers called ventricles. They are separated by a partition called interventricular septum. On the right side there are four chambers: two large ones called atria and two small ones called auricles. The atria are separated from the ventricles by a partition called the atrioventricular valve. The valves of the heart open during systole and close during diastole. The atria receive blood from the superior and inferior venae cavae. The superior vena cave empties into the atrium and the inferior vena cave empties into the ventricle. The left atrium receives blood from the coronary sinus and the right atrium receives its blood supply mainly from the superior and inferior cardiac veins. The atrial appendages attach the atria to the ventricles. The left atrium is connected to the left ventricle by the mitral valve. The right atrium is connected to the right ventricle by the tricuspid valve. The valves of the heart are not stiff but flexible allowing them to change shape during the pumping action. The valves prevent backflow of blood. If the valves were rigid they would cause stenosis which is narrowing of the passage way.
Within the thorax is another important cavity called the abdominopelvic cavity. It is divided into an anterior and posterior portion. The anterior portion is bounded laterally by the abdominal wall and medially by the pelvis. The abdomen lies below the abdominal wall and above the pelvis. Posteriorly the abdominopelvic cavity opens into the vagina. Anteriorly it opens into the rectum. Also included within the abdominopelvic cavity is the urinary bladder. The bladder is contained within the pelvis. Its opening is at the base of the pubis. Urinary bladder is connected to the urethra which leads to the external genital area. The uterus is also included in the abdominopelvic cavity. It is the female reproductive organ that gives birth to offspring. The cervix is found at the top of the uterine cavity. At the bottom of the uterus is the opening to the fallopian tubes. The fallopian tubes are responsible for transporting egg cells from ovaries to the uterus. Ovaries are attached to the lateral sides of the abdominopelvic cavity. Ligaments around the ovaries hold them firmly within the abdominopelvic cavity. The ligaments attach the ovary to the uterus. Uterus develops from the paramesonephric ducts. The mesonephros provides precursor elements for the kidney. Mesonephros is also the origin of Wolffian bodies. Wolffian bodies secrete male hormones and develop into testes.
In summary, the lungs are located within the thorax, which is part of the torso. They contain gas exchange tissue and fluid-filled compartments. Air enters the lungs through the nose and is distributed throughout the lung tissue. Oxygen diffuses across the thin membrane of type I pneumocytes. Carbon dioxide diffuses out through the thin membrane of type II pneumocytes. Type I pneumocytes make up 90 percent of the total number of lung cells. Their function is to produce surfactant proteins that reduce surface tension. Type II pneumocytes cover approximately 10 percent of the total cell population of the lungs. They are involved in secretion of mucous glycoproteins that trap pathogens and aid in their removal from the airspaces. Surface tension is reduced by the presence of protein rich mucous in the airspaces. Mucous is produced primarily by goblet cells in the submucosal glands. Goblet cells are tall columnar epithelial cells. Submucosal glands are present in the peripheral regions of the airways. Epithelial cells lining the airways are flat cuboidal cells called type 2 pneumocytes. Pulmonary circulation begins in the left atrium of the heart. Blood is pumped through the lungs by specialised muscle tissues. Left atrium receives blood from the systemic circulation and pumps it into the left ventricle of the heart. The left ventricle sends the blood through a network of elastic bands called the heart valves. The mitral valve is situated at the connection between the left atrium and left ventricle. The aorta is the main artery leading to all areas of the body. The pulmonary trunk extends downward from the left ventricle to the lungs. Branching arteries give rise to arterioles that extend peripherally to take over blood supply to the entire lung. Arterioles end in capillary beds. Capillaries collect red blood cells from nearby veinules and release them into the alveolar airspace to return to the systemic circulation. Veinules bring blood from the deeper layers of the skin and fat. Venule endings are usually surrounded by nerve endings and lymphatic channels. Veinules are narrow cylindrical passages lined with endothelium. Endothelium lacks pinocytic activity. Pinocytic activity occurs on the apical surfaces of endothelial cells. A basement membrane surrounds the endothelium except at bifurcations where new branches form. Basement membrane is made up of collagen fibrils embedded in a ground substance. Veinules are followed by capillaries on account of their greater size compared to other types of blood vessel. All of the blood returning to the heart must first pass through the lungs. Therefore, the lungs play a very important role in the circulatory system.
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