Identifying Respiratory and Endocrine Organs - Anatomy

Alveoli are small grape-like clusters that branch off of the respiratory bronchioles. These alveoli are the sites where oxygen diffuses into the capillaries, and carbon dioxide is exchanged in order to be exhaled.

The respiratory tract begins with the mouth and nasal passages and carries air to and from the alveoli for gas exchange. After entering the mouth and nasal passages, air travels through the pharynx and larynx before entering the trachea. The trachea divides into two primary bronchi before subdividing into numerous smaller bronchioles. Alveoli are located in clusters at the ends of bronchioles and are surrounded by capillaries for gas exchange to occur.

The epiglottis is a structure just above the glottis at the upper part of the larynx, and is composed of elastic cartilage. It prevents food from entering the trachea during swallowing by bending horizontally and covering the glottis. This allows the epiglottis to redirect food to the esophagus.

The uvula is the posterior projection of the soft palate and can cover the nasal cavity when swallowing so that food cannot enter. The pharyngeal tonsils are masses of lymphatic tissue found behind the uvula.

The pleura is a thin membrane that is made of the parietal and visceral pleura. The parietal pleura serves as lining for the thoracic cavity and the mediastinum. It is comprised of four parts: cervical, mediastinal, diaphragmatic, and costal. The parietal pleura is supplied by the intercostal nerves and the phrenic nerves, while the visceral pleura contains vasomotor nerves and sensory fibers from the vagus nerve. The parietal pleura is sensitive to pain, while the visceral is only sensitive to stretch. The visceral pleura lines the lungs and is delivered oxygen by the bronchial arteries.

The lungs are central to respiration and have connections with the heart and trachea. The lungs expand downwards during inspiration and upwards with expiration due to movement by the diaphragm situated below them. Lung tissue is innervated by parasympathetic and sympathetic nerve fibers that control secretory glands and smooth muscle.

The right lung is much larger and heavier when compared to the left lung. It is divided into three lobes by the oblique and horizontal fissures: lower, middle and upper. The left lung is divided into the upper and lower lobes solely by the oblique fissure. However, it does contain a small tongue-like portion attached to the upper lobe called the lingula. The lungs are supplied by the bronchial arteries and drained by the pulmonary veins.

From the embryonic period to the age of almost 8 years, the lungs will go through four stages to become fully developed. The four stages are glandular, canalicular, terminal sac period, and alveolar period. The glandular stage begins from week 5 of the prenatal period until week 17 and involves the formation of the terminal bronchioles. The canalicular period is from week 13 until week 25 of prenatal life. Respiratory bronchioles and alveolar ducts form, but they are not mature enough to support breathing outside the uterus. The third stage is called the terminal sac period and takes place from prenatal weeks 24 until birth. This stage forms more terminal sacs and surfactant. Respiration is possible at this time and premature babies can survive if given proper treatment. The last stage of lung development is called the alveolar period, which is from very late into fetal life until the age of 8 years. The alveoli continue to replicate in numbers and the lungs further mature.

The mediastinum is the area found in the thorax contained by the pleural cavities, sternum, and vertebral column. It is further divided into four main divisions: the superior, anterior, middle, and posterior. The superior mediastinum is bordered by the first rib superiorly, anteriorly by the manubrium of the sternum, and posteriorly by the 4th and 5th thoracic vertebra. An imaginary line can be drawn from the intervertebral disk between the 4th and 5th vertebrae to the sternal angle to mark the inferior limits of the superior division. This region contains important structures, vessels, and nerves such as the arch of the aorta, the trachea, and the esophagus. It also contains the thymus. The thymus is the location where immature T-cells mature, and can then contribute to an immunological response. This lymphatic structure will involute with the start of puberty.

The trachea is the structure through which air is transported to the bronchi and the lungs. Its superior border is the cricoid cartilage at the 6th cervical vertebra, and it ends with its bifurcation into the right and left main bronchi at the level of the sternal angle. The trachea is on average 9cm to 15cm long and is lined by hyaline cartilage that hold its shape.

The trachea bifurcates into the left main and right main bronchus at the level of the sternal angle in the thorax. When an object is accidently inhaled, it will most likely lodge in the right main bronchus or the inferior lobar bronchus, which is a further division of the right main. The right bronchus is shorter, wider, and more vertical than the left, leading to a more direct path for any objects inhaled and a higher probability that they will enter the right branch than the left.

The trachea, or windpipe, is a rigid tube that carries air from the larynx into the bronchi. The rigidity comes from C-shaped rings of cartilage.

The pharynx, or throat, is a muscular funnel that receives air from the nose, and food and drink from the mouth. The larynx, or voice box, is also formed from cartilage. The uppermost cartilage is the epiglottis, which separates the respiratory tract from the digestive tract. The thyroid cartilage, or "Adam's apple," forms the anterior and lateral walls of the larynx. The cricoid cartilage connects the larynx to the trachea. The bronchi are also supported by C-shaped cartilages. The bronchi transport air into the lungs following bifurcation of the trachea.

The right lung has 3 lobes while the left lung has 2 lobes. This is because the right lobe has 2 fissures, while the left lobe only has 1. The right lobe is separated into the superior, middle, and inferior lobes by the horizontal and oblique fissures, respectively. The left lobe is divided into the superior and inferior lobes by the oblique fissure.

In the right lung, the pulmonary artery is anterior to the bronchus. Instead, in the left lung, the pulmonary artery is superior to the bronchus. The mnemonic "RALS" is a helpful tool to remember this. RALS stands for in the Right lung, the pulmonary artery is Anterior to the bronchus, while in the Left lung, the pulmonary artery is Superior to the bronchus. It is important to be able to identify these features because they will help us know which lung we are looking at.

In the right lung, the pulmonary artery is anterior to the bronchus. Instead, in the left lung, the pulmonary artery is superior to the bronchus. The mnemonic "RALS" is a helpful tool to remember this. RALS stands for in the Right lung, the pulmonary artery is Anterior to the bronchus, while in the Left lung, the pulmonary artery is Superior to the bronchus. It is important to be able to identify these features because they will help us know which lung we are looking at.

The diaphragm is innervated by C3-C5 (phrenic nerve). The phrenic nerve receives innervation from parts of both the cervical plexus and the brachial plexus. The phrenic nerve contains motor, sensory, and sympathetic nerve fibers, providing motor supply to the diaphragm as well as sensation to the central tendon. Pain from the diaphragm can be referred to the shoulder.

The left is smaller and has only two lobes because it allows room for the heart in its cardiac notch. The right lung has three lobes. Remember, if you are looking at the anterior side of a human (face side), the right lung is on your left side as the observer.

Air from the nose or mouth meets the trachea, then the bronchi, then the bronchioles (primary, secondary, tertiary, terminal, then respiratory), then to the alveolar sacs and ducts, and finally the alveoli. Each structure after the bronchi is more branched and thinner to allow the successive expansion of air volume to meet the alveoli. The first part in the respiratory tract where gas exchange occurs is across the respiratory bronchioles, every structure leading to these have been purely for ventilation. However, the alveoli are the main site of gas exchange in the lungs.

The epiglottis is a flaplike cartilaginous structure. During breathing it stands upright, allowing air to enter the larynx. However, upon swallowing the epiglottis folds downward to a more horizontal position in order to cover the opening of the windpipe. This movement directs food to the esophagus and prevents food from entering air passages.

The right lung consists of 3 lobes: the superior lobe, the middle lobe, and the inferior lobe (also known as: upper, middle, and lower lobes). The superior and middle lobes are divided by the horizontal fissure, while the middle and inferior lobes are separated by the oblique fissure. The left lung is made up of 2 lobes, the superior and inferior lobes. These are separated by the oblique fissure.

The thoracic cavity contains the lungs and the heart (the heart is located within the mediastinum which is the central compartment of the thoracic cavity). The diaphragm forms the floor of the thoracic cavity and separates it from the more inferior abdominopelvic cavity. The abdominopelvic cavity is the largest cavity in the body. The thoracic cavity is protected by the thoracic wall which consists of the ribcage and associated skin, muscle, and fascia. The cranial and vertebral cavities are the dorsal cavities in which the central nervous system are encased.

The trachea (windpipe) is a tube that connects the pharynx and larynx to the lungs, allowing for the passage of air. The trachea extends from the larynx and branches into the two primary bronchi. There is a right bronchus and a left bronchus and these branch into secondary and tertiary bronchi which branch into smaller tubes, known as bronchioles, then eventually to terminal bronchioles. No gas exchange occurs in the bronchi. The first site of gas exchange is the respiratory bronchioles, which lead into alveolar ducts, alveolar sacs, and alveoli.

At the top of the trachea the cricoid cartilage attaches it to the larynx. The epiglottis closes the opening of the larynx during swallowing.