Endocrine organs are capable of secreting hormone signals into the blood. The heart releases atrial-natriuretic hormone, which stimulates vasodilation to reduce blood pressure and affects kidney function. The liver releases insulin-like growth factor in response to growth hormone, which has direct effects on stimulating cell growth and division. The kidneys release renin, which acts to increase blood pressure via sodium retention. The pancreas secretes insulin and glucagon to regulate blood glucose concentration.

The medulla oblongata is located in the brain stem and regulates several vital functions, such as respiration and heart rate. It performs these actions via action potentials and innervation, rather than the secretion of hormones.

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.