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 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.

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 adrenal (suprarenal) glands are trianglular glands situated above the kidneys. They are retroperitoneal and are surrounded by a capsule and renal fascia. The adrenal glands have a cortex (this makes mineralcorticoids (aldosterone), glucocorticoids (cortisol), and sex hormones). The adrenal glands also have a medulla that secretes epinephrine and norepinephrine.

The adrenal gland functions purely as an endocrine gland, while the other choices do not. The pancreas and stomach contain endocrine cells, but they also function in digestion; they are not purely endocrine glands. The ovary also contains endocrine cells, but it also functions in reproduction and is thus not a purely endocrine gland.

The respiratory tract is divided into the upper and lower tracts. The upper respiratory tract consists of the nose (including nasal sinuses) and pharynx. The lower respiratory tract consists of the larynx, trachea, bronchi, and lungs.

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.

Type 1 pneumocytes (alveolar cells) are responsible for gas exchange between the alveoli and blood. They have a thin cytoplasm. Type 2 pneumocytes also reside in the alveoli, but they produce surfactant which prevents the alveoli from collapsing. Macrophages and neutrophils can be present in the alveoli or lung blood vessels, but they do not participate in gas exchange,but are involved in the response against microbial infections. Oligodendrocytes are neuroglia in the central nervous system that produce myelin sheets.

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.

Of the pneumocytes, type II cells are responsible for secreting pulmonary surfactant, serve as precursors to type I cells, proliferate during lung damage and decrease alveolar surface tension.

Type I cells, on the other hand, line the aveoli and consist of 97% of the alveolar surface. The cells are squamous and thin for optimal gas diffusion.

An easy way to differentiate between the two types of lung cells is to remember that type I cells are responsible for the physical lining and makeup of pneumocytes, while type II cells are responsible for the functioning of the pneumocytes.