Respiratory and Circulatory Systems: Anatomy and Function

Airway

Includes a conduction pipeline connecting it with the exterior lungs, which are:

• The nasal cavities: Two open cavities covered by nasal mucous. They communicate with the exterior through the nostrils and with the pharynx through the choanae (posterior openings).
• The pharynx: It is a common respiratory tract through the digestive tube and the epiglottis. The epiglottis is located above the larynx and prevents food from entering during swallowing, thus avoiding choking.
• Larynx: Communicates with the trachea and contains some folds (vocal cords) that vibrate and emit sounds.
• The bronchial tree: It consists of two bronchi that penetrate the lungs and branch into increasingly smaller bronchioles. The cells of the walls secrete mucus and have cilia, beating in the direction of the pharynx (and any possible foreign body is expelled).
• Lungs: They are found in the thoracic cavity, protected by the ribs and covered by two membranes, the pleura, including a space filled with a liquid. They are separated from the abdomen by a dome-shaped muscle called the diaphragm. The internal lungs are composed of many cells of spongy appearance, which are tiny sacs surrounded by very fine capillary networks in which the bronchial tree ends.

Functioning

Pulmonary Ventilation

It is the circulation of air from outside the lungs and vice versa. It produces the renewal of the air in the lungs and is carried out using two movements: inspiration and expiration, which are involuntary, although there is some control.

The Exchanges of Gases

It is a process that takes place by diffusion through the membranes of the alveoli. The fine and wet oxygen is more concentrated in the alveoli and air tends to spread around to the blood. In contrast, the blood reaches the lungs with a higher concentration of CO2 than the alveolar air, so it goes outward. For similar reasons, when the blood reaches the cells, it leaves the oxygen inside and collects the CO2 that is produced during cell metabolism.

Distribution of Food

The organism needs to distribute nutrients and oxygen to cells and remove waste and CO2, which will be eliminated by the excretory organs. To perform these functions, it has the circulatory and lymphatic systems. The lymphatic system is constituted by a network of lymphatic vessels.

• Blood: It is the means of transport.
• Blood vessels: They constitute a network of pipes.
• Heart: It is an organ that works like a pump, and makes the blood circulate through the interior of blood vessels, thereby distributing it throughout the body and fulfilling its duties.

The blood vessels form a network of pipes that leave the heart, branch out to reach all organs of the body, and return to the heart. Depending on their caliber, they can be of three types:

• The arteries: They carry blood from the heart to the organs. The walls of these vessels are thick and elastic, as they have to bear the blood pressure to which the heart is subjected. The arteries branch into arterioles and then into capillaries.
• Veins: They conduct blood from the organs to the heart. Their walls are finer and less elastic, since the blood pressure is lower on the return from the organs. Inside, there are valves that prevent the retreat of the blood. The smaller veins are venules, leading blood from the capillaries into the veins.
• The capillaries: They are very small blood vessels with very thin walls. They form a network that reaches all body tissues, allowing for the exchange of nutrients and waste gases.