Sir Frederick Smith Memorial Lecture. A superb transport system–the circulation.

This research article describes the intricate workings of a horse’s circulatory system, from the journey of oxygenated blood from the left atrium, to the distribution of blood between the pulmonary and peripheral circulation, and the role of the thorax in this process.

Understanding Circulatory Physiology

The paper dives deep into the study of circulatory physiology, particularly in horses. The authors explain the circulation journey which begins from the left atrium. Here are some key details shared in the article:

• The process starts in the left atrium where oxygen-rich blood flows in from the pulmonary veins, one of four veins responsible for carrying oxygenated blood from the lungs back to the heart.
• This blood is then pushed via the mitral valve into the left ventricular pump, where it is propelled under high pressure through the peripheral circulation.

Peripheral Circulation and Beyond

The authors further discuss how this high-pressure push affects peripheral circulation and what follows afterwards.

• The blood, now under high pressure, travels through the arterioles (small arteries leading into capillaries) and capillaries, which are the smallest and thinnest of the body’s blood vessels and where the exchange of oxygen and nutrients for carbon dioxide and waste occurs.
• After this exchange, the blood now deoxygenated, and under significantly lesser pressure, is collected into the venules (small veins that collect blood from the capillaries) and larger veins.

The Role of Muscles and Intrathoracic Pressure

This research article then explores further aspects of the circulatory process, specifically the influence and role of the muscles and the negative intrathoracic pressure.

• The pumping action of the muscles and the negative pressure within the thoracic cavity act as a suction, helping to pull the blood back up towards the right atrium (one of four chambers of the heart that receives deoxygenated blood from the body) and consequently exerting a pull on the great veins.
• The blood is then discharged from the right ventricle (the chamber of the heart responsible for pumping deoxygenated blood to the lungs) into the lower-resistance, higher capacitance pulmonary circuit, simultaneously collecting oxygen, releasing carbon dioxide, and making its return journey to the left atrium – a process known as pulmonary circulation.