Cardiorespiratory System Overview - Anatomy & Physiology

Introduction

The mammalian cardiovascular and respiratory systems have evolved primarily to provide the tissues of the body with oxygen and to remove carbon dioxide. The cardiorespiratory system also has metabolic and heat exchange roles.

Respiratory System

Air is inhaled and passes through the upper respiratory tract via the nares, nasal cavity, pharynx, larynx, and trachea; it is heated and moistened en route. It then passes to the lower respiratory tract traveling through the lungs via the bronchi, bronchioles and alveoli where oxygen diffuses across the alveolar wall and into the blood, forming oxyhaemoglobin. The active process of continuous gas exchange in the lungs is known as ventilation.

Other associated structures of veterinary interest within the respiratory tract include the paranasal sinuses, the pleural cavity & membranes and the guttural pouches.

Cardiovascular System

Blood, which has been oxygenated by the lungs, flows through the pulmonary vein to the left atrium of the heart and subsequently to the left ventricle from which it is ejected by the heart during ventricular systole. Oxygenated blood is then distributed to the different parts of the body via the aorta. The distribution of blood is controlled by vascular tone which dictates the degree of perfusion of capillary beds and therefore the amount of oxygen available to the various tissues. Carbon dioxide produced from cellular respiration is removed from the tissues and transported either attached to proteins, in solution or as bicarbonate via the venous system to the vena cava and ultimately to the right atrium. The movement of venous blood is a product of blood flow, vascular valves and muscular and respiratory function. Carbon dioxide rich blood enters the right ventricle and is then pumped to the lungs via the pulmonary artery. The arteries, veins and capillaries are collectively referred to as the vascular system.

Integration

The function of the cardiac and respiratory systems are tightly linked and regulated to maintain blood pressure, tissue oxygen delivery and carbon dioxide removal. Cardiac function is controlled by baroreceptors (pressure receptors) which result in changes to the heart rate, contractility and vascular tone. Respiratory function is controlled centrally by chemoreceptors to maintain rate and both centrally and locally to maintain bronchiolar tone.

References

• McGeady, T.A., Quinn, P.J., FitzPatrick, E.S. and Ryan, M.T. (2006) Veterinary Embryology. Oxford: Blackwell Publishing.
• Dyce, K.M., Sack, W.O. and Wensing, C.J.G. (2002) Textbook of Veterinary Anatomy. 3rd ed. Philadelphia: Saunders.

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