Circulatory System: Pulmonary and Systemic Circuits

Circulatory System
Circulatory System. Credit: PIXOLOGICSTUDIO/Science Photo Library/Getty Images

The circulatory system is a major organ system of the body. This system transports oxygen and nutrients in the blood to all of the cells in the body. In addition to transporting nutrients, the circulatory system also picks up waste products generated by metabolic processes and delivers them to other organs for disposal.

The circulatory system, sometimes called the cardiovascular system, consists of the heart, blood vessels, and blood. The heart provides the "muscle" needed to pump blood throughout the body. Blood vessels are the conduits through which blood is transported and blood contains the valuable nutrients and oxygen that are needed to sustain tissues and organs. The circulatory system circulates blood in two circuits: the pulmonary circuit and systemic circuit.

Circulatory System Function

Blood Cells Within a Blood Vessel
The circulatory system transports blood throughout the body. Kateryna Kon/Science Photo Library/Getty Images

The circulatory system performs a number of vital functions in the body. This system works in conjunction with other systems to keep the body working properly.

  • Respiratory System: The circulatory system and respiratory system make respiration possible. Blood high in carbon dioxide is transported to the lungs where carbon dioxide is exchanged for oxygen. Oxygen is then delivered to cells via blood circulation.
  • Digestive System: The circulatory system works with the digestive system to carry nutrients processed in digestion (carbohydrates, proteins, fats, etc.) to cells. Most digested nutrients reach blood circulation by absorption through the walls of the intestines.
  • Endocrine System: Cell to cell communication is made possible by cooperation between the circulatory and endocrine systems. The circulatory system regulates internal body conditions by transporting endocrine hormones to and from targeted organs.
  • Excretory System: The circulatory system helps to remove toxins and waste from the body by transporting blood to organs such as the liver and kidneys. These organs filter waste products including ammonia and urea, which are removed from the body via the excretory system.
  • Immune System: Germ-fighting white blood cells of the immune system are transported to sites of infection via blood circulation.

Circulatory System: Pulmonary Circuit

Pulmonary and Systemic Circuits
Pulmonary and Systemic Circuits of the Circulatory Sytem. Credit: DEA PICTURE LIBRARY/Getty Images

The pulmonary circuit is the path of circulation between the heart and the lungs. Blood is pumped to the various places of the body by a process known as the cardiac cycle. Oxygen depleted blood returns from the body to the right atrium of the heart by two large veins called vena cavae. Electrical impulses produced by cardiac conduction cause the heart to contract. As a result, blood in the right atrium is pumped to the right ventricle.

On the next heart beat, the contraction of the right ventricle sends the oxygen-depleted blood to the lungs via the pulmonary artery. This artery branches into left and right pulmonary arteries. In the lungs, carbon dioxide in the blood is exchanged for oxygen at lung alveoli. Alveoli are small air sacs that are coated with a moist film that dissolves air. As a result, gases can diffuse across the thin endothelium of the alveoli sacs.

The now oxygen-rich blood is transported back to the heart by the pulmonary veins. The pulmonary circuit is completed when pulmonary veins return blood to the left atrium of the heart. When the heart contracts again, this blood is pumped from the left atrium to the left ventricle and later to systemic circulation.

Circulatory System: Systemic Circuit

Circulatory System Vessels
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The systemic circuit is the path of circulation between the heart and the rest of the body (excluding the lungs). After moving through the pulmonary circuit, oxygen-rich blood in the left ventricle leaves the heart via the aorta. This blood is circulated from the aorta to the rest of the body by various major and minor arteries.

  • Coronary Arteries: These blood vessels branch off from the ascending aorta and supply blood to the heart.
  • Brachiocephalic Artery: This artery arises from the aortic arch and branches into smaller arteries to supply blood to the head, neck, and arms.
  • Celiac Artery: Blood is supplied to abdominal organs through this artery which branches from the aorta.
  • Splenic Artery: Branching from the celiac artery, this artery  supplies blood to the spleen, stomach, and pancreas.
  • Renal Arteries: Branching directly from the aorta, these arteries supply blood to the kidneys.
  • Common Iliac Arteries: The abdominal aorta divides into two common iliac arteries in the lower abdominal region. These arteries supply blood to the legs and feet.

Blood flows from arteries to smaller arterioles and on to the capillaries. Gas, nutrients, and waste exchange between blood and body tissues takes place in the capillaries. In organs such as the spleen, liver, and bone marrow that do not have capillaries, this exchange occurs in vessels called sinusoids. After passing through the capillaries or sinusoids, the blood is transported to venules, to veins, to the superior or inferior vena cavae, and back to the heart.

Lymphatic System and Circulation

Lymphatic System
Lymphatic System. Pixologicstudio/Science Photo Library/Getty Images

The lymphatic system plays an important role in the proper functioning of the circulatory system by returning fluid to the blood. During circulation, fluid gets lost from blood vessels at capillary beds and seeps into the surrounding tissues. Lymphatic vessels collect this fluid and direct it toward lymph nodes. Lymph nodes filter the fluid of germs and the fluid, or lymph, is eventually returned to blood circulation through veins located near the heart. This function of the lymphatic system helps to maintain blood pressure and blood volume.