The Circulatory System: An Overview
The circulatory system is a vital component of the human body, responsible for the transportation of nutrients, oxygen, and waste products throughout the organism. This closed system consists of the heart, blood vessels, and blood, working in harmony to maintain life.
Definition: A closed circulatory system is one where blood remains contained within vessels throughout its journey.
The heart, a muscular organ located in the thoracic cavity, serves as the central pump of the circulatory system. It is divided into four chambers: two atria and two ventricles.
Vocabulary:
- Atrium (plural: atria): The upper chambers of the heart that receive blood.
- Ventricle: The lower chambers of the heart that pump blood out.
The heart's structure is complex, with three layers:
- Epicardium (outer layer)
- Myocardium (middle layer, responsible for contraction)
- Endocardium (inner layer)
Highlight: The myocardium is the layer that contracts, enabling the heart to pump blood effectively.
Blood vessels are categorized into three main types:
- Arteries: Carry blood away from the heart
- Veins: Transport blood towards the heart
- Capillaries: The smallest vessels, facilitating material exchange
The circulatory system is divided into two main circuits:
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Pulmonary Circulation: This circuit involves the movement of blood between the heart and lungs. Deoxygenated blood is pumped from the right side of the heart to the lungs, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then returns to the left side of the heart.
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Systemic Circulation: In this circuit, oxygenated blood is pumped from the left side of the heart to the rest of the body through the aorta. After delivering oxygen and nutrients to tissues, the deoxygenated blood returns to the right side of the heart via the superior and inferior vena cava.
Example: In pulmonary circulation, blood travels from the right ventricle to the lungs via pulmonary arteries and returns to the left atrium via pulmonary veins.
Blood pressure, a crucial aspect of circulation, is regulated by the body's nervous system. Sensory receptors detect changes in blood pressure and send signals to the medulla oblongata in the brain stem. The autonomic nervous system then releases neurotransmitters that cause smooth muscle in blood vessels to relax or contract, thus regulating blood flow.
