During a single cycle blood goes twice in the heart which is known as doublecirculation. It is necessary in human being to separate oxygenated and de-oxygenated blood because this makes their circulatory system is more efficient and helps in maintaining constant body temperature.

HOP€ IT'S H€LPFUL :) :)

**Circulation in Human Beings**

Circulation refers to the movement of blood through the cardiovascular system, delivering oxygen and nutrients to cells and tissues and removing waste products. This process is essential for maintaining homeostasis and ensuring the proper functioning of the human body. Let's explore the detailed process of circulation in human beings.

**Components of the Circulatory System:**

The circulatory system consists of the heart, blood vessels, and blood. The heart is a muscular organ that pumps blood, while blood vessels include arteries, veins, and capillaries that transport blood throughout the body. Blood is a fluid connective tissue that carries oxygen, nutrients, hormones, and waste products.

**Pulmonary and Systemic Circulation:**

Circulation in human beings can be divided into two main pathways: pulmonary circulation and systemic circulation.

1. **Pulmonary Circulation:**
- Begins in the right atrium of the heart, where deoxygenated blood from the body enters through the superior and inferior vena cava.
- The blood is then pumped into the right ventricle, which contracts and pushes the blood into the pulmonary artery.
- The pulmonary artery carries the deoxygenated blood to the lungs.
- In the lungs, carbon dioxide is exchanged for oxygen through the process of respiration.
- Oxygenated blood returns to the heart through the pulmonary veins and enters the left atrium.

2. **Systemic Circulation:**
- Oxygenated blood from the left atrium enters the left ventricle, which contracts and pumps the blood into the aorta.
- The aorta is the largest artery in the body and branches into smaller arteries, which deliver oxygenated blood to all body tissues and organs.
- Within the organs and tissues, the arteries divide into smaller vessels called arterioles and then into microscopic capillaries.
- Capillaries allow for the exchange of oxygen, nutrients, and waste products between the blood and surrounding cells.
- Deoxygenated blood, along with waste products, is collected by venules and then enters larger veins.
- Veins carry the deoxygenated blood back to the heart, entering the right atrium to begin the pulmonary circulation again.

**Regulation of Circulation:**

The circulatory system is regulated by several mechanisms to ensure an adequate supply of oxygen and nutrients to all body tissues. These mechanisms include:

1. **Heart Rate and Blood Pressure Regulation:**
- The heart rate is controlled by the sinoatrial (SA) node, which initiates electrical impulses that stimulate heart contractions.
- The SA node is regulated by the autonomic nervous system, with the sympathetic division increasing heart rate and the parasympathetic division decreasing heart rate.
- Blood pressure is regulated by vasoconstriction (narrowing of blood vessels) and vasodilation (widening of blood vessels), which are controlled by the nervous system and hormones such as adrenaline and noradrenaline.

2. **Oxygen and Carbon Dioxide Levels:**
- The levels of oxygen and carbon dioxide in the blood are monitored by chemoreceptors located in the aorta and carotid arteries.
- If oxygen levels are low or carbon dioxide levels are high, the chemoreceptors send signals to the brain and respiratory system to adjust breathing rate and depth.

In conclusion, circulation in human beings involves the