I am participating in science expo held in our school . I choose the topic cardiovascular system . So can anyone do me a favour and tell important points related to cardio vascular system , thanks.

Nutrients are required for living. For example, oxygen is required by all cells in the body. How does atmospheric oxygen reach the cells? The waste materials that are produced are thrown out of the body. Is there a system that transports nutrients and collects wastes materials in the body?

The system that transports nutrients and collects waste materials for disposal in the body is the circulatory system also known as cardiovascular system. The circulatory system consists of the central organ i.e., the heart, blood vessels, and circulating fluid i.e., blood. Another system, called the lymphatic system,transports immune cells.

Let us explore the components of the circulatory system and how each component functions for the efficient transport of materials in the body.

Blood vessels

Arteries are tough, elastic tubes that carry blood from the heart and supply it to various organs of the body. As the arteries move away from the heart (i.e., on reaching organs and tissues), they divide into smaller vessels. The smallest vessels called capillaries have very thin walls. Arteries are red in colour because they carry oxygenated blood.

Capillaries (in organs and tissues) join together to form veins. Veins collect blood from different organs and tissues. Veins are thin-walled as compared to arteries. This is because they bring back blood from the organs to the heart and blood is no longer under pressure. These veins carry deoxygenated blood into the heart.

Components of blood:

Blood consists of red blood cells, white blood cells, and platelets (present in the blood plasma).

Blood is red because of the presence of haemoglobin. What is its function in blood?

The main function of haemoglobin molecule is to transport oxygen molecules to body cells for cellular respiration. When we breathe in, we take in O_2, which reaches the lung alveoli. O₂ then diffuses into blood of the surrounding capillaries from the alveoli, which has a high concentration of O₂. The haemoglobin pigment present in the blood gets attached to four O₂molecules and forms oxyhaemoglobin, oxygenating the blood.

This oxygenated blood is then distributed to all the body cells by the heart.

After supplying O₂ to the body cells, the blood collects CO_2, which is produced after cellular respiration in the cells. Thus, the blood becomes deoxygenated.

The haemoglobin pigment has less affinity for CO₂. Therefore, it is mainly transported in the dissolved form. This deoxygenated blood brings back CO₂ to lung alveoli.

The lungs have a high concentration of O₂. Therefore, it diffuses into the blood. Blood, on the other hand, has more concentration of CO_2, which moves into the area of its lower concentration in the lung alveoli. Thus, the exchange of gases occurs in the alveoli. The oxygen inhaled is transported to all parts of the body while the CO₂ produced in the cells is collected from the cells and exhaled out.

How does the heart distribute oxygenated blood?

In human beings, the heart is a muscular organ. It is divided into four chambers – right auricle, right ventricle, left auricle, and left ventricle. The walls of these chambers are made up of a special muscle called myocardium, which contracts continuously and rhythmically to distribute blood to all the body cells.

Flow of blood in the human heart

• The heart has superior and inferior vena cava. They carry deoxygenated blood from the upper and lower regions of the body respectively and supply the deoxygenated blood to the right auricle of the heart.

• The right auricle contracts and passes the deoxygenated blood to the right ventricle, through an auriculo-ventricular aperture (tricuspid valve).

• The right ventricle contracts and passes the deoxygenated blood into the two pulmonary arteries, which pumps it to the lungs where the blood is oxygenated. From the lungs, the pulmonary veins transport the oxygenated blood to the left atrium of the heart.

• The left atrium contracts and through the auriculo-ventricular aperture (bicuspid valve), the oxygenated blood enters the left ventricle.
• The blood passes to aorta from the left ventricle. The aorta gives rise to many arteries that distribute the oxygenated blood to all the regions of the body.

Since the blood goes twice through the heart, it is known as double circulation.

Warm-blooded animals such as mammals have this type of blood circulation.

The body temperature of cold-blooded animals is the same as that of their surroundings. In hot environments, their blood becomes warm and in colder environments, their blood becomes cold.

Therefore, they do not require energy to maintain their body temperature. Hence, cold-blooded animals such as fishes, amphibians, and many reptiles can tolerate some amount of mixing of oxygenated and deoxygenated blood. Therefore, they have two or three chambered hearts.

Two chambered heart of fishes:

Circulatory system of fishes: The oxygenated blood from the gills does not enter the heart. It is directly distributed in the entire body. Only the deoxygenated blood enters the auricle and then the ventricle. The deoxygenated blood enters the gills for oxygenation from the ventricle.

Thus, in fishes, the blood passes through the heart only once during one cycle of passage. This type of circulation is referred to as single circulation.

Blood pressure

Rohan visited a doctor with his grandfather.

The doctor measured his blood pressure using a sphygmomanometer. Rohan observed that the doctor placed the sphygmomanometer cuff around his upper arm and attached a fastening belt by folding the leftover flap. Then, he placed a stethoscope at his elbow joint and inflated the squeezable ball to make the pressure go above 180mm Hg (observed in the attached column of mercury).

The doctor then released the air by opening the air valve and carefully observed the pressure drop.