Transportation of essential nutrients, waste materials and other life-saving activities that happen within our body are influenced by the flow of blood from one part to the other part. Blood Circulatory System is the a collection of human heart, blood vessels and blood that perform the above-mentioned activities.
Structure of Blood
Blood is a heterogeneous, viscous and red connective tissue. It comprises of two major components: Plasma and Blood corpuscles (cells).
- Plasma: Plasma is a hay-colored fluid that constitutes around 55% of the total composition of the blood. The blood corpuscles are free to float on the plasma. It is responsible for the transmission of digested food, waste materials, hormones, and other important or harmful chemicals from the site of production to the site of consumption or excretion. It regulates the body temperature, amount of water, chemical compositions and pH value of the blood. It contains fibrinogen that helps in blood clotting.
- Blood Corpuscles: These are the blood cells present in the blood. They constitute around 45% of the blood.
- Red Blood Cells (RBCs)or Erythrocytes: RBCs are red colored, biconcave and enucleated(lack the presence of a nucleus)disc like structure present in the plasma. They contain hemoglobin that provides them the red-color. In the body of a healthy man, number of RBCs ranges from 5 – 5.5 million per cubic mm and in the body of a healthy woman, it ranges from 4.5 – 5 million per cubic mm. The life span of RBCs is around 120 days. They are destroyed in the liver.
Its major function is to help in exchange of gases, maintain the viscosity of blood and ion-balance. - White Blood Cells (WBCs)or Leucocytes: WBCs are irregular in shape and have a nucleus. In the body of a healthy human being, number of WBCs ranges from 4000 to 11000 per cubic mm. Their life span is very short, i.e., few days only. They are destroyed in the liver, spleen and at the site of infection.
Its major function is to protect the human body from foreign bodies. It produces antibodies that functions to kill and/or neutralize the germs, viruses, and bacteria that enter our body and destroy the damaged cells by phagocytosis. It keeps human body healthy. - Platelets or Thrombocytes: They are colorless, oval or round, blood corpuscles that do not have a nucleus. In the body of a healthy human being, number of platelets varies from 2.5 lakhs to 4.5 lakhs. Their life span is around 5 to 10 days. They are destroyed in the spleen.
Its important function is to help in the coagulation or clotting of blood by releasing a chemical called thromboplastin.
- Red Blood Cells (RBCs)or Erythrocytes: RBCs are red colored, biconcave and enucleated(lack the presence of a nucleus)disc like structure present in the plasma. They contain hemoglobin that provides them the red-color. In the body of a healthy man, number of RBCs ranges from 5 – 5.5 million per cubic mm and in the body of a healthy woman, it ranges from 4.5 – 5 million per cubic mm. The life span of RBCs is around 120 days. They are destroyed in the liver.
Functions of Blood
- Transportation: Blood transports essential materials like water, nutrients, hormones and oxygen to the tissues. It also transports waste substances like urea, carbon dioxide, etc. to the site of excretion.
- Protection: It protects body by fighting against germs and toxic materials. Fibrinogen and prothrombin proteins present in platelets and plasma help in blood clotting.
- Regulation: It maintains body temperature and balance the amount of water to the constant level. It also regulates different chemicals like salt, sodium ,potassium, calcium, acidity, alkalinity etc.
Blood Circulation
In human blood circulatory system, the blood is transported to the heart twice: once from all parts of the body and second from the lungs. So, the blood circulation in human is called double circulation.
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium. As the atrium contracts, blood flows from right atrium to right ventricle through the open tricuspid valve. When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts. As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated. The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium. As the atrium contracts, blood flows from your left atrium to left ventricle through the open mitral valve. When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts. As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.
The double circulation of the blood occurs through two ways:
- Pulmonary circulation
The circulation of blood from the right ventricle to the left auricle via lungs is called pulmonary circulation.
2. Systemic circulation
The circulation of blood from the left ventricle to the right auricle via body tissues (except lungs) is called systemic circulation.
Heart
The human heart is a four-chambered muscular organ, shaped and sized roughly like a man’s closed fist with two-thirds of the mass to the left of midline.
External Morphology
The human heart contains four complete chambers. It is divided into two halves (right half and left half) by septa. Each half consists of two chambers: the upper, small-sized atrium or auricle and the lower, large sized ventricle. The human heart remains enclosed in a double layered membrane sac called pericardium. The space between two pericardial layers is filled with a slippery fluid known as pericardial fluid. This fluid enables the heart to contract smoothly, keeps tissues of the heart moist for proper beating and also protects the heart from mechanical injury.
Internal Morphology
Right Atrium:
- Receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus and transfers.
- Functions to transfer blood thru the tricuspid valve during diastole (ventricular relaxation) into the right ventricle.
Left Atrium:
- Receives oxygenated blood from the pulmonary veins and transfers it through the mitral valve during diastole (ventricular relaxation) into the left ventricle.
Right Ventricle:
- Receives blood from the right atrium via the tricuspid valve during diastole and is responsible for moving deoxygenated blood to the lungs for oxygenation and CO2 elimination during systole (ventricular contraction).
- Considered a low-pressure system.
Left Ventricle:
- Receives blood from the left atrium via the mitral valve during diastole and is responsible for moving oxygenated blood to the systemic vasculature and organs during systole (ventricular contraction).
- Considered a higher-pressure system compared to the right ventricle.
Blood Vessels
The path through which the blood flows in human body are called blood vessels. They are generally of the following types:
- Arteries: All arteries, except Pulmonary Artery, carry pure or oxygenated blood. They have thicker walls to bear the high pressure of the blood. They do not contain valves. They are placed deep under the human skin.
- Veins: All veins, except Pulmonary Vein, carry impure or deoxygenated blood. They have thinner walls because the blood pressure is low. They do contain valves to prevent the backflow of the blood. They are superficially placed on human skin.
- Capillaries: They are extremely narrow and thin-walled blood vessels. Capillaries connect arterioles to the venules and act as the site of transmission of various chemical substances.
Blood Pressure
The pressure exerted by blood on the walls of the arteries when the left ventricle contracts and relaxes is known as blood pressure. The unit of blood pressure is millimeters of mercury(mmHg). It is represented by two numbers. The upper-level number is called systolic blood pressure and the lower one is called diastolic blood pressure. The normal blood pressure of human body is 120/80 mm of Hg where 120 is the systolic pressure and 80 is the diastolic pressure.
- Systolic blood pressure
Systolic blood pressure is the measure of maximum pressure in the arteries when left ventricle contracts. The contraction of heart is also called as systole. The normal systolic blood pressure is considered 120mmHg.
- Diastolic blood pressure
Diastolic blood pressure is the measure of minimum pressure in the arteries when left ventricles relaxes. The relaxation of heart is called diastole. The normal diastolic blood pressure is considered 80mmHg.
A sphygmomanometer and stethoscope are used to measure blood pressure manually. If the blood pressure increases above the value 120/80mmHg, it is called high blood pressure. Similarly, if it drops below 120/80mmHg it is called low blood pressure.
Blood Sugar
Insulin is a hormone secreted by pancreas that helps in glucose utilization. Thus, Insulin helps to remove excess glucose present in the blood by utilizing in the cells. Lack of insulin causes high level of glucose in the blood. This condition is called diabetes. It is also called sugar disease .Blood Sugar is a diseased condition of human body caused due to imbalance of insulin hormone in the blood.
Gestational Diabetes (GD): The diabetes which occurs due to low insulin production or due to insulin resistance during the pregnancy is known as gestational diabetes. It occurs in the middle or late pregnancy. But it may completely disappear after pregnancy.
Symptoms of Diabetes:
- Frequent urination,
- Passing out of sugar in urine,
- Excessive thirst and hunger,
- Delay in wound healing,
- Tiredness,
- Blurred vision,
- Muscle cramping.
Preventive measures of Diabetes:
- Obesity should be reduced.
- Balanced diet should be taken.
- Hypertension should be reduced.
- Physical exercise should be taken regularly.
- We should walk in the morning.
- We should avoid smoking and drinking alcohol.
- We should consume sufficient amounts of fruits and vegetables.
Uric Acid
Uric acid is a compound which is produced by the breakdown of an organic compound called purine. The high concentration of uric acid is harmful to our body. The normal level of uric acid in blood is 3.4-7.2 mg/dL. The condition in which there is excess of uric acid in the body is called hyperuricemia which can lead to gout(a type of arthritis), cardiovascular disease, obesity, hypertension, etc.
Symptoms and effects of Uric acid(Gout)
- Increased concentration of uric acid in the body.
- Swelling of the skin and joints of the legs with burning sensation.
- Difficulty in walking and movement.
- Reddish or purple skin.
Preventive and control measures of uric acid(gout)
- We should drink adequate water at regular intervals.
- We should consume baking soda or its products.
- We should reduce weight through physical exercises.
- We should eat 10-40 cherries a day.
- We should avoid drinking alcohol.
- We should avoid red meat, legumes and sea foods.
- We should eat low purine diet.