Blood

 What is blood?

Blood is a constantly circulating fluid providing the body with nutrition, oxygen, and waste removal. blood is mostly liquid, with numerous cells and proteins suspended in it, making blood "thicker" than pure water.


How is blood carried to and from the heart?

Blood moves through many tubes called arteries and veins, which together are called blood vessels. these blood vessels are attached to the heart. blood going towards the heart is carried through veins. blood going away from the heart is carried through arteries.


How does blood travel through the heart?

The pathway of blood through the human heart consists of a pulmonary circuit and a systemic circuit. deoxygenated blood is oxygenated in the pulmonary circuit. deoxygenated blood flows through the heart in one direction, entering through the superior vena cava(heart's veins) into the right atrium. from here, it is pumped through the tricuspid valve into the right ventricle before being pumped out through the pulmonary valve to the pulmonary arteries into the lungs. From the lungs, the oxygenated blood flows back toward the heart through the pulmonary veins to the left atrium. from here, it is pumped through the mitral valve into the left ventricle before leaving through the aortic valve to the aorta. in the systemic circuit, blood leaves the heart through the aorta goes to all the organs of the body through the systemic arteries, and then returns to the heart through the systemic veins. 


What is the function of the valves in the heart?

The four valves - tricuspid, pulmonary, mitral (bicuspid), and aortic - found in the human heart ensure that blood only goes one way, either in or out. they open up to let the blood move ahead, then they close quickly to keep the blood from flowing backward.


What is the heartbeat?

A heartbeat is the sound of the pumping of the heart, also called the cardiac cycle. the closing of the mitral and tricuspid valves causes the first part fo the "lubb-dubb" sound made by the heart as it beats. the second part of the "lubb-dubb" is caused by the closure of the aortic and pulmonary valves. The average human heart beats 72 times per minute and takes less than 60 seconds to pump blood to every cell in the body. normally, with each beat, the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body.


How does the heart get its own supply of oxygenated blood?

The heart receives its own supply of oxygenated blood from the coronary arteries. two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet.


What is blood composed of?

Blood is composed of several types of cells, floating around in a fluid called plasma. the most important cells that compose blood are the red blood cell(RBC), the white blood cell (WBC), and the platelets. plasma is a relatively clear, yellow-tinted water (92+%), sugar, fat, protein, and salt solution. the average adult has a blood volume of roughly 5 liters.


what are red blood cells (RBCs)?

RBCs, also called erythrocytes, are relatively large microscopic cells without nuclei. they normally make up 40-50% of the total blood volume. they contain hemoglobin and transport oxygen from the lungs to all the living tissues of the body and carry away carbon dioxide. in men, there is an average of 5,200,000 RBCs per cubic millimeter (microliter), whereas, in women, they are an average of 4,600,000.


What is hemoglobin?

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates and makes up 95% of red blood cells. hemoglobin in the blood carries oxygen from the respiratory organs (lungs) to the rest of the body (i.e. the tissues) where it releases the oxygen to burn nutrients to provide energy to power the function of the organisms and collects the resultant carbon dioxide to bring it back to the respiratory organs to be dispensed from the organism.


What are WBCs?

The WBSs, called leukocytes, protect the body from infection; they attack and destroy foreign particles like dust, pollen, and viruses. they exist in variable numbers and types, but make up a very small part(about 1% in a healthy adult) of the blood's volume. a drop of blood cells at a time. leukocytes are not limited to blood; they occur elsewhere in the body as well, most notably in the spleen, liver, and lymph glands.


Where are the various blood cells made?

The RBCs are produced continuously in our bone marrow from stem cells at a rate of about 2-3 million cells per second. the RBC has a life span of about 120 days. most WBCs are produced in our bone marrow from the same kind of stem cells that produced RBCs. others are produced in the thymus gland, which is at the base of the neck.


What are the platelets? 

Platelets, also called thrombocytes, are irregularly-shaped, colorless present in the blood. their sticky surface lets them, along with other substances, form clots to stop bleeding to prevent blood loss. platelets flow freely in the blood in an inactive state; but when an injury is sustained, platelets become sticky to plug the injured area. the mineral calcium, vitamin k, and a protein called fibrinogen to help the platelets form a clot when the blood is exposed to air.



Why different people have different blood groups?

The differences in human blood are due to the presence or absence of certain protein molecules called antigens and antibodies. the most common type of grouping is the ABO grouping, according to which there are four kinds of blood groups: A, B, AB, or O. another factor that plays an important role in the grouping of blood is a protein called the Rh (Rhesus) factor. if this is present, the particular blood type is called positive; if not, it is called negative.

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