RBSE Class 8 Science Notes Chapter 7 Blood Circulation

Rajasthan Board RBSE Class 8 Science Notes Chapter 7 Blood Circulation

We get energy from food after its digestion. Living beings take in O2 in respiration and give out CO2. To carry substances to different part of our body, red pigment (fluid) is found in our body which is called blood.

Blood Composition and Blood Groups:
If any scratch on cut occurs on any part of our body blood flows out. Blood is found in every vertebrate like fishes, frog, lizard, goats and human being etc.
Structure of blood: Blood of human body has two parts:
1. Plasma (in liquid form)
2. Corpuscles (in solid form)

  • Plasma: it is light yellow colored, clear, sticky, transparent liquid. About 50 – 60 percent part of blood is plasma. Generally it has 90 % water and 10% organic and inorganic substances due to the presence of Inorganic alkaline salts, plasma is alkaline in nature. Blood contains proteins, glucose, fatty acids hormone etc organic substances in it. Plasma acts to keep blood in liquid form, hence blood is called liquid connective tissue. Blood corpuscles-Approximately 40% part of the blood is formed of corpuscles.
  • They are of three kinds:
    • Red blood corpuscles (RBC) or erythrocytes.
    • White blood corpuscles (WBC) or leucocytes.
    • Platelets or thrombocytes.
  • RBC or Erythrocytes:
    • Shape – Spherical disc shaped.
    • Nucleus – absent.
    • Contain red pigment called hemoglobin. It carries oxygen in the form of oxy-hemoglobin in whole body.
    • RBC are formed in bone marrow.
  • Function of RBC
    • To carry oxygen to every cell of the body.
    • To carry food.
    • To maintain balance of body temperature i.e. fixed temperature of the body.
  • WBC or Leucocytes
    • They are longer than RBC
    • Contain nucleus.
    • They are irregular in shape, example: amoeba.
    • They are colourless due to absence of any pigment.
    • Less in number compared to RBC. They are also called as soldier cells.
  • Function of WBC: They perform as antibodies to secure body from any infection. They destroy the disease, viruses and bacteria to keep body healthy. They eat dead body cells and keep the blood clean.
  • Blood platelets or Thrombocytes:
    • They are small in size nucleated, and irregular in shape.
    • Less in number, they are also formed in bone marrow like RBC
  • Function of Platelets:
    • They help in blood clotting.
    • Controls blood flow due to any injury.
  • Blood groups: Karl Landsteiner was the first who gave information about presence of blood groups in human blood in (1863-1943). Researches proves that the group of donor and the receptor should be the same. Unknowingly if the blood of different groups is given to the patient then clotting of the blood occurs in the body. It blocks the flow of blood. In such condition death of receptor takes place.
  • Why this happens :After getting the knowledge of blood groups it was discovered that two types of proteins are found in human body:
    • Antigen
    • Antibody
  • Antigens: found in human blood are of two types antigen A and antigen B.
  • Antibody:  They are also of two types antibody a and antibody b.
    It is essential for the presence of antigen A with antibody b and antigen B with antibody a to form the clotting of blood. To stop the bleeding or if wrong group is transferred in the patients body the blood clotting occurs which stops the circulation of blood and patients dies. On the basis of the presence of these antigens and antibodies Karl Landsteiner had divided the human blood into four  groups -A, B, AB, and O.
  • Human blood groups:
    S.NO Blood group Antigen Antibody
    1. A A b
    2. B B a
    3. AB A and B None
    4. 0 none a and b

Importance of blood group: Due to the knowledge of blood group, blood donation has been proved as a boon for the society. By this if the blood is required for the accidental victims and sick persons then blood of appropriate group could be made available by the blood banks or registered voluntary blood donors easily.

They are important in the field of law and justice by taking samples and tests of DNA culprits could be caught. Deficiency of blood in the body is fulfilled by blood donation and given that blood to person who has deficiency.
Information related to the blood:

Blood group of Donar Blood group of Receptor
A B AB O
A × ×
B × y ×
AB × × ×
0

NOTE:
Symbol {✓) Means blood can be given, Symbol (×) means blood cannot be given. The person of group AB can receive blood from any one.
The person of group O can give blood to any person.
In this way group AB is the universal receptor while group O is the universal donor.

Blood donation and Blood bank:
As far as possible blood should be taken from relatives but if it is not possible then blood could be received from blood bank opened by government in government hospital of every district or private blood banks run by social service institutions. To preserve blood in the blood bank, Sodium citrate is mixed. It can be preserved for 30 days in blood banks.

Who can donate blood?
Any as a man or woman can donate blood-

  • Whose age is 18 to 60 years.
  • Whose weight is more than 45 kg.
  • Who is not suffering from AIDS, hepatitis B and C, syphilis, malaria or any serious disease.
  • Who hasn’t donated blood for last 3 months.
  • Who has not get operated in 6 months interval.
  • Whose hemoglobin is more than 12.5.
  • Whose blood pressure is normal.
  • Whose body temperature is 37.5° C and pulse rate is normal.
  • Woman who is not pregnant.
    They all can donate blood.

Things to be noted after blood donation:

  • After blood donation intake liquid substance within 24 hours like: Juice, milk, etc.
  • Do not exercise or work hard for next 24 hrs, after donating blood.

Functions of blood:

  • It carries O2and CO2 in our body.
  • Nutrient and waste product are carried by it.
  • It protects our body from diseases and from foreign viruses and bacteria’s.
  • If body gets injured it stops bleeding by making blood clots.
  • Carries antigens and antibody.
  • Maintain the body temperature.
    Circulation of blood is carried by heart and veins together.
  • Blood vessels: There are many types of blood vessels in our body which carry blood in the body from one place to another.
    There are two main types of blood vessels found in the body: artery and vein.
  • Arteries: it takes oxygenated blood to every part of the body. As the blood flows with great pressure, hence the wall of arteries are thick and flexible. Arteries divided into small venules and reach to the tissues and divides into tiny vessels called capillaries.
  • Veins: They collect CO2 contained blood or deoxygenated blood and take back to the heart. The wall of veins are thin compared to arteries. They have such valves which allow blood to flow only in one direction i.e. towards heart. Capillaries present in the tissues join together to form veins.
  • Pulse: If we put middle and index finger on our wrist we feel some beats. These beats are due to flow of blood. Such vibrations are called pulse beats. The pulse beats of a normal person is 72 times in a minute.

Human Heart and Blood Circulation:
The heart is a hollow muscular organ in the middle of the chest, that pumps blood around the body supplying cells with oxygen and nutrients. It does pumping without break. Its size is like our fist. It is divided into four chambers, to avoid mixing of O2 and COmixed blood, the upper two parts are called auricles and lower two ventricles. A muscular wall, called the septum divides the heart lengthwise into left and right.

A valve divides each side into two chambers-an upper atrium and a lower ventricle. When the heart muscles contract it squeezes blood through the atria and through the ventricles. Oxygenated blood from the lungs flows from the pulmonary veins into the left atrium, through the left ventricles and then out via the aorta to all parts of the body. Deoxygenated blood returning from the body flows from the vena cava into the right atrium, through the right ventricle and then out via the Pulmonary artery to the lungs for reoxygenation. At the rest, heart beats between 60 – 80 times a minute. During exercise or a time of stress rexcitement the rate may increase to 200 beats a minute contraction and expansion of heart is called heart beats or pulse. Doctors by counting these beats of heart or pulse presumeslhe status of health.

Stethoscope: It is an instrument to measure heart beats. It was invented by a French Dr. R. Laennec in 1816.
The invention of blood circulation was done by Dr. William Harvey (1518-1657). He was honoured for this and was called circulator.

Diseases caused by Blood Infection:
Due to deficiency of blood or blood infection, some diseases occur like – anemia, polycythenia blood cancer, hepatitis B, AIDS etc.
AIDS has not cure yet. It’s virus is called HIV. It is an incurable syndrome, only prevention we cure. The full form of AIDS is Acquired Immuno Deficiency Syndrome. By ELISA test it could be traced. On 1 December World AIDS day is celebrated
every year.

RBSE Class 8 Science Notes