Notes-Class 8-Science-Chapter-11-Human Body and Organ System-Maharashtra Board

1) External respiration :

• Intake of air from the outside into the body and release of air from the body to outside is called external respiration.
• Air is taken in through nose and sent towards the lungs through trachea (wind pipe).
• External respiration occurs between cells and the external environment.
• It involves processes of inspiration and expiration.
• External respiration involves breathing and gaseous exchange.
• Oxygen combines with haemoglobin in external respiration.

2) Internal Respiration :

• Exchange of gases between cells and tissue fluid is called internal respiration.
• Internal respiration occurs only in the cells of the body.
• It involves movement of O₂ from blood into tissue fluid and movement of CO₂ from tissue.
• Internal respiration involves neither breathing nor gaseous exchange.
• Chemical reactions occur in the cells to form energy.

3) Cellular respiration :

• During respiration, the glucose molecules along with some other soluble nutrients are slowly oxidized with the help of oxygen in each cell.
• In this process the energy is released in the form of ATP, CO₂ and water vapours are produced.
• These products are not needed for the body and hence given out of the body in exhalation.
• This process of cellular respiration is shown by the following reaction :
• C₆H₁₂O₆ + 6O₂ = 6CO₂ + 6H₂O + Energy (38ATP)

(4) Lungs : Pair of lungs is the main respiratory organ in the human body. They are located in thoracic cavity. They are present on either sides of heart.

•  Each lung has double layered pleural membranes.
• Trachea bifurcates into two bronchi. Each bronchus enters lung on its side and divide and re-divide into fine bronchioles.
• At the end of each bronchiole there is alveolus. Alveolus is surrounded by capillary network.

Working of Lungs:  

• Each alveolus is extremely thin walled and hence gaseous exchange can occur through diffusion here. Due to thousands of alveoli, the lung surface is increased many a times.
• Deoxygenated blood coming from heart by pulmonary arteries is purified here in the lungs.
• It is mixed with oxygen due to gaseous exchange and returned back to the heart by pulmonary veins. Lungs thus continuously help in oxygenation of blood with the help of all of the alveoli.

Function :

• Elastic and spongy structures. Provides place for gaseous exchange. (O₂ and CO₂).

(5) Alveoli : Rich network of capillaries surround every alveolus. Their walls are extremely thin.

• Function : Gaseous exchange takes place in alveoli.

(6) Diaphragm : Function : Movement of air in and out of the body caused due to upward and downward movements of the diaphragm.

• Diaphragm is a muscular partition that divides the thoracic and abdominal cavity.
• Located at the base of thoracic cage, it is very important in breathing movements.

Movements of Diaphragm :

• Diaphragm can undergo consecutive upward and downward movements.
• These movements along with movements of thoracic cage cause rise and fall of the pressure in the thoracic cavity.
• Rising up of ribs and lowering of diaphragm causes the decrease in air pressure which makes the air to move into the lungs through nose. This is inhalation.
• When the pressure rises in the thoracic cavity again, the air is given out. This is exhalation.
• This is caused due to ribs returning to their original position and rising diaphragm. This simultaneously increases the pressure in thoracic cavity.

Human heart : Human heart is four chambered muscular organ.

• The size of the heart is about one’s own fist and its weight is about 360 gm.
• For protection, it is covered over by double layered pericardium.
• The wall of the heart is made up of cardiac muscles which are involuntary in nature. They have the capacity of rhythmic beating.
• The upper two chambers are called right and left atrium and lower two chambers are called right and left ventricle.
• Between right atrium and right ventricle there is tricuspid valve which guards the opening. Similarly between left atrium and left ventricle there is bicuspid valve.
• On entire right side of the heart there is deoxygenated blood.
• On entire left side of the heart there is oxygenated blood.
• Right atrium receives deoxygenated blood by superior and inferior vena cava.
• These two major veins bring deoxygenated blood from entire body to the heart.
• Left atrium receives oxygenated blood from lungs by pulmonary vein.
• Right ventricle sends the deoxygenated blood to lungs for oxygenation, through pulmonary artery.
• Left ventricle supplies oxygenated blood to entire body through systemic aorta.

(a) Artery : Blood vessels which carry the blood away from heart are called as arteries

• Transporting blood from the heart to the body.
• Deeply located in the body.
• Walls are thick.
• No valves inside
• Transporting oxygenated blood (exception : Pulmonary artery)

(b) Veins : Vessels carrying the blood towards the heart from various parts of body are called as veins.

• Transporting blood from the body to the heart.
• Superficially located in the body.
• Walls are thin.
• Provided with valves.
• Transporting deoxygenated blood (exception : Pulmonary vein)

Valves in veins prevent the backflow of the blood. Blood in the veins is not under great pressure so it is likely that it may flow back. But valves prevent such movements.

(c) Capillaries :

• Arteries keep on branching out to form their branches and sub-branches, ultimately forming capillaries. Capillaries in turn join to form veins.
• Capillaries are fine hair-like vessels with extremely thin single-celled layered walls.
• Every important vital organ has network of capillaries.
• The oxygen, nutrients, hormones, vitamins, etc. are transported to the cells and waste materials of the cells are removed from the cells through capillaries.
• Thus capillaries carry out exchange of materials in and out of the cell.

Blood components :

Human blood is a fluid connective tissue consisting of blood plasma and blood corpuscles suspended in it.

(1) Plasma : Plasma is the fluid part of the blood which is pale yellow in colour. It is slightly alkaline in nature. It has 90-92% water, 6-8 % proteins and 1-2 % inorganic salts.

• It contains proteins such as albumin, globulin, fibrinogen, etc. There are inorganic ions such as Ca, Na and K.

(2) Blood cells :

• Blood cells are mainly of three types, viz. RBCs, WBCs and blood platelets. They are produced in the red bone marrow.
• RBCs are small, circular and enucleated cells. They are full of haemoglobin which is essential in transporting oxygen.
• RBCs are red blood cells which are 50 to 60 lakh per cubic millimetre. Their life span is 100 to 127 days.
• WBCs are large, nucleated and colourless. They are of five subtypes, viz. neutrophils, basophils, eosinophils, monocytes and lymphocytes. They are 5.to 10 thousands per millimetre of blood.
• Platelets are very small disc-shaped blood cells which are 2.5 to 4 lakh per cubic millimetre of blood.

Distinguish between RBCs and WBCs :

Function of human blood :

Transport functions :

• Gases: Oxygen is carried via blood from lungs to cells in various parts of body and carbon dioxide from tissues to lungs.
• Nutrients: Simple nutrients like glucose, amino acids, fatty acids are taken up by blood from wall of alimentary canal and transported up to each cell in the body.
• Waste materials : Nitrogenous wastes like ammonia, urea, creatinine are released by tissues into blood which carries those to kidney for excretion.
• Enzymes and hormones : Blood transports the enzymes and hormones from the site of their production to the site of their action.
• Protection : Antibodies are produced in the blood and they protect the body from microbes and other harmful particles.
• Thermoregulation : Body temperature is maintained constant at 37 °C by vasodilation and vasoconstriction.
• Maintaining the balance of minerals like Na, K in the body.
• If bleeding occurs at the injury, platelets and a protein called fibrinogen of the blood form a clot and seal the injury.

Functions of blood cells :

• RBCs : With haemoglobin it carries out transport of respiratory gases.
• WBCs : Soldiers of the body. Produce antibodies and give immunity to body.
• Platelets : Help in blood clotting.

Blood Groups :

• The A, B, O blood group system is the most popular and medically important blood group system of human beings.
• The blood group is determined due to antigenic protein present on the RBCs and the antibody present in the plasma.
• The four main groups of human blood are A, B, AB and O.
• According to the presence or absence of Rh antigen the blood groups are further said to be Rh positive or Rh negative.
• This makes total eight blood groups which are taken into consideration at the time of blood transfusions. These are - A Rh +ve, A Rh -ve; B Rh +ve, B Rh-ve; AB Rh +ve, AB Rh -ve; O Rh +ve, O Rh —ve.
• Blood groups are dependent on genes and are thus hereditary in nature.

From where the blood is supplied for blood transfusion? :

• Blood bank : In blood bank the blood from the healthy donor is extracted by specific method with proper care and kept in sterile and refrigerated condition.
• Blood Donor: The person who gives the blood.
• Recipient of blood : The person to whom blood is given.
• Universal donor: The persons with O blood group.
• Universal recipient : The persons with AB blood group.
• Who is in need of blood? : The persons who had haemorrhage (blood loss) such as victims of accidents, persons who have undergone surgery, patients of thalassemia and anaemia or cancer, at the time of delivery.
• Blood group is decided according to the heredity/ childbirth. As per the blood groups of mother and father, the blood group type is formed in children due to genes concerned with type of blood group.
• The blood type of donor and recipient should be perfectly matched before the transfusion.
• Blood donation is considered as the best donation as it can save someone’s life.
• About 350 ml. of blood is taken at the time of donation.
• Pregnant and nursing mothers cannot donate the blood.
• Persons in the age group of 18 to 60 can donate blood for 3-4 times in a year.
• National Voluntary Blood Donation Day is observed on 1st October every year.

Blood pressure :

• The force of flowing blood which is exerted on the arterial wall is called blood pressure.
• Due to contraction of the heart the blood pressure is created on the arteries.
• Systolic pressure : 120-139 mmHg, Systolic pressure is the maximum pressure in blood vessels when heart is contracting.
• Diastolic pressure : 80-89 mmHg, Diastolic pressure is the minimum pressure in blood vessels when heart comes back to normal or relaxes.
• Blood pressure is described as 120/80 in medical terms.
• Sphygmomanometer is the instrument that is used for the measurement of the blood pressure.

Hypertension (High Blood Pressure) :

• Blood pressure values more than 140-90 is hypertension or high blood pressure.
• In hypertension, there is stress on blood vessels and heart and thus person has to be careful for controlling it.
• Hypertension can cause variety of damage in the body which may lead to paralysis, heart disorder or death.