Lesson 11: Human Body and Organ System

In the figure : In the figure respiration has three steps: external (lungs and blood), internal (blood and body cells) and cellular, in which energy is made as ATP.

Rule 1: Three steps of respiration — External respiration: inspiration (air goes through the nose and trachea to the lungs) and expiration (oxygen goes into blood; blood carries CO₂ to the lungs and it is exhaled). Internal respiration: oxygen moves from blood to tissue fluid and CO₂ from tissue fluid into blood. Cellular respiration: nutrients like glucose are slowly burnt with oxygen in cells and energy is released as ATP.

• Easy : We breathe in air through the nose: external respiration begins.
• Medium : Oxygen reaches body cells through blood: this exchange is internal respiration.
• Exam-type : Running makes you breathe faster because muscle cells need more oxygen for more ATP.

In the figure : In the figure one glucose molecule burns with 6 oxygen molecules in the cells and gives 6 carbon dioxide, 6 water and 38 ATP.

Rule 2: Cellular respiration equation — C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (38 ATP). CO₂ and water vapour are the wastes.

• Easy : Atoms of oxygen: left 6 × 2 = 12 plus glucose 6 = 18. Right 6 × 2 = 12 plus 6 = 18. Balanced.
• Medium : 2 glucose molecules give 2 × 38 = 76 ATP.
• Exam-type : 5 glucose molecules need 5 × 6 = 30 oxygen molecules.

Spot the difference

In the figure : In the figure air passes through the nose, pharynx, sound box and wind pipe into the two lungs, which rest on the diaphragm.

Rule 1: Path of air — Nose: air is filtered by hair and mucus. Pharynx: food pipe and wind pipe start here; a lid at the beginning of the wind pipe closes it when food passes into the food pipe. The wind pipe has a sound box at its beginning and splits in the thorax into the right and left lungs.

• Easy : The hair in the nose filters dust.
• Medium : Food enters the food pipe because the lid of the wind pipe closes while swallowing.
• Exam-type : Do not talk or laugh while swallowing, so that food does not go into the wind pipe.

In the figure : In the figure, in an alveolus, oxygen enters the blood of the surrounding capillary, and carbon dioxide with water vapour leaves it.

Rule 2: Lungs and alveoli — The lungs lie one on each side of the heart in the thoracic cavity, with a double-layered covering called pleura. They are elastic like a sponge and made of many small compartments, the alveoli, each with a rich network of capillaries. Very thin walls and a large surface allow easy gas exchange. Hemoglobin, an iron-containing protein in RBCs, absorbs oxygen in the alveoli, while CO₂ and water vapour move from blood into the alveoli.

• Easy : Alveoli have thin walls, so gases pass easily.
• Medium : If you spread out all the alveoli, they would cover a very large area; this is why the exchange is fast.
• Exam-type : Hemoglobin carries oxygen because it contains iron.

In the figure : In the figure, when the ribs rise and the diaphragm lowers, air moves in; when the ribs return and the diaphragm rises, air moves out.

Rule 3: Breathing movements — The diaphragm (मध्यपटल) is a muscular partition between the thoracic and abdominal cavities. When the ribs rise and the diaphragm lowers, pressure on the lungs decreases and air moves in. When the ribs return and the diaphragm rises, pressure increases and air moves out.

• Easy : Breathing in: ribs rise, diaphragm lowers.
• Medium : Breathing out: ribs return, diaphragm rises.
• Exam-type : Place your hands on your ribs and feel them move when you breathe.

Spot the difference

In the figure : In the figure the heart has four chambers, two upper atria and two lower ventricles. The blue side holds oxygen-poor blood and the red side oxygen-rich blood.

Rule 1: The heart — The heart lies almost at the centre of the thoracic cage between the two lungs, slightly inclined to the left. It is as big as one's fist and weighs about 360 g. It is made of involuntary cardiac muscles that contract and relax rhythmically (heart beat). It has four chambers: upper atria and lower ventricles.

• Easy : Your heart is about as big as your closed fist.
• Medium : Heart muscles are involuntary: they work without our control.
• Exam-type : A healthy person has about 72 beats a minute; a rest or sleep gives fewer, exercise or fear more.

Rule 2: Heart rate and output — The sounds of the heart are 'lubb' and 'dub'. About 75 ml of blood is pumped per beat. In 1628 William Harvey described blood circulation.

• Easy : At 72 beats per minute and 75 ml per beat, one minute pumps 72 × 75 = 5,400 ml = 5.4 litres.
• Medium : In one hour the heart pumps 5.4 × 60 = 324 litres.
• Exam-type : Beats in a day: 72 × 60 × 24 = 103,680.

In the figure : In the figure an artery is deep, thick-walled and has no valves, a vein is superficial, thin-walled and has valves, and a capillary has a one-cell wall for exchange.

Rule 3: Blood vessels — Arteries carry blood away from the heart (oxygenated, except the pulmonary artery), are deeply located, thick-walled and without valves. Veins carry blood towards the heart (deoxygenated, except the pulmonary vein), are superficial, thin-walled and have valves. Capillaries are fine vessels with walls of a single layer of cells that allow exchange of materials; they unite to form veins.

• Easy : The pulse you feel on your wrist is from an artery.
• Medium : Veins have valves so that blood does not flow backward.
• Exam-type : Capillaries are the places where oxygen and nutrients pass from blood to cells.

In the figure : In the figure blood goes to the lungs by the pulmonary artery and returns by the pulmonary vein. Another artery takes it to the body and a vein brings it back.

Rule 4: Two loops — Deoxygenated blood goes to the lungs by the pulmonary artery and returns oxygenated by the pulmonary vein. The aorta carries oxygenated blood to the body, and veins bring deoxygenated blood back.

• Easy : The pulmonary artery carries oxygen-poor blood to the lungs.
• Medium : The pulmonary vein carries oxygen-rich blood from the lungs to the heart.
• Exam-type : These are the two exceptions to the rule that arteries carry oxygenated blood.

Spot the difference

In the figure : In the figure plasma is the pale yellow fluid part of blood, with 90 to 92 percent water, 6 to 8 percent proteins and 1 to 2 percent salts. The red part holds the blood cells.

Rule 1: Plasma — Oxygenated blood is deep red, salty and has pH 7.4. Plasma is pale yellow and slightly alkaline: 90-92% water, 6-8% proteins, 1-2% salts. Albumin distributes water; globulins protect; fibrinogen and prothrombin help clotting; Ca, Na and K control muscles and nerves.

• Easy : Plasma is mostly water.
• Medium : The parts of plasma must add up to 100 percent, for example 91 + 7 + 2 = 100.
• Exam-type : Of 500 ml of plasma at 91 percent water, water = 500 × 91 ÷ 100 = 455 ml.

In the figure : In the figure red blood cells carry gases, white blood cells attack pathogens like soldiers and platelets help the blood to clot.

Rule 2: Blood cells — RBCs: small, circular, enucleated, red due to hemoglobin; 50-60 lakh per mm³; made in red bone marrow; live 100-127 days. WBCs: large, nucleated, colourless; 5000-10000 per mm³; five types; made in red bone marrow; the 'soldiers' that attack pathogens. Platelets: tiny, disc-shaped; 2.5-4 lakh per mm³; help in clotting.

• Easy : RBCs carry oxygen; WBCs fight germs; platelets clot blood.
• Medium : 50 lakh RBCs per mm³ = 5,000,000. If WBCs are 10,000, RBCs are 5,000,000 ÷ 10,000 = 500 times more.
• Exam-type : An RBC lives about 120 days, which is about 4 months, so the body keeps making new ones in red bone marrow.

Spot the difference

In the figure : In the figure a tick shows that the donor group can give blood to the receiver group. O is the universal donor and AB the universal recipient.

Rule 1: Blood groups — The main blood groups are A, B, AB and O, each Rh positive or negative: eight in all. Blood groups are hereditary. Transfusion is done only after blood group matching. Group O is the universal donor; group AB is the universal recipient. Landsteiner discovered A, B, O in 1900 (Nobel Prize 1930); Decastello and Sturli found AB in 1902.

• Easy : 4 groups × 2 (Rh positive or negative) = 8 blood groups.
• Medium : A person with group O can donate to anyone, while a person with AB can receive from anyone (as per the lesson).
• Exam-type : Landsteiner's discovery of 1900 got him the Nobel Prize in 1930, which is 30 years later.

In the figure : In the figure blood pressure is highest when the heart contracts (systolic) and lowest when it relaxes (diastolic).

Rule 2: Blood pressure — Blood pressure is the pressure on artery walls due to heart contraction: systolic during contraction and diastolic during relaxation. It is measured with a sphygmomanometer. Pressure higher than normal is hypertension, in which the heart has to work more.

• Easy : Systolic pressure is higher than diastolic.
• Medium : A reading of 120 over 80 means systolic 120 and diastolic 80; the difference is 120 − 80 = 40.
• Exam-type : Less salt, regular exercise and a doctor's check help control high blood pressure.

In the figure : In the figure about 350 ml of blood is collected from a donor above 18 years of age, who can donate 3 to 4 times a year, and the fluid part is restored in 24 hours.

Rule 3: Blood donation — About 350 ml is collected and the fluid part is restored within 24 hours. Healthy persons above 18 years can donate 3-4 times a year; pregnant and breast-feeding women cannot donate. 1 October is National Voluntary Blood Donation Day.

• Easy : A donor gives 350 ml per donation.
• Medium : Four donations a year: 4 × 350 = 1,400 ml, which is 1.4 litres.
• Exam-type : A school student under 18 cannot donate, but can motivate the family and arrange a camp.

Spot the difference