Mechanism Of Breathing In Human

Respiration of Class 7

Mechanism Of Breathing In Human

  • Breathing is a complex mechanical process involving muscular movement that alters the volume of the thoracic cavity thereby that of the lung.
  • Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.
  • The floor of the thoracic cavity is completely closed by diaphragm. It is a thin muscular septum separating the abdominal and thoracic cavities.

Breathing mechanism involves two steps:

  • Inhalation
  • Exhalation

Inhalation (Breathing in)

  • Energy requiring process.
  • Simultaneous contraction of intercostals muscles and diaphragm results in the movement of ribs outwards and upwards.
  • This action increases the volume of thoracic cavity, thus increasing the lung volume.
  • It reduces air pressure in the lungs and air rushes into the lungs through air passage.

Exhalation (Breathing out)

  • Due to relaxation of intercostals muscles and diaphragm, the ribs return to their original position and diaphragm becomes dome-shaped.
  • These movements reduce the volume of thoracic cavity and lungs return to their original volume.
  •  Air rushes out of the lungs due to increase in pressure above that of atmospheric pressure inside the lungs.

GAS EXCHANGE IN ALVEOLI

Blood rich in carbon dioxide, i.e., the deoxygenated blood enters the capillary network of alveoli.

Alveolar air has a higher concentration of oxygen and lower concentration of CO2 than the blood in capillaries. Therefore, O2 diffuses into the capillaries and combines with haemoglobin of red blood cells to form oxyhaemoglobin, to be transported throughout the body. CO2 from  blood capillaries diffuses out into the alveolar air.

Gas Exchange in Tissues

Breathing  is followed by gaseous exhange between the blood and the body tissues where carbon dioxide is produced in various metabolic activities and oxygen is used up. The blood brings oxygen from lungs and carries it to tissues which have a lower concentration of oxygen and higher concentration of carbon dioxide. Due  to the difference in concentration, exchange of gases takes place between blood and tissues.This is called tissue respiration  and is followed by the last step in which food (glucose) is oxidized insidethe cells (in mitochondria) and energy is released. This is called cellular respiration.

Transport of Respiratory GAses in the Blood

Blood is the transporter of all substances in the body hence transport of O2 from lungs to the tissues and CO2 from tissue to lung.

Transport of Oxygen :

Since oxygen is very less soluble in water only 0.3 ml of O2 per 100 ml of blood is transported as dissolved in plasma, this is only a negligible amounts, most of it is covered by RBC which contain haemoglobin that forms unstable compound with O2.    Combining with Oit form oxyhaemoglobin (HbO2) – an unstable compound which dissociated at lower pressure of Oin the tissue undergoing metabolism.One grams of haemoglobin binds about 1.34 ml of O2 when fully saturated.

Transport of carbon dioxide

Out of 3.7 ml of CO2 that is carried by each decilitre of blood from various tissues, a small portion of it (about 7 percent) is carried in dissolved form by blood plasma. About 23 percent of COof it (about 
7 percent) is carried in dissolved form by blood plasma. About 23 percent of COenters RBCs and combines with haemoglobin to form carbaminohaemoglobin and the rest 70 percent enters the erythrocytes (RBC), reacts with water and forms carbonic acid in the presence of enzyme carbonic anhydrase. In RBCs, the carbonic acid is converted to bicarbonate, most of which comes out in plasma and is carried by it.

NCERT SOLUTION FOR CLASS-7 SCIENCE (Science for grade-7 NCERT solutions)

NCERT Solution for Class 7 Science Chapter 1 - Nutrition in Plants

NCERT Solution for Class 7 Science Chapter 2 - Nutrition in Animals

NCERT Solution for Class 7 Science Chapter 3 - Fibre to Fabric

NCERT Solution for Class 7 Science Chapter 4 - Heat

NCERT Solution for Class 7 Science Chapter 5 - Acids, Bases and Salts

NCERT Solution for Class 7 Science Chapter 6 - Physical and Chemical Changes

NCERT Solution for Class 7 Science Chapter 7 - Weather, Climate and Adaptations of Animals to Climate

NCERT Solution for Class 7 Science Chapter 8 - Winds, Storms and Cyclones

NCERT Solution for Class 7 Science Chapter 9 – Soil

NCERT Solution for Class 7 Science Chapter 10 - Respiration in Organisms

NCERT Solution for Class 7 Science Chapter 11 - Transportation in Animals and Plants

NCERT Solution for Class 7 Science Chapter 12 - Reproduction in Plants

NCERT Solution for Class 7 Science Chapter 13 - Motion and Time

NCERT Solution for Class 7 Science Chapter 14 - Electric Current and Its Effects

NCERT Solution for Class 7 Science Chapter 15 – Light

NCERT Solution for Class 7 Science Chapter 16 - Water: A Precious Resource

NCERT Solution for Class 7 Science Chapter 17 - Forests: Our Lifeline

NCERT Solution for Class 7 Science Chapter 18 - Wastewater Story

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