Page 6 - class-XI-ch.8-Lesson notes

Mechanism of Respiration

Respiration is a process by which the lungs expand to take in air
and after that contract to expel the air outside. The complete
respiration process involves all the muscles of the head, neck,
thorax and abdomen in addition to the involuntary muscles of
larynx, trachea and bronchi. However, the main muscles of
respiration in normal breathing are the intercostals muscles
and diaphragm. Mechanism of respiration involves inspiration
and expiration, which are stated below.
Inspiration

When we inspire or inhale the intercostals muscles contract
actively to expand the chest cavity. Ribs and sternum move
upwards and outwards. Width of the chest increases from side to side from front to back and from top to bottom.
The diaphragm Mechanism of respiration also contracts, moves downwards and the depth of the chest increases.
The capacity of the thorax increases. The pressure between pleural surfaces is reduced. Lungs expand to fill thoracic
cavity. Air pressure within alveoli is now less than atmospheric pressure. Air is sucked into alveoli from atmosphere.

Expiration
When we exhale or expire, the intercostals muscles relax. Ribs and sternum move downward and inwards.
Diaphragm moves upwards. The depth of the chest diminishes. The capacity of thorax decreases. The pressure
increases and forces the air to go out of the lungs.

Structure and Functions of Circulatory System

Meaning of Circulatory System circulatory system is a group of organs that transport the blood and other
substances to and from all parts of the body. For the body to be maintained in a state of good health, the individual
cells, tissues and organs must have a continuous supply of oxygen and other nutrients. Along with this, there must
be continuous removal of carbon dioxide and waste products. The body system with the specialized function of
transporting these materials to and from various parts of the body is the circulatory system. The heart and blood
vessels through which the blood is constantly moving are the parts of the circulatory system.

The circulatory system includes the heart and blood vessels (arteries, veins and capillaries) and is a closed system
through which blood flows continuously.

This system can be studied under the following heads.
1. Heart 2. Arteries 3. Veins 4. Capillaries

Heart
The human heart is made up of cardiac muscles. It is a hollow, cone-shaped muscular organ. It is a sort of pump.
The pumping action of the heart is fundamental to adequate nutrition of cells and maintenance of internal
environment. Without the pumping action of the heart, cells would starve; waste products such as C02, lactic acid
and acid phosphate would build up; and life of the cell and of the individual would cease.

1. Location of the Heart: The heart is located in the thorax between the lungs and above the central depression of
the diaphragm. Its weight is approximately 300 g. The base of the heart remains above and the apex below. It is
about the size of the closed fist of a person. The apex is inclined towards the left side. As placed in the body, it
has an oblique position and the right side is almost in front of the left. The impact of heart during contraction is
felt against the chest wall in the space between the fifth and sixth ribs, a little below the left nipple and about
8 cm to the left of the median line.