Respiration in human beings

Date: December 09, 2014

Respiration in Human Beings

Human beings, like other land animals, are air breathers.

The Respiratory System in Human Beings– The human respiratory system beings from external nostrils, through which air is drawn into nasal cavities. The nasal cavity is separated from oral cavity by a bony palate, so we can breathe in air even while we eat. In the nasal cavity air is warmed, moistened and dust particles are entrapped in the mucous (secretion of glands inside nasal cavity). Nasal cavities end in internal nostrils, through which air enters pharynx.

The phaynx leads into trachea or wind pipe through a slit called glottis. While swallowing food, glottis gets covered by a small cartilaginous callapse when there is not much air in it, as it is supported by rings of cartilage. Trachea runs down the nech and divides into bronchi, which lead into the lungs.

The lungs lie in the thoracic cavity which is separated from the abdominal cavity, by a muscular partition called diaphragms. Within lungs, bronchi branch into many bronchioles. Each bronchiole terminates in a sac called alveolus or alveolar sac, giving the appearance of a bunch of grapes. Walls of alveoli are extremely thin and covered by blood capillaries. The lungs are covered by two thins membranes called pleura.

The Voice Box– the voice box, also called larynx, is an enlarged part of trachea. It is covered by pieces of cartilage forming a box. In males, the “adam’s apple” is the protruding cartilage of the voice box. Stretched across the larynx are two vocal cords. Vocal cords vibrate to produce sound, which results in speech.

Mechanism of Breathing – When we breathe in, air from outside rushes into the alveoli of the lungs. This is called inhalation and occurs when the thoracic cavity expands. Thoracic cavity expands when the diaphragm and muscles attached to ribs contract. This makes the thorax move upwards and outwards, thereby increasing the volume inside thoracic cavity. Thus, air pressure decreases inside and air from outside rushes into lungs through nostrils, trachea and bronchi. The alveolar sacs set filled with oxygen rich air. The alveoli are richly supplied with blood capillaries. Through the thin walls of alveoli and blood capillaries, exchange of gases takes place. From the alveoli, oxygen diffuses into blood and is supplied to the tissues. Carbon dioxide is absorbed by blood from for exhalation. Carbon dioxide is subsequently pushed out of lungs through trachea and nostrils. This happesn when thoracic cavity comes back to its orginal size as diaphragm and rib muscles relax. Breathingout carbon dioxide is called exhalation. Thus, during vigorous exercise, the demand for oxygen increases the rate by about 20 to 25 times.

Exchange of Gases in Tissues – Breathing is the first step in respiration. In the next step of respiration, exchange of respiratory gases occurs between the blood and tissues. In the tissues, oxygen gets used up and carbon dioxide is released. The blood which brings oxygen from lungs and carries it to tissues has a higher concentration of oxygen and lower concentration of carbon dioxide. Due to the difference in concentration, the gases get exchanged between tissue and blood capilloaries.

The last step in respiration is the oxidation of simple food molecules like glucose for release of energy. This occurs in the mitochondria of cells.

The total area for gas exchange provided by our 300 million alveoli in two lungs is 36 to 72 square metres.

In the cycle of inhalation and exhalation, repeated 15 to 18 times in a minute about 500 ml of air is breathed in and out. In 24 hours, we breathe in 15000 litres of air! That is why we must breathe clean and unpolluted air.

Emphysema – The area for gaseous exchange in lungs gets reduced in smokers. Walls separating alveoli breakdown. Leading to abnormal alveoli with lesser area. Gaseous exchange is thus reduced. As a result, hear has to pump more blood and an ouver-straned heart may lead to hear failure.