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Respiratory System In Man
The Structure Of The Human Respiratory System
1- Nose & mouth
The air passes through nose & mouth to enter into the body. The passage of air through nose is healthier because of
The adaptation of the nose
a- The nose contains blood capillaries to warm the air.
b- The nose secretes mucous to moist he air.
c- The nose contains heirs to filter the air.
2- Pharynx: It is a common passage for air & food.
3- Larynx: This is the voice box
It is a tube through which the air passes to enter into the lungs.
Structure and adaptation of the trachea
a- The trachea is supported by cartilaginous rings to prevent the trachea from being collapse
b- The inner surface of the trachea is lined with cilia to reject foreign bodies.
Because the cilia move upwards making air & mucous current directed towards to the pharynx.
c- The trachea is divided into two branches called bronchi which are then divided into smaller & smaller branches called bronchioles which open at air sacs called alveoli a
5- lungs ( 2 lungs, left & right)
The lung is made of bronchioles, alveoli & a net work of blood capillaries. Alveoli have thin wall to allow exchange of gases between the air in the alveoli and the blood in the blood capillaries.
Each lung has about 60 millions alveoli of the lungs to increase the respiratory surface.
The mechanism of human respiration (Ventilation of the lunges)
Breathing depends on the presence of two types of muscles.
a- The diaphragm which is a disc shaped muscle found across the human body separate the chest cavity from the abdominal cavity.
b- The intercostal muscles
c- which are found between the ribs to move them.
The air enters into the lungs & come out from the lungs in 2 steps.
1- Inspiration (breath in) (Inhalation)
The intercostal muscles contract where the ribs move upwards and diaphragm muscle contract downwards, this leads to increase the size of chest cavity while its internal pressure decrease, this causes air to get into the lungs through the nose..
2- Exhalation or expiration
The intercostal muscles relax where the ribs move downwards and diaphragm muscle relax upward, this leads to decrease the size of chest cavity, while its internal pressure increase, this causes air to
get out from lungs to outside.
Comparison between inhalation and Exhalation
1. Any change in the rate and depth of respiration must be accompanied with similar change in the rate of heartbeats, which is regulated, by the respiratory center of the brain.
2. Each respiratory cycle (inspiration and expiration), the aeration of the lungs does not usually exceed 10 % from the whole volume of lungs (its capacity) but this ratio may be increase or decrease according to
a-The state of individual between rest and exhaustion.
b-The depth of inspiration.
3. During respiration in man, the respiratory system get rid about 500 cm3 of water through his lungs in each day from the total amount of water which reaches about 2500 cm3 that get rid from human body (thorough skin and kidneys) So, the respiratory system has an execratory function
4. After the end of expiration, a part of the air is always left in lungs. G.R.
This will help: a. In warming the new air coming to the lungs.
b. In protecting the external alveoli membranes against collapse.
The role of respiratory system in Excretion
The respiratory system plays an important role in the excretion of water.
The expiration air contains water vapour this is due to the evaporation of the water that moistens the alveoli membranes, this water is necessary for dissolving oxygen and CO2 where the exchange of gases occurs between air of the alveoli & the surrounding blood in the blood capillaries.