Human Breathing

• The human respiratory system consists of the following:

• Nose
• Pharynx
• Trachea and subdivisions                                                      *diagram respiratory system*
• Lungs
• Alveoli

The nose:

• Air inhaled through the nose through 2 openings called nostrils which are separated by the nasal septum.
• Each nostril leads to nasal passages

Why is breathing through the nose beneficial?

1. Air is filtered by mucous and hairs in the nose
2. Air is moistened
3. Air is warmed

Result:  When air is warm and moist it diffuses from lungs to bloodstream easier!

The Pharynx:

• Contains the epiglottis (flap that prevents food/water entering trachea when we swallow)
• Contains the larynx which contains 2 vocal chords i.e. allows speech
• Glottis is the area that contains the larynx

Trachea and subdivisions:    Trachea subdivides as follows: Trachea – bronchi – bronchioles

• All of above are made of cartilage (rings of cartilage) except bronchioles – these contain muscle and elastic fibres only
• All are lined with cilia (tiny hairs) and mucous secreting cells
• Cartilage is a strong material and prevents tubes from collapsing when we breathe in

The lungs:  These are large spongy structures and are where gas exchange takes place

• Outer pleura – lines chest wall and diaphragm
• Inner pleura – lines the lungs
• Pleural cavity – gap between the outer and inner pleura membranes and is full of a liquid which reduces friction during breathing

Alveoli:  Bronchioles end in alveoli – hollow, balloon like air sacs

They are enclosed in a network of blood capillaries                                         

Function: Gas exchange                                                                                     

Adaptations of alveoli and capillaries to improve gas exchange:

1. Alveoli have thin walls (one cell thick)
2. Alveoli very numerous (over 700 million in the two lungs)
3. Alveoli are moist (moist air diffuses faster)
4. Capillaries have thin walls (one cell thick)
5. Capillaries are numerous

Gas Exchange:

What diffuses out of body cells? Carbon dioxide and water

What diffuses into body cells? Oxygen out of blood plasma

What diffuses out of alveoli? Oxygen                                                                     *picture of diffusion *

What diffuses into alveoli? Carbon dioxide and water out of blood plasma

Table !: Inhaled vs. exhaled air – person at rest

Mechanism of breathing:

• Involuntary process

Inhalation (breathing in)

1. Diaphragm and intercostal muscles contract – therefore inhalation is an active process
2. Ribs – up and out
3. Diaphragm – down
4. Volume chest cavity – increase
5. Pressure chest cavity – falls
6. External air pressure is higher than air in chest so air is forced (pushed) into the lungs

Exhalation (breathing out)

1. Diaphragm and intercostal muscles relax
2. Ribs – down and in
3. Diaphragm – up
4. Volume chest cavity – increase
5. Pressure chest cavity – increases
6. Air is forced out of the lungs

• Exercise increases both the rate and depth of breathing

Breathing disorder:     Asthma

• Caused by smaller bronchioles becoming narrower
• Triggered by allergens (e.g. dust)
• Controlled by avoiding known allergens
• Treated by drugs i.e. inhalers

Control of human breathing:

• Controlled by the brain
• High levels of carbon dioxide – form an acid – decrease pH – trigger brain to cause breathing

Therefore: Carbon dioxide is a controlling factor in gas exchange in leaves and in human breathing.

Useful videos:

https://www.youtube.com/watch?v=HiT621PrrO0

https://www.youtube.com/watch?v=Mf8xTqfspp4&feature=related