Post-text assignments

1 Answer the questions:

1 Through what organs and in what order does the air get into the lungs?

2 Lungs of humans are symmetrical. Is this statement correct?

3 What is surfactant? What is it necessary for?

4 Is there any difference between lung capacities of smokers and non-smokers (male and female, tall and short people)?

5 What is the tidal volume?

6 What quality makes the diaphragm unique?

2 Say what organ is spoken about:

1. Tiny, multi-lobed air sacs made of simple squamous cells. They have very thin walls, which enables air exchange with the equally thin-walled capillaries of the circulatory system.

2. A tubular structure with 1 inch diameter and a length of 4.25 inches, composed of around 15 – 20 C-shaped pieces of hyaline cartilage.

3. An organ through which air is inhaled and exhaled.

Unit 10

Pre-text assignment

Learn the key words and phrases:

energy expenditure, ambient air, pulmonary capillaries, oxygen absorption, apnea, respiratory acidosis.

Respiration

In human physiology, respiration is the transport of oxygen from the clean air to the tissue cells and the transport of carbon dioxide in the opposite direction. This is only part of the processes of delivering oxygen to where it is needed in the human body and removing carbon dioxide waste.

Not all of the oxygen breathed in is replaced by carbon dioxide; around 15% to 18% of what we breathe out is still oxygen. The exact amount of exhaled oxygen and carbon dioxide varies according to the fitness, energy expenditure and diet of that particular person.

Air-breathing of humans, respiration of oxygen includes four stages:

1 Ventilation from the ambient air into the alveoli of the lung.

2 Pulmonary gas exchange from the alveoli into the pulmonary capillaries.

3 Gas transport from the pulmonary capillaries through the circulation to the peripheral capillaries in the organs.

4 Peripheral gas exchange from the tissue capillaries into the cells and mitochondria.

Note that ventilation and gas transport require energy to power mechanical pumps (the diaphragm and heart respectively), in contrast to the passive diffusion taking place in the gas exchange steps. Nasal breathing of respiration process refers to the state of inhaling and exhaling through the nose.

It is considered superior to mouth breathing for several reasons. Breathing through the nose has numerous health benefits due to the fact that the air travels to and from the external environment and the lungs through the sinuses as opposed to the mouth. The sinuses do a better job of filtering the air as it enters the lungs.

In addition, the smaller diameter of the sinuses creates pressure in the lungs during exhalation, allowing the lungs to have more time to extract oxygen from them. When there is proper oxygen-carbon dioxide exchange, the blood will maintain a balanced pH. If carbon dioxide is lost too quickly, as in mouth breathing, oxygen absorption is decreased.

Nasal breathing is especially important in certain situations such as dehydration, cold weather, laryngitis, and when the throat is sore or dry because it does not dry the throat as much.

Nasal breathing in public is considered to be more socially acceptable and attractive than mouth breathing. Mechanism of respiration

There are two types of physical movements associated with the respiration. They are:

• inspiration or inhalation;

• expiration or exhalation;

During inspiration, the outer intercostal muscles contract, which raises the chest cavity or the ribs. This is accompanied by the lowering of the diaphragm. Together these movements serve to increase the area of the thoracic cavity, which reduces the pressure. The air from outside rushes into the lungs.

After the internal respiration in the lungs, the impure air is expelled in the following manner:

The inner intercostal muscles contract bringing the ribs back to the original position and the diaphragm is also raised back by the action of the abdominal muscles. This reduces the space in the chest cavity and increases the pressure. This expels the air out of the lungs.

Under normal conditions, humans cannot store much oxygen in the body. Apnea of more than approximately one minute's duration therefore leads to severe lack of oxygen in the blood circulation. Permanent brain damage can occur after as little as three minutes and death will inevitably ensue after a few more minutes unless ventilation is restored. However, under special circumstances such as hypothermia, hyperbaric oxygenation, apneic respiration, or extracorporeal membrane oxygenation, much longer periods of apnea may be tolerated without severe consequences.

Apnea, is a technical term that means suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged. Depending on the patency (openness) of the airways there may or may not be a flow of gas between the lungs and the environment; gas exchange within the lungs and cellular respiration is not affected.

Apnea can be voluntarily achieved (e.g., «holding one's breath»), drug-induced (e.g., opiate toxicity), mechanically induced (e.g., strangulation), or it can occur as a consequence of neurological disease or trauma.

Apneic respiration and oxygen uptake

Because the exchange of gases between the blood and airspace of the lungs is independent of the movement of gas to and from the lungs, enough oxygen can be delivered to the circulation even if a person is apneic. This phenomenon (apneic oxygenation) is explained as follows:

With the onset of apnea, an under pressure develops in the airspace of the lungs, because more oxygen is absorbed than CO² is released. With the airways closed or obstructed, this will lead to a gradual collapse of the lungs. However, if the airways are patent (open), any gas supplied to the upper airways will follow the pressure gradient and flow into the lungs to replace the oxygen consumed.

If pure oxygen is supplied, this process will serve to replenish the oxygen stores in the lungs. The uptake of oxygen into the blood will then remain at the usual level and the normal functioning of the organs will not be affected.

However, no CO² is removed during apnea. The partial pressure of CO² in the airspace of the lungs will quickly equilibrate with that of the blood. As the blood is loaded with CO² from the metabolism, more and more CO² will accumulate and eventually displace oxygen and other gases from the airspace. CO² will also accumulate in the tissues of the body, resulting in respiratory acidosis.

Under ideal conditions (i.e., if pure oxygen is breathed before onset of apnea to remove all nitrogen from the lungs, and pure oxygen is insufflated), apneic oxygenation could theoretically be sufficient to provide enough oxygen for survival of more than one hour's duration in a healthy adult. However, accumulation of carbon dioxide (described above) would remain the limiting factor.

Figure 4 – Respiration