Gas exchange

Gas exchange occurs in the lungs between the alveoli and a capillary network within the alveolar wall. Capillaries are microscopic blood vessels that exchange material between the blood and body tissues. In the lung capillaries, blood from tissues where cellular metabolism is occurring is called deoxygenated blood because it contains many carbon dioxide molecules and few oxygen molecules.

Respiration

The respiration process has two parts: inspiration (inhaling) and expiration (exhaling). During inspiration, the diaphragm contracts, moves downward, and causes the thoracic cavity volume to increase. Because the lungs are closely associated with the interior chest wall, they expand as the thoracic cavity expands. When the diaphragm relaxes (upward position), the thoracic volume decreases and the lungs partially deflate. This process is called expiration. The elastic recoil of the expanded thoracic wall and lungs also helps expiration.

After inhalation, the alveoli contain many oxygen molecules. The alveoli are in close contact with the capillary network. This proximity enables the minuscule oxygen molecules to diffuse (pass freely) from the alveolus to the bloodstream, flowing from a region of higher concentration to a region of lower concentration. In the bloodstream, the oxygen attaches to red blood cells and is transported to the rest of the body. Likewise, carbon dioxide diffuses from the bloodstream into the alveolus where it is transported out of the body during exhalation.

During respiration, the pleurae (pleural membranes) help the lungs to expand and contract. These membranes are sacs that tightly cover the lungs and the chest inside wall. Between these two linings is a space called the pleural cavity that contains a thin layer of fluid. This fluid allows the lungs to move freely against the thoracic cavity inside.

Answer the questions

What is the difference between internal and external ventilation?

Where do air and blood come into intimate contact?

Where are the lungs situated?

Where do blood vessels, nerves, and bronchi (air passages) enter the lungs?

What divides lungs into lobes?

What is the function of the thick hairs lining the nostrils?

What is the function of the epiglottis?

What prevents trachea from collapsing?

What are alveoli in the lungs like?

What is another pair of terms for inhaling and exhaling?

What happens in the lungs after inhalation?

What gas is inhaled and what gas is exhaled?

What is the average volume of air brought into human lungs during one minute at rest?

What lies inferior to the lungs?

Are the left and right lungs identical, and if not, what is the difference?

How are the partitions in the lungs called?

How do they call small hair-like projections in the nasal cavities?

What helps to expel foreign materials getting into the larynx during deglutition?

Where do the smallest bronchioles end?

How do they call microscopic blood vessels that exchange material between the blood and body tissues?

What makes the lungs expand and deflate?

ASTHMA

Asthma is an inflammatory disorder of the airways, characterized by periodic attacks of wheezing, shortness of breath, chest tightness, and coughing.

CAUSES, INCIDENCE, AND RISK FACTORS

Asthma is a disease in which inflammation of the airways causes airflow into and out of the lungs to be restricted. When an asthma attack occurs, the muscles of the bronchial tree become tight and the lining of the air passages swells, reducing airflow and producing the characteristic wheezing sound. Mucus production is increased.

Most people with asthma have periodic wheezing attacks separated by symptom-free periods. Some asthmatics have chronic shortness of breath with episodes of increased shortness of breath. Other asthmatics may have cough as their predominant symptom. Asthma attacks can last minutes to days, and can become dangerous if the airflow becomes severely restricted.

In sensitive individuals, asthma symptoms can be triggered by inhaled allergens (allergy triggers), such as pet dander, dust mites, cockroach allergens, molds, or pollens. Asthma symptoms can also be triggered by respiratory infections, exercise, cold air, tobacco smoke and other pollutants, stress, food, or drug allergies. Aspirin and other non-steroidal anti-inflammatory medications (NSAIDS) provoke asthma in some patients.

Asthma is found in 3-5% of adults and 7-10% of children. Half of the people with asthma develop it before age 10, and most develop it before age 30. Asthma symptoms can decrease over time, especially in children.

Many people with asthma have an individual and/or family history of allergies, such as hay fever (allergic rhinitis) or eczema. Others have no history of allergies or evidence of allergic problems.

SYMPTOMS

1. wheezing

2. usually begins suddenly

3. is episodic

4. may be worse at night or in early morning

5. aggravated by exposure to cold air

6. aggravated by exercise

7. aggravated by heartburn (reflux)

8. resolves spontaneously

9. relieved by bronchodilators (drugs that open the airways)

10. cough with or without sputum (phlegm) production

11. shortness of breath that is aggravated by exercise

12. breathing that requires increased work

13. intercostal retractions (pulling of the skin between the ribs when breathing)

Emergency symptoms:

1. extreme difficulty breathing

2. bluish color to the lips and face

3. severe anxiety due to shortness of breath

4. rapid pulse

5. sweating

6. decreased level of consciousness (severe drowsiness or confusion) during an asthma attack

Additional symptoms that may be associated with this disease:

1. nasal flaring

2. chest pain

3. tightness in the chest

4. abnormal breathing pattern, in which exhalation (breathing out) takes more than twice as long as inspiration (breathing in)

5. breathing which temporarily stops

SIGNS AND TESTS

Your doctor will listen to the chest during an episode, to listen for wheezing sounds. However, lung sounds are usually normal between asthma episodes.

Tests may include:

1. Lung function tests

2. Peak flow measurements

3. Chest x-ray

4. Allergy skin or blood tests

5. Arterial blood gas

6. Eosinophil count (a type of white blood cell)

TREATMENT

Treatment is aimed at avoiding known allergens and respiratory irritants and controlling symptoms and airway inflammation through medication. Allergens can sometimes be identified by noting which substances cause an allergic reaction.

Allergy testing may also be helpful in identifying allergens in patients with persistent asthma. Common allergens include: pet dander, dust mites, cockroach allergens, molds, and pollens. Common respiratory irritants include: tobacco smoke, pollution, and fumes from burning wood or gas.

There are two basic kinds of medication for the treatment of asthma:

I. Long-term control medications -used on a regular basis to prevent attacks, not for treatment during an attack.

1. inhaled steroids (Azmacort, Vanceril, AeroBid, Flovent) prevent inflammation

2. leukotriene inhibitors (Singulair, Accolate)

3. long-acting bronchodilators (Foradil, Serevent) help open airways

4. cromolyn sodium (Intal) or nedocromil sodium

5. aminophylline or theophylline (not used as frequently as in the past)

6. combination of anti-inflammatory and bronchodilator, using either separate inhalers or a single inhaler (Advair Diskus)

7. anti-IgE therapy (Xolair), a new injection treatment used in patients with more severe asthma

II. Quick relief (rescue) medications -- used to relieve symptoms during an attack.

1. short-acting bronchodilators (Proventil, Ventolin, Xopenex, and others)

2. oral or intravenous corticosteroids (prednisone, methylprednisolone) stabilize severe episodes

People with mild asthma (infrequent attacks) may use relief medication as needed. Those with persistent asthma should take control medications on a regular basis to prevent symptoms from occurring. A severe asthma attack requires a medical evaluation and may require hospitalization, oxygen, and intravenous medications.

A peak flow meter, a simple device to measure lung volume, can be used at home to help you "see an attack coming" and take the appropriate action, sometimes even before any symptoms appear. If you are not monitoring asthma on a regular basis, an attack can take you by surprise.

Peak flow measurements can help show when medication is needed, or other action needs to be taken. Peak flow values of 50-80% of an individual’s personal best indicate a moderate asthma attack, while values below 50% indicate a severe attack.

EXPECTATIONS (PROGNOSIS)

There is no cure for asthma, though symptoms sometimes decrease over time. With proper self management and medical treatment, most people with asthma can lead normal lives.

COMPLICATIONS

1. respiratory fatigue

2. pneumothorax

3. death

4. side effects of the medication used

PREVENTION

Asthma symptoms can be substantially reduced by avoiding known allergens and respiratory irritants. If someone with asthma is sensitive to dust mites, exposure can be reduced by encasing mattresses and pillows in allergen-impermeable covers, removing carpets from bedrooms, and by vacuuming regularly. Exposure to dust mites and mold can be reduced by lowering indoor humidity.

If a person is allergic to an animal that cannot be removed from the home, the animal should be kept out of the patient's bedroom. Filtering material can be placed over the heating outlets to trap animal dander. Exposure to cigarette smoke, air pollution, industrial dusts, and irritating fumes should also be avoided.

Allergy desensitization may be helpful in reducing asthma symptoms and medication use, but the size of the benefit compared with other treatments is not known.