Anatomy and Physiology - The Lungs

The Lungs

The Larynx:

• Part of the vocal cords and is located between the pharynx and the trachea.
• It is made up of cartilage.

The Lungs:

• There are two and they are surrounded by the plural membrane.
• The lungs are divided up into lobes; two on the left and three on the right.

The Trachea:

• Connects the larynx with the bronchus and progressively into the smaller dimensions called the bronchiole.
• It is a flexible fibro elastic and muscular structure which allows the neck to move.
• Allows the transport of oxygen from the atmosphere to the lungs and carbon dioxide from the lungs into the atmosphere.
• It is strengthened by rings of cartilage to prevent it come collapsing.
• Contains cilia and mucus, which are hair like structures which traps dust and bacteria which is within the air, as it passes down the trachea.

Ciliated Lining:

• A collection of fine hairs that cover the inside of the trachea.
• They help to trap small particle and foreign bodies. 
• Move in waves in one direction back up towards the head.
• Goblet cells / mucus moving, wafting.

The Bronchus:

• It splits into two tubes and so enables air to pass into both lungs.
• Cells in the bronchi contain cilia to trap pathogens and prevent disease.
• It splits into smaller divisions called the bronchioles.

The Bronchioles:

• They are tiny tubes within the lungs.
• They are connections of the bronchus.
• The bronchioles are attached to tiny air sacs called the alveoli, where gas exchange takes place by the use of diffusion into the pulmonary capillaries. 

The Alveoli:

• They are very thin – only one cell thick (epithelium).
• They have a large surface area to volume ratio.
• They are moist to assist with the diffusion of gases.
• Their function is gas exchange.
• Small air sacs that allow the diffusion of oxygen across their membrane into red blood cells in the surrounding capillaries.
• They also allow the diffusion of carbon dioxide from the blood plasma to diffuse back into the alveoli.
• Elasticised tissue to allow expansion.

Pleural Membranes:

• They are lubricated and surround the whole lungs to keep them moist.
• Without the pleural membranes, the lungs would face resistance and friction from the chest wall while they are expanding and contracting, which may cause shortness of breath ect.

The Diaphragm:

• It is a sheet of internal muscle.
• It is dome shaped when relaxed.
• Extends across the bottom of the rib cage.
• Divides the lungs and hearth from the stomach, kidney, liver etc.
• Helps with the mechanism of breathing.
• The intercostal muscles help bring enlargement of the thorax.
• A large dome shaped muscle that contracts and relaxes causing the chest cavity to increase and decrease in volume allowing the lungs to expand and contract (breathing).
• Changes pressure / maintains pressure within the lungs. 

Mechanisms of Breathing

This is done by two processes:

• Inspiration - breathing in.
• Expiration - breathing out.

These processes rely on pressure changes within the lungs, these are controlled by two sets of muscles:

• The diaphragm:
• A sheet of muscle which separates the thorax from the abdomen.
• The intercostal muscles which lie between the ribs, there are two sets of intercostal muscles, these are:
• External intercostal muscles which contract during inspiration.
• Internal intercostal muscles which contract during expiration.

Inspiration:

Breathing in is an active process and occurs in the following:

• The external intercostal muscles contract, while the internal intercostal muscles relax.
• The ribs are pulled upwards and outwards, increasing the pressure within the thorax.
• The diaphragm contracts causing it to flatten, this also increases the pressure within the thorax.
• The increased volume in the thorax results in reduction of pressure within the lungs.
• Atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lung.

Expiration:

Breathing out is a passive process and occurs as follows:

• The internal intercostal muscles contract, while the external intercostal muscles contract.
• The rib cage moves downwards and inwards, decreasing the volume of the thorax.
• The diaphragm flattens and returns to a dome shape, also decreasing the volume of the thorax.
• The decreased volume of the thorax increases the pressure within the lungs.
• Pulmonary pressure is now greater than the atmosphere, so air is forced out.

Gas Exchange

For efficient gas exchange, the lungs have to have the following characteristics:

• A large surface area - to speed up the rate of gas exchange.
• Very thin - makes the diffusion pathway short so materials cross rapidly.
• Partially permeable - only allows selected materials to diffuse easily.
• Movement of environmental medium - for example, air to maintain a diffusion gradient.
• Movement of internal medium - for example, blood to maintain a diffusion gradient.

Role of Alveoli in Gas Exchange:

• Each alveolus is mostly lined with epithelial cells.
• The alveolus is surrounded by a network of pulmonary capillaries, which are so narrow that the red blood cells are flattened against the thin capillary walls in order to squeeze through.
• Capillaries are only one cell thick.
• Diffusion of gases between the alveoli and the blood will be very rapid because:
• Red blood cells are slowed as they pass through the pulmonary capillaries allowing more time for diffusion.
• The distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls.
• The walls of both alveoli and capillaries have a very large surface area.
• Breathing constantly ventilates the lungs and the heart pumping constantly circulates the blood around the alveoli; this ensures the steep concentration gradient of gases to be exchanged is maintained.
• Blood flow through the pulmonary capillaries maintains a concentration gradient.

The Process of Gas Exchange:

• Gas exchange happens by passive diffusion of gases; this is across the very thin walls of the alveoli.
• In order to maximise the amount of diffusion taking place, the alveoli have a huge total surface area to volume ratio.
• The alveoli have a moist lining to help dissolve the gases.
• They are surrounded by many tiny capillaries so there is a high volume of blood for the gases to pass into and out of.
• As a result of gas exchange, the proportion of oxygen and carbon dioxide in the inhaled/exhaled air changes, maintaining the steep concentration gradient.
• The air breathed in containing a higher percentage of oxygen and a lower percentage of carbon dioxide than the air we breathe out.
• The carbon dioxide in the blood being dissolved in the plasma. 
• The percentage change of oxygen and carbon dioxide between inhaled and exhaled air may be mentioned as follows:
• rib cage moves upwards 
• diaphragm flattening, decreasing pressure 
• diaphragm relaxing, increasing pressure 
• role of pleural membrane in the movement of the chest 
• role of inter-costal muscles in the movement of the chest
• All gases move across the alveolar wall according to the principle of simple diffusion: gas moves from areas of higher concentration to lower concentration.
• According to FICK’S LAW, the amount of gas that moves across a sheet of tissue is proportional to the area of the sheet but inversely proportional to its thickness.

Functions of The Respiritory System

• To provide a supple of oxygen for carriage by the blood and body cells.
• To remove waste products, carbon dioxide and water, from the blood to the atmosphere.
• To help maintain a balanced hydrogen ion concentration in the body tissues.
• To assist in homeostasis.

Dysfunctions of The Respiritory System - Asthma

• Asthma is characterised by recurring episodes of breathlessness, a feeling of tightness in the chest and wheezing.
• It can be mild, moderate of severe at different times of the day and year.
• It commonly starts in childhood and often clears up in early adult life, although many adults also suffer from asthma and it can occur at any age.
• It causes constriction of the bronchus and so makes breathing difficult and so results in tightness in the chest and wheezing.
• During a severe attack the individual gets very distressed and sweating and raised heart rate occurs, they are sometimes also unable to talk. Their lips can turn a bluish colour due to the poor oxygenation of the blood during an attack.

Causes of Asthma:

• There is no obvious cause of what triggers asthma as it varies for each individual.
• It has been found that the most common cause is when an individual inhales and allergen, the most common are as follows:
• Pollens.
• House dust and dust mites.
• Animal fur.
• Feathers.
• Skin flakes.
• Food.
• Drugs.
• Attacks can be triggered by stress, anxiety, exercise (especially in winter), tobacco smoke and air pollutants.
• Asthma is not directly inherited but there is a strong tendency for it to run in the family.
• Smoking during pregnancy also increases the risk of the child developing asthma.
• There is no evidence that air pollutants cause asthma, there is evidence that they considerably worsen it.

Diagnostic Techniques for Asthma:

• Peak-flow monitoring:
• Peak flow can measure the maximum volume rate of air someone can blow during the first second or so of expiration 
• By checking what an individual’s ‘personal best’ peak flow is 
• during times of no symptoms, the decrease in peak flow during 
• an asthma attack can be identified and monitored 
• When the peak flow drops significantly, concern about the 
• dysfunction rises 
• Conversely, a peak flow which remains at a high level helps in 
• reassuring that the dysfunction is under control and perhaps 
• any medications being used may be decreased 
• Peak flow can help when dysfunction is getting worse and may 
• show changes before you feel them. It can allow the doctor to 
• adjust the treatment to prevent emergency hospitalisations 
• Peak Flow Meter may help the doctor identify causes of your 
• asthma at work, home or play. It can help to determine what 
• might be triggering the dysfunction 
• Peak Flow Meter can also be used during an episode 
• It can help you determine the severity of the episode and if further medication is required 
• Spirometry:
• This is a breathing test where the individual breaths into a spirometre machine.
• The spirometer takes two measurements: the volume of air you can breathe out in one second and the total amount of air you breathe out.
• This is normally repeated a few times to make sure that the results are consistant.
• The readings are compared with average measurements for people your age, which can show if your airways are obstructed.
• Sometimes an initial set of measurements is taken, then you are given a medicine to open up your airways (a reliever inhaler) to see if this improves your breathing. Another reading is then taken and, if it is much higher after taking the medicine, it can support the diagnosis.
• Allergy Test:
• Skin testing or a blood test can be helpful to confirm whether your asthma is associated with specific allergies, for example dust mites, pollen, or foods.

Treatment for Asthma:

• Steriods:
• Corticosteroids (steroids) are used to reduce inflammation 
• Reduces mucus production in the airways of the lungs 
• They also reduce the swelling and narrowing of the airways 
• Help other quick-relief medicines work better
• Inhalers:
• This is a device that deliver the drug directly into the airways through your mouth when you breath in.
• Inhaling a drug is an effective way of taking an asthma medicine as it goes straight to the lungs, with very little ending up elsewhere in the body.
• However, each inhaler works in a slightly different way.

How Asthma affects an Individual's P.I.E.S Development:

• Physical:
• Acute asthma symptoms often occur during the night, disrupting sleep.
• People with asthma, however, begin to wheeze and cough in the night.
• Sleep deprivation can lead to psychological disturbances.
• Asthma can also prevent the individual from taking part in fun physical activities due to breathlessness caused by the constricted bronchus.
• Intellectual:
• Individual's often have a lack of knowledge of asthma and so do not know what is the best way to keep it under control.
• Asthma can make individual's more vulnerable to virus' and infections and so end up missing school, affecting their intellectual development.
• Emotional:
• Some people may feel embarrassed about their condition, because they feel that they are different in comparison to other people.
• They may live in fear and worry of an asthma attack occuring.
• Social:
• They may not be able to participate in some social activites which involve high physical activity or is around something that triggers their asthma, for example, not being able to go to a friends house because they have loads of pets.

General Treatment for Respiritory Dysfunctions:

• Antibiotics:
• An antibiotic inhibits or kills the growth of micro-organisms, such as bacteria, fungi, or protozoa. 
• They are used to treat secondary infections. 
• They have no effect on viruses e.g. Influenza.