Respiration

Respiration is:

• Ventilation: getting air in/out of the lungs.
• External respiration: gaseous exchange between lungs and blood.
• Transport of gases.
• Internal respiration: exchange of gases between blood in capillaries and body cells.
• Cellular respiration: the metabolic reactions and processes that take place in a cell to obtain energy from fuels such as glucose.

Process of respiration:

• Air is drawn into the body through the nose, where it is warmed and filtered by a thick membrane and cilia.
• It then passes thorugh the pharynx and onto the larynx.
• The epiglotis covers the opening of the larynx to prevent food form entering the lungs.
• The air moves into the trachea.This is held open by rings of cartilage. Mucus cells line the trachea anf filter the air. The traachea divides into the right and left bronchi.
• Air moves through the bronchi and sub-divides into secondary bronchi, these get progressively thinner and divide into bronchus and bronchioles.
• The alveoli are responsible for the exchange of gases between the lungs & blood.

The alveoli are tiny air sacs inside the lungs.

A dense capillary network supplies them with oxygen. Their walls are extremely thin and together they create a huge surface area to allow for greater uptake of oxygen.

What is special about alveoli?

• One cell thick
• Large surface area
• Millions of alveoli
• Moist surface lining
• Huge blood supply
• Short diffusion pathway

Gaseous exchange involves getting oxygen air into the lungs so that it can diffuse into the blood and be transported to the cells of the body. It also removes carbon dioxide from the blood.

Air will always move from an area of higher pressure to an area of lower pressure via diffusion.

The graeter the difference in pressure, the faster air will flow.

Inspiration:

• Intercostal muscle contract, lifting ribs up and out causing the chest to expand.
• Diaphram contracts, it pulls down and flattens.
• Lungs increase in thoracic cavity volume.
• The higher pressure of air outside means that air is now sucked into the lungs through the nose and mouth.

Expiration:

• Intercostal muscles relax, ribs move downwards and inwards under their own weight.
• Diaphram relaxes, it is pushed back into resting position.
• Expiration decreases the volume of the thoracic cavity.
• Pressue inside the lungs increases as they get smaller. Air pressure outside is now lower than in the lungs.
• Air is forced out of the lungs through the nose and mouth due to a high pressure of air inside the thoracic cavity.

During exercise, more accessory muscles are invlolved because air needs to be forced in and out of the lungs more quickly.

The extra inspiratory muscles are the scalenes, sternocleidomastroid, which lifts the sternum, and the pectoralis minor, which helps to lift the ribs.

The extra expiraotry muscles are the internal intercostals, which pull the ribs down and in and the abdominal muslces, which push the diaphram up.

Breathing: Inspiration and expiration caus volumes of air to enter and exit the lungs. It increases suring exercise.

Tidal volume: Volume of air breathed in or out per breath. It decreases during exercise.

Inspiratory resreve volume: Volume of air that can be forcinly inspired after a normal breath. There is a decrease during exercise.

Expiratory reserve volume: Volume of air that can be forcibly expired after a normal breath. There is a slight decrease during exercise.

Residual volume: The volume of air that remains in the lungs after maximum expiration. It remains the same during exercise.

Minute ventilation: Volume of air breathed in or out per minute. There is a big increase during exercise.

Total lung capacity: Vital capacity + residual volume. There is a smal decrease during exercise.

Minute volume: the amount of air breathed in or out per minute. The more demanding the physical activity, the more breathing increases to meet the extra oxygen demand.

Partial pressure and diffsuion are used when describing the gaseous exchange process. Oxygen exerts partial pressure.

Diffusion is the movenet of particles from an area of higher concentraion to an area of lower concentration.

Partial pressure is the movement of gas particles from an area of higher air pressure to an area of lower air pressure.

The partial pressure of oxygen in alveoli is higher than the partial pressure of oxygen in the cappilary blood vessels. This is because oxygen has been removed by the working muscles so its concentration in blood is lower, and therefore so is its partail pressure. This difference in partial pressure is reffered to as a concentration gradient. The bigger the concentration gradient, the faster diffusin will be. Oxygen will diffuse form the alveoli into the blood until the pressure is equal.

1) Hydro-carbonate ions combine with water to form carbonic acid. 

2) This acid combines with haemoglobin to form carbomino haemoglobin.

3) This can then be disolved by plasma and removed throught the transport system back to the lungs to be expired.

Carbon dioxide is much more soluble than O2 therefore more CO2 disolves in a liquid.

Partial pressure is the pressure exerted by an individual gas that is proportional to its concentration within the whole mixture.

Atmoshperic pressure = 79% Nitrogen

                                        21% Oxygen

                                        0.03% CO2

External respiration occurs because:

• Vast number of alveoli and capillary network increase the surface area and diffusion rate.
• Thin capillary walls squash red blood cells which distorts their shape and slows them down which increases their exposure to oxygen.
• Thin capillary walls Lead to efficeint diffusion and gas exhcnage as there is only a short distance to travel.

Internal respiration occurs because:

• Available surface area
• Partial pressure gradient
• Rate of blood flow varies
• Myoglobin within muscle cells have a higher affinity for oxygen than haemoglobin
• Thin capillary walls and increase in surface area = efficeint diffusion 

Defenition - the difference in oxygen content of the arteriol blood arriving at the muscles and the venous blood leaving the muscles.

Change during exercise - at rest, the arteriol-venous difference is low becuase the muscles do not require much oxygen. 2) during exercise, the muscles need more oxygen from the blood because they are contracting and respiring areobically, therefore using up oxygen so the AV difference is high.

Effect of training - training increases the AV difference because trained performers can extract more oxygen from the blood.

Pulmonary ventilation means breathing.

Three factors are involved in pulmonary ventilation:

• Hormonal control
• Neural control - involves the brain and nervous system.
• Chemical control - invovles blood acidity

Both work together to regulate breathing. When blood acidity is high, the brain is informed and sends an impulse through the nervous system to increase breathing.

Sympathetic nervous system: increases breathing rate when preparing body for exercise.

Parasympathetic nervous system: lowers breathing rate.

The respiratory centre, located in the medulla, contros the rate and depth of breathing and uses both neural and chemical control.

Increase in concentration of the blood stimulates the respiratory centre to increase respiratory rate. The inspriatory centre then sends out nerve impulses via the phrenic nerve to the inspiratory muscles to make them contract. 

During exercise, blood acidity increase as a result of an increase in plasma concentration of carobn dioxide and an increase in lactic acid produciton. These changes are detected by chemoreceptors which send impulses to the respiraotry centre which send impulses down the phrenic nerve to stimulate inspiratory muscles such as the sternocleidomastoid, scalenes and pectorials minor in order to increase ventilation until the blood acidity goes back to normal.

Other factors affecting neural control of breathing:

• Mechanical factors - proprioceptors are sensory receptors located in the joints and muscles that provide feedback to the respiratory centre to increase breathing during exercise.
• Baroreceptors - a decrease in blood pressure detected by baroreceptors in the aorta and cartoid arteries results in an increase in breathing rate.
• Stretch receptors - during exercise the lungs are stretched more. Stretch receptors prevent over - inflation of the lungs by sending impulses to the expiratory centre and then down the intercostal nerve to the expiratory muscles so that expiration occurs.

Adrenaline:

• Natural stimulation made in the adrenal gland of the kidney.
• Transported in blood and affects the nervous system.
• Before exercise, brain sends impulse to renal gland to pump adrenaline into the blood wich increases breathing and heart rate.

Smoking causes irritation of the trachea and bronchi.

It reduces lung function and increases breathlessnes caused by swelling and narrowing of the lungs' airways.

Cilia are damaged with causes exess mucus to build up and blocks the lung pasages, leading to smokers cough.

Alveoli become damaged and their walls breaak down and for larger spaces than normal, decreasing the surface area for gas exchange, which increases the risk of COPD.

Oxygen transport is also affected as the carbon monoxide in cigarettes binds to haemoglobin in the red blood cells much more readily than oxygen. This reduces the oxygen carrying capacity of red blood cells, which increases breathlessness during exercise.