The word respiration describes several processes:

Internal respiration is the exchange of respiratory gases between blood and the tissues.

Cellular respiration is the process by which glucose or other small molecules are oxidised to produce energy: this requires oxygen and generates carbon dioxide.

External respiration (breathing) involves simply the stage of taking oxygen from the air and returning carbon dioxide to it.

Identify and give functions for each of the following:

- larynx - To conduct air and, through the vocal cords, to produce sound. The entry of food and drink into the larynx is prevented by the structure of the larynx (epiglottis) and by the complicated act of swallowing. The larynx is protected by three pairs of folds which close off the airway.

- trachea- The trachea (windpipe) extends from the neck into the thorax, where it divides into right and left main bronchi. Its function is to clean, moisturize, heat, and conduct inhaled air. [Below the larynx the trachea is usually open, and kept so by rings of cartilage in its walls. However it may be necessary to ensure that this condition is maintained by passing a tube (endotracheal intubation) to maintain the airway, especially post operatively if the patient has been given a muscle relaxant. Another common surgical procedure, tracheotomy, involves a small transverse cut in the neck. If this is done with anatomical knowledge no major structure is disturbed and the opening may be used for a suction tube, a ventilator, or in cases of tracheal obstruction as a permanent airway.]

- bronchi, bronchioles, alveoli - To conduct, moisturize, and warm inhaled air and, by bronchiolar sphincters, to regulate the passage of air into the alveoli. Bronchi enter the right and left lungs, breaking up as they do so into smaller bronchi and bronchioles and ending in small air sacs or alveoli, where gaseous exchange occurs. The structure of the alveoli facilitates their function. • They are moist which increases the rate of diffusion of gases. • They are highly vascularized which allows more exchange of gases. • The thin walls of the alveoli allow materials to be exchanged quickly

and easily. • A layer of lipoprotein reduces surface tension and prevents the alveoli

from collapsing. • They are small and number in the millions. This increases their surface area and allows for speedy gas exchange.

• Stretch receptors in their walls signal medulla oblongata to stop inhalation.

- diaphragm and ribs - The diaphragm is a layer of muscle which is convex above, domed, and squashed in the centre by the heart. When it contracts it flattens and increases the space above it to assist in bringing in and expelling air from the lungs. The ribs are elevated as we inhale to further expand the volume of the cavity and assist in bringing in air.

Explain the relationship between the structure and function of alveoli

Gaseous exchange relies on simple diffusion. In order to provide sufficient oxygen and to get rid of sufficient carbon dioxide there must be a large surface area for gaseous exchange and a very short diffusion path between alveolar air and capillaries.

(Below is a blow up of the boxed area in the diagram)

The alveoli have very thin walls and a vast total surface area across which respiratory gases diffuse into and from the numerous alveolar capillaries that surround them (fig 14.2 pg. 242). A film of lipoprotein lining the alveoli of mammalian lungs prevents them from closing/collapsing. [The surface available is around 140m2 in an adult, around the area of a singles tennis court].

Explain the roles of cilia and mucus in the respiratory tract

The cilia (tiny hairs) found in the lining of the nostrils and trachea entrap dust and soot particles from the inhaled air. In the trachea their sweeping movements, move these particles to the pharynx for expectoration. [Smoking will eventually kill the cilia causing scar tissue to form in their place, thus depriving the body of a way to clean and clear inhaled dust and pose a health hazard to the air passages and the lungs]

The fact that at the alveoli an area of our body the size of a tennis court is separated from the outside air by a very narrow barrier imposes demands on the respiratory tract.

Outside air:

- varies in temperature. At the alveolar surface it must be at body temperature

- varies from very dry to very humid. At the alveolar surface it must be saturated with water vapour

- contains dust and debris. These must not reach the alveolar wall

- contains micro-organisms, which must be filtered out of the inspired air and disposed of before they reach the alveoli, enter the blood and cause possible problems.

It is easy to see that the temperature and humidity of inspired air will increase as it passes down a long series of tubes lined with a moist mucosa at body temperature. The mechanisms for filtering are not so obvious.

Mucus - The respiratory tract, from nasal cavities to the smallest bronchi, is lined by a layer of sticky mucus, secreted by the epithelium assisted by small ducted glands. Particles which hit the side wall of the tract are trapped in this mucus.

Cilia - Once the particles have been sidelined by the mucus they have to be removed, as does the mucous. This is carried out by cilia on the epithelial cells which move the mucous continually up or down the tract towards the nose and mouth. (Those in the nose beat downwards, those in the trachea and below upwards). The mucus and its trapped particles and bacteria are then swallowed, taking them to the sterilising vat of the stomach.

 

 

 

 

Compare and contrast the mechanics of the processes of inhalation and exhalation

[In common with all mammals humans ventilate their lungs by breathing in and out. This reciprocal movement of air is less efficient and is achieved by alternately increasing and decreasing the volume of the chest in breathing. The body's requirements for oxygen vary widely with muscular activity. In violent exercise the rate and depth of ventilation increase greatly: this will only work in conjunction with increase in blood flow, controlled mainly by the rich innervation of the lungs. Inadequate gas exchange is common in many diseases, producing respiratory distress.]

The medulla sends motor impulses (via the phrenic nerves) to the intercostal muscles which will then contract and raise the ribs and to the diaphragm which will contract (lower). In this way the thorax is enlarged and air taken into the chest. Inhibitory effects on the medulla will cause the reverse of the noted effects.

During inspiration (active) the diaphragm tenses (contracts) and moves down (lowers). During exhalation (usually passive) the diaphragm relaxes and is raised.

During inspiration the intercostal muscles elevate the ribs; during exhalation these muscles relax and the ribs lower themselves.

With the expansion of the thorax during inspiration (inhalation) the air rushes in and the lungs inflate; they deflate with the contraction of the thorax during exhalation.

Describe the interaction of the lungs, pleural membranes, ribs, and diaphragm in the breathing process

Like most internal organs, each lung is enclosed in a double-layered sac the pleural membranes. The inner-most of these membranes (the visceral pleura) is intimately connected to the lung itself. Between the inner and outer (parietal pleura) membranes is a space in which the pressure is less than atmospheric (less by 5-10 atm.); this is what is often referred to as "negative pressure". As the thorax expands during inspiration (ribs raised, diaphragm lowered), the pleural space expands and the sub-atmospheric pressure is further decreased (due to Boyle's Law of gases); this assists in drawing air into the lungs. The reverse takes place during exhalation. If you get stabbed in the chest, the lung would collapse due to the destruction of the sub-atmospheric pressure in the pleural sacs in which the pressure would now be equal to that of the atmosphere. It is known as a pneumothorax.

[Breathing works by making the cage bigger: the pleural layers slide over each other and the pressure in the lung is decreased, so air is sucked in. Breathing out does the reverse, the cage collapses and air is expelled. The main component acting here is the diaphragm. When it contracts it flattens and increases the space above it. When it relaxes the abdominal contents push it up again. The proportion of breathing which is diaphragmatic varies from person to person. For instance breathing in children and pregnant women is largely diaphragmatic, and there is said to be more diaphragmatic respiration in women than in men. The process is helped by the ribs which move up and out also increasing the space available. The complexity of breathing increases as does the need for efficiency. In quiet respiration, say whilst lying on ones back, almost all movement is diaphragmatic and the chest wall is still. This will increase thoracic volume by 500-700ml. The expansion of the lung deforms the flexible walls of the alveoli and bronchi and stretches the elastic fibres in the lung. When the diaphragm relaxes elastic recoil and abdominal musculature reposition the diaphragm again. Deeper respiration brings in the muscles of the chest wall, so that the ribs move too. We must therefore understand the skeleton and muscular system of the thoracic wall. The 12 pairs of ribs pass around the thoracic wall, articulating via synovial joints with the vertebral column - in fact two per rib. The ribs then curve outwards then forwards and downwards and attach to the sternum via the flexible costal cartilages. Between the ribs run two sets of intercostal muscles, the external intercostals running forward and downwards, the internal intercostals running up and back. These two muscle sheets thus run between ribs with fibres roughly at right angles. When they contract each rib moves closer to its neighbors. The ribs are all, therefore pulled up towards the horizontal, increasing anterior-posterior and lateral thoracic diameters.

With more and more effort put into deeper and deeper breathing the scalene muscles of the neck contract, raising the first rib and hence the rest of the cage, then other neck muscles and even those of the upper limb become involved. A patient with difficulty in breathing often grips a table edge in order to stabilize the limbs so that their muscles can be used to help in moving the thoracic wall.]

Explain the roles of carbon dioxide and hydrogen ions in stimulating the breathing centre in the medulla oblongata

As the carbon dioxide levels in the blood increase, respiratory centers in the brain (medulla) are stimulated and the respiratory rate increases. Too little carbon dioxide in the blood will decrease respiratory stimuli. The hydrogen levels in the blood (i.e., blood acidity or low blood pH) will have a similar effect to that of carbon dioxide.

Respiratory rates are controlled by the respiratory centers in the medulla oblongata which stimulate the diaphragm and intercostal muscles via the phrenic nerves.

- If hyperventilation occurs it will "wash out" the carbon dioxide and hydrogen ions and thus decrease the respiratory rate and depth.

- Holding your breath causes accumulation of carbon dioxide and hydrogen ions in the blood and will thus increase the rate and depth of respiration when breathing is resumed.

Describe the exchange of carbon dioxide and oxygen during external and internal respiration

In the lung alveoli the partial pressure of carbon dioxide in the blood is greater than the partial pressure of carbon dioxide in the alveoli so the carbon dioxide will diffuse out of the blood and into the alveoli. The partial pressure of oxygen in the alveoli is greater than that in the blood capillaries so oxygen diffuses in.

During external respiration, the following reactions involving gases occur in the capillaries:

- oxygen combines with hemoglobin to form oxyhemoglobin (O 2 + Hb à HbO 2 )

- carbaminohemoglobin releases carbon dioxide ( HbCO2 à CO2 + Hb )

- bicarbonate ions combine with hydrogen ions to release carbon dioxide

Conditions in the capillaries that affect the rate of the reactions above include:

- Blood at the lung capillaries has a lower temperature.

- Blood at the lung capillaries has a higher pH / less acidic.

- Blood at the lung capillaries has a lower oxygen concentration.

- Blood at the lung capillaries has a higher carbon dioxide concentration.

- Low amounts of hemoglobin will reduce the amount of O 2 diffused per minute.

- Changes in blood pressure and blood velocity will affect the rate of gas exchange.

In the tissues the partial pressure of oxygen is less than that in the tissue capillaries so

oxygen diffuses into the tissues. The partial pressure of carbon dioxide is greater than that in the capillaries so carbon dioxide diffuses out of the tissues into the capillaries.

Gaseous exchange relies on simple diffusion. In order to provide sufficient oxygen and to get rid of sufficient carbon dioxide there must be a large surface area for gaseous exchange a very short diffusion path between alveolar air and blood concentration gradients for oxygen and carbon dioxide between alveolar air and blood. The surface available in an adult is around 140m2 in an adult, around the area of a singles tennis court. The blood in the alveolar capillaries is separated from alveolar air by 6 hundredths of a mm in many places.

Diffusion gradients are maintained by ventilation (breathing) which renews alveolar air, maintaining oxygen concentration near that of atmospheric air and preventing the accumulation of carbon dioxide the flow of blood in alveolar capillaries which continually brings blood with low oxygen concentration and high carbon dioxide concentration

Distinguish between the transport of CO2 and O2 in the blood by explaining the roles of oxyhemoglobin, carbaminohemoglobin, reduced hemoglobin, and bicarbonate ions

Oxyhemoglobin in the red blood cells carries most of the oxygen from the lungs to the tissues. When the respiratory pigment hemoglobin gives up the hydrogen ions it has been carrying it is called deoxyhemoglobin and can more readily take up oxygen to become oxyhemoglobin.

Carbaminohemoglobin in the red blood cells carries a small amount of carbon dioxide from the tissues to the lungs. Carbaminohemoglobin is formed when hemoglobin takes up CO2.

Bicarbonate ions are the forms in which most of the carbon dioxide is transported in the blood plasma from the tissues to the lungs. Carbon dioxide combines with water to form carbonic acid which dissociates to hydrogen ions and bicarbonateions. The globin portion of hemoglobin combines with excess hydrogen ions produced by the reaction and becomes reduced hemoglobin.

 

 

The following substances found in the plasma will cause an increase in the rate of air intake during exercise?

• adrenalin

• hydrogen ions (H + )

• carbon dioxide (CO 2 )

• bicarbonate ions (HCO 3•)

• reduced hemoglobin

The chemical reactions that occur during internal respiration that return the rate of air intake during exercise to the resting rate are:

• CO2 + H2O à H2CO3 à HCO3- + H+

• H+ +Hb à HHb +

• Hb +CO 2 à HbCO 2

• HbO 2 à Hb+ O 2

When the body encounters an environment that contains lower than normal oxygen levels several things happen:

• The rate of cell division in the bone marrow will increase thus increasing the number of hemoglobin / red blood cells. The increased number of red blood cells will allow more oxygen to be carried to the tissues.

• Breathing rate will increase. As the breathing rate increases the rate of gas exchange also increases. More O2 is accepted by the hemoglobin. There is more external respiration.

During a climb, as the oxygen concentration gets lower, the blood pH decreases. The body compensates for this change by:

• excretion of H+ by the kidneys

• excretion of NH 3 by the kidneys

• reabsorption of HCO 3• by the kidneys

• the increased amount of H + combines with hemoglobin producing more reduced hemoglobin (HHb)

• breathing rate increases to exhale more CO 2 • buffers maintain pH by accepting H +