Learning Outcomes Gaseous Exchange Explain how carbon dioxide and oxygen are exchanged Explain / describe how oxygen and carbon dioxide is transported around the body Video Clip Summary

Gaseous exchange There are two sites for gaseous exchange in the body: 1. Between the air in the alveoli of the lungs and blood in the surrounding alveolar capillaries 2. Between the tissues/muscles of the body and surrounding blood capillaries

External Respiration External respiration Gaseous exchange at the alveoli The object is to convert deoxygenated blood returning from the body into oxygenated blood. As the blood circulates through alveolar capillaries, oxygen is picked up from the alveoli and carbon dioxide is lost to be expired.

Gases flow from an area of high pressure to an area of low pressure Called Diffusion Diffusion The movement of gases from a higher partial pressure to a lower partial pressure until equilibrium is reached. Partial Pressure The pressure that is exerted by an individual gas when it exists within a mixture of gases

Partial pressure (pp): The actual pressure of a gas as it exists in a mixture of gases. For example: Atmosphere pressure is composed of three main gases: Nitrogen (approx 79%) Oxygen (approx 21%) Carbon Dioxide (approx 0.03%) Together they exert a pressure of 760mmHg (mm of mercury to measure the partial pressure of a gas) Respiration in exercise

GAS TRANSPORT GAS TRANSPORT ACROSS THE RESPIRATORY MEMBRANE oxygen diffuses from alveolus across the alveolar wall, respiratory membrane, and capillary wall towards red blood cells carbon dioxide diffuses in the opposite direction from the red blood cell and from blood plasma to the alveolus Video 1 video gaseous exchange

Respiration The partial pressure of 02 in the alveoli (alveolar / found in the lungs) is higher than the partial pressure of the 02 in the blood vessels surrounding the lungs Atmosphere air Alveolus Atmosphere air From heart To heart C02 High pressure 02 Direction Of blood flow Direction Of blood flow Low pressure

Blood returning from the body is low in oxygen because it has been removed by the tissues. (to fuel movement) The difference in pressure is even greater during exercise as more oxygen diffuses into the muscle tissue. The difference between the two pressures is known as the diffusion gradient. Oxygen moves from areas of high pressure (alveoli) to areas of low pressure (blood vessels surrounding lungs). The greater the gradient the faster the diffusion When we exercise the gradient will be greater: therefore faster

Features that Facilitate Diffusion at the Alveolar 1. Alveolar membrane is very thin = short diffusion distance between the air in alveoli and the blood 2. Numerous (millions) of alveoli creates a VERY LARGE surface area for diffusion to take place 3. Alveoli are surrounded by a vast (large) network of capillaries = huge surface area for diffusion 4. The diameter of the capillaries is slightly narrower than the area of a red blood cell. This forces the blood flow slowly in single file.

Internal respiration Gaseous exchange at the tissues At the tissue-capillary membranes surrounding the muscles, the p02 in the capillary is higher than in tissues, therefore oxygen moves into the muscle tissue.

Gaseous exchange at muscles and tissues Capillary walls just one cell thick – with thin membranes so a short distance to travel Myoglobin within the muscle cell attracts oxygen to it Diameter of capillaries is narrow which forces blood cells to travel through them slowly in single file maximising diffusion Extensive network of capillaries provide huge surface area for exchange of O2 & C02 Carbon dioxide moves into blood

What happens when we start taking part in exercises? Increases in Lactic Acid Increases in CO2 Increases in blood and muscle temperature Decreases in pH thus acidity levels increase. These changes mean that the body needs oxygen quickly.

Altitude At high altitude (above 1500m) the PP of oxygen in the atmospheric air is significantly reduced. At altitude pO2 is less which means that haemoglobin cannot carry as much o2 as at sea level, therefore reducing the ability to perform physical work (hypoxia) This results in a decreases O2 transport in the blood causing a reduction in the O2 available to working muscles. It thus decreases VO2 max or aerobic capacity also can increase breathing which leads to hyperventilation. Can also lead to dehydration quicker.

EFFICIENCY OF GAS PROCESS

Dissociation curve shifts to the RIGHT The Bohr Effect During exercise muscles need more oxygen so the dissociation (release) of oxygen from haemoglobin happens more readily This is known as the Bohr effect and frees up more oxygen = used by working muscles Dissociation curve shifts to the RIGHT

Factors shifting the dissociation curve to the right are: 1. Increase in blood and muscle temperature 2. Decreases in PP oxygen within muscle increasing the oxygen diffusion gradient. 3. An increase in carbon dioxide during exercise, increasing the carbon dioxide gradient. 4. Bohr effect – increase in acidity (lower pH) These factors increase during exercise. The effect is that the working muscles: Generate more heat when working Use more oxygen to provide energy, lowering the PP oxygen Produce greater carbon dioxide as a by-product Increase lactic acid levels which increase muscle/blood acidity

Transport of oxygen 3% dissolves in plasma. 97% combines with haemoglobin to form oxyhaemoglobin At the tissues, oxygen dissociates from haemoglobin due to the lower pressure of oxygen that exists there. In the muscle, oxygen is transported by myoglobin. Myoglobin has a high affinity for oxygen and transports the oxygen from the capillaries to the mitochondria (where aerobic respiration takes place, power house of the cell). oxygen moves from haemoglobin to myoglobin.

Myoglobin Iron based protein Similar to Hb In the muscle oxygen is transported by myoglobin. Myoglobin has a high affinity for oxygen. It stores oxygen and transports it from the capillaries to the mitochondria. Mitochondria are the centres in the muscle where aerobic respiration takes place. Much higher affinity For 02 than Hb

Arterial-venous oxygen difference (a-vo2 diff) The amount of oxygen removed from the blood by muscles This represents how much oxygen is actually extracted and used by the muscles Measured by: Analysing the difference in oxygen content of the blood in the arteries leaving the lungs and that in the mixed venous blood returning to the lungs

Control of Respiration Breathing happens automatically and is under the influence of the Respiratory Control centre (RCC) located in the medulla oblongata of the brain. Inspiratory control centre (ICC) – basic rhythm of breathing Expiratory control centre (ECC) – passive process

Control of Ventilation The nervous system can increase or decrease the rate, depth and rhythm of breathing. The respiratory centre located in the medulla oblongata of the brain controls breathing.

Neural Control AT REST Inspiratory centre is responsible for rhythmic cycle of inspiration and expiration to produce a respiratory rate of 12-15 breaths a minute. Impulses are sent and when stimulated muscles contract, increasing the volume of the thoracic cavity, causing inspiration (active) When their stimulation stops, the muscles relax, decreasing the volume of thoracic cavity, causing expiration (passive) The expiratory centre is inactive during quiet/resting breathing. It is passive as a result of the relaxation of the diaphragm and external intercostals.

Activity Put the sentences in the correct order…

DURING EXERCISE Pulmonary ventilation increases during exercise, which increases both the depth and rate of breathing. This is regulated by: The Inspiratory Centre which: (a) increases the stimulation of the diaphragm and external intercostals (b) stimulates additional inspiratory muscles for inspiration, the sternocleidomastoids, scalenes and pectoralis minor, which increase the force of contraction and therefore the depth of inspiration.

DURING EXERCISE The Expiratory Centre which: (a) stimulates the expiratory muscles, internal intercostals, rectus abdominus and obliques, causing a forced expiration which reduces the duration of inspiration. (b) the inspiratory centre immediately stimulates the inspiratory muscles to inspire, which results in an increase in the rate of breathing.

Control of ventilation Proprioceptors -detect movement Thermo receptors -detect increase in blood temperature Chemo receptors -detect changes in blood acidity pH -detect decrease 02 Respiratory Control Centre (RCC) Located in the Medulla Oblongata -determines basic rate and depth of breathing Baro receptors -detect increase in blood pressure Stretch receptors -prevent over-inflation of the lungs by sending impulses to the expiratory centre (Hering-Bruer reflex)

Control of Ventilation Chemoreceptors (detect changes in blood acidity) Stretch receptors (prevent over inflation of the lungs; if these start to get excessively stretched they send impulses to the expiratory centre to induce expiration (Hering Breur reflex)) Thermoreceptors Baroreceptors (detect changes in blood pressure) Proprireceptors (detect movement) Expiratory Centre Respiratory Centre (Medulla Oblongata) Inspiratory Centre Phrenic nerve Phrenic nerve Intercostal nerve Diaphram and external intercostals Abdominals and internal intercostals Increase breathing rate Increase expiration

Hering-Breuer Reflex Expiratory centre acts as a safety mechanism in the lungs to ensure they are never over inflated. Stretch receptors in the lungs detect when the depth of breathing increases and stimulate the RCC to inhibit the inspiratory centre and stimulate the expiratory muscles.