F211: Exchange & transport Exchange surfaces & breathing (pulmonary system & ventilation) By Mr. Wilson

The pulmonary system (ventilation/breathing*) Air is drawn into the lungs via the nasal and buccal cavities, which are separated by the palate to allow feeding and breathing at the same time. Air is drawn into the lungs via the nasal and buccal cavities, which are separated by the palate to allow feeding and breathing at the same time. Inspired air is warmed, particularly when inhaled via the nasal cavity. Inspired air is warmed, particularly when inhaled via the nasal cavity. Q - Why is this useful? Q - Why is this useful?

The pulmonary system; upper Nasal hairs trap dust particles and some microbes. Nasal hairs trap dust particles and some microbes. The epiglottis covers the TRACHEA when swallowing to prevent food from entering. The epiglottis covers the TRACHEA when swallowing to prevent food from entering. Q - What is the importance of these mechanisms? Q - What is the importance of these mechanisms? The larynx contains vocal cords, which are adjusted as air passes over them to produce sounds. The larynx contains vocal cords, which are adjusted as air passes over them to produce sounds.

The upper pulmonary system

The pulmonary system; thorax The THORAX with its THORACIC CAVITY in humans is the area between the bottom of the neck and the DIAPHRAGM. The THORAX with its THORACIC CAVITY in humans is the area between the bottom of the neck and the DIAPHRAGM. It contains the LUNGS and the heart (with associated structures), and some important membranes, all of which are protected by the RIB CAGE. It contains the LUNGS and the heart (with associated structures), and some important membranes, all of which are protected by the RIB CAGE. Q – Why is it important that the lungs are contained in an enclosed cavity? Q – Why is it important that the lungs are contained in an enclosed cavity?

The thoracic cavity Q – What major organs are contained in the thoracic cavity? Q – What major organs are contained in the thoracic cavity? Q – Why is the heart situated in the thoracic cavity in close proximity to the lungs? Q – Why is the heart situated in the thoracic cavity in close proximity to the lungs?

The pulmonary system; full

The pulmonary system; trachea The TRACHEA is supported by C-shaped cartilage rings. This is important for keeping the airway open when thoracic pressure falls. The TRACHEA is supported by C-shaped cartilage rings. This is important for keeping the airway open when thoracic pressure falls. It is lined with CILIATED EPITHELIAL CELLS and MUCUS secreting GOBLET CELLS. It is lined with CILIATED EPITHELIAL CELLS and MUCUS secreting GOBLET CELLS. Q – What is the importance of mucus & cilia? Q – What is the importance of mucus & cilia?

The pulmonary system; ribs, intercostal muscles and diaphragm The ribs protect the lungs and heart and have EXTERNAL and INTERNAL INTERCOSTAL muscles between them. The ribs protect the lungs and heart and have EXTERNAL and INTERNAL INTERCOSTAL muscles between them. The external muscles contract to lift the RIB CAGE upwards and outwards during INSPIRATION (relaxing for EXPIRATION). The external muscles contract to lift the RIB CAGE upwards and outwards during INSPIRATION (relaxing for EXPIRATION). INTERNAL INTERCOSTAL MUSCLES aid expiration. INTERNAL INTERCOSTAL MUSCLES aid expiration. At the bottom of the thoracic cavity is a strong dome- shaped MUSCULAR DIAPHRAGM, which can increase the volume of the thorax when contracted (pulled down/flat). At the bottom of the thoracic cavity is a strong dome- shaped MUSCULAR DIAPHRAGM, which can increase the volume of the thorax when contracted (pulled down/flat).

The pulmonary system; pleural membranes & cavity The lungs are surrounded by PLEURAL MEMBRANES (pleurae). The lungs are surrounded by PLEURAL MEMBRANES (pleurae). Between the 2 membranes is a PLEURAL CAVITY, which contains pleural fluid and is kept at negative pressure so the lungs follow the movement of the rib cage. Between the 2 membranes is a PLEURAL CAVITY, which contains pleural fluid and is kept at negative pressure so the lungs follow the movement of the rib cage. The inner (visceral) pleura is attached to the lungs and the outer (parietal) pleura is attached to the wall of the chest The inner (visceral) pleura is attached to the lungs and the outer (parietal) pleura is attached to the wall of the chest

The pulmonary system; pleural membranes & cavity The pleural fluid lubricates the membranes so they can slide against each other with ease during ventilation allowing the lungs to move ‘friction-free’ against the wall of the thorax. The pleural fluid lubricates the membranes so they can slide against each other with ease during ventilation allowing the lungs to move ‘friction-free’ against the wall of the thorax. The pleural membranes also separate the lungs; so if one is punctured the other can still function. The pleural membranes also separate the lungs; so if one is punctured the other can still function. Pleurisy (pleuritis) is a an inflammation, often from infection, of the pleural membranes. Pleurisy (pleuritis) is a an inflammation, often from infection, of the pleural membranes. It leads to painful breathing and disruption to the negative pressure system. It leads to painful breathing and disruption to the negative pressure system.

Pleural membranes

The pulmonary system; bronchi, bronchioles & alveoli The trachea divides into 2 BRONCHI (singular = BRONCHUS), which are also held open, under low thoracic pressure, by rings of cartilage. The trachea divides into 2 BRONCHI (singular = BRONCHUS), which are also held open, under low thoracic pressure, by rings of cartilage. The bronchi divide into many BRONCHIOLES, which are less than 1mm thick and generally contain no cartilage. The bronchi divide into many BRONCHIOLES, which are less than 1mm thick and generally contain no cartilage. Bronchioles terminate in air sacs called ALVEOLI, which are the site of GAS EXCHANGE. Bronchioles terminate in air sacs called ALVEOLI, which are the site of GAS EXCHANGE.

Alveoli (singular = alveolus) Alveoli are highly specialised for gas exchange with adaptations that speed up the rate of DIFFUSION. Alveoli are highly specialised for gas exchange with adaptations that speed up the rate of DIFFUSION. They have a LARGE SURFACE AREA. They have a LARGE SURFACE AREA. They have an EXTREMELY THIN EXCHANGE SURFACE. They have an EXTREMELY THIN EXCHANGE SURFACE. The epithelial layer is ONE CELL THICK. The epithelial layer is ONE CELL THICK. There is a STEEP CONCENTRATION GRADIENT between their contents and their surrounding capillaries. There is a STEEP CONCENTRATION GRADIENT between their contents and their surrounding capillaries.

Gas exchange at alveoli Alveolar septal cells secrete a phospholipid SURFACTANT; lowering the surface tension of the water lining them. Alveolar septal cells secrete a phospholipid SURFACTANT; lowering the surface tension of the water lining them. This prevents alveolar collapse. This prevents alveolar collapse. Oxygen diffuses across the alveolar epithelium then across the capillary endothelium and combines with the HAEMOGLOBIN of RED BLOOD CELLS. Oxygen diffuses across the alveolar epithelium then across the capillary endothelium and combines with the HAEMOGLOBIN of RED BLOOD CELLS. Haemoglobin has a high affinity for oxygen thus making this process more efficient. Haemoglobin has a high affinity for oxygen thus making this process more efficient.

Gas exchange at alveoli The oxygen diffuses into the capillary down it’s concentration gradient. The oxygen diffuses into the capillary down it’s concentration gradient. Carbon dioxide diffuses from the blood plasma the opposite way down it’s concentration gradient and is breathed out. Carbon dioxide diffuses from the blood plasma the opposite way down it’s concentration gradient and is breathed out.

Gas exchange at alveoli The alveoli have an extensive blood supply. The alveoli have an extensive blood supply. De-oxygenated blood is supplied to the lungs by branches of the PULMONARY ARTERY, which branch again into capillaries. De-oxygenated blood is supplied to the lungs by branches of the PULMONARY ARTERY, which branch again into capillaries. Oxygenated blood is carried via capillaries to branches of the PULMONARY VEIN from where it will be taken to the left atrium of the heart. Oxygenated blood is carried via capillaries to branches of the PULMONARY VEIN from where it will be taken to the left atrium of the heart. Can you remember the many ways the alveoli are adapted for gas exchange? Can you remember the many ways the alveoli are adapted for gas exchange?

Gas exchange at alveoli

Comparison of inhaled and exhaled air InhaledAlveolarExhaledNotes O 2 CO 2 N2N2H2OH2ON2N2H2OH2O Temp.

When inhaling & exhaling… Inspiration/InhalationExpiration/exhalation External intercostal muscles Diaphragm Thorax volume Thorax pressure (pressure on lungs) Air movement

Inhalation

Expiration

Measuring the volume of air in the lungs Lung volume/capacity (pulmonary activity) can be measured using a SPIROMETER. Lung volume/capacity (pulmonary activity) can be measured using a SPIROMETER. A KYMOGRAPH on a revolving drum can be produced showing the volume of air entering and leaving the lungs over time. A KYMOGRAPH on a revolving drum can be produced showing the volume of air entering and leaving the lungs over time. The TIDAL VOLUME is the volume of air exchanged during normal breathing. The TIDAL VOLUME is the volume of air exchanged during normal breathing. This is the volume of air in each breath in & out. Usually around dm 3 per breath at rest. This is the volume of air in each breath in & out. Usually around dm 3 per breath at rest.

Spirometers through the years In the old days. In the old days. These days. These days.

Lung volumes; inspiratory & expiratory reserve volumes IRV = Maximum additional reserve volume that can be inspired on top of tidal inspiration. IRV = Maximum additional reserve volume that can be inspired on top of tidal inspiration. ERV = Maximum additional volume that can be expired on top of tidal expiration. ERV = Maximum additional volume that can be expired on top of tidal expiration.

Lung volumes; vital capacity Maximum volume of air that can be breathed in (inspired) and breathed out (expired). Maximum volume of air that can be breathed in (inspired) and breathed out (expired). Q - Why is this different for different people? Q - Why is this different for different people?

Lung volumes; residual volume Volume of air that cannot be expired from the lungs even after forced deep expiration. Volume of air that cannot be expired from the lungs even after forced deep expiration. About 25cm 3 for each Kg of body mass. About 25cm 3 for each Kg of body mass. RV + ERV = Functional residual capacity (the volume of air available for gas exchange after tidal expiration). RV + ERV = Functional residual capacity (the volume of air available for gas exchange after tidal expiration).

Ventilation rate (minute volume) Ventilation rate (minute volume) A measure of the volume of air taken into the lungs in 1 minute (expressed A measure of the volume of air taken into the lungs in 1 minute (expressed in dm 3 min -1 ). Breathing rate x tidal volume. Breathing rate x tidal volume. An increase on either side will produce an overall increase in ventilation rate. An increase on either side will produce an overall increase in ventilation rate. During exercise ventilation rate increases as the tidal volume and then the breathing rate increase. During exercise ventilation rate increases as the tidal volume and then the breathing rate increase.

Hmmm…Interesting A drop in O 2 concentration in the blood has almost no effect on the rate of ventilation. It is usually changes in carbon dioxide concentration that affect ventilation rate. A drop in O 2 concentration in the blood has almost no effect on the rate of ventilation. It is usually changes in carbon dioxide concentration that affect ventilation rate. If you are healthy it is not possible to stop breathing. You could hold your breath and become unconscious, but the body will resume breathing by itself. If you are healthy it is not possible to stop breathing. You could hold your breath and become unconscious, but the body will resume breathing by itself. Lungs also act as a shock absorber for the heart. Lungs also act as a shock absorber for the heart. Lungs can filter out small blood clots formed in veins. Lungs can filter out small blood clots formed in veins.