Ventilation and gas exchange in the lungs Flashcards
Define ventilation
The exchange of air between the lungs
and the surroundings.
What is the respiratory system/ ventilation system consisted of?
The respiratory system consists of the:
▸ trachea
▸ bronchi
▸ bronchioles
▸ alveoli
▸ intercostal muscles ▸ diaphragm.
Function of the Trachea
Carry air in and out of your lungs. Because it’s a stiff, flexible tube, it provides a reliable pathway for oxygen to enter your body and Carbon dioxide to leave.
Function of the Bronchi
Distributes air through the lungs until reaching the respiratory bronchioles and alveolar sacs
Glandular tissue
Secretes mucus to trap any pathogens and reduce the risk of infection. Further mucus is produced by the goblet cells of the epithelium tissue that lines the airways.
Finish the sentence; Smooth muscle
Contracts to restrict airflow onto the lungs.
Elastic fibres
Elastic fibres recoil as the smooth muscle relaxes, helping the airway to widen.
Epithelium tissue
Airways are lined with epithelium tissue, which consists of ciliated epithelium cells and goblet cells. Ciliated epithelium move in a synchronised pattern to waft mucus up and out of the airways.
Bronchioles
Narrower than the bronchi. Bronchiole walls are made of smooth muscle and elastic fibres. Larger bronchioles consist of some cartilage and the smaller bronchioles dont. The smallest
bronchioles have clusters of alveoli at the end.
Alveoli
Finally, when the air reaches tiny sacs called alveoli, gas exchange takes place between the air in the alveoli and the blood in the capillaries that surround the alveoli. Gases pass both ways across the walls of the alveoli to ensure efficient provision of oxygen for respiration, whilst also ensuring that carbon dioxide is removed for efficient production of adenosine triphosphate (ATP) during cellular respiration.
What structures ensure efficient gas exchange?
▸ Large surface: there are millions of alveoli, providing more space for the gas molecules to pass through.
▸ Short diffusion pathway: the walls of the alveoli are made of squamous epithelial cells and are only one cell thick. This reduces the distance these molecules have to diffuse through.
▸ Capillary network: each alveolus is close to a capillary which has a well which is also one cell thick to give a short diffusion pathway to molecules.
▸ Diffusion gradients: oxygen diffuses from a high concentration inside the alveoli down a concentration gradient to an area of lower concentration in the blood capillary, where it joins with haemoglobin in the erythrocytes. Carbon dioxide diffuses from a high concentration inside the blood capillary down a concentration gradient to an area of lower concentration in the alveoli. If it stayed in the blood it could be toxic because it lowers the pH.
▸ Moisture: a layer of moisture lines the alveoli. Gases can only diffuse across the membrane if dissolved. Therefore this moisture allows gases to dissolve in order to cross.
▸ Surfactant: this is a chemical produced by the lungs to stop the alveoli from collapsing by reducing the surface tension of water.
Concentration gradient
The difference in the concentration of a substance between two regions.
Inspiration
Breathing in is called inspiration. The following steps explain what the body does in order to breathe in oxygen.
1 The intercostal muscles between the ribs contract and raise the rib cage up and out.
2 The diaphragm muscle contracts and the diaphragm flattens and moves down.
3 Both these actions increase the volume in the thoracic cavity.
4 This reduces the air pressure inside the thoracic cavity.
5 As a result, air moves down the trachea, bronchi,
bronchioles and into the alveoli from the higher atmospheric air pressure to the lower air pressure of the thoracic cavity.
6 Oxygen diffuses through the alveolar membrane into the blood capillaries and carbon dioxide diffuses from the blood capillaries across the alveolar membrane into the alveoli.
Expiration
Breathing out is called expiration. This is done in order to push air with a high concentration of carbon dioxide out of the body.
1 External intercostal muscles relax and the rib cage moves down and inwards.
2 The muscles of the diaphragm relax and the diaphragm moves up in a dome shape.
these actions reduce the volume in the thoracic cavity.
4 This increases the air pressure inside the thoracic cavity.
5 As a result, air is pushed out.
6 In the case of expiration during exercise, the internal intercostal muscles contract to reduce the volume of the thoracic cavity further so that a larger volume of air can be breathed out to get rid of the extra carbon dioxide (CO2) that has been produced by a higher rate of respiration in muscle tissue.
The role of pleural mebranes
Protects the lungs because lung tissue is delicate and can be easily damaged. The pleural membranes enclose a fluid-filled space surrounding the lungs which provides lubrication. Our lungs are constantly expanding and contracting so the pleural membranes and fluid enable the lungs to move easily, minimising friction from other organs.
Spirometer readings of lung volumes
One way to investigate pulmonary ventilation (breathing) is by using a spirometer. A spirometer consists of a chamber filled with medical grade oxygen that floats on a tank of water. A disposable mouthpiece is connected to a tube. This is connected to the tank, and the patient breathes
in and out (see Figure 5.15). Breathing in removes oxygen from the chamber so it moves down, while breathing out pushes carbon dioxide in so the chamber moves up. The movement of the chamber up and down is recorded using a datalogger and produces a trace.
What’s the role of soda lime?
Soda lime is attached to the tube to absorb carbon dioxide that is breathed out. This means that the total volume of gas in the spirometer will gradually decrease. The volume of carbon dioxide breathed out is the same as the volume of oxygen breathed in. Therefore, as carbon dioxide is removed, this total decrease equals the volume of oxygen used up by the person breathing in and out. The trace will show a slope and this can be used to measure the volume of oxygen used in a specific period, such as when exercising.
Tidal volume
The volume of air that is taken in and breathed out during each breath when you are at rest. At 3 rest TV is approximately 0.5 dm
Inspiration reserve volume
The volume of air that can be breathed in when you take a big breath, over and above normal tidal volume. This is approximately 2.5-3 dm3
Residual volume
The volume of air that always remains in your lungs even after you have breathed out. This is approximately 1.5 dm
Expiratory reserve volume (ERV)
The amount of extra air abovenormal volume that’s exhaled during a forceful breath out. This is approximately 1 dm3.
Vital capacity
The maximum volume of air that can be moved in and out of your lungs in one breath. This varies depending on size, age and sex of the person; it is approximately 5 dm3
Total lung capacity
This can be calculated by adding together the person’s vital capacity and the residual volume. This will provide you with data to suggest the total lung volume of a person. TLC = RV+IVC
Peak expiratory flow
A peak flow measures the speed of air flowing out of a person when they breathe out as fast and as much as they can. A peak flow reading can indicate how well the lungs are functioning. A peak flow is commonly used to determine how well an asthmatic person’s lungs are working. The test is carried out three times and the best reading is recorded.
