Human Gas Exchange

• Pulmonary ventilation rate = breathing rate x tidal volume
• Tidal volume is the volume of air filling the lungs in a normal breath
• By having lungs internally, there is reduced water and heat loss and the lungs are protected by the ribcage
• During human inspiration, the diaphragm contracts and flattens and the the external intercostal muscles contract whilst the internal intercostal muscles relax, increasing the volume of the thorax and decreasing the pressure
• When the pressure in the thorax decreases, air rushes into the lungs down a pressure gradient
• When air enters the alveoli, oxygen diffuses across the squamous epithelium and the capillary endothelium into the bloodstream where it associates with haemoglobin
• The alveoli are specially adapted to gas exchange, they have thin squamous epithelium to provide a short diffusion pathway, and there are many alveoli to provide a large surface area
• The pleural membrane surrounds the lungs in the thorax
• The epiglottis is a cartilage flap covering the trachea to prevent food from entering the airways
• The left lung is smaller because the heart is on the left hand side of the body
• The trachea has c shaped rings of cartilage to prevent collapse whilst allowing movement of the spine
• Goblet cells line the trachea and bronchi, they have many mitochondria and golgi apparatus to secrete mucus via exocytosis
• Bronchioles lead to the alveoli, in cases of dust particles or lung disease such as asthma, the bronchioles can contract, reducing airflow
• During exercise, the bronchioles dilate to allow more airflow
• There are phagocytes in the alveoli to keep bacteria out of the lungs that have entered through the airways
• Elastic fibres in the alveoli allow their recoil and expansion, when exhaling the recoil expels air from the lungs
• The capillaries surrounding the alveoli are plentiful and are very thin, only one red blood cell can pass at a time, slowing passage and increasing diffusion rate
• Vital capacity is the total volume of air that a person can exhale and inhale in one breath
• Inspiratory reserve volume is the highest volume of air a person can inhale
• Expiratory reserve volume is the total amount of air a person can exhale in one breath
• Residual volume is the remaining air left in the lungs after exhalation
• If lungs lose elasticity, there will be less air exhaled in each breath, reducing the concentration gradients between alveoli and bloodstream as the residual volume will increase
• Ficks law is ROD = SAD/TOES
• Diffusion distance between red blood cells and alveoli is short because red blood cells are pressed up against the capillary endothelium
• Surfactant in the lungs separates water molecules, preventing surface tension from collapsing the alveoli
• During a spirograph, the participant wears a nose clip to keep a closed system
• There is a counter balance on the spirometer to ensure that the lid is not to heavy to be lifted by breathing
• The total lung capacity is residual volume + vital capacity