Gas exchange surface humans

• Describe the gas exchange surface of a human

  The mouth leads to the trachea that is held open by rings of cartilage so it can resist pressure changes. The trachea leads to the bronchi, then bronchioles, a series of branching tubes that deliver the gas to the alveoli. The bronchioles have muscle surrounding them, which can be used to constrict the airflow in and out of the alveoli. The alveoli are minute sacs that are made of epithelial cells, collagen and elastic fibres so the alveoli can stretch and recoil. Having many alveoli give a large surface area for exchange.
• Describe and explain the feature of an alveolus that allows efficient gas exchange

  The alveolar epithelium is one cell thick; Creating a short diffusion pathway
• Describe the pathway an oxygen molecule takes from an alveolus to the blood

  Across alveolar epithelium; then the endothelium of a capillary
• Describe how we breathe in

  To breathe in - the diaphragm contracts and flattens/moves down and external intercostal muscles contract moving the ribcage upwards and outwards; This causes an increase in volume of the thoracic cavity which decreases pressure so air moves into the lungs down the pressure gradient;
• Describe how we breathe out

  To Breathe out - The diaphragm relaxes and external intercostal muscles relax and lung tissue is elastic so recoils. This causes volume decrease and pressure increase in thoracic cavity so air moves out down the pressure gradient.
• Describe the gross structures of human gas exchange system

  The tracea, then the bronchi, then bronchioles then alveoli
• Describe and explain the mechanism s that cause forced expiration

  Contraction of internal intercostal muscles pulls the ribcage further inwards

  Relaxation of diaphragm muscles and external intercostal muscles

  Causes decrease in volume of thoracic cavity

  Air pushed down pressure gradient.
• Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs

  Oxygen moves down the trachea and bronchi and bronchioles

  down pressure gradient into the alveoli;

  Then down a diffusion gradient

  Across alveolar epithelium.
• How can pulmonary ventilation rate be calculated

  PVR = tidal volume (the volume breathed in) x breathing rate (the numbers of breaths per time)
• Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them

  Many alveoli provide a large surface area

  Many capillaries provide a large surface area

  So fast diffusion; Alveoli and capillary walls are thin so short distance between alveoli and blood

  There is a flattened epithelium so a short diffusion pathways

  There is ventilation and circulation to maintain a concentration gradient so increased rate of diffusion