3: EXCHANGE SYSTEMS AND MASS TRANSPORT - HUMAN GAS EXCHANGE + VENTILATION Flashcards
Describe the structure of the human gas exchange system
- as you breathe in air enters the trachea
- the trachea splits into 2 bronchi (1 bronchus leading into each lung)
- each bronchus branches off into smaller tubes called bronchioles which end in small air sacs called alveoli where gas exchange occurs
- the ribcage, intercostal muscles and diaphragm all work together to move air in and out of the lungs
Describe the process of inspiration
- external intercostal muscles contract, internal intercostal muscles relax
- ribcage moves upwards and outwards
- diaphragm contracts and flattens
- volume of thoracic cavity increases
- lung pressure decreases below atmospheric pressure
- air enters lungs down pressure gradient
Describe the process of expiration
- both sets of intercostal muscles relax
- ribcage moves downwards and inwards
- diaphragm relaxes and curves upwards
- volume of thoracic cavity decreases
- lung pressure increases above atmospheric pressure
- air moves out of lungs down pressure gradient
Describe the process of forced expiration
- internal intercostal muscles contract, external intercostal muscles relax
- ribcage moves downwards and inwards
- diaphragm relaxes and curves upwards
- volume of thoracic cavity decreases
- lung pressure increases above atmospheric pressure
- air forced out of lungs down pressure gradient
Is inspiration an active/passive process and why?
- active
- external intercostal muscles contract
Is expiration an active/passive process and why?
- passive
- both sets of intercostal muscles relax
Is forced expiration an active/passive process and why?
- active
- internal intercostal muscles contract
Describe the movement of O2 from the air to the blood
air -> mouth -> trachea -> bronchi -> bronchioles -> alveoli -> alveolar epithelium -> capillary endothelium -> blood -> binds to Hb
Where is O2 moving down a pressure gradient?
down trachea, bronchi and bronchioles and into the alveoli
Where is O2 moving down a diffusion gradient?
across the alveolar epithelium and capillary endothelium into the blood
What are the adaptations of the alveoli?
- millions of alveoli, folded walls and large network of capillaries increase surface area for gas exchange
- the alveolar epithelium and capillary endothelium are both only 1 cell thick so there is a short diffusion pathway
- ventilation and good blood supply maintain steep conc. gradient
- walls of alveoli contain elastin which allows them to recoil to their normal shape after inhalation and exhalation
- layer of surfactant inside alveoli prevents them from collapsing on exhalation
- partially permeable to allow for gas exchange
What is the epiglottis and what is its function?
- flap of cartilage
- prevents inhalation of food and fluid
What does the inner lining of the trachea consist of and why?
- ciliated epithelial cells and goblet cells
- microbes/dust/pathogens get trapped in the mucus produced by goblet cells and cilia beat to move mucus up and out of the trachea
What are the functions of cartilage in the human gas exchange system?
- trachea has C-shaped rings of cartilage which hold it open. the C-shape means it can change shape (expansion potential)
- bronchi and larger bronchioles have cartilage in their walls in smaller sections (not in rings) connected by muscle and elastic fibres
