9.0 Gas exchange Flashcards
process of gas exchange between air in alveoli and blood in capillaries
1. Structure of Alveoli and Capillaries:
* Alveoli are tiny, balloon-like air sacs in the lungs with a large surface area, thin walls (one cell thick), and are surrounded by a network of capillaries.
* Capillaries also have thin walls (one cell thick) to minimize the diffusion distance between the air in the alveoli and the blood.
2. Diffusion of Oxygen (O₂):
* When air is inhaled, the alveoli fill with oxygen-rich air.
* The partial pressure of oxygen (pO₂) in the alveoli is higher than in the deoxygenated blood of the capillaries.
* Oxygen diffuses down its concentration gradient from the alveoli into the blood in the surrounding capillaries.
* In the blood, oxygen binds to hemoglobin in red blood cells, forming oxyhemoglobin for transport to tissues.
3. Diffusion of Carbon Dioxide (CO₂):
* The partial pressure of carbon dioxide (pCO₂) is higher in the blood (from tissues) than in the air in the alveoli.
* Carbon dioxide diffuses from the blood into the alveoli down its concentration gradient.
* Once in the alveoli, CO₂ is expelled from the lungs during exhalation.
4. Factors Facilitating Gas Exchange:
* Thin walls: Both alveoli and capillaries have very thin walls (one cell thick), reducing the distance gases must diffuse.
* Large surface area: The large number of alveoli provide a vast surface area for gas exchange.
* Moist surfaces: The inner surface of alveoli is moist, aiding the diffusion of gases.
* Rich blood supply: Capillaries are closely wrapped around the alveoli, ensuring a constant supply of blood for gas exchange.
5. Concentration Gradients:
* Gas exchange relies on the maintenance of steep concentration gradients for oxygen and carbon dioxide, which are maintained by the flow of blood in capillaries and the ventilation of the lungs (inhaling and exhaling).
Structures compared
Lungs
STRUCTURE:
* In the thoracic cavity
* Surrounded by the pleural membranes
* Contains fluid to allow friction-free movement
Trachea
STRUCTURE:
1. lumen
2. ciliated epithelium cells
3. submucosal layer
4. hyaline cartilage (c shaped)
5. mucous glands
6. smooth muscles
Bronchi
STRUCTURE:
1. lumen
2. ciliated epithelium cells w/ goblet cells
3. elastic fiber
4. mucus secreting glands
5. blood vessels
6. smooth muscles
7. irregular blocks of cartilage
Bronchioles
STRUCTURE:
- lumen
- cilliated epithelium cells w/ few goblet cells, may be folded due to contraction
- surrounded by smooth muscle NO cartilage
- close to alveoli
FUNCTION:
- smooth muscle: contract or relax to adjust the diameter of these tiny airways
Alveoli
STRUCTURE related to FUNCITON:
Thin walls one-cell thick:
- a single layer of squamous epithelial cells
- provide short diffusion distance for gas
exchange
Elastic fibers:
- allows alveoli to increase in volume
- stretch during inspiration: increases surface area
- recoil during expiraiton
- prevents bursting
Network of capillaries:
- maintians steep diffusion gradient
- blood is also slowed in capillaries
- good ventilation of the lungs and good circulation of blood, maintains the necessary concentration gradient for carbon dioxide and oxygen
Capillary network
DISTRIBUTION:
- surrounds alveoli
FUNCTION:
- maintians steep diffusion gradient
- blood is also slowed in capillaries
- good ventilation of the lungs and good circulation of blood, maintains the necessary concentration gradient for carbon dioxide and oxygen
Cartilage
DISTRIBUTION:
- Trachea: C-shaped rings
- Bronchi: irregular blocks
FUNCTION:
- keeps airways open and prevents
collapsing or bursting due to changes in air pressure
Squamous epithelium
STRUCTURE:
- Simple squamous epithelium cells are one-cell thick: used in diffusion
- stratified squamous epithelium cells are multi layered
DISTRIBUTION:
- endothelium (lining of blood vessels)
- alveoli of lungs
FUNCTION:
- facilitates rapid diffusion, osmosis and filtration due to its thin and permeable nature
Ciliated epithelium
STRUCTURE:
- ciliated cells (hair-like extensions)
- goblet cells often interspersed among ciliated cells
DISTRIBUTION:
- trachea
- bronchi
- bronchioles
FUNCTION:
- beating of cilia carries the mucus
upwards towards the larynx.
- then swallowed so that
pathogens are destroyed by the acid in the stomach.
Goblet cells
STRUCTURE:
- microvilli on surface
- contains secretory vesicles containing mucin
- rough endoplasmic reticulum
- gogli apparatus
- nucleus
DISTRIBUTION:
- trachea
- bronchi
- very few in bronchioles
FUNCTION:
- produces mucus
- mucus traps pathogens, microorganisms, dust etc.
Smooth muscle
DISTRIBUTION:
- trachea
- bronchi
- bronchioles
FUNCTION:
- controls size of airways
- by contracting or relaxing
- regulates amount of air entering and exiting the lungs
Mucous glands
STRUCTURE:
- mucous cells bundled together
- large nucleus
- contains mucin which absorbs water to form mucus
- ducts which transports the mucus from secretory cells into lumen
DISTRIBUTION:
- trachea
- bronchi
FUNCTION:
- excrete mucin through exocytosis
- to trap pathogens, dust etc
- prevents them from reaching lungs
- maintains moisture in air ducts keeps airway from drying out in gas exchange
Elastic fibre
DISTRIBUTION:
- alveoli
- lungs
FUNCTION:
- help expand and contract
- prevents rupturing
- provides elasticity and flexibility
- allows structure to return to original shap
- expand during inhalation
- recoil during exhalation
