Respiration and lung effects of lifestyle
Organisation • Animal tissues, organs and systems
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Airway structure: trachea and bronchi
The trachea is a wide tube that connects the mouth and nose to the lungs. The trachea divides into two bronchi, one bronchus leading to each lung. The bronchi branch into progressively smaller tubes called bronchioles that direct air to the gas-exchange regions of the lungs. These conducting airways remain open to allow continuous ventilation and move air to the alveoli .
Alveoli and surrounding capillary network
Alveoli are microscopic air sacs at the end of bronchioles and form the primary gas-exchange surface. Each alveolus has a thin, one-cell-thick lining covered by a moist layer, and a dense network of capillaries on the other side of the membrane. Oxygen diffuses from alveolar air into blood in the capillaries; carbon dioxide diffuses in the opposite direction. The proximity of alveolar air to blood reduces diffusion distance and speeds gas exchange .
Lung adaptations for gaseous exchange
Large total surface area: millions of alveoli give a combined area that maximises the surface available for diffusion. Thin diffusion distance: alveolar and capillary walls are usually one cell thick, minimising the distance gases travel. Rich blood supply and ventilation: capillaries continually replace blood with low-oxygen/high-carbon-dioxide content while breathing replaces alveolar air, maintaining steep concentration gradients for diffusion .
Effect of smoking on lungs and cancer
Tar and other chemicals in cigarette smoke act as carcinogens that cause mutations in cells, increasing the risk of cancer. Smoking damages lung tissues and airways, causing conditions such as bronchitis, emphysema and other chronic lung diseases. Destruction of alveolar walls reduces total surface area for gas exchange, causing breathlessness and reduced oxygen uptake. Smoking also correlates with many cancers beyond the lungs, including mouth and throat cancers .
Effect of alcohol on liver and brain function
Excessive alcohol consumption causes progressive liver damage. Long-term alcohol use replaces functional liver cells with scar tissue (cirrhosis), reducing the liver’s ability to detoxify substances, store glycogen and produce bile. Alcohol alters brain chemistry by changing neurotransmitter systems, leading to reduced cognitive function, mood changes and increased risk of anxiety and depression .
Effects on unborn babies from smoking and alcohol
Chemicals from cigarettes and alcohol pass from the mother’s blood through the placenta into the foetus. The foetal liver lacks a fully developed ability to detoxify these substances, so exposure causes direct harm. Consequences include miscarriage, premature birth, low birth weight and impaired brain development, which can lead to reduced learning and behavioural problems later in life .
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