There are two types of alveolar cells. The type I alveolar cells which lines the alveoli and much more abundant than type II alveolar cells. Then the type II alveolar cells lesser in number but functions differently than type I alveolar cells. Type II alveolar cells secrete surfactant (composed of lecitin and sphingomyelin) for the lungs. Surfactant reduces the surface tension inside the alveoli, preventing alveolar consolidation. This is important as babies with dysfunctional type II alveolar cells (usually preterm babies less than 32 weeks age of gestation) will have respiratory distress syndrome in the absence of surfactant.
Answer: Eating a diet high in saturated fats, trans fats, and cholesterol has been linked to heart disease and related conditions, such as atherosclerosis. Also too much salt (sodium) in the diet can raise blood pressure. Not getting enough physical activity can lead to heart disease.
Explanation: Diet is an important risk factor in coronary heart disease. Heavy drinking may well increase heart attack, heart failure, stroke, and high blood pressure. A limit for men is 2 drinks a day, for women 1 drink a day.
The answer is; the melanin in darkly pigmented skin protects DNA from UV radiation, and UV radiation can cause skin cancer
In Africa, due to its equatorial latitude location, receives direct sunlight at more or less 90 degrees most of the year. These highly concentrated rays increase the UV radiation exposure that can cause damage to cell DNA. Selection pressure, therefore, favored individuals with high melanin concentrations that protect against UV. Therefore population evolved towards high melanin densities in the skin.
