The dark pigmentation around the nipple. Will vary in color depending on the natural skin tone.
Through capillary beds surrounding the walls and alvoli in the lungs; the 'cavity' contains no blood as it is gas filled
Alveolar macro-phages uptake debris which reach the alvoli. they are derived from circulating monocytes as well as mitotic division of already present macrophages.
It decreases the effective surface area of the lungs, so less gas will be exchanged during each breath.
Cigarettes contain many harmful ingredients like Tar, Arsenic (which is a poison), Nicotine (this is what makes you addicted to the cigarette) etc. The effect to the respiratory system varies from how much and the period of time you have been smoking. The damage to the respiratory system is the Alvoli in your lungs (Look like little sacs in your lungs) die and your lungs go black from the tar in the cigarette.
Air enters through the nose or mouth, this air then travels down the wind pipe, past the voice box and to the lungs. The lungs divide into two small tubes called bronchi, these bronchi then split into thousands of tiny tubes called bronchioles, at the end of these tiny bronchioles are millions of small 'air sacs' called alveoli. Once in the alvoli gas exchange of carbon dioxide and oxygen in the capillary walls happens. The oxygen which you have breathed in through your nose or mouth is diffused through the capillary walls to meet red blood cells, which then take the oxygen to the heart, where it pumps the blood cells to cells all over the body that need oxygen to function and do its job correctly. when this oxygen reaches the cells it kind of 'swaps' positions with the carbon dioxide (CO2) which has been created as a waste product by the body's cells. Once the CO2 is attached to the blood cells, it is returned to the heart where it pumps the blood cells back to the lungs, where gas is diffused again and the cycle starts again. sorry, a bit confusing.