skin surface (integumantary system) and the lungs (alveoli) .
haemoglobin
When blood that is rich in oxygen re enters the heart, the blood enters through the pulmonary valve. The pulmonary valve brings the oxygen rich blood to the pulmonary trunk of the pulmonary artery.
They are called alveoli
Oxygen enters the blood in the alveoli of the lungs
The act of vasodilation is the widening of blood vessels when the walls of blood vessels relax. The purpose is to increase blood flow to areas of the body that are in need of oxygen.
The mother's blood supply enters the foetus via the umbillical cord and allows oxygen to diffuse from the mother's blood into the foetus.
Blood enters the coronary arteries just above the aortic semilunar valve. After systole (a ventricular contraction), the valve closes. The closing valve causes blood to back flow against the valve. At this time, the backward flow of blood enters into the coronary arteries.
The lungs. Oxygen enters our lungs as part of the air that we breathe. It goes to the blood vessels deep in our lungs and then on to all parts of our body.
Blood entering the left ventricle is rich in oxygen. In contrast, oxygen-poor blood enters the right ventricle.
Oxygen enters the blood in the alveoli of the lungs
Oxygen enters the pulmonary blood in the capillaries of the alveoli -- the air sacs of the lungs.
Oxygen-poor blood enters the heart through the right atrium