Oxygen enters the blood stream via the erythrocyte (Red blood cell, RBC), I am not sure what you are asking but the hemoglobin inside the RBC has 4 "oxygen holder molecules" called Heme's where an iron molecule (Fe++) is stored, the Fe++ is what oxygen attaches to.
NUTRIENTS AND OXYGEN also water, minerals, and vitamins
Hemoglobin
Oxygen enters the blood through the process of respiration in the lungs. In the lungs, oxygen diffuses from the alveoli into the blood capillaries surrounding them. It then binds to hemoglobin in red blood cells for transport to tissues throughout the body.
Hemoglobin is the iron containing protein in our red blood cells that combines with and carries oxygen.
diffusion
'c' heart pumps oxygen rich blood, 'a' oxygen rich blood arrives at capillaries, 'd' oxygen moves through capillary walls, 'b' oxygen enters body cells.
When oxygen combines with red blood cells, it binds to the hemoglobin protein within the cells to form oxyhemoglobin. This process occurs in the lungs, where oxygen is loaded onto hemoglobin. The oxyhemoglobin then travels through the bloodstream to deliver oxygen to tissues throughout the body.
after the oxygen from the air enters the lungs,the oxygen gets sent to the heart and then travels through the arteries with the blood.
Oxygen enters our body through the process of respiration. When we inhale, air containing oxygen enters our lungs. The oxygen then diffuses from the air sacs in the lungs into the bloodstream, where it is carried by red blood cells to tissues throughout the body.
When oxygen enters the body, it is carried to the cells by red blood cells. These red blood cells contain hemoglobin, a protein that binds to oxygen in the lungs and transports it to tissues throughout the body. Once oxygen-rich blood reaches the cells, it is able to participate in cellular respiration to produce energy.
Hemoglobin combines readily with oxygen.
Oxygen enters intestinal cells through passive diffusion from blood vessels in the intestinal walls. The oxygen is transported in the bloodstream and then diffuses across the capillaries into the cells where it is used for cellular respiration.