The digestive system is linked to the circulatory system so that the endproducts of digestion can be transported to the cells of the body that require the nutrients. In the small intestine, are tiny hairlike structures called villi. These contain both capillaries (part of the circulatory system) and lacteals (part of the lymph system). Glucose and amino acids are absorbed by the capillaries and the circulating blood carries these nutrients to the cells for respiration and for protein synthesis. Fatty acids and glycerol and vitamins are absorbed into lacteals, transported in the lymphatic system to a vein in the neck, where these substances will then enter the circulation and will then be transported.
The digestive system is related to the respiratory system because when we inhale, we take in oxygen with the air. Your lungs separate out the oxygen from the air and when oxygen combines with the food we eat, it "unlocks" the energy in the food so that our bodies may use it. This is why "needing food AND oxygen" is one of the characteristics of life. This is called respiration; it's more than just inhaling and exhaling like many people think.
The digestive system is related to the circulatory system because once the food we eat is broken down into substances our bodies can use (through chemical reactions that actually start taking place right in your mouth) those nutrients are taken all over our bodies (circulated) by the circulatory system.
the digestive system is related to the respiratory system because the respiratory system breaks down food and turns them into glucose for uses in the body, and the respiratory system provides oxygen to the body. Both glucose and oxygen are important substances for cellular respiration to occur, Cellular respiration is the process in which atp is produce. (ATP is used by every cell in the body for energy, without atp we would die)