HGH (Human Growth Hormone) is a protein hormone which is produced by the endocrine system in the human body. It is made from 190 individual amino acid molecules, and is secreted by the pituitary gland.
However, in pulmonary circulation, the arteries carry deoxygenated blood from the heart to the lungs, and veins return blood from the lungs to the heart. The difference between veins and arteries is their direction of flow (out of the heart by arteries, returning to the heart for veins), not their oxygen content.he pulmonary veins carry relatively oxygenated blood from the lungs to the heart. The superior and inferior venae cavae carry relatively deoxygenated blood from the upper and lower systemic circulations, respectively. The portal venous system is a series of veins or venules that directly connect two capillary beds.
A SecondsCount.org answered. Most veins carry blood that is low in oxygen back to the heart. After the oxygen and nutrients have been delivered to the bodyâs tissues by the arteries and capillaries, a second network of venules and veins carries blood and waste products back to the heart. Smaller tubes, venules, pick up the oxygen-depleted blood and transfer it to the veins, which carry it back to the heart. Once the veins return blood to the heart, it is pumped to the lungs. Here, the carbon dioxide from the venous blood is expelled as we breathe out. The oxygen we breathe in is picked up by the blood flowing through the lungs.