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.
1 The pulmonary veins carry oxygen-rich blood from the lungs to the left side of the heart so it can be pumped to the body. 2  The superior and inferior vena cavae are large veins that carry oxygen-poor blood from the body back to the heart.he left side of the heart receives the oxygen-rich blood from the lungs and pumps it to the body. The heart has four chambers and four valves and is connected to various blood vessels. Veins are blood vessels that carry blood from the body to the heart.